Magnetic Rail Rocket Assist For Starship X

[Spacescifi]

 

Starship X is intriguing mainly because it is the only legitimate scifi spaceship mankind is developing right now.

Yet I think Elon is going about it wrong, assuming he is willing to pay more money... which I am not sure he is.

 

We have magnetic rails for trains. We have vacuum chambers. Combine the two into a long tube and what have you got?

A space launch tube!

There is nothing about thus that impossible either, since both are established technologies. The cost would be high due to reinforcing the rails to hold starship's weight, and also cooling systems for the rails as well as powerful magnets.

 

Here is one proposition (although I am users here can calculate better ratios than I), construct a magnetic rail 400 kilometers long, seal it inside a vacuum tube. Close and open the end of the tube via a plasma window (plasma screens that can screen off air, they are real). Toggle it on and off with ease so that the high velocity starship x will encounter minimal air inside the tube as it flies out angled toward the sky at supersonic speeds. The nose can be part ablative and part 'sweating' so that it survives the rigors of the lower atmosphere.

High mass is our friend here, as the atmosphere will slow a heavy spaceship's ascent to orbit slower than a lightweight one.

The goal is to at least clear 100 kilometers of atmosphere on the inertia given by the tube alone.

Next engage the engines to finish off our orbital velocity. And done!

Results? More payload to orbit and also better resuability, since the propelkant saved can be used for a forced thrust landing if the need arises.

 

 

Edited October 27, 2019 by Spacescifi
Plasma

[Shpaget]

49 minutes ago, Spacescifi said:

There is nothing about thus that impossible either, since both are established technologies.

Neither are established technologies.

Existing maglev trains are little more than technology demonstrators.

Vacuum chambers for transport are not even that. What Elon Musk happily appropriates and calls Hyperloop has been talked about for over 200 years and is no closer to "established" than in the 18th century. It's a gimmick.

When you run out of vacuum tube and hit the atmosphere, you die.

Finally, ideas of space guns have been around since Jules Vern. They don't work.

[Spacescifi]

16 minutes ago, Shpaget said:

Neither are established technologies.

Existing maglev trains are little more than technology demonstrators.

Vacuum chambers for transport are not even that. What Elon Musk happily appropriates and calls Hyperloop has been talked about for over 200 years and is no closer to "established" than in the 18th century. It's a gimmick.

When you run out of vacuum tube and hit the atmosphere, you die.

Finally, ideas of space guns have been around since Jules Vern. They don't work.

 

Japan uses mag-lev rails as do some trains. If we can build it, we can do it I say.

And vacuum chambers we know how to make... just suck all the air out a room. Granted, not as good a vacuum as outer.space, but we take what we can do.

When you run out of atmosphere you die?

Not necessarily. It is all in the calcultations, as my numbers may well be waay off.

Even so, there is a calculated sweet spot speed for how fast you can go through atmosphere before ablation kicks in. There is also a calculated limit on how much certain materials can take before melting.

Make no mistake, I expect my version of starship x to have a glowing nose in orbit.

The propellant savings may be less than I hoped if we have to limit it for the sake of surving the atmosphere, but it would still be greater than simply launching into space solely using onboard propellant.

Edited October 27, 2019 by Spacescifi

[AngrybobH]

This is something I always wished would work but, sadly, it does not. The forces experienced upon instantaneously hitting the atmosphere would shred anything we could build. Think about it this way, would you rather slow down in a car from 100 to 0 in 200 meters or 200 millimeters? The energy is the same but the time it happens in is vastly different. Another thought for you. Why do rockets worry about max Q? 

5 hours ago, Spacescifi said:

The goal is to at least clear 100 kilometers of atmosphere on the inertia given by the tube alone.

What speed would you be going at the exit? at what altitude/air density? what is the drag coefficient of the ship? Answer those questions and you will see that you would kill all the crew with Gs and tear the ship apart on exit unless it was made from unobtanium with an unrealistic profile. But the crew would be dead and all the cargo squished so, what would be the point? Lowering the exit speed would easily make the whole system irrelevant. And sure, more mass slows down less in atmo but then you have more mass. So more engines and fuel for circularization, more thrusters for attitude control, more fuel needed for a given DV, harder to slow it down when needed...this makes the whole ship worse for everything else. I'm not even sure the math would allow you to get the mass and drag into the correct ratio for this to even happen.

Now if you ditched the vacuum chamber and then built a mag rail system higher than anything humans have ever built and it was capable of accelerating something to a typical first stage speed then you could eliminate the first stage. But, that definitely has both feet firmly planted in scifi territory. And it would have a fixed angle so, only one inclination would be possible. Great for orbital construction but not so for every other mission.

[cubinator]

A maglev might be of use on the Moon, but not on Earth. The atmosphere is too thick - in order to escape it from very low, your ship would burn like a meteor, and at similar speed. To build the rail above the atmosphere where it could actually be used would require a superstructure magnitudes bigger than anything we can actually construct - there are no materials we have which could do it. Remember, our largest spire is only 0.8 km tall.

By the way, recall the instance of a nuclear bomb that was detonated below ground and launched a manhole cover into the air at 60 kilometers per second. The manhole cover is thought to have immediately disintegrated due to the immense force and heat of the air, failing to leave the atmosphere.

Edited October 28, 2019 by cubinator

[Shpaget]

9 hours ago, Spacescifi said:

 

Japan uses mag-lev rails as do some trains. If we can build it, we can do it I say.

For tests only.

There are only a handful operational maglev systems (all in China), and only one of them is high speed.

9 hours ago, Spacescifi said:

And vacuum chambers we know how to make... just suck all the air out a room. Granted, not as good a vacuum as outer.space, but we take what we can do.

It's a lot more complicated than that. You are proposing to build the largest vacuum chamber in the world, by a huge margin, shove the highest speed (by large margin) land vehicle in it and shoot it out the other end, suddenly making it the fastest atmospheric flying vehicle (by large margin).

9 hours ago, Spacescifi said:

When you run out of atmosphere you die?

Not necessarily. It is all in the calcultations, as my numbers may well be waay off.

You haven't presented us with any numbers.

9 hours ago, Spacescifi said:

Even so, there is a calculated sweet spot speed for how fast you can go through atmosphere before ablation kicks in. There is also a calculated limit on how much certain materials can take before melting.

The sweet spot for how fast you can go through atmosphere and the sweetspot for how fast you can make your train go won't necessarily be the same number.

9 hours ago, Spacescifi said:

Make no mistake, I expect my version of starship x to have a glowing nose in orbit.

The propellant savings may be less than I hoped if we have to limit it for the sake of surving the atmosphere, but it would still be greater than simply launching into space solely using onboard propellant.

Propellant is cheap.

Megastructures are not.

[farmerben]

We should have this for airliners.  Ramjet passenger planes.  Save a turbine.  

[magnemoe]

On 10/27/2019 at 10:41 PM, Spacescifi said:

 

Japan uses mag-lev rails as do some trains. If we can build it, we can do it I say.

And vacuum chambers we know how to make... just suck all the air out a room. Granted, not as good a vacuum as outer.space, but we take what we can do.

When you run out of atmosphere you die?

Not necessarily. It is all in the calcultations, as my numbers may well be waay off.

Even so, there is a calculated sweet spot speed for how fast you can go through atmosphere before ablation kicks in. There is also a calculated limit on how much certain materials can take before melting.

Make no mistake, I expect my version of starship x to have a glowing nose in orbit.

The propellant savings may be less than I hoped if we have to limit it for the sake of surving the atmosphere, but it would still be greater than simply launching into space solely using onboard propellant.

problem with mag-lev trains is that they are not that much faster than high speed rail and much more expensive and less flexible. 
With high speed rails you can easy switch the train over to the other track if needed as an example. yes this reduces capasity and speed but make maintenance much easier  

Downside with an large space gun is that its an extremely expensive mega project, even worse something the size to launch something like starship. 

[wumpus]

20 hours ago, farmerben said:

We should have this for airliners.  Ramjet passenger planes.  Save a turbine.  

Would only really make sense for a Concorde replacement.  Ramjets might be a plausible replacement for jets, high bypass turbofans not so much.

Back on topic, before asking this forum about something fairly well studied (ground-based launch schemes) you might try googling our patron saint:

 

Considering Elon Musk came up with the whole hyperloop idea and then gave it away (presumably because he couldn't afford to develop it, nor was worried about people using it to compete with him), I don't see why you would think that he never considered using it to launch rockets.

The biggest issue for this type of thing is simple: fuel doesn't matter.  It is hard for anybody new to rocket science to get through their head (and probably doesn't help any sci-fi work to get it right), but until rocket science becomes incredibly more mature, there's no reason to optimize for fuel.  Fuel means mass, and optimizing for mass makes sense, but real rocket science isn't like KSP and fuel tanks are far, far lighter than you might think.  We can typically afford to lift the fuel.  Last I heard, Spacex charges ~$60-100Megabucks to launch a rocket.  Fuel costs are $0.1Megabucks.  Until you get rocket re-use to be a trivial thing and make launching a rocket almost as cheap as launching a plane (some of the people cheering in the background of spacex launches are presumably non-launch employees, but plenty of them are certainly doing required work).  And spacex is only used as they are both far more transparent to their competition and tend to have reduce costs elsewhere more aggressively.  It will take some time before anyone cares enough to try to reduce the cost of fuel.

Long ago I computed a rule of thumb that said that a rocket basically consumed half it's mass in fuel for every "mach 3's" worth of velocity.  I think it was based on the Saturn V (with a TWR of ~1.2) and I doubt that it true of a Falcon (or similar) that can take off with a TWR of ~1.5.  Even so, the amount of design needed to add ramjets or scramjets to a rocket to get it to mach 3-9 would be formidable.  I could see such a thing [possibly just some sort of "starship heavy" with air-augmented boosters] for a "starship refresh" (of 2030-2040), but no earlier.  And even then I suspect that there would be plenty of lower-lying fruit before they would bother with trying to reduce fuel consumption.

PS: I heard that Blue Origin scooped up DC-X team members early on.  One thing that DC-X is said to have clearly demonstrated is reduced launch costs.  If Blue Origin can get something like New Glen (or New Armstrong) out the door and into orbit, they might be far enough along the "low lying fruit" path to proceed to fuel efficiency...

 

 

[Bill Phil]

The best proposal for this I've seen is StarTram, though I think Lofstrom Loops are a better design with more interesting engineering details - not to mention the ability to potentially build a full on orbital ring with similar, but more advanced technologies.

2 hours ago, wumpus said:

The biggest issue for this type of thing is simple: fuel doesn't matter.  It is hard for anybody new to rocket science to get through their head (and probably doesn't help any sci-fi work to get it right), but until rocket science becomes incredibly more mature, there's no reason to optimize for fuel.  Fuel means mass, and optimizing for mass makes sense, but real rocket science isn't like KSP and fuel tanks are far, far lighter than you might think.  We can typically afford to lift the fuel.  Last I heard, Spacex charges ~$60-100Megabucks to launch a rocket.  Fuel costs are $0.1Megabucks.  Until you get rocket re-use to be a trivial thing and make launching a rocket almost as cheap as launching a plane (some of the people cheering in the background of spacex launches are presumably non-launch employees, but plenty of them are certainly doing required work).  And spacex is only used as they are both far more transparent to their competition and tend to have reduce costs elsewhere more aggressively.  It will take some time before anyone cares enough to try to reduce the cost of fuel.

It's not the cost of the fuel, it's the performance of the vehicle and the subsequent gains in payload mass or reduction in vehicle complexity.

I remember the ratio is something like 10 kg on the rocket gets you 1kg of extra payload, for some recent designs at least. We can get rid of dozens, if not hundreds of tonnes on the rocket, potentially improving payload to LEO dramatically. Or conversely making the vehicle itself cheaper since its performance requirements are lower. Provided of course you aren't doing this low in the atmosphere.

Basically reusable SSTOs become possible with relatively little starting velocity, even more so the faster you launch. And this is without any improvement in the rocket engines at all.

I remember some analysis done a while ago that found that even a modest velocity allows for pretty big reductions in vehicle size, making SSTO vehicles like Venturestar far more practical with already existing technologies, which is the real advantage.

It was the Maglifter concept- you can find it referenced on this page:

https://en.wikipedia.org/wiki/Rocket_sled_launch#cite_note-MaglifterMankins-5

Remember the most expensive delta-v, in terms of propellant mass per unit velocity is the initial velocity. 

"For the launch of 25,000 pounds to LEO, a preliminary analysis of the addition of MagLifter (for the reference case of 10,000 feet, 600 mph, 45 degrees), results in a 25 % reduction in vehicle dry mass and a 33 % reduction in engine mass (assuming use of a Space Shuttle Main Engine, SSME, class propulsion system)."

The gross mass (from a figure in the paper) was reduced by nearly 35%.

This greatly alleviates some of the biggest problems with SSTOs, and its only 268 m/s. The required vehicle mass ratio was also reduced but not by a tremendous amount. Still, with faster velocities the vehicle could be even lighter. The only real obstacle to such an approach is dynamic pressure.

Edited October 30, 2019 by Bill Phil

[wumpus]

12 hours ago, Bill Phil said:

The best proposal for this I've seen is StarTram, though I think Lofstrom Loops are a better design with more interesting engineering details - not to mention the ability to potentially build a full on orbital ring with similar, but more advanced technologies.

It's not the cost of the fuel, it's the performance of the vehicle and the subsequent gains in payload mass or reduction in vehicle complexity.

True, but you still need an unimaginable launch cadence to get to the point that any gains in lowering vehicle complexity outweigh the additional launcher complexity.  Adding fuel and thrust is pretty easy (adding solid boosters to non-crewed vehicles is even easier for increased thrust, then all you have to do is add additional fuel).

Once you are at the point where a somewhat supersonic rocket is relatively easily recoverable, the only question comes down to is the launcher less complex than the rocket (doubtful, although you might want to leave the atmosphere for staging) and which uses less fuel.

I'm also curious just how much benefit would be gained by merely moving the vertically launched rocket to the maglifter launch site.  That would almost certainly built at elevation, and the lower air pressure would bring a lot of gains.  Strap on some solid boosters to get your TWR up, and you have a similar system without bothering with building the whole rail assembly (and issues of getting the rocket structure to support its full weight in multiple directions).

[magnemoe]

17 hours ago, wumpus said:

Would only really make sense for a Concorde replacement.  Ramjets might be a plausible replacement for jets, high bypass turbofans not so much.

Back on topic, before asking this forum about something fairly well studied (ground-based launch schemes) you might try googling our patron saint:

Considering Elon Musk came up with the whole hyperloop idea and then gave it away (presumably because he couldn't afford to develop it, nor was worried about people using it to compete with him), I don't see why you would think that he never considered using it to launch rockets.

The biggest issue for this type of thing is simple: fuel doesn't matter.  It is hard for anybody new to rocket science to get through their head (and probably doesn't help any sci-fi work to get it right), but until rocket science becomes incredibly more mature, there's no reason to optimize for fuel.  Fuel means mass, and optimizing for mass makes sense, but real rocket science isn't like KSP and fuel tanks are far, far lighter than you might think.  We can typically afford to lift the fuel.  Last I heard, Spacex charges ~$60-100Megabucks to launch a rocket.  Fuel costs are $0.1Megabucks.  Until you get rocket re-use to be a trivial thing and make launching a rocket almost as cheap as launching a plane (some of the people cheering in the background of spacex launches are presumably non-launch employees, but plenty of them are certainly doing required work).  And spacex is only used as they are both far more transparent to their competition and tend to have reduce costs elsewhere more aggressively.  It will take some time before anyone cares enough to try to reduce the cost of fuel.

Long ago I computed a rule of thumb that said that a rocket basically consumed half it's mass in fuel for every "mach 3's" worth of velocity.  I think it was based on the Saturn V (with a TWR of ~1.2) and I doubt that it true of a Falcon (or similar) that can take off with a TWR of ~1.5.  Even so, the amount of design needed to add ramjets or scramjets to a rocket to get it to mach 3-9 would be formidable.  I could see such a thing [possibly just some sort of "starship heavy" with air-augmented boosters] for a "starship refresh" (of 2030-2040), but no earlier.  And even then I suspect that there would be plenty of lower-lying fruit before they would bother with trying to reduce fuel consumption.

PS: I heard that Blue Origin scooped up DC-X team members early on.  One thing that DC-X is said to have clearly demonstrated is reduced launch costs.  If Blue Origin can get something like New Glen (or New Armstrong) out the door and into orbit, they might be far enough along the "low lying fruit" path to proceed to fuel efficiency...

Agree, next step would be to use an air breathing first stage, this is far more challenging to design I guess they do this on smaller rockets first and only using stuff like air argumented rockets.  

[wumpus]

5 hours ago, magnemoe said:

Agree, next step would be to use an air breathing first stage, this is far more challenging to design I guess they do this on smaller rockets first and only using stuff like air argumented rockets.  

I doubt air breathing is anywhere near the next step.  I thought it was, then space-x decides to try to catch fairings.

Cost of a fairing: $6MBucks
Cost of fuel: $0.2MBucks

Even occasionally reusing a fairing is going to save more money than if they were magically gifted the ability to use seawater instead of fuel & oxidizer (although obviously using less fuel means less complexity, although nearly all this mass savings would be mostly limited to the first stage).  Obviously, low fuel will someday become important, but how unimportant it is (especially when you already have working inefficient systems.  Competitors might think about higher Isp rockets.  Unfortunately one of them was Stratolaunch who completely got the idea wrong).

[magnemoe]

6 hours ago, wumpus said:

I doubt air breathing is anywhere near the next step.  I thought it was, then space-x decides to try to catch fairings.

Cost of a fairing: $6MBucks
Cost of fuel: $0.2MBucks

Even occasionally reusing a fairing is going to save more money than if they were magically gifted the ability to use seawater instead of fuel & oxidizer (although obviously using less fuel means less complexity, although nearly all this mass savings would be mostly limited to the first stage).  Obviously, low fuel will someday become important, but how unimportant it is (especially when you already have working inefficient systems.  Competitors might think about higher Isp rockets.  Unfortunately one of them was Stratolaunch who completely got the idea wrong).

You have an valid point, cheaper turnaround will be more important,