
Launch loop - jpatokal
https://en.wikipedia.org/wiki/Launch_loop
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wklauss
For those interested in the topic, the series Upward Bound by Isaac Arthur on
Youtube cover various methods to achieve orbit, including Launch Loops.

[https://www.youtube.com/playlist?list=PLIIOUpOge0LsGJI_vni4x...](https://www.youtube.com/playlist?list=PLIIOUpOge0LsGJI_vni4xvfBQTuryTwlU)

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DesiLurker
came here to post just that. Issac's channel is definitely worth the time.

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Zancarius
If you like Isaac Arthur, don't forget John Michael Godier[1]! His videos tend
to be short (3-5 minutes on average, sometimes longer) and cover a similar
range of topics albeit with a focus on current events in addition to scifi and
futurism. Isaac Arthur has done a couple of collaborations with JMG, too.

The thing I love about Isaac Arthur is that he does these collaborations in
part to drive some of his traffic to smaller channels that are just as
interesting. He's a fantastic guy.

[1]
[https://www.youtube.com/channel/UCEszlI8-W79IsU8LSAiRbDg/vid...](https://www.youtube.com/channel/UCEszlI8-W79IsU8LSAiRbDg/videos)

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PaulHoule
The trouble with these things is that rockets are not that bad, at least to
get into LEO.

The amount of fuel required to circumnavigate around the world on a jetliner
is on the same order of magnitude of going into orbit. The spacecraft has to
carry about three times as much fuel when loaded than the jetliner does (it
can stop three times.) The vehicle is more expensive than a jetliner but not
impossible so, the ticket price could drop to 3x to 10x what it costs to fly
around the world.

The main advantage that the airliner has is that they can get you out of the
airliner, check and clean the plane up in 30 minutes to an hour, fuel up, and
be flying another bunch of passengers to the next destination.

If you are using throwaway vehicles you can't approach the cost of air travel.
You can't do that with a Space Shuttle that takes 6 months for technicians to
check out every single thermal tile.

Speculative concepts such as space elevators and scramjets don't compete
against the Space Shuttle and the Saturn V, they compete against highly
evolved versions of current technology, which can achieve huge cost reductions
by accelerating reusability.

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NegativeLatency
Aircraft also can glide if they lose power, and they don’t carry oxidizer with
their fuel. I prefer the failure modes of an aircraft to those of a rocket.

It would be nice to get to orbit without sitting on top of a marginally
controlled bomb.

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theothermkn
> I prefer the failure modes of an aircraft to those of a rocket.

Then you would _hate_ a launch loop. A flexible steel rod traveling at above
orbital velocity and magnetically suspended inches away from an enclosing
sheath is basically 200 miles of kiloton explosions waiting to happen,
followed by an unimaginably large rain of debris.

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GW150914
As it points out in the article, for safety and astrodynamic reasons a loop
would be situaties over an ocean, and most failure modes would be limited in
scope.

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orbital-decay
Another problem not mentioned in the article is that it would be a fixed
inclination launch system. Changing inclination costs _a lot_ , especially in
low orbits. For example, from a pure dV standpoint, a GEO satellite would be
cheaper to launch from Baikonur by circumnavigating the Moon, than by changing
the inclination during the flight as it's currently practiced due to different
constraints (the tricky thermodynamics of compact upper stages being the big
one).

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blauditore
If hauling mass into orbit relatively cheaply would be possible, wouldn't it
be easy to just send along a counter-mass (or actually a second useful item)
and split them when in orbit (e.g. with some explosives)? So you would end up
with two symmetrically orbiting items, but without having to deal with rocket
propellants.

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CompelTechnic
Low earth orbit is at a speed of 28,080 km/h. If you want to separate the two
halves of your satelite at a significant angle from their starting trajectory,
you have to provide a lot of impulse perpendicular to the direction of travel
(or from a zero-orbital speed vertical launch at apogee, which would be
weird). More impulse than an explosion could make, probably even if you built
your satellite like a brick shithouse.

Rockets conveniently spread the impulse out over a long period of time.

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mathewsanders
Everyone’s probably read it by now, but second part of Seveneves there’s a lot
of great non-rocket systems for getting stuff into space (like skyhook also
mentioned in Wikipedia article) there’s one part of the story where a bolo-
type setup is used for an emergency extraction from earth which still makes me
gasp in amazement to think about :)

In conclusion: if you liked the launch loop idea but haven’t read Seveneves
then go buy/download it right now!

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madeuptempacct
The bolo concept was interesting, but most of Seveneves was pretty bad
technologically (or maybe I didn't get it). There is also the part where I
didn't care about a single character, though I guess the cannibal leader kid
was a little memorable.

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stcredzero
Sonar Taxlaw is the perfect woman, after my wife, of course!

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madeuptempacct
I don't even remember who that is. Sounds Idan.

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stcredzero
Post apocalyptic woman whose duty was to memorize the encyclopedia. I wouldn't
say Idan. I picture her as quite feminine.

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api
Here's a dumb idea:

Could you drill a tunnel that's basically a chord (line between two points on
a circle) that runs through the Earth between two surface locations, put a
fully evacuated Hyperloop type system into it, and fire objects into space
with maglev acceleration? It would be a full vacuum until the object neared
the exit end at which point it would open. Air would rush in of course, but
the object would need a heat shield anyway and would have to be traveling many
times faster than escape velocity.

I guess it's a variation on gun launch.

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jpeanuts
If you can just dig and evacuate the tunnels, you can get energy-free
transportation to anywhere on earth:
[https://en.wikipedia.org/wiki/Gravity_train](https://en.wikipedia.org/wiki/Gravity_train)

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black6
Link to Lofstrom's paper on the loop, which is need of some editing:

[http://slides.launchloop.com//launchloop.pdf](http://slides.launchloop.com//launchloop.pdf)

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jpatokal
Lofstorm's (rather messy) site:
[http://launchloop.com/LaunchLoop](http://launchloop.com/LaunchLoop)

A 20-minute video explaining the concept:
[https://www.youtube.com/watch?v=J1MAg0UAAHg](https://www.youtube.com/watch?v=J1MAg0UAAHg)

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debt
I'm curious how he came up with this idea.

I think many times we start with the ideal: what if we just had a cable
reaching into space that allowed us to easily get up there?

And then from there, they work backwards on how that would be engineered.

Or was it, he had some fascination with rotors and thought of a really big
version of some similar, smaller version he had thought of before.

idk

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growlist
I'm all for new space launch concepts - it just intuitively seems like a mass
driver or spacegun should be a cheaper method for cargo etc. But has anyone
attempted to validate the Launch loop concept with even a scale model? It
seems so far beyond what we know that I have trouble taking it seriously.

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chris_va
First rule of any hardware system: Something is always going to go wrong.

When your system is one giant 62,000mT cable with the kinetic energy of 62
Hiroshima bombs, I think you'll lose your $30B investment pretty quickly.

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nayuki
What do you mean by mT? Millitesla?

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chris_va
Failed capitalization... metric ton (MT or mt, I guess)

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RIMR
I couldn't help but to notice that in every drawing of this thing, "Support
Cables" are shown beneath this gigantic floating structure, and they
apparently keep it in the sky.

I may not know too much about spaceflight, but I do know that gravity tends to
pull downward, towards the earth. I don't see cables doing a good job of
suspending these things in the air when they are constructed beneath the
structures...

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chriswarbo
The cables don't keep it up, they're like guide wires on radio masts
[https://en.wikipedia.org/wiki/Radio_masts_and_towers](https://en.wikipedia.org/wiki/Radio_masts_and_towers)

The "support" comes from the momentum of the moving parts within the cable.

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RIMR
Oh, so it's just one mechanical failure away from crashing down to Earth...

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chriswarbo
It depends what sort of failure. Many sorts of failure would not be a problem
[https://en.wikipedia.org/wiki/Redundancy_(engineering)](https://en.wikipedia.org/wiki/Redundancy_\(engineering\))

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qop
All you need is a megastructure 50 miles tall!

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stcredzero
It's physically realizable. We could physically build such a thing as a static
structure out of aerospace grade materials. (Carbon fiber or balloon tanks
made out of Boron. People have done the calcs.) It's just that no one would do
it, because it's not economically justifiable.

Apparently traditional skyscraper building techniques could be used to build a
single structure 11 miles tall. Again, no one would do it, because it's not
economically justifiable. Maybe if there was a space tower cold war?

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qop
Do you have citations or further reading on this? I am not trying to nitpick
you, I want to read more about this but I googled megastructure and I get back
a bunch ofnonsense. I find it interesting what architecture experts have
thought about the extreme end of human structure.

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stcredzero
I just did a search, and only found my earlier HN account of reading the
USENET post from someone working at JPL. Yes, you can discount such towers as
fanciful nonsense. Physically possible, but politically and economically
infeasible as of now. Another rec.arts.sf.science post described how our
civilization could sterilize the biosphere, but it would involve global
civilization spending decades doing nothing but seeding the surface with
nukes, just to set them all off simultaneously. A number of prominent
scientists used to post there with wild back of the envelope calcs. Someone
working at JPL did write up a proposal to build an exponential truss tower
using hyper pressurized balloon tanks made from boron. I'm sure of this. In
any case, it's interesting only as an intellectual exercise.

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qop
It's fascinating stuff. Those are the types of people our society will need a
thousand years from now when we're coordinating larger structures in space.
Maybe even coordinating builders/supplies from different planets!

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jlebrech
it would also be possible do this by going around in a circle at 2g (a train?)
the train could then drag a capsule and let go at a certain speed.

it might have to be at the poles.

another option would be to build a bridge from south america to west africa,
and at 1g you'd reach escape velocity.

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dsr_
You seem to be confused between acceleration and escape velocity.

A Tesla Model S can accelerate at 1.14g while going from 0-60mph, but it can't
continue that acceleration for long.

A dragster can accelerate at 5g for almost a second. It won't get into orbit
if you send it off a ramp.

The train with a centripetal acceleration of 2g will not launch anything into
orbit unless it can magically keep providing that acceleration to the vehicle.

On the other side, you don't need to accelerate particularly hard if you want
escape velocity, you just need to get up to that speed after accounting for
atmospheric drag. You could launch a winged rocket that accelerates at
1.12meters/s^2 -- in ten thousand seconds or so, it would be up to escape
velocity.

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shawnz
I don't think the parent is confused, I think they are talking about the
velocity you'd reach after being subjected to that acceleration over the whole
2000km track.

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jlebrech
1G for 2000km is really really fast IMHO.

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logfromblammo
1G over 2000 km gets you to 6261 m/s, after 639 s. That isn't escape velocity.
That isn't even orbital velocity.

But Fortaleza, Brazil, to Dakar, Senegal, is about 3100 km. 1G over that
distance gets you to 7795 m/s, after 795 s. That can _almost_ get you to a
LEO, with a 40 degree inclination. You'd still need to overcome atmospheric
drag.

Fortaleza, Brazil, to Libreville, Gabon, is 5350 km. 1G over that distance
gets you to 11240 m/s, after 1045 s. That will get you into an orbit with 4
degree inclination, and after accounting for drag and the angular velocity at
the equator, you might even still be at escape velocity after exiting the
atmosphere.

