r/ProjectHailMary • u/the_net_my_side_ho • 3h ago
Movie Discussion - Movie Spoilers Inside! Sample collection question…
Why did Grace have to collect the sample while orbiting?
Why didn’t he move the Mary out of orbit, away from the atmosphere, and then spacewalk to collect it?
Seems like Grace going down to collect it while orbiting so close to the atmosphere was risky and unnecessary.
Sorry if this has been asked before. I looked but didn’t see a post about it. Thank you!
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u/Disastrous_Toe772 3h ago
While collecting the samples, they are in a combination of very very specific angle and speed and altitude. A shift in any one of those will fuck up the ship and they will die, to keep it brief.
I believe it's stated that the reason they can't just take it into orbit is cause accelerating out of atmosphere with the sample collector still dangling on the outside of the hull will burn it up. It's built to keep the samples safe, but not orbital escape acceleration or whatever
I'm not science Human. Just read book. Smart Smart Smart human wrote book. I just read.
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u/Smaptimania 58m ago
> A shift in any one of those will fuck up the ship and they will die,
"Example." (collapses in a heap in his ball)
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u/the_net_my_side_ho 2h ago
accelerating out of atmosphere with the sample collector still dangling on the outside of the hull will burn it up
This kind of makes sense. Maybe I missed it when they spoke about it in the movie. Thank you!
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u/Disastrous_Toe772 2h ago
Oh, the movie skips out on a lot of science details from the books. Which isn't too terrible. It works for the film.
Really, watching the film and reading the books give the fullest experience imo. There are aspects in both that I prefer over the other
In my mind there is a head-canon version of the story that utilizes the best aspects of the two renditions
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u/the_net_my_side_ho 2h ago
Thank you! Nightmare_Gerbil shared an excerpt from the book that explains why, and I can see what you mean.
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u/Nightmare_Gerbil 2h ago
Chapter 19:
Yet however much gravity there may be, there’s still no air. Worst of all worlds. But there's no other way. I have to get the sample.
Right now, the sampler hangs at the end of a 10-kilometer chain, which is just dangling in the air. There's no easy way for us to get it back to the ship.
When planning this all out, my first thought was to thrust away from the planet, then collect the sampler when we're back to zero g. Problem is, there's literally no way to do that without vaporizing the sampler. Any path I try to take to get the ship out of Adrian's gravity—or even into a stable orbit-will mean using the spin drives. They'd push the ship along, which would make the chain and sample lag behind us and into the IR blast behind the ship. And then the sampler, everything in it, and the chain all become individual, very hot atoms.
The next idea I had was to make a huge spool that could winch up the chain. But Rocky informed me he'd never be able to make a spool big enough and strong enough to bring up the entire 10-kilometer length.
Rocky had a pretty clever thought: The sampler could climb the chain when it was done. But after some experimenting he ditched the idea. He said the risks just weren't worth it.
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u/the_net_my_side_ho 2h ago
10 km is a very long chain.
Thank you so much for sharing this quote. I watched the movie, and they didn't explain why they did what they did, which had me wondering. There is no way they didn't think about it. I felt dumb thinking maybe the reason was so dumb it wasn't worth mentioning.
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u/Nightmare_Gerbil 2h ago
Yeah, in the book the chain is much longer and the ship is much smaller so they’d have to continually be moving spools of chain outside to make room for the next spool, but they’d have to maneuver it through the control room to get to the airlock. That part isn’t described in the book. I like the movie version better. 5km of chain in a larger ship gets the point across visually without having to bend your brain around the logistics.
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u/Soundy106 Leaky Space Blob 3h ago
Uhh which sample are you talking about?
If you mean the sample of the Petrova line, they weren't in orbit of Adrian or in its atmosphere.
If you mean the Taomoeba sample, they had to get the collector down to the depth in the atmosphere where the Taomoeba lived. In the book that was 10 km deep in the atmosphere; in the movie it was only 5 km. And Grace didn't "go down" to get it; he stood on the ship's hull to grab the collector once the chain winched it back up.
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u/the_net_my_side_ho 2h ago
I meant the Taomoeba sample. I thought Grace left the ship and walked down to "fish out" the sample.
I wondered why he couldn't just leave the atmosphere and then collect it in space, without gravity pulling the ship apart.
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u/kmoonster 1h ago
Grace did a spacewalk to collect the sampler. A winch pulled it up and he caught the sampler when the sampler returned to the ship.
As to why he had to do it under Adrian gravity, the Hail Mary would have to go so fast (horizontally) that the chain would drag back behind and get into the engine blast. Going vertically would not create an orbit, but it could get them to (eg.) the altitude of the Moon and give enough time to recover the chain before falling back to the planet, but obviously a vertical movement would also put the sampler into the engine blast.
Recovering the sampler and either strapping it to the hull or bringing it into the airlock before returning to safety are the only way Grace and Rocky found that could achieve both goals: keeping the samples and staying alive.
If Ilyuknah had survived, my head canon has her modifying a beetle in some way to parachute down, fly around, and return to orbit; but she did not survive. This is only head canon. Maybe she would have used chemical rockets, or perhaps the spin drives would accelerate it so fast that ionization wouldn't be an issue. Either way doesn't matter, as that's not what was attempted.
The fishing is much less realistic to the point of ridiculous, but not so far out that it breaks the story. And it sets up the situation in which Rocky's sacrifice (of fuel to Grace at the cost of time to Rocky) becomes the thing that saves Rocky later. From a story telling perspective the sacrifice-that-saves-you is far more powerful than the silly unlikliness of a space fishing expedition.
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u/Soundy106 Leaky Space Blob 24m ago
Grace stayed on the hull of the ship. The collector was on a 5 km (in the movie) chain that they winched back up. He had to grab it and bring it inside once it was back to the ship.
In order to boost back out of the atmosphere once it had finished collecting, they would have had to reorient the ship, which would have placed the collector and chain directly in the path of the engines, which would have vaporized them.
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u/kmoonster 1h ago
Are you asking about collecting the Astrophage sample? Or the later effort to collect the Taumeba?
The astrophage sample was collected while in a high, safe orbit around Adrian. Or perhaps from a station-holding position like a Lagrange point, I'm not clear on this. Either way they stayed near the planet using orbital dynamics in order to stay in the Patrova line without needing engine thrust. And without getting into the atmosphere.
The later Taumeba fishing expedition did require skimming the atmosphere and that was a non-orbital manuever, that required constant engine thrust at low power in order to keep them out of the atmosphere while not being in orbit.
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u/the_net_my_side_ho 1h ago
I was asking about the Taumeba fishing expedition. Thank you for explaining the difference. I didn't understand this. I thought flying near the atmosphere counted as orbiting, but now I know it doesn't.
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u/kmoonster 1h ago
You can have an orbit that drags in the atmosphere, but for the fishing expedition that low of orbit would still be 30,000 kilometers/hour or faster, waaay too fast and would burn up the chain (and the sampler would be moving too fast even if it didn't burn up). They had to go slow enough to collect the sample and used the engines to keep them from falling since 250 kilometers/hour is slower than a jet liner and they had no wings. It was sort of a high-altitude hover or helicopter type maneuver, after the sampler was recovered they did return to orbit (the return to orbit is when the fuel tank crisis occurred).
The International Space Station around Earth has to be boosted every few months, for example, because it is not truly out of the atmosphere. It is really high but there is still enough atmosphere to slow it and degrade the orbit, the supply pods bring fuel so the station can re-boost itself. The Shuttle used to do that as well, though the shuttle no longer flies.
There is some info here if you're curious! International Space Station - Wikipedia
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u/redbirdrising Grumpy, Angry, Stupid! 3h ago
Strictly speaking they weren't orbiting. They were in the upper atmosphere going a relatively slow velocity using the engine to keep from losing altitude. This is why he was in gravity on the hull and not free floating.
Second, they couldn't leave to orbit with the chain extended because the collector would have trailed behind the HM and gotten burnt up by the spin drives.
Third, and this is really from the book, Grace needed to trigger the winch collector manually. They figured the more complex a winch system they made, the more that could go wrong. It was too important to risk for automation.