The Fu­ture of Con­struc­tion in Space

Hint: Air pump re­quired.

Air & Space Smithsonian - - Front Page - BY BRUCE LIEBER­MAN

LATE THIS YEAR OR EARLY NEXT, NASA WILL BUILD AN AD­DI­TION to the In­ter­na­tional Space Sta­tion, in­creas­ing the or­bital lab­o­ra­tory’s size from eight rooms to nine. The new room is like no other on the sta­tion, and will be very easy to con­struct: Just con­nect to a dock­ing port, fill with com­pressed air, and voilà! In­stant space habi­tat.

The hard part was the 15 years of re­search and de­vel­op­ment that Bigelow Aerospace in North Las Ve­gas needed to cre­ate the Bigelow Ex­pand­able Ac­tiv­ity Mod­ule, or BEAM. Ini­tially sched­uled for a Septem­ber launch, BEAM’S test de­ploy­ment is now de­layed due to the post-launch ex­plo­sion of a Spacex Fal­con 9 rocket bound for the ISS on June 28 — and no one yet knows how long that de­lay will be. Once BEAM does reach its des­ti­na­tion, it will un­dergo two years of in­ten­sive test­ing, a trial run for a tech­nol­ogy that could play a sig­nif­i­cant role in fu­ture hu­man space­flight and low-earth-or­bit com­mer­cial ven­tures: in­flat­able space­craft.

Bigelow’s in­flat­able is, in a sense, the res­ur­rec­tion of a can­celed NASA pro­gram. In the 1990s, NASA de­vel­oped Tran­shab, or Transit Habi­tat, an in­flat­able liv­ing area to test in space with the goal of us­ing such a con­tainer to trans­port hu­mans to Mars and to re­place the In­ter­na­tional Space Sta­tion’s alu­minum habi­ta­tion mod­ule. Tran­shab got only as far as ground test­ing be­fore Congress cut the pro­gram’s fund­ing in 2000. Real es­tate bil­lion­aire and space en­thu­si­ast Robert T. Bigelow pur­chased the rights to the patents that NASA filed for the tech­nol­ogy.

Bigelow Aerospace picked up where Tran­shab left off, ad­vanc­ing re­search and de­vel­op­ment and even­tu­ally putting two in­flat­able test mod­ules—ge­n­e­sis I and Ii—into or­bit in 2006 and 2007. Both mod­ules, each the size of a van, re­main in or­bit to­day. Their bat­ter­ies ran out years ago; even­tu­ally they’ll reen­ter the at­mos­phere and burn up. But they served their pur­pose. “Ge­n­e­sis I and II val­i­dated our ba­sic ar­chi­tec­ture,” says Mike Gold, Bigelow’s Di­rec­tor of Washington, D.C. Oper­a­tions & Busi­ness Growth. “From a tech­ni­cal per­spec­tive, these space­craft showed that ex­pand­able sys­tems could sur­vive the rig­ors of launch, that our de­ploy­ment process would work, and that we could suc­cess­fully in­te­grate win­dows into an ex­pand­able habi­tat struc­ture.”

In­flat­able habi­tats in space have ad­van­tages over con­ven­tional me­tal struc­tures. First, they’re a lot cheaper to get into or­bit. One rea­son is weight: BEAM, de­signed to ex­pand to 16 cu­bic me­ters, or about the size of a 10- by 12-foot room, weighs only 3,000 pounds at launch. Its den­sity—that is, its mass di­vided by its vol­ume—is 88 kilo­grams per cu­bic me­ter. By com­par­i­son, the den­sity of the U.S. lab at the In­ter­na­tional Space Sta­tion, Des­tiny, is 137 kilo­grams per cu­bic me­ter. The ISS’S

Tran­quil­ity mod­ule has a den­sity of 194 kilo­grams per cu­bic me­ter.

In­flat­a­bles are also ap­peal­ingly com­pact. Folded into its launch con­fig­u­ra­tion, BEAM takes up a space five feet by seven feet. Gold cites BEAM’S mod­est cost— 17.8 mil­lion—as one of its key ad­van­tages over older tech­nolo­gies: “I can’t think of any other sub­stan­tial hard­ware that has been done, or al­most any other pro­ject that’s been done, for such a rel­a­tively mi­nor amount of money,” he says.

Re­duc­ing the size and weight of the pay­load at launch is what saves taxpayers money. “You gain tremen­dously in terms of launch ef­fi­ciency, and that’s the hard­est, most ex­pen­sive thing about space—get­ting out of Earth’s grav­ity well,” says Ge­orge Zamka, a for­mer shut­tle as­tro­naut who worked for the FAA’S Of­fice of Com­mer­cial Space Trans­porta­tion be­fore join­ing Bigelow Aerospace last year.

Ra­jib Das­gupta, BEAM pro­ject man­ager for NASA, says in­flat­a­bles are one con­cept that the space agency is study­ing for habi­ta­tion in­side cis­lu­nar space—the sphere formed by the moon’s or­bit of Earth. “Suc­cess­ful BEAM demon­stra­tion on ISS will cer­tainly be a gi­ant step­ping stone to fu­ture deep-space ex­plo­ration habi­tats,” he says.

In­fla­tion Eval­u­a­tion

BEAM was sched­uled to be launched by Spacex CRS-8, a cargo re­sup­ply mis­sion to the ISS in­tially sched­uled for Septem­ber 2, though it will now be de­layed as a re­sult of the Spacex ex­plo­sion. (Bigelow’s Gold will only say he re­mains hope­ful that BEAM will reach the sta­tion “this cal­en­dar year.”) Once BEAM ar­rives, it will face two years of en­gi­neer­ing tests. But its first hur­dle maybe be sim­ply over­com­ing neg­a­tive as­so­ci­a­tions with the word “in­flat­able.”

“Peo­ple some­times have a bad per­cep­tion of in­flat­able struc­tures be­cause of their ex­pe­ri­ence with low-cost, poorly made prod­ucts such as pool toys that leak, or party bal­loons that burst,” says David Cado­gan, di­rec­tor of en­gi­neer­ing for ILC Dover in Fred­er­ica, Delaware, a firm that has worked with NASA for decades, de­vel­op­ing space­suits, airbags for the Mars rovers, and airbags for Boe­ing’s pro­posed Crew Space Trans­porta­tion-100 ve­hi­cle. But ev­ery day we en­trust our lives to in­flat­able struc­tures: car tires and air bags, emer­gency es­cape slides in air­planes, an­gio­plasty surg­eries.

Of course, in­flat­able habi­tats have never housed hu­man be­ings in space be­fore. NASA and its con­trac­tors have half a cen­tury’s worth of ex­pe­ri­ence with alu­minum pres­sure ves­sels; they know how to as­sem­ble them in space, how to in­spect and main­tain them, how to an­a­lyze their struc­tural loads, and how to con­trol frac­tures in them. They also know alu­minum’s tol­er­ance of—and vul­ner­a­bil­ity to—im­pacts from mi­crom­e­te­oroids and or­bital de­bris. Engi­neers have de­vel­oped ways to mon­i­tor im­pacts, find leaks, an­a­lyze dam­age, and even make lim­ited re­pairs.

Steve Stich, di­rec­tor of ex­plo­ration, in­te­gra­tion and science at NASA’S John­son Space Cen­ter, says in­flat­able habi­tats may some­day be in­te­grated with me­tal pres­sure ves­sels, but the agency needs to learn a lot more about how in­flat­a­bles hold up against the haz­ards of space: ra­di­a­tion ex­po­sure, ther­mal cy­cling, de­bris im­pact. For ex­am­ple, BEAM has a me­tal struc­ture at the end that berths to the Iss—it’s known as a com­mon berthing mech­a­nism. Load­ing forces from the sta­tion will place stresses on BEAM, par­tic­u­larly where the berthing mech­a­nism at­taches to the sta­tion, and also where the berthing mech­a­nism at­taches to BEAM’S fab­ric shell.

No one yet knows whether in­flat­able habi­tats can safely dock to other space­craft, and whether an air­lock can be in­te­grated into an in­flat­able habi­tat.

Stich be­lieves that for high-stress ap­pli­ca­tions like dock­ing, alu­minum will likely re­main: “I don’t see us to­tally ever phas­ing out me­tal­lic struc­tures,” he says.

One chal­lenge, Stich adds, is how to de­velop in­flat­a­bles that can be out­fit­ted with life sup­port, crew quar­ters, and other sys­tems prior to launch; if not, astro­nauts will have to set those up once the habi­tat is de­ployed in space. Con­ven­tional mod­ules at the space sta­tion typ­i­cally ar­rive with equip­ment al­ready in­te­grated into the struc­ture.

Ge­orge Stu­dor, a re­tired NASA se­nior pro­ject engi­neer who now con­sults, through var­i­ous con­trac­tors, for the NASA En­gi­neer­ing and Safety Cen­ter, says in­flat­able habi­tats face an up­hill bat­tle to win the kind of con­fi­dence NASA has in the me­tal ships it has been build­ing for half a cen­tury.

“It takes her­itage to have con­fi­dence in a tech­nol­ogy,” Stu­dor says. “Even if the in­flat­able Bigelow space sta­tion turns out re­ally great, it doesn’t mean that there aren’t faults with that thing…. There haven’t been enough of them made. There hasn’t been enough ma­te­ri­als ex­pe­ri­ence and test­ing. It be­comes a more risky space ven­ture than what we would nor­mally do. But be­cause of its po­ten­tial, NASA has been work­ing with Bigelow for many years to help the tech­nol­ogy ma­ture.”

An idea Nearly as Old as NASA

NASA first be­gan study­ing the pos­si­bil­i­ties of in­flat­able struc­tures around 1960, when re­searchers at NASA’S Langley Re­search Cen­ter in Vir­ginia drew up plans for a dough­nut-shaped space sta­tion. In another in­flat­a­bles pro­ject, known as Echo, NASA launched gi­ant My­lar-coated bal­loons into or­bit in 1960 and 1964 and bounced ra­dio sig­nals off them. In 1965, the agency de­vel­oped con­cepts for in­flat­able moon habi­tats, and in 1967 it stud­ied the idea of an air-filled space sta­tion nick­named Moby Dick, ap­par­ently due to its large di­men­sions.

Tran­shab emerged 30 years later as a pro­ject at NASA’S John­son Space Cen­ter. The ef­fort was led by Wil­liam Sch­nei­der, who had worked on mi­crom­e­te­oroid pro­tec­tion for the space shut­tle. Sch­nei­der had al­ready re­tired when Tran­shab was can­celed in 2000, but he has con­sulted with Bigelow Aerospace.

Tran­shab faced skep­ti­cism from the start. NASA’S Kriss Kennedy, a space ar­chi­tect who helped cre­ate the in­flat­able and coined the name, re­called in Air & Space (“Launch. In­flate. In­sert Crew,” May, 1999) that dur­ing public talks he would pop a bal­loon to drive the point home that this is a bal­loon; in­flat­able struc­tures are not. Dur­ing the short-lived Tran­shab pro­gram, NASA engi­neers de­vel­oped in­flat­able habi­tats with a foot-thick, 16-layer shell of foam and fab­ric that stood up to bal­lis­tics tests de­signed to sim­u­late strikes by mi­crom­e­te­oroids and or­bital de­bris.

The ac­tual ar­chi­tec­ture of Tran­shab in­cluded three thin-film air bladders cov­ered by al­ter­nat­ing lay­ers of ce­ramic fab­ric, polyurethane foam, and Kevlar. The ce­ramic fab­ric, called Nex­tel, was sand­wiched by three-inch lay­ers of foam. To­gether, the lay­ers served to pro­tect against mi­crom­e­te­oroids. The Kevlar web­bing made up Tran­shab’s pres­sure-hold­ing re­straint layer, which was wo­ven like a rug to re­duce the num­ber of seams and max­i­mize strength. In­side Tran­shab, two- inch-thick walls sur­round­ing bed­rooms would be filled with wa­ter to shield crew mem­bers from ra­di­a­tion.

BEAM rep­re­sents a gen­er­a­tion of re­fine­ment to that ear­lier de­sign. From in­side to out­side, says Das­gupta, it in­cludes a blad­der, re­straint sys­tem, mi­crom­e­te­oroid/or­bital de­bris pro­tec­tion, in­su­la­tion, and an ex­ter­nal ther­mal blan­ket. (BEAM’S pre­cise makeup is pro­pri­etary.) Gold says BEAM’S “Kevlar-like” pro­tec­tive lay­ers will mea­sure up. “We have done side-by-side hy­per-ve­loc­ity im­pact test­ing with por­tions of the ISS’S [mi­crom­e­te­oroid/or­bital de­bris pro­tec­tion] lay­ers,” he says. “Our sys­tem of­fers equal if not su­pe­rior pro­tec­tions to what’s on the ISS to­day.”

He pauses be­fore choos­ing a dra­matic ex­am­ple. “If you’re about to get shot, would you rather have alu­minum in front of you or a Kevlar vest?”

Trial in Space

Once Spacex’s un­crewed Dragon cargo space­craft reaches the ISS, the sta­tion’s ro­botic arm will be used to at­tach BEAM to the aft sec­tion of the Node 3 mod­ule. With the hatch to the sta­tion closed, air tanks in­side BEAM will pres­sur­ize the mod­ule. In­side, a tele­scop­ing struc­ture will ex­pand as BEAM in­flates. Made of an alu­minum al­loy, the struc­ture is de­signed to pro­vide rigid­ity in case a mi­crom­e­te­oroid or piece of or­bital de­bris pen­e­trates the habi­tat, says Das­gupta.

The pri­mary per­for­mance re­quire­ment for BEAM is to demon­strate that it can be launched, de­ploy on the ISS, in­flate, and main­tain long-term pres­sure with­out leak­age. Another key ob­jec­tive is to de­ter­mine how well an in­flat­able struc­ture in low Earth or­bit can pro­tect astro­nauts from ra­di­a­tion. BEAM will be out­fit­ted with ra­di­a­tion sen­sors, and data from them will be com­pared to cor­re­spond­ing data col­lected on the ISS alu­minum mod­ules. So­lar flares pose an ad­di­tional ra­di­a­tion risk.

Gold says BEAM should of­fer bet­ter ra­di­a­tion pro­tec­tion than me­tal: When me­tal­lic struc­tures ab­sorb ra­di­a­tion, the shield­ing ma­te­rial can it­self emit “sec­ondary ra­di­a­tion.” When high-energy par­ti­cles smash into atoms in a space­craft’s me­tal­lic shield­ing, the col­li­sions

pro­duce a shower of nu­clear byprod­ucts— neu­trons and other par­ti­cles—that then en­ter the space­craft. Sec­ondary ra­di­a­tion can be more dan­ger­ous than the orig­i­nal ra­di­a­tion from space. “The non-me­tal­lic struc­ture of the BEAM sub­stan­tially re­duces the sec­ondary ra­di­a­tion ef­fect that oth­er­wise oc­curs within me­tal­lic struc­tures,” Gold adds.

Once you’re be­yond low Earth or­bit and ex­po­sure to cos­mic ra­di­a­tion in­creases, nei­ther me­tal­lic nor fab­ric con­struc­tion can fully pro­tect astro­nauts—a longer-term con­cern as fu­ture astro­nauts travel to the moon, Mars, and be­yond. “The only thing you could do there is pro­vide a very mas­sive dense ma­te­rial to ab­sorb it, ba­si­cally,” Zamka ac­knowl­edges. “It’s parts of atoms com­ing at you.”

Apart from the need to pro­tect astro­nauts, the great­est en­gi­neer­ing chal­lenge for BEAM is likely main­tain­ing struc­tural in­tegrity over time—specif­i­cally, avoid­ing a phe­nom­e­non known as “creep rup­ture,” says ILC Dover’s Cado­gan. Creep rup­ture oc­curs when the con­stant load­ing of ma­te­ri­als at high per­cent­ages of their ul­ti­mate strength leads to an elon­ga­tion of the ma­te­rial, and even­tual fail­ure.

How­ever, if you can de­sign and test a struc­ture so load­ing is kept be­low 25 per­cent of the ma­te­ri­als’ ul­ti­mate strength (for most struc­tural ma­te­ri­als), creep rup­ture shouldn’t be a prob­lem. Although some ma­te­ri­als are more sus­cep­ti­ble to this type of stress than oth­ers, all ma­te­ri­als have some de­gree of sus­cep­ti­bil­ity, says Cado­gan. Good en­gi­neer­ing can mit­i­gate the prob­lem. One fa­mil­iar ex­am­ple? Win­dow glass. Two hun­dred years ago, glass would sag over time—an ef­fect of grav­ity. Mod­ern ma­te­ri­als de­sign has solved this vul­ner­a­bil­ity.

Cado­gan says that BEAM’S man­u­fac­tur­ing chal­lenges are even more daunt­ing than its en­gi­neer­ing chal­lenges. For ex­am­ple, ILC Dover welds poly­mer-coated fab­rics to cre­ate bladders that re­tain in­fla­tion gas. These seals are made by ap­ply­ing heat and pres­sure to the ma­te­ri­als in a highly con­trolled process. “Then there are the sewing oper­a­tions that are used to cre­ate the re­straint—the part that goes over the blad­der and sup­ports all the pres­sur­iza­tion and struc­tural loads,” Cado­gan says. “Sewing also has pa­ram­e­ters that re­quire con­trol, in­clud­ing thread ten­sion, nee­dle sharp­ness, stitches per inch, etc…. you just have to set up the ma­chines cor­rectly, have pro­fi­cient op­er­a­tors, and in­spect and test ev­ery­thing well be­fore flight.”

At the end of BEAM’S two-year mis­sion, its last test will be when the sta­tion’s ro­botic arm suc­cess­fully jet­ti­sons it from the ISS. The ro­botic jet­ti­son of a large, 3,000-pound struc­ture from the sta­tion has never been at­tempted. Once de­tached, BEAM is ex­pected to en­ter the at­mos­phere and burn up within a year.

Room to Move

In­flat­a­bles of­fer another clear ben­e­fit: more hab­it­able space. BEAM is rel­a­tively small, but an op­er­a­tional mod­ule that Bigelow is de­vel­op­ing, called B330, will of­fer 330 cu­bic me­ters of hab­it­able vol­ume. The In­ter­na­tional Space Sta­tion con­tains 916 cu­bic me­ters of pres­sur­ized vol­ume—only about three times that of a sin­gle B330 mod­ule.

As a rule, astro­nauts en­joy about dou­ble the vol­ume of a sim­i­lar space on Earth, be­cause in mi­cro-grav­ity they have ac­cess to the en­tire area, from ceil­ing to floor, and in any ori­en­ta­tion. The space sta­tion is a mas­sive struc­ture—with its ex­tended so­lar ar­rays, about the size of a

football field. But think­ing about the ISS in that way can be de­ceiv­ing. “In­side, you don’t get all that,” Zamka says. “It’s small and con­strained by what­ever node you hap­pen to be in, whether it’s Tran­quil­ity or Seren­ity or Unity…. You’re in this kind of tube-like ex­is­tence.”

In­flat­able mod­ules would of­fer astro­nauts more space. “I think they’ll no­tice that dif­fer­ence, par­tic­u­larly if they look at this ex­panded vol­ume for trav­el­ing on long mis­sions in deep space,” says Zamka.

The cur­rent plan calls for crew mem­bers to en­ter BEAM once ev­ery three months, although that may change, says Das­gupta. Their job will be to col­lect sen­sor data, per­form sur­face sam­pling, change out ra­di­a­tion area mon­i­tors, and in­spect the gen­eral con­di­tion of the mod­ule. BEAM’S ven­ti­la­tion is pas­sive; it takes air pushed from the sta­tion through a duct. Air cir­cu­la­tion in­side BEAM will help pre­vent con­den­sa­tion. The mod­ule has no win­dows, though fu­ture de­signs could con­ceiv­ably ac­com­mo­date them.

“No hard time limit has been es­tab­lished for crew ingress, but since the ISS crew is busy all year round con­duct­ing ISS re­search, we would like to limit crew ingress to a few hours,” Das­gupta says.

NASA doesn’t plan to stow any equip­ment or hard­ware in­side BEAM, and the mod­ule will have no in­ter­nal power. In­side, crew mem­bers will carry bat­tery-op­er­ated lights.

BEAM could be­come pop­u­lar with astro­nauts, not only be­cause of the ex­tra space but also be­cause it should be rel­a­tively quiet com­pared with other mod­ules. Gold says, “We be­lieve the BEAM could be an oa­sis.”

As­sum­ing BEAM per­forms well, Bigelow Aerospace en­vi­sions B330 mod­ules used as stand-alone space sta­tions for the pri­vate sec­tor. Phar­ma­ceu­ti­cal and ma­te­ri­als science firms, for ex­am­ple, could use B330 mod­ules as lab­o­ra­to­ries for prod­uct de­vel­op­ment, says Gold. (He declines to say how the B330 mod­ules will be priced.) The B330s ac­com­mo­date six, and Bigelow hopes they will be­come in­te­gral to deep-space mis­sions—crash­pads to keep astro­nauts from be­ing con­fined to a capsule, like NASA’S planned Orion space­craft.

“Ob­vi­ously there is not suf­fi­cient vol­ume [with Orion alone] for long-du­ra­tion mis­sions,” says Gold. How­ever, if “you at­tach a habi­tat to a propul­sion sys­tem and/or capsule, you’ve got a pretty ro­bust sys­tem for be­yond-leo ex­plo­ration to the moon, Mars and be­yond.”

In this re­spect, NASA’S shelved Tran­shab pro­gram is truly on the verge of be­ing reborn. Zamka says the B330 per­fectly com­ple­ments NASA’S Orion space­craft. “[Orion] is a trans­fer ve­hi­cle. It’s sup­posed to trans­fer astro­nauts from Earth to another place,” he says. “We’re that other place.”

This model moon colony at Bigelow’s Ne­vada head­quar­ters rep­re­sents the firm’s ob­jec­tive to put lu­nar op­er­a­tion within reach of pri­vate cus­tomers.

BEAM packed into its cost-sav­ing 5- by 7-foot launch con­fig­u­ra­tion. “That’s the hard­est, most ex­pen­sive thing about space— get­ting out of Earth’s grav­ity well,” says as­tro­naut-turnedBigelow em­ployee Ge­orge Zamka. In­flat­a­bles of­fer more vol­ume for less...

In­te­rior mockup of a 330-cu­bic-me­ter habi­tat (see man­nequin for scale), which Bigelow hopes to sell to pri­vate com­pa­nies with space­far­ing am­bi­tions.

In 1961, NASA built this mockup of an in­flat­able space habi­tat. Thirty feet in di­am­e­ter and ex­pand­able, it was de­signed for one or two in­hab­i­tants. It never flew.

Robert T. Bigelow (above) has de­vel­oped the in­flat­able Bigelow Ex­panded Ac­tiv­ity Mod­ule to test in space (one-third scale model, op­po­site).

Con­cept il­lus­tra­tion of BEAM docked to the ISS. Bigelow hopes the two-year test flight will demon­strate space in­flat­a­bles are ver­sa­tile, eco­nom­i­cal, and safe.

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