Totally crazy idea: Space launch site on Mt Kilimanjaro?

[hkultala]

Not sure why this thread is zombified, but since it is:

Why bother with existing mountains? Build your own.

Open frame towers can be built taller than the tallest buildings for orders of magnitude lower costs. For a long time, antenna masts had to be excluded from "tallest building in the world" records, because of they always won. (We don't really need tall antennas any more, so buildings are back in front.)

For the price of Burj Khalifa, and with no exotic materials, you could go many, many times taller with a simple open frame tower. Above the bulk of the atmosphere, taller than any mountain. String many such towers in a row near the equator and hang a long platform from the top like a suspension bridge, but upwardly sloping towards the east. Run a rail up the length. Launch a rocket on a sled on the rail.

Perhaps the "first stage" would be permanently mounted to the sled, braking before the end, fully and immediately reusable. "Second" stage would ignite during the loft towards apogee after it leaves the end of the platform.

Sure it would cost billions. And billions. But how much has SLS cost so far?

An antenna mast has to hold an antenna and basestation that weight maybe some tens of kilograms.
And the weight of a 100kg maintainance person.

A heavy lift rocket weighs over million kilograms.

Bulding a super-high tower for launch use MUCH more expensive than you think.

[IRobot]

For the price of Burj Khalifa, and with no exotic materials, you could go many, many times taller with a simple open frame tower.

For the price of Burj Khalifa you can launch 21 Falcon 9 disposable rockets.
What about maintenance and operational costs? Forget it, the improvement is marginal compared to the costs.

Sure it would cost billions. And billions. But how much has SLS cost so far?

Compare with commercial launch providers, not with SLS.

[gin455res]

If we consider reusable rockets, the F9 uses the thick atmosphere to slow down. What’s the fuel penalty for F9 to land at 19,000 feet?

And I always thought the point of Kilimanjaro was to rocket sled up the slope and launch already at some speed.

I'm interested if an upper-stage with perhaps 3 or 5 engines would gain any useful ISP improvement (on the way up) with a higher expansion-ratio* central landing engine, and/or any engine mass reduction** that might end up in an improvement in mass fraction.

*enabled by a high altitude landing pad
**enabled by better T/W after staging. i.e. all engines thrusting for longer after staging, instead of just the vacuum engines. Might this allow the engine to be slightly downsized?
And what constrains landing engine expansion ratio, landing air pressure or 'effective air pressure' during supersonic retro-propulsion?

[RobLynn]

19000 feet engine Isp would only be something like 5% higher than at sea level.  with air density about half of sea level terminal velocity will be approximately 40% higher, so would need something like 40% more landing fuel.

[2008rlctx]

Reviving this old thread!

Does anyone know of any threads that consider the effect on this idea of tunneling (a la BoringCompany) straight down into the mountain as deep as you'd like to go with the intent to then evacuate said tunnel of air for a launch, thus eliminating air resistance for the first 18km of the 100km? The first 18km also having the highest density of air compared to the rest of the 82km distance to space. Per this link: https://upload.wikimedia.org/wikipedia/commons/9/9d/Comparison_US_standard_atmosphere_1962.svg , the density of air at 18km seems to be about 1/10 of that at sea level. So this concept would get you past 90% of the air?!

One step further, the "first stage" could be integrated into the tunnel via a vertical electric sled that accelerated the LV as much as possible and stayed in the tunnel.

Some type of system would need to be employed to keep the air out during the LV's trip through the tunnel, as well as release the LV out the end, but doesn't seem like an insurmountable obstacle.

[Phil Stooke]

Wouldn't you need a mountain 18 km tall to make that work? 

[2008rlctx]

Ooops...it appears as though I misread the picture posted in the thread. The Mountain is much shorter. Back to reality.

[Paul451]

In addition to the height thing...

the density of air at 18km seems to be about 1/10 of that at sea level. So this concept would get you past 90% of the air?!

The air inside the tunnel will have the same height-variance as the air outside. So if you evacuate it to 10% pressure at the bottom of the tube, it will be much less than outside air pressure at 18km. Hence you'll still have the problem of hitting a wall of pressure as you exit.

[deruch]

Back to reality.

Oh, there goes gravity.

[tl6973]

Reviving this old thread!

Does anyone know of any threads that consider the effect on this idea of tunneling (a la BoringCompany) straight down into the mountain as deep as you'd like to go with the intent to then evacuate said tunnel of air for a launch, thus eliminating air resistance for the first 18km of the 100km? The first 18km also having the highest density of air compared to the rest of the 82km distance to space. Per this link: https://upload.wikimedia.org/wikipedia/commons/9/9d/Comparison_US_standard_atmosphere_1962.svg , the density of air at 18km seems to be about 1/10 of that at sea level. So this concept would get you past 90% of the air?!

One step further, the "first stage" could be integrated into the tunnel via a vertical electric sled that accelerated the LV as much as possible and stayed in the tunnel.

Some type of system would need to be employed to keep the air out during the LV's trip through the tunnel, as well as release the LV out the end, but doesn't seem like an insurmountable obstacle.

You need to read Terminal World by Alastair Reynolds :-)

[hkultala]

Reviving this old thread!

Does anyone know of any threads that consider the effect on this idea of tunneling (a la BoringCompany) straight down into the mountain as deep as you'd like to go with the intent to then evacuate said tunnel of air for a launch, thus eliminating air resistance for the first 18km of the 100km?

You cannot easily both keep the air out and also let the rocket out

You would need some kind of huge air-tight doors, but the millisecond you start opening the doors, the tunnel starts to pressurize at huge speed, and the rocket hits a huge wave of air dropping very fast from the opening.

Some kind of huge airlock might help and decrease the mass of the air in the wave, but flying through an airlock at very high speed does not sound very safe..

[Asteroza]

Don't most designs have a mixed exit technology setup, with a primary physical airlock door, and a plasma window that the projectile/spacecraft passes through?

[Paul451]

Don't most designs have a mixed exit technology setup, with a primary physical airlock door, and a plasma window that the projectile/spacecraft passes through?

Out of curiosity, what's the largest plasma window anyone has produced?

[edit: My reason for asking is that looking around the googles, the diameter numbers are typically given in single-digit millimetres, not multiple metres.]

[RobLynn]

You cannot easily both keep the air out and also let the rocket out

You would need some kind of huge air-tight doors, but the millisecond you start opening the doors, the tunnel starts to pressurize at huge speed, and the rocket hits a huge wave of air dropping very fast from the opening.

Some kind of huge airlock might help and decrease the mass of the air in the wave, but flying through an airlock at very high speed does not sound very safe..

Even at 10m diameter it would be quite feasible to fully open a door in less than 0.1s - About 50g opening acceleration on two half doors would suffice.  Magnetically restrained pneumatic rams, pyrotechnic ram actuators etc.

The air running down the end of the opening tube is (from bernoullis equation) at just the same total pressure (dynamic+static) as the outside air.  A ring of high powered steam nozzles at 45° to nozzle end might also provide some reduction in inflow.

Capital costs, siting issues and inflexible trajectories of catapults make them unlikely choice for foreseeable future.  air-augmented boosters of some type (like tip-rocket driven transonic fans similar to Roton concept) might eventually have a chance if flight rates are high enough to cover their higher development cost.

[IRobot]

Reviving this old thread!

Please, please, please, let bad ideas die!

[speedevil]

Reviving this old thread!

Please, please, please, let bad ideas die!

Or find a billion dollars, and build a launch pad on top of Kilimanjaro. That'd be cool too.

[sghill]

Reviving this old thread!

Does anyone know of any threads that consider the effect on this idea of tunneling (a la BoringCompany) straight down into the mountain as deep as you'd like to go with the intent to then evacuate said tunnel of air for a launch, thus eliminating air resistance for the first 18km of the 100km?

You cannot easily both keep the air out and also let the rocket out

You would need some kind of huge air-tight doors, but the millisecond you start opening the doors, the tunnel starts to pressurize at huge speed, and the rocket hits a huge wave of air dropping very fast from the opening.

Some kind of huge airlock might help and decrease the mass of the air in the wave, but flying through an airlock at very high speed does not sound very safe..

Let it burst through several bladders of reinforced cellophane or something similar. It's not in a complete vacuum in the tunnel, just a partial one. Each bladder only needs one or two PSI difference between the next one. Then it becomes a balancing act between the burst strength of the bladder and the impact force the projectile experiences as it bursts through each new bladder.  The lower the burst strength, the less impact the projectile feels, but the more bladders are needed. It is easy to replace each bladder between flights. Just slide in a new "wafer" and pull out the old ones.

BTW, Kilimanjaro is a world heritage site. It won't be the launch site mountain. Something in the Andes would fit the bill nicely though.

[Paul451]

Let it burst through several bladders of reinforced cellophane or something similar.

Without doing the maths, my gut reaction is that the strength of the plastic, in order to hold the pressure difference (the weight of the air it is supporting), must be higher than the pressure difference itself. So hitting the "bladder" will always be worse than hitting the air itself.

BTW, Kilimanjaro is a world heritage site. It won't be the launch site mountain. Something in the Andes would fit the bill nicely though.

Well, if we're dreaming up magic launch systems, why not just build a stay-supported tower at the required height, hang the launch tube from that. With modern materials and engineering, you should be able to go higher than a mountain. And probably cheaper than drilling a vertical shaft through a mountain. Or if money is no object, then using the most advanced composites, you might be able to get a line of towers up around 30-50km in height, running a few hundred km or so across a suitably friendly continent. Then your launch rail can be open-air and mostly horizontal (30°?). Add more sections as technology improves, going higher and longer, until you've got a 1000km line going up to 100km release point; 4g on the rail and no need for a second stage to LEO, just a circularisation burn.

[Kaputnik]

Reviving this old thread!

Does anyone know of any threads that consider the effect on this idea of tunneling (a la BoringCompany) straight down into the mountain as deep as you'd like to go with the intent to then evacuate said tunnel of air for a launch, thus eliminating air resistance for the first 18km of the 100km?

You cannot easily both keep the air out and also let the rocket out

You would need some kind of huge air-tight doors, but the millisecond you start opening the doors, the tunnel starts to pressurize at huge speed, and the rocket hits a huge wave of air dropping very fast from the opening.

Some kind of huge airlock might help and decrease the mass of the air in the wave, but flying through an airlock at very high speed does not sound very safe..

Would it not make more sense to open a door at the bottom of the shaft, allowing air pressure to surge up the shaft from behind the vehicle, thus giving it a boost? You would want to time this so that by the time the vehicle reaches the exit, there is little pressure differential between the air around it in the tube, and the air at the exit.

[Asteroza]

Don't most designs have a mixed exit technology setup, with a primary physical airlock door, and a plasma window that the projectile/spacecraft passes through?

Out of curiosity, what's the largest plasma window anyone has produced?

[edit: My reason for asking is that looking around the googles, the diameter numbers are typically given in single-digit millimetres, not multiple metres.]

I was under the impression that plasma windows proposed to cover the neutron spallation target of an accelerator driven subcritical nuclear reactor to separate the spallation target boiloff vapor from the particle accelerator beamline vacuum were somewhat large, but now that I think about it, the pressure difference would be a lot less than between atmosphere at the top of a mountain based vacuum tube and a vacuum accelerator tube.

That said, in literature a plasma window is usually mentioned as part of the muzzle exit architecture. Somebody clearly thought large diameter plasma windows are a thing (perhaps at increased energy cost)?

That sudden slamming by the spacecraft/projectile into the pressure differential is still pretty brutal however.

I wonder if you could cheat a little, by using inflatable rings strung together to form a long hollow floating tube anchored to the muzzle and appropriately tethered to match the trajectory, and shift the airlock/plasma window to the top of of the floating tube, where the pressure inside the inflatable tube hollow zone more closely matches the atmosphere at the top of the tube. You get no acceleration in the floating tube, but you do get an evacuated pathway to a lower pressure region.