Sierra Space Tests Its LIFE Habitat System Once Again
Sierra Space has a host of exciting projects all making progress such as Dream Chaser and the LIFE Habitat. LIFE in particular has been going through very consistent testing as the company works to approve the system and make sure it’s safe for humans and strong enough to withstand the various forces in space.
In the last few months alone, we watched not one but two Ultimate Burst Pressure tests on a subscale LIFE Habitat. In these tests, engineers loaded the test units with a sustained amount of pressure over time until they failed. Just yesterday the company announced that it had completed a third test. While similar to the previous ones, this specific burst is called an Accelerated Systematic Creep Test.
Once again it provided promising results that help prove the viability of this system and what it has to offer. With this third important test complete, the company now is working toward another similar test very soon and full scale tests later this year. Here I will go more in-depth into yesterday’s test announcement, what exactly it helped prove, what to expect in the coming months, and more.
New LIFE Test
Yesterday on the 31st Sierra Space tweeted saying, “Sierra Space has completed its third successful test of its inflatable LIFE Habitat. This latest assessment called an Accelerated Systematic Creep Test, exceeded #NASA certification requirements in Duration Test for Extended Human Missions.” Specifically, this latest assessment, called an Accelerated Systematic Creep Test, is a destructive materials testing method by which test engineers load the test unit – a subscale version of the inflatable habitat – with a sustained amount of pressure over time until it fails. The unit’s “softgoods” pressure shell burst after over 150 hours, exceeding NASA’s short-term, recommended creep duration target of 100 hours. High-strength softgoods materials are sewn and woven fabrics – primarily Vectran – that become rigid structures when pressurized and can provide safe and sustainable architecture for space habitation.
Since late last year, Sierra Space has been performing a number of tests on subscale LIFE Habitats. LIFE (Large Integrated Flexible Environment) is a habitat that launches on a conventional rocket and inflates on-orbit to a large structure that is three stories tall, and 27 feet in diameter. This latest creep test is a different kind of stress test than the two previous ones conducted in July and November, which pressurized units with increasing loads until they burst at maximum or Ultimate Burst Pressure (UBP). What’s most impressive is the fact that all three of these tests took place within six months, a key step in facilitating extended human missions to low-Earth orbit, the moon, and Mars.
The company, its partner ILC Dover and NASA subject matter experts performed the subscale Accelerated Systematic Creep Test in December 2022, at NASA’s Marshall Space Flight Center in Huntsville, Alabama. The purpose of the test was to determine the duration of time that LIFE Habitat’s pressure shell could last during its on-orbit operational mission life. They highlighted that NASA designed a climate-controlled, disposable building in which the test was performed. This building was specifically built to meet two requirements: 1) to protect the test article (Sierra Space’s pressure shell) during the duration of the test and 2) to be expendable once the article successfully burst upon maximum creep pressure and duration. Due to the explosive nature of the test, the team placed the sub-scale space habitat adjacent to the flame trench of the Saturn 1/1B test stand, where NASA tested rockets for the Apollo program.
“Sierra Space’s LIFE Habitat pressure shell has an on-orbit performance requirement of 15 years, but with softgoods, there is a ‘times four’ safety requirement set by NASA, so we must ultimately prove we’re viable for 60 years,” said Shawn Buckley, LIFE Chief Engineer and Senior Director of Engineering at Sierra Space. “Based on data from this first subscale creep test, we well exceeded the on-orbit mission performance requirement of 60 years for inflatable structures within our current architecture.” The company will conduct a second subscale Systematic Accelerated Creep Test early in 2023. Stress tests on full-scale LIFE™ Habitat units will begin later in the year as part of Sierra Space’s ongoing softgoods certification process.
Sierra Space CEO Tom Vice also commented, “Habitat units are a key element in Sierra Space’s platform in space, and this crucial milestone illustrates that our team has exceeded programmatic requirements that validate critical aspects of the LIFE Habitat design. These results will propel us in 2023 as we mature the technology via full-scale development and continue toward full NASA certification.”
LIFE Habitat
Now that we know more about the most recent LIFE Habitat Test, we can take a closer look at the design and future of this unique system. The two sub-scale UBP tests in July and November achieved maximum burst pressure rates of 192 and 204 psi, respectively. Exceeding the safety requirement of 182.4 psi demonstrates that Sierra Space can meet the 4x safety factor required for softgoods inflatables within its current architecture at one-third scale. There are so many different safety factors and testing required because this system is meant for humans. Future projects such as Orbital Reef for example is planning to use this system for a majority of its livable space.
The LIFE habitat is 27 feet in diameter and 27 feet long. The LIFE habitat’s pressurized volume is 300 cubic meters, or about 1/3 of the pressurized volume on the International Space Station. The 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. However, while the 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.
One of the most interesting aspects of this system is the fact that it’s made of fabric and inflates on orbit. All of which starts at the inner layer, called the bladder, which is made of urethane and is designed to keep the air inside the habitat without leaking. Next is the pressure shell layer, known as the restraint layer, this is a Vectran fabric weave strong enough to withstand the internal pressure needed for the crew to live & work comfortably in space. To put it in perspective this layer is stronger than steel. Lastly, you have the outer layers consisting of Micro Meteroroid Orbital Debris (MMOD) and Multi-Layer Insulation (MLI) which provide orbital debris and thermal protection. Sierra Space points out that the restraint layer guards the habitat against space debris such as micrometeoroids. In addition, the layers of fabric, plus the internal outfitting, create ample safeguards against radiation.
Since LIFE is meant to inflate on orbit and not on the ground, it features a lot more launch opportunities. LIFE 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. Once in space and humans are living inside it, 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.
This recent series of sub-scale tests are designed to support LIFE’s overall, full-scale development and future inflatable habitats, as Sierra Space builds the next generation of inflatable habitat architectures. These early “fleet” leader tests provide the design and analysis data to determine the safety and reliability of the inflatable architecture systems. “Sierra Space is making incredible strides in the inflatable habitat technology development roadmap. In working with our partners ILC Dover and NASA, Sierra Space is quickly moving closer to softgoods certification,” added Shawn Buckley, LIFE Chief Engineer and Senior Director of Engineering at Sierra Space. “This second successful UBP test proves we can demonstrate design, manufacturing and assembly repeatability, all of which are key areas for certification.” Now with this third test complete, the company is one more step closer.
Conclusion
Sierra Space is working extremely fast and continuing to test the subscale LIFE habitat. Just yesterday the company released the successful results of the first Accelerated Systematic Creep Test. Soon we should expect a similar test before full scale LIFE tests later in the year. We will have to wait and see how it progresses and the impact it has on the space industry.