Why no Star Tram?

[3blake7]

The ISS cost a lot of money, I've seen estimates as low as 100 billion and as high as 400 billion. I've also seen arguments that it wasn't really worth it. I was just wondering why we didn't spend that money on a Star Tram.

 

Right now, current rockets cost about $18000 per kilogram of payload. Space X, with their reusable first stage rockets, could bring that down to as low as $1200 per kilogram. I also learned about the Star Tram and on their site they claim that it could bring the cost down to $40 per kilogram. The site claims that the Star Tram can be built with known technology and materials unlike the Space Elevator. The Space Elevator gets so much attention even though there is no known material strong enough (not even carbon nanotubes).

 

I feel like I'm missing something, am I?

 

http://www.startram.com/

https://en.wikipedia.org/wiki/StarTram

http://www.maglaunch.com/

Edited July 18, 2017 by 3blake7

[Phi for All]

I find your incredulity misplaced. Isn't this like asking why we bothered with vinyl and tape recording media when we should have spent that money on compact disk technology?

[swansont]

The site claims that the Star Tram can be built with known technology and materials unlike the Space Elevator.

 

 

 

Until they build it, we don't really know how accurate these claims are. "More advanced technology would be required for the Generation 2 system for passengers, with a longer track instead gradually curving up at its end to the thinner air at 22 kilometres (14 mi) altitude," 22 km? Seriously? And right there is an admission that unknown technology would be required.

 

The wikipedia page mentions feasibility studies. But presumably these studies use the same fundamental approach that told us the ISS would cost a lot less than it did, and that the shuttle program would launch every month for a lot less money. They want to build this tunnel in a mountain. What's the track record of tunnels for other projects coming in under budget?

[Manticore]

I came up with a similar idea several years ago. The tunnel would have been up the west slope of Kilimanjaro (19,000 ft).

The main problem I thought of was the air in the tunnel compressing ahead of the launch vehicle - once you get close to supersonic that's going to be like trying to push through a brick wall.

[Endy0816]

Could pump the air out. Would add to the cost though.

[Carrock]

IIRC Robert Heinlein in "The man who sold the moon" came up with a similar idea in the 1940s or 1950s, to eliminate the first stage in a manned lunar spacecraft.

[Manticore]

Pumping the air out gets complicated. Remember, you have 19,000 feet's worth of pressure differential. If you just pump air out at the bottom then you will get more air rushing in at the top to replace it - giving you yet more resistance. If you close off the top, you are going to be faced with the problem of opening a massive door in a ridiculously short time at exactly the right instant (assuming you don't actually want a huge explosion at that point).

IIRC Robert Heinlein in "The man who sold the moon" came up with a similar idea in the 1940s or 1950s, to eliminate the first stage in a manned lunar spacecraft.

I suspect it goes back much farther than that (you might even make a case that the giant cannon in Jules Verne's "From the Earth to the Moon" is basically the same principle - even though he got the figures hopelessly wrong).

[swansont]

Pumping the air out gets complicated. Remember, you have 19,000 feet's worth of pressure differential. If you just pump air out at the bottom then you will get more air rushing in at the top to replace it - giving you yet more resistance. If you close off the top, you are going to be faced with the problem of opening a massive door in a ridiculously short time at exactly the right instant (assuming you don't actually want a huge explosion at that point).

 

 

This is covered in the OP's wikipedia link. There is a mechanical valve at the end, and a plasma window for when the valve is briefly opened. There would be no explosion, unless someone actually detonated some explosives.

 

19,000 feet of pressure differential is roughly half of an atmosphere, which makes it marginally easier to pump out. Pumping out the volume itself to much lower pressure is the challenge.

[Manticore]

Can you avoid Murphy's law? Sooner or later there will be a failure of the mechanical valve. The explosion is when your launch vehicle hits it. You almost certainly can't abort the mission halfway up the tube.

Edited July 18, 2017 by Manticore

[swansont]

Can you avoid Murphy's law? Sooner or later there will be a failure of the mechanical valve. The explosion is when your launch vehicle hits it. You almost certainly can't abort the mission halfway up the tube.

 

 

You have the plasma window, too. So there's redundancy. You would have interlocks. The launch can't proceed past a certain point if the valve fails.

 

The proposal has lots of question marks, IMO. This isn't one of them. Large-scale vacuum has been in operation at CERN for years.

[Manticore]

I can't find any reference to tube exit speed on their site. (OK. I've got bad stomach pain at the moment & could easily have missed it.)

My own intention was to exit at Mach 3 and fire up a scramjet.

The thought of any kind of instability in the Maglev system at those speeds combined with the necessarily small clearance between the vehicle and tube would also worry me. (A reliable, working scramjet is another problem altogether.)

[3blake7]

You need like 8 km/s to orbit. The Gen 1 probably needs to have a higher exit velocity since it exits at a lower altitude and has to deal with more atmospheric friction. The Gen 2 exits at 22 km so it's probably less than Gen 1. They have a book which goes into more detail but it's about $10 on Amazon.

Edited July 19, 2017 by 3blake7

[swansont]

I can't find any reference to tube exit speed on their site. (OK. I've got bad stomach pain at the moment & could easily have missed it.)

My own intention was to exit at Mach 3 and fire up a scramjet.

The thought of any kind of instability in the Maglev system at those speeds combined with the necessarily small clearance between the vehicle and tube would also worry me. (A reliable, working scramjet is another problem altogether.)

 

 

It's mentioned in the wikipedia article. Around 9 km/s, to allow for loss of speed when entering the atmosphere and still maintaining (close to) escape speed. Plus a small rocket for orbit circularization.

[3blake7]

On 7/17/2017 at 2:09 PM, Phi for All said:

I find your incredulity misplaced. Isn't this like asking why we bothered with vinyl and tape recording media when we should have spent that money on compact disk technology?

I looked up the timeline of the ISS, maglev tech, etc and yea, you are right, it's like asking why no CD instead of tapes. I also recently saw a documentary on the space shuttle and they originally estimated that it would be a lot cheaper and could be flown a lot more frequently than it turned out. The Star Tram estimates are probably really optimistic, there would be cost over-runs, engineering hurdles, etc.