Putting up the Ritz
Can pneumatic buildings breathe life into space tourism?
PHOTO: Bigelow Aerospace
The goal: to rent out a privately funded, inflatable space station.
What happens when a Las Vegas real-estate tycoon who’s made a pile of money building hotels starts thinking big—really big? In the case of Robert T. Bigelow, he starts working out a way to build hotels in outer space. And he just might be smart enough, rich enough, and driven enough to pull it off.
Bigelow made his money in extended-stay hotels, banking, and real estate. In 1999 he founded Bigelow Aerospace, which he personally manages and which now has 125 people in Las Vegas, Houston, and Washington, D.C., to do the nuts-and-bolts engineering required to build the world’s first space hotel. Bigelow’s aim is not to operate his own space tourism business but rather to build habitable structures that others will lease or purchase for their own purposes, including research and manufacturing in addition to providing the ultimate getaway destination.
Bigelow is the latest in a long line of dreamers looking to make money off the nascent human orbital economy. Dozens of aerospace companies with similar notions have come and gone over the years, with little more to show for their existence than a pile of feasibility studies, government grant applications, and whizzy drawings of futuristic hardware. But Bigelow has something none of those predecessors ever had: a functioning prototype of his hardware in orbit,right now . And he also has something else that might prove even more important. It’s a design approach that could dramatically improve the size, cost, and safety features of space habitats, quite different from the technology used to build every other habitat to date—from the old Soviet Salyuts to today’s International Space Station.
Now, with space entrepreneurship developing into something more than a hopeful fantasy, this scrappy Las Vegas operation is emerging as one to watch. It has been 28 months since Elbert Leander (”Burt”) Rutan’s Ansari Xprizewinning, privately funded suborbital flight in SpaceshipOne jolted the field. With popular interest stoked by the first privately funded human space flights to the International Space Station, the entire idea of commercializing some human space flight finally seems here to stay. Even NASA has joined the push, granting development funds to teams trying to set up FedEx-style delivery of cargo and personnel to the ISS.
Amid this futuristic fervor, you’ve got to admire Bigelow’s audacity. While others are hammering out the details of how to launch cargo and wealthy tourists into orbit, Bigelow is already thinking further out, to the day when travelers will want to camp out up there. And he’s focusing on other businesses and organizations that will need orbiting workspace to produce the kind of zero-gravity materials and research that decades of small-scale experiments on space stations have only been able to hint at.
Mockup of the Genesis-I, shown in Bigelow's desert laboratory. The real satellite was successfully launched in June.
I visited Bigelow’s heavily guarded facility this past July with a few other aerospace journalists. Several kilometers north of the fabulously glitzy heart of Las Vegas, it’s located in the scrubby Nevada desert and surrounded by razor-wire fences and armed guards. There, inside the cavernous building known simply as Building A, I saw a looming gray fabric-covered cylinder, 4.4 meters long, that is supposed to represent the wave of the future in habitable space structures.
The fabric of the cylinder represents the crux of Bigelow’s leap, and it’s what separates him from the many who have come before him. Instead of just draping the walls of a solid structure to provide additional thermal insulation (as seen in many spacecraft), the fabric is the wall of the spacecraft. Like a balloon, the habitat is held in shape by the pressure of the air inside.
Of course, the fabric isn’t anything like the materials that the term calls to mind. Rather it’s a technologically advanced, multilayer creation, tens of centimeters thick that simultaneously provides thermal control, structural strength, and an absolutely airtight seal. Bigelow wants to build entire orbiting complexes out of clusters of similar cloth-covered, inflatable structures, with each cylinder enclosing hundreds of cubic meters of habitable space. It’s hard to pin down exact figures, but this inflatable-module concept could cut the cost of building and launching space habitats by a remarkable 25 to 50 percent, compared with traditional rigid-walled modules.
A back-of-the-envelope calculation shows why. The largest single ISS module—the centerpiece of Japan’s contribution to the station—is scheduled to be launched into space in October 2008. The pressurized volume inside this metal-walled module will be about 150 cubic meters, or about half the size of a squash court. In contrast, an inflatable module could easily have an internal pressurized volume well over twice that, requiring less than half as many modules and launches to build a space complex of a given size. Quite apart from the cost of the modules, reducing the number of launches translates directly into major bottom-line savings, because it can cost as much—or more—to launch a module into space as to build it.
Standing in front of the cylinder in Building A, I remember an incident said to have happened in World War I: a British army officer, confronted with a very similar structure, had flicked his fingertip at the surface to see what sound it would make. ”Blimp,” he heard—and is supposed to have repeated to himself—thereby naming the unconventional aerial vehicle that would patrol the coasts of wartime England.
I raise my arm, try the same trick, and get a satisfying ”blimp” sound, too—because this structure in front of me is also inflated and straining at its airtight envelope. This SUV-sized vertical cylinder is an engineering mock-up of a craft called Genesis I, which is now orbiting Earth 560 kilometers up. Like a blimp, Genesis I maintains its shape thanks to air pressure. Unlike a blimp, which uses helium gas to pressurize the vehicle and whose crew works in a rigid gondola attached to the outside of the inflated structure, Genesis I is testing the idea that breathable air could be used to pressurize the structure, which would allow people to live and work inside it.
At least, that’s the plan. At the moment, Genesis I doesn’t have any astronauts onboard. Rather, it’s a test bed that, at 4.4 meters in length and 2.5 meters in diameter, is about one-third the size of the planned habitable modules that Bigelow hopes to begin launching around 2010, each of which will have an internal volume of over 300 cubic meters.
Fitted with cameras and other sensors, the interior of the orbiting Genesis I has 11.5 cubic meters of internal volume. It is pressurized to a little more than half of sea-level atmospheric pressure as a conservative first step to test the structure’s ability to deploy properly and stay inflated in space.
During my visit to Building A last July, I got to see the control room, the nerve center where the Genesis I team monitors and controls the orbiting craft. The room, a house-size black enclosure, sits along one interior edge of the massive building, its outer walls painted with murals on interplanetary themes. That day the company let us meet with its top engineers and managers, including Bigelow himself, who seemed elated and eager to talk after years of secrecy.
The swagger of Bigelow and his team was justifiable: they had pulled off a space spectacular in getting Genesis I up and running in orbit on the company’s very first space shot, and they knew it. Genesis I was launched flawlessly this past 12 July, atop a Dnepr booster from a pad in the Orenberg region of Russia. ”I’m on cloud nine over this success,” said Bigelow, whose radiant grin was hard to reconcile with the recluse who had dodged the news media for years. But he added, ”I don’t want to give the impression we think we’ll have this much success every time.”
His chief engineer, 30-year old Eric Haakonstad, put it bluntly: ”The amount of success on the first launch was probably the biggest surprise.” The team went on to explain why they believe their inflatable technology gives them some key advantages over other private ventures in space construction. The first is size. Currently, space station modules are rigid metal cylinders with volumes that are constrained by the dimensions of the booster rockets used to put them into orbit. For example, ISS modules brought up by the shuttle are limited by the size of the shuttle’s cargo bay to about 4.4 meters in diameter and 14 meters long. An inflatable module, on the other hand, can be launched deflated, fitting neatly on top of its booster. Once in space, it can balloon to several times the size of any rigid module that could be brought up on the same booster.
An inflated module also weighs less than a comparably sized rigid module. An inflatable design that NASA studied and that was the direct ancestor of Genesis I, dubbed the TransHab, provided 340 cubic meters of pressurized space with a mass of 13.2 metric tons, a volume-to-mass ratio of 25 to 1. By comparison, the Japanese module mentioned earlier, with its 150 cubic meters of space, has a mass of 15.9 metric tons, a volume-to-mass ratio of just 9 to 1.
Inflatable space modules should also be safer than their rigid counterparts. This may seem counterintuitive at first: shouldn’t solid metal walls offer better protection against temperature extremes, micrometeoroids, and space debris than a skin of fabric? And in the worst-case scenario, in which a hurtling bit of debris does puncture a module wall, wouldn’t a metal module at least offer the guarantee of not collapsing around you while you try to deal with the loss of atmosphere?
It turns out that the surprising answer is no, as NASA itself demonstrated a decade ago in the TransHab project. Before TransHab, ”people doubted you could fly humans in a vehicle walled with cloth,” recalls William Schneider, who directed the project for NASA. During TransHab, Schneider knew he’d have to come up with something good to convince other engineers that the skin of an inflatable module could be made tough enough to stand up to the hazards of space, so he set a high bar for the project. ”I chose a safety factor of four,” he says—meaning that the flexible fabric and underlying structure had to be able to handle stresses four times greater than the maximum that engineers expected them to be subjected to over their lifetime.
”That’s far stronger than any other material ever used,” adds Schneider, who is now a visiting professor of mechanical engineering at Texas A&M University, in College Station. For comparison, most aerospace systems are designed with safety factors ranging from 1.4 to 2.0.
View from Genesis-I shows outer hull, solar panel--and the Earth.
The secret of TransHab’s success is the multilayer skin Schneider’s team developed. Moving from the inside out, the first layer is the scuff layer. It’s made of the fire-resistant material Nomex, and it protects the walls from wear and tear by the module’s occupants. Then come a number of airtight bladder layers made of Combitherm, a nylon-based film used in the food industry as a packaging material. Each bladder layer is separated from the next by a layer of felt to prevent them from sticking together while the module is in its deflated state. Next, come the all-important set of restraint layers, made of Kevlar, that give the skin its structural strength when inflated.
The TransHab team demonstrated just how strong such an arrangement can be by successfully inflating and pressurizing a test module under water. The module reached the equivalent of a pressure difference of four times normal atmospheric pressure between the inside and the outside of the structure.
Protection from orbital debris and micrometeors comes from shielding layers that wrap the restraining Kevlar. Here, a kind of open-cell foam padding—similar to that used in office chairs—is sandwiched between sheets of Nextel, an insulating textile material made from ceramic fibers.
When a piece of space debris strikes any surface at orbital speeds (typically measured in kilometers per second) it gouges a hole, typically breaking up into smaller fragments as it does so. If the surface material isn’t strong enough to absorb the damage from the impact entirely, the fragment will not just punch a hole in the surface, it will spray high-speed particles into whatever is behind that surface—a shotgunlike blast that could cause great damage to occupants and delicate internal systems if a module wall were to be breached. So a multilayer approach is dictated, with an outer layer that breaks up incoming objects, followed by one or more layers designed to block or absorb subsequent fragments.
However, with traditional rigid shell modules, because of launch weight constraints, these shielding layers are only millimeters thick. But on the TransHab, the shielding layer was about 30 centimeters thick, and in testing it easily withstood 1.7-cm-diameter aluminum projectiles being blasted into it at 7 km per second. Finally, a thermal blanket covers the whole module. TransHab’s entire skin was an astounding 41 cm thick and had no fewer than 60 separate layers.
As for fears of occupants getting tangled up in a deflating structure, the lack of external air pressure means the structure would not collapse quickly, and the large internal volume of air would leave ample time for occupants to put on emergency masks and evacuate, if necessary.
Schneider left NASA in mid-2000, but by then the TransHab concept had won enough converts to be actively considered for incorporation into the ISS. In the end, though, the proposal fell victim to the budget ax in 2002. Soon afterward, NASA terminated the TransHab project.
Along came Bigelow. As NASA’s interest had waned, Bigelow’s had waxed. He purchased the patents, signed formal technology-utilization agreements with NASA, and hired Schneider in 2002 as a consultant.
Schneider still can’t contain his glee when recalling his first glimpse of Bigelow’s giant building full of mock-ups. ”When I walked in, it was out of my dreams,” he remembers. Bigelow had outfitted the plant with state-of-the-art manufacturing gear, and Schneider jumped right in, helping to fabricate designs for the habitat’s windows.
Although TransHab had already proven many aspects of the inflatable module technology, there was still much work to be done. For example, although the NASA team had begun working on how to incorporate windows, putting holes in the module walls to accommodate them complicated the engineering of the skin so much that they left windows out of the proposed ISS module design entirely.
But a space hotel without windows is an obvious nonstarter, so the Las Vegas team conducted many pressurization tests of different module designs and blew up—as in exploded , not just inflated —a lot of them. Often deliberately pushing designs beyond their limits to establish safety margins, the team followed NASA’s experience in doing the pressurization tests under water, in a large pool that damped down the explosive force when structures tore open. At one point they tried a fill-to-fail test in open air—and discovered why NASA hadn’t: the test module exploded with such force that, Schneider recalls, ”it almost moved the building off its foundation.” Noise complaints came in from kilometers away. Based on these and other tests, Genesis I ended up with a multilayer skin 15 cm thick with one 10-cm-wide window; the final version’s skin will be closer to 40 cm thick. But the engineering of the skin, as revolutionary as it was, was just the beginning, especially in this case—lacking a space station to connect to, Genesis I must function independently in orbit.
As a stand-alone orbiting capsule, the Genesis I is basically an entirely new spacecraft, with a new complement of power, control, communication, and other flight systems. Many of these were adapted from existing aerospace systems, according to chief engineer Haakonstad. ”We wanted low-cost, low-risk systems,” he explained. But he declined to give any further details about the technologies or their subcontractors, citing the highly competitive environment of commercial space development. Nevertheless, one employee did confide that ”there’s at least one component from Home Depot.”
To enhance reliability, Bigelow engineers made extensive use of a technique called ”dissimilar redundancy.” Genesis I is equipped with two different means of performing all critical functions, such as monitoring internal conditions or distributing electrical power from its solar panels. The engineering team decided early on that ”we are not just going to have backups,” said Haakonstad. ”We will have physically independent systems. The reasons are robustness, and to perform Product A versus Product B evaluations.”
In fact, as many as a third of the systems aboard Genesis I are there purely for evaluation for use on future test flights. As an example of redundancy, Genesis I has two communications systems, with nearly identical installations at each end of the spacecraft. With this setup, whichever end of the cylindrical spacecraft ends up pointing toward Earth will be the one having full communications capability. This redundancy was needed because Genesis I does not have a way to control its attitude in space, relying on gravity to torque it into a position with its long axis pointed toward the ground.
The Genesis I designers also had the unusual luxury of essentially no weight constraints—a dream for aerospace engineers, who must typically sweat out every last nonessential kilogram from their designs in order to meet strict launch limits. But because Bigelow Aerospace had chosen to launch Genesis I with the powerful Dnepr rocket—provided by Moscow-based, state-owned ISC Kosmotras—weight concerns were minimal.
The Dnepr is essentially an ICBM converted for use as a commercial lift vehicle, and the Genesis I launch weight of about 2000 kilograms (the exact figure has not been disclosed) used only half of the Dnepr’s capability. ”We were very heavy,” one engineer said, ”[but] we didn’t want to spend a lot of time fine-tuning the structure.” Major weight savings will be tested on the next prototype vehicle, he added.
Despite all the planning and the generous weight margin, some features had to be dropped, sometimes very late in the construction of the vehicle. Bigelow had planned to put his wife’s name—Diane—on the outside of the module in glowing LEDs. (”You need all the brownie points you can get,” he quips.) But ”for technical reasons, we had to take it off,” says Bigelow, who still managed to earn some points with his wife when the Russians wrote her name on the fairing of the rocket, next to the American flag.
Later this year Bigelow will launch the next in his series of prototypes, Genesis II. Ultimately, he plans to be launching test modules twice a year until he has the human-rated version perfected. ”We will be tasked with managing a lot of spacecraft,” Haakonstad explains, ”We may have up to five active vehicles” at a time in space.
Unlike NASA, Bigelow Aerospace does not track its spacecraft itself. Instead, it relies on the U.S. Department of Defense, which routinely observes and measures the orbits of thousands of near-Earth objects and then publishes the results. Bigelow Aerospace crunches these measurements using off-the-shelf orbital-prediction software to predict the 5- to 12-minute windows when Genesis I is within line of sight of the company’s ground stations in Las Vegas and Arlington, Va. Only during these windows can the control room receive telemetry and transmit commands. Two more ground stations that will provide more communications windows are due to come online this month in Alaska and Hawaii.
Each test module will be in orbit for a long time. ”We had aimed for an orbit with three to seven years of life,” says Haakonstad. In the end, he says Genesis I ended up in an orbit with a lifetime of ”seven to 13 years.” During that period, he went on, ”we will collect long-term data on the robustness of the system, the power system, and the integrity of the hull.” With the ability to rapidly deploy and test improvements in space, Bigelow Aerospace believes it can orbit a habitable module within three years.
Of course, a hotel is pointless if no one can afford to visit it. As a consequence, Bigelow Aerospace is closely watching the attempts of other private entrepreneurs to build low-cost spacecraft and boosters, such as those being encouraged by NASA’s program for private transportation to and from the ISS. Ultimately, though, despite all the cunning engineering in the world, it’s still impossible to say if Bigelow’s vision of a vibrant orbital economy will mature into reality—or become just another desert mirage.
About the Author
James Oberg, a veteran of NASA’s mission control, is a frequent contributor to IEEE Spectrum and the author of several books on the U.S. and Russian space programs . He is based in Houston.