# Can Maglev trains ever reach escape velocity?

NASA is planing to build a levitating train system on the Moon.

For Moon, would it be possible to build a large scale system equivalent to maglev trains, to accelerate (for example) a mining cart of ice to reach escape velocity and to get it into orbit or may be all the way to Earth? Since there is no air friction, with Moon’s gravity being quite low and plenty of flat areas there similar some salt deserts on Earth where people go racing.

Alternatively it could be a miniature size for launching small payloads (cubesat size) and spewing them with large or continuous frequency.

• This is currently really two questions - an orbital velocity railway most/all the way around the moon and a magnetic space gun on earth. Suggest editing to focus on the single question about the moon based concept and have a look at space.stackexchange.com/q/9156/26356 and space.stackexchange.com/questions/tagged/high-altitude-launch and decide if you want to ask a separate earth question. Certainly there is no way to run a train extended distances in any meaningful atmosphere. Commented May 25 at 4:57
• That NASA proposal - not plan - is a long way from an electromagnetic launcher. Commented May 25 at 11:25
• Isn't it just a rail gun? Commented May 25 at 12:16
• Also note that the definition of "escape velocity" means it escapes orbit. Launching into orbit would need less velocity (And also a turn once you get to the right height, so... orbit isn't an option) Commented May 28 at 5:11
• @MooingDuck unless your a lunar seismologist, then it's an option - though you're right that that the surface-intersecting Keplerian trajectory still wouldn't be called "orbital". But about direction, it turns out that in a $1/r^2$ force field, the direction doesn't matter. As long as you are energetically unbound ($½ m v^2 > GM/r^2$) you're good to go and the Moon can't hold you. The direction only determines where you end up. cf. vis-viva equation
– uhoh
Commented May 28 at 9:04

What you are proposing is known as a mass driver, and the concept goes back at least to the 1960s. It was discussed by Gerard O'Neill in the 1970's as part of a method to build space colonies, and also mentioned in the 1966 Heinlein novel The Moon is a Harsh Mistress. As the Wikipedia article indicates, they have also been proposed for earth launch, although atmospheric drag does make it very difficult. So, yes, absolutely.

Added later: You could argue the headline question, taken alone, has a different answer than the full question. If you just ask "Can a maglev train reach escape velocity," then the answer is arguably "No, not in a practical way," because engineering something that could serve as a point-to-point passenger maglev train, but that could also reach escape velocity, is probably unrealistic, or at least wasteful.

But, if the question is,

For Moon, would it be possible to build a large scale system equivalent to maglev trains, to accelerate (for example) a mining cart of ice to reach escape velocity and to get it into orbit or may be all the way to Earth?"

Then the answer is "yes, that's a mass driver."

• @uhoh idk, the OP’s proposal sounds an awful lot like a mass driver described by someone who doesn’t know what one is. To your point, though, I’m seeing estimated speeds for maglev trains in vacuum that are roughly equal to lunar escape velocity. Commented May 25 at 7:39
• Thanks, after comparing maglev to mass driver can’t see the difference. Also found this after some googling: forum.nasaspaceflight.com/index.php?topic=58047.0 Commented May 25 at 13:27
• @uhoh The speed at which you are in orbit on the surface is smaller than the escape velocity. You'll need to invert the track (ride upside down) if you want to accelerate to escape velocity; the track will then be above the vehicle and prevent it from, well, escaping... the benefit is that you still have the lunar stationary resources available to accelerate the vehicle. Commented May 26 at 18:02
• Maglev is basically the simple case of mass driver. Low speed, low acceleration and you have gravity to ensure your vehicle rides on two tracks rather than the four you need if you're going to approach escape velocity. It's all that's practical when you need to deal with geography and atmosphere, but without those limits your speed is only limited by how much acceleration you're willing to tolerate. One wrapped around the moon can do anything from sun grazing to solar escape with human-tolerable acceleration. Commented May 26 at 20:50
• Heinlein also gave what is probably the biggest reason why not to build such a mass driver: It would be a devastating weapon system... Commented May 27 at 15:25

Yes, maglev trains / mass drivers can potentially reach escape velocity, but a mechanical centrifugal launcher may be more viable.

Lunar escape velocity at ground level is 2.38 km/s.

Orbital velocity is sqrt(1/2) of that, so 1.68 km/s (but a ballistic trajectory from a ground-based catapult will always intersect with the ground elsewhere, unless an in-flight correction is made.

Spinlaunch are looking to achieve speeds around 4,700 mph (7,500 km/h; 2.1 km/s) in their earth-based centrifugal launcher (a rocket stage is required to complete acceleration.) A lunar centrifugal launcher would have numerous advantages. Besides the lower gravity, there is no need to be concerned about the atmosphere. This in turn would allow for a much larger radius (perhaps a tether that can gradually extend to a kilometre or more) to reduce the acceleration forces. Note that even at 1km radius, a velocity of 2.1 km/s corresponds to a centripetal acceleration of 450 times earth's gravity. At 10 km radius, this reduces to a more reasonable 45 times earth's gravity.

To achieve the same 10 km radius with a track, 10 × 2 × π = 62.8 km of track would have to be laid. While this would give greater control and help reduce some of the materials issues, it would require more investment and would therefore need to be in regular use to be justified.

• There is no need to go in circles. If you are willing to pull 45 g, then a linear track would get you to the same speed in about 5 km. Even if you take twice that to slow down any hardware that should not be launched, that is far less than any circular track.
– mlk
Commented May 27 at 8:31
• @mlk that checks out but the energy transfer rate is insane. Commented May 27 at 8:51
• True, but as an engineering challenge, it is probably on the same level as spinning around a 10km tether at orbital velocity. In practice though, using a longer track might be simpler, as lower acceleration also allows for less rugged payloads.
– mlk
Commented May 27 at 9:07
• @mlk A 10km tether at 2.1km/s has rotational speed 2rpm. That should be no problem. Cables approaching 10km are used for tethered balloons & suspension bridges. A single-diameter cable 10km long at 45g is achievable but tapered cable would be more efficient. Challenge is in cable management (paying out, winding in, vibration control.) Maglev requires very high velocity in close proximity to track. In my opinion, centrifugal tether launch based on existing tech is easier to achieve but a mass driver can be preferred if used regularly. It requires either long track or hefty energy infrastructure Commented May 27 at 9:42
• Wind Turbine balloon tethers are ~200 g/m, and you'll need something way stronger than that for the centrifugal forces to handle 1.68km/s laterally. Commented May 28 at 17:55