# Novel idea for space travel (launch track around the moon)

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1. Sep 3, 2015

### udtsith

What if we built an electromagnetic track around the circumference of the moon? We could then accelerate a spacecraft to a very high speed. In theory it would only be limited by the strength of the materials holding the craft to the track and the centripetal acceleration that the craft/people could endure. The energy could come via the sun via a solar sail that would be positioned with it's reflective side face toward the sun. In that scenario you would not even need the track to be an electromagnet. You could simply keep it like a simple rail track. Or if you did do the electromagnetic rail you could simply gather the energy via solar panels. Since there is very little atmosphere around the moon I don't think friction would be much of a concern.

Based upon my calculations for people (tolerate ~20g), radius of the moon is 1,737m, then the velocity that would be achieved would be 5888 m/s...which means that the craft would arrive at mars in 1.2 years. Now that isn't exactly quick but...if we could increase the tolerance for acceleration or used robots the time required would quickly drop. Or if we added an additional propulsion system. The best part is that you could make the craft as large as you want and accelerate it as fast as you want.

Thoughts?

2. Sep 3, 2015

3. Sep 3, 2015

### udtsith

Thank you for the link and reply but the information it contains seems very different from what I am proposing. For example, the wiki article involves a cable and sheath on earth that basically pulls a craft into orbit. My scheme is on the moon and involves basic physics. And from an engineering standpoint seems far more simpler.

4. Sep 3, 2015

### DEvens

Sigh.

https://en.wikipedia.org/wiki/Launch_loop#See_also

5. Sep 3, 2015

### newjerseyrunner

Sounds like a circular railgun, I see no reason why it wouldn't work.
20gs however, would be lethal, with a flight suit, pilots only take about 10, most people pass out around 5.

6. Sep 3, 2015

### udtsith

The closest thing they have is an orbital ring around the earth. Also if you feel the need to patronize then please don't even reply.

7. Sep 3, 2015

### udtsith

Well they would be in near zero g so...9.82 to simulate earths gravity and then throw on another 10g.

8. Sep 3, 2015

### newjerseyrunner

You are mixing terms. 1g is 9.82m/s/s. You mean 20m/s/s, that's actually just 2 gs, which would be a fairly pleasant ride.

9. Sep 3, 2015

### udtsith

oh yea, you are right. Well then that would make the amount of centripetal acceleration they could handle even greater and so the velocity and shorten the time.

10. Sep 3, 2015

### newjerseyrunner

Yes, humans should be able to handles up to 40m/s/s without too much physical discomfort.

One thing to consider though, your rail would have to be able to both repel and attract your ship. When you are first starting out, the ship has weight, so the rail has to repel it to make it float with negligible friction. As the ship got faster, you'd have to turn down the magnets holding it to the track because the ship gets lighter. Then, when the ship hits orbital velocity, it actually will have negative weight and have to be held down to continue to accelerate. Remember that the escape velocity at the surface is higher than the escape velocity higher up.

11. Sep 3, 2015

### DEvens

https://en.wikipedia.org/wiki/Launch_loop#See_also

https://en.wikipedia.org/wiki/Mass_driver
https://en.wikipedia.org/wiki/Non-rocket_spacelaunch
https://en.wikipedia.org/wiki/StarTram

Your idea has been considered. There have been numerous variations considered, both on the Earth and the moon. Several have been tweaked out for use on Mars or Venus. Many of them have been incorporated into SF stories published in national magazines. Some even work both for take-off and landing, though landing can be pretty scary. The materials required, the failure modes, the provision of power, the duty cycle, and the approximate cost per kg all worked out.

12. Sep 3, 2015

### udtsith

I think where my idea is original in that it uses the Moon as the stabilizing platform for the incredible force that would be generated by moving a large craft at high velocity AND that the track is effectively infinite in length. The mass driver concept is just a linear shot from the moon so the need to quickly accelerate on a short track requires alot of power and the acceleration wouldn't be as great. Taking the track all the way around the moon has never been proposed and offers some great advantages such as not needing such a high power. I know there are concepts where they do maglev up the side of the mountain into orbit but my concept would allow a much higher velocity with out needing to have such a high power system.

For example, one of the problems of orientating the ring like a donut to the surface is that the large centrifugal force would cause waves on the ring as the craft moved around it. However, if you took the donut and put it around the moon like a ring around a finger those waves can't be generated as the 1700 Km of track would press into the moon.

13. Sep 3, 2015

### Janus

Staff Emeritus
A couple of points: g-force tolerance is time dependent. The longer the time the force is experienced, the lower the g- force tolerance.

Centripetal acceleration is found by v^2/r = a, so v = sqrt(ar). Thus 4g at at the moon radius of 1737 km (1737000 m) is sqrt(4*9.8*1737000) = ~8252 m/s. The circumference of the moon is 10,913,893 m which takes 22 min to travel at 8252 m/s. 22 min at 4g is likely doable for someone in good health. Of course, this also depends on just how much acceleration your rail system can deliver to the payload. For example, to reach 8252 m/s in one loop around the moon you would need to accelerate at ~1/3 g. So you would start the loop at a one g force and end with a higher one when you reach launch speed. When you start it would be a vector sum of the lateral acceleration and the Moon's gravity. As you speed up, the centrifugal effect will start to cancel out the moon's gravity, and it the force you feel will start to drop until you reach orbital speed, when it will equal the lateral acceleration. Then it will start to build again to the where it equals the vector sum of the difference between moon gravity and centrifugal effect and the lateral acceleration. Since this means that the direction of the felt acceleration changes, passengers would have to ride in a cradle that rotates with the g-force direction.

You can't directly use the final velocity upon leaving the accelerator to get your travel time. A part of that velocity will be used up pulling away from the Moon's gravity, and once you escape that, you still need to escape the rest of the Earth's gravity. On the other hand, the moon is already traveling around the Earth at 1000 m/s second, and if you choose your launch time correctly, you can use this to your advantage. So in the end, you would end up with a net 8767 m/s net velocity with respect to the Earth. (38767 m/s) heliocentric velocity.)

To work out the travel time to Mars, you have to work out what type of heliocentric orbit this translates to. Doing a quick calculation and unless I made a mistake somewhere along the way, I get an answer of around 80 days for the trip time ( for a shortest trip time). This is short trip, however, there is a catch. You will moving pretty damn fast when you get there and at a steep angle compared to Mars' orbital path. So unless you have an engine and are carrying a great deal of fuel so that you can match speeds with Mars, you are going to do a fast flyby.

14. Sep 3, 2015

### TeethWhitener

It's not entirely clear that you've actually done the calculations you think you've done. What do you mean by the acceleration won't be as great? To reach the Moon's escape velocity (~2.3 km/s) only requires applying 1g of acceleration for ~4 minutes (v=gt). You would need ~270km of straight track (x=0.5gt2). Even with 10% efficiency, the power you'd need to accelerate a 1000kg object to 2.3 km/s is ~110MW (P=0.5eff*mv2/t), which could easily be generated by a small nuclear plant. This is true regardless of what your acceleration is. What makes you think that your proposal (an 11000 km loop around the moon) is anywhere near as cost-effective or relieves anywhere near as many engineering snags as a 270 km straight track?

15. Sep 3, 2015

### udtsith

Thank you so much!
I could be completely wrong but it just seemed to me that if you have 270Km on a straight shot versus an infinite circular track and you wanted to send a probe as fast as you can to Pluto e.g. then...you wouldn't be concerned about giving the probe as much power as possible in 270Km versus an infinite circular track where you could apply low power but alot of energy over time.

So for example, you could rely upon solar power versus having to build a nuclear power plant on the moon.

Also, it is interesting to think on what the possible limit to velocity would be if the track were circular around the moon. For example, just take a sputnick type metal ball and launch it into interstellar space. Could a velocity of .1-.5c be achieved? I am guessing that at that speed even the moons little atmosphere might vaporize the probes tether before it were launched.

Last edited: Sep 3, 2015
16. Sep 3, 2015

### TeethWhitener

https://en.wikipedia.org/wiki/Andasol_Solar_Power_Station
Here's a solar plant that generates 150 MW. It seems to me that it would be easier to build this and 270km of track than it would to build a smaller solar plant and 11000km of track.

17. Sep 3, 2015

### udtsith

Okay but your estimate is to simply break the moons escape velocity and...as your velocity increases the track you need is longer to apply the 1g of acceleration. E.g. by the time you reach 2.4Km/s it would take 2.4Km of track to apply 1g of acceleration. But I see your point, and maybe it wouldn't need to be around the entire 1700Km.

18. Sep 3, 2015

### CalcNerd

Have you considered where you are going to get the steel (or other magnetic material) from? If I recall, isn't the moon iron deficient? Even a 270 Km rail is a major undertaking, especially given the resource scarcity of material. And we will probably need to develop much more advanced robotics/robots for the work as people consume much more resources than machines running off of batteries that are recharged from photovoltaics.

19. Sep 3, 2015

### TeethWhitener

What? I have no idea what you're talking about. If you apply 1g of acceleration to a mass initially at rest, after ~4 minutes, the mass will have traveled ~270km and will be moving at ~2300m/s.

[EDIT]: I should be more specific: this is true if you apply 1g of acceleration continuously for 4 minutes.

Last edited: Sep 3, 2015
20. Sep 3, 2015