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sinspawn1024 t1_j5wyzal wrote

Reply to comment by notjordansime 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

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?

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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.

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paaaaatrick t1_j5xztog wrote

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

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R3lay0 t1_j5z7t18 wrote

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

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WeDrinkSquirrels t1_j5zc0p8 wrote

You mean like every resupply mission they send up?

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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.

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