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I'm writing a novel that takes place in a future where we've just begun to go interstellar, but the costs are still quite high and the purpose is definitely scientific study, exploration, and so on. FTL is not an option. Within the solar system we are quite advanced in the sense that we have colonized Mars, Venus, a good number of asteroids, various moons of Jupiter, Saturn . . . . not long has passed (a few centuries at the most; still working out the details) so terraforming is in very early stages or not being attempted at all; but asteroid mining is extremely lucrative and humanity is overall very well-established in terms of orbital colonies, space travel, and such.

I'm not sure all that background is helpful, but wanted to give the general picture. My question is what methods of non-rocket spacelaunch are going to be most prominent at various stages of human advancement? I've done a bit of research and it seems like, with the sorts of resources I'm giving my civilization, an orbital ring might be a very strong option . . . . augmented of course by individual projectile launchers and whatnot used by individual corporations and so on . . . . but I'm going after the overall most efficient method, here. I haven't found anything comparing exact building costs and payload capacities and such. Does anyone have a link? If not, any ideas?

As humanity advances of course, we have to assume some degree of technological innovation. So a space elevator might be unfeasible today partly because of technological limitations; but in the future should I assume it will be possible? Probably, at least EVENTUALLY. So at what point in the future will such things become possible enough to make them more cost-effective than, say, a less advanced method that might be more realistic in the near term? Would something like an orbital ring be unfeasible for so long that startrams or mass drivers or guns or whatever would become predominant first? Is my impression that they would be easier correct or totally off?

Does my question make sense? Also, I am asking paticularly about Earth here but any random thoughts on other matters, like Mars' lighter atmosphere making a space elevator more realistic, would be welcome. Thanks!

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    $\begingroup$ How big are we talking? There's a difference between building a tether-based system (which we could technically do today), a space elevator (which we will be able to do soon), and a full orbital ring (which will take quite a while yet) $\endgroup$
    – Dragongeek
    Jan 7 at 21:55
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    $\begingroup$ en.wikipedia.org/wiki/Non-rocket_spacelaunch There's a good overview of most popular systems here. $\endgroup$ Jan 8 at 5:30
  • $\begingroup$ Multiple array of lasers fired at the thruster to superheat the water to generate lift... very fun but the cost makes it seems impractical. $\endgroup$
    – user6760
    Jan 8 at 6:38
  • $\begingroup$ Alt+F12, Set Orbit $\endgroup$ Jan 8 at 7:15
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    $\begingroup$ @user6760 Isn't that still a rocket? You're kicking off reaction mass to generate thrust... $\endgroup$ Jan 8 at 17:45
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You really only have three main options to get into orbit:

  1. Rockets / continuous thrust
  2. Space elevator
  3. As a Projectile from a "Big Gun" (All of your velocity acquired at once)

Space elevators have been discussed to death and back. They are the gold standard for cheap space access but are by far the most difficult to construct and maintain. Not to mention they would be a huge failure point for any hostile group to strike.

You want to move away rockets, so the next thing to look at are "Projectile" based launches. The general concept is you get your orbital payload up to speed on the ground.
The issue with accelerating your spacebound payload to orbital velocities within an atmosphere is the atmosphere... and the acceleration. The G forces caused by drag alone would probably be beyond human survival (if launched from sea level).

You could have an unmanned vessel launch from a massive, multi-mile long railgun inside a vacuum tube, installed at as high of an elevation as possible to mitigate those challenges. Even then you'll need a rocket burn to correct your orbit into something stable.

One interesting approach is a form of rocketry called Laser Ablation Propulsion (https://en.wikipedia.org/wiki/Laser_propulsion) where you have a ground based laser system vaporize a plate at the bottom of your launch vehicle, and the pressure from the plasma plume pushes you away.

Realistically, the future will probably combine multiple approaches rather than relying entirely on any one approach.

Imagine a huge circular magnetic accelerator track that gradually brings a manned launch vehicle up to "pretty fast but survivable" speeds. That launches and gains some additional velocity from a ground based laser system. Then it uses chemical rockets to reach a skyhook (https://www.youtube.com/watch?v=dqwpQarrDwk) and is off!

There's also the potential for Nuclear rockets, but those will probably be taboo for Earth bound launches for.... ever.

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    $\begingroup$ ...but I LIKE nuclear rockets... :( Still +1 $\endgroup$
    – DWKraus
    Jan 7 at 22:33
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    $\begingroup$ @anaximander - did... you read the whole answer? The last paragraph of the "gun" section ends: "Even then you'll need a rocket burn to correct your orbit into something stable." $\endgroup$
    – codeMonkey
    Jan 8 at 13:40
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    $\begingroup$ @anaximander: There is literature (Verne 1865) of a "big gun" moon launch where the trajectory was calculated to result in lunar impact. I wonder if the hypothetical post-impact trajectory would have continued all the way back to near the gun's site. Now I have to go visit the library and do research and math. $\endgroup$ Jan 8 at 14:39
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    $\begingroup$ @codeMonkey Apparently I should stay away from Stack Exchange when insufficiently caffeinated. $\endgroup$ Jan 8 at 17:02
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    $\begingroup$ @abestrange, I guess I missed that sentence and was more commenting about other comments. Sorry for any confusion. I did up vote your answer, since it give a good synopsis of the different methods you mention. You got the space elevator and laser propulsion that I was going to Answer with. :-) $\endgroup$ Jan 8 at 19:51
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Space Elevators

The key here is to use a very thin ribbon of carbon nano-fiber cables instead of one big ginormous metal cable as is most often depicted in science fiction.

While it used to be assumed that a space elevator would cost over a trillion dollars, advancements in carbon nano-fiber technology has lead to newer ideas on the design of space elevators that could cost as little as 6.2 billion USD to construct the first one and only about 2 billion per elevator after that. And they could have an operational cost of only ~100 USD per kilogram.

For comparison, the final cost of the US Interstate system was about 129 billion USD... and that was decades ago; so, inflation wise think closer to 740 billion USD. So for the same relative price as the US interstate building project, one could construct about 370 space elevators with a total lift capacity of about 1.5 million lb per day and operate at a cost that is 27 times cheaper than a SpaceX Falcon 9 rocket per kg and about 545 times cheaper than a space shuttle.

The human race would need to seriously ramp up our ability to mass produce high quality carbon nano-fibers to make this happen, but being able to reach the required levels of refinement and production should not take more than a few decades from now when you look at current trends.

I'd be very surprised if the first space elevators were actually as cheap as this since there are bound to be some unforeseen hurdles to overcome, but once a country gets the first dozen or so of these built, it seems pretty reasonable to assume that the price could come down to the more conservative 2 billion dollar figure.

So shipping things up and down to space would still be more expensive than normal freight, but in comparison, very affordable. Since you mention space mining, many of the precious metals you can get from an asteroid are worth well over 100$/lb so silver, gold, platinum, Iridium, etc. could all become economically viable to import.

... As For Mars

Mars would benefit a lot from sticking with rockets for a while because the lower gravity turns the "tyranny of rockets" problem into more of the "inconvenience of rockets" problem. Whereas rockets on Earth are made from expensive alloys and filled with premium grade fuels just to waste 95% of their mass on getting into orbit, on Mars you can produce much lower grade fuels and use less efficient materials to build rockets that can carry 20-40 times as large of a payload for their size. On Mars you also need to consider the limitations of industrialization. It is not Earth; so, man power is VERY limited and industrialization much more risky. So a super precise and large scale manufacturing project like building a space elevator may be outside of their abilities for a while compared to Earth while simple methane powered rockets could be built relatively early on.

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    $\begingroup$ I'm not going to cast doubts on your 6.2 B figure for a space elevator, but the 2021 budget for Nasa is 23.3 billion. I would like to imagine that if a space elevator was truly that cheap, we'd start looking into production yesterday. $\endgroup$
    – abestrange
    Jan 7 at 21:58
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    $\begingroup$ To be fair, Mars has some benefits for space elevator use: The length is shorter, and if you can move it, Deimos is almost in the orbit you'd want your upper anchor for the space elevator to be. Downside: Phobos is in the way, and you'll either have to move it or build your elevator to avoid it when it comes trundling by. $\endgroup$
    – notovny
    Jan 7 at 22:30
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    $\begingroup$ While NASA does have the budget to try a space elevator, they would have to cancel a LOT of contracts to free it up those funds which is hard in an age where their budget keeps getting cut already. $\endgroup$
    – Nosajimiki
    Jan 7 at 22:46
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    $\begingroup$ Nitpick: 95% of the mass isn't wasted on getting to space, much of it is spent on getting to orbit. Sending a payload above 100km (the Karman line) isn't as fuel-intensive as giving it the lateral speed to stay there. Source: I've been playing the app Spaceflight Simulator lately, and getting my ships into orbit takes much more fuel than simply making my up-goers go straight up. $\endgroup$ Jan 8 at 14:44
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    $\begingroup$ @Nosajimiki The 2003 Edwards proposal made some optimistic assumptions about the readiness of carbon nanotubes. There have been some more recent technological feasibility assessments done by the International Academy of Astronautics in 2013 and 2019. The principle finding was that sufficiently strong tether material might be ready around ~2030. en.wikipedia.org/wiki/Space_elevator#21st_century $\endgroup$
    – abestrange
    Jan 8 at 16:30
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There are two structures that have not been mentioned yet:

Space Fountain##

enter image description here

Wikipedia article here: https://en.wikipedia.org/wiki/Space_fountain This is a very clever design, and relatively easy to build. The basic principle is this: Shoot a stream of metal pellets at high speed through a vacuum tube. Twist the tube upwards 90 degrees with a big magnet so that the pellets travel upwards. Turn the pellets at the top 180 degrees so they travel downward again. The stream of pellets will lift the entire assembly into the air

Launch Loop

enter image description here

Wikipedia article here: https://en.wikipedia.org/wiki/Launch_loop This is a superstructure which is 2 000km long and similar to the space fountain. It sounds great, but the big hurdle is where to build it, as 2 000km is a lot of space, and the only real-estate that I think would work on earth would be North africa, or floating on the ocean

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Space Whip

I'm not sure I can do this justice but in his book Seveneves, Niel Stephenson posited a novel means of getting into orbit. You have a satellite with two very long, thick cables on either side, which is rotating on an axis tangent to the curvature of the earth, so at all times, one cable is approaching the earth and the other is moving away. Thing is, the satellite's rotation does not need to be very fast in order for the movement at the end of the whip to be much, much faster, like cracking a whip. So you simply need to fly up high enough to reach the end of the whip (in the book, a character did so using a nanotech flying wing suit, just lazily catching updrafts until she reached the required altitude, but you don't need to get that exotic, any regular aircraft could do the trick), and latch on to the end of the whip as it passes overhead. The resulting whip-crack will launch you into orbit, simply detach when you get high/fast enough. The whip on the other side of the satellite will then descend towards Earth and pick up another passenger, so it stays in a stable rotation in orbit. A number of these satellites could be placed in various geostationary orbits to provide easy access to space from each of their locations. The book also featured a larger one with a non-geostationary orbit that can visit several proscribed locations as it circles the planet.

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No launch system can really do the job entirely without rockets, even a space elevator will need rockets to shift stuff to orbits that don't intersect the space elevator. (You will want to put stuff into such orbits, in part because intersecting the space elevator will make people angry.) Making the needed changes to orbits can easily take a good chunk of the rocket propulsion that would be needed to get into the destination orbit directly.

It turns out that rockets are really good at what they do, and it's really hard to come up with an alternative that's better than just making the rocket portion a little bigger. Alternatives like mass drivers and elevators also have throughput issues...you've got one big bottleneck on your traffic...and again, only target specific orbits. Rockets can more or less go anywhere from anywhere with a launch mount and stacking/fueling infrastructure, making them a much more scalable approach to moving material.

Maybe beam-assisted launch could be useful, launch vehicles using laser or microwave beams from the ground to heat their propellant. The vehicles would be more complicated and more infrastructure would be required, but could get better specific impulse. Note that this hasn't historically been a trade that has resulted in lower costs. It might be an approach that works better away from Earth, where less thrust and power are needed and there's less weather to mess with the beams.

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  • $\begingroup$ This is true as long as you classify ion or plasma thrusters as rockets, as those could be used to adjust orbits. We'll be using some form of "throw matter out the back as fast as you can" for a VERY long time. $\endgroup$
    – abestrange
    Jan 8 at 16:57
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    $\begingroup$ @abestrange I am considering those to be rockets, but also note that anything less than an elevator will require something higher thrust, and even with an elevator you'll probably want a high thrust system to shift the payload's orbit clear of the elevator and get it to its destination in a reasonable time. $\endgroup$ Jan 8 at 17:34
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In increasing order of launch volumes required for viability:

  1. Things to assist the rocket launch process in some way. Things like balloons to get you past most of the atmosphere before you start with the rockets, spaceplanes, skyhooks et al and the like. These have relatively low costs, work with currently available technology, and can generate cost savings at relatively low launch volumes. These will likely be the first things taking over from rockets, being used to build up our orbital infrastructure.
  2. Localised rocket replacement systems. These are things that can be made in a relatively small geographical area. They're all much more expensive than the above, but don't involve mass-scale international cooperation, and can be net cost savings at moderate (relatively speaking) launch volumes. Things like space elevators, space fountains, mass drivers (and variants thereon), building up to, at the outer limits of "localised", launch loops. These will come in once we have orbital infrastructure (at least enough of it to make them financially viable), and be used for expansion beyond that.
  3. Orbital rings. These get their own category, because they're just that ridiculous. These are end-game for methods of getting from earth to space: ludicrously expensive at the outset, but dropping launch costs down to almost nothing, essentially the world over, and requiring global cooperation to even begin constructing. There's essentially no point in building them until a significant percentage of our industry is in space, when you want things like commuting to space for work to be viable.
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  • $\begingroup$ One of the main inefficiencies I see in ground based rocket launches is the atmosphere is primarily a burden rather than an asset. Air is just a source of drag for the most part. Spaceplanes take a lot of that drag and turn it into useful lift. $\endgroup$ Jan 8 at 20:29
  • $\begingroup$ @Crazymoomin large rockets lose almost nothing to atmospheric drag, because they climb out of the atmosphere so quickly. The Saturn V had 1534 m/s in gravity losses but only 40 m/s in drag losses (gravityloss.wordpress.com/2008/01/10/…). Lift doesn't come from nowhere, hypersonic L/D ratios suck, and spaceplanes have to deal with aerodynamic drag for a lot longer than conventional rockets do. It adds up: islandone.org/Propulsion/SCRAM-Spencer1.html $\endgroup$ Jan 8 at 22:48
  • $\begingroup$ @ChristopherJamesHuff You don't need to go hypersonic until the atmosphere is thin enough, close to or at when you'd be in rocket mode anyway. It's true there's not that much drag, but the air is still a burden, it would be better if the rocket was taking off in a vacuum. Not to mention the need to carry a lot less oxidiser. It will be possible to calculate a velocity curve that optimises L/D ratio for atmospheric density while still achieving orbital velocity. If it takes a bit longer to get to orbit, that's no matter. $\endgroup$ Jan 8 at 23:00
  • $\begingroup$ @Crazymoomin if you aren't going hypersonic in the atmosphere, before switching to rockets, you also aren't getting much benefit from air breathing or aerodynamic lift...just altitude gets you very little. Worse, you're carrying more wing mass to get that altitude at a lower velocity. As for LOX, LOX is easy to carry, being only moderately cryogenic and high density. $\endgroup$ Jan 8 at 23:55
  • $\begingroup$ @ChristopherJamesHuff SSTO spaceplane designs I have seen go into rocket mode around Mach 5, so they aren't really getting into hypersonic territory until then. Wings are not enormous but sizable enough to generate some lift. I'd contend LOX still adds a significant weight penalty. If there was no performance benefit to spaceplanes we wouldn't be developing them. Maybe the maths doesn't work out for the largest payloads, but for smaller launches the numbers are likely different. $\endgroup$ Jan 9 at 0:52
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Two main categories of non-rocket space launch:

  1. Other Vehicles:

Space Planes are currently in development. A plane that flies to the edge of the atmosphere then keeps going. Very similar to a rocket in some ways, but not a rocket. See some development/details at: https://www.reactionengines.co.uk/

  1. Structures:

Examples include the famous Space Elevator, the Orbital Ring you mention, the Space Tower and various "big guns" like the Victorians thought space travel might look like. Skyhooks are also worth a mention, they are kind of Space-Elevator like in concept but maybe more near-future (not so reliant on super-materials).

See this series of YouTube videos that goes through a large number of space-launch technologies and their potentials.

https://www.youtube.com/playlist?list=PLIIOUpOge0LsGJI_vni4xvfBQTuryTwlU

Think about the tone you want to set with these machines in your story. Do you want to "wow" the reader with the sheer scale of the future? ("One hundred billion people called Earth home"). Do you want technology that feels so advanced its like magic? (The Space Elevator cable super material). Or do you want the opposite? (It feels so possible, so real). Do you want to actually dedicate time talking about these things? (A Space-plane requires no explanation, a space elevator it probably needs a few lines of description so that readers know what to picture.)

Final point of warning. We don't have these machines yet, they are speculative. If any of these things do one day exist they will not look quite the same. It will be like the difference between a modern, real Helicopter and a Leonardo da Vinci sketch. Or between a Zeppelin and this thing.

Francesco Lana de Terzi's flying boat concept c.1670, from Wikipedia

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