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Comment by huhtenberg | Hacker News Reader

The source - https://blogs.nasa.gov/webb/2022/06/08/webb-engineered-to-en...

  As a result of this impact, a specialized team of engineers
  has been formed to look at ways to mitigate the effects of
  further micrometeoroid hits of this scale.

It sounds like they weren't expecting this happening so soon after the launch.

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It could just be statistical outlier, but better to be safe then sorry. Compared to the cost of the JWST, a couple of people looking into ensuring it gets the longest lifetime viable are incredibly cheap.

Wonder if its related to its orbit in the lagrange point? Seems like it might make sense that lots of meteoroids hang out around there for a bit longer before drifting away.

I had not thought of that angle, but maybe the lagrange points are like the garbage patches in the oceans-- natural minima where objects can rest.

I would think the stuff that coalesces there does so because it has very low velocity relative to the Lagrange point and thus the JWST. Anything moving fast enough to pass through the satellite won't be staying there.

There are stable and unstable Lagrange points.

The L4 and L5 Lagrange points are stable. Objects orbiting near those will tend to remain near that point. Well-known examples of these are the Trojan asteroids, in the orbit of Jupiter, at the L4 and L5 points of the Jovian-Solar orbit.

L2, near which JWST orbits, is an unstable point. The JWST must continuously expend propellant to "drive uphill" toward the point (it orbits nearer Earth than the actual Lagrange point). At end of life, a final burn will drive the satellite beyond the point, from which it will eventually drift into a solar orbit.

Other orbiting material similarly will fail to aggregate near the L2 point.

As I understand, the L2 (beyond Earth), L1 (between Earth and Sun), and L3 (opposite side of Earth, behind the Sun) are all unstable liberation points.

That said, plans for structures at L4 / L5 might want to consider the general attractor property of those orbits.

https://en.wikipedia.org/wiki/Lagrange_point#L2

How can it be mitigated? I can't think of a single idea. For future missions, sure, but this one?

RMA the device.

You probably can't do much about strikes to the heat shield because that has to point towards the sun at all times, but if you knew that a micrometeoroid is on route to strike your mirror you can turn the telescope and let the meteoroid strike a less sensitive part instead.

Of course you can't predict single strikes, but maybe you can create a statistical model which direction strikes are most likely to come from, and prefer observations that point the telescope in the least dangerous orientations. Maybe there's even some seasonality to it due to interactions with the moon or with other planets, and you can just schedule observations in a particular way that reduces risk.

Those things are tiny and easily travelling at a few km/s, not sure how you could detect that

You can't detect them, but, like meteor showers, they may sometimes come from certain directions.

GP's entire second paragraph addresses that point.

It does not as the same detection problem precludes meaningful statistical modeling (we do not have enough objects that can detect and report hits, and we would create too much debris collecting that data.)

If there were any dangers obvious enough to detect from here, that destructive, we already wouldn’t be using that point since the mission is expensive and long-lasting enough that a statistical approach to protection would fail too quickly. (The suggestion made me think of “gun kata” in Wimmer’s Equilibrium which had the same problem, given the performance ratios stated in the opening monologue.)

In addition, some orientations may decrease the collision cross-section entirely. Even a 20% decrease may mean a ~20% increase in mission lifetime if these strikes are common.

That's not always possible, any orientation that would require the instruments to point at nearby sources of heat would ruin observations for a long time, possibly forever. Webb is severely constrained in being able to point to many places but not 'backwards' to where it came from and certainly not upside down.

They don't really have to do a full turn, if they can predict direction with any sort of accuracy they could at least reduce the exposed surface area with a minor shift.

Spare mirrors and a repairing robot-arm!

Spacecraft used to have double walls. Micrometeorites would strike the outer wall, piercing it but shattering. The 'dust' would strike the inner wall and not penetrate.

The problem is the 1st surface mirrors not the vehicles structural walls.

Which, curiously, has no wall around it. A tube or shroud outside its visual collection range, could eliminate a huge fraction of impacts. Unless they came straight on, which if direction were randomly distributed would be another decimal place better.

There’s no way to mitigate the risk of statistically random meteorites that can come from any direction.

The primary mitigation is to use predictions of larger events, such as meteor showers, and move the observatory to an orientation that reduces the risk of damage.

Sure there is! Put a shroud around it in every direction but the light-collection direction. That'd mitigate like 90% of the meteors.

I think the only way is to make launching these telescopes so cheap that losing a couple isn't that big of a deal. Let it crash like Erlang's motto

Could be one of those needles.

Not sure we're you getting this from.

They made plenty of simulation s and probably enough around this topic. They had enough time after all

They had a ton of time indeed, but they didn't cover this particular eventuality. It's literally in the same post. Perhaps give it a read?

  Since launch, we have had four smaller measurable micrometeoroid 
  strikes that were consistent with expectations and this one more
  recently that is larger than our degradation predictions assumed.

This still doesn't indicate anything.

It doesn't say how much bigger.

My point I'm trying to make: the original comment indicates to me that we need to worry. For me it conveys much more speculation than I think is reasonable right now.

For example they were also not expecting to have such a great optical resolution.

> This still doesn't indicate anything.

It does indicate something. It indicates that

> they weren't expecting this to happen so soon after the launch

The delta matters, but no matter the delta, the fact that it defied expectation stands.

How does one even collect information about the probability of being hit by something that big in space ? They counted hits on things (ships) that came back from space ?

They've launched flat plates made of aerogel to capture orbital debris.

For example: https://solarsystem.nasa.gov/stardust/home/index.html

The lagrange point itself has a probability how realistic it is that something can be cought in it / if it stays there.

There are other points were stones collect like l4 and l5.

Then we have Hubble (and over 100 others as a benchmark, a few ships/missions like to the moon and Mars.

Herschel space observatory was also on l2. There is a wiki Artikel called 'list of objects at langrange points'

Simulations don't matter if your starting parameters don't fit reality, maybe the population of dust in this range was poorly understood around the L2 point? We've got loads of missions there, but maybe none of them would notice anything like this.

In the current situation with this amount of information it could be a lot of different things.

Also from a statistical standpoint it's totally valid that this event happened now as it could just mean that a similar event is not happening for the next 50 years.

> it could just mean that a similar event is not expected to happen for the next 50 years.

Fixed that for ya. There are no guarantees. Micrometeorites are both fast and tiny, and you can only make statistical estimates. But when the rubber hits the road, it's entirely possible for 100d20 to come up 100 twice in a row.

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