7/28/2019 STRATOS Weather Balloon Information Display for The
Big Bang Fair 2013, National Science and Engineering
Competition
1/1
2mmNylonCord
v=verticaldescentvelocity,inm/s-1w=weightoftheparachute+payload,inNrho=airdensityatsealevel(1.225Kg/m3)dc=parachutedragcoefficient(0.75)s=totalsurfaceareaoftheparachute(*0.3
2
)
=2
Theparachutewechosewasoriginallydesignedforusewithmodelrockets.Its
lightweightnylonfabriciswoveninacrosshatchpatterntopreventtearing,whichis
essentialforourpurpose,sincethepayloadcoulddoconsiderabledamageifitdescended
atterminalvelocity!Weu
sedthefollowingequationtocalculatethedescentspeedofthepayloadwithour
24"parachuteattached.Wethentestedthisfigurebytiminghowlongittooktofall
fromthetopofourschoolbuilding.
Althoughthin,thisbraidednyloncordisverystrong-ithasabreakingstrainof22.5kg.Weused10mofitbetweentheballoonandthepayload.
Theteamwasconcernedthattheparachutewouldgettangledduringitsascent,soweusedaninnovativesolution:securingawashertothecordjustunderwherethestretchedoutparachutewouldrest,asshowninthescanofouroriginalsketch:
Washer
24"RipstopParachute
where,
1.81m3helium(V-SizedCylinder)
600gMeteorologicalWeatherBalloon
ByusingInternetdataforourballoon,wefoundthatthevolumeofgasneededto
filltheballoonatlaunchwas1.81m3ofhelium-thesizeofastandardV-sizedBOCgas
cylinder-toachieveourtargetaltitudeof30km.Ifwefilledmorethanthisvolumeofgas,
theballoonwouldexpandtoitsburstingpointataloweraltitude-thevolumeatburstbeing
over120m3at6mdiameter-thesizeofahouse.Thevolumeofheliumfilledwasalsousedin
theflight-pathprediction-toomuchgas,andtheballoonwouldrisefasterthanpredicted,too
littleandtheballoonandpayloadwoulddriftfurtherthanpredicted.
Thereareseveraldifferenttypesofweatherballoons.Weusedanatural
latex"sounding"balloon,whichisusedinhighaltitudescience
experimentsbyweatherstations.Weatherballoonsaremeasured
accordingtotheirweight,withheavieronescostingmorebutreachinga
higheraltitude.Weuseda600gballoon,asitcouldachieveourtarget
altitudeof100,000ft,withlessheliumneededthanalargerballoon.We
usedheliumgasasopposedtohydrogensinceheliumissafertohandle.
Anotherinnovationofourswastoattachthemultiple
cordsrunningfromthepayloadtoacurtainringattached
tothemainsinglecorduptotheballoon.Thisway,we
couldindividuallygaffertapeeachknottoensurethey
weresecure,and thatthelineswouldnottangle.
CurtainRing
PolystyreneContainer
Ourpayloadwasoriginallygoingtobeawintertapcover,thoughwecouldn'tfindonewhilstpurchasingequipmentsoinsteadchosetorecycleanolddry-icecontainerfromtheschool'ssciencedepartment,whichhadpreviouslybeenusedasastageprop.Thehollowpolystyreneboxmeasures27cmwx24cmlx25cmh.
AttachingcordtopayloadAsshownintheoriginalsketchtotheleft,wegaffertapedthecordsfromthecurtainringtoeachsideofSTRATOS'spayloa
d,toensureitsst
abilityduringflight.Thegaffertapealsohelpedtowater-sealthepayloadarounditsopening-importanttoprotecttheelectronicsifitwasrainingwhereitlanded.
GPSTrackerTheGPSTrackerinthepayloadenablesustotrackthepayload'slocationonceithaslanded.Toreceivethecoordinates,wephonethedevice,andittextsbackitslocationandinformationsuchasbattery
lifeandalinktoamobileversionofamap.
WeusedasmallCanonpoint-and-shootcamera,theA550,"borrowed"fromtheGraphicsdepartmentatschool(inexchangeforanewcamera).Wehadtousethisoldcamerabecauseithastherareabilitytobe"hacked",thatis,tobeprogrammedtotakephotographsatregulartimed
intervalsautomatically,
essentialforourSTRATOSproject.
Camera
Insulation
HandWarmers
Tokeeptheelectronicsinsidethepayloadfunctioningdespitethefreezingtemperaturesoutside,thepolystyrenepayloadactedasagoodinsulator,andasanaddedmeasure,wetightlypackednewspaperinsidetotraplayersofair.Thenewspaperalsohelpedtokeepthecontentsinplaceinthehighwinds.
Regularhand-warmersonlystayhotforhalfanhour-tooshortforSTRATOS's4hourflight.
After
someresearch,welearntaboutironoxidisinghandwarmerswhichremainwarmforupto7hoursata70C,icturedontheright.
Wesetthecameratotakeaphotoevery10secondsatitsbestquality,witha2GBmemorycardinside.Byusingthefactthecameratook1,486photos,wecalculatedtheexactflighttimewas4.13hours.
