Considering next-generation commercial spacesuitsby Steve Hoeser
|
| There are existing, largely unexploited, higher pressure spacesuit design options, along with related technology and hardware advances that have already been made; in some cases, prototype hardware even exists. |
The key to a safe, user-friendly, and practically functional spacesuit is pressure levels that are essentially equivalent to Earth sea level pressures of around 14 pounds per square inch (psi). However, today’s soft suits are practically limited to suit pressure of only around 4.3 psi. This is mandated because, at higher pressures, these soft suit designs do not allow occupants to bend their arms without strained effort, which is not only exhausting but prevents them from conducting certain critical emergency EVA functions. This low pressure is an inherent soft suit condition that is a fundamental design limit of fabric suits, because they tend toward a “ballooning effect” under higher pressure. This ballooning forces the suit to seek maximum volume so that arms and legs extend into an ineffective outstretched position.
On the Space Shuttle and now on the International Space Station, the cabin atmosphere is a mixture of nitrogen, oxygen, and other gases at an Earth sea level pressure of about14 psi. This imposes tight safety restrictions along with strict processes and procedures in order to don current space suits for any EVAs. These procedures include a time-consuming astronaut pre-breathe protocol. It also includes a period of high-intensity exercise at the beginning of the pre-breathe procedure. This is followed by the astronaut breathing pure oxygen for a minimum of 2 hours and 20 minutes prior to being helped into the space suit for their EVA.
Perhaps more important, according to Johnson Space Center’s medics, during the shuttle program there was a 20 percent chance of the “bends” for astronauts prone to that conditionon any given EVA using current low-pressure soft suits. This occurred for these astronauts who conducted the two hours of “pre-breathing” 100 percent oxygen and living in a lower cabin pressure of 10.2 psi for at least 12 hours.
Even if the current time-consuming EVA protocol had no chance of the bends, a higher pressure spacesuit that eliminates this rigid and time consuming pre-breathe and long repressurization upon return would eliminate such risks. A higher pressure spacesuit will also save valuable on-orbit time increasing astronaut productivity. As time is money in business, commercial space ventures will certainly be interested in a more practical spacesuit solution.
Fortunately there are existing, largely unexploited, higher pressure spacesuit design options, along with related technology and hardware advances that have already been made; in some cases, prototype hardware even exists. This advanced spacesuit technology and available prototype hardware offers the opportunity for a program for rapid integration and flight testing of a next generation “X”-spacesuit. Properly focused, such a program would be capable of demonstrating superior operational features and enhanced safety for spacesuits of lower costs that are far more compatible with commercial space business profit models.
The hard space suit option
One such existing technologic option for this higher pressure space suit demonstration is to use something like the NASA Ames Experimental or AX-5. The AX-space suit is actually a family of “hard” all-metal exoskeleton suits that Ames developed and tested over a five-year period in the late 1980s. It is designed to operate, and has been proof tested to operate, at up to 14.7 psi.
| One space “glove” design option is to bypass the development of conventional over-the-hand gloves in favor of “virtual gloves.” |
At tested pressures from 8.3 to 14.7 psi, this suit shows remarkable flexibility with no reduction in mobility detectable by the wearer. This is because, unlike soft suits, the AX-5 is a true “constant volume” suit. Regardless of movement, the internal volume does not change. This is the result of an ingenious design of the joints and bearings, modeled in part after late medieval armor. Prior to its “retirement” by NASA JSC, the AX-5 was given a thin coating of gold thermal reflective material, making it qualifiable for actual space trials. The AX-5, however, was never flown in space.
Hard suits such as the AX-5 have numerous advantages over soft suits.
- They can be donned and doffed in a few minutes (five to ten) while current suits require as much as an hour.
- They require very little maintenance and servicing, with safety checks done using non-destructive scanning techniques such as those commonly used by airline maintainers. The current soft suits, on the other hand, are made from multiple layers of fabric and have no means for pressure testing without destroying the suit.
- The AX-5 suits have the added feature that they are rapidly resizable to pre-determined measurements, making “stock fittings” for a wide range of different sized wearers possible. Although using some standard sized parts, current soft suits are essentially tailor made for each user and must be laboriously fitted to each potential wearer before launch.
- Hard suits like the AX-5 are produced using computer-controlled machine tools while current soft suits are handmade, significantly reducing a hard spacesuit’s modification and production costs.
- Unlike soft suits, hard suits can accept snap-in lead parts to enhance radiation resistance or special mission functionality.
Another of the big problems of higher pressure space suits is the glove. With multiple finger and wrist joints in today’s soft suits, astronauts can quickly experience hand fatigue when conducting dexterously intensive EVAs. Any near-term X-Spacesuit capability demonstration that uses current space suit “gloves” will have pressure limits imposed by the practical mobility, durability, and dexterity of today’s glove.
NASA Ames developed a 10-psi glove in the 1990s and prototypes have been designed, built, and tested that allow “reasonable dexterity” when compared to present soft suit gloves. A 10 psi atmosphere is equivalent to the pressure just over one third of the way up Mt. Everest. At this pressure, however ,increasing the percentage of oxygen in the air mixture is needed for a person to breathe essentially as if you were at sea level. This is the reason mountain climbers use oxygen at higher levels. Unfortunately, these 10-psi gloves did not solve the hand fatigue, dexterity and durability issues.
Another space “glove” design option is to bypass the development of conventional over-the-hand gloves in favor of “virtual gloves.” This latter approach could exploit emerging virtual reality technologies. Using active electronic force-feedback and biomechanical-driven tooling technologies to create an external mechanical hand or other tool-effector, dexterity could be maintained at attractive fatigue levels. In these designs, the person’s hand is encased in a shielded canister at the end of the suit arm with plenty of room for conventional hand movements. The mechanical hand could be controlled by an exoskeleton and sensor glove, giving the user both freedom of movement and a pressure touch-feedback sensation. Operated in conjunction with cognitive software, these virtual gloves could allow normal hand dexterity similar to the NASA Robonaut or DARPA-developed advanced prosthetics at suit pressures up to the desired 14.7 psi, without the hand fatigue of current soft slip-on gloves.
It should be noted that this general method is currently in use in deep sea diving hard suits that look and operate remarkably like the AX-5 (such as this example.) However, the end-effectors are normally controlled via mechanical linkages.
| In the late 1980s and early 1990s, the NASA Ames people had submitted well-developed program plans to adapt the Shuttle PLSS and utilize it on the AX-5 in tests. The funding and forward progresses of these initiatives were subject to JSC approval. |
Central to any space suit is the Primary (Portable) Life-Support System (PLSS) The PLSS is a self-contained backpack unit containing an oxygen supply, carbon-dioxide-scrubbing equipment, caution and warning system, electrical power, water-cooling equipment, ventilating fan machinery, and communication equipment. The Apollo PLSS could be augmented with a Secondary Oxygen Pack (SOP) that held an additional two oxygen tanks with a 30-minute supply, along with associated valves and regulators. The SOP was attached to the Apollo PLSS but could be removed for servicing and maintenance.
Today, the ISS PLSS provides life support to sustain the user for up to eight hours at moderate exertion levels. This EVA time is reduced, however, when more strenuous EVA activities are demanded. The ISS PLSS also supports and provides the power for communication, cooling web-tube under garment circulation and other spacesuit support equipment operations.
Fitted with an appropriately modified existing PLSS, the Ames AX-5 suit could provide a complete suit for ground and space testing. To do this, the current ISS suit PLSS would be adapted to at least 8.3 psi in “relatively short order” according to an engineer’s estimates to support an X-suit capability demonstration program.
Another PLSS option might be to exploit a PLSS developed by Lockheed Martin, who had a fully assembled PLSS in a museum. As has been the case in the past for Smithsonian museum space hardware, this unit could perhaps be made operational to at least 8.3 psi or higher as well. Allied Signal has also in the past indicated an ability to provide such a PLSS at remarkably (but unofficial) low costs. The possibility of modifying a Russian PLSS (which now operates at 6.3 psi) has not been investigated, but may also be an option.
A number of years ago, the Hamilton Standard (HS) Division of United Technologies had proposed adapting the current Shuttle PLSS to operate at 8.3 psi at a cost of over $300 million. Remarkably, according to sources the changes necessary consisted primarily of a stiffer pressure regulator spring and some slightly stronger internal baffles and associated parts. The knowledgeable sources speculated that Hamilton Standard quoted this “discouragingly high” price for making these modifications as a means to dissuade the pursuit of the program and maintain their more lucrative soft US spacesuits business line.
The politics of new spacesuits
In the late 1980s and early 1990s, the NASA Ames people had submitted well-developed program plans to adapt the Shuttle PLSS and utilize it on the AX-5 in tests. The funding and forward progresses of these initiatives were subject to JSC approval. At the time, JSC was the lead NASA center for all human space flight. However, with tight budgets and the cost demands of the shuttle missions at the time, these initiatives always seemed to fall below the funding cutoff, and thus never pursued.
In 1993, the GAO reported that there was little hope of tracking how NASA spent its funding, including NASA’s spacesuit programs. Costs were spread across multiple centers to develop new suit upgrades, build new suits, operate and maintain the neutral buoyancy suit test and training facility, fix and resize shuttle suits, conduct maintenance, and obtain spare parts. Such spreading of the wealth across many states tends to help gain broader congressional support and is an often used program strategy by various government agencies for their programs.
It was suggested in that GAO report that the closest benchmark to project spent funding would be a cost per EVA hour, based on the direct costs of all of NASA’s spacesuit acquisition, support, and operations. To the best knowledge of the authors, such a cost investigation was never completed.
| The evidence is clear that technically advanced spacesuit hardware exists that, when combined using a capability demonstration program approach, could provide clear and meaningful next-generation higher-pressure commercial spacesuits. |
According to one JSC annual report done during the ISS build-up, “as assembly of the International Space Station approached, the Center faced a period of intense planning for this activity. To join more than 100 components of the space station during 45 space flights over five years, approximately 160 space walks spanning 850 hours are planned for station assembly. That equals as many space-walking hours as have been conducted in the history of [U.S.] human space flight to date.” This spacewalk time estimate did not include the extended day-to-day EVAs that have been needed over the life of the this facility, which as of last month, totaled 200 spacewalks and more than 2,450 hours.
The evidence is clear that technically advanced spacesuit hardware exists that, when combined using a capability demonstration program approach, could provide clear and meaningful next-generation higher-pressure commercial spacesuits. Done using a small program office and streamlined acquisition approach, such a Commercial-X-Suit capability demonstrator would reduce commercial technical and cost uncertainties to level that is more acceptable for motivated private companies. In conjunction with teleoperated robonauts, such commercial LEO hard suit operators will likely quickly find the best and most profitable mix of human and robotic EVA skills for whatever space support jobs arise.