Beyond the Moon
It’s not a place, exactly. But it could be NASA’s next destination.
- By Guy Gugliotta
- Air & Space magazine, April 2013
(Page 2 of 3)
“This is a trick that NASA has been using in robotic missions for the last 40 years, but it would be the first time for human spaceflight,” says University of Colorado space scientist Jack Burns, director of the NASA-funded Lunar University Network for Astrophysics Research, who has been studying options for L2 missions. “We’re talking a week to get to L2 because of the gravity assist and the resulting trajectory.”
By early last year, Gerstenmaier’s in-house NASA group had worked up a PowerPoint prospectus on a Gateway mission, emphasizing its value as a training ground for deep space. Astronauts would gain critical experience operating their spacecraft in a new and unfamiliar environment beyond Earth orbit, would use dosimeters to monitor radiation levels, and would work more independently of Earth-based controllers. All this could be done from Orion, which will be about two and a half times roomier than the Apollo spacecraft and weigh nearly 11 tons, almost twice Apollo’s weight. With its European-built service module, it will carry four astronauts instead of Apollo’s three.
For an L2 mission, Orion wouldn’t simply fly to the far side of the moon and park at the Lagrange point. Instead, the spacecraft would be placed in a halo orbit around L2. “You set it up so you can always see the Earth,” says Josh Hopkins, Lockheed Martin’s space exploration architect and a close collaborator with the Burns team in Boulder. Hopkins describes the preferred orbit as asymmetrical, its dimensions and shape dictated by the changing gravitational forces at L2. The orbit would have a radius of 22,000 miles east to west, and 3,000 to 6,000 miles north to south. It would not quite lie in a flat plane, Hopkins adds. “It looks like a Pringles potato chip.”
A spacecraft in this orbit requires very little fuel compared with the space station, which needs regular burns to overcome the drag of Earth’s atmosphere, and occasional tweaks to steer it past space junk. At L2, the only real problem would be a tendency for the spacecraft to drift. “If you start out a little behind L2, the moon pulls you back,” Hopkins says. “You need very small bursts of energy to keep station.”
This, Gerstenmaier says, “may be more complicated than it looks.” An L2 orbit “is a little bit of a trade-off,” he explains. “From a propellant standpoint, it’s easy, but we don’t have a lot of experience navigating around a gravity point.”
Besides mastering the orbital mechanics of deep space, the Gateway astronauts would have work to do. In a recent paper for the journal Advances in Space Research, the Burns group described some possibilities, beginning with a first-ever comprehensive robotic exploration of the far side of the moon. This mission would begin with the landing of an unmanned rover in the South Pole–Aitken basin, a favored target for geologic exploration because it offers a broad swatch of lunar history. The basin includes some of the oldest rocks on the moon, but there also is evidence of more recent volcanism.
Orion, with astronauts on board, would arrive at L2 after the rover lands. With a signal delay of only 0.2 second (it takes about two seconds for a signal to travel from Earth to the moon), astronauts could steer the vehicle in near-real time. “We’re talking about a surface rover that can move kilometers in a day instead of meters,” Burns says.
Astronauts could also use the rover to deploy an array of antennas for a radio telescope. Shielded by the moon from Earth-generated radio interference and ionospheric distortion, the far-side telescope could examine the formation of the first stars, 85 million to 250 million years after the Big Bang.
The Burns team envisions a month-long L2 mission, limited in part by concerns about galactic cosmic rays, high-energy particles from outside the solar system. The effects of cosmic rays on human tissue are neither beneficial nor well understood, and radiation is currently a show-stopper for expeditions to Mars. An L2 mission offers opportunities to study the hazards of radiation without risking a lethal dose. “Six months to a year is the limit,” says Lockheed Martin’s Hopkins. “The best way to avoid the effects of radiation is not to stay out in space too long.”
Month-long Gateway missions could be done with Orion alone. Beyond a month, “you need an outpost,” Hopkins said during a recent briefing to a National Research Council panel on technologies for human spaceflight. According to Hopkins, Lockheed and other “major space industry players” from around the world have been meeting to discuss future exploration plans and “talk about what could we do together”—an informal parallel to the official planning exercises at the national space agencies. “L2 outposts and lunar surface mission support popped out as a logical thing to do for a couple of reasons,” Hopkins told the NRC. “One is that because L2 is easy to get to, it’s something that other countries can contribute to, using the assets they already have…. The other reason was that there’s a lot of different things you can do from L2, so you don’t have to agree on why we’re going before you go there.”
If the Gateway outpost were to grow, the Burns group has thought about placing a storage depot there, “something modest, stocked with consumables,” he says. Astronauts would have extra lab space and “more room to maneuver,” he adds. Orion could dock with the depot and have a small, reusable lunar lander berthed there. Burns says the depot would most likely use modules similar to those on the space station.
With this infrastructure or something more elaborate, astronauts, at least in theory, could also use L2 as an orbiting tank farm, mining ice robotically from the lunar poles or taking water extracted from asteroids and converting it to hydrogen and oxygen—the basic components of rocket fuel. NASA has said nothing specific about mining ice, but “as we push out, we’re going to try to take advantage of whatever resources are there,” Gerstenmaier says. “If it’s there, we’re going to figure out a way to do it, it makes sense.”
The L2 Gateway idea has its critics. Some can’t accept a spot in empty space as a legitimate destination. Lunar expert Paul Spudis, a staff scientist for the Lunar and Planetary Institute in Houston (and Air & Space blogger), worries that sending astronauts to L2 will do nothing to build a durable human presence in deep space. He characterizes the mission as a NASA “one-off,” with little value beyond “getting people to L2 and figuring out something for them to do.”