A glimpse at a gateway
by Jeff Foust
|The idea of using either the Earth-Moon L1 or L2 point has been promoted by a number of people in the space industry in recent years.|
Members of Congress who have also been outspoken on space issues, like Sen. Bill Nelson (D-FL), also won reelection, maintaining the current balance of power with the White House. (Sen. Kay Bailey Hutchison (R-TX), who worked closely with Nelson on space issues, is retiring and did not run for reelection.) Congress, in fact, will be back this week for a “lame duck” post-election session that includes some space issues like launch indemnification and export control reform (see “A space policy to-do list for after the election”, The Space Review, October 15, 2012), as well as broader budget issues—such as the threat of “sequestration” that, if it goes into effect in January, would slash NASA’s budget by more than eight percent—with implications for space policy.
However, some question whether a second-term Obama Administration would, in fact, simply continue the same approach to human space exploration that the president laid out in 2010. Last week, SPACE.com reported that NASA is considering the development of an outpost in cislunar space, at one of the Earth-Moon Lagrange points. Longtime space policy expert John Logsdon suggested in the article that those plans likely have already been cleared by the Obama Administration and that “they’re holding off announcing that until after the election.”
That report got plenty of attention, although some of the details were lost or distorted in the coverage of that article. However, it’s not the first time word has leaked out regarding such a mission concept. In September, the Orlando Sentinel reported NASA was studying designs for such an outpost and had even briefed White House officials about it. Neither the White House nor NASA would comment on the plans, other than a NASA spokesman saying the agency was studying “many options” for future human exploration.
The idea of using either the Earth-Moon L1 point, between the Earth and the Moon, or the L2 point, beyond the Moon, has been promoted by a number of people in the space industry in recent years (see “Human operations beyond LEO by the end of the decade: An affordable near-term stepping stone”, The Space Review, January 10, 2011). Such a “gateway” facility, proponents argued, could help NASA gain experience in deep space operations and also support telerobotic operations on the lunar surface far more effectively than from the Earth. However, whatever NASA was examining—if anything—for such mission concepts was largely unknown.
On Saturday, however, a NASA official provided a glimpse about what the agency was currently studying. Speaking at SpaceVision 2012, the annual conference of Students for the Exploration and Development of Space (SEDS) in Buffalo, New York, Harold White, Advanced Propulsion Theme Lead at the Johnson Space Center, discussed the current state of NASA’s studies of what it calls the Gateway Exploration Architecture. White, better known in some circles for his work on advanced propulsion physics (see “Building a starship’s foundation”, The Space Review, September 24, 2012), is the propulsion lead on the architecture study.
“This is a multi-center team that’s been working on trying to figure out what the agency’s going to be doing next,” he said in a presentation that was part of a panel session on advanced concepts at the conference. “In principle, this is an incremental approach to human space exploration. We’re trying to take small steps and use as much of the stuff that we have in hand, and incorporate advanced technologies where appropriate to close the architecture.”
|“Using the electric propulsion, we can actually accomplish all of those delta-v requirements over the ten-year campaign without having to resupply propellant,” White said.|
The architecture starts in 2019 with the launch of the core spacecraft—a generic service module plus a docking node similar to those on the US segment of the International Space Station—on a Space Launch System (SLS) heavy-lift rocket to the Earth-Moon L2 point. “Then we would have a cadence of missions, about once every year,” White said, “increasing the mission duration and, in some cases, also increasing the capability of the platform by bringing up additional modules.”
The initial crewed mission would fly to the platform at L2 on an Orion spacecraft launched by an SLS. That mission would last about 30 days, in order to gain experience on operations there. Before departing, the platform would transfer from the L2 to the L1 point on the other side of the Moon. After the crew left, the station would then move into a “near rectilinear orbit”, a stretched version of the halo orbits used to stationkeep around Lagrange points that, in this case, gives long dwell times over the lunar poles.
That new orbit would be maintained for the second crewed mission in order to support telerobotic operations on the lunar surface. On that second mission, White said, a robotic spacecraft would collect lunar samples and transport them to the platform for return to Earth along with the crew.
The current architecture features what White called a “decision tollgate” in 2022: in effect, a fork in the road with two options. In one approach, the platform moves to low lunar orbit, where it could later support human missions to the lunar surface. That would feature the addition of other elements to the platform to support sorties to the lunar surface, including the use of an upgraded version of the SLS with a 105-ton payload capacity, versus the 70-ton capacity of the baseline SLS.
In the other option, the platform would move out into deep space, perhaps out to the Earth-Sun L2 point, about 1.5 million kilometers from the Earth, for unspecified missions. (The L2 point is used by a number of astronomy missions, including the upcoming James Webb Space Telescope.) That would require the addition of a second service module with a regenerative life support system to accommodate mission durations of 90 to 180 days. Notably absent from the architecture was any mission to a near Earth asteroid, although White did indicate that this option could support missions beyond Earth-Sun L2. “All those things are still in work, so I’m not prepared to talk about what those other destinations might be,” he said.
A key technical element of this architecture, White said, is the use of solar electric propulsion by the platform to move from one orbit to another and maintain position at the Lagrange points. “Using the electric propulsion, we can actually accomplish all of those delta-v requirements over the ten-year campaign without having to resupply propellant,” he said. “That’s been a significant benefit in closing the architecture and minimizing the amount of logistic launches we have to have.”
|“In principle, this is an incremental approach to human space exploration,” White said.|
Work on the Gateway Exploration Architecture started about a year ago and recently completed a second iteration of the concept, called design cycle two. One difference between the first and second design cycles apparent in the presentation was with the service module used on the platform. The original design used a module that closely resembled the Russian Zvezda module on the ISS, while the second iteration used a more generic cylindrical design. White added that the updated design features larger solar panels that can generate more power for the electric propulsion system.
White also said that NASA had been “dialoguing with the internationals”—NASAese for talking with representatives of other national space agencies—during the initial phase of work on this architecture. “Anything we do, we’ll be trying to engage them,” he said, adding after his presentation that more international discussions are planned for the near future.
While NASA may be talking with potential international partners, it’s keeping a fairly tight wrap on the details here at home. White said his presentation, at a relatively low-key forum with an audience primarily of college students (plus a handful of people watching a live webcast), was the first time any details about the design cycle two version of this architecture were publicly presented. He later said he was unable to distribute copies of his presentation, whose slides were marked with the disclaimer “Pre-Decisional Study Material.”
White didn’t say when a final version of this architecture would be ready, and warned that later versions may look very different than what he presented in Buffalo. It is clear, though, that NASA is giving serious consideration to not just human missions beyond Earth orbit in the next decade, but the development of infrastructure to support a series of such missions to the vicinity of the Moon and beyond.