"Destination Moon" question

Pat Flannery wrote:
So would this work any way, shape, or form? Maybe if they took the
fins and warhead off of the V-2, considering that it wouldn't have
to deal with air drag,

I am not quite able to tell from what I see at
http://en.wikipedia.org/wiki/V-2_roc...hnical_details if the "jet
vanes" are attached to the fins or to the body.

rick jones
--
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these opinions are mine, all mine; HP might not want them anyway...
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They were running "Destination Moon" today, and towards the beginning
one of the characters claims a V-2 missile fired from the surface of the
Moon could travel to Earth.
Max velocity of a V-2 was 1.6 km/s, but that was in a ballistic, not
vertical, trajectory.
According to the Wikipedia article escape velocity from the Moon is 2.38
km/s, but that's escape velocity, not kicking something into Earth's
gravity field.
So would this work any way, shape, or form? Maybe if they took the fins
and warhead off of the V-2, considering that it wouldn't have to deal
with air drag, and the engine's thrust would be higher when fired in vacuum?
It sounds like something a aerospace writer from around the time of the
movie would point out.

Pat

On 1/11/2011 5:01 PM, Rick Jones wrote:


I am not quite able to tell from what I see at
http://en.wikipedia.org/wiki/V-2_roc...hnical_details if the "jet
vanes" are attached to the fins or to the body.

Luckily, you've just run into a V-2 maniac. :-)
The graphite exhaust vanes run off a seperate set of electrical motors
and drive connections than the aerodynamic control surfaces on the tail
fins. The graphite vane assembly attaches to the base of the rocket body:
http://www.v2rocket.com/start/makeup/infopic05.jpg

Pat

Max velocity of a V-2 was 1.6 km/s, but that was in a ballistic, not
vertical, trajectory.
According to the Wikipedia article escape velocity from the Moon is 2.38
km/s, but that's escape velocity, not kicking something into Earth's
gravity field.

I'm having trouble understanding the use of Max Velocity here. Did the V-2
attain a maximum velocity of 1.6 km/sec in the Earth's Gravitational Field
at the end of the powered portion of the trajectory. To get there it
expended potential energy equivilent of approximately average mass x g x
height, and Kinetic energy of 1/2 final mass x velocity squared, plus air
resistance term. On the moon g is one sixth of earth, and there's no air
resistance. So reaching escape velocity seems more than reasonable, or am I
missing something in the way Max Velocity is defined.


Val Kraut

On 1/12/2011 8:28 AM, Val Kraut wrote:
Max velocity of a V-2 was 1.6 km/s, but that was in a ballistic, not
vertical, trajectory.
According to the Wikipedia article escape velocity from the Moon is 2.38
km/s, but that's escape velocity, not kicking something into Earth's
gravity field.

I'm having trouble understanding the use of Max Velocity here. Did the V-2
attain a maximum velocity of 1.6 km/sec in the Earth's Gravitational Field
at the end of the powered portion of the trajectory. To get there it
expended potential energy equivilent of approximately average mass x g x
height, and Kinetic energy of 1/2 final mass x velocity squared, plus air
resistance term. On the moon g is one sixth of earth, and there's no air
resistance. So reaching escape velocity seems more than reasonable, or am I
missing something in the way Max Velocity is defined.

Max velocity for the V-2 would be the speed it was going at the moment
its engine stopped firing (its impact speed was considerably lower due
to air drag on the way down) but at engine cutoff it was moving very
near to horizontal on its ballistic arc. If launched vertically it would
be ascending against the Earth's gravity field during the entire engine
burn, so its velocity on engine burn-out would be lower than on
ballistic flight to London (the altitude record for a V-2 launched
vertically was 206 km). The trick is figuring out what "lunar escape
velocity" means.
If the Moon were an independent planetary body rather than in orbit
around the Earth, that would be easy to do... escape velocity would
mean the velocity that an object would need to get to to leave its
gravitational influence and enter orbit around the Sun.
But in this case an object doesn't need to do that, it just needs enough
velocity to get to the point between the Moon and Earth where the
attraction of the Earth's gravity becomes greater than that of the Moon,
and it will fall all the rest of the way on its own.
So I need to figure out
A.) How much weight could be stripped off of a V-2 by removing
everything not needed for operation in Earth's atmosphere.
B.) How much of an improvement in specific impulse the engine gets by
operating in vacuum during its whole burn
C.) If those two together give it enough "umph" to get to to the point
where it would fall towards Earth rather than back into the Moon.

Pat

On Jan 11, 10:43*pm, Pat Flannery wrote:
They were running "Destination Moon" today, and towards the beginning
one of the characters claims a V-2 missile fired from the surface of the
Moon could travel to Earth.
Max velocity of a V-2 was 1.6 km/s, but that was in a ballistic, not
vertical, trajectory.
According to the Wikipedia article escape velocity from the Moon is 2.38
km/s, but that's escape velocity, not kicking something into *Earth's
gravity field.
So would this work any way, shape, or form? Maybe if they took the fins
and warhead off of the V-2, considering that it wouldn't have to deal
with air drag, and the engine's thrust would be higher when fired in vacuum?
It sounds like something a aerospace writer from around the time of the
movie would point out.

Pat

According to this Astronautix page the V-2 had a gross mass of 12,805
kg and empty mass of 4,008 kg, and a vacuum Isp of 239 sec:

V-2.
http://www.friends-partners.org/part...ade/lvs/v2.htm

From this we can calculate the delta-V in vacuum as
239*9.8ln(12,805/4,009) = 2,720 m/s.

This page gives a table of delta-V's in the Earth-Moon system:

Delta-v budget.
Earth–Moon space.
http://en.wikipedia.org/wiki/Delta-v...0.93Moon_space

With aerobraking it gives the delta-V as 2,740 m/s. So likely it
could have made it back to Earth orbit.
BTW, the movies is available on YouTube:

Destination Moon.
http://www.youtube.com/watch?v=DsisGSBlQqo


Bob Clark