Long cables to power plasma rockets to orbit.

Magnetoplasmadynamic thrusters have the advantage that they can be
scaled up to produce large amounts of thrust, while still maintaining
the high ISP of ion drives:

Magnetoplasmadynamic Thrusters.
"Testing for these thrusters has demonstrated exhaust velocities of
100,000 meters per second (over 200,000 mph) and thrust levels of 100
Newtons (22.5 pounds) at power levels of 1 megawatt. For perspective,
this exhaust velocity will allow a spacecraft to travel roughly 11
times the top speed of the space shuttle (18,000 mph)."
http://www.nasa.gov/centers/glenn/about/fs22grc.html

MY ELECTRIC ROCKET ENGINE.
http://www.waynesthisandthat.com/mpd.htm

The problem is the high amount of power required. However high
electrical power has been delivered up to hundreds of kilometers on
Earth over power lines. Then this could be used to deliver the
required electrical power to the thrusters from the ground.

Bob Clark

c.f.,
Newsgroups: sci.astro, sci.space.policy, sci.physics
From: "Robert Clark"
Date: 20 Mar 2006 20:23:18 -0800
Local: Mon, Mar 20 2006 11:23 pm
Subject: Long cables to power arcjet rockets to orbit?
http://groups.google.com/group/sci.p...d3fba4a33a6d13

"Robert Clark" wrote in message
...
| Magnetoplasmadynamic thrusters have the advantage that they can be
| scaled up to produce large amounts of thrust, while still maintaining
| the high ISP of ion drives:
|
Wow! Ion drives have internet service providers. Learn something
new every day.

On a sunny day (Fri, 11 Jan 2008 13:50:53 -0800 (PST)) it happened Robert
Clark wrote in
:

Magnetoplasmadynamic thrusters have the advantage that they can be
scaled up to produce large amounts of thrust, while still maintaining
the high ISP of ion drives:

Magnetoplasmadynamic Thrusters.
"Testing for these thrusters has demonstrated exhaust velocities of
100,000 meters per second (over 200,000 mph) and thrust levels of 100
Newtons (22.5 pounds) at power levels of 1 megawatt. For perspective,
this exhaust velocity will allow a spacecraft to travel roughly 11
times the top speed of the space shuttle (18,000 mph)."
http://www.nasa.gov/centers/glenn/about/fs22grc.html

MY ELECTRIC ROCKET ENGINE.
http://www.waynesthisandthat.com/mpd.htm

The problem is the high amount of power required. However high
electrical power has been delivered up to hundreds of kilometers on
Earth over power lines. Then this could be used to deliver the
required electrical power to the thrusters from the ground.

Bob Clark

Seems like the perfect candidate for a nu-cu-lear power plant.
Wires, and this thing likely only works nicely in vacuum, weight
tons and tons (copper), do not think you could get it up there,
and then there is orbital speed, wind the cable around the earth?
No, nu-cu-lear is the solution in my view.

On Jan 11, 4:50*pm, Robert Clark wrote:
[snip]
Magnetoplasmadynamic Thrusters.
"Testing for these thrusters has demonstrated exhaust velocities of
100,000 meters per second (over 200,000 mph) and thrust levels of 100
Newtons (22.5 pounds) at power levels of 1 megawatt.

Hmm... 100 Newtons from 1 MW.

For perspective,
this exhaust velocity will allow a spacecraft to travel roughly 11
times the top speed of the space shuttle (18,000 mph).

The thing is, this is a useless perspective. What you really
want is specific impulse.

http://en.wikipedia.org/wiki/Specific_impulse

If you need to trail 100 km of cable behind you, this is
going to cut into your budget.

Also, the space shuttle produces a bit more than 100 N
of thrust. Indeed, shortly after liftoff the combined thrust
will be about 25 million N. You'd need about 250,000's
mega Watts to get the same thrust. Now, I don't know
what kind of cable you plan to use.

You should look up power capacity of Copper wire and figure
out what area of wire you'd need to transmit 250,000 MW.
Don't forget that you need a complete circuit up and down,
so you need to double it.

This is starting to look like a honking-big roll of cable you
have to start with.

Now you've also got to consider that this cable is getting
strung out the back of the rocket. It has to take it's own
weight at least for about five minutes to get to orbit, never
mind whatever forces it will experience from being dragged.
Again, I don't know what you plan to use. But I don't
feature this thing standing up to the stress, even if you
could get a rocket to lift it and push it out the back at
the right rate.

And even if you did get it to do all that, now you've got
100 km of cable, the upper end of which is moving at
orbital speeds. And the bottom end of which is still
attached to the ground. The people down-range are
going to complain. Loudly. Even the folks close to the
launch site may get annoyed when the cable motion
does nasty things along its length.

*The problem is the high amount of power required. However high
electrical power has been delivered up to hundreds of kilometers on
Earth over power lines. Then this could be used to deliver the
required electrical power to the thrusters from the ground.

*The* problem? You've got lots of problems before you even
get to that.

Ion drives are not useful as launch thrusters.

But the real problem is, you can't do simple arithmetic. This notion
has been thoroughly trashed before. And could easily be so trashed
by a good highschool student.

Get serious.
Socks

On Jan 11, 5:29 pm, Puppet_Sock wrote:
On Jan 11, 4:50 pm, Robert Clark wrote:
[snip]

Magnetoplasmadynamic Thrusters.
"Testing for these thrusters has demonstrated exhaust velocities of
100,000 meters per second (over 200,000 mph) and thrust levels of 100
Newtons (22.5 pounds) at power levels of 1 megawatt.

Hmm... 100 Newtons from 1 MW.

For perspective,
this exhaust velocity will allow a spacecraft to travel roughly 11
times the top speed of the space shuttle (18,000 mph).

The thing is, this is a useless perspective. What you really
want is specific impulse.

http://en.wikipedia.org/wiki/Specific_impulse

If you need to trail 100 km of cable behind you, this is
going to cut into your budget.

Also, the space shuttle produces a bit more than 100 N
of thrust. Indeed, shortly after liftoff the combined thrust
will be about 25 million N. You'd need about 250,000's
mega Watts to get the same thrust. Now, I don't know
what kind of cable you plan to use.

You should look up power capacity of Copper wire and figure
out what area of wire you'd need to transmit 250,000 MW.
Don't forget that you need a complete circuit up and down,
so you need to double it.

This is starting to look like a honking-big roll of cable you
have to start with.

Now you've also got to consider that this cable is getting
strung out the back of the rocket. It has to take it's own
weight at least for about five minutes to get to orbit, never
mind whatever forces it will experience from being dragged.
Again, I don't know what you plan to use. But I don't
feature this thing standing up to the stress, even if you
could get a rocket to lift it and push it out the back at
the right rate.

And even if you did get it to do all that, now you've got
100 km of cable, the upper end of which is moving at
orbital speeds. And the bottom end of which is still
attached to the ground. The people down-range are
going to complain. Loudly. Even the folks close to the
launch site may get annoyed when the cable motion
does nasty things along its length.

The problem is the high amount of power required. However high
electrical power has been delivered up to hundreds of kilometers on
Earth over power lines. Then this could be used to deliver the
required electrical power to the thrusters from the ground.

*The* problem? You've got lots of problems before you even
get to that.

Ion drives are not useful as launch thrusters.

But the real problem is, you can't do simple arithmetic. This notion
has been thoroughly trashed before. And could easily be so trashed
by a good high school student.




The impetus for this was this proposal by Launchpoint Technologies
to launch small satellites by magnetic fields:

Huge 'launch ring' to fling satellites into orbit
http://technology.newscientist.com/article/dn10180

However, there are many difficulties with getting large mass objects
up to orbital velocity with EM fields alone, discussed in this thread:

Subject: Coilguns and EM launchers.
http://groups.google.com/group/sci.s...806dc6417ca8a/

And this article describes research dating back from 1977 able to
get a 3 gm object up to about 6000 m/s, and that record still hasn't
been exceeded for larger mass objects:

For Love of a Gun By Carolyn Meinel
First Published July 2007
The tumultuous history of electromagnetic launch.
http://www.spectrum.ieee.org/jul07/5296

If the launch system is to stay on the ground and for low mass
payloads you can just as well use reaction mass methods, i.e, rockets,
at high ISP to get the craft up to orbit velocity at short distances.
You wouldn't need to have hundreds of kilometers of cable extending
into air trailing from the craft. You could have a cable lying on the
ground and a short length of cable extending from the craft to the
cable on the ground, say 10 to 100 meters long. Keep in mind, just as
for the magnetic launch proposal, the main thing is getting that
horizontal velocity component required for orbit. To get to the
altitude for LEO is just a small proportion of extra velocity and
energy of that required for orbital velocity.
Note that for large launch systems such as the space shuttle a large
amount of thrust is needed just to accelerate that huge mass of fuel
that needs to be carried along. But when the exhaust velocity is much
larger than the ending velocity, say 100,000 m/s compared to 8,000 m/s
then by the rocket equation the mass of the fuel will be about the
same small proportion to the mass of the rocket, 8/100. (The exhaust
velocity being 100,000 m/s for this MPD thruster means the ISP,
specific impulse, actually is a quite high 10,000 s.)
The Launchpoint magnetic launch proposal only talked about launching
small satellites, 10 kilograms or so. Only one of the NASA Glenn
magnetoplasmadynamic (MPD) thrusters would be needed to accelerate a
10 kg mass to 1 g. Five of them could accelerate it to 5 g's at 5
MWatts power.
However, I should say key for this proposal is the idea the MPD
thrusters could be made lightweight. From the descriptions of the mode
of operation, essentially only requiring two electrodes, I'm assuming
this is the case. The images of them shown also suggest they would be
small and light weight.
Assuming that it is indeed the case the weight of the thrusters would
stay low when the thrust is scaled up, this might be used to launch
most satellites and also astronaut passengers. Most satellites are
less than around 1,000 kg. A 1 Gwatt power plant assuming power to
thrust scales up could accelerate this at 10 g's. Transportable gas
turbine electric generators at the 100's of megawatts scale can be
bought in the 10's of millions of dollars range. So 1 Gwatt total
would cost in the range of 100's of millions of dollars.
NASA documents give the human endurance level for acceleration
according to duration, as described he

G tolerance (Dani Eder; Henry Spencer; Jordin Kare; James Oberg)
http://yarchive.net/space/science/g_tolerance.html

At 9 g's it's about 3 minutes for astronauts lying down in
acceleration seats. The formula for speed v attained at an
acceleration a over distance d is v^2 = 2ad. So for v = 8,000 m/s and
a = 10 g's = 100 m/s^2, d is 320 km. They would have to undergo this
for t =v/a = 80 s.
You could have the craft go in a circle at a smaller radius to reduce
the scale of the distance covered by the cable on the ground, but this
would result in a higher acceleration according to the formula a = v^2/
r. For a radial distances of a few km's you get accelerations at the
1,000's of g's scale, which would greatly reduce the payload and make
it impossible for human passengers.
However, for small satellites, a few kilos, it might be easier to use
such small linear or radial distances of just a few kilometers.


Bob Clark

On Jan 12, 3:51 pm, Robert Clark wrote:
...
The impetus for this was this proposal by Launchpoint Technologies
to launch small satellites by magnetic fields:

Huge 'launch ring' to fling satellites into orbithttp://technology.newscientist.com/article/dn10180

However, there are many difficulties with getting large mass objects
up to orbital velocity with EM fields alone, discussed in this thread:

Subject: Coilguns and EM launchers.http://groups.google.com/group/sci.s...frm/thread/e6b...

And this article describes research dating back from 1977 able to
get a 3 gm object up to about 6000 m/s, and that record still hasn't
been exceeded for larger mass objects:

For Love of a Gun By Carolyn Meinel
First Published July 2007
The tumultuous history of electromagnetic launch.http://www.spectrum.ieee.org/jul07/5296

If the launch system is to stay on the ground and for low mass
payloads you can just as well use reaction mass methods, i.e, rockets,
at high ISP to get the craft up to orbit velocity at short distances.
You wouldn't need to have hundreds of kilometers of cable extending
into air trailing from the craft. You could have a cable lying on the
ground and a short length of cable extending from the craft to the
cable on the ground, say 10 to 100 meters long. Keep in mind, just as
for the magnetic launch proposal, the main thing is getting that
horizontal velocity component required for orbit. To get to the
altitude for LEO is just a small proportion of extra velocity and
energy of that required for orbital velocity.
...

For larger sized payloads and for manned craft you would probably
want the craft to be at high altitude when it reached the high Mach
numbers. Then you could have the hundreds of kilometers long, ground
lying cable instead be raised in the air, reaching from the ground to
the desired altitude. You would as before use a short cable say 10 to
100 meters long to connect the craft to this longer cable that is held
aloft.
Then a large helium balloon could keep the longer cable aloft if the
cable were say 1 mm wide. But you might need a cable 1 cm wide or
larger to carry sufficient current to power the craft. Possibly
several helium balloons along its length would work to keep it aloft
in this case.
Another possibility would be to use separate plasma thrusters along
its length to keep it aloft since raising a payload to a high altitude
requires far less energy then getting it to orbital velocity.
It might also work instead to have the long cable be hollow filled
with helium to provide its own buoyancy. High altitude helium balloons
are typically composed of mylar 20 microns thick, able to reach 30 km
altitudes. A hollow aluminum cable with a thickness of 1 micron and a
diameter or 100 meters would have the same cross-sectional area as a
solid cable 1 cm wide.


Bob Clark

Robert Clark :

Makes my head hurt...

--Damon

"Robert Clark" wrote in message
...

For larger sized payloads and for manned craft you would probably
want the craft to be at high altitude when it reached the high Mach
numbers. Then you could have the hundreds of kilometers long, ground
lying cable instead be raised in the air, reaching from the ground to
the desired altitude. You would as before use a short cable say 10 to
100 meters long to connect the craft to this longer cable that is held
aloft.
Then a large helium balloon could keep the longer cable aloft if the
cable were say 1 mm wide. But you might need a cable 1 cm wide or
larger to carry sufficient current to power the craft. Possibly
several helium balloons along its length would work to keep it aloft
in this case.
Another possibility would be to use separate plasma thrusters along
its length to keep it aloft since raising a payload to a high altitude
requires far less energy then getting it to orbital velocity.
It might also work instead to have the long cable be hollow filled
with helium to provide its own buoyancy. High altitude helium balloons
are typically composed of mylar 20 microns thick, able to reach 30 km
altitudes. A hollow aluminum cable with a thickness of 1 micron and a
diameter or 100 meters would have the same cross-sectional area as a
solid cable 1 cm wide.

You can't be serious. All of this handwavium doesn't prove anything.
Where's the actual numbers to back all of this up?

For starters, how about showing the math which shows conclusively that your
intended engines can support the force of a cable that's actually big enough
to provide enough power to them. Let's assume 3G's for launch loads, since
that's a nice round number that NASA likes to use for the maximum
acceleration of a manned spacecraft (ignoring aborts). After all, it's not
going to work unless you can actually accelerate the vehicle using this
setup.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein

On Jan 15, 6:08 pm, Robert Clark wrote:
...
For larger sized payloads and for manned craft you would probably
want the craft to be at high altitude when it reached the high Mach
numbers. Then you could have the hundreds of kilometers long, ground
lying cable instead be raised in the air, reaching from the ground to
the desired altitude. You would as before use a short cable say 10 to
100 meters long to connect the craft to this longer cable that is held
aloft.
Then a large helium balloon could keep the longer cable aloft if the
cable were say 1 mm wide. But you might need a cable 1 cm wide or
larger to carry sufficient current to power the craft. Possibly
several helium balloons along its length would work to keep it aloft
in this case.
Another possibility would be to use separate plasma thrusters along
its length to keep it aloft since raising a payload to a high altitude
requires far less energy then getting it to orbital velocity.
It might also work instead to have the long cable be hollow filled
with helium to provide its own buoyancy. High altitude helium balloons
are typically composed of mylar 20 microns thick, able to reach 30 km
altitudes. A hollow aluminum cable with a thickness of 1 micron and a
diameter or 100 meters would have the same cross-sectional area as a
solid cable 1 cm wide.

Bob Clark

For making the cable buoyant we might use the principle of a hot air
balloon instead. Since the large power going through the cable would
create a lot of heat, why not use that heat instead of trying to get
rid of it? You would put a thin hollow, flexible shell around the
cable that expanded and rose from the air rising due to the heat given
off by the cable. We could make the thin hollow shell itself
conducting to be contacted by the tether from the rocket or have an
additional cable running above it.
From this idea we see this could be used to control the cable from
whipping around from winds. Along the cable we would have rocket
nozzles that just used the heated air produced but directed it so as
to counteract the wind forces.
This suggests a different propulsion technique for the rocket thruster
itself. Power from a rocket increases according to the square of the
exhaust velocity. You can get high thrust while keeping the power low
by having high mass flow and low exhaust velocity. Here we would just
heat the air electrically. A problem though is that at high rocket
speeds the air would be moving past at high speed. You would have to
heat the air quickly in order to give it additional momentum to create
thrust. Electrical heating elements within the air stream would also
create shock waves. You might want to use instead a microwave
generator carried on board to heat the air. In either case electrical
heating elements or microwave heating this should be easily calculable
to find how much power would be needed at the high Mach numbers.
On another board a suggestion was made about using for example ducted
fans to move large amounts of air at low speed. Using large amounts of
air at low additional speed (to the air steam speed) may indeed be a
good idea. However, it won't work to use propellers or ducted fans or
even turbines at the high Mach numbers since they become very
inefficient or even fall apart at high Mach numbers.
So I suggest instead using methods of heating the air to generate the
thrust.


Bob Clark

Robert Clark wrote:
[snip crap]

For making the cable buoyant we might use the principle of a hot air
balloon instead. Since the large power going through the cable would
create a lot of heat, why not use that heat instead of trying to get
rid of it?
[snip rest of crap]

1) If your power conduit is cooking at 1500 C it isn't any ****ing
good as a power conduit.
2) Idiot
3) Do the math for hot air balloon boyancy vs. cable weight vs.
cooling rate.
4) Idiot
5) Ask a hot air balloonist how much propane he burns/hour.
6) Idiot
7) Momentum of the cable
8) Idiot
9) mgh of the cable.
10) Idiot
11) Length of the cable.
12) Idiot
13) Return of the cable
14) Idiot

Hey Clark, were you the idoiot who designed the Space Scuttle thus
achieving a small fraction of Saturn V throw weight at four times the
cost/gram? It requires a special kind of idiot (short bus!) to have a
reusable system cost way ****ing more than a use once and toss system.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2