### Author Topic: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz  (Read 51367 times)

#### vt_hokie

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #100 on: 03/14/2009 06:17 pm »

Inappropriate analogy. Trains are on tracks. You know where the train is going and you know whether or not you are on the track with the train. If you are on the track when the train goes through the probability of collision is 100%. If you are even a few feet off the track in either direction the probability of collision is zero. This is not the case with debris trajectories.

It basically becomes an excercise in covariance analysis, right?

#### Jorge

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #101 on: 03/14/2009 06:23 pm »

Inappropriate analogy. Trains are on tracks. You know where the train is going and you know whether or not you are on the track with the train. If you are on the track when the train goes through the probability of collision is 100%. If you are even a few feet off the track in either direction the probability of collision is zero. This is not the case with debris trajectories.

It basically becomes an excercise in covariance analysis, right?

Pretty much. The state vector itself defines a "mean" trajectory and the covariance matrix essentially defines an ellipsoid in space about the mean, within which there is a given probability of finding the actual object.

If a train's trajectory were defined not by the track but by a diffuse "probability cloud" around the track, which way do you jump in order to avoid the train?
JRF

#### Lee Jay

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #102 on: 03/14/2009 06:33 pm »

Inappropriate analogy. Trains are on tracks. You know where the train is going and you know whether or not you are on the track with the train. If you are on the track when the train goes through the probability of collision is 100%. If you are even a few feet off the track in either direction the probability of collision is zero. This is not the case with debris trajectories.

It basically becomes an excercise in covariance analysis, right?

Pretty much. The state vector itself defines a "mean" trajectory and the covariance matrix essentially defines an ellipsoid in space about the mean, within which there is a given probability of finding the actual object.

If a train's trajectory were defined not by the track but by a diffuse "probability cloud" around the track, which way do you jump in order to avoid the train?

Doesn't matter, as long as you get several sigma out from the center of the elipse, before the train gets there!

#### vt_hokie

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #103 on: 03/14/2009 06:36 pm »
Doesn't matter, as long as you get several sigma out from the center of the elipse, before the train gets there!

LOL!

#### rdale

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #104 on: 03/15/2009 07:12 pm »
Radio comms from the event have been posted at http://www.nasa.gov/mission_pages/station/main/index.html

#### Warren Platts

##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #105 on: 03/16/2009 12:23 pm »
Space station may have to duck orbiting debris

Again.

http://news.yahoo.com/s/ap/20090316/ap_on_sc/space_shuttle_28
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

#### Comga

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #106 on: 03/17/2009 12:29 am »
The Baltimore Sun got it correct.  (Unlike Fox News, they know what that funny hat thing and the number two mean in m^2.  )

"The debris, part of a mechanism to put a satellite in proper orbit, measured about 5 inches, a size that "will wreck your whole day," said Mark Matney, an orbit debris scientist for NASA."

It was traveling 5.5 miles per second -- about 20,000 mph.

The debris is likely a small weight followed by a 39-inch string or strand that was used to stabilize a global positioning satellite placed in orbit in May 1993, said Harvard astrophysicist Jonathan McDowell, who tracks all objects in orbit.

One of the reasons NASA got such late warning on the debris is that it is an unusual orbit that keeps dipping into the atmosphere and changing, McDowell said. It was in the worst kind of orbit to track, Matney said.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

#### aquarius

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##### Re: RED threshold late notice conjunction threat to ISS - Crew may evac into Soyuz
« Reply #107 on: 04/16/2009 11:11 am »
I read somewhere that the station crews had to take temporary refuge in escape ships 5 times previously due to orbital debris threats.

Does anybody know exactly when or during which expeditions these events happened?

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