Samstag, 6. August 2016 - 11:17 Uhr
As part of its comprehensive review to the NASA Advisory Council, the US space agency has presented its review of progress on the development of a Deep Space Habitat that will allow astronauts to perform multi-month and multi-year missions in deep space – all while guiding the agency towards its ambitious plan of landing humans on Mars by the end of the 2030s.
Challenges to developing a Deep Space Habitat module:
One of the primary benefits of exploration in Low Earth Orbit (LEO) is that all of the currently human operated vehicles in space fly inside the sphere of protection from damaging radiation expelled from the Sun that Earth provides.
That risk assessment changes the farther from Earth one travels – and is a primary concern for missions in cislunar space and the eventual push of humans to Mars.
Understanding the radiation risk environment is one of the primary aspects in developing habitation that can successfully shield astronauts against damaging radiation.
But radiation protection is not the only challenge in developing deep space habitation, as noted by the Habitation Module presentation of the Advanced Exploration Systems Directorate to the NASA Advisory Council (NAC).
Environmental Control and Life Support Systems (ECLSS), autonomous systems, fire safety, human performance, exercise, nutrition, and Extra-Vehicular Activity (EVA) needs for maintenance of the spacecraft are all listed as part of the challenges facing this endeavor – as well as a critical need to test these systems in situ in cislunar space.
Adding to the challenge of deep space habitat systems is a need to greatly – in some areas – improve upon the abilities currently available aboard the ISS.
In terms of life support, the Station is currently able to recover approximately 42% of its oxygen supply from carbon dioxide scrubbing, 90% of its water from onboard systems and water/urine purification, and carries less than a six-month meantime before a critical systems failure in the life-support realm would either need to have a spare brought up from Earth or result in the crew abandoning the Station.
For the Deep Space Habitat (DSH), more than 75% or more of its oxygen needs to be recovered from CO2 scrubbers, 98% or more of its water needs to be recovered from onboard systems, and the craft itself has to carry a greater than 24 month mean time before system failures would result in abandonment of the habitat.
Likewise, current environmental monitoring is limited and extremely crew-intensive aboard the Station and carries a reliance on sample return to Earth for analysis.
For DSH, onboard analysis capability with no sample return would be mandatory as well as in situ identification and quantification of species and organisms in the air and water.
Crew health also needs to change from the bulky fitness equipment, limited medical capabilities, and frequent food resupply currently used aboard ISS to smaller, more efficient exercise equipment, onboard medical capabilities, and long-duration food systems for a DSH.
Moreover, fire safety is a huge consideration not just for the station but for DSHS well.
Currently aboard Station, large CO2 suppressant tanks, two cartridge masks, obsolete combustion production sensors, and depress/repress are the only avenues available for a crew should a fire break out aboard Station.
For DSH, a “unified, effective fire safety approach across small and large architecture elements” would be needed, notes the Habitation Module presentation.
DSH development – Phase 1 ends, NASA looks to Phase 2:
In all, the DSH development approach has three distinct phases, with Phase 1 including the creation of “innovative cislunar habitation concepts that leverage commercialization plans for LEO, [developing] required deliverables including concept description with concept of operations, [delivery of] Phase 3 proposals, and initial discussions with international partners.”
Phase 1 began in 2015 and is slated to wrap officially in September 2016 for the four companies selected for participation, at which point the industry-developed concepts will be delivered to NASA and decision on whether those four company’s contracts will continue into Phase 2 will be made.
Phase 2, slated to last from 2016-2018, according to the Habitation Module presentation, will then include [continuation] of concept refinement and development of domestic ground prototype modules and … development of standards and common interfaces domestically and internationally.”
In all, the presentation to NAC notes that Phase 2 will “Develop long duration deep space habitation capabilities that lead towards a deep space transit habitat and can be flown on SLS flight(s) (or alternative launch vehicles) starting by the early to Mid 2020s.”
For this phase, contract companies will be responsible for concept description and operations as well as providing NASA with Phase 3 proposals and the delivery of the ground prototype modules.
Under this approach, the contractors selected for participation in Phase 2 will “Advance the long duration deep space habitation capability concepts and mature the design and development of the integrated system(s) to achieve a high level of fidelity [by] developing prototype deep space habitation capability options to test a full size ground prototype unit(s) by the end of Phase 2 in 2018 to support first flight opportunities in early- to mid-2020s.”
These ground prototypes will be full-scale models of each company’s proposed DSH and will be used to test standard interfaces for mechanical, power, thermal and data testing as well as layout, installation and fit access.
The habitats will also provide the ability to conduct human mission simulations to test the habitability, mission operations, health and medical aspects, logistics and waste management operations, EVA operations, and emergency scenarios of long-duration missions, notes the Habitation Module presentation.
For NASA’s part, phase 2 will include the “definition of reference habitat architecture based on contractor and international concepts and identified GFE (Government Furnished Equipment) in preparation for Phase 3.”
Proposals for Phase 2 concepts were due on 15 June and are currently being evaluated. Selection of Phase 2 participants is anticipated for sometime this month, with negotiations and contract awards coming in September 2016.
NAC presentation – current status of DSH development:
“Overall, our habitation development challenge is the systems and crew health and combining those with the overall habitation capability itself – the physical structure of where all these things are housed and how their interactions affect all of these systems,” noted Jason Crusan, Advanced Exploration Systems Director.
“We are approaching this fundamentally from the top level of trying to encourage the meeting of our goals with the overlap of needs for LEO advancement as well.”
In fact, this dual approach of meeting NASA’s needs as well as those of the commercial community is why NASA is issuing BAAs (Broad Agency Announcements) instead of RFPs (Requests For Proposals) because, as Mr. Crusan related, an RFP potentially makes a contracted company focus on NASA’s stated goals while ignoring commercial and LEO needs.
“We’re going in a very systematic and structured way to drive affordability into our overall development strategy.”
Of particular interest to the NAC, in addition to the technical and contract overviews, was the number of flights needed to build such a habitation spacecraft in cislunar space.
For this, Mr. Crusan noted that the answer was dependent on the overall strategy NASA chooses to employ in meeting the cubic volume requirement for a 4-person mission to Mars, which would last between 800 and 1,100 days.
The cubic volume number could be met via an aggregate series of small modules like the ISS or one giant transit habitat.
But, as was noted, even if an aggregate structure of smaller modules were chosen, the total number of flights needed to build such a structure would in no way equal the number of flights needed to construct the ISS.
This led to a follow-up question by the committee regarding the need for commonality in elements and parts across all systems if an aggregate structure were chosen.
Bill Gerstenmaier, Associate Administrator for Human Exploration and Operations Directorate, addressed this question, stating, “We think that’s one of our biggest challenges. When we go to this Earth-independent region, we’re going to have to be very autonomous. What spares we carry with us are the spares we’re stuck with.
“We have to make some huge philosophical changes that I don’t think we’ve fully addressed. We’re very used to ‘if a part’s not there, we’ve got a cargo flight coming up in a couple months, we’ll put it on the cargo flight and life is good.’ We’ve done well with strained supply systems [close to Earth], but it isn’t the level [we’ll need for these multi-year missions].
Additionally, there was some interest by interim chair of NAC, Wayne Hale, regarding the use of potential artificial gravity on such long-duration transport habitats.
Specifically, Mr. Hale was interested in how artificial gravity might help address some of the issues facing long-duration microgravity missions.
Mr Gerstenmaier responded that NASA had no studies showing the need for artificial gravity, leading Mr. Hale to point out “you’ve got a lot of really critical things that you’re trying to investigate, and if it pans out that you can’t mitigate one of those risks” with what is currently under development, might artificial gravity be something to consider.
Mr. Gerstenmaier responded that all microgravity considerations are currently mitigatable with the systems in place or under development.
Further, Mr. Gerstenmaier noted that “you’re never gonna provide a partial gravity environment throughout the entire vehicle.
“I think the changes associated with trying to provide partial gravity are so fundamental and large … that I don’t think that’s an area that’s really a problem. [We have] real problems that need to be addressed, and partial gravity isn’t something that we should be spending quality time on right now.”
(Images: NASA and L2 – including SLS renders from L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)