Senior Design Project I
Senior Design Project I EE 481
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CHAPTER SIX Near Space Recovery Systems quot What happens to the parachute ifit rains quot quotIt gets wet quot Conversation with a fourth grader Chapter Objectives 10 Recovery quot 1 39 t 1 20 How the Parachute Works 2 30 Making a Hemispherical Parachute 6 40 The Parachute Ring 19 50 Parachute Testing and Proper Storage 24 60 Flight Termination Systems 33 70 Audio Beacons 44 Good to Know 47 Near Space Humor 49 10 Recovery Requirements FAR 101 the Federal Aviation Regulation Section 101 that governs untethered balloon ight requires that we y near space ights in 7 such a manner that they are not a hazard to uninvolved persons and their property Because a basic near space capsule costs at least 500 in parts you have an additional incentive to recover it without damage A lateX balloon with sufficient helium is guaranteed to burst so a recovery system guaranteed to operate is vital This chapter explains how to construct or purchase if you want to go that route the most popular recovery system the parachute Speci cally the hemispherical parachute is discussed In addition a means to terminate a ight and initiate recovery is also described Note that a ight termination system is not required for the basic near space mission but it can prevent the loss of a near space capsule when something goes wrong like the balloon becoming neutrally buoyant events which have occurred on Balloons Over Idaho B01 and Sky Science Over Kansas SSOK missions 11 The Parachute The simplest and most frequently used recovery device is the parachute The balloon carries the parachute by its apeX which places the parachute in a position where it opens immediately upon balloon burst A length of load line about 30 feet long separates the parachute from the balloon Once the balloon bursts we want what s left of the balloon to drop over the side of the parachute rather than on top of it A load line this long ensures this will occur In near space the air is too thin for an opened parachute to break the capsule s descent very much Even though the near space Parallax Inc Rev 10 Page 2 of49 Near Space Exploration with the BASIC stamp by Paul Verhage capsule is descending faster than 100 mph the parachute is opened and ready to recover the near spacecra at a safe speed A near spacewalk and its recovery parachube a beautiful thing no see There are several requirements for a parachute First the parachute must be large enough to slow down the descending capsule to a safe landing speed Second the pamchute must be constructed of materials that are not porous to the Wind or stiff in the very cold tempemtures of near space Third the parachute must be durable and must limit the size of any rips or snags put in the canopy F ourth it must be made of materials insensitive to UV exposure Finally it should be constructed of bright colors that can be seen from the ground and that contmst With any landscape Where it might recover 20 How the Parachute Works The parachute design in this chapter is a hemispherical cap that creates drag by catching moving air A descending capsule travels at a terminal velocity that occurs When Weight always pointed down at the center of the Earth is opposed by the same amount of drag which always opposes the direction of movement Parallax Inc Rev 10 chapter Six Neal Space Recovery systems Page 3 of 49 777ere are two opposing I39oroes acting on a descending near spaoeclal Weight pulling down and drag pulling p When the forces are equal the near spaoecral falls at a oonsbant speai The force of weight is given by the equation W m g Physics Halliday and R3nick John Wiley and Sons 1978 Where In is the total mass of the descending equipment balloon capsules and parachute and g is the accelemtion due to gravity which changes by 1 in middle near space but can be treated as a constant in this case The drag created by a pamchute is given by the equation Fr1 cr1 A dm vi2 Encyclopedia of Physics Lerner and 77739gg VL H HIbishers 1990 Where Cd is the coef cient of dmg a dimensionless constant of the parachute A is the area of the parachute exposed perpendicularly to the air during descent dTn is the density of the air the pamchute is traveling through and very nearly equal to the pressure and v is the velocity the parachute is moving through the air Of these factors the coef cient of dmg and area of the parachute are constants for a given parachute At balloon burst the payload begins descending with increasing downward speed Fortunately for the payload the amount of dmg generated by the parachute increases faster than the speed of descent increases This is because dmg depends on the square of the speed Therefore if you double the speed of descent the amount of drag created by the pamchute increases by a factor of four This applies to more than parachutes it39s true in geneml for all objects falling through a uid media however I wouldn39t be surprised to see that this relationship doesn39t hold at extremely high speeds Parallax Inc Rev 10 Page 4 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Drag Force re force of Fame nlDrzg 5 Descent Speed At some velocity the drag equals the force of gravity pulling the payload down At this point there is no net force remember the force of weight acts in the opposite direction as the force of drag When there is no net force acting on the parachute the parachute no longer accelerates and falls at its terminal velocity Dense bodies tend to fall with a greater terminal velocity than less dense objects because the higher density body has more mass per exposed surface area The denser body has a greater ratio of weight pulling it down to surface area slowing it down To increase the ratio of surface area to mass of a descending near spacecraft we use parachutes as recovery devices In near space there is one more complication that we don39t usually concern ourselves with here on the surface In addition to surface area the drag also depends on air density If the air density doubles so does the drag experienced by a moving object Increasing the altitude decreases the air pressure and therefore the air density For a falling body its terminal velocity decreases as it approaches the ground The terminal velocity ofa body can be calculated by equating the force of gravity to the force of drag By rearranging the terms we end up with the following equation for terminal velocity Vl 2 WCddmAm In this case we see that every term in this equation is a constant except for air density We therefore conclude that the terminal velocity of a falling body is proportional to the square root of the air density A graph of air density compared to air pressure as a function of altitude shows that the terms air pressure and air density are closely proportional to each other We get similar resulw if we substitute air pressure for air density As far as a descending parachute is concerned it is descending through the air at a constant speed This speed is called the Indicated Air Speed IAS and is affected by the mass of the air passing by the parachute in a given amount 0 time Air mass is in uenced by the air s density and since air density depends on the altitude the IAS is also in uenced by altitude The speed at which the parachute descends through the air relative to the ground is called the True Air Speed TAS The TAS is equal to the IAS only at sea level where the air pressure is approximately one bar At higher altitudes and therefore at lower air density the IAS is greater than the TAS by a factor of the inverse square root of the air densi So if the air density is 14 of its value at sea level this occurs at an altitude of36000 feet the IAS is 1140 5 or twice as great as the TAS Parallax Inc Rev 10 chapter Six Neal Space Recovery WStemS Page 5 of 49 As another example suppose a parachute lands apayload at 22 sec TAS of 22 sec At 100000 feet where the air pressure density is only 10 millibars or 1 of surface air pressure or l100th of sea level pressure the parachute descends at a speed ten times greater than it does at sea level or at 220 sec So do not be alarmed when you see your near spacecra at 100000 feet begin its descent at a speed of 145 mph But do be alarmed if the descent speed continues to be 220 feetminute below altitudes of 50000 feet Note Changes in air density closely match changes in air pressure If air pressure is substituted for air density the calculated descent speeds are almost identical Let39s look at another example I39ve taken data from one of the TVNSP ights that reached an altitude factor The resulting graph is illustrated below Notice that the inverse square root of air density tmcks the TAS of the parachute almost perfectly DeScent Speed Altitude vs DescentSpeed Due to the extremeh low air pressure in near space the initial descent speed of the near spacecIat can be Den times higher than at sea level Feet W mm The author recommends you genemte a similar graph or table from your rst ight data and laminate it The graph or table should be le with Mission Control so they know what kind of speeds to expect during descent Seeing a fast descent for the rst time puts people into a panic Before balloon burst 777e parachute and balloon shorty e balloon Note how black the sky is and that the parachute is not experiencing any Wind Parallax Inc Rev 10 Page 6 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage After balloon burst The parachute shortly after balloon burst It appears that some of the balloon remains are wrapped around the parachute ring At this point descent speed is around I 00 mph 30 Making a Hemispherical Parachute The hemispherical parachute Imagine cutting a pingpong hall in half Shroud Line 1 DP 4 A simple sheet of fabric can make a parachute as well I remember when I was in grade school but is wasteful of material The hemispheric parachute is a simple design and ef ciently uses the fabric it is constructed from Expect to spend about 75 making a sevenfoot parachute If time is more important than money or if the handcrafting a parachute doesn t appeal to you then purchase a Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 7 of 49 complete parachute from a highpower rocket company like RocketMan Check the list of suppliers at the end of the book for recommendations As the hemispherical parachute descends air pressure builds up inside of it and eventually escapes In the simple hemispherical parachute builtup pressure escapes from under the parachute s canopy by forcing the parachute to rock or tip from side to side One way to reduce this tendency to rock back and forth is to cut a spill hole in the top of the parachute Spill holes keep the pressure from getting so high that the parachute has to rock from side to side to release it The spill hole needs to be about 20 the diameter of the parachute 31 Materials Canopy fabric amount depends on parachute diameter 16 yards should be the maXimum Note More than one color of fabric can be used on the parachute canopy A 150 foot roll of l 50 test woven DacronA kite line 50 feet of 12 twill tape for a sevenfoot parachute Four or ve sheets of poster board Eight bearing swivels 100 test One bearing swivel 200 test Cotton thread Colored pencil in a color that contrasts with the canopy color Fabric label or fabric marker Scissors or soldering gun with a cutting tip 311 Notes on Parachute Fabrics I recommend making the parachute out of ripstop nylon the kind found in local fabric stores This material is coated with a water repelling lm making it less porous to the air but still supple and exible Kite fabrics have a harder coating to them making them more crinkly The lower porosity of the fabric means a smaller parachute is required to slow the near space capsule down In addition to reducing fabric porosity the urethane coating also protects the ripstop nylon from damage due to UV eXposure which is at greater levels in near space Being a ripstop fabric the growth of rips and tears in the parachute canopy is reduced by the thicker threads woven into the fabric Finally ripstop nylon is readily available and dyed in many bright colors Use a combination of several different colors of ripstop when making the parachute so it has the best chance of standing out If you decide to use a single color then think about using a orescent color to increase the parachute s visibility If the cost of ripstop fabric about 7yd is a concern then another source of parachute canopy material is a retired hot air balloon envelope After 500 hours of use the FAA requires that these fabric envelopes be replaced You can purchase a lot of ripstop this way on a budget If you decide to use balloon material you ll have fewer color options You ll also have to wash the fabric several times to get the gas smell out of it 32 Procedure Determine the Qarachute s diameter Notes on Parachute Diameter The equation below is typical of parachute formulas used in model rocketry It calculates the diameter of a circular parachute at sheet of round fabric based on the weight of the payload to land at 15 mph and a typical coefficient of drag Parallax Inc Rev 10 Page 8 of 49 Neal Space Exploration with the BASIC stamp by Paul Verhage Diameter inches weight pounds 0454m 396 From httpwwwinfocentralorgrecoveryj zerhfml I modify the results by assuming the calculated diameter is actually half of the circumference of a sphere So multiply the results by 1r2 or about 15 to determine the diameter of the hemispherical pamchute The results match the diameter of the hemispherical parachute I currently use One factor has a big in uence on the accuracy of an equation like the one above That is the porosity of the fabric being used to make the canopy If a leaky fabric With a higher porosity is used then increase the diameter of the pamchute For most cases assuming apayload Weight of 13 pounds is suf cient Why 13 pounds Because you can assume the parachute Weighs one pound Which must be added to the near space capsule Weight of 12 pounds Making a Parachute Gore Pattern The parachute described here is a simple hemispherical cap made from eight identical gores To increase the parachute s stability there is a hole in the top of the parachute to vent excess pressure inside the canopy The vent is 20 of the parachute39s nal diameter The pattern for this hemispherical parachute Was calculated by dividing a hemisphere into 90 rings each onedegree thick The diameter of each ring With respect to the central axis of the parachute is proportional to the angular elevation of each ring From this the diameter of each ring Was calculated Next from the calculated diameters the circumference of each ring Was determined At this point the distance of the ring from the apex of the pamchute and its circumference has been determined Divide each circumference by eight the number of gores and the Width of the ore at each point has been determined Add a little billoW to the parachute by adding another 5 to 10 to the gore Width Gore dimensions are calculztai by measuring the W39 7 and length of piesliapai Wedges cut out via hemisphere 321 Generating Your Own Pattern If you Wish to design your own parachute using your own spreadsheet progmm the commands I used are shown below Parallax Inc Rev 10 Chapter Six Near Space Recovery systems Page 9 of 49 Spreadsheet Commands A B Degrees Radians Length along Gore Half width of Gore Procedure Enter the diameter of the parachute to design in cell Cl diameter in feet Column A values begin at one degree cell A6 and increments in units of one degree until the angle of 90 degrees is reached Remember the number generated in column F is half the width of the gore at the distance down the center ofthe gore indicated in columnE Before cutting parachute gores out of fabric a pattern in poster board is needed The poster board pattern is placed on top of a sheet of fabric and the outline of the gore traced in pencil Then the fabric can be cut into eight near identical gores Several pieces ofposter board are needed to make a gore pattern The maximum dimensions of the gore pattern determine the number of sheets of poster board required to make a gore pattern Tape the poster board sheets together to make a single sheet large enough to t the pattern Draw a stmight line down the center this sheet of poster board Mark along the length of this centerline at every point listed in column ve of the spreadsheet Draw a perpendicular line from each marked point that extends both directions away from the centerline Mark a distance on the perpendicular line equal to the distances indicated in column six of the spreadsheet Every 15 line make an extra dot near each end to indicate where seammatching marks will be transferred to the fabric Ignore the spreadsheet values where the angle is less than about 9 degrees as that is the location of the spill hole You can use your spreadsheet39s graphing ability to take a peek at the nal pattern but remember the gmph will not by default print the X and Yaxis to the same scale Your nal pattern should look similar to this one below Parallax Inc Rev 10 Page 10 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage Gare Peeeem ater ial Renewed re 5n l I He IE 777a patbem fora singe gore Make eight of them HaIF weer l i one Inch Sear1 Length Before cutting the poster board pattern add a oneinch seam allowance to the top and bottom edge There already is a oneinch seam allowance included on the sides 322 Tables of Gore Patterns If you would rather not calculate your own gore pattern I have included several calculated gore patterns below Add a oneinch seam allowance all the way around the dimensions given below Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 11 of 49 Seven Foot Diameter Parachute Length Half Width Length Half Width Parallax Inc Rev 10 Page 12 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage Transfer the desired gore pattern to poster board Every 15 h line make an extra dot near each end to indicate where seammatching marks will be tmnsfeiIed to the fabric Note Lfyou don39t want to make 90 sepamte measurements on the gore throw out every other one the result should be just as good Be sure to make as many seammatching dots Note There s no reason the gore has to be in a single piece The gore pattern can be cut into two pieces and a different color of fabric used on each piece Be sure to include an extra seam allowance where the panels overlap and extra twill tape to sew over the extra seams Some possible parachute patterns Transferring Gore patterns to Fabric 39 the poster board pattern along the major threads in the ripstop Trace the gore pattern on to the fabric with a contrasting colored pencil Make an extra mark on the fabric on each side at every location where you indicated seammatching dots on the pattern about 2 inch in from the edge Trace a total of eight gores onto the fabric Cutting the Fabric Parallax Inc Rev 10 chapter Six Neal Space Recovery Systems Page 13 of 49 To cut the gores out of the ripstop nylon it s best to use a hot soldering iron equipped with a cutting tip The hot tip melts the nylon threads of the fabric together keeping the fabric from unmveling Sewing the Cores into a Canopy Note I am not a seamstress so ifyou re an expert please do not get upset with my sewing directions At the time of this writing I have constructed ve pamchutes successfully and experienced no failures No doubt there is a better way to construct a parachute than I am describing here sounds like another topic for a sequel to this book Sew the parachute with a strong cotton thread and use a needle with an eye to match the diameter of the thread Lock the beginning and ending of each seam by backstitching a few times running the sewing machine brie y inreverse each time Draw aline 2 from the edges of the long sides only on each gore Fold the fabric along these lines folding the rightside edges up and over and the le side edges down and under You may run a ngernail along the seam as you fold to iron in the creased hem Sew these folded hems in place with a single line of stitching on each gore Take two gores and overlap their hemmed edges with a downfolded hem facing an up folded hem so the seam allowances are sandwiched in between Align and pin the top and bottom edges of the two gores and also align and pin the seam matching marks you made Sew down the middle of the overlapping edges You will be sewing through four layers of fabric Pull out the pins as you approach them try to avoid sewing over pins Rotate the sewn seam by 180 degrees interlocking the folded seams You may use pins to keep the seam rotated and taut Sew down the interlocked seams You will now be sewing through six layers of fabric ltlt ltltltltltlt 9 single hemmed Elan l Overlapping seams before sewing them Dogether sew here sew her e Edge an v i aw Parallax Inc Rev 10 Page 14 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage SEN i n5 Tun coras Together 1 l 777a hop and bottom seams of the wwwpwa meamqw s i cch Here Tun auras Sewn Tu Ether With Falded Over Ear15 w L s i tah Here Rabatai Seams Inberoced Add the next gore in the same fashion until all the gores are sewn together to form a single sheet Close the pamchute by sewing the rst and last gores together If you re like me the edges of the canopy will not line up In this case I start the seam at the spill hole first and make that my reference Top and Bottom Seams of the Parachute Trim the top and bottom edges of the parachute canopy to make even edges all the way around Hem the top and bottom edges by folding the edge over by 2 inch and sewing it down then turning this hem by 2 inch again and sewing through all three layers The doubled over seams protect the raw edges of the fabric from the force of the passing air during descent and add strength to the pamchute s edges X lazy View of Top and Bottom Parachube Seams l 87 Twill Reinforcement The eight gore seams of the pamchute canopy will be overlaid with twill tape The twill tape will add reinforcement to the seams and will also form loops at the bottom edge of the canopy where the shroud lines will connect Only four pieces of twill tape are used each covering one seam crossing Parallax Inc Rev 10 chapter Six Neal Space Recovery Systems Page 15 of 49 over the spill hole then covering the seam directly opposite Therefore you will need to cut four strips of 12 wide twill tape to a length that begins at one end of the parachute crosses over the top apex and back down to the opposite side plus an additional twelve inches for shroud line loops TWIY tape l To calculate the required length multiply the radius one half the diameter of the pamchute by 1 and add twelve inches Cut four lengths of 2 inch twill tape to the calculated length Mark each tape at four inches and at six inches from each end Note Ideally the sixinch mark on the twill tape will align with the bottom edge of the canopy The fourinch mark is where the twill doubles back on itself and gets sewn to the underside of the cano Use the gore pattern to determine the radius of the canopy s spill hole Find and mark the center of each ta e From the center of each twill tape place two diameter marks on the twill tape at a distance equal to the spill hole mdius plus an additional couple of inches for slack Note These marks are where the twill tape begins to be sewn to the canopy The table below gives the expected spill hole radii However since sewing skills vary the diameter of the spill hole never comes out as expected The better your sewing skills the less slackthe twill tape requires The author recommends two inches of slack for the rst parachute the excess is tied offat alater time 47 in Note A second method to determine the placement of the diameter marks is to measure the current diameter of the spill hole To do so grab two opposite ends of the spill hole and pull them apart as far as they will go This collapses the spill hole Measure the distance between the extreme points which is half the circumference of the spill hole Divide this distance by 1 to calculate the radius of the spill hole Lay the tape on top of the canopy and over a seam between two gores Align the spill hole mdius markings with the top edge of the canopy Parallax Inc Rev 10 Page 15 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage Starting at the spill hole sew along one edge of the twill tape About 4 inches before sewing to the edge of the canopy fold the end of the twill tape two inches past the edge of the canopy Ideally the edge will line up with the sixinch mark and you can fold the tape under atthe 4 inch mark Align the end of the tape with the underside of the seam Continue sewing the twill tape to the end of the canopy making sure you sew the end of tape to the underside of the canopy This will leave a two inch loop at the bottom of the canopy Turn the canopy around and continue sewing up along the other edge of the twill tape returning to the beginning position at the edge of the spill hole Examine the twill tape loops at the bottom of the canopy to make certain that the ends are secured rmly underneath It the tape spilled out of place and was not sewn down properly resew the ends of the twill tape from the inside Reinforce the area were the twill tape meets the edge of the canopy at top and bottom by sewing crosswise over and slightly beyond the tape several times Repeat forthe three remaining twill tapes Twill nape alberbeing sewn to canopy Gather together the twill tapes at the top of the canopy over the spill hole Align the center marks of each ta e Cut a twelveinch length of woven Dacron kite line and tie on a strong 200 bearing swivel in its center Tie the other ends of the line around the center of the twill tapes Take out the slack in the twill tapes by tying a knot in the twill tapes between the bearing swivel and spill hole edge The position of the knot depends on the amount of slack in the twill tape so be prepared to experiment with the knot placement 4ltlt lt4 323 Shroud Lines Each shroud line begins at twill loop on the canopy drops to a bearing swivel at the parachute ring and returns to the next twill loop on the canopy Shroud line knots are covered with heat shrink tubing to reduce the chances of the knot from coming undone Make the shroud lines from 150 woven Dacron kite string Use kite line mther than purchasing the twistednylon cord as the woven kite line stays together as aunit better than the twisted cord does Cut four shroud lines eachwith a length four times the pamchute39s diameter Mark the center of each shroud line Parallax Inc Rev 10 Chapter Six Neal Space Recovery Systems Page 17 of 49 V Run the shroud line through one loop of a 100 bearing swivel Center the mark in the loop and tie an overhand knot trapping the bearing swivel inside the loop formed by the knot The bearing swivel will be used to attach the parachute ring 777a end oft7e shroudI39ve It bermpanes in a bearing swivel Mark each end of the line 6 from the end lt4 Cut eight twoinch lengths of thin heat shrink tubing alittle more than twice the diameter of the shroud lines lt Slip two pieces of tubing on each shroud line from opposite ends and pushthem toward the center of the shroud lines where they are temporarily out of the way Tie one end of a shroud line to a twill loop at the bottom of the chute matching up the knot with the mark that was made 6 from the end of the line Use a blood knot as it will resist pulling loose of the pamchute during descent Tie the other end of the Dacron line to a neighboring twill loop again aligning the knot with the mark on the line Repeat this for the other three Dacron loops Do not yet shrink the tubing over the knots until the shroud lines are checked 4 4 ltlt Test the parachute as follows Take the pamchute outside and grab the shroud lines at their bottoms on the center marks youmade V Run as fast as you can and the parachute should open making it dif cult for you to continue running You should do this when the neighbors aren t looking Look at the opened pamchute and make sure it looks symmetrical and that none of the shroud lines are grossly slack If the shroud lines do not match then untie the longest shroud line and retie it to match the others and then repeat the parachute test again Lfthe parachute looks good cut the excess string from each knot back to about 12 and carefully use a lighter to melt the ends slightly Slide the heat shrink tubing over the knots and shrink it down taking great care not to damage the nylon lines withthe heat gun Parallax Inc Rev 10 Page is of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage Tying the Knot SDep 1 Top Left Wing the shroud line to the canopy Start by making this quot gure 8 Step 2 Top Right Pass the free end of the shroud line though the anopy then loop the end back through the knot exactly as in came Without canopy Do Inae it clearer Step Both Righ t Knot tI39ghDened and an oVerhand shopper knot added 324 Documentation At least two items should be recorded on the canopy where they can t get lost Document the following items on the canopy 0 Diameter of pamchute 0 Weight of the pamchute Either write these measurements on the canopy with a fabric marker or have the measurements embroidered onto a cloth label and sew the label to the canopy Along with the previous two there are three other recommended markings The rst is useful when untangling the shroud lines and the other two are just nice to know items To simplify untangling the shroud lines label the bottom of each shroud line with a tag The tag contains the number of the shroud line The numbers are written in either clockwise or counterclockwise sequence as are the positions on the parachute ring The shroud lines are disconnected from the parachute ring while they are being untangled Labeling the shroud lines and pamchute ring makes quicker work of reattaching the shroud lines to the pamchute ring The author labels the gores inthe canopy The numbers on the gores uniquely identify each gore If the canopy is damaged during a mission the damaged gore can be recorded using its identi cation number Finally lpersonally like to record the number of missions the parachute has been used on I set aside ea of the canopy and label it with the word Flights A er each ight or mission I draw another hash mark Use a permanent ink fabric marker to make the parachute s hash marks Parallax Inc Rev 10 chapter Six Neal Space Recovery Systems Page 19 of 49 Recording the number of missions 40 The Parachute Ring The parachute ring keeps the shroud lines of the parachute from twisting up during a near space mission The ring does not take the stress of the weight of the near spacecra pulling down and the balloon trying to li up the pamchute shroud lines do that Instead the pamchute ring only forces the shrouds lines apart so they don t tangle Described below are two methods of m 39 amchute rings The simplest design uses a needlepoint ring and has been tested by KNSP and TVNSP The more elabomte design uses minicapsule containing recovery aids and had not been adequately tested yet at the time of this 41 Needle Point L009 Design Neede point parad7 uDe ring This is the fastest method to create aparachute ring Parallax Inc Rev 10 Page 20 of49 Neal Space Exploration with the BASIC Stamp by Paul Velhage 411 Materials Twelveinch diameter wood needlepoint loop 18 thick B asswood stock Woven Dacron kite line 150 recommended Twelve bearing swivels at least 100 test Eight oneinch split rings Heat shrink tubing 18 diameter Heat shrink tubing 14 diameter Fine tip fabric marker oeooooooe 412 Procedure The loop actually consists of two rings The inner ring is a solid piece of wood and the outer iing is split with a clamping mechanism Assembling a pamchute ring requires that the individual rings be epoxied together to make a single stronger ring A er the epoxy is set the clamp is removed and the remaining gap lled The parachute ring is completed a er adding loops of Dacron kite line A neede point rlhg before it is con Verbed mm a parachute ring Openai ring shows the clamp and rivets Loosen the outer ring of the needlepoint loop Separate the inner ring from the outer ring Coat the outer surface of the inner ring with e oxy Slip the two rings back together and tighten down the clamp Let the epoxy set overnight Remove the clamp by grinding off the rivet heads with either a metal le or a Dremel with an abrasive cutting wheel Note leave the metal rivets inthe ring just grind off the heads of the rivets Cut and epoxy apiece of basswood to ll the gap le between the clamps Clamp the basswood into place until the epoxy sets Drill four equally spaced holes 18 diameter in the parachute ring Cut a length ofwoven Dacron kite line ten feet lo Melt the cut ends of the Dacron line with a lighter carefully Slide eight bearing swivels on the Dacron line Slide aoneinch length of 14 heat shrink tubing on the Dacron line Lay the ends of the Dacron line together and tie a doubled overhand knot V V V V V V 4ltltlt44lt4 Parallax Inc Rev 10 v 4 44 ltltltlt 4 lt44 Chapter Six Near Space Recovery Systems Page 21 of 49 Slide the heat shrink tubing over the knot and shrink it Heat Shrink Tubing Securing 76 knot Stretch out the loop of Dacron into a straight line positioning the covered knot about 6 inches from one end Mark the opposite ends with a fabric marker Stretch out the loop again this time by placing the marks together Mark the new ends This will make four marks on the loop Use these marks to find the midpoint between each pair making 8 equally spaced marks on the loop On each mark position a bearing swivel and tie a knot trapping the bearing swivel Now there should be eight bearing swivels tied around the Dacron loop equally spaced Trapped bear77g swivel Cut four lengths of woven Dacron 14 long Perform the following steps on each piece Mark the midpoint of the Dacron cord this is point B Mark two more locations on the 14 Dacron two inches in each direction from the previous midmark Label these marks as A and C Slide one bearing swivel on the Dacron at mark A and tie an overhand knot trapping the bearing swivel at mark Parallax Inc Rev 10 Page 22 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Slide a short length of heat shrink tubing over the knot and shrink the tubing to prevent the knot from loosening Slide a second piece of heat shrink tubing over the Dacron and push it up against the rst knot temporarily do not shrink this tubing yet Slide a second bearing swivel on the Dacron to mark C and tie an overhand knot trapping the bearing swivel at mark C Slide the second piece of heat shrink tubing from its temporary location to cover the second knot and shrink the tubing Line gong through the needlepoint loop Pass the two free ends of each 14 Dacron line through a hole in the needlepoint loop from the outside of the needlepoint loop Lay the free ends of the 14 Dacron line together and tie a doubled overhand knot on the inside of the ring O O OBear Vr lg Swivel y m 0 o Parachute ring Needle Po i mt R i mg andmes o O Q o At this point the needlepoint loop has four small loops of woven Dacron tied to it with each tiny loop containing two bearing swivels Connect every other bearing swivel of the tenfoot Dacron loop to the bottom bearing swivels of the parachute ring with split key rings When completed the tenfoot Dacron loop forms a zigzag beneath the parachute ring The altemating bearing swivels are connected to the top module of the near spacecraft Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 23 of 49 Connect the top bearing swivels to the ends of the parachute shrouds with oneinch split rings 42 MiniCapsule Parachute Ring An alternative to a simple wooden hoop is to construct aminicapsule in place of the hoop The mini capsule keeps the shroud lines apart while allowing recovery aids and ight termination systems close to the parachute This should be considered an experimental design The author has constructed one minicapsule but it has not been thoroughly tested atthe time of this writing 421 MiniCapsule Design Build a near spacecm module as described in Chapter One but only a few inches tall Add the normal abmsion jacket and link loops Add the same 10foot Dacron loop used in the parachute ring to the bottom link loops ofthe minicapsule Q Q P Mini Capsule Design 422 Electronics For MiniCapsules Good electronics to incorporate into a minicapsule are recovery aids like trackers and beacons and ight ermination sys ems MiniiTrackers A good recovery aid is the Tiny ka 11 based near space tmcker as described in Chapter Two Section Three A exible 2 m or 70 cm dipole antenna with the top element tied loosely to a shroud line or a 70 cm wire dipole makes good antenna choices Let the bottom element of the exible dipole antenna dangle free Parallax Inc Rev 10 Page 24 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Audio Beacons Another recovery aid although of a different nature from the previous one is the audio locating beacon Commercial models are available through high power rocket dealers Quite a serviceable one can be constructed for about 6 from Radio Shack Check Section Seven of this chapter for details Flight Termination Systems Since the HT s receive capability isn t used in the Tiny ka based near space tmcker a programmable DTM39F decoder can be incorporated into the minicapsule This keeps the ight termination system close to the parachute Again consider this experimental as there are no formal plans in this book for DTMFcontrolled Flight Termination Units Complete Flight Termination Systems are discussedin Section 6 below 423 Wrapping Up Your pamchute and parachute ring is complete The authored tested his rst pamchute by dropping it from a tall building but found this hard to do successfully Below a different way to test the pamchute for proper opening dmg and stability is explained The testing lets you characterize the pamchute s performance 50 Parachute Testing and Proper Storage 1 recommend that you test your completed parachute before use don t rely on the pamchute to work properly although it probably will during a mission without rst testing it Testing ensures the hute opens without tangling and determines the landing speed of the parachute for different payload weights With the landing speed of the pamchute and knowledge of air pressure at various altitudes you can genemte a descent pro le of the parachute Proper stomge of the pamchute between missions increases the reliability of the parachute A pamchute that is stored wadded up in a tight ball may not function properly during descent 51 Parachute Testing One way to test the parachute at various air speeds is to rent time on a wind tunnel This author assumes this is not a realistic option Instead to accumtely measure the descend speed of the pamchute you39ll perform drop tests The dro test measures the parachute s performance under mious payload weights and records the descent speed of the parachute Pamchube and nearspaaecrat raised beneath the tethered Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 25 of 49 This test is in The TVNSP crew performed this test in a soccer eld in Boise and attmcted quite a bit of attention This test requires the use of a tethered helium lled weather balloon to carry the parachute and capsule over 100 feet above the ground for a drop test 5 1 1 Collect the following items for the parachute drop test 00000900000090 512 lt4 Parachute away pin was pulled loose parad7 ute descends 777e release and the Materials Latex balloon the balloon can be used for a missionifhandled carefully Two rolls of strong nylon twine 2 7 3 metal 1i 2 wood dowel cut six inches long Hard hats Completed pamchute Near spacecra modules Small so weights andor packing material Duct tape Gloves Scale to weigh capsules andballoon Li H liurn e Groundbased APRS tmcker Camcorder or camera you ll want to record this test as it is awesome fun Construction Construct the release mechanism Drill a hole perpendicularly through the dowel near one end with a diameter large enough to pass the nylon line through This is the release pin Taper the other end of the release pin to a dull point Tie anylon cord through the hole inthe release pin Parallax Inc Rev 10 Page 25 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage Release H39n Round the end no help prevent snagging Prep the near spacecra Progmm the tmcker or ight computer to transmit the GPGGA sentence every couple of seconds The time and altitude data will be recorded in this test Move the HT off the APRS frequency so the test does not interfere with local APRS tmf c Test that the tracker ight computer is tmnsmitting properly Attach the second module to the tracker module Test that the weights t inside the empty module and are secure Parachute Prep Tie alarge loop about six inches in diameter to the top of the parachute with sisal line 513 Procedure Weigh and record the near spacecra Include the parachute s weight in the total Attach the parachute to the near spacecra Power up the near spacecra Start up amobile APRS tmcker this is a good opportunity to test a chase vehicle s tracker Start logging APRS data see Chapter 11 Sections 113 through 115 for directions on setting up the TNC and APRS Consult Chapter 10 Section 3 for directions on lling and sealing aweather balloon In place of the 30foot long load line use a line over 100 feet long In this test the lanyard ring is used as the pamchute release A er lling the balloon but before beginning the test tie the free end ofthe load line to a car or other object that the balloon cannot c away Select several people as the Balloon Crew to operate the balloon It is their task to wise and lower the balloon for each test All of them must wear gloves for protection against string burn Parallax Inc Rev 10 chapter Six Neal Space Recovery Systems Page 27 of 49 Raising the tethered balloon It s safest Do Wear a hard hat as there s stufalbg from the sky in 39 232 The release line is a separate line from the load line and is opemted by a single individual the Release pemtor It is best that this person be separate from the Balloon Crew to prevent the load line and release line from tangling This person must Wear gloves and a hardhat as the release pin is overhead When they release the pamchute from the tethered balloon Pass the loop of sisal at the top of the parachute through the lanyard ring on the Weather balloon and lock it into place with the releas 39 Parallax Inc Rev 10 Page 25 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Release Mechanism Release pin connecting the line to the shop 100 feet AGL V The Balloon Crew raises the balloon on the load line Note keep tension on the parachute until the weight of the capsule is pulling on the pamchute A erthe balloon is at altitude con rm the pamchute and release line are not tangled Have the Release Operator call HEADS UP before pulling the release pin loose Observe that the parachute opens properly Under no circumstances attempt to catch a falling capsule when its parachute has failed as the risk of injury is too great in comparison to the cost of the capsule ltltlt4 lt Repeat the Pamchute Test with various weights inside the empty module recording the total weight of the capsule in each test A er completing the tests carefully lower the balloon and remove the tape wrapped aron the nozzle It will take awhile to dump the helium out of the balloon However if the balloon is handled with care it can be repacked inside the bag it came in and used for your rst ight The interior of the balloon is filled with talcum powder so be sure no one attempts to breathe the helium being vented A Final Observationto Make Mimges occur when pockets of air warmer than the surrounding atmosphere bend or refract light from its original path One effect is the shimmering observed over warm pavement of more distant objects as pockets of warm air rise and mix with the cooler air higher above the pavement Helium is avery lowdensity gas and is capable of refracting light in just the same fashion As you vent helian from the balloon observe the scene behind the helium stream leaving the balloon nozzle and look for shimmering 514 Analysis of Drop Test Data Change HT frequency back to 144390 MHz Con rm that the parachute opened promptly when released and did not collapse Look for asymmetries in the canopy if there is a problem Make sure the shroud lines look even and are under the same amount of tension The time and altitude are the two most important elds during the drop test Use only the last few GPGGA sentences when the capsule is descending at a constant mte Record the capsule weight and last three or four GPGGA sentences from each drop 4 Parallax Inc Rev 10 4 444 44444 Chapter Six NearSpaoe Recovery Systems Page 29 of 49 altitudes and UTC times Calculate the change in altitude by subtracting the last altitude from the third altitude Convert the change in altitude from meters to feet by multiplying meters by 328 Calculate the change in time by subtracting the last UTC time from the third UTC time being sure to take into account any roll over in minutes You want the results in seconds Divide the change in altitude by the change in time Record the descent speed and capsule weight in a spreadsheet Record the same data for each drop test Create a graph of parachute descent speed as a function of payload weight use best t The graph should be close to a straight line linear Calculate a descent speed for the parachute Note As an example use the last three GPGGA Why Are There Errors The descent speed of the parachute may not be as low as calculated Factors that affect the true descent speed of a parachute includes sewing errors variations in parachute diameter or spill hole size and canopy porosity 515 Generating a Descent Profile You just measured the characteristic descent speed of a parachute at your local elevation The Descent Pro le determines the speed of the recovering near space capsule as a function of altitude V 444 4 4 Begin by creating a spreadsheet with altitudes for every 1000 meters starting at your elevation Add a second column with the Standard Atmosphere density at those altitudes found in the table below Create a third column of altitude in feet by multiplying the rst column by 328 Create a fourth column of the inverse square root of air density Create a th column of predicted descent speeds by multiplying the fourth column by the landing speed of the parachute and divide by the inverse air density at the elevation the drop test was performed Graph the third altitude in feet and fth columns descent speed in feet per minute Spreadsheet Commands A B C D E 12 Descent 1 Altitude Densrty Altitude lDensrty Speed 2 meters feet fee second 3 1000 A3328 lSQRTB3 D315 Standard Altitude Density Parallax Inc Rev 10 Page 30 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage The resulting graph predicts the descent pro le for this particular parachute for a given weight The descent speed of a parachute above 100000 feet is usually greater than 150 feet per second or 100 miles per hour Again don t let this worry you The air pressure at this altitude is so low that high speeds are necessary to generate enough drag As far as the parachute is concerned it appears that the force of the rushing air on the parachute at this altitude is equal to the force of the slower rushing air at a lower altitude The force on the parachute is constant all the way down One test to perform is to calculate the actual descent of the parachute during a mission and comparing the results to the predicted descent speeds 52 Storing And Transgorting Parachutes 521 Storing Parachutes Between Missions Parachutes should never be stored folded up Instead let the parachute s apeX hang from a nail in the wall or ceiling Place the parachute where it is protected from direct sunlight and drafts of cold or hot air 522 Untangling Shroud Lines Parallax Int Rev 10 Chapter Six Near Space Recovery Systems Page 31 of 49 07 joy Untangling shroud lines Someone must have responsibility for untangling the shroud lines during amission s Flight Readiness Review FRR Link the split rings at the ends of the shroud lines together with a h split ring to keep the lines from tangling again Mike Manes of EOSS recommends wrapping the stretchedout untangled shroud lines with several twist ties That s such a good ideathat lwish I had thought of it E keep shroud121 under trol Wrap Wire twist ties around the bundled shroud lines A suggestion from Mike Manes of 055 Alternatively a parachute transport bag also helps keep shroud lines from tangling during tmnsport 523 Transporting a Parachute to a Launch Only on the night before a ight should the parachute be folded into a transporting bag One good bag for transporting apamchute is a laptop case a er the shroud lines are tiedtogether Another option is to sew a tmnsport bag from a heavyduty nylon fabric Below are directions for m 39 ne type of transport bag This bag is a long narrow tube sewn closed at both ends VelcroB closure along the length of the bag makes it easy to lay out the parachute inside and avoids snagging the pamchute in a zipper A ap of fabric inside the opening protects the parachute s shroud lines from making contact with the Velcro Small gaps at the top and bottom of the Velcro closure allow the ends of the pamchute to protrude preventing it from sliding down and tangling inside the bag Parallax Inc Rev 10 Page 32 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Materials Two yards of heavy cloth like a nylon canvas Several sheets of poster board Five feet of sewon Velcro tape Procedure V 44444 4 4 Determine the dimensions of the rectangular bag pattern Lay out the parachute and measure its length The length of the pattern is two inches longer than parachute s length Determine the circumference of the canopy when it is wrapped in a tight roll The width of the pattern will be 7 inches wider than this circumference Make a pattern on poster board and cut out Trace the cardboard pattern onto the cloth and cut out Fold over all four sides by one inch then fold again to form a hem that is one inch wide Sew the hems down you will be sewing through three layers of fabric Cut the Velcro strip siX inches shorter than the length of the bag This leaves a small opening at each end of the tube Sew one face of the Velcro furry side up on the faceup side on the right hand hem equidistant from both ends Flip the cloth over and sew the other side of the Velcro strip on the opposite side of the cloth with its edge two inches from the edge of the cloth These two inches of overlapped fabric will be on the inside of the bag forming a ap to protect the parachute from coming in contact with the Velcro Fold the rectangle lengthwise forming a tube with the Velcro strips sealed together and with the twoinch overlap inside Sew the tube closed across both ends This will leave a small opening between the Velcro and the end seam at both ends of the bag Directions for Use 4 4444 444 Untangle the parachute during the FR and tie shroud lines with twist ties Open the tube and place the parachute inside at the top Lay the shroud lines inside the bag keeping them straight Cover the parachute and shroud lines with the inner ap leaving parachute s apeX ring and the ends of shroud lines extending from the bag Fold the tube closed by rst folding the inner ap over the parachute then folding the outer ap over to line up the Velcro Seal the Velcro closure Fold bag in half and link parachute s top and bottom rings together Roll the tube into a ring Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 33 of 49 You can either buy a bag or sew your own 60 Flight Termination Systems thirtyfoot load line As long as the near space capsule meets the weight limits imposed by FAR 101 the stack doesn39t require a ight termination device But in the long run you should carry one of these to prevent losing an expensive near space capsule in case the balloon becomes neutrale buoyant or if a main battery begins to fail during a mission 61 Tyges of Failures Requiring Flight Termination There are two broad categories of failures requiring ight termination Near Spacecm Emergencies NSEs and Flight Path Violations F PVs NSEs occur when some event compromises telemetry such as when ight cells fail and telemetry is no longer being sent FPVs occur when the course of the near space capsule deviates substantially from the predicted ight path and it risks landing in hazardous areas like tall mountains great lakes or restricted areas Another FPV is when the stack becomes neutrally buoyant When events like these occur you have no other option thanto terminate the ight early By terminating missions early the near space capsule lands sooner and closer to its current position This section describes the construction of a Flight Termination Unit F TU The FTU uses athermal knife to sever the load line between the balloon and parachute At ight termination the near spacecm drops from the balloon the recovery parachute deploys and the balloon begins rising much more mpidly Since near space missions described in this book are own on latex balloons the balloon is guamnteed to terminate meeting the requirements of the FAA a balloon capable of lo ing a near spacecra does not become neutrally buoyant when the near spacecm is released The FTU design in this section allows one or more sources to terminate a mission Using sepamte batteries and termination signals lets the FTU meet the FAR 101 requirement for multiple independent and redundant termination methods for larger payloads At the time of this writing the FTU described in this section has only been tested in ight with timers and on the ground with apager Parallax Inc Rev 10 Page 34 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage 62 The Near SDace Fliaht Termination Unit FI39U The FTU is an electronically controlled thermal knife designed to cut the load line between the pamchute and the balloon The ml Seveml signaling sources can opemte the FTU The rst method described in this section is with a stopwatch With a stopwatch the FTU acts as a standalone device that ensures the termination of a ight in cases where the balloon becomes neutrally buoyant The second termination method is a telecommand method and uses triggering devices like a pager ight computer or DTMF decoder Flight computer connection to the FTU allows a so ware command to terminate the ascent when events like when balloon burst is detected a low main volt e alarm occurs or telecommands to the ight computer are transmitted from ground stations Pagers and DTMF decoders allow telecommands from ground stations to terminate near space missions at the detection of a failure The stopwatch method is described in detail while other methods of triggering the FTU are described only in general details I have not had the time to complete my tests of telecommanding the F TU so I leave it as an exercise for the reader 621 Theory of Operation Refer to the schematicbelow The resistance of a threeinch length of 30gauge nichrome wire is less Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 35 of 49 Ucc Head Relay 1N4Z 1 Nichrome Coil Schematic of FT U Trigger Signal ENSSZ4 Ground FTU Schematic According to Ohm s and Watt s Laws when sufficient voltage is present on the nichrome wire the voltage creates enough current and power to make the nichrome wire glow incandescently Nichrome is also designed to tolerate such high temperatures without melting or otherwise failing Temperature sensitive cords like nylon or Dacron melt from the heat produced by a glowing nichrome wire coil According to Ohm s Law when siX volts is present on a 075 ohm nichrome wire it generates a current of I VR Ohm s Law I 675 substitute the voltage and resistance into the equation I 8 Amps According to Watt s Law when eight amps of current ows through a volt difference of siX volts the current generates a power of P IV Watt s Law P 86 substitute the current and voltage into the equation P 48 Watts Dissipating a power of 48 watts within a coiled threeinch length of nichrome wire generates enough heat to make the nichrome wire coil glow orange hot within a second Any nylon or Dacron cord threaded inside of this glowing coil melts the cord into two pieces very quickly However a stopwatch microcontroller pager or DTMF decoder is incapable of sourcing or sinking enough current 8A to operate a coil of nichrome wire The FTU uses a reed relay to sink the necessary amount of current This creates a new problem Not every stopwatch microcontroller pager or DTMF decoder can source or sink enough current to ensure the reed relay operates reliably To ensure reliability a bipolar NPN transistor triggers the reed relay External signaling devices can provide sufficient current to saturate the transistor when the proper base resistor is used When the proper value is used the current from the signaling device is low enough not to damage it but high enough to saturate the transistor Parallax Inc Rev 10 Page 36 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage The entire FTU sequence of operation goes as follows initially there is no current owing into its base With no base current the resistance between the transistor s emitter and collector is so high that effectively no current ows so the transistor behaves like an opened switch When triggered a small current ows from a signaling device into the transistor s base saturating the transistor The resistor R1 limits the amount of current owing into the base of the transistor Q1 protecting the transistor from excessive cun39ent However the value of R1 must be small enough to allow sufficient current to ow into the base of Q1 to saturate it When saturated there is virtually no resistance between the transistor s emitter and collector The transistor now acts like a closed switch letting current ow from between the battery and the coil of the reed relay When the relay s coil is energized contacts inside the relay close letting several amps of current ow through the nichrome wire coil The current owing through the coil produces enough heat to melt the load line passing through the coil When the signal to the transistor ends the transistor is no longer saturated completely cutting off current to the relay s coil As a result the contacts in the relay open stopping the ow of current to the nichrome coil Diode D1 protects the transistor Q1 from current induced by the coil inductor within the relay When current stops owing through the relay the magnetic eld created by current owing through the coil collapses generating a new current owing in the opposite direction It s this current that the diode protects the transistor from 622 Materials F TU PCB One resistor with a value between 330 ohms and 10k ohmsC One 1N4001 diode One 5volt reed relay Radio Shack 275232 One 2N3904 transistor Three inches of 30 gauge nichrome wire 2 mounting hardware nuts bolts and washers One pair of PowerpoleD connectors Stopwatch or other triggering deviceE 623 Construction Modifying the Stopwatch Locate on the back of the stopwatch the four small screws that hold the two halves of the stopwatch s case together Use a small jeweler s Phillips screwdriver to remove them They re small so set them in a safe location where they can t drop or roll out of sight Inside the back of the stopwatch you ll notice a oneinch diameter brass disk with the piezo crystal Use small cutters or an Exacto knife to trim the plastic lip holding the piezo speaker down Remove the speaker Save the speaker for fun science experiments Now turn your attention to the front half of the stopwatch case Keeping the face of the stopwatch face down rotate the stopwatch so that the buttons are at the top Be careful not to knock the three stopwatch buttons loose They are springloaded and are easily replaced should they come loose Remove the lanyard from the stopwatch Notice that the piezo speaker received its power from two spring contacts mounted to the back of the stopwatch PCB These two springs provide the connection to the timer signal and power Use either 26 or 24 gauge stranded wire to eXtend the springs Cut a siXinch length of two pieces of wire red for positive and black for ground Strip back 1 inch of insulation from one end of both wires Stick the stripped end of the bright wire into the right spring and stick the dark wire into the spring on the left side Get a soldering iron hot and heat up one spring and its wire 444 Parallax Int Rev 10 Chapter Six Neal Space Recovery Systems Page 37 of 49 Use solder sparingly and solder the wire into the spring Do this as quickly as you can and don t let the soldering iron touch the stopwatch PCB Repeat this to the other spring A er the soldered has cooled cut short lengths of 116 heat shrink tubing and slip them over the soldered springs Shrink them down increasing the strength of the wires connection to the springs nd the springs connecting the plea speaker and wider Wires inside the springs Fold the wires down and pass them outside the stopwatch case through one of the lanyard holes Use a small amount of hot glue and seal the wires to the opening of the stopwatch to ovide a stmin relief Close the back plate of the stopwatch and screw it back on Now instead of ringing the stopwatch sources a current when the alarm rings Assembling the PCB Soldering Discrete Components Refer to the folllowing diagmm when placing components into the FTU PCB Only the diode and transistor are sensitive to orientation With the PCB turned with the nichrome pads at the top the transistor is mounted with its at face to the right The diode is mounted so that the band of the diode is atthe top Parallax Inc Rev 10 Page 38 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage I l i l Tap Silk of FT U Solder the components in this order 1 The reed relay 2 The 2N3904 transistor 3 The 1N4001 diode 4 The current limiting resistor Recommended resistors are Pager 500 Ohm CCPS 10k Ohm DTMF lk Ohm Coil Power Connection Power to heat the nichrome coil comes from the two bottom right pads of the PCB the coil power pads Depending on the current from the triggering device the power source for the nichrome coil may be the same power source for the transistor For example if a stopwatch is used to trigger the FTU the nichrome coil battery must be used to also operate the transistor However if a ight computer that is capable of sourcing several milliamps of current is used to trigger the F TU then the nichrome coil s battery is not needed to operate the transistor If using the coil s battery only for the coil then solder heavy wire 12 gauge or higher to the coil power pads The length of the wires should be as short as realistic for the application If instead the FTU is sharing the battery between the coil and the transistor then split the positive wire from the battery into a Y and solder one arm of the Y to the coil power pad marked POWER and the other arm of the Y to the pad marked 5V on the bottom left of the FTU PCB Crimp and solder pins and attach Powerpole housings on the ends of the coil power wires The polarity of these wires does matter so use one black and one red housing Back ll the Powerpole housings with hot glue for additional strength Making and Mounting the Nichrome Coils Wrap three inches of 30gauge nichrome wire around a 18 dowel like a jeweler s screw driver leaving 12 to 3A of wire sticking straight out from the ends of the coil These ends are connected to the FTU coil pads not the coil power pads located at the top center of the FTU PCB Nichrome does not solder well so 256 hardware is used to bolt the coil to the FTU Bend a kink into the ends of the coil arms to lock the bolts around Enlarge the coil pads if necessary to get the mounting hardware into the PCB Tighten the bolts securely locking the ends of the coil to the FTU Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 39 of 49 The nichrome 07 Triggering Device If using a stopwatch or pager solder the wires extending from the stopwatch to the FTU to the bottom pads marked SIGNAL and GROUND the stopwatch does not connect to the 5V pad If instead of using a stopwatch you use a triggering device that provides enough current to operate the transistor then connect wires from the triggering device to the three bottom left pads marked SIGNAL 5V and GROUND The pad marked 5V will not trigger the FTU until the SIGNAL pad is energized The length of the triggering wires depends on the application If using a lightweight triggering device like a stopwatch or pager then the wires can be short and the triggering device kept close to the FTU If the triggering device is a ight computer or DTMF decoder from a radio then the wires must terminate in Powerpole connectors A wire cable like 20gauge zip wire speaker wire can make the run from the ight computer or radio to the FTU Finally there is no reason the pager or stopwatch must be permanently connected to the FTU PCB A set of Powerpole connectors on the pagerstopwatch and a second set on the PCB will let you disconnect the triggering device from the Mounting the Flight Termination Unit Securely mount the FTU PCB to a base that is fire resistant A 18 thick sheet of polystyrene plastic works well Make the backing large enough to hold the FTU its battery and the stopwatch if used Tie everything down to the plastic base with nylon wire ties To protect against fires the FTU and its nichrome coil must be mounted inside a block of StyrofoamF Also any device triggering the cutdown must limit its signaling time to only a few seconds However in the case of the stopwatch it has such a low duty cycle that it can ring for a minute without significant fire risk Make the Styrofoam block in two halves so that the two halves trap the FTU between them Cut a notch into the top and bottom of both halves where the load line enters and exits the nichrome coil Parallax Inc Rev 10 Page 40 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Epoxy dowels or Popsicle sticks to the foam halves so that rubber bands can clamp the foam halves around the FTU On one of the foam halves tie a heavy cord and a split ring This line and ring secures the FTU to the apeX of the parachute after the load line is cut free Load Line StHPDFDaM Box two halves Hubberband Nsattocph The closed Ff U on a load line Hubberband Complete FTU Package 624 Operation The night before a launch test that the nichrome coil battery has sufficient capacity to make the coil glow Then cut 12 of load line and thread it through the cooled nichrome coil Tie loops into both ends of the line Close the foam halves around the FTU PCB leaving the ends of the load line sticking outside the block Clamp the foam halves together with rubber bands trapping the FTU inside Test that the load line can slide within the block but be careful not to pull the load line out of the block Secure the FTU to the apeX of the parachute with the split ring and the bottom end of the load line coming out of the FTU The parachute now has two attachments to the FTU one being the F TU s load line and the other is the split ring Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 41 of 49 Load Line XRay View FT U batter FTU box and load line Battery XHay View FTU Battery and Box The next morning during balloon fill tie one end of the load line to the loop at the top of the FTU and the other end of the load line to the balloon Tape all knots If using the stopwatch set the timer Be sure the time is long enough for the balloon to reach its predicted max altitude If using a pager instead of the stopwatch then be sure to disconnect the pager from the FTU before switching on the pager Pagers test their alarms when first powered up and the pager selftest will trigger the FTU if the pager is attached it s embarrassing to launch a balloon without the near spacecraft After the pager selftest attach the pager to the FTU signal connectors If using a ight computer to trigger the FTU then make sure the signal from the ight computer is low at power up If there s a risk the signal may be high momentarily then disconnect the signal line from the FTU at ight computer power up Also make sure the ight code loaded into the ight computer will not trigger the FTU before launch While the stack is still on the ground GPS altitude errors may fool the ight computer into thinking the balloon has burst It s best if the ight computer will not check for balloon burst until several minutes after launch 625 CCPS as Flight Termination Signals The Block 1 and Block 2 CCPS are capable of sourcing 20 mA of current This is sufficient current to trigger the FTU s NPN transistor with a 1k resistor in series with the base The command cable should be sewn into the parachute s canopy then tied to a shroud line on the parachute ring Create a tube from twill tape along a previously sewn twill tape Pass the cable through the tube after it is sewn The tube lets the parachute canopy ex without binding from the command cable From there a cable can connect the CCPS to the command cable A command cable that drops through the spill hole of a parachute risks tangling shroud lines Make the command cable from thin speaker cable The cable contains two stranded wires enclosed in exible insulation Parallax Inc Rev 10 Page 42 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage A paradlube with the signal linesor the H39Usewn in Top L uL doMn signal line at apex of canopy Bottom iTUSIyIJa line at bottom of canopy If the CCPS has control of the FTU then it should terminate the ight When the mainbattery voltage drops too low Experiment With low voltage conditions on the ground before giving the CCPS control of the FTU To terminate the ight use the following BSZp commands assuming the FTU signal is connected to 10 pin 8 626 Pagers as Flight Termination Signals The simplest independent receiver you can use to terminate ight is apager Pagers have thousands of hours of development and testing to insure reliability and are durable and inexpensive The following directions explain hoW to modify a 20 pager so that it can terminate a near space ight Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 43 of 49 There are two types of pagers in use The rst kinduses a ve number cap code as an ID When this type of pager is called a set of ve tones is sent over the radio Only the pager with that speci c cap code will respond to the signal and all other pagers will ignore it The typical frequency used for these pagers is 15224 MHZ just above the twometer band You can use a scanner to hear these tones The second type of pager uses a seven digit data string made up of digital tones The tones are sent FSK frequency shi keying Rather than develop a new mdio receiver which could fail due to construction errors or use a heavy HT I decided to experiment with a dependable pager So ware at the Paging Service allows passwords to be required to ring a pager preventing an accidental or malicious termination event Pagers opemte intwo modes beep and vibmte modes These directions take advantage of the vibmte mode The vibmtor in a pager is atiny motor with an offcenter weight When the motor spins the offcenter weight rocks the pager creating the vibmtion sensation In its new Life the pager is used sans motor to opemte an FTU Construction 777a opened pager lt Purchase a pager do not modify a rented pager as the Paging Service does look kindly to this Open the back of a pager Locate the vibrator motor this is a tiny motor with an offcenter weight Physically disconnect the motor from the pager case Cut the power leads to the motor close to the motor leaving the leads as long as possible Strip about W of insulation from the ends of the motor leads Cut two 24 or 26 stmnded AWG wires to a length of 12 inches Strip W of insulation from one end of the wires and about 2 of insulation from the other ltlt4ltltltlt ends Cut two 2 lengths at least of heat shrink tubing large enough to cover the above wires Solder the stmnded wire to the motor leads and cover the solder joint inheat shrink tubing Find alocationin the pager case to pass the wire through Cut a small notch in the pager case at this location Test t the wires making sure the pager cover can still close ltltltltlt Parallax Inc Rev 10 Page 44 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage ltlt Close the pager cover Terminat wires with connectors like Powerpoles or Dean s Connectors Note the uthor recommends using a different style of connector than is normally used for battery connections in the near spacecra 777e pager alter removing the Vibrating motor and sobering Wires to the mobor s pads on the PCB 45 Procedure for Using Pager Before powering up a pager disconnect the pager from the FTU Power up the pager ltltltlt E E 1 g S 3 E Fa Connect the pager to the FTU Note A er powering up the pager the pager performs a selftest The test will trigger the FTU if it is connected To prevent a premature and embarrassing surface termination of the balloon disconnect the pager from the F TU before powering up the pager A er a few seconds you can reconnect the pager During a mission the pager listens for a signal to vibrate If an FPV occurs Chase Crews or Mission Control calls the pager number To protect the ight from being terminated by accident ask the Paging Service to install a password on the pager Only authorized individuals are given the password NSP has performed two tests on pagers in near space The missions experienced pager failures because the radiating pattern from paging tower antennas is concentmted on the horizon n selecting a Paging Service make sure they have antennas seveml hundred miles from the launch site these antennas are located on the horizon during a ight 70 Audio Beacons A good recovery aid to add to all near space capsule is the audio beacon Amateur rocketry has used similar devices for years to located model rockets in tall grass A recovered near space capsule may not be visible one hundred feet away from its last recorded GPS location but the beeping of the audio beacon can be heard Check with Adept rocketry for one of their loudest models or make your own recommended Parallax Inc Rev 10 71 Chapter Six Near Space Recovery Systems Page 45 of 49 Constructing an Audio Beacon A suitable audio beacon can be constructed from materials available at Radio Shack In addition to the satisfaction of constructing more of the near space program is the money that is saved 711 712 ltltltltltlt lt4ltlt ltltlt lt4 M ate ri a Is One loud 12V DC piezo buzzerG Radio Shack 273060 will work Ninevolt battery sna SPST or SPDT toggle switch Two colors of 24 AWG stranded wire Red and black are good color choices 3 16 diameter heat shrink tubing Remove Before Flightquot tagH Proced u re Cut 30 inches of both colors of wire Strip 2 of insulation from both ends of both wires Twist 30inch wires to the leads of buzzer and solder Use a meaningful combination of colors Cut four pieces of heat shrink tubing 2 long Slide two pieces of tubing onto the solderedwires and shrink Solder battery snap to other end of the 30inch wires Cover soldered connection with heat shrink tubing and ShI JILk Note Ensure the red battery lead is connected to the red lead of buzzer Cut positive red lead ten inches from battery snap Strip 2 39 39on from each wire end Cut two pieces ofheat shrink tubing and slide one onto each cut wire Tin the ends of the wires and the terminals of the switch Solder the wires to the switch terminals Note If using a SPDT switch one wire must be soldered to the center terminal otherwise the terminals solderedto are not important Cover exposed solder joint with heat shrink tubing and shrink Twist wires to keep them neat 777a compabed audio beacon Parallax Inc Rev 10 Page 46 of 49 Neal Space Exploration with the BASIC Stamp by Paul Velhage 72 Recommendations for Audio Beacon Find alocation for the buzzer on the outside of the near space capsule or its recovery system A good location is on aboom like the antenna boom Attach the buzzer to the exterior of the capsule with rubber bands Then slide the power wires battery snap andpower switchthrough an opening in an E Quad Port Using the passthrough hole for an antenna coax is a good idea Install the beacon battery where it can39t pop loose and then give the capsule a real good shake just to make sure Since the beacon is loud and annoying don t power it up until just before launch Attach a quotRemove Before Flightquot tag to the beacon power switch to remind launch crews to power up it A silent beacon is useless deadweight Place the audio beacon securely on a boom Don t forget a little reminder to start the beacon before launch the buzzer is placed on a different module and on the opposite side from the camcorder lens and noise is reduced on the camcorder s audio recording On thing to notice a er recovery of the e videotape is the change in the audio beacon s volume during the ight because of the reduced air pressure in near space Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 47 of 49 Good to Know Air Pressure Air molecules are matter and like all other forms of matter have mass Gravity pulls on anything with mass giving it weight What we measure as air pressure is the weight of the air column above us In terms most Americans are familiar with the weight of the air colunm above us is 147 pounds per square inch In the SI it is equal to 1013 millibars mb or 1013 kilopascals Think of it this way Every square inch you can draw on a ground table or person has almost fteen pounds of weight pressing down on it As seen from above I measure approximately six inches by twentyfour inches This gives me a surface area of 144 square inches At approximately fteen PSI there is 2160 pounds of weight pushing straight down on me I am carrying an automobile s worth of weight on my shoulders No wonder I feel tired at the end of the day Since air is a uid medium it ows around and inside of me exerting pressure in all directions The balance of air pressure inside and outside of me keeps me from being crushed by the weight of the air colunm above me Without this I would be crushed just as if there was car placed on my shoulders As a balloon ascends into near space it leaves more air below it and less air above it So as the balloon climbs higher there is less weight from the air above the balloon In the standard atmosphere air pressure drops by a factor of two every 18000 feet The average air pressure at mean sea level is 1013 millibars mb A millibar is one thousandth of a bar Let s round this gure down to 1000 mb for this exercise in air pressure If the air pressure is 1000 mb at sea level then when the balloon reaches an altitude of 18000 feet the air pressure will be 500 mb At 36000 feet which is 18000 feet higher still the air pressure drops another factor of two So at 36000 feet the air pressure is 250 mb A constant factor of change for one variable for every xed change in a second variable creates a logarithmic curve Here is a second way to state the change in pressure as a function of altitude For every 50000 feet change in altitude the pressure drops by a factor of ninety percent At 50000 feet the air pressure is 90 lower than at the surface Using our rst example the air pressure is 100 mb at 50000 feet At an altitude of 100000 feet the air pressure is 10 mb or one percent of surface pressure Air Pressure Graph of Pressure vs Altitude Altitude feet o 100 200 300 400 500 500 700 800 900 1000 Pressure mh Parallax Inc Rev 10 Page 48 of 49 Near Space Exploration with the BASIC Stamp by Paul Verhage Vapor Pressure Boiling Water In Near Space According to the book Chemical Principles and PropertiesI vapor pressure is the pressure exerted by a vapor when in equilibrium with its liquid A gas and liquid at equilibrium occurs when the number of molecules evaporating from a liquid in a unit of time equals the number of molecules condensing back into the liquid in the same unit of time Vapor pressure for a liquid depends on the temperature of the liquid When the vapor pressure of a liquid equals the ambient pressure then the liquid begins to boil Let us take water as an example When you bring water to a temperature of 100 degrees C vapor pressure of the water equals the atmospheric pressure at mean sea level As a result the water begins to boil If you try boiling water at the top of a mountain the water boils at a lower temperature because the ambient air pressure is lower The water needs to be at a lower vapor pressure or lower temperature to boil Room temperature water 20 degrees C or 68 degrees F has a vapor pressure of 234 mb This pressure occurs at an altitude of around 82000 feet So if you bring room temperature water up to an altitude of just below 82000 it begins to boil Body temperature is 37 degrees C At body temperature water boils at a pressure of 60 mb This pressure occurs at an altitude of around 62000 feet the Armstrong Line Before you can reach near space your blood begins to boil Of course the bends will kill you rst Here is a table from Chemical Principles and Properties covering vapor pressures of water at various temperaturesI Temperature Vapor Pressure Temperature Vapor Pressure Parallax Inc Rev 10 Chapter Six Near Space Recovery Systems Page 49 of 49 Performing Your Own Low Pressure Experiments Educational Innovations makes a wonderful and affordable vacuum apparatus However to make it affordable it is micro scale Do not let this be a detractor it s a great toy For less than forty dollars you can play with lowpressure effects on water and marshmallows Order your own micro scale vacuum apparatus VAC10 from the Teacher Source at httpwwwteachersourcecom Near Space Humor Top Ten Things NOT To Say When the Near Space Capsule Lands in a Homeowner39s Yard 1 You didn t touch that did you K 2 Are you familiar with the movie The Andromeda Strain 3 Hello we re from the UN This is guaranteed to get you shot in some locations in the rural West 4 We re from the government We will help you recover from this incident Something else to say to get yourself shot 5 We re from the FBI We d like to discuss with you what we monitored you doing through that capsule that landed in your yard 6 It landed here only 20 minutes ago Good you should still be safe 7 It depends on what you mean when you say dangerous L 8 You have ten minutes to pack your most important possessions 9 Your homeowner s insurance should cover this event 10 Look at the tip of this pen please A DACRON is a registered trademark of INVISTA B Velcro is a registered trademark of Velcro Industries BV C The value of the resistor depends of the triggering device You may have to experiment with various resistors to find the appropriate value D Powerpole is a registered trademark of Anderson Power Products E Use Wal Mart s inexpensive stopwatch the ATQ2 It costs 495 F Trademark of The Dow Chemical Company G Do not use a piezo speaker as they require a driver H Available at places like the Boeing Surplus Sales store in Seattle WA I Chemical Principles and Properties Michael J Sienko and Robert A Plane Second Edition 1974 McGraw 1 I Converted from units of atmospheres to mb by the author Use this data along with the table of the Standard Atmosphere in section 514 K Suggested by Mark Conner L Suggested by my mother Erma Verhage Parallax Inc Rev 10