

Equipment Failure May Cut Kepler Mission Short - danhak
http://www.nytimes.com/2013/05/16/science/space/equipment-failure-may-cut-kepler-mission-short.html?emc=na&_r=0

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ANH
It's worth pointing out that they still have terabytes of data on the ground
that hasn't been sifted through, so even if the spacecraft's mission isn't
resurrected, we can still expect to hear about new Kepler discoveries over the
next year or two.

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EvanKelly
From the article, this is the second reaction wheel to fail in 8 months. They
had redundancy, but I wonder what the cost/benefit would have been to have
more backup wheels.

Obviously, I'm an armchair/hindsight 20/20 observer here. I have no clue
whether it would have been an been an infeasible engineering feat to have more
than 4 wheels. Also, I don't really have a clue what a reaction wheel is.

EDIT: Wikipedia to the rescue <http://en.wikipedia.org/wiki/Reaction_wheel>

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speeder
Reaction.Wheels.are vert heavy, adding too much redundancy of then make they
all more prone to failure, add to rocket fuel costs, and also increase the
needed fuel on the ship thrusters and battery size, thus making everything
even more heavy.

In short, add more reaction wheels and end with a much more heavy machine,
more complex, expensive, and more expensive to launch.

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EvanKelly
I had a hunch that was the case, but this quote from Wikipedia suggests
otherwise

> Since the reaction wheel is a small fraction of the spacecraft's total
> mass...

The gist from the Wikipedia article suggests momentum wheels (used in Hubble)
are very heavy, but reaction wheels, not so much, due to their use for
precision movement.

Obviously I defer to someone that has more than a cursory Wikipedia articles
breadth of knowledge on the subject.

Am I misinterpreting Wikipedia, or are the reaction wheels on Keppler more
than a "small fraction of the mass"?

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sbierwagen
Momentum wheels are reaction wheels. I'm not sure why the wikipedia article on
them thinks differently-- Hubble wasn't gyrostablized at all, it's a
telescope, it can't be allowed to spin.

Hubble also masses eleven times that of Kepler. (11,000kg vs 1,000kg) I don't
know the actual numbers, but attitude control systems possibly take up a
larger percentage of spacecraft mass on Kepler than it does on Hubble.

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kiba
Given that the kepler telescope exceeds its original mission lifespan by 4
years, it's safe to say that the kepler mission is not really "cut short",
more like "cannot keep going".

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breadbox
Kepler was launched 4 years ago, so I think your first sentence is misworded.
Its original 3.5-year mission was pushed out 3 years due to issues with noisy
data, so it hasn't really completed its original mission yet.

(Not that it hasn't done a great deal of excellent work already, but much more
is/was still to come.)

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kiba
I stand corrected.

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wikiburner
An obvious question that wasn't addressed in the article - could they manually
fix it? I don't think most people remember what a punchline Hubble was
immediately after its launch, until the rescue mission turned things around.

Obviously, our access to space is much more limited currently, but it seems
like finding a way to make it happen via the Russians or even SpaceX
(depending on how quickly they can get to manned launch capability) would make
a lot of sense.

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nitrogen
Kepler is very far away, orbiting the sun:
[http://en.wikipedia.org/wiki/Kepler_(spacecraft)#Spacecraft_...](http://en.wikipedia.org/wiki/Kepler_\(spacecraft\)#Spacecraft_orbit_and_orientation)

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wikiburner
Yep, I'm an idiot. I was just about to update my post after doing a bit of
wikipediaing.

Looks like I'll have to turn down that job as head of NASA now.

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androidb
The saddest news I've read today. However there's still hope that they might
resurrect one of the 2 reaction wheels that are currently down so maybe
they'll be able to figure that out (in the article they mention that they'll
even try that with the first reaction wheel that was shut down a year ago).

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krschultz
Very sad, this is one of the more important NASA programs at the moment.

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drivebyacct2
$600 million is nothing. Why can't we spend more on this? Do people really
lack such forethought or is it the 100-yr-lifespan selfishness?

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robryan
Yeah, the killer is the lead times, if it were decided right now to build a
replacement it would be a long time before any results would be seen. Too bad
the program wasn't devised it terms of building more than one from the start.

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drivebyacct2
"Why build one when you can build two for twice the price".

God I'm such a nerd.

