Station-derived base at Earth-Moon L-2 is attractive, but details need work
International space partners are starting to feel their way beyond their orbiting station for mankind's next step into the Solar System. Some of them at the 63rd International Astronautical Congress (IAC) in Naples are finding a lot more to like about the Earth-Moon Lagrangian points, and particularly the L-2 site beyond the far side of the Moon.
While cash-strapped governments scramble to squeeze as much value as they can out of the International Space Station (ISS), scientists and market-hungry space companies around the world are leading the way toward the curious regions in space where gravity is largely nulled by pairs of celestial bodies. As a result, spacecraft can essentially hover there without using much energy. The infrared James Webb Space Telescope (JWST) is being developed for the supercold temperatures at the Sun-Earth L-2 point.
Space-exploration architects have long eyed the Earth-Moon L-2 as a way point where spacecraft carrying humans bound deeper into the Solar System can be assembled. More recently, it has drawn attention as a possible hand-off point where astronauts could rendezvous with vehicles transporting samples collected robotically on Mars (AW&ST Oct. 1, p. 36). Spacecraft circling in “halo orbits” around the far-side L-2 point can move on with relatively little change in velocity, compared to taking off or landing in the “gravity wells” of the Earth, Moon or Mars.
“We're trying to learn how to use these gravity lanes to maneuver around space with humans,” says William Gerstenmaier,'s associate administrator for human exploration and operations, who likens the routes between Lagrangian points to the rivers that took explorers into uncharted continents in the days of sail. He is also quick to stress that the idea has not even reached the “pre-study phase” at .
But it is not being ignored at the U.S. space agency, which is spending $3 billion a year to develop the deep-space crew vehicle and heavy-lift rocket needed for exploration beyond low Earth orbit. “Crude” simulations have given way to more sophisticated computer models as engineers delve into the issue, Gerstenmaier says. And NASA contractorhas generated enticing architectures using the L-2 point as an early target for the Orion multipurpose crew vehicle it is developing for NASA (AW&ST July 2, p. 22).
, too, is working in the area, as are large aerospace companies in Europe, Japan and Russia. “Space infrastructure should be international,” says Alexander Derechin, the deputy chief designer at Russia's RSC Energia, who co-authored an IAC technical paper on the subject with Michael Raftery of Boeing Defense, Space & Security in Houston. “It's too big for any country.”
The very uncertainty about the next stop in human space exploration—the Moon, an asteroid, Mars or one of its moons—argues for development of a human-tended facility at the cislunar L-2 point, Derechin says.
“If we're talking about infrastructure to support unclear goals, we need to make a decision about infrastructure that might be useful for all our goals,” he said during his IAC presentation on the subject.
A pressurized module derived from those that make up the habitable volume of the ISS could sustain Orion crews at L-2 much longer than they could remain there in the big capsule alone, and the linked vehicles could use Gerstenmaier's gravity lanes to reach more interesting destinations such as lunar orbit, an asteroid, the vicinity of Mars or even the JWST for upgrades or repairs.
“It doesn't take much delta-v to do that,” says Gerstenmaier, using the term for change in velocity. “It takes a long time.”
At the 62nd IAC in Cape Town, South Africa, Gerstenmaier and others were considering recycling space station modules to one of the Earth-Moon Lagrangian points (AW&ST Oct. 10, 2011, p. 46). Closer examination has proved that idea impractical—station modules were not built for the radiation, thermal and gravity environments, all of which are poorly understood. “We have different gravitation conditions at Lagrangian points,” says Derechin. “It may be simple, but we will need new technology for rendezvous and docking.”
The Russian engineer suggests the time to begin addressing those problems is now, while the ISS is still functioning and can be used as a starting point.
Space-agency chiefs who partner with NASA on the ISS are much more focused on finding funds to operate the station now than they are on figuring out how to move pieces of it somewhere else after 2020. In an IAC press conference, they were unanimous in their support for keeping the station running as long as possible after that date.
“Myself, I would like to make sure we extend the ISS beyond 2020 because it is useful,” said Jean-Jacques Dordain, director general of the European Space Agency, which will learn at a ministerial conference next month if its partner nations are willing to fund ESA at the station until 2020. He was joined in that view by Keiji Tachikawa, president of the, and Steve MacLean, president of the Canadian Space Agency.
Sergey Saveliev, deputy head of the Russian space agency, also agreed with Dordain on the need to focus on the station after 2020. Russia, which plans to invest $1 billion a year in human spaceflight activities in 2015-25, expects that the ISS will be used to support future exploration, no matter what the destination.
In May, Alexey Krasnov, head of human spaceflight at Roscosmos, said Moscow needs to begin planning by 2014 if Russia is to remain in the partnership beyond the end of this decade.
“We don't need firm commitments then, but indications of what the partners want to do,” Krasnov told an ISS-utilization symposium in Berlin. “We know this deadline might create some difficulties. But we have to have some idea of what we are going to do for this 10-year budget.”
While the ISS partners debate the future of their facility, China is moving ahead steadily on its plan to build a smaller space station in low Earth orbit by 2020. To that end, crew members on China's next mission to the Tiangong-1 mini-space station will start practicing on-orbit repairs and refueling techniques, according to Wang Zhaoyao, director of the China Manned Space Engineering Office.
The mission next year will continue work started with the Shenzhou 9 flight in June, Wang told an IAC audience, adding to China's experience with rendezvous and docking. Under present planning, he said, Shenzhou 10 will be China's only human spaceflight in 2013, and the last to Tiangong-1. After that, the mini-station will remain in orbit as an outpost for experiments operated from the ground. A second version, Tiangong-2, is planned for launch in the 2014-16 time frame.
During that same period, China will test the unmanned cargo vehicle it is developing and complete work on the Long March 7 launch vehicle. Scheduled for its first flight in 2013, that launcher will have a 30,000-lb. lift capability (AW&ST March 12, p. 33).
Taikonauts, as the Chinese space crews now call themselves, will visit Tiangong-2 for longer “mid-term” stays, Wang said, and continue to develop their skills in on-orbit repairs, while the cargo vehicle will be used for additional refueling demonstrations. The work is building toward deployment of the space station by 2020, after which plans call for three-member crews to conduct six-month tours there and, in theory, play host to space travelers from other countries.
“The Chinese space station is open to all,” said Yafeng Hu, a top international affairs official at the China National Space Administration, during a separate session, drawing applause from his IAC audience.