In 1978, the International Sun-Earth Explorer (ISEE-3) spacecraft began its mission to study Earth's magnetosphere from a position at one of the Earth-Sun Lagrange points -- specifically, the L1 point, located between Earth and the Sun where the two bodies' gravity cancels. In 1983, ISEE-3 was renamed the International Cometary Explorer (ICE) and used the Moon's gravity to send it on to encounter comet Giacobini-Zinner, which it encountered in 1985. Later, ICE performed distant observations of comet Halley. Ever since then, it's been in solar orbit, traveling slightly faster than Earth. It has outdistanced us, traveling very close to 31 times around the Sun in the time that it has taken us to complete 30. And now it's approaching us from behind. It will make its closest approach again in August, 2014.
Although out of contact for a long time, the Deep Space Network successfully communicated with it five years ago today, on September 18, 2008. That's the last time we've heard from it, but there's no particular reason to think it's not still functional; the 2008 contact happened after nine years of no communication.
When it comes back to Earth, it would be possible to recapture it into a halo orbit (that is, an orbit at the L1 point). But to do that, we'll have to reestablish regular communications with, and control of, the spacecraft. It won't be easy, but it's doable. But it will cost money, and given the current financial problems in Washington, it's unclear where that money will come from. Recognizing they have an uphill battle, ICE's supporters put together a video as well as a Facebook page:
It's ironic, really. ICE left Earth in the darkest days of NASA, and it is returning to Earth when NASA is experiencing its biggest crisis since. When it left in 1983, ICE was the last American spacecraft to depart Earth for deep space for six years, until Magellan in 1989. Since then, NASA has expanded across the solar system, but now it's contracting once more. Amid rumors that such great spacecraft as Cassini may see their missions end early for lack of funds, how can we afford spending even a little money on a mission as old as ICE?
There's nothing that I can do but be optimistic. I know others are working on the funding problem; let me tell you about the engineering problems, and the science we could achieve.
I got an email today from Leonard Garcia, one of several people at different institutions who are trying to figure out how to regain control of ICE and recapture it into halo orbit. "We have less than 11 months until Earth close approach and we need to make a trajectory correction maneuver several months before that," he wrote. They need to command its rockets to fire before June 2014. The sooner they do it, the less fuel it will cost. They have plenty -- 150 meters per second worth, more or less -- so as long as they regain control in time, they should have fuel to operate for a while.
A big question is whether we even still know how to communicate with the spacecraft. It was built in the 1970s, at the same time as the Voyagers. But we've been in continuous communication with the Voyagers since their launch; the same isn't true of ICE. So the first step is for a team at Goddard Space Flight Center to research that question. Can we figure out how to talk to ICE? What will those communications cost?
Once they've confirmed that communications are possible, the next thing we need to do is to assess the spacecraft's health, and the health of its instruments. It wouldn't be worth the effort if all the instruments were dead. There's no reason they should be -- most of the Voyager instruments are still working fine -- but we have to check.
What data could ICE send us? Garcia explained its utility in monitoring the solar wind: "There are currently a couple of spacecraft serving the science community in [the L1] region and they will be supplemented soon by the DSCOVR satellite. The plasma medium however, can be quite complex and an additional reference point will be of great value if it can be provided at a reasonable cost. As you noted in your 2008 blog about the initial contact with the spacecraft, ISEE-3/ICE has an impressive suite of scientific instruments on board well suited for this effort. "
But the question of whether it's all worth it comes down to cost. One interesting way that ICE advocates are talking about keeping costs low is to make spacecraft operation a student effort. In an article written for Space News, Daniel Baker explained: "At the University of Colorado at Boulder, for example, a space research institute — the Laboratory for Atmospheric and Space Physics (LASP) — has successfully operated numerous NASA space missions. The most recent example is the Kepler mission searching for Earth-like planets around other stars in our galaxy. By emphasizing students in the mission operations roles, LASP is able to carry out mission functions in an extraordinarily effective way. Moreover, the mission operation using students is a highly productive way to educate and train the next generation of young engineers, scientists and managers. It is proposed that the University of Colorado at Boulder work with a consortium of leading spacefaring universities in the United States to develop a program to command, control and scientifically operate the ISEE/ICE spacecraft."
One major challenge that Garcia mentioned to me is that ICE has no onboard data storage capability. That means it can only return data while in contact with a ground station, which means you need ground stations all over the world. Therein lies an opportunity, though: Baker says "There is every reason to believe that spacefaring partners in the international community would love to participate in the restored ISEE mission. For example, colleagues at the Russian Space Research Institute have expressed a strong desire to join the ISEE/ICE program. Through active involvement of academia in the U.S. and separately funded agencies abroad, it should be possible to revivify the ISEE/ICE spacecraft at a very low out-of-pocket cost. In doing so, U.S. taxpayers would be able to further recoup benefits of investments made some 40 years ago."
The clock is ticking. Orbital mechanics won't wait for us to get our financial act together.