1) China’s first science satellite, Double Star TC-1, burned up in re-entry this week after a successful four-year mission studying Earth’s magnetosphere.
2) China’s first lunar probe — and the first of their claimed series of steps to putting a man on the Moon — will launch sometime between October 22 – 25.
3) NASA’s Far Ultraviolet Spectroscopic Explorer — FUSE — will be shut down after more than eight years of observing high-energy objects in space. I had a lot of friends who worked on FUSE (my old boss worked on the calibration of its very complicated spectrometer), so this makes me even sadder than usual. There aren’t a whole lot of UV missions right now; for example STIS shut down a few years back (though it may be repaired in the next Hubble servicing mission). GALEX is still going strong, which is nice. But the UV region of the spectrum is where a lot of dynamic things happen, and we still don’t know all that much about it. It sure would be nice to see us doing more in that area, not less.
FUSE, like most astronomical satellites, moves its view from target to target by using "reaction wheels"; a set of heavy, rapidly rotating disks. When they are slowed down or sped up, they transfer their angular momentum to the spacecraft, which responds by rotating around one axis. Over the years, the reaction wheels have been failing — they’re moving parts, after all — and the last one quit last spring. There is no choice but to shut down the observatory. A little weirdly, NASA has invited reporters to the FUSE control room when they switch it off on Thursday, a sort of viewing, I suppose. I’ll be curious to see what reporters write after seeing this.
October 16th, 2007 at 3:29 pm
That seems to be the fate of UV satellites. While the infrared ones usually run out of cooling agent, I remember IUE had the same problems and re-entered the atmosphere with two of six reaction wheels working , which was one of the major problems in the late mission stages (failure of the last two were expected basically every day).
October 16th, 2007 at 5:21 pm
BA,
The links in your first two items both point to the same place — the ESA site dealing with TC-1. You might want to double check your Chang’e link…
Sam
October 16th, 2007 at 7:02 pm
IUE? I thought it is still on geosynchronous orbit. Wikipedia also agrees with me: http://en.wikipedia.org/wiki/IUE
October 16th, 2007 at 8:31 pm
D’oh! Sometimes cut-and-paste is funky on the Mac. I fixed it, thanks.
October 16th, 2007 at 9:45 pm
Does the HST also use reaction wheels to orient itself?
October 17th, 2007 at 3:28 am
HST? Yes. It have six gyros, whom all will be replaced by 2008 service mission.
October 17th, 2007 at 6:47 am
At the risk of pedantry, gyros are not the same as reaction wheels. Gyros are spinning doodads that are free to change orientation relative to the spacecraft, and are used to determine the rotation rate of the spacecraft. Reaction wheels are the ones bolted to the spacecraft which are spun up and down to make the spacecraft rotate.
Gyros are also much tastier than reaction wheels. Unless I’m thinking of something else.
You basically have three options for stabilizing a spacecraft: One, don’t bother and let it tumble. This is rarely used. Two, spin the whole spacecraft, or most of it. This was quite common in the past, less so now. And three, use reaction wheels. Any spacecraft that has to point, like HST, has reaction wheels. And they do wear out.
October 17th, 2007 at 7:37 am
There are some other options for stabilization, though most of them are pretty rare:
1. Gravity gradient – use the differential force gravity exerts on one side of your spacecraft compared to the other to fix your attitude. This works best on ‘long’ spacecraft, but the long duration exposure facility (LDEF) aligned along one axis as well.
2. Zero-momentum managed – use a large momentum wheel within the spacecraft to offset the structure’s spinning in the other direction. This allows small thrusters to control the attitude.
3. Thrusters can work alone, though the use of consumables is a bit of a pain. I heard recently that the Voyager missions use thrusters for attitude control, and that prevents them from contributing to knowledge about the Pioneer effect.
October 17th, 2007 at 7:53 am
Ah, right,
I wrote this post not really fit. It is in a strange type of pseudo-synchroneous orbit that brought it 8h long in the range of the European control station and 16h in the range of the american ones. It is still up there, though shut down.
October 17th, 2007 at 8:23 am
For orbits around planets with decent sized magnetic dipoles, you could also stabilize entirely magnetically, if you really wanted to. I don’t know whether any spacecraft have done that, but it has the advantage of no moving parts.
I think it would be hard to get enough torque to stabilize well enough for astronomical observations. Also the ideal place to use it would be a planet like Jupiter, with a large magnetic field. But the plasma scientists would be really mad if you were constantly generating large fields to control the spacecraft. And let me tell you, you don’t want to get plasma scientists mad.
October 17th, 2007 at 9:41 am
Offtopic, sorry…
But there’s yet another horoscope/love calculator add (by Google?) on your page. Can you do anything to remove these completely? Or is it just the way things are here in the wonderful world of the internets?
October 18th, 2007 at 12:22 pm
IMAX’s Latest Space Film Comes to DVD!
Magnificent Desolation:Walking on the Moon will be released November 6th!
Hey!
I just wanted to let everyone know about Magnificent Desoltion:Walking on the Moon, a new Space DVD from HBO Video. Kids and Adults will experience one of the greatest accomplishments in human history with this DVD that includes accounts from Astronauts, Exclusive NASA Footage and an Interactive Bonus Feature that focuses on the Apollo missions! This DVD will surely make a great gift for children and adults this holiday season…so look out for this! Out on November 6th!