Any plausible non chemical rocket based space launch system on Earth?

[GTOM]

I write an sf story, and an important part is an attack on a big, expensive space launch system on Earth.
But what system could be built without pretty much magic? Looks like space elevator couldnt be made even from carbon nanotubes.
Maybe a space cannon, that could launch cargo to space with suborbital speed, then lifted further with nanotube cables and a space station below GEO orbit?

 

[.Scott]

Perhaps "SpinLaunch", which is cargo-only.
Also, if you are looking to avoid "big, expensive", then a space elevator wouldn't fit the bill.
There is also "Air-launch-to-Orbit".

This paper describes a proposed 120-foot super-sonic jet carrying a SpaceX Falcon 1 for launch to orbit. For comparison, the Concorde SST was about 200 feet long.

 

[phyzguy]

It's a story. Just say there was a breakthrough in high strength materials that made the space elevator possible.

 

[Filip Larsen]

Depending on how "feasible" the launch system must be, it may be quite tricky to come up with a system that doesn't use chemical rockets.
One option could of course be a nuclear SSTO, if such will fly with your story universe.
Or perhaps some kind of air breather (meaning chemical jet propulsion rather than chemical rocket) to bring the cargo high into the atmosphere and then something like a skyhook to lift it into orbit, but even then both the skyhook and the orbital cargo would require additional momentum change and there are only so many ways you can that while in orbit. For instance, circularizing cargo orbit from a sub-orbital injection trajectory is not super feasible to do with electric rockets.

 

[DaveC426913]

Sorry, what's wrong with the Beanstalk (space elevator)? It's not happening now, but do you really think it's a dead-end?

OK, what about a skyhook then?

 

[GTOM]

Perhaps "SpinLaunch", which is cargo-only.
Also, if you are looking to avoid "big, expensive", then a space elevator wouldn't fit the bill.
There is also "Air-launch-to-Orbit".

This paper describes a proposed 120-foot super-sonic jet carrying a SpaceX Falcon 1 for launch to orbit. For comparison, the Concorde SST was about 200 feet long.

It describes a rocket in the stratosphere phase. Could it really withstand such big acceleration?

 

[GTOM]

Sorry, what's wrong with the Beanstalk (space elevator)? It's not happening now, but do you really think it's a dead-end?

OK, what about a skyhook then?

i dont want to bring some sort of unobtanium to explain how it can hold the weight. the structure should be still ruinable without nukes.

 

[.Scott]

By "It", I am guessing you mean the SpinLaunch system ... And by "it", I am guessing you mean the SpinLaunch second stage.
Yes, a second stage rocket can be designed to withstand the 10,000Gs inflicted by a SpinLaunch launch.

 

[DaveC426913]

i dont want to bring some sort of unobtanium to explain how it can hold the weight. the structure should be still ruinable without nukes.

An incremental advance in carbon nano-fibre tech?

Last I heard, the rate-limiting step wasn't the strength of the fibre, it was the ability to produce 35,000 miles of it (and do so in space).

 

[Hornbein]

Rail gun? It would big and expensive, I think.

 

[GTOM]

An incremental advance in carbon nano-fibre tech?

Last I heard, the rate-limiting step wasn't the strength of the fibre, it was the ability to produce 35,000 miles of it (and do so in space).

Well, for story purposes, it should be destructible from the ground.

 

[oz93666]

Imagine a long tube about a meter in diameter , 100km long . The start of the tube is horizontal but gently curves upwards using a tall mountain , like Everest , for support , perhaps tunneled through the mountain at places , end of the tube is about 30deg to horizontal ...
So the tube has air evacuated , the capsual is electromagnetically accellerated , low g force due to long length and gentle curve , when capsule reaches end of tube closure (door) is opened at end of tube to let capsule out.

 

[GTOM]

Imagine a long tube about a meter in diameter , 100km long . The start of the tube is horizontal but gently curves upwards using a tall mountain , like Everest , for support , perhaps tunneled through the mountain at places , end of the tube is about 30deg to horizontal ...
So the tube has air evacuated , the capsual is electromagnetically accellerated , low g force due to long length and gentle curve , when capsule reaches end of tube closure (door) is opened at end of tube to let capsule out.

the nasty part is when air hit it. At another place, they said no present day material withstand that if cargo reach orbital speed in thick air.

 

[oz93666]

Well , there won't be much air to hit way above the height of Mt Everest .. Search shows it's a third of sea level atmospheric pressure .... at Mach 20 a nicely pointed nose on the capsule should cut through the remaining air without too much drag or heating , and then a very small booster rocket ignites.

 

[oz93666]

The above is a bit like Bransons 'Virgin Orbit' idea which failed from lack of finance ... only he took the payload (in a small rocket ) up to Mt Everest height in a 747 , then fired it into orbit ... If you can get above those first 10km of dense atmospher you save a lot of fuel/energy.... The big difference is , his rocket didn't even have Mach 1 at launch.

 

[.Scott]

How about using a balloon to carry the second stage to 30Km altitude.
If you use this in your story, I wouldn't call it "Acme Space". Not only would that be a hokey name, but it's also the name of the company that plans on doing it (and the source of the rendition above).

 

[Drakkith]

If you can get above those first 10km of dense atmospher you save a lot of fuel/energy....

Not really. You need about 7800 m/s of delta V to get to orbital speed, and an additional 1,500 to 2,000 m/s to account for gravity losses, drag, etc. Of that additional delta V, the majority of it, between 1,000 and 1,500 m/s will be lost to gravity losses. So you're looking at maybe 500 m/s of delta V lost to drag. This accounts for only around 5% of total delta V. Raising a multi-thousand-ton rocket up to any altitude would be far more expensive, complicated, and dangerous than simply launching it from the ground.

I do like the idea of a long launch tube that accelerates the rocket up to several km/s. It would be a massive project, but maybe you could get the end of the tube above 50,000 ft. Additionally, since you aren't accelerating the rocket using chemical engines during this whole process (which means mass isn't nearly as much of an issue), you have much more leeway as to how you build it. You could build some sort of cheap protective cover around the fragile rocket that better withstands the large aerodynamic forces and heating, which could then be jettisoned to fall back to Earth once the rocket is above 300,000 ft to save weight. Then you ignite the rocket engines and accelerate up the rest of the way conventionally.

Even if you could get just 2.5 km/s, this is an ENORMOUS weight savings. The Saturn V first stage had a mass of 2,200 tons out of a total of 2,800-2,900 tons for the total mass of the launch vehicle, but only accelerated the vehicle up to about 2.4 km/s. You could potentially reduce the size/mass of the rocket by 2/3 using this method.

 

[.Scott]

Not really. You need about 7800 m/s of delta V to get to orbital speed, and an additional 1,500 to 2,000 m/s to account for gravity losses, drag, etc. Of that additional delta V, the majority of it, between 1,000 and 1,500 m/s will be lost to gravity losses. So you're looking at maybe 500 m/s of delta V lost to drag. This accounts for only around 5% of total delta V.

It's worse than that. At low altitudes, the rocket needs to throttle back to limit aerodynamic forces. So, you have a combination of drag and throttle that's holding you down at the worse possible time. At launch, it's not just delta V, it's specific impulse and those "gravity loses". The lower your specific impulse, the more costly those "gravity loses" will be. In the worse case, your specific gravity would fail to move the rocket from the launch pad - no matter how long it burns.

 

[DaveC426913]

Raising a multi-thousand-ton rocket up to any altitude would be far more expensive, complicated, and dangerous than simply launching it from the ground.

This is only true for early attempts.

Spaceports get established wherever the conditions are best for the mission.

If the future GTOMites decide they've got a technology that works well if it's launched from a high altitute, then from a high altitude is where it will get launched. A city and industry at the top of the mountain will follow. Any costs will taper off with use.

Other than that, I agree with your analysis.

 

[Drakkith]

Forgot to post a source for my last post:

On another note, my copy of Space Propulsion Analysis and Design gives the following delta-v losses for various rockets (I'm only going to give the gravity and air resistance losses for comparison):

Ariane A-44L: Gravity Loss: 1576 m/s Drag Loss: 135 m/s
Atlas I: Gravity Loss: 1395 m/s Drag Loss: 110 m/s
Delta 7925: Gravity Loss: 1150 m/s Drag Loss: 136 m/s
Shuttle: Gravity Loss: 1222 m/s Drag Loss: 107 m/s
Saturn V: Gravity Loss: 1534 m/s Drag Loss: 40 m/s (!!)
Titan IV/Centaur: Gravity Loss: 1442 m/s Drag Loss: 156 m/s

From Reply #3 at this link.

Drag losses are miniscule, representing something like 1% or less of total delta V capability of the launch system.

At launch, it's not just delta V, it's specific impulse and those "gravity loses". The lower your specific impulse, the more costly those "gravity loses" will be. In the worse case, your specific gravity would fail to move the rocket from the launch pad - no matter how long it burns.

Indeed. Note how the Saturn V is almost tied for the most Gravity Loss. I suspect this is due to its low thrust-to-weight ratio of roughly 1.15 at liftoff. I don't know the numbers of the other vehicles, but my 1000+ hours in Kerbal Space Program make me believe that this is the case. I may not be a rocket scientist, but I play one in video games.

This is only true for early attempts.

Spaceports get established wherever the conditions are best for the mission.

If the future GTOMites decide they've got a technology that works well if it's launched from a high altitute, then from a high altitude is where it will get launched. A city and industry at the top of the mountain will follow. Any costs will taper off with use.

Other than that, I agree with your analysis.

Without getting into near-magic levels of technology it's difficult to imagine any way to lift a rocket multiple kilometers into the sky that would be cheaper, easier, and less risky than just making the rocket slightly larger and more powerful.

Launching from high altitude sites is usually avoided in the present day because of difficult and expensive transportation costs (among other reasons) compared to, say, sailing it to the launch site via barge.

Now, if you want to create an entirely different launch technology that works best from high altitudes, then all this goes out the window.

 

[DaveC426913]

Without getting into near-magic levels of technology it's difficult to imagine any way to lift a rocket multiple kilometers into the sky that would be cheaper, easier, and less risky than just making the rocket slightly larger and more powerful.

Launching from high altitude sites is usually avoided in the present day because of difficult and expensive transportation costs (among other reasons) compared to, say, sailing it to the launch site via barge.

Except, if the industry of space launches ramps up, the overhead of formerly remote location drops to near zero as the dependent indistries and infrastructure come to the launch facilities to form fully-fledged, lively permanent cities. Eventually, there are no transportation costs because it has become the hub of the space industry.

Now, if you want to create an entirely different launch technology that works best from high altitudes, then all this goes out the window.

Which is essentially what the OP asked for.

 

[Drakkith]

Except, if the industry of space launches ramps up, the overhead of formerly remote location drops to near zero as the dependent indistries and infrastructure come to the launch facilities to form fully-fledged, lively permanent cities. Eventually, there are no transportation costs because it has become the hub of the space industry.

There are always transportation costs. Either the fully/partially assembled spacecraft and launch vehicle, or the materials to build it. But I agree with the spirit of what you're getting at in that if the launch technology favors high alititude vs low altitude launches then transportation costs are essentially already built in to the "favors high altitude" thing. That is, it wouldn't be favored if the transportation costs were too high to make it favorable.

Well , there won't be much air to hit way above the height of Mt Everest .. Search shows it's a third of sea level atmospheric pressure .... at Mach 20 a nicely pointed nose on the capsule should cut through the remaining air without too much drag or heating , and then a very small booster rocket ignites.

I wouldn't be too sure about that. Reentry from orbital or above-orbital speeds takes place almost entirely above 150,000 ft. Slamming into the air at mach 20 at 30,000 ft would place incredibly high forces and heating on the front of the vehicle.

You're also not likely to get out of that thick air very quickly, because you can't go mostly upwards at mach 20 or you'll be put into one hell of an eccentric orbit when you do finally light up your engine. That is, your apogee will be very, very high while your perigee will be very low. So you'll be making a very shallow rise which will dramatically increase the time you're stuck with that extremely high force and heat.

To me the most reasonable improved launch system just needs to get the vehicle up to about 2,000 m/s. That shaves off nearly two-thirds of launch vehicle mass and is essentially removing the need for the entire first stage of a some conventional rockets. That's a pretty substantial gain for only modest requirements.

Note that I'm not saying that launching from high altitude is not beneficial. It is. But not enough, at least currently, to offset all the costs of launching from a mountain. With increased engine efficiency from the reduced air, and if you design your rocket a little lighter to account for reduced max Q, you'd probably save 10-15% total weight. This is a non-negligible amount, but not quite enough to make it worth it at this time.

 

[Rive]

I write an sf story, and an important part is an attack on a big, expensive space launch system on Earth.

A bit against the title, but you can consider chemical rockets assisted by linear electric motors (on rails).
Look up 'StarTram'.

 

[Algr]

I write an sf story, and an important part is an attack on a big, expensive space launch system on Earth.
But what system could be built without pretty much magic? Looks like space elevator couldnt be made even from carbon nanotubes.
Maybe a space cannon, that could launch cargo to space with suborbital speed, then lifted further with nanotube cables and a space station below GEO orbit?

If you story needs big infrastructure on Earth, then I don't think you are going to find anything less "magic" than a space elevator. Since this is an established idea in both fiction and real science, you'll be able to avoid getting into too much detail about how it works. This is a very good thing, as it future-proofs your story.

As other have said: If there were significant benefit from launching at high altitudes, we'd already be launching from Colorado, and not Florida. Spin launch might someday work for blocks of lead, steel or ice, but humans or any kind of electronics would never survive all the G forces.

If you want some plausible tech, you could say that someone invented a jet engine that can transition to a rocket once it gets high enough. This would reduce the need to cary oxidizer, and would not need to travel at high energy-wasting speeds while in the atmosphere. But that could launch from all sorts of places, and might undermine your story's need for the big expensive space launch system.

 

[DaveC426913]

See post 11

OP needs it to be attacked from ground level.
Magic beanstalks are (mostly) immune from ground level attacks.

 

[Ken Fabian]

Ground based lasers fired up the butt, to superheat air or vaporise an onboard (non-flammable) propellant is another hypothetical launch method. I seem to recall that being used in a novel by Donald Kingsbury, along with an orbital rail gun style 'station' that could capture them and relaunch back to Earth or send them out towards the moon, with a moon colony.

I must admit none of the possibilities actually seem feasible to me - fiction seems an appropriate use for them.

 

[Filip Larsen]

Ground based lasers fired up the butt, to superheat air or vaporise an onboard (non-flammable) propellant is another hypothetical launch method. I seem to recall that being used in a novel by Donald Kingsbury

I recall first reading about such a launch system in The Millenial Project where it is step 3 out of 8 easy steps to colonizing the galaxy. Apparently (and news to me) the technology has already been pioneered a fair bit by Leik Myrabo.