Launch loop | Hacker News Reader

Launch loop

en.wikipedia.org

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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...

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

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...

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.

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.

> 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.

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.

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).

I wonder if, once both technologies are more advanced, a network of solar sail "tugboat" drones could be used to transfer launches to other inclinations and orbits after orbital insertion - with the exception of normal wear and tear, there should be little to prevent such a network from operating indefinitely with negligible material cost once launched.

The biggest issue is that'd take a really really long time. The amount of dV you get out of a solar sail is minuscule at scales that will work well in the neighborhood of Earth.

Oh, absolutely - solar sails in general only really work for things like satellites and probes (and, possibly, asteroids) where you can afford to give them quite a while to get into place, so no manned solar boats here. Although you can do some interesting things with them in gravity wells (statites, anyone?).

Still, you only need to perturb your orbital plane a very tiny bit to be out of the way of future launches, and then you have all the time in the world to navigate to where you want to go.

Yeah the months to years it would take depending on the payload and size of the change though would be pretty costly for the businesses. I think a more likely solution would be having a handful of launch loops on common inclinations and anyone requiring a very specific inclination launching with a booster attached to take care of it. Depending on how high these loops could launch using the Moon to change inclinations might work. I think more likely though is that basically everyone would find ways to make do with the handful of standard inclinations that there were launch loops for.

That's probably not a huge deal ultimately. Being able to get things into orbits very cheaply will make the dV cost of inclination changes much easier to bear because you don't have to haul all that fuel to orbit on your initial launch any more.

Also how many different inclinations are actually required to serve 90-95% of all launches? There's really only a handful of inclination 'classes' out there that would need to be fulfilled; 0 for geostationary, 51.6 for ISS (assuming it's still up when we build the loop), 80-90 for various Earth observation and communication satellites. If we can super cheaply launch satellites into a couple defined inclinations most customers would probably be able to make do with one of these common inclinations rather than today where they'd go with the perfect one.

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.

so basically a "rocket" (two rockets?) with a high reaction mass?

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.

Changing inclination costs a lot because dV costs a lot. If you can easily bring hundreds of tons of fuel to orbit, that's no longer the case.

The launch loop changes everything, because your launch costs are in the neighborhood of $3 per kg. That's a total shift in the way we think about rocketry.

Imagine if gasoline was $4000 a gallon. In that world, driving 20 miles to the store to pick up some groceries would be unthinkable.

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!

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.

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

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

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

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.

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

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

http://slides.launchloop.com//launchloop.pdf

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

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

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

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.

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.

What do you mean by mT? Millitesla?

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

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...

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

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

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

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

All you need is a megastructure 50 miles tall!

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?

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.

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.

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!

If you wish to make apple pie from scratch, you must first create the universe

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.

you could also build a space fountain using drones attached to each other like a snake

Or just drive any matter up by any means to hold the tower. No special materials, just a lot of electricity.

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.

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.

1G for 2000km is really really fast IMHO.

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.

I think you could accomplish this more easily with a semi-evacuated floating tunnel heading east from the Galapagos Islands, and up the west slope of Chimborazo, whose peak is the closest to space of any other mountain on Earth.

That means it already has higher angular velocity by virtue of being close to the equator, and is further from the Earth's center of gravity by virtue of being situated on the equatorial bulge. The peak is also 45% the atmospheric pressure at sea level.

The floating tunnel would be about 1100 km, and then about 150 km up the volcano. At a constant acceleration of 30 m/s^2, relative to the launch tube, 1250 km of track gets you up to 8660 m/s after 289 s. Then you get 464 m/s from changing reference frames from Earth-fixed to Earth-relative at the peak of the volcano. Subtract about 1300 m/s for drag, and 7824 m/s is roughly a LEO at 200 km. About 3 Gs for about 5 minutes is easily tolerated by healthy humans in the correct orientation--we do that in amusement park rides for fun.

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