An anniversary worth remembering

Tomorrow, Saturday, October 4th, 2008, is the 51st anniversary of the launch of Sputnik 1.




This first orbital satellite only remained operational for three weeks, but began the Space Race in earnest, and has been followed by thousands of more and more sophisticated descendants.

One of those descendants is also making headlines at present.

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.

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.

More details at the link.

Now that's exciting! A thirty-year-old satellite, still almost fully functional after three decades in the most inhospitable, life-bereft environment imaginable? And under consideration for yet more experiments? The best of luck to the engineers and scientists involved!

Peter