Double trouble: ESA's Gaia hit by micrometeoroid and solar storm | Hacker News Reader

Double trouble: ESA's Gaia hit by micrometeoroid and solar storm

esa.int

155 pointsgnabgib21 comments

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.

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.

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.

> 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.

> 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...

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.

Possible covers a broad range of effort levels and outcome risks. At a minimum a solution for controlled deorbit is required within 10 years or so. You'd think that something that could use the SCM [0] to catch it could also reboost it or stage a human repair mission, but some involved are not as sanguine as a lay person.

"The last time we went to Hubble, it was on the space shuttle, and it was quite a long time ago," Clampin said. "And, of course, Hubble is an old spacecraft now; a lot of the people who were very involved in the early serving missions have retired and there's a lot of work we would have to do to get back up to speed on how to do that." [1]

On the other hand, even keeping a program running while a solution is developed might be too much given the rules NASA must follow. "Announced on Wednesday is the cancellation of the VIPER mission to the moon, this is shocking because the Rover is finished construction and just needs a test session. Moreover, NASA is contractually required to pay Astrobotic to fly a NASA payload to the moon, so they have to pay for this anyway. Instead of a rover NASA will send ballast to the moon." [2]

0. https://esahubble.org/about/general/soft_capture/

1. https://www.space.com/jared-isaacman-hubble-space-telescope-...

2. https://www.youtube.com/watch?v=4OS9kq0-ssg

> Instead of a rover NASA will send ballast to the moon.

This is borderline criminal.

It is certainly a strong and recent example of how intent qualities are orthogonal to outcome qualities.

Certainly. It's all a cost-benefit and risk-reward analysis. Servicing it would require brand new, untested procedures, and Hubble's technology is now more than 30 years old. While designing a new space telescope is not an easy, cheap endeavor, putting the resources into helping Hubble last longer might not make sense, when those resources could go to something new and better, that can still cover Hubble's current use cases. And especially since they believe we can get another 10+ years out of Hubble without touching it, that gives time to develop alternatives, if that's what turns out to be what's needed.

At some point it's just cheaper to send a new better one. As we know the failing point we can add tons of gyros.

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.

Isn't JWST limited by the chilling hydrogen onboard?

No, it has a cryocooler for MIRI that keeps the relevant components at <7K without cryogen.

https://www.youtube.com/watch?v=FUH61gx149c

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.

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.

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.

> the right thrust at the right time

That’s quite tricky.

How long will the thrust gas last before needing a refill?

> 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?

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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