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A nitrogen cold jet thruster system called SAFER (Simplified Aid For EVA Rescue) is part of the US EVA suit ensemble. If a crewperson gets loose they can fly back using SAFER. (Image source) SAFER is not used in the normal course of an EVA. There is no other propulsive system on a US EVA suit. SAFER was deemed necessary for the ISS era because either ...


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Although this has indeed "worked to bits" on the Physics and other SE sites it's worth looking at, for the sake of Space Exploration, the interesting history behind the analysis of the falling cat. For the fully rigorous description of the cat's righting reflex - perfectly in keeping with conservation of angular momentum - only came about because it was ...


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This is a great question. I wanted to provide an answer which cited some specific, real-world situations. Currently the only people in space are those aboard the International Space Station. If anyone could potentially get into a scenario as you describe in your question, it would be them. Currently, on spacewalks, a huge number of safety procedures are ...


27

This video published on YouTube on Zero-G: "Movement in Microgravity: Skylab to Space Shuttle" 1988 NASA Weightlessness Footage, starting at 2:10 into it, shows a Skylab astronaut doing a front roll and a spiral roll in the Skylab Orbital Workshop without touching anything to push against to change his orientation. And the same video from 5:45 to 6:00 shows ...


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Once the astronaut & space vehicle part ways, they're on two separate orbits. If the force that separated them is impulsive (instantaneous force in a single direction - as in pushing off the spacecraft and forgetting your tether) those orbits intersect at the point of departure. If you can wait 1 rev (about 90 minutes in LEO) you will cross the ...


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Problem with what you propose, a kind of harpoon with probably a soft-tipped and magnetic head tethered projectile so it doesn't damage / penetrate the station's hull yet still holds onto it once it would reach it, is that the shooting of a kinetic projectile in one direction would propel you with equal force in the opposite direction since there's nothing ...


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They didn't have an application that couldn't be done better by maneuvering the shuttle itself and using the shuttle arm and tethered astronauts (sometimes with astronauts serving as the end effector on the arm). There was little to no benefit to the MMU, so even a small risk outweighs a non-existent benefit. Also the things are big and heavy. In space, ...


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As you said, action = reaction, Newton's third law. In a rocket engine, a fuel is burned, creating gas that expands. Now this gas wants to expand equally in all directions. In the 'front' and 'side' directions, the gas encounters the rocket nozzle and pushes against it. In the 'rear' direction, the gas goes out the end of the nozzle and into the vacuum of ...


13

Unfortunately steam rockets would not be practical because they're not very efficient. I don't know how much you know about rocket propulsion so I'll begin with a discussion of one of the most important metrics: exhaust velocity, the speed of the gas coming out of the engine's nozzle. The higher that speed, generally the more efficient the engine. There ...


10

None of them were particularly far. The first flight shows a distance of 325 feet (99 m). The best record I can find for STS-41-C says the shuttle came within 200 feet (63 m) of the satellite, and the last was done via the MMU. and the best guess I have from STS-51-A is 35 feet. The tests of SAFER on STS-64 was just around the robotic arm, so I'm assuming ...


7

To my knowledge, there isn't anything for the gas to push against. That is not how a reaction engine - a family of which rockets and thrusters are a part - works. In short: you got it backwards. The gas that is expelled is not pushing against a medium (such as the atmosphere)... the gas is pushing against the thruster. Or - to be accurate - they are ...


5

If your loose astronaut has no thruster capability of her own, all may not be lost if she was operating from a capable spacecraft with a crew member aboard. Any of Gemini, Apollo, or the US space shuttle were able to make small translational maneuvers under pilot control. At tethered distances the spacewalker and pilot should be able to see each other, and ...


4

You're right, losing a spacewalk tether by itself isn't an unrecoverable situation. In fact, on a normal spacewalk, anytime the tether isn't taut, it's effectively the same as not having it. With a bit of maneuvering, it's certainly possible to recover an extra-vehicular object, without having to reel it in by tether. The problem, at least in movies, is ...


3

While picking up ice and putting it in one's space suit support system would come in handy as a way to keep a space suit cool (Will suits worn on Mars lose kilograms of “expendable water” each time they are used?) its use as a propellant is pretty limited. To hover above the surface the force is say 120 kg x 9.8 m/s2 x 1/6 or about 400 Newtons. You get that ...


3

The short answer is "conservation of momentum" (as Bob Stein answers), but the question belies a fundamental misconception. A propeller, helicopter rotor, or jet engine derives its thrust not from the bulk atmosphere "pushing back" but because it has accelerated some quantity of air in some direction; that air has mass, so accelerating it requires force (F =...


2

By conservation of the center of momentum. The center of mass of a jetpack plus it's propellant stays on a constant course (along an inertial frame of reference, e.g. the ISS orbit). This remains true whether the propellant is inside or outside the jetpack. By moving a mass of propellant one way, the jet-pack-wearing astronaut moves the other way, ...


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For launch, no. For MMU in orbit, sure. There have been designs for lunar ascent vehicles that use steam, but they require a nuclear power plant to get a decent TWR (thrust to weight ratio). A backpack simply wouldn't have the energy to heat the water hot enough with any technology we know of. But in orbit it is different. I can imagine a backpack full of ...


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For high thrust, you have to make a lot of steam in a hurry. Electrical heating is impractical. Chemical heating works: you burn hydrogen to make the steam, as the Space Shuttle main engines did. A really hot, high-powered nuclear reactor might work. A bunch of people are working on steam for small, low thrust systems. For low thrust, electricity is a good ...


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On a more positive note than the other answers, what you could do is make use of the relatively plentiful solar power to melt, then use electrolysis to provide you with hydrogen and oxygen, which is well known and well understood as a rocket fuel. The biggest fault with that idea is that the majority of your solar power would be used up not in the ...


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