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View Full Version : LASKO shutdown today til Thursday



chaiyah
2003-Mar-03, 05:42 PM
"Notice: LASCO doors have been closed for a spacecraft orbit trim since Monday at 15 UT.
Observations are expected to resume 18 UT on Thursday."

If they would say, WHY, I would be less inclined to think it's because they need to >>DUCK!<< something.

Yes, I'm perennially susss-pishhh-usssss.

Nobody's perfect.

sts60
2003-Mar-03, 05:48 PM
Uhh.... they did say why. They're maneuvering the vehicle.

You always cover up your imager when you're maneuvering a vehicle. Avoids pointing sensors at the Sun, avoids pointing the sensor into the velocity vector and collecting debris, etc.

Hale_Bopp
2003-Mar-03, 05:51 PM
Interesting...the most recent LASCO image is from 16:42 UT. Guess they are a little behind schedule.

Rob

chaiyah
2003-Mar-03, 06:00 PM
What are some of the reasons that they might want to move or maneuver the vehicle?

I presume nothing because I'm a newbie.

sts60
2003-Mar-03, 07:53 PM
Off the top of my head - not that's there's much else left up there to come off /phpBB/images/smiles/icon_biggrin.gif - it sounds like ("orbit trim") they're doing a routine maneuver to keep the orbit parameters the way they want them.

In plain English, all spacecraft orbits need tweaking periodically - gravitational perturbations, radiation pressure, atmospheric drag (for vehicles orbiting close enough to the Earth), whatever, tend to nudge it a little bit. It will eventually drift away from its desired orbit if uncorrected.

The Shuttle and Station do indeed occasionally maneuver to "duck" something (space junk). Probes way out like SOHO rarely if ever do this.

<font size=-1>[ This Message was edited by: sts60 on 2003-03-03 14:57 ]</font>

ktesibios
2003-Mar-03, 09:32 PM
On 2003-03-03 13:00, chaiyah wrote:
What are some of the reasons that they might want to move or maneuver the vehicle?

I presume nothing because I'm a newbie.


I humbly beg to differ about that second sentence.

The general pattern of your posts indicates two consistent presumptions:

1. That any astronomical Doomsday prediction on the Web, no matter how unlikely/implausible/riddled with basic errors/unsupported by real, relevant evidence, deserves to be taken seriously.

2. That any mishap/inconvenience/scheduled work/whatever which prevents expensive resources and skilled people who already have work cut out for them from immediately being diverted to checking/debunking the crackpot theory from #1 must be the doing of the Evil Conspiracy.

Sorry, the "butter wouldn't melt in my mouth" posture don't wash.

Now I think I'll go back to lurking and hoping to learn something real.

Kaptain K
2003-Mar-04, 12:06 PM
chaiyah,
SOHO is stationed at the L1 LaGrange point (between the Earth and the Sun). This point is only quasi-stable and the space craft needs to be repostioned occasionally. For safety reasons, it is SOP to close down the optics during such maneuvers.

calliarcale
2003-Mar-04, 01:52 PM
To add a little to that, there's an excellent layperson's description of Lagrange points at the WMAP website. WMAP is at the point opposite from SOHO's perch (L2). WMAP Observatory: Lagrange Points (http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html).

Short version: the only stable points are L4 and L5. The others are unstable; an object at L1, L2, or L3 will slowly drift away, so spacecraft at those points have to periodically push themselves back.

L1 and L2 can also be regarded as "portals" to heliocentric orbits. An object in a high geocentric orbit that happens to pass through L1 or L2 may slip into heliocentric orbit; these points are a sort of equilibrium where an object is, in a sense, orbiting both bodies (the Sun and the Earth). In fact, this phenomenon is being exploited by the Genesis mission, which is currently collecting particles of the solar wind near the L1 point. (It won't bang into SOHO, though; there's plenty of space between them.) Genesis will be allowed to fall naturally out of its "halo orbit" around L1, and it's been timed in such a way that when it does drift away, it will drift towards the Earth onto a natural free-return trajectory. Pretty cool, huh? This has also happened unintentionally; the S-IVB upper stage booster from the Apollo 12 mission wandered through the L1 point sometime in the 70s and disappeared into heliocentric orbit, where it could not be tracked. But last year it returned, wandering through L1 again to be recaptured by Earth's gravity -- it was for a short time believed to be a natural object and therefore a second moon of the Earth (it even got the provisional asteroid designation J002E3). It will eventually wander away from Earth again when it next passes through L1.

Jupiter's L4 and L5 points are both occupied by clusters of asteroids. Such objects are sometimes called "trojan companions". Mars has a few as well, and it is expected that Saturn, Uranus, and Neptune likely do as well, although those are much harder to find because they are so distant. Several moons of Saturn do have trojan companions of their own, though. For instance, Tethys actually has two companions. Telesto leads Tethys in the L4 point, and Calypso trails it in the L5 point.