James Webb Space Telescope hit by a tiny meteorite | Hacker News Reader

James Webb Space Telescope hit by a tiny meteorite

bbc.com

156 pointshuhtenberg114 comments

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.

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.

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.

This is like when I scratched my new monitor right after buying it.

Except the monitor costs 10 billion dollars.

I'm curious about the nature of the damage. article mentions that the affected mirror will be adjusted to minimize the distortion that was introduced, so obviously not a crack. So, more like a tiny scratch? It's hard for me to conceptualize the impact of hypersonic dust on a mirror

More like a tiny crater or pockmark, although they don’t say exactly how large the meteoroid was or how much damage it caused. Apparently “micrometeoroid” refers to objects with less than a gram of mass, although I assume that this one was likely significantly less heavy than a gram, which is the case for most.

Should've paid the extra billion for the wiper blade package

Throw a few dozen Rain-X wipers from AutoZone on that baby, she'd be good.

How do you define "hypersonic" in a vacuum?

Ha! Greater than 0 m/s I suppose - so still technically accurate :-P

>1715 m/s same as in air but without the air.

In space, nobody can year you go transsonic...

The mirrors are gold plated beryllium so it wouldn't be a crack anyway, or at least not a crack like one would think about glass cracking.

Beryllium is fairly brittle as far as metals go, so a crack wouldn't be out of the question.

But alloys don't behave like the individual elements, so Beryllium being brittle doesn't mean that the alloy also is. Just like Carbon has multiple crystallization forms with wildly different mechanical properties (graphite vs diamond)

Plating is not an alloy though?

str.replace(?,.)

Tangential question, but how is high speed space travel supposed to work with tiny space debris like this? You hear a lot about how a small constant acceleration can get you to effective speeds for galaxy hopping over time, but doesn't extreme velocity make tiny objects like this a massive threat? Like orders of magnitude larger than they are for current space vehicles? Is that a solveable problem?

Well as big an issue is the energy required, ie., acceleration requires energy and your mass isnt constant as you increase velocity.

So by the time you're anywhere near "galaxy hopping" you're requiring near infinite amounts of energy.

Also note that there really isnt any "galaxy hopping" speed. The speed of light is incredibly slow compared to space distances. Even travelling at light, you're not getting many places in a human life time.

You can actually cross the whole galaxy in a lifetime if you get really close to light speed, but measuring time from the perspective of your ship... for everyone on Earth, due to time dilation, it would take you hundreds of thousands of years though :(.

Notice that if you could travel exactly at light speed, time would cease to exist and you could get anywhere in the universe instantly, as light itself experiences no time.

> Notice that if you could travel exactly at light speed, time would cease to exist and you could get anywhere in the universe instantly, as light itself experiences no time.

This is not true. The easiest way to see why, is to realize that speed is relative: there is no difference in considering the observer to move with the speed of light towards the foton, or the foton to move with the speed of light towards the observer. Yet as you know, we observe light all the time and still we experience time.

Note that speed is relative, but time dilation is not. That's the twin paradox, they're both relatively moving away from each other, but only one 'ages slower'.

Though I don't know what it means to say a photon doesn't experience time, and even more so for hypothetical humans travelling at the speed of light. That's outside the scope of what relativity predicts.

You could also say “only one ages faster” so this is not a paradox because of that.

Ok so let's say two humans pass each other by somewhere in the universe, each in their own spaceship, in opposite directions. They both travel with half the speed of light, so relative to each other with full light speed. Which one is the one aging slower?

They won't see each other moving at the speed of light though. This example is covered in any class on relativity. Having an approach velocity between two objects at the speed of light or greater is different than accelerating a frame of reference to c. When an approach velocity is c, nothing is actually _moving_ at c.

In particular, it's acceleration you need to account for when talking about time dilation, not speed. And acceleration is less symmetric.

Love the Fermilab series of videos. Here's the one that covers the Twin Paradox:

https://www.youtube.com/watch?v=GgvajuvSpF4

Just because you can describe velocity from any frame of reference doesn't mean all frames of reference are valid for describing time dilation. They're not. If you're not accelerating, you're not accelerating.

Either way, supposing you were accelerating towards a photon at rest, at the speed of light, that doesn't mean you would suddenly experience time in slow mo. You're going to feel "time" normally. It means that the photon would appear to be in slo mo, which isn't something easy to imagine. Hence the preference for imagining clocks that turn slower.

Talking about a "photon at rest" is kind of nonsensical. From any frame of reference, c is c, and you'd measure the photon moving at the same speed.

Yes, that's true. Just a contrived example to try and illustrate why it's not correct to say time dilation isn't real because you experience time despite moving at c relative to a photon's frame of reference.

Probably more distracting than helpful

> Also note that there really isnt any "galaxy hopping" speed. The speed of light is incredibly slow compared to space distances. Even travelling at light, you're not getting many places in a human life time.

Only from the perspective of an observer from earth though, no?

Just wind the windows up

It starts with something like this https://en.m.wikipedia.org/wiki/Whipple_shield and probably moves on to superconducting magnetic shielding as well. It will have to be defense in depth. There could easily be some kind of liquid layer also so that it's capable of being renewed over time.

Micrometeorite impacts are one of the many many many issues still outstanding for high speed space travel. Manned interstellar travel is one of those things that is more "centuries away" than "decades away", if humanity will manage to do it at all.

A lot of science fiction about space travel brings up this issue. Sometimes it is hand waving about “shields”. The harder the sci-fi the more “realistic” the author will explain how the ship is shielded from impacts, but I don’t think I’ve ever read one that uses any technology we currently have.

> I don’t think I’ve ever read one that uses any technology we currently have.

Is 'ice'[1] a technology? :)

[1]: https://revelationspace.fandom.com/wiki/Lighthugger

Giant laser beam fields that search the trajectory for any backscatter along with super sensitive superconducting single photon sensors to understand the precise debris field.

At "galaxy hopping" velocities, i.e. relativistic, even light can be a problem.

Even the emptiest of empty space still has photons moving around from the cosmic microwave background, and go fast enough, and these photons will turn into deadly ionizing radiation because of blueshift. And even before that, the term "object" starts to lose meaning when it comes to collisions, it becomes a bunch of elementary particles with enough energy to cause fusion reactions. It could be one of the xkcd "What If?" scenarios, Randall loves to imagine stuff moving at relativistic speeds, and usually, it doesn't end well...

Yepper.

This was actually the core of one of my questions that actually stumped a professor back in college. We were trying to write a simulation of a ship traveling through space.

As usual, I got way too deep into it that I probably missed the entire point of building up fundamental simulation writing skills but stumbled onto much more fundamental problems/tradeoffs, like the tradeoff between detection/classification/reaction/dispatch/execution times and not ending up splattered across space by plowing into a semi-truck sized rock nobody saw in the space between stars at relativistic speeds.

Because once you're at those soeeds relative to anything else, anything else is a huge problem by definition. Looking at our current technology, we can carve up time into multiples of billionths of seconds for 1 action on one datum, but that chain of decisions that leads to resolving the difference between first hand experience at high energy particle accelerator physics and safely avoiding said first hand experience requires time for:

>Sensing equipment to generate an image/digital rendering of space ahead of you. Fundamental constraints exist on resolution and sensitivity here

>Tranlation to a digital line format, and transmission to a system capable of consuming that representation and classifying threats

>Propagating that list of threats to a system capable of quickly formulating a response (Second marshalling\transmission/unmarshalling cycle)

>Getting that list of responses resolved to courses of action translated to instructions dispatched (marshalled/transmitted/unmarshalled), then dealing with the physical latency of the various effector systems

All of this signal prop happening on a vessel yeeting itself along through space so quickly it can get to the next system (say Proxima Centauri) in say a decade, which means even with speed of light signal propagation, your vessel is going healthy fractions of a light-second per second, and you kinda needed this done yesterday.

All of this clockwork potentially ruined by the possibility of an errant chunk of rock, sand or hydrogen just minding it's own business while a bunch of apes spend countless generations of focused effort to end up ruining it's day, and hopefully, surviving. The Apes, that is. The rock'll have a new story for the post Universal debrief.

This was how science kinda ruined my life. Because even hydrogen hitting is ionizing at these speeds. Fleet Of Worlds plays with the idea a bit using handwavium inertialess drives to accelerate a gravitational rosette of worlds on the way out of the Galaxy, with their occupants terrified at the mere thought anyone may be charting their trajectory, and laying something in the way that could result in the sterilization of their species due to the relative speeds involved.

Mind you, at that point, I was barely out of my first programming course. I don't even remember if I actually completed that assignment with a coded deliverable. I just remember several hours in deep discussion with my professor over how to model things like detection thresholds and things like that.

Might have converged on "Just ignore it", but the more I think about it, the more I smile, because it really was a very good question that at the time I had no idea of how good it actually was.

If this incident happened 5 months after getting to C3, can we expect that on average we should see a similar collision event every few months, on the order of one to three (detected) collisions per year?

A single incident will not give you any sort of sense for how often this happens. It could be luck either way. Might be this was a relatively calm period and it happens way more often in the future or incredibly unlucky and we never see another event for the rest of the mission.

Fwiw, the article mentions this was the fifth time it's been hit.

This being the most serious of the incidents.

I think this is too pessimistic. One always gains some information, even from a single event. If you're catching the bus one and shows up literally the minute that you arrive at the bus stop, yes, you may have been very fortunate and in fact the bus runs only once per day, but you really ought to assign a lower probability to that possibility now, given your recent single new piece of information. There are ways to express this quantitatively too - but your own intuition ought to be enough of a guide here.

This is classical Bayesian inference. You update your priors when new information comes in. If something happens that you thought was unlikely, you update your credence about this event.

yes and perhaps the difficulty of using a frequentist approach on a sample size of 1 is why the parent post thought that you cannot learn anything from a sample size of 1...

Hacker News is a very peculiar place. You make a statement that is fundamental to understanding statistics and you get downvoted till your post dies. On the other hand it's the place where the smartest people get together to discuss things. Smart people don't like statistics?

It helps to remember that the downvote button is so close to the upvote button that it’s very easy to hit it by mistake on mobile. And I reckon most people don’t take the time to double check and undo the downvote.

I feel you, and it’s a natural worry. I deal with it too. But remember, the point of HN is for the discussion to be for the readers. And reading about downvotes is boring.

One hint that helps me, is when I write things like “Smart people don’t like statistics?” —- it sort of helps me realize that I’m in the frame of mind where I should step back and close orange website for awhile. And I mean all of this genuinely; I’m not patronizing or just saying it. It happens a lot.

Oh I did. I got 99 problems and a downvote on HN isn't one.

To be fair, the statement rests on the assumption that it's a singular strike that TFA doesn't support.

Basically there is now a probability distribution for how frequently the JWST will be struck by meteorites. The most probable amount is once per five months. However it’s a distribution with pretty fat tails, almost equally likely is every four or six months, slightly less is every three or seven, etc.

It's a question of sample size. There might be frequent events out there that kill the entire mission but we've been lucky so far. This might be an anomalously "noisy" period. We just need more data to make the determination.

New data will adjust the probability distribution and flatten the tails, but even 1 data point is enough to get an initial probability distribution.

Just a tiny nitpick, "meteoroid" and "meteorite" are not the same thing. The BBC article gets it right, but the title here is wrong.

For anyone who may be wondering what the difference is:

> When a meteoroid survives a trip through the atmosphere and hits the ground, it's called a meteorite.

https://solarsystem.nasa.gov/asteroids-comets-and-meteors/me...

I've been wondering if the Lagrange Point attracts more things to collide with?

They said parking it at L2 was akin to giving your car just enough speed at the bottom of a hill to exactly come to rest at the top of the hill. Given that mental model, I think L2 wouldn’t be a natural point for things to congregate. It’s not a gravity well, but a gravity “dimple”? Or local minimum? But it sounds like this is so new to us that humility is warranted and probably dangerous to neglect.

Edit-they did say they’ve done simulations and they did expect small collisions. It sounds like this was much larger than expected for this point in time, but not catastrophically so.

Edit2-also they’re not at L2 but in orbit around it. The lifetime of the craft is in part limited by how many course corrections it will take to stay in their orbit. That really makes me think this should be rarer.

L1-3 are saddle points, convergent on the tangent plane between the two stellar bodies and divergent on the normal axis.

Seems like being divergent on any access would push matter away over time.

It does, which is why, as a commenter above mentioned, the Telescope needs to burn fuel to remain in orbit around the Lagrange point.

Space outside of Lagrange points and gravity wells isn't attractive along any axis, the unstable Lagrange points have a plane which allows unstable orbits which have longer or shorter durations, depending on how exactly aligned with that plane the vector is.

We should expect more junk, not necessarily a lot more, and this is of course simulated in the models used to design JWT... but not necessarily with perfect fidelity.

- "But Senator Collins why did the front of the telescope fall off?"

- "Well a meteorite hit it."

- "A meteorite hit it?"

- "A meteorite hit the telescope!"

- "Is that unusual?"

- "Oh yeah! In space? Chance in a million!"

> The speed at which things move through space means even the smallest particles can impart a lot of energy when colliding with another object. Webb has now been hit five times with this latest event being the most significant.

> Webb has an open design; its mirrors are not guarded by the kind of tubular baffle seen on other space telescopes, such as Hubble.

So previous telescopes did have more protection against this kind of events.

The good part is:

> The damage inflicted by the dust-sized micrometeoroid is producing a noticeable effect in the observatory's data but is not expected to limit the mission's overall performance.

>> Webb has an open design; its mirrors are not guarded by the kind of tubular baffle seen on other space telescopes, such as Hubble.

>So previous telescopes did have more protection against this kind of events.

I would expect Webb to be less vulnerable though, due to the open design. So many possible trajectories would just go through the empty space between the beams and trusses (sorry for using the wrong terminology) and not hit anything at all?

It would be the same for like hubble, any trajectory will just hit the tube

I have always wondered, let’s say we eventually invent some technology that allows us to travel through space at .1c or .5c or even .99c, wouldn’t the ship colliding with a tiny piece of space dust/debris rip the whole thing apart at that speed?

Yes.

https://www.quora.com/In-movies-spaceships-often-accelerate-...

Definitely. There's a scifi story I read some years back with relatavistic space travel and battle where the primary weapon they'd use is dust.

yeah hopefully by the time we're traveling that fast we have energy shields

Question that pops to mind: Was the Hubble telescope ever hit by one such tiny corpuscles?

Yes! The solar panels were made by ESA and replaced twice. The old ones are hanging on a wall at ESA in the Netherlands and you can see micrometeorite damage with the naked eye!

There's a picture at [1] but its hard to know what the scale is

[1] https://www.esa.int/ESA_Multimedia/Images/2009/05/ESA_built-...

That looks brutal!

Echoing this. That’s a level of damage that seems hard to prepare for. Even the smaller one towards the lower center seems like it would cause havoc for camera equipment.

The long edge of one cell is probably 4-8cm long. It’s in that ballpark anyway.

Another photo says the hole is 2.5mm https://www.esa.int/ESA_Multimedia/Images/2005/03/Hubble_sol...

That looks like it got hit from the back.

Holy cow! I thought hail damage was bad!

That brings to mind a (very non-realistic) animation I'd seen of a meteor impact on the Moon, seen from the perspective of two astronauts there.

The meteor impacts and a cloud of dust billows out.

My first thought: "dust doesn't billow in space". Instead, there'd simply be ejecta, moving with a distribution of initial velocities (speed & direction), which would move in independent parabolic arcs. Billowing requires an atmosphere.

The Apollo 12 mission landed about 600 feet (200m) from an earlier mission, the unmmaned Surveyor 3 probe. Ejecta from the descent was blasted out at > 2,400 m/s (5,400 mph), and the side of the Surveyor craft facing the landing site was sandblasted by the resulting particle spray. The concept of sub-grade landing pads on the Moon might actually have a great deal of validity, as otherwise the ejecta flows would tend to degrade structures and terrain for tremendous distances.

https://www.nbcnews.com/id/wbna23130776

https://www.space.com/4956-lunar-landers-sandblasted-moon.ht...

Huh, so I could perhaps hop on a train and take a look one day.

What on earth is the ESA doing in Noordwijk though.

Hubble's optics are contained within the spacecraft structure and would only have been damaged by a likely catastrophic strike that would have disabled the entire spacecraft. Webb's mirrors are completely exposed.

what if it was aliens testing our equipment. Throwing rocks disguised as space dust to throw us off thinking it was a natural signal.

James Webb might find aliens. or there might already be aliens in the james webb space program. or both.

Should've installed a deflector dish... ;)

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