Are Inflatable Space Habitats A Realistic Future?
Even as modern launch vehicles continue to grow and provide larger payload opportunities, when it comes to big structures and station segments, we are still limited in what can be launched. This is a major reason why for many years now different companies and agencies have been testing and working with inflatable modules.
These have a bunch of different applications from use on the Moon to low Earth orbit and beyond. All of which could help astronauts significantly expand the space available for research, manufacturing, living, etc. In this case, they are deflated and integrated on the launch vehicle and once in orbit, inflate to a full size habitat often bigger than whats possible with a hard structure.
Sierra Space and the LIFE habitat are one great example of this process however it has been tested for decades and is even used on the ISS right now. Here I will go more in-depth into the design behind inflatable space habitats, some of the pros and cons, what companies like Sierra Space are working on, and more.
Inflatable Modules
Inflatable habitats or expandable habitats are pressurized structures capable of supporting life in outer space whose internal volume increases after launch. They have frequently been proposed for use in space applications to provide a greater volume of living space for a given mass. All the way back in 1960, the Erectable Torus Manned Space Laboratory concept was proposed with Goodyear Aircraft Corporation. The
laboratory was a 24-ft diameter torus that had the major advantage of being a single unit, not requiring in-space assembly of multiple modules. It could be carried into orbit by a single booster, use a deployable solar array, and have a life support system for six crew members.
The biggest concern for the inflatable was related to the potential MMOD damage of the habitat in space. Small pinhole impacts were not a concern for the Echo satellite, but for a crewed habitat, a small hole would cause a leak that could turn catastrophic for the crew. This concern, coupled with the large price tag, led NASA to abandon the concept and solely chase the Moon with the Apollo program.
While different designs vary the construction of an inflatable space habitat is determined by its design objectives. However common elements include interwoven layers of highly durable materials such as Kevlar and mylar around a flexible air bladder which is used to retain an atmosphere. The shape of the module is maintained by the pressure difference between the internal atmosphere and the outside vacuum. The inflatable Bigelow Aerospace modules have an internal core which provides structural support during its launch into orbit.
The Bigelow Expandable Activities Module (BEAM) was developed by Bigelow Aerospace and installed on the ISS as the first ever human occupied inflatable module. BEAM is 13-ft (4m) in length and 10-ft (3m) in diameter when fully inflated, offering 565-cubic ft of living volume. The module was attached to the aft port of the Tranquility node of the ISS on April 2016 and remains in operation today. The demonstration has performed better than expected and proves that inflatable habitats are feasible and applicable for future use.
Expandable habitats greatly decrease the amount of transport volume for future space missions. These “expandables” require minimal payload volume on a rocket, but expand after being deployed in space to potentially provide a comfortable area for astronauts to live and work. They also provide a varying degree of protection from solar and cosmic radiation, space debris, atomic oxygen, ultraviolet radiation, and other elements of the space environment.
The journey to Mars is complex and filled with challenges that NASA and its partners are continuously working to solve. Before sending the first astronauts to the Red Planet, several rockets filled with cargo and supplies will be deployed to await the crews’ arrival. Expandable modules, which are lower-mass and lower-volume systems than metal habitats, can increase the efficiency of cargo shipments, possibly reducing the number of launches needed and overall mission costs. Projects like BEAM are testing these future opportunities as well.
BEAM is composed of two metal bulkheads, an aluminum structure, and multiple layers of soft fabric with spacing between layers, protecting an internal restraint and bladder system; it has neither windows nor internal power. The module was expanded about a month after being attached by its Common Berthing Mechanism to the space station. As far as the current state of BEAM, in July 2019, an engineering assessment certified BEAM’s ability to remain attached to the station until 2028, as it has exceeded performance expectations and become a core cargo storage module on the volume-constrained station. A contract extension will be required to allow BEAM to serve its extended operational lifetime.
The LIFE Habitat
While there have been many different designs throughout the past, Sierra Space and the LIFE habitat are a modern option that is making impressive progress. Sierra Space’s LIFE (Large Integrated Flexible Environment) habitat launches on a conventional rocket and inflates on-orbit to a large structure that is three stories tall, and 27 feet (8.2m) in diameter. To put the size of a single module in perspective, the LIFE habitat pressurized volume is 300 cubic meters, or about 1/3 of the pressurized volume on the International Space Station.
Sierra Space’s LIFE habitat consists of three floors outfitted with everything a crew of four astronauts would need to live in space and perform science missions. This includes science labs, robotics work stations, medical and sick bay, sleep and hygiene quarters, galley, exercise equipment, Sierra Space’s Astro Garden plant growth system, and ample storage room for crew supplies. For human application, all of the air and water required to survive in space is delivered by logistics carriers to the habitat, where it is then stored until needed. The LIFE habitat has life support systems that regulate the air to maintain proper pressure, temperature, humidity, and oxygen levels. These life support systems recycle some of the air and water that is used to reduce the amount that has to be delivered to the habitat.
Sierra Space’s LIFE habitat is currently being designed to support four crew members living and working on long-duration missions, such as those to Mars. It comfortably houses six for missions in LEO, but can accommodate 12 crew for shorter periods of time such as those during which crew members transition. Because of its modular nature, additional habitats can be joined to each other to accommodate more crew, or for a variety of other purposes.
When creating the materials and physical structure of the habitat, a lot of considerations were factored in. The LIFE habitat prototype is constructed of several soft goods layers including, but not limited, to: The inner layer, called the bladder, which is made of urethane and is designed to keep the air inside the habitat without leaking. The pressure shell layer, known as the restraint layer, is a Vectran fabric weave that is strong enough to withstand the internal pressure needed for the crew to live & work comfortably in space. It is stronger than steel. And finally the outer layers, consisting of Micro Meteroroid Orbital Debris (MMOD) and Multi-Layer Insulation (MLI) which provide orbital debris and thermal protection.
The LIFE habitat has a woven structural layer (pressure shell), called the restraint layer, which is strong enough to withstand the internal pressure required for the crew to live and work. It is protected by an MMOD multi-layer soft-goods shield that guards the habitat against space debris such as micrometeoroids. The layers of fabric, plus the internal outfitting, create ample safeguards against radiation.
The LIFE habitat is specifically designed to launch on commercial launch vehicles with a 5m fairing, providing multiple, low-cost launch options. It can also launch on the Space Launch System (SLS) since it expands only after it is on-orbit, making it easier and less expensive to transport.
As of right now, Sierra Space’s prototype is not going to space. The company has built a full-scale prototype of the LIFE habitat to determine the best approach to constructing, inflating and outfitting the LIFE habitat that will go to space in the future. In addition, the ground prototype only has two floors – the middle and top – because the first floor of the flight-qualified LIFE habitat is upside down when on-orbit.
As far as recent progress, just last month, Sierra Space announced that it formed a long-term strategic partnership with ILC Dover, the leading provider of softgoods technologies and spacesuits. The partnership will accelerate the on-orbit installation of affordable and high-volume LIFE inflatable modules that will be the catalyst for the commercialization of space leveraging the Sierra Space platform. The two companies have also partnered to design the next generation of spacesuits for both extra- and intra-vehicular activity (EVA and IVA). This is expected to speed up and improve the LIFE system going forward.
Conclusion
Inflatable space habitats are very interesting structures that have been tested for over half a century. The goal is to avoid the launch vehicle payload constraints and expand to a much larger structure once in orbit or at its final space destination. We will have to wait and see how it progresses and the impact it has on the space industry.