Asteroid samples escaping from jammed NASA spacecraft | Hacker News Reader

Asteroid samples escaping from jammed NASA spacecraft

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As with all "current events in space", Scott Manley has an excellent video on this.

https://youtu.be/cmQfWuFbLNg

> Blowing a raspberry in the surface of the asteroid

Classic Manley

From TFV:

"In order to be able to perform the landing they needed to update their software to give it optical navigation abilities ..."

Imagine being part of the team that had to do that, fast, chop-chop, or else their billion dollar space mission would fail miserably.

"Oh, you only need us to implement vision. Ok, no biggie."

I assume it was more a case of "We have an algorithm that successfully lands the craft 80% of the time, but we would like it to be 99% of the time, so get to working on it..."

Usually its 99.7% percent of the time: three standard deviations.

"So they actually performed a software upgrade of on the spacecraft to give it optical navigation capabilities..."

God dammit. And here I have trouble getting software updates into a server I have full control over on Earth.

Sadly, most of us don't have the luxury of working in environment where (a) it's mandated that we set up a 1-for-1 test rig with the production infrastructure and (b) management will accept the answer "I need to test for all possible contingencies because failure is not an option."

(Most of us are writing code in an environment where failure is totally an option, as long as it's fast and restoration is quick ;) ).

Another part of the difficulty with updating servers is that updates are rather opaque. My own software on any given server is maybe 0.1% of all the software running on it (if even that). The other 99.9% is someone else's code: the operating system, the software runtime, the libraries, etc. So one doesn't really have a lot of insight into what is about to happen to the server without running a duplicate setup, which as you point out is pretty difficult to get right. I'm sure NASA has much more visibility into all the software that is running on their spacecraft.

While the abstractions is lesser for a spacecraft, I don't think any one is hand compiling or writing machine code directly. There will always be some abstraction layers.

While the requirement is there, often it falls through the cracks. A recent example is the wrong mapping of the Starliner thrusters. This wasn’t found until the simulator changed due to brownouts after it was already in orbit. Just by luck, the new simulator was of sufficient fidelity to catch the mapping error.

Had 1) they not missed the correct orbit due to a different issue and 2) not had to switch simulators it could have potentially collided with the space station.

So yes, the requirements are there but often not followed but luck was on our side

Then again NASA has a $22B budget.

Many large corporations have budgets in excess of that and still struggle with delivering solutions and software updates. Internally or externally.

Sure, but I was trying to cheer `moron4hire` up, who I assume has a lot fewer zeroes in their budget.

Hell, I'd take a comma over some of those zeros!

Yeah, I'm the only zero in the budget

The mission has a very small sliver of that budget. Trust me, there's no "NASA" that comes running when things go wrong: It's on the mission team to handle it.

And now optical navigation has been flight proven so it can be used on other missions.

Optical nav was flight proven a long time ago. For deep space (autonav, deep space 1), and for mars landers.

At 2:15 he discusses how NASA was completely wrong about the surface of the asteroid based on their initial thermal inertia analysis. While I don't pretend to be an expert, it's stuff like this that really makes me doubt how much we really know about distant parts of the universe. This asteroid is so much closer to Earth than many galaxies and other objects scientists claim to know something about. Of course, science is all about being wrong, refining the model, trying again etc. but my default reaction to any claim made about age/size/composition/distance, is immediate skepticism for this reason.

Well, we're entering the golden age of space exploration right now, so let's see how that gap closes by the next decade or so.

After watching the video from Scott Manley (great video) I can see how the sampling mechanism is supposed to work.

I wonder whether they can make use of momentum to close the sample doors and capture the samples preventing closure.

Since there are some chunks preventing closure and they had planned to be able to sample more than once in the event that the first attempt didn't recover enough material that means that they can control the opening and closing of the sample doors.

It seems to me, having grown up as a kid being transported in an old Pontiac station wagon back before seat belts, that you could extend the arm behind Osiris-Rex pointing opposite the direction of travel and then trigger the doors open just as you fire to decelerate and the particles preventing closure should zoom into the collector like preschoolers into the windshield of that old station wagon when the brakes were applied.

The sample doors are just a flap that gets blown open by the nitrogen during sample gathering then springs shut, there's no direct control over them, the solution is to just pack it away in the return canister very carefully.

I figured it couldn't be that easy or they would already have considered it. Springs are probably more reliable for that application on a spacecraft. Thanks for clarifying that for me.

My rule of thumb is NASA/JPL/JAXA/ESA are full of far smarter people than me so if I think of it in 5 minutes they definitely thought of it already and have a binder full of reasons it's not the best option.

If the container is open, how are they planning to retrieve the sample without losing it on reentry?

The container will be loaded inside a sealed reentry capsule.

> "Lauretta said there is nothing flight controllers can do to clear the obstructions and prevent more bits of Bennu from escaping, other than to get the samples into their return capsule as soon as possible."

This, I'm guessing.

Also, I found these parts interesting:

>"Regardless of what’s on board, Osiris-Rex will still leave the vicinity of the asteroid in March — that’s the earliest possible departure given the relative locations of Earth and Bennu. The samples won’t make it back until 2023, seven years after the spacecraft rocketed away from Cape Canaveral."

>Because of the sudden turn of events, scientists won’t know how much the sample capsule holds until it’s back on Earth. They initially planned to spin the spacecraft to measure the contents, but that maneuver was canceled since it could spill even more debris.

>“I think we’re going to have to wait until we get home to know precisely how much we have,” Lauretta told reporters. “As you can imagine, that’s hard. ... But the good news is we see a lot of material.”

Thanks. That means there are two containers: the open one where the samples are now, and the sealed return capsule, where the contents will be transferred soon.

In that light, this quote confuses me:

> scientists won’t know how much the sample capsule holds until it’s back on Earth.

They wanted to spin the spacecraft to measure the mass, but they can't risk losing more samples from an open container.

But why can't they spin the spacecraft after the sample is secure in the return capsule, but before reaching Earth? Is it precisely in the center of mass?

I recommend the scott manly video another commenter linked to for a more full explanation, but:

The sample container that's currently jammed open is on the end of a long arm, while the sample return capsule is mounted on the body of the spacecraft. The only way to measure mass in free-fall is to spin the entire craft and measure where the center of rotation is compered to before the sample capture. The difference is then used to calculate the sample mass.

With the sample at the end of a long arm, the spacecraft doesn't have to rotate very fast to get a large enough difference in rotation to measure the sample. If the sample is in the return capsule, the moment is so much smaller that it's probably below the sensitivity of the instruments they were planning to use.

Bright side - they have so much material, that weighting it is not really that much of a concern. They were hopeful to get maybe 50 grams of material, they got about 400g, but maybe 100g will be lost. They won't have exact number, but they will have more than expected anyway.

Won't the extra weight require a change in earth re-entry fuel calculation etc. ? Without knowing the exact change in weight, they are going to be firing in the dark, as it were.

I don't know that much, but I suppose they will do a burn and then some corrections. If mass difference is big enough to be detectable for reentry, it will be detectable when they are going back to earth.

A key difference is that spinning the full satellite with the arm extended and measuring the center of rotation measures the mass of the samples collected regardless of the thrusters/reaction wheels.

Measuring the trajectory of the reentry vehicle gives a parameter that can be used to estimate the sample mass assuming nominal thrust values, but you can't distinguish between an underperforming or overperforming rocket engine and heavier or lighter samples. This ambiguity doesn't really matter for the purposes of burn correction - you need to get to the correct reentry trajectory no matter what caused the deviation - but your sample mass estimate may be off.

I don't think there's a whole lot of utility in knowing the sample mass, as long as you've got enough (and they've definitely got enough!), it would just help satiate the curiosity of the scientists and engineers who otherwise have to wait a few more years to see their results.

It's not enough to make a difference either way around it. The sample return container could be filled to the brim with pure osmium or iridium and would make it through the atmosphere just fine.

The scientists are mostly worried because they want as much of the sample as they can possibly get, and they're a little worried about closing the sample container - if there's a rock that gets stuck somewhere, the container might not seal shut and then they've got a real bad problem they've gotta contend with.

It's 2020, they don't want to jinx it, just shut it up in the container and wait for the time capsule to arrive in 2023.

Instead of adjusting fuel you can probably compensate by changing when you do the burn. And there are likely to be midcourse corrections anyways.

That makes me wonder: how is it possible to even determine what the correction should be? Space is vast, how do they determine the position of a microscopic vessel precisely enough to know how much to burn?

The primary instrument is probably a star tracker. It's possible to position yourself within the galaxy to a very high degree of accuracy by looking at changes in relative position of stars and planets which have a known "position" (really orbits).

Multiple correction burns along the way. For equivalent burns, the later along the trajectory the burn, the smaller its net effect on final position. So it's a series of increasingly better approximations.

Try it in ksp. It's quite illuminating to plan your burns and see their effect graphically and build an intuition for celestial mechanics and astrogation.

They should also be able to figure it out via delta-V per unit of thrust when they execute any orbit-change maneuvers to return to Earth, but that's a much less accurate metric (perhaps not accurate enough to differentiate a spare 100 grams of material).

They might not even be able to measure that small of a difference in the spacecraft's acceleration, to be honest. We're talking about a difference in grams of a spacecraft that's somewhere north of 1000kg right now - wet mass was maybe 1529kg at launch [according to NASA; Lockheed said the bus could be up to 2000kg at launch, so I'm not sure who to believe being honest - it's a little hard to believe they'd risk things and short the mission on that much hydrazine], dry mass 860kg, split the difference and it's probably around 1200kg [or up to 1500kg] currently.

It's a little easier to believe they could detect whether or not they got 60g by the last significant digit change in the moment of inertia from their instruments by nulling out the rotation... It's a little harder to believe they could detect a difference between 0 and maybe 500g in the sample return container via their acceleration data. I doubt they even know how much hydrazine and helium is left with all that much precision - at more than hundred grams a second burned, it's easy to believe there's some amount of accounting slop.

The sample return vehicle is much closer to the center of the vehicle so the change in the moment of inertia will be much smaller than if they had been able to extend the arm as planned. The change would be pretty slight and maybe on the edge of what is meaningfully measurable.

> But why can't they spin the spacecraft after the sample is secure in the return capsule, but before reaching Earth? Is it precisely in the center of mass?

They might be able to, but there’s no reason to. The purpose of the sample mass measurement was to determine if they needed to try again, however that’s not an option with a jammed container.

And the criterion for trying again is that they didn't collect enough material on the first try. If there's so much sample in the container that it's jammed open, they're probably fine in that regard. :)

There's a sample return vehicle that detaches with the sample canister inside of it. There's some concern with so much material floating around from the sample head no sealing properly that some bits might get in the way though. Scott Manley has a pretty good video about it as per usual when there's slightly vague space news. I've linked directly to where he's talking about the sample return portion of the mission.

https://youtu.be/cmQfWuFbLNg?t=443

At the original 60oz/$800 million dollars, would that make it the most expensive bit of mineral on Earth in 2023?

Probably still cheaper than 1st-party printer ink.

only about 10x more expensive than tritium.

That's $13,333,333.33/oz, if you charge the whole cost to sample collection. They also get plenty of other science observations, but the main point was sample return.

Apollo brought back 842lb of samples for something like $260 billion (inflation adjusted), that being $19,299,287.41/oz.

Of course, science was basically a side-effect of Apollo, so you can't really charge it all to sample collection. But if you did, the moon rocks are pricier.

I appreciate you doing the math! Kinda amusing that it comes out to roughly the same order of magnitude!

Stardust cost 200 million and collected a few grams at most. Hayabusa cost 100 million and collected less than 1 gram. I think those two beat Osiris in price/weight.

I'm sure NASA has thought of this, but won't the mylar film close if the sampling disk loses some material, before it loses all of its material? Why not give it a shake to get some of it out so the seal can close?

If there's a piece wedged tightly in there it could let most of the rest of the sample out without dislodging the piece holding it open.

How bad would it be if a piece large enough to wedge the entire container open was the _only_ piece we recover? How big would that piece have to be? Are they expecting a certain diversity in the sample that would be lost if they only got one huge piece?

I think the scientific goal was 60 grams which is more than just one piece at the size of the gathering head so they'd have to decide which tests they would actually do instead of being able to do all of the planned tests. So yeah just getting one larger piece would be a loss for the mission.

"Why didn't they plan for a soft asteroid?" is the annoying question I am sure the team will be asked, and I do not the answer.

Is a second touchdown possible?

No, the spacecraft is already on a trajectory away from the asteroid, and any further maneuvering is not an option until the sample capsule has been stowed to avoid more debris spilling.

Disagree. The sample arm was designed with spare gas for up to 3 sampling attempts, so they could go back and get more if they didn't have enough.

Since their sample-cup is filled to the brim and spilling over on the first attempt, they are choosing to stow the sample container, rather than go for another (redundant) attempt with an already-full sample container.

Second touchdown would be required if they didn't caught enough material first time. Since they got 10x too much, even if they lose half it's not a tragedy.

Not really 'jammed', I think they mean 'jam packed'

edit: ok I see, it jammed because it was jam packed

It's jammed. There's a film that was supposed to close on the collector to keep the material inside, but because of debris it wasn't able to close, so material is escaping.

I'm concerned that they'll have a hard time closing the reentry vehicle, that its hinge and hermetically sealing systems will become jammed open as well. There's no one available to wipe the gravel and dust off the sealing surface with their finger...

I'm not involved in the project, but I do work on terrestrial automation projects, often involving CNCs - chip management to prevent swarf accumulating on your hard stops and tapers is a real problem! Here, we have plenty of compressed air as well as gravity to clear chips, and preventative maintenance schedules for the stuff that the automated cleanup processes missed, and we remove parts to cleanrooms for important measurement stages, but that spacecraft is basically floating in a cloud of gravel...not a good environment for precision seals!

So no max depth set into the software controlling the excavating arm?

"Bugs are boundary conditions we refused to take seriously."

Watch the Manley video linked elsewhere in the comment thread. The capture was entirely analog.

That is the weirdest sampling tool I've seen NASA build.

I disagree that it was an analog system. They were measuring force as a proxy for contact, with no depth-finding system in place. The arm just sank in and never hit the force threshold for the automated system to react.

It was expected to hit the surface, NOT plow into it like a pile of gravel, use the blower to grab particles in the bucket, then blast backwards. Instead, it DID plow into the asteroid like a pile of gravel, even at a slow 40cm/sec. It was thought it would be much more solid than it turned out to be. It had no way of controlling how far it went in.

I think due to Newton's 2nd law retracting the arm prematurely would've caused the rest of the probe to strike the surface of the asteroid

Edit: and by 2nd law, I really mean 3rd

Imagine the pickup managed to deviate the asteroids course so that it hits us! You wanted 100 grammes of rock, 78 billion kg incoming! :D

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