[HN Gopher] Double trouble: ESA's Gaia hit by micrometeoroid and...
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Double trouble: ESA's Gaia hit by micrometeoroid and solar storm
Author : gnabgib
Score : 142 points
Date : 2024-07-18 21:27 UTC (1 days ago)
(HTM) web link (www.esa.int)
(TXT) w3m dump (www.esa.int)
| perlgeek wrote:
| I'm always fascinated by these spacecraft that far outlive their
| designed mission lifetime, and then sometimes need a software
| hacks to continue operating, often with reduced capabilities.
|
| Just recently we had the news about Voyager 1 needing a remote
| updated to avoid some corrupted memory region, and I believe
| Hubble runs with only one gyroscope now, because the other ones
| either died or were slowly dying (while still far exceeding the
| original mission duration).
|
| I can imagine the satisfaction the software engineers feel if
| they can eek out a few more years of mission life out of a piece
| of expensive hardware that too far out to service directly.
| eb0la wrote:
| Probably the key is to assume worst case scenario will always
| apply. After all space is an hostile enviroment you cannot
| control, and you need to have the device working for at least
| the whole mission lifetime.
| its_ethan wrote:
| Another factor is that when NASA says the expected mission
| life is like 30 days or whatever, it doesn't mean they are
| designing to just meet that 30 day target. I can only speak
| to mechanical design, but the margins that NASA uses are
| _huge_ , at least compared to consumer tech (I've worked in
| both). The 30 days is more like what they are "liable" for
| achieving per their directive. Liability isn't quite the
| right word, but the missions are pretty small in their
| official spec/definitions.
| kelnos wrote:
| > _Hubble runs with only one gyroscope now, because the other
| ones either died or were slowly dying_
|
| IIRC there are six total gyros on Hubble. Some of them have
| failed. Earlier this year, one of the three remaining failed as
| well, so they're down to two. They've dropped to a one-gyro
| mode now so they won't wear out both at the same time. Once the
| one they're using fails, they'll switch to the last one.
|
| The two remaining gyros are of a set of "better" gyros that
| were installed on a servicing mission 15 years ago or so.
|
| They could repair it (as well as give the satellite a much-
| needed orbit re-boost), but for now they've passed on doing so,
| presumably for budgetary reasons.
|
| Regardless, completely agree that it's incredible that these
| spacecraft often outlive their mission plan, sometimes
| drastically so. Hubble was projected to have 15 useful years
| (1990-2005), but it's still kicking (though not without the
| cost of past repair and upgrade missions), and should hopefully
| last well into the next decade. Longer, presumably, if it
| becomes compelling enough to spend the money to further service
| it.
| adolph wrote:
| > They could repair it (as well as give the satellite a much-
| needed orbit re-boost), but for now they've passed on doing
| so, presumably for budgetary reasons.
|
| It isn't clear anyone could "repair it." Part of NASA's
| reticence has to do with Hubble's sensitivity and that any
| docking would be completely new since the Space Shuttle was
| the only vehicle to service Hubble. Additionally at least
| some see good science continuing '"There's a greater than 70%
| probability of operating at least one gyro through 2035,"
| Crouse said.' [0] A more conspiratorial part of me says there
| are imaging secrets the makers prefer to keep.
|
| On the other hand, there is the viewpoint that '"Up until
| now, there's only been, you know, one group that would ever
| touch Hubble. And I think that they have an opinion of
| whether -- of who should or shouldn't be allowed to touch
| it," Isaacman said. "I think a lot would say, 'I'd rather it
| burn up' than, you know, go down a slippery slope of, you
| know, the space community growing. So I think that's a factor
| now, unfortunately."' [1]
|
| Personally, I see sunk cost fallacy as being a strong force
| in humanity. Additionally, the back and forth that may delay
| is resistance that will make Isaacman's solution better and
| certainly won't deter him.
|
| 0. https://www.space.com/jared-isaacman-hubble-space-
| telescope-...
|
| 1. https://www.npr.org/2024/05/16/1250250249/spacex-repair-
| hubb...
| rbanffy wrote:
| It _is_ possible to repair it and we know that because it
| was repaired many times before. It'd need at least some
| brand new hardware though.
|
| Until reusables make it cheap to launch a replacement (and
| so cheap the replacement doesn't need to be built as
| carefully and expensively) it's preferable to repair it. Or
| not, as ground-based observatories have evolved
| considerably since the Hubble was launched.
| mbonnet wrote:
| Expected mission lifetime is often a function of "if thing X,
| Y, Z goes wrong". As you get past X, Y, and Z, mission lifetime
| will grow significantly. For example, for the James Webb
| telescope, its expected lifetime was limited by expected
| precision of orbit insertion by the Ariane 5 that launched it.
| Ariane 5 performed perfectly, so the resulting precision means
| the lifetime of the telescope is extended.
| dotancohen wrote:
| Isn't JWST limited by the chilling hydrogen onboard?
| OldGuyInTheClub wrote:
| No, it has a cryocooler for MIRI that keeps the relevant
| components at <7K without cryogen.
|
| https://www.youtube.com/watch?v=FUH61gx149c
| nullc wrote:
| Gaia is such a cool instrument, but I can imagine that it's
| pretty fragile due to clever elements in its design like using
| rotation-synchronous time delay integration-- it has to be
| rotating just right.
| GuB-42 wrote:
| From what I've seen, it is actually a simple design, with very
| few moving parts, which should make it quite robust.
|
| This simplicity is what allows it to be "rotating just right",
| as it is very close to a rigid body, it is just a matter of
| applying the right thrust at the right time from cold gas
| thrusters. There are no gyros, reaction wheels, etc... to take
| into account.
| rbanffy wrote:
| > the right thrust at the right time
|
| That's quite tricky.
| tonynator wrote:
| How long will the thrust gas last before needing a refill?
| ISL wrote:
| Final two paragraphs:
|
| _Thanks to the hard work and efficient collaboration of all the
| teams involved, Gaia was recently returned to routine operations.
|
| In fact, the engineers took the opportunity of this unscheduled
| disturbance to refocus the optics of Gaia's twin telescopes for
| the final time. As a result, Gaia is now producing some of the
| best quality data that it ever has._
| FartyMcFarter wrote:
| > In April, a tiny particle smaller than a grain of sand struck
| Gaia at high speed. Known as a micrometeoroid, millions of these
| particles burn up in Earth's atmosphere every day.
|
| > This object, however, struck Gaia at a very high speed and at
| just the wrong angle, damaging the spacecraft's protective cover.
|
| How do they know all this? Did they perform some simulations to
| find out what kind of particle could have done the observed
| damage?
| ijustlovemath wrote:
| These satellites have pretty sophisticated Attitude
| Determination and Control Systems, whose whole job is to
| measure and reject disturbances. I'd guess the torque applied
| by the meteorite was found in the telemetry and they worked
| backwards from there.
|
| Here's a paper describing Gaia's ADCS (they use the acronym
| AOCS to mean the same thing):
| https://www.researchgate.net/publication/261710181_THE_GAIA_...
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