Factual error: A nuclear explosion couldn't kick start a rocket on its journey home as shown. There's no atmosphere, hence no shockwaves to help propel the ship forwards.
odelphi
24th Sep 2019
Ad Astra (2019)
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Suggested correction: The explosion itself is still a projection of energy that would push the ship. The plan itself is stupid, as it would be impossible to correctly set a trajectory, but the explosion would still push the ship.
The only way the explosion could transfer energy to the ship would be if massive pieces of the Lima slammed into the ship, destroying it.
What the spacecraft needs is some way to acquire momentum from the explosion. The explosion does convert a great deal of nuclear energy in the form of radiation, but not very much useful momentum. This was a major hurdle attacked during Project Orion back in the early 1960s, which was a program to develop an interplanetary spaceship propelled by exploding a series of nuclear bombs near to an aft pusher plate. The solution was to coat the plate's surface with a material which would ablate off the plate. The material would rise in temperature under the intensely hot radiation, with its molecular constituents vibrating violently. At a critical temperature the outermost molecules would attain escape velocity and scatter off the plate aftward. Momentum is conserved, so the aftward momentum of each escaping molecule would be balanced by an equal increase of forward momentum by the spacecraft.
The explosion creates violently expanding gases that apparently were great enough to offer some push to the rocket. Since there is no friction in space to act against the force, theoretically the ship would be pushed at the same speed as the expanding gases.
Sorry but there's no such thing in physics as 'a projection of energy that would push the ship'. Maybe you are thinking of the photoelectric effect, but this is much too small. The only thing from the explosion that would propel the rocket is mass - the Lima ship's vaporised matter which would radiate in all directions, so only a few pounds of gas would hit it - even at a huge velocity, just a little nudge.
24th Sep 2019
Ad Astra (2019)
Character mistake: Brad Pitt has control jets on his space suit - he uses them to accelerate him back towards his ship at the end, but somehow doesn't think to turn himself around and use them to slow down, hence slamming into the ship at great speed. Given the skill he demonstrates every other time in the movie, this only seems to happen for the sake of a dramatic arrival.
Upvote valid corrections to help move entries into the corrections section.
Suggested correction: It is not unfeasible that he used the RPS fuel to accelerate and had none left, since he already wasted a certain amount after his father pulled him away from Lima station.
In space you can't just swing around and change directions because there is no friction or gravity. He would have to have a jet that shoots forward (a retrorocket) or he would have to turn using the jets which would make him go in the opposite direction, not slow him down. From what I saw, there was no retrorocket on his pack.
There were retrorockets in his father's suite, he was flying in space using them. Why there was no such rockets in Roy's suite, wasn't it exactly the same? Helmets were identical, and other details too. He could slow him down.
There are no 'rockets' or 'retro rockets' on an EVA space suit, just thrusters that used in combination and with direction of the nozzles, can make it move any way they want, including turning and yes, slowing down. It's just Newton's Laws.
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