Fu­ture tech Pluto hop­per

NASA is look­ing at an in­ge­nious way of slow­ing space­craft with a dwarf-planet leap­ing mis­sion

All About Space - - Contents -

Plan­e­tary ex­plo­ration mis­sions are al­ways a trade off of tech­nol­ogy and cost. The very first ones just flew past or crashed into their tar­gets, then came sta­tion­ary soft lan­ders and an in­crease in the use of wheeled rovers. If you're vis­it­ing a planet you want to explore as much of it as pos­si­ble but, as the Google Lu­nar XPrize has demon­strated, it re­mains pro­hib­i­tively ex­pen­sive and chal­leng­ing to place some­thing on the Moon, let alone on a dis­tant planet. The prob­lem be­comes more pro­nounced the fur­ther away the tar­get is, and each des­ti­na­tion has its own chal­lenges: Venus has a thick at­mos­phere but a toxic en­vi­ron­ment, Mars has lower grav­ity but hardly any at­mos­phere to aid brak­ing. Pluto is per­haps the ul­ti­mate chal­lenge, be­ing so dis­tant the trip re­quires the most en­ergy of any in the So­lar Sys­tem. It took New Hori­zons, one of the fastest-ever space probes, over nine years just to get there just to fly past. How­ever, Pluto has an ad­van­ta­geous com­bi­na­tion of at­mo­spher­ics and grav­ity that a team from the Global Aero­space Cor­po­ra­tion (GAC) are hop­ing to ex­ploit to open up Pluto for ex­plo­ration.

GAC are an aero­space en­gi­neer­ing com­pany based in Ir­win­dale, Cal­i­for­nia. They have ex­pe­ri­ence in the use of in­flat­able struc­tures in

space, which they are us­ing to de­sign an in­ge­nious space­craft brak­ing sys­tem. Although Pluto's sur­face pres­sure is only ten mil­lionths of Earth's, its low grav­ity (6.7 per cent of the Earth) means the at­mos­phere stretches out a long way from the plan­ets sur­face. It stretches to about 1,600 kilo­me­tres (1,000 miles), or 135 per cent of the ra­dius of the planet – Earth's at­mos­phere is in the re­gion of 12 or so per cent of its av­er­age ra­dius. GAC have en­gi­neered Earthly bal­loons, in­flat­able space habi­tats and drag sails for satellites, and plan to ef­fi­ciently de­liver a pay­load to Pluto's sur­face with a bal­loon de­cel­er­a­tor that ex­pands in space to some­thing like the di­men­sions of a foot­ball pitch. De­spite a likely ap­proach speed of about 14 kilo­me­tres (8.7 miles) per se­cond, the huge, light­weight cross sec­tion of the bal­loon should en­able a space­craft to gently de­cel­er­ate into the at­mos­phere, need­ing less than 3.5 kilo­grams of pro­pel­lant for the fi­nal soft touch­down.

Ex­ploit­ing the in situ re­source of the at­mos­phere to land al­most for ‘free‘ would free up valu­able pay­load space for a lo­cal propul­sion sys­tem. GAC have a spec­tac­u­lar plan to re­use the rocket propul­sion that the craft has to have any­way. Af­ter mak­ing its ini­tial soft land­ing and in­ves­ti­gat­ing the area, GAC's de­sign will fire up its en­gine with the pro­pel­lant not needed for land­ing and launch it­self off across the land­scape in a se­ries of hops. In this way it would be able to col­lect data from a num­ber of land­ing sites, at dif­fer­ent heights through the at­mos­phere and take aerial pho­to­graphs.

Although in its early stages, GAC pro­pose test­ing sub-scale ver­sions of the sys­tem packed into a cube­sat that could be de­ployed from the In­ter­na­tional Space Sta­tion. This way, com­plete craft could be eval­u­ated in Earth or­bit be­fore fi­nal launch to Pluto. Such an in­flat­able drag sail could also be use­ful in help­ing space­craft brake into or­bit around any body that has an at­mos­phere. In the fu­ture GAC hope to be able to de­velop a com­plete mis­sion in col­lab­o­ra­tion with a NASA cen­tre like JPL or LaRC, within a time­frame be­tween ten to 15 years.

“Pluto has an ad­van­ta­geous com­bi­na­tion of at­mo­spher­ics and grav­ity which can be ex­ploited to open up Pluto for ex­plo­ration"

De­ploy­ment

GAC's bal­loon de­cel­er­a­tor would be un­furled in space as a prospec­tive space­craft neared the planet. De­cel­er­a­tion

Fully in­flated the bal­loon would be 80 me­tres across – large enough to bleed off the ma­jor­ity on the 14km/s ap­proach speed in the dif­fuse at­mos­phere. De­flated en­ve­lope The bal­loon it­self would float off to an­other land­ing point be­fore de­flat­ing; it could carry other in­stru­ments for an ex­tra sur­vey lo­ca­tion.

Ground sur­vey The space­craft would carry out a typ­i­cal lan­der mis­sion, sur­vey­ing and sam­pling its

land­ing area. Soft land­ing

Once the speed had dropped to 50 me­tres per se­cond GAC's de­sign would sep­a­rate from the bal­loon to make a con­ven­tional (but eco­nom­i­cal) rock­et­pow­ered land­ing.

In­ter­plan­e­tary trans­fer A flight to the outer plan­ets takes a long time and a lot of en­ergy.

New Hori­zons was boosted di­rectly to­wards Pluto, be­com­ing one of the fastest space­craft ever,

but it still took over nine years. Hop!

The weight sav­ing from us­ing the bal­loon and at­mos­phere for de­cel­er­a­tion en­ables the mis­sion to have spare pro­pel­lant. This can be used for mul­ti­ple hops, some­times kilo­me­tres at a time, across the land­scape. Aerial sur­vey

The hops pro­vide re­peated op­por­tu­nity to col­lect high res­o­lu­tion aerial pic­tures, as well as ad­di­tional ground sur­veys.

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