Viewing a single comment thread. View all comments

sinspawn1024 t1_j5wep8o wrote

Reply to comment by electric_ionland in Why do sample return missions such as OSIRIS-REx use their own reentry vehicles instead of just going to the space station for pickup and return with ISS equipment? by PromptCritical725

also, don't forget that if something fails to work on slow-down, you have an 11.5 km/s projectile heading straight for the ISS... Full of astronauts...

50

notjordansime t1_j5wtq6o wrote

If it didn't slow down at exactly the correct rate, it'd more likely miss than anything

57

FolkSong t1_j5x2jme wrote

Yeah, the risk scenario would probably be more like everything goes perfectly until the last second and then it explodes.

11

sinspawn1024 t1_j5wyzal wrote

Even if the probability of collision was very low, do you think Congress will fund a NASA mission where there was a small chance the craft might smash the International Space Station, all its active experiments, and the astronauts of multiple countries into the Pacific Ocean for all the world to see?

−3

FriendlyDespot t1_j5x8bme wrote

The risk would be substantially lower than any number of other risks that are accepted daily for the ISS mission. With the maneuvers required to match an orbit, any failure would put the intercepting vehicle somewhere other than where the ISS is.

Consider that the scenario you're describing is a risk that's faced every single time a crew or supply mission is launched to the station.

22

paaaaatrick t1_j5xztog wrote

You are overestimating what “very low” looks like for something like this

14

R3lay0 t1_j5z7t18 wrote

The risk of it crashing into the ISS is just as high when just going directly into the atmosphere

3

WeDrinkSquirrels t1_j5zc0p8 wrote

You mean like every resupply mission they send up?

2

sinspawn1024 t1_j6kpdgy wrote

Resupply missions are moving up earth's gravity well. If an engine malfunctions, the craft will lose velocity and altitude due to Earth's gravity. Return missions are falling into Earth's gravity well, so engine malfunction results in continued acceleration. Also, retropropulsion is fundamentally unstable (the force balance is the same as balancing a ruler vertically on your finger), which means that if a system loses attitude control, the craft will much more likely enter a tumbling condition, which if not arrested, will dramatically widen the cone of possible collision.

1

lethal_rads t1_j5x2p6x wrote

It wouldn’t go straight at the iss. It’d have to go into a different orbit first, and then do the standard approach for capture/docking.

11

LordOverThis t1_j5wz0uy wrote

It’d be pretty unlikely to collide with the ISS, since it’s already like trying to shoot a bullet with a smaller bullet on a completely different trajectory. Just guesstimating that it’s probably a margin of error of like a milliarcsecond between “intercepted successfully” and “it flew by so far away it couldn’t be seen”, which would put the difference between “intercepted successfully” and “everyone aboard was killed” at even smaller.

8