The Space Reviewin association with SpaceNews

Boeing hab module
A Boeing concept for a small, low-cost habitation module in cislunar space it is studying under a NASA contract awarded earlier this year. (credit: Boeing)

Planning the proving ground of cislunar space

Bookmark and Share

NASA has, for several months, promoted an overarching strategy for human space exploration called the “Journey to Mars.” At one end is the current-day “Earth Reliant” phase, where humans live and work on the International Space Station. At the other end is the “Earth Independent” phase, where humans travel to, and live and work on the surface of, Mars. There is little debate about those two endpoints.

“The next big thing we need to do if we’re going to go long distances is the habitation system,” Hatfield said.

Between those endpoints is what NASA calls the “Proving Ground.” This phase is intended to cover operations in cislunar space, primarily around—but not necessarily on—the Moon. NASA’s Asteroid Redirect Mission fits into the Proving Ground phase, as the boulder grabbed from the surface of a near Earth asteroid would be transported into a distant retrograde orbit (DRO) for astronauts to visit (see “NASA rearms in its battle with mission skeptics”, The Space Review, March 30, 2015). However, NASA has offered few details for its plans there beyond that. Many in the space community are left uttering the punch line of a famous cartoon: “I think you should be more specific here in step two.”

NASA is starting to drop hints about what that slate of Proving Ground missions might be like. The agency is slowly crafting plans for a series of missions in cislunar space in the 2020s of durations ranging from a few weeks to as long as a year. Those missions would test out habitation modules and other technologies the agency believes are critical for those long-term, long-duration human missions to Mars.

At the Humans to Mars Summit in Washington last month, NASA and industry officials described some of those planning efforts, including sketching out mission plans and awarding contracts for studying habitat module concepts that could be used for those 2020s missions.

“The concepts that we’re working on today call for us to begin in the early ’20s with a set of missions involving Orion to gain some early experience in cislunar space, leading to a series of longer missions,” said Skip Hatfield, manager of the Development Projects Office at NASA’s Johnson Space Center, during a panel session on “Stepping Stones” at the conference.

Those missions, he said, would likely start with durations of one to two months, and eventually last for one year. “The idea for that is that we expect, at the end of the Proving Ground period, when we’re ready to declare that we’re ready for Earth independence,” he said, “that we will have conducted an approximately 300-day mission, basically simulating a one-way transit to Mars.”

Those missions, Hatfield said, would make use of the Space Launch System (SLS) heavy-lift booster and Orion spacecraft. “The next big thing we need to do if we’re going to go long distances is the habitation system,” he said.

NASA has started to look at how to carry out those missions. One approach would be to launch a large habitat module on a dedicated SLS flight, delivering it to DRO or elsewhere in cislunar space. SLS could accommodate modules up to 8.4 meters in diameter, far larger than modules used on the ISS today.

David Smitherman, technical manager of the Advanced Concepts Office at NASA’s Marshall Space Flight Center, said that larger modules actually provide a way to save mass for a cislunar habitat. He has done studies comparing habitats based on several ISS-sized modules versus a single larger module, including one for a thousand-day Mars round trip.

“This was an interesting study and made for an interesting comparison,” he said. “The mass actually comes down as you go from a three-module set to a two-module set to a single-module set.”

Using Orion’s systems, Hopkins said, “means you can keep the outpost for the first several flights to be relatively small and inexpensive.”

There are, though, advantages to the smaller module approach. Matthew Duggan, space systems manager at Boeing, noted that smaller modules could be included as secondary payloads on SLS/Orion missions. The Block 1B version of the SLS, he said, could accommodate modules with masses of up to 10 to 12 metric tons.

The key advantage of that approach is that the launch is, in effect, free: modules can be included in SLS/Orion missions without the need for a dedicated—and likely expensive—SLS launch. “With every Orion mission, you’re adding something useful and you’re aggregating this larger and larger vehicle in cislunar space,” he said.

Lockheed Martin hab module
Lockheed Martin’s habitat module concept makes use of many of the life support and other systems available on Orion when docked. (credit: Lockheed Martin)

Boeing is one of several companies studying cislunar habitat concepts under NASA awards called the Next Space Technologies for Exploration Partnerships, or NextSTEP. Seven of the twelve awards under the program, announced in late March, cover habitat technology. Besides Boeing, NASA issued contracts to Bigelow Aerospace, Lockheed Martin, and Orbital ATK for habitat module studies. Three others—Dynetics, Hamilton Sundstrand, and Orbitec—received contracts for life support systems for habitat modules.

Lockheed Martin’s approach is based on its Jupiter concept for ISS cargo resupply the company unveiled in March (see “For commercial cargo, ideas old and new”, The Space Review, March 23, 2015). Lockheed Martin space architect Josh Hopkins said this approach could be launched commercially. “We could conceivably offer this as a commercial or industrial capability to NASA without relying on NASA for launch services,” he said.

That concept would use a hab module with twice the volume of Orion. It would also make use of many of Orion’s life support and other capabilities while docked. “Orion is a highly capable spacecraft designed to keep crews alive in this environment for a long period of time,” he said. “That means you can keep the outpost for the first several flights to be relatively small and inexpensive.”

Hopkins said Lockheed plans to refine that concept during its year-long NextSTEP study. The panelists acknowledged that there are a lot of technical issues that need to be addressed in putting a habitat module in cislunar space. Duggan noted that one challenge will be that, unlike ISS modules that are continuously occupied, the cislunar habitat will be vacant for extended periods between missions.

“One of the key assumptions we’ve struggled with is the long dormancy period. We’re going to put a vehicle out there and then essentially abandon it for a long period of time,” he said. “There are some systems that just will not deal with that well.” That’s particularly true, he added, of systems with lots of moving parts, or designed to move fluids.

NASA is also looking beyond technical issues to programmatic ones, including how to incorporate both commercial and international partners. A lot of those details, he said, will depend on the results of the NextSTEP studies over the next year.

He and other panelists, though, were optimistic that other nations would be willing to cooperate on development of cislunar habitats, or use them as springboards for other missions. “One of the reasons that exploring the Moon on the way to Mars is attractive to other countries is that it is so much easier and so much cheaper,” Hopkins said, making such missions more compelling to other space agencies than infrequent, expensive Mars missions.

That could include human missions to the lunar surface, using landers provided by partner nations. Hatfield said a lander mission could be combined with an “excursion” mission where a habitat goes deeper into space. “That would be very much an analogue to a Mars mission, where a transit would occur followed by a descent to the Mars surface,” he said, adding that this concept was still “very early in discussion.”

“The ’20s sound like a long time away,” Hatfield said. “They’re really not, from a development standpoint.”

All the proposed cislunar missions are still in their conceptual study phases, and Hatfield said it was would likely be a couple of years before plans firmed up and potential partnerships identified. That fits into the planning schedules of major potential partners like Europe and Japan, he said. “We have, maybe, something next fall that might affect our budget,” he added, alluding to the November 2016 presidential election.

At the same time, though, there was at least a mild sense of urgency about the planning for those missions. “NASA does not have any official plan beyond 2021,” Hopkins said, referring to the first crewed SLS/Orion mission, Exploration Mission 2 (EM-2). While there are notional plans for EM-3 and beyond, NASA hasn’t committed to specific missions, or schedules, for them.

And those missions are, in some respects, just around the corner. “The ’20s sound like a long time away,” Hatfield said. “They’re really not, from a development standpoint.”