Maglev assisted launch SSTO

"Roger Stokes" wrote:
I have read ideas of air-launched rockets gaining about 300m/s, but how
about a rocket mounted on a maglev "cart" built onto a track going over a
mountain? If (say) 3g was selected, the cart would reach 2km/sec after 67
seconds and 67 km. If this was the peak of the mountain, the rocket would
then fly free, ignite it's engines and continue to orbit. The cart would
flip over the peak, rapidly decelerate and return to the base of the
mountain on a circular track. The track would be dug into a groove to direct
sonic booms upward so the NIMBYs wouldn't whine.
[snip]

OK, first you've got a huge error in your plan. Inertia is a
vector (mass and velocity (which is speed and direction)),
changing direction is as much an acceleration as changing
speed. So your "flip over the mountain top thing", while it
sounds like it ought to work based on experience at low speed
on the ground, it ain't gonna work at those speeds. When you
go over a hill at high speed you are actually accelerating
(even if your ground speed is constant) which is why you feel
that bump pushing you up (that's your inertia pulling you
where the car was headed (up) while the car pulls you down).
At Mach 6, that sort of "flip" would result in tremendous
g-loads, most likely your car would rip loose from the track
and fly off into the air (where it would come crashing down
some (hundreds of?) km away). So you need to do the release
and deceleration on a straight course, and take the flip at
slow speed (or just not take the flip at all, since it's
not necessary). Or, you could throw away your maglev train
each launch.

That's just a minor error though really, as it just means you
need a bigger mountain than you think. The real problem is
that it takes a *lot* of energy to push something to mach 6,
and doing so for objects on the ground is *not* an easy task.
Just think about the supersonic shock wave from the train
hitting the stationary rail and ground and you'll see a huge
problem right away. And it takes a lot of power to reach
those speeds, a lot more power than maglev systems can
provide currently. Maybe a superconducting maglev could do
it, but 67 km of superconducting maglev line ain't cheap.
Even a non-superconducting maglev line 67 km long is going
to be very expensive. In comparison, even expensive rockets
look cheap.

In article ,
Roger Stokes wrote:
I have read ideas of air-launched rockets gaining about 300m/s, but how
about a rocket mounted on a maglev "cart" built onto a track going over a
mountain?

Such things have been proposed. Generally speaking, though, it is much
easier to build a rocket sled than to build a maglev sled. (Supersonic
and even hypersonic rocket sleds already exist.) The maglev approach is
attractive mostly to people angling for maglev research funding.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

"Roger Stokes" wrote in message . ..
I have read in this newsgroup that chemical fuel SSTO proposals have a mass
ratio of around 8:1, leaving very little left over for payload. However if
the launch could be assisted by an initial velocity of about 2 km/sec the
vehicle mass ratio would drop to about 4:1, permitting a much bigger
payload.

I have read ideas of air-launched rockets gaining about 300m/s, but how
about a rocket mounted on a maglev "cart" built onto a track going over a
mountain? If (say) 3g was selected, the cart would reach 2km/sec after 67
seconds and 67 km. If this was the peak of the mountain, the rocket would
then fly free, ignite it's engines and continue to orbit. The cart would
flip over the peak, rapidly decelerate and return to the base of the
mountain on a circular track. The track would be dug into a groove to direct
sonic booms upward so the NIMBYs wouldn't whine.

I am sure there must be a lot of mountains of the required size, near the
equator, and pointing east.

The cart would be electrically powered. If we assume a payload of 20 tons, a
vehicle dry weight of 80 tons, 400 tons of propellant, and a cart weight of
100 tons, we get about 18 GW power requirement for 67 seconds (I think).
Maybe something like a giant flywheel storage generator that is spun up over
several hours - it would take a 100MW generator about 3.5 hours to do this
neglecting losses. I haven't even thought about the mechanical stresses on
the flywheel.

I am sure this is not an original idea, in fact I have some vague memory of
something like it being suggested for a Hawaiian site in the 1960's - but
since then, total silence. Was it judged infeasible with present or
near-future technology, or too costly, or what? And what were the infeasible
things?

Roger


I am pretty sure it is feasible and it is also a good launch concept.
Somebody would have to invest in it to build the tracks. I am not sure
how the maglev is effected by the high speeds. Any aerodynamic lift or
downforce would be a problem. The same track can be used to bring the
car back and some energy could be regained by decelerating it at the
end.

It might be cheaper to use a shorter track and a ramjet to accelerate
the vehicle further.

Zoltan

"Gordon D. Pusch" wrote in message
...
"Roger Stokes" writes:

The track would be dug into a groove to direct sonic booms upward so the
NIMBYs wouldn't whine.

Shock waves don't work that way.

Thanks - I guess I was visualizing from the anti-sound walls sometimes seen
along freeways.

How do shock waves propagate from a supersonic object in a trench?

Gordon D. Pusch wrote

There are NO mountains tall enough anywhere on Earth that Mach 5 airspeeds
will not cause problems.
[...]
The Hawaiian proposal was for an electromagnetic catapult that would
accelerate small payload all the way to more that orbital velocity,
in order to overcome drag. Mach 25 at sea level was considered even
more unreasonable than Mach 5 on a mountaintop --- and the sonic booms
every few minutes plus the eye-searingly bright UV from the plasma sheath
were not thought to be good for Hawaii's primary industry --- tourism.

There's a nice high mountain near Quito in Ecuador, and it's slap bang on
the equator, so if you launched at 80-odd minute intervals the projectiles
would end up in the same place in the same orbit. You could have several
"stations" on the orbit too, and launch more often.

It's also got a nice flat 300km plain to the West, so you could even use it
for human cargo.

I once worked out that it would then cost around $400 Bn to build, and
around $6,000 per ton to operate, a two-ton per launch maglev (actually a
linear motor/ railgun hybrid with a hydrogen airgun initial boost). Around
30k tons per annum capacity, though not suitable for humans.

I was going to set up a shop in LEO for boosters, fuel, solar panels, water,
food, batteries and the like. But then there was an earthquake in Quito...


--
Peter Fairbrother

"Christopher M. Jones" wrote in message
...
"Roger Stokes" wrote:
I have read ideas of air-launched rockets gaining about 300m/s, but how
about a rocket mounted on a maglev "cart" built onto a track going over
a
mountain? If (say) 3g was selected, the cart would reach 2km/sec after
67
seconds and 67 km. If this was the peak of the mountain, the rocket
would
then fly free, ignite it's engines and continue to orbit. The cart would
flip over the peak, rapidly decelerate and return to the base of the
mountain on a circular track. The track would be dug into a groove to
direct
sonic booms upward so the NIMBYs wouldn't whine.
[snip]

OK, first you've got a huge error in your plan. Inertia is a
vector (mass and velocity (which is speed and direction)),
changing direction is as much an acceleration as changing
speed. So your "flip over the mountain top thing", while it
sounds like it ought to work based on experience at low speed
on the ground, it ain't gonna work at those speeds. When you
go over a hill at high speed you are actually accelerating
(even if your ground speed is constant) which is why you feel
that bump pushing you up (that's your inertia pulling you
where the car was headed (up) while the car pulls you down).
At Mach 6, that sort of "flip" would result in tremendous
g-loads, most likely your car would rip loose from the track
and fly off into the air (where it would come crashing down
some (hundreds of?) km away). So you need to do the release
and deceleration on a straight course, and take the flip at
slow speed (or just not take the flip at all, since it's
not necessary). Or, you could throw away your maglev train
each launch.

point taken - I hadn't thought of that.
If we limit the "flip" acceleration to 3g, and the change of angle to 40
degrees, the peak of the mountain (+20 degrees to -20 degrees) must occur
over a distance of 86km - this may severely limit the number of mountains
available.

In article ,
Roger Stokes wrote:
Such things have been proposed. Generally speaking, though, it is much
easier to build a rocket sled than to build a maglev sled...

but the rocket sled approach limits the total SSTO mass to less than about
10 tons...

Why? There is no particular limit on how big you can build a rocket sled.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

"Henry Spencer" wrote in message
...
In article ,
Roger Stokes wrote:
Such things have been proposed. Generally speaking, though, it is much
easier to build a rocket sled than to build a maglev sled...

but the rocket sled approach limits the total SSTO mass to less than
about
10 tons...

Why? There is no particular limit on how big you can build a rocket sled.

Whoops - I read your earlier post carelessly and missed what you meant - I
thought you were talking air-launched.

Presumably such a rocket sled couldn't use wheels at mach 5, so how is it
confined to the track?

And at the risk of reprising another current thread, would it be a pure
rocket or could it be a rocket/ramjet combo if it only has to do mach 5.

I suppose the disadvantage of a rocket sled is the cost of building the
track, while the advantages are a simpler and lighter rocket moter (no
steering is needed as the sled is confined to the track) and gauranteed
re-usability - it always finds its way back to the launch site.

In article ,
Roger Stokes wrote:
...There is no particular limit on how big you can build a rocket sled.

Presumably such a rocket sled couldn't use wheels at mach 5, so how is it
confined to the track?

I think they just use sliding contact, with expendable contact surfaces.
(Mach 5+ rocket sleds have been built -- this is off-the-shelf technology,
not speculation -- but I'm not very familiar with the details.)

And at the risk of reprising another current thread, would it be a pure
rocket or could it be a rocket/ramjet combo if it only has to do mach 5.

You could add ramjets, but by comparison, they are heavy and complex and
difficult to adapt to rapid acceleration through a wide speed range --
their specialty is cruise at constant speed. The justification for them
is arguable even for a flight vehicle, and it vanishes completely for a
sled, where propellant mass is not a major concern. As far as I know, all
existing supersonic and hypersonic sleds are pure-rocket designs, for
simplicity, high acceleration, and elimination of aerodynamic complexity
(high-supersonic air-intake design is not for the faint of heart or the
short of budget).

I suppose the disadvantage of a rocket sled is the cost of building the
track, while the advantages are a simpler and lighter rocket moter (no
steering is needed as the sled is confined to the track) and gauranteed
re-usability - it always finds its way back to the launch site.

Also, the use of a track essentially eliminates gravity losses, at the
price of somewhat higher friction losses and the need to operate in
relatively thick air.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

(MSu1049321) writes:

Integrate the "cart" into the spacecraft structure, and don't worry about
slowing and recovering a sled, just keep a-goin'.

Sorry, bad idea. The "cart" is dead weight once you leave the track;
every ton of mass in the cart is a ton of lost payload that _can't_
be delivered to orbit.


-- Gordon D. Pusch

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