3
$\begingroup$

So, I designed a mass driver on Mt. Everest.

The mass driver is powered by "PERMANENT" magnet rings with a strength of 5 teslas each (the black lines in the tube). The mass driver then climbs up Mt. Everest, extending 30km into the atmosphere, where air is extremely thin. A large low-pressure hydrogen balloon is used to lift the heavy tube, so as to prevent it from sinking to the ground. The tube is about 500km long, so as to prevent instant crushing accelerational forces

Would the mass driver be able to propel machine payloads or even passenger? If no, then why?

Do give me some opinions on this idea.enter image description here

$\endgroup$
2

11 Answers 11

40
$\begingroup$
  • First big NO NO: a gas balloon will do nothing to oppose winds and air currents. You are basically letting 22 km of pipe free to wiggle in the wind, with the balloon going after it or even pulling it. Expect catastrophic failure very soon.

  • Second big NO NO: have you ever seen a water hose letting out water with its end unconstrained? Have you seen how it shakes around? This is what is going to happen here, again because the balloon offers no anchor, it will just move following the resulting of all the forces acting on it.

$\endgroup$
4
  • 25
    $\begingroup$ That balloon is going to have to be immense to lift 30 km of pipe. Bigger balloon = more surface area for wind to love $\endgroup$
    – Willk
    Aug 17 at 13:41
  • 22
    $\begingroup$ On the bright side, you might be able to pivot that project into the biggest used-car-lot-flappy-air-man-thing the world has ever seen. $\endgroup$ Aug 18 at 11:35
  • $\begingroup$ Plus I'm not sure the balloon would provide much useful lift. Kinda like a ship floating in water, a balloon is displacing air. It stops rising when it reaches equilibrium between its displacement and its own weight (assuming it doesn't burst first). At 120,000 feet a hydrogen balloon has little to no lift. I doubt it has "a lot" of lift at 30,000 feet, even. (The Hindenberg stayed under 1000 feet but I think it was more due to bag pressure limits than lift capacity.) $\endgroup$
    – JamieB
    Aug 18 at 14:12
  • 6
    $\begingroup$ @AmiralPatate Wacky waving arm flailing countryside destroying inflatable tube man! $\endgroup$ Aug 18 at 22:36
28
$\begingroup$
  • Thirdly: No, not at all. You need a wave of modulated magnetic field pushing the vehicle. Permanent magnets would freeze it to the launchpad.
$\endgroup$
4
  • 1
    $\begingroup$ A coil-gun style launcher would use changing magnetic field. A rail-gun style launcher would be fine with a static field. $\endgroup$
    – codeMonkey
    Aug 18 at 16:22
  • 7
    $\begingroup$ @codeMonkey that requires driving a very high electrical current through the projectile, though, and clearly isn't compatible with the described "magnet rings". You could also put electromagnets on the projectile to alternately push and pull on the magnet rings, but that's a quite backwards way of designing things, and it'd be utterly impractical to put the power supply needed on the projectile. $\endgroup$ Aug 18 at 17:22
  • $\begingroup$ @codeMonkey A Railgun doesn't use any magnets at all. The only field it needs is the one generated by the current traveling through the rails and payload. $\endgroup$ Aug 20 at 15:47
  • $\begingroup$ @HiddenWindshield a railgun doesn't need magnets, but it can use them. A real launch-assist mass driver would have more in common with a coilgun than a railgun, though. $\endgroup$ Aug 21 at 5:08
21
$\begingroup$

You'd be very much ahead to choose a somewhat lower mountain that's on or very close to the equator, rather than choosing the highest mountain many hundreds of kilometers off the equator.

First, the closer you are to the equator the more of your orbital velocity you already have just standing on the ground. At the equator, this comes to about half a kilometer per second (out of a total of around 8 km/s minimum orbital velocity requirement) -- very significant.

Second, most places you'd want to go once in orbit are easier to get to if you're already in a low inclination orbit -- the Earth's axial tilt is already more inclination than you want, but you don't have launch windows of minutes per day (or worse) if you launch into equatorial orbit vs. launching at higher inclination (Florida is bad enough, Kazakhstan is terrible, and Everest is a little further north than Canaveral).

Chimborazo, in Ecuador, is a far better choice. Not only is it actually further from Earth's center than Everest (due to Earth's equatorial bulge), it's practically on the equator, and it doesn't stand among dozens of other similarly high peaks, so it has a much clearer run-up for your maglev launcher.

Beyond that, another answer has indicated why the long, balloon-supported extension to the vacuum tunnel is a bad idea; better to simply have a series of timed doors to minimize air entry into the evacuated tunnel while the vehicle passes, and end the tunnel at whatever point it's no longer practical to support it on the mountain.

Also, don't forget your launched vehicle will still need some amount of rocket propulsion and active guidance, because even if launched at greater than orbital velocity, its orbit will still intersect Earth's surface (never mind significant atmosphere); it will need to have its perigee raised before it completes a single orbit else it will come back down like a Falcon 9 with a second stage ignition failure.

This also solves the problem of impacting air (even at 30 km altitude, never mind the 6 km actual height of Chimborazo) at 8 km/s -- you just don't. It's easy enough to toss your payload above the atmosphere, and only requires a couple kilometers per second instead of the whole 8 km/s. Once near apogee (over the mid-Atlantic, give or take) the "second stage" fires to finish the job of putting the payload into orbit. You've save the cost of a booster -- but watch out, SpaceX didn't have to build hundreds of kilometers or evacuated tunnel and thousands of superconducting magnet rings to do the same...

As noted in comments, you'll need to delete the upward curve near the end of the tunnel; it would produce more G load than the launch itself, and at right angles (one direction is far easier to deal with than two). If you launch at "only" 2 km/s, however, you need a lot less tunnel -- at 3 G, it would be just over a minute of acceleration, and require less than 70 km of tunnel; this could be virtually straight from near Guayaquil to the mountain peak (though that would be one heck of a trestle, even if the entry port was quite deep underground).

$\endgroup$
10
  • 5
    $\begingroup$ Also, a ~500 km long straight line ending in a ~5 km radius bend is no better in terms of peak accelerations than a 5 km radius circle. You can't stretch most of your accelerator out in a straight line to reduce accelerations, but make it curve at the end. $\endgroup$ Aug 17 at 15:17
  • 1
    $\begingroup$ "but watch out, SpaceX didn't have to build hundreds of kilometers or evacuated tunnel and thousands of superconducting magnet rings to do the same...": and you'll need to surround your mountain with a fan of mass drivers to access all the orbital inclinations that can be reached with a simple launch pad. $\endgroup$ Aug 17 at 15:20
  • 1
    $\begingroup$ @ChristopherJamesHuff No, because you're doing most of the orbital velocity with the "second stage" above the atmosphere to keep from hitting air at 8 km/s. Also, since you're only doing 1/4 the velocity, you can make the tunnel much shorter, and virtually straight, and keep things down to a few G. $\endgroup$
    – Zeiss Ikon
    Aug 17 at 15:43
  • 1
    $\begingroup$ My comment was specifically about the original proposal of stretching the mass driver out to 500 km to keep accelerations down, and then putting a bend at the end...such a feature defeats the purpose of stretching the rest of the accelerator out straight. However, even a 2 km/s mass driver needs to be very long: at 3 g, 68 km. It also still has to be essentially straight: at 2 km/s, even a curve with a radius of 100 km will exert 4 g without any increase to velocity. Realistically, you're only doing this with a very shallow path out through the atmosphere, with a lot of heating and losses. $\endgroup$ Aug 17 at 16:24
  • 1
    $\begingroup$ "Second, most places you'd want to go once in orbit are easier to get to if you're already in a low inclination orbit" This paragraph is incorrect Launching from low latitude locations allows reaching more orbits. But not because changing inclination after reaching orbit is easy - it's not - but because you pay a large performance penalty to launch to inclinations lower than your current latitude. Going higher is easy, it just requires launching to anything other than directly due east. $\endgroup$ Aug 18 at 20:17
11
$\begingroup$

Additional showstopper problems:

  1. Mt. Everest is surrounded by other really tall mountains and deep ravines, not a flat plain, all of them made out of an assortment of metamorphic rock, so that underground tunnel is going to be really hard to dig.
  2. Once you've dug it, you have to contend with the fact that the Himalayas are an earthquake zone.
  3. The atmosphere above the Himalayas is incredibly windy, so much so that airplanes won't regularly fly over them. So your extended tunnel would blow away before you could even get it assembled.
  4. Also, Mt. Everest is holy to the Tibetans, so you'd be fighting a campaign to shut the project down by the Dalai Lama. You do not want to do this.
$\endgroup$
4
  • 3
    $\begingroup$ Planes avoid the Himalayas because a standard airplane can't legally fly over them. You need special oxygen systems to be allowed to go there. The thing is the standard passenger oxygen system is only built to keep you going while the pilot dives to a safe altitude. In the Himalayas you encounter terrain before reaching a safe altitude, you need a lot more oxygen on board so you can fly off the mountains before descending. $\endgroup$ Aug 19 at 0:13
  • $\begingroup$ They also regularly have 150kph winds around the peaks. This is why rescue copters often can't get Everest climbers out. $\endgroup$
    – FuzzyChef
    Aug 19 at 16:59
  • 2
    $\begingroup$ 150kph winds won't stop airplanes. The problem is oxygen--there are a few specially modified planes that do fly over the Himalayas for sightseeing purposes. $\endgroup$ Aug 19 at 17:51
  • $\begingroup$ Regardless, the OP is not gonna be able to float a tube on balloons. $\endgroup$
    – FuzzyChef
    Aug 19 at 21:01
8
$\begingroup$

So is the tube evacuated in some way? Air pressure at 30 km up is very low but air will still get into the tube and will fill it up. If it is evacuated then there would need to be some form of barrier on the end of the tube to stop the air getting in. Any such barrier would be punctured by the projectile leaving the end of the gun and at that point the orbital velocity projectile would hit the air outside. At such extreme velocity even the very low pressure air at 30 km up would be like hitting a brick wall. The projectile would do reentry in reverse and would lose so much energy that even if it didn't burn up completely it would never reach orbit.

Everest has 100mph+ winds and any kind of crazy giant balloon and 30km tube will be blown to destruction very quickly.

I'm not sure that the Nepalese or the Chinese Governments would be very keen either as debris from the wreckage of the tube and projectile might fall on their territory

$\endgroup$
5
$\begingroup$

This is something that's been explored already, known as a rocket sled launch. You don't need to extend the tip of the launcher up so that it's unsupported by your mountain, you just need to make the sled go faster - and that's a lot easier when you can provide power from the ground.

As for your propulsion method, I'd suggest looking at how maglevs work - they don't use rings of fixed magnets like that. I think the design you're using is somewhat inspired by a coil gun mixed with a maglev, in a way that won't do much. The primary difference is that a coil gun uses electromagnets that turn on and off in sequence, kind of like a magnetic bucket brigade; with fixed magnets, it's like a person in the bucket brigade refuses to hand the bucket off to the next person.

$\endgroup$
3
$\begingroup$

Marshall T. Savage's inspirational book The Millennial Project: Colonizing the Galaxy in Eight Easy Steps goes into great detail about this in its BIFROST chapter, which describes such a space launch tube using Mount Kilimanjaro as its base. One drawback that he glosses over is that the cargo is required to undergo an acceleration of 225g for two seconds mid-launch, which strikes me as too much for human passengers to survive.

This book was written in 1992, but you should definitely read it -- as others have pointed out, your proposal is completely unrealistic, whereas BIFROST is simply wildly optimistic. It seems to be available as a free PDF download, but I haven't tried that, as I don't know if it's legitimate.

$\endgroup$
2
$\begingroup$

The biggest problem with reaching orbit, and the one where most of the energy of the launch rockets go, isn't with the height, but with SPEED.

You need to go freaking fast to stay in orbit.

You need to so fast you are falling sideways instead of down. That's why astronauts float in the ISS, by the way.

Even if every other problem pointed in every other answer is solved, a maglev tube won't give its payload the speed necessary to stay in orbit.

$\endgroup$
1
  • 1
    $\begingroup$ I do agree on speed, but you can reach low orbit with a near-vertical ejection, a small burn, a fair chunk of time and a heat shield. Your initial launch takes you out to near the edge of the Hill Sphere, at apoapsis you burn (tiny--and I suspect you could use Earth's rotation to do it, no burn needed) to raise your periapsis to the outer fringes of the atmosphere. Drop your apoapsis with gentle aerobrakes, then a final burn to raise your periapsis when your apoapsis has dropped enough. $\endgroup$ Aug 19 at 0:21
1
$\begingroup$

This design presents several challenges. Some miraculous engineering could solve many of them. Simply evacuating the air from a 500km long 6km diameter tube will require enough power for a small city. Structurally stabilizing a 12km diameter balloon so that it takes on a spherical shape (rather than the natural inverted teardrop) will require discovery of previously unknown materials to manage the tension involved. There are also the logistical challenges of bringing resources to such a remote and sparsely populated location. Oh and weather, some of the worst on the planet. All of which I do believe talented, determined, and inspired engineers could overcome.

What I don't believe is that Nepali officials would ever zone you for this. They have a tourist site to protect.

$\endgroup$
2
  • $\begingroup$ 12 km diameter balloon? Who says that? No-one does. So, no wonder materials are needed. But congrats on the Nepali officials bit. You're the first to remark something like that. $\endgroup$ Aug 21 at 3:25
  • $\begingroup$ Never mind the Nepalis, what does the Chinese Communist Party say? $\endgroup$ Aug 21 at 9:35
1
$\begingroup$

Eh, you can stabilize the structure by turning it into a active structure. https://en.wikipedia.org/wiki/Active_structure Still gets you into a sort of trouble though. Atmosphere provides tremendous resistance to the type of acceleration you want to go. So it needs to part ways.

Lucky you we are starting to have that technology. What you need is a vacumed tube, a laser lightning rod and some pretty powerfull capacitors. The laser lightning rod, produces a plasma channel upwards, thorugh wich your lightning surges, producing the same vacum tunnel that claps when thunder strikes.

And through all that comotion, your capsule races spacewards. Only problem left is the acceleration speed up, which has to be linear < 3g to be survivable for normal humans, with no sudden breaks or tumbles.

We need volunteers.

$\endgroup$
1
  • $\begingroup$ Eeeeh NO. Your first error is that there's NO way to make a plasma tunnel like that. It requires 8 MWH for 2 seconds to make just a 2 square meter plasma dóór, so a tunnel? And where your incompetence really shows is with the human-acceptable acceleration. The maximum is more around TEN G's, not 3 G's. Sure, more is unhealthier, but especially young and well trained astronauts can withstand more G's than 3. Try again. And this time, with better spelling, if only to demonstrate to us that you've at least got that basic level of competence. And yes, you HAVE TO do that. Don't ask why. $\endgroup$ Aug 21 at 3:23
0
$\begingroup$

Yes, I see an issue that hasn't been explicitly addressed in the previous 10 answers:

The environmental impact of building the tunnel would be enormous, as would sucking it vacuum be, every time there is a launch. Human engineer have never-ever built a 500 km anything, let alone a vacuum tunnel, let alone one that goes STRAIGHT for the entire length, and surely not a vacuum one. The CO2 foot print might be totally offsetting the footprint of rockets.

$\endgroup$
2
  • $\begingroup$ Human engineer have never-ever built a 500 km anything? Are you sure? Because roads, highways and railways longer than 500 km have been built for quite some time. $\endgroup$
    – L.Dutch
    Aug 21 at 4:39
  • $\begingroup$ Roads& railways AREN'T one thing, 500 km long, in the sense which is meant here and you know it. Or, you should. They're constructed out of multiple things. The parts differ. Also, we can't even build a road that is straight for longer than, say, 20 km, on a horizontal plain (the left-right sense) let alone build a 500 km road that is straight in the up-down sense, since it has to follow the curvature of Earth. Then there's the vacuum problem. Even in a lab, vacuums aren't 100% vacuum, and there we DO have vacuum chambers built from one piece. So, barring major breakthroughs...NUH-UH $\endgroup$ Sep 9 at 11:05

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .