
NASA has recovered the Kepler Space Telescope from 'emergency mode' - wanderer42
http://www.theverge.com/2016/4/11/11408620/nasa-kepler-telescope-emergency-mode-stable
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Altaer
I work on software for a few satellites (not Kepler) and they have gone into
an emergency or safe mode a couple times over their long lifetime. None of
those times ended up being because of a serious problem. While I am interested
to hear back on what exactly tripped the emergency mode, I think the main sad
news here is the loss of the finite supply of fuel on board, which will
ultimately shorten Kepler's operational lifetime.

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pc86
Can someone explain why emergency mode is the most fuel-intensive despite
being the lowest powered?

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dtparr
Stolen shamelessly from the Ars Technica comment that explained it to me:
[http://arstechnica.com/science/2016/04/kepler-exits-
emergenc...](http://arstechnica.com/science/2016/04/kepler-exits-emergency-
mode-re-establishes-full-communication/?comments=1&post=30987657)

>Normally Kepler (in K2 mode) uses the pressure from sunlight combined with
the two remaining reaction wheels to maintain orientation. It still does need
periodic thruster usage but the heavy lifting is done by solar pressure and
reaction wheels which makes the propellent usage very efficient. However it is
a complicated and precarious balancing act. It needs full instrumentation,
computer operation, and periodic updates from Earth to work.

>When it goes into emergency mode it falls back on 100% station keeping
thrusters because that is simpler although far more expensive in terms of
fuel. They don't know exactly why it went into emergency mode but for whatever
reason Kepler believed it could not maintain orientation without it.

>In emergency mode it has to expand propellent because without some station
keeping it would begin to tumble uncontrollably. If you have a spacecraft
millions of kms away from Earth, tumbling out of control with its
communication array no longer pointed at Earth you will probably never regain
control. So it is a last ditch effort to maintain proper orientation on the
hope that command & control update can fix the problem. It begins "looking"
for an command & control signal from Earth (using propellent to orient the
spacecraft). If/when it finds it, it then tries to keep that orientation using
100% station keeping thrusters regardless of fuel consumption. It will
continue to do so until standard operation is restored or it runs out of fuel.

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pc86
Perfect explanation, thank you!

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cyphar
Kepler is definitely one of the most important space telescopes that we have
(and will have for the foreseeable future). It has both long and short cadence
data for many very interesting targets over 3 month periods. TESS will only
give us data for one month on each arc of the sky it is scanning (although, it
means we'll get a full picture of the sky) but it won't observe the K2 field
(the ecliptic plane). It's such a shame to see it losing so much fuel and
energy.

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miander
Is there a more detailed/technical article available?

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LeifCarrotson
After a few links in the article pointing to other Verge articles, I found
this:

[http://www.nasa.gov/feature/mission-manager-update-kepler-
re...](http://www.nasa.gov/feature/mission-manager-update-kepler-recovered-
from-emergency-and-stable)

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Tzunamitom
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