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[Phys-L] broken telescope keeps spotting new planets



IIn today's Gomorrah Post:
"This broken space telescope keeps spotting new planets"
https://www.washingtonpost.com/news/speaking-of-science/wp/2016/01/08/nasas-kepler-telescope-has-discovered-hundreds-of-new-planets-after-breaking/?tid=a_inl

The article would be interesting enough if it said "telescope has
discovered hundreds of new planets" ... but I would like to call
attention to the other aspects of the story.

1) Minor point: The telescope aims itself using "reaction wheels"
i.e. using the principle of gyroscopic precession. So if a student
ever asks what precession is good for, here is a fine example.

It's also interesting to see an example where radiation pressure
is large enough to be useful.

2) As a related point: Angular momentum is conserved, but angular
rate and angular orientation are not. This should be be obvious
to anyone who has ever done (or even watched) gymnastics or high
diving ... but physics books are often confusing (or outright
wrong) on this point.

3) Major point: It's amazing what they can do with a /broken/
spacecraft.

This is a tremendous lesson for students (and everybody else).
Consider the contrast:
-- Student X turns in a lab report that says "the apparatus
broke so I didn't take any data."
-- Student Y turns in a lab report that says "the apparatus
broke so I jury-rigged it and obtained a truckload of
interesting data, namely ......"

This is how science is done in the real world. There is /always/
something broken or almost-broken in the apparatus. So usually
you deal with it and keep going. However, ........

4) On the other hand: On 01/28/2016 01:58 PM, Anthony Lapinski
wrote:

space shuttle Challenger

That's the other side of the same coin: Sometimes when things
are not quite right you do *not* want to keep going. Sometimes
the Admiral Farragut approach is exactly wrong.

5) To reconcile the two previous ideas, you need to understand
which failures can be contained, and which are going to snowball
into catastrophic failure.

Also it depends on the timing. They would not have launched the
Kepler telescope with a broken reaction wheel. They would have
delayed the launch until it got fixed. However, when something
fails after launch, they find a way to cope with it.