

The Slingatron: Building a Railroad to Space - gurvinder
http://www.kickstarter.com/projects/391496725/the-slingatron-building-a-railroad-to-space?ref=category

======
msandford
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](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](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](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.

~~~
jamesaguilar
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.

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

~~~
diziet
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](https://en.wikipedia.org/wiki/Orbit)

~~~
msandford
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.

~~~
jamesaguilar
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.

------
ChuckMcM
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.

~~~
Daniel_Newby
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.

------
zeteo
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](http://en.wikipedia.org/wiki/.220_Swift)

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

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

~~~
3327
yes but this is purely mechanical

------
czottmann
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...](http://www.kickstarter.com/projects/2027072188/plasma-jet-electric-
thrusters-for-spacecraft)

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

The kickstarter aesthetic

~~~
czottmann
> 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. :)

------
binarymax
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.

------
realrocker
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.

------
kevinpet
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.

~~~
yew
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.

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

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

~~~
emhs
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.

------
danthewireman
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.

~~~
DanBC
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?

------
riemannzeta
Life imitates art?

[http://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress](http://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress)

Is Mike already lurking in some massive instance?!

~~~
Blahah
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.

------
daniel-cussen
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.

------
chrischen
This is sooo going to be weaponized.

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

~~~
rbanffy
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?

~~~
Tloewald
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.

~~~
chrischen
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.

------
valtron
Reminds me of a Lofstrom Loop:
[http://en.wikipedia.org/wiki/Lofstrom_loop](http://en.wikipedia.org/wiki/Lofstrom_loop)

~~~
msandford
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.

~~~
jessaustin
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.

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

------
jessaustin
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.

------
Aqueous
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!

------
zw123456
If it does not work they can always re-purpose it and totally clean up in the
next punking-chunkin competition.

------
DigitalSea
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.

------
alinspired
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...](http://en.wikipedia.org/wiki/Super_High_Altitude_Research_Project)

------
DanielBMarkham
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.

~~~
Tloewald
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.

~~~
DanielBMarkham
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.

------
microDude
Shouldn't DARPA being funding this sort of thing?

------
Selfcommit
But.. Does it work in Kerbal space?

~~~
electronous
+1 for the xkcd ref ;)

~~~
Selfcommit
Someone found the humor =)

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

