Emily LakdawallaOct 03, 2008


That's the subject line of an email that Lou Friedman forwarded to me last week. He'd received it from Robert Farquhar, who has a long and distinguished career as flight director for numerous space missions. The "IT" in his email was ISEE-3/ICE. Never heard of it? ISEE-3 was originally launched on August 12, 1978, as the International Sun-Earth Explorer to a halo orbit about one of the Earth-Moon libration points to study Earth's magnetosphere and its interaction with the solar wind. Then, in 1983, it employed several lunar gravity assist flybys to send it on a new journey, for which it was rechristened the International Cometary Explorer, through the tail of comet Giacobini-Zinner. ICE approached within 7,800 kilometers of the comet on September 11, 1985. In 1986, it turned its instruments toward Halley's comet, participating in the international observation campaign, and becoming the first spacecraft to investigate two comets.

ICE is now in a solar orbit. I had assumed that it, like lots of other spacecraft from the Old Days of planetary exploration (which is any time before I graduated from college), was derelict, nonfunctional, and dead. It turns out I was wrong. Farquhar wrote in his message:

At 2049 UTC on September 18, 2008, DSS-14 locked onto the carrier signal of the ISEE-3/ICE spacecraft. The remainder of the 3-hour track was then used to gather Doppler data for future use.

Okay, you may say, it's pretty cool we made contact with such an old spacecraft. What's the point, though? I got in touch with Farquhar on the phone to ask him that question -- though I did put it a bit more politely, and I'm glad I did, because it turns out it'd be much more worthwhile for me to be mentioning ICE's status in my weekly roundups than it is for me to mention the hibernating Genesis.

International Sun-Earth Explorer (ISEE-3)
International Sun-Earth Explorer (ISEE-3) The International Sun-Earth Explorer (ISEE-3) launched in 1978 on a mission to study Earth’s magnetosphere. In 1983, it became ICE, the International Cometary Explorer, and was sent on a new mission to study comets Giacobini-Zinner and Halley.Image: NASA

First I asked him when the last time was that Earth had spoken with ICE. He said that, as far as he could tell, the last time was nine years ago, in 1999. I remarked that it's pretty amazing that they were able to pinpoint it in the sky after nine years, and he said that since the spacecraft is spin-stabilized, it's very, very stable. (The Pioneers are stable and were relatively easy to track for the same reason.) The spacecraft was so close to its predicted position that the Deep Space Network was able to lock on to its signal very quickly, without having to execute much of a search pattern around the possible point in the sky.

Farquhar said that in a meeting held at the Jet Propulsion Laboratory about six months ago, they were discussing ICE, and it was revealed that the fellow who was supposed to have instructed ICE to turn off its radio transmitters during the last communications session maybe had not done so. He was right; ICE was ready and waiting to communicate with Earth.

ICE is actually on a return trip to Earth now; it's in an orbit similar to, but slightly faster than, Earth's, so measured relative to us, it's taking a long, slow trip around the Sun. It will return to our neighborhood on August 10, 2014, targeted to return to the Moon, which is what originally launched it on this journey. A lunar flyby can recapture it back into Earth orbit, after which, Farquhar said, they are thinking of parking it in its original halo orbit again, from which they could launch it back out to explore more cometary targets.

Is it worth it? Yes. ICE is a highly capable spacecraft, it's just not been one I've paid attention to because it has no camera. Although it lacks a camera, it did launch with 13 science instruments for measuring fields and particles, only one of which is known to have failed.

There's work to be done, of course. Farquhar said they have to "reestablish the entire command structure, and that's going to take a little while. We were already working on this anyway. We've got time; we don't need to get it operating fully again until 2012. And it's got about 150 meters per second of fuel still on board." The cometary targets he's looking at would involve encounters in 2017 and 2018, though he declined to tell me what comets those are.

The reason for his caginess is because of NASA's new way of funding extended missions on spacecraft, through a program called Missions of Opportunity. Any team can get together and propose to use a spacecraft that's completed its mission and any extensions through a Mission of Opportunity; that's how the new Deep Impact (EPOXI) and Stardust NEXT missions are being operated. Farquhar said they're now getting a Mission of Opportunity proposal together, with Jim Slavin as principal investigator. It's not that he expects another team to swoop in and write a better proposal for this spacecraft, because "others will have a tough time commanding it," but still I understand why he'd want to hold his cards close to the vest until new funding came through.

"Old spacecraft never die, and so far the former Flight Director has not expired either," he said in his email. "Let's return ISEE-3/ICE to the halo orbit, and go on to another comet!

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