The Slingatron: Building a Railroad to Space | Hacker News Reader

The Slingatron: Building a Railroad to Space

kickstarter.com

114 pointsgurvinder76 comments

It's an interesting idea to be sure. And it's definitely one that seems kinda crazy, which probably means it could work. But there's one crucial detail missing: calculations on the centripedal/centrifugal force necessary to continue acceleration and/or direct the payload from horizontal to partially/completely vertical.

http://en.wikipedia.org/wiki/Centrifugal_force

a = v^2/r

so let's go with 1km/sec and a diameter of 5m. a = 1,000 x 1,000 / 2.5 = 400,000 m/s^2 or roughly 40,000 g

Now let's assume that it's a 1/4lb weight as described or 0.1kg.

F = m x a = 0.1 x 400,000 = 40,000 newtons.

Next let's assume that the piece of metal is steel and roughly cubic. It's density is around 8g/cm^3 (http://hypertextbook.com/facts/2004/KarenSutherland.shtml).

Mass = density x volume => volume = mass / density = 100g / 8g/cm^3 = 12cm^3

cube root(12) ~= 2.3 so we've got a cube with faces around 2.3cm on a side.

They've said that they're going to encase it in plastic so let's neglect the strength of the plastic and call it 2x the size of the cube. That brings this to 5cm x 5cm.

Now let's translate that into pressure.

P = F / a = 40,000 / (.05 x .05) = 16 MPa

The tensile yield strength for a regular, boring steel (A36) is 250MPa and the ultimate tensile strength (the max it can hold prior to breaking but after deforming) is 400MPa so this is fine for now.

http://en.wikipedia.org/wiki/Ultimate_tensile_strength

At 2km/sec you get 64MPa needed and at 7km/sec you need 784MPa all of which are within the realm of possible but rapidly heading towards the limits of material strength.

The 784MPa number would go down if you made the diameter bigger, too.

Ultimately they aren't building a thing which will disintegrate the slug (my initial thought) but it's going to have to be extremely well engineered and precisely made for balance in order to ensure that it doesn't tear itself apart. The technical combination of a steel rolling mill and a swiss watch. And due to balance issues definitely harder from a technical perspective than even the really tough portions of a rocket.

EDIT: didn't realize that "*" did formatting so I fixed it.

EDIT2: Screwed up on the calcs, assumed 10,000m/sec instead of 1,000/msec. Fixing those.

Also, if I'm reading Wikipedia right, delta v to LEO is 10km/sec, and that's not counting the insane atmospheric drag on something travelling that speed at sea level. Good luck.

So assume 1000 meters in diameter and 15km/sec for giggles.

a = v^2 / r = 15,000 x 15,000 / 500 = 450,000 m/sec^2 or 45,000g. It's on the same order of magnitude as the previous calcs.

That's obviously also a big engineering challenge because it's freaking HUGE, especially for the precision required.

The really great thing about going super-super fast is that at 15km/sec you're in space in ~10 seconds. Obviously you're going to start scrubbing speed really fast since drag is proportional to velocity squared. But you can evacuate the whole launch assembly and put some kind of an explosively opened door at the exit point and maintain your speed up until the last second.

The amount of drag during the acceleration phase is going to be inconsequential compared to tearing through the entire atmosphere at an angle.

what if you launched two vehiucles, but the first vehicle is more like a bullet that disintegrates and causes a wake in front for the second vehicle to pass thru with less drag?

That still involves sending the first at the requisite speed, and any drafting you might get is limited at best. It'd also leave a highly unstable wake trail, as any object ripping through the air at 7-8km/s is going to tear things up.

As soon as the first one hits the air it starts to slow down. The second one, as it's hauling ass through the wake, doesn't slow down. The difference in speeds gets very big, very quickly. As such the second one, the payload, would find itself smashing into the first one in short order.

Since this thing can launch stuff continously maybe you could lunch few hundreds punchers to push air aside before the actual payload.

It doesn't matter how many you send. If your scenario relies on the fact that the last in line must be the fastest of the group, it's always going to run in to the object directly in front of it.

I was imagining air behaving like water. If you send first projectile it'll slow down but move some water to the sides. Second will slow down less so it'll catch up with the first one but it will also push some water to the sides. Third also will catch up with the previous ones but each subsequent one will get farther as it travels through space punched out by previous ones.

I don't think it's practical in any manner but I think such brute-forcing stream of projectiles out of atmosphere by literally punching hole in it might be nice to look at.

Since it's such a crazy idea, why not build a gigantic dirigible to take it up to high altitude? No problem, right?

I love it!

Because what matters for getting into space / orbit is velocity to achieve orbit. An object without that velocity will simply fall down to earth instead of orbiting.

https://en.wikipedia.org/wiki/Orbit

I believe his suggestion is to use the dirigible to lift the Slingatron into the high atmosphere where the tremendous atmospheric drag will be substantially reduced, thus making a crazy idea slightly less crazy and at the same time, more crazy.

All I can say is I love the kind of crazy going on in this thread and all of you should buy kerbal space program.

Newton's third law gets in the way of that proposal.

When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body.

If you plan to generate acceleration using mechanical force like the reference design, you'd need a massive counterweight. An equal and opposite energy would be transferred to the counterweight, so you need a lot of mass, which would require an even more massive dirigible. You also need somewhere to dissipate that energy. In the reference design, the Earth is used as the counterweight.

Alternatively, you could generate the circular motion using something like a rocket engine, in which case you might as well just use a rocket for linear acceleration and ditch the gyration mechanism.

You would, i assume, build the real thing on an equatorial mountain.

In the video, they address that you would still need a rocket both to circularize your orbit, and possibly recover kinetic energy lost in the atmosphere.

This is so funny, I was just watching "Modern Marvels - Weird Weapons of WWII (The Axis)". Turns out, a similar approach was discussed by Werner von Braun (the father of modern rocket science, basically the most important guy other than Goddard in that whole field) to create a "space plane" with the capability of quickly dropping a (radioactive, but not atomic) bomb on a target anywhere in the world, but more specifically major US cities. One major difference was that the track to launch the space plane was straight, and not curved. Given it was curved, would they have still been able to launch the lightweight space plane with just enough fuel it needs to get up to LEO, or would they still have run into the issue that they can't get the plane to go fast enough and point upward enough to break the atmosphere?

Source: http://youtu.be/EHZC9Hab05s?t=2m26s

In the book "The Moon is a Harsh Mistress" (1966), an electromagnetic catapult is used to deliver goods from the Moon to Earth. It is similar to what you described -- just a really long tube (or rail) at the highest elevation possible.

my bet is that the next important guy in this field - Musk - will build Hyperloop v2.0 as a launch system (the Hyperloop 1.0 supposedly being a supersonic electromagnetically driven mini-Concorde in a tunnel seems like a nice prototype)

"rapidly heading towards the limits of material strength"

indeed. tho, we should also note that we are looking at a weakest link thing. can that one bolt sustain that much pressure? or maybe that one weld? or any of the concrete parts that attach to the earth itself?

shrug

m3mnoch.

The first thing that struck me was that curved ramp at the end of the track. So, that curve is going to deflect masses going at 7km/s. Really. (And this thing is 100m-1km in diameter and built to the tolerances of a watch...)

1) how about carbon fiber as material? 2) what about internal friction during acceleration?

It could use quantum locking to keep payload on track. No friction and some people say that the locking effect is pretty strong.

The thing with the tightly curved track idea is it introduces many difficult problem while solving only a few less pressing problems - the problem I can think of would getting a long track of land and having to around that long track. But there's the centrifugal force, there's it's effect on any delicate machinery inside the capsule and there's the potential for electromagnetic weirdness from any charge in the capsule. Also, the curve track would mean that a capsule going off the rails could go in a totally unpredictable direction.

Also, you'd durability as well as raw strength of materials will come in here since they'll be trying to use the thing repeatedly.

When I first got the space bug as a young man (was going to be an astronaut like many of my peers) I realized that if you ran around the equator fast enough you could put yourself "in orbit" at ground level. There is an orbital velocity where your angular momentum is in balance as Galileo figured out.

Of course you burn up because you are moving so fast. But imagine that you put a big tube around the planet and pulled a vacuum in that tube. Then you could be in orbit just off the ground, how fun would that be?

Just as impractical as this idea however as you'd have to hold the vacuum in a very very long tube.

Sigh, the challenge of magnetic rail launchers and this slingatron thing is the atmosphere. Sure if you could pull a vacuum around the launch facility you might get close, but consider that the typical rocket launch gets maximum dynamic pressure as it goes supersonic on its way out of the atmosphere. This thing is going to hit that and live in that space while its going around the loop. Now compute the effect of a supersonic shockwave that is curling in on itself. The standing wave you generate it going to generate some amount of overpressure, back of the envelope, looking at four to six wavefronts collapsing on themselves as you go around the final loop of maybe 6 atmospheres?

There is a reason fish don't swim in a circle to build up speed to jump out of the water, because their own wake would stop them cold.

I wonder if someone could do a quick CFD of a payload travelling in a 7.6km/s at sea level is in the 'high hypersonic' regime (> MACH 10 closer to MACH 25) The energy you are dumping into the air at that point is going to create a pretty impressive flame front by itself. This is perhaps the coolest things about the really high speed videos of the Navy railgun project.

Re. the flame front, they say that the payload will be supported from the rail by a plasma bearing. You mean an air bearing? No.

A plasma bearing.

You have to admire their chutzpah.

While 250k is peanuts compared to regular costs of rocket research, I feel 1 km/s is not that impressive of a demonstration. Rifles have achieved higher muzzle velocities as far back as 1935 [1], and ground-based systems capable of over 3 km/s have been demonstrated in the '60s and '90s only to meet with little interest [2] [3].

[1] http://en.wikipedia.org/wiki/.220_Swift

[2] http://en.wikipedia.org/wiki/Project_HARP

[3] http://en.wikipedia.org/wiki/Super_High_Altitude_Research_Pr...

yes but this is purely mechanical

Backed.

Super-interesting concept, and the people at HyperV Technologies Corp seem to know what they're talking about, so I am excited about this. For example, their other KS project—the Plasma Jet Electric Thrusters for Spacecraft[^1]—was successful both in funding and delivering what was promised.

Also, you gotta love their pretty low-key / somewhat amateur'ish videos. ;)

[^1]: http://www.kickstarter.com/projects/2027072188/plasma-jet-el...

The right hand rule thing reminded me of my physics teacher, or pretty much any physics teacher ever.

Everyone grows up. Except physicists. Physicists are special.

Or else, how do you explain a grown man sitting in front of a leynhurst generator for an entire noon just turning the wheel and marveling at the discharge?

|Also, you gotta love their pretty low-key / somewhat amateur'ish videos. ;)

The kickstarter aesthetic

> The kickstarter aesthetic

I disagree. Most KS videos I watched were very upbeat/chippy/hipster'ish/enthusiastic pieces of semi-professional ad/film making. The HyperV videos, not so much. They look like transfers from a VHS camcorder. :)

Posted this a couple days ago, and it didn't take. Very glad to see that this finally made it on the front page. Hyper-V had an impressive plasma thruster campaign, so I know they can deliver. I hope this gets funded and they can pull of the proof of concept...it seems so much better than many other ideas for small payload launch.

If this takes off one of the common uses would be flinging the last remains of dear loved ones into space.A "human dust" would surround the lower orbit. Anaerobic bacteria will thrive in the dust fed upon by deadly viruses. Skeletal remains would form microscopic spherical super-strong bone pods encasing these deadly viruses. This dust will stick to spacecraft on re-entry. The deadly viruses infect the human population resisting any medical intervention(since cooked in space) leading to the inevitable apocalypse: Zombies. Totally worth the 5$ I say. Please down vote me. I am bored.

The key number is 40-60,000 Gs.

Wikipedia helpfully informs me that this is 3-4 times the rating of the electronics used in artillery fuzes.

One possible use is launching solar reflectors to reduce global warming. https://en.wikipedia.org/wiki/Space_sunshade

G forces are less problematic when launching bulk materials (fuel, air, water, foodstuffs, metals - as I see the project proposal suggests). If you're 'catching' the payload at the other end, you can make the launch vehicle very dumb. Even more so if you can leave your engine at home and still use it (see also "ablative laser propulsion").

Radial forces on the launch platform itself are more of a concern. You have to stop it from tearing itself apart while it overcomes friction/drag and reaches escape velocity.

Their proposal also suggests that the capsule will need it's own rocket motor (and hence guidance and telemetry system) to get to orbit.

I was hoping the $10K slot would get you a tiny payload of your choice flung into space.

I'd hoped so too, at first, but since this is just to build a non-orbital mid-scale demonstration, I figure building this one doesn't ensure that the orbital one will get built, and thus they couldn't guarantee that a full-size slingatron would ever exist to deliver the promised launch. Would've been nice, though. They'll probably offer that if they kickstarter the first orbit-capable one.

Still trying to get rid of all those old CRT monitors out in the storage shed?

This looks fantastic if it'd work, but I wonder if it'd be more useful to build in space, and then use it to launch little probes. No atmospheric drag.

I realize building it in space would be a good bit harder than on the ground. I'm just in wouldn't-it-be-cool land.

Build it on the ground, and use that ground based version to sling up the moon based version, and use that to sling out the stuff for the Mars colony?

Life imitates art?

http://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress

Is Mike already lurking in some massive instance?!

My thoughts exactly. I'm actually amazed it has taken so long for this idea to come to anything close to fruition. Heinlein really grokked the future.

I thought this would be totally hokey, but it wasn't. If Freeman Dyson says it's a brilliant idea, then maybe it is. I see it as being in the same category as the Hyperloop--at least worth a look at.

This is sooo going to be weaponized.

The fact that this has obvious military applications suggests to me that if it was practical, militaries would have already done it.

Indeed. It looks like an obvious ship killer. What can you do to a one ton steel brick travelling in your direction at Mach 10?

It's hard to imagine scaling this up to be able to throw a ton at a time.

If you want to throw something that heavy, you'll have a much easier time using explosives to do it -- and we've been able to do that for quite a long time now (multi-ton shells were fired in WWI).

All you have to launch is a nuclear warhead.

Sure, but that's frowned upon in the international community.

Given the spin-up time and the fact it's a giant gyro (and thus can't be aimed) the ability of a 15" gun to fire payloads at enemy ships seems far more useful.

Yea but you can shoot things into space. So now you can shoot things into space so that it lands on the other side of the planet.

There's no proof they haven't.

Or are just about to start testing it ;)

The Navy is working on a railgun[1]. Probably a bit more pragmatic than something this large.

[1] http://www.smartplanet.com/blog/bulletin/navy-gets-another-h...

Reminds me of a Lofstrom Loop: http://en.wikipedia.org/wiki/Lofstrom_loop

This idea to me seems a lot more feasible. Read about it years ago and it makes me sad to see that it's not happening.

A structure 2000 km (actually, 4000 km) long is envisioned, with internal speeds of 14km/s. We're just not very good at building that sort of thing yet.

At those scales, it's considerably harder than building high-speed rail NYC<->LA, and the latter is usually ruled out as infeasible.

From other comments, it seems there are a number of basic physics and materials challenges involved in reaching orbit. However, this sort of technology used with self-guided projectiles could produce the UP/Ex launcher described by Vinge in Rainbows End, used for very rapid local and interstate deliveries. It takes much less energy to hit the next town over than it does to reach LEO.

I'd be all for it if it could get organic materials to space, including humans, and if it could do so without a rocket stage. The demo videos are really impressive (especially the blowing of the hole through that rug - be careful! Looks like you might have a modern weapons technology here as well) but it seems unstable and not versatile enough payload wise!

If it does not work they can always re-purpose it and totally clean up in the next punking-chunkin competition.

This is an interesting idea, but one that heavily relies on factual mathematics to work correctly. Even slightly get your calculations on force required to launch the vehicle and continue acceleration wrong and you've got a potential disaster on your hands when whatever it is you are launching comes falling out of the sky in your direction.

I really like the outside-of-the-box approach and idea, it will be interesting to see if $250,000 is enough to build something of this magnitude which will need to be tested and tested and then tested 100 more times before you could even attempt to try it in the real world.

interesting "mechanical" idea for sure, why can't you use magnetic loop to speed up the object more gradually and fire up afterwards.

Also really interesting references to HARP in this thread: http://en.wikipedia.org/wiki/Super_High_Altitude_Research_Pr...

A few years ago, I was interested in the physics of getting LEO costs down, so I did some computer modeling.

This general idea was the best I could find. Put the mechanics and fuel for the vast majority of orbital insertion inside some ground-based system, instead of trying to carry it. Impossible to use with humans, but for lots of other stuff like supplies, more fuel, habitats, etc -- should work fine. At least as far as I could tell. It's much more feasible than a Space Elevator, and no new tech needs to be invented.

Having said that, I'm not so sure this is going to work in KickStarter format. Sure, build a bigger laboratory model, but to make this really work it's going to need a lot of cash.

If we're not going to worry about living payloads, why not just use a circular rail gun? (A macro scale cyclotron if you will.) It has no moving parts (except perhaps the exit point), it doesn't need to be a spiral, it doesn't all need to be mounted on a moving platform.

I agree. I didn't use this specific configuration either. All I meant was the general idea of slinging cargo from the surface into LEO. Much, much cheaper than using explosives to dead-lift things out of the gravity well.

Shouldn't DARPA being funding this sort of thing?

But.. Does it work in Kerbal space?

+1 for the xkcd ref ;)

Someone found the humor =)

I'll suck on the -2 Karma for a while...

Reply on news.ycombinator.com