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An alternative I somehow never hear discussed in these threads is railguns. How practical is using railguns for launch compared to nuclear thermal propulsion a
by pmoriarty 6y ago
An alternative I somehow never hear discussed in these threads is railguns.
How practical is using railguns for launch compared to nuclear thermal propulsion and the other alternatives discussed here?
At the very least, it seems to be much safer than something that risks nuclear fallout.
- detaro 6y agoAll gun-style launches have the problem that they have to do the entire acceleration in a very short amount of time, which means very high g-forces. Also happens at the ground, so needs even more speed to compensate for loss in the atmosphere. For small & robust payloads it might be an option, but for large satellites? E.g. Gerald Bull did high-atmosphere studies using payloads fired from converted artillery guns in the 60s. Not sure if railguns in particular add much over chemical guns that justifies the complexity.
- pmoriarty 6y agoI have read of very long railgun designs (on the order of many kilometers), where the acceleration should be more gradual.
- magicalhippo 6y agoAka a very fast maglev train.
- hinkley 6y agoI knew a futurist who proposed using a railgun on Kilimanjaro as stage 1 of a rocket launch system. A lot of fuel is burned just trying to shove a lot of fuel through the lower atmosphere. But as you say, a human-rated railgun has a much lower acceleration. And there's the problem of what happens when you hit the atmosphere at the end of the gun...
- sparker72678 6y agoRail guns have a lot of problems for orbital insertion from an atmosphere: 1. Storing the energy to accelerate the payload. 2. Not accelerating the payload so quickly that it breaks apart. 3. Thermal heating from atmospheric drag. 4. The energy required to overcome atmospheric drag itself. 5. Strength/size of materials to build the sled and contain a payload with that much momentum. My understanding is that 3 & 4 on this list tend to make rail guns a non-starter on earth.
- pmoriarty 6y agoWhy are 3 & 4 different more challenging for railguns than other means of propulsion?
- rbanffy 6y agoOn a railgun you'll have to pass orbital speed by the end of the rail, because, from that point on, you will only lose speed to the atmosphere and you have most of it still above the end of the rail. Rockets, OTOH, go up vertical for most of the atmosphere and then get horizontal in order to get to orbital speed, preferably where there is little or no atmosphere. You'll also need to carry some form of propulsion to circularize your orbit, unless you are aiming for escape velocity, in which case your speed at the end of the rail will have to be much higher. Whatever engine you have will need to survive the acceleration.
- hinkley 6y ago> Rockets, OTOH, go up vertical for most of the atmosphere and then get horizontal in order to get to orbital speed, preferably where there is little or no atmosphere. And yet most launch systems have to throttle down the engines during the transition between the two, because the atmosphere is still just a bit too thick to safely plow through it at full tilt.
- black6 6y agoMass Drivers Cost Way Too Much (https://settlement.arc.nasa.gov/Nowicki/SPBI1SI.HTM https://settlement.arc.nasa.gov/Nowicki/SPBI1SI.HTM)
- nickik 6y agoOn the moon, railguns are perfect. On Mars Space Elevators are prefect. On earth rockets are prefect.