Apollo 10 reusable crasher stage

When Snoopy, the overweight LM of Apollo 10, tested the abort mode and
did the last dress rehearsal for the lunar landing, they may have
demonstrated something which could be useful. Without knowing it.

They separated the descent module, while still in orbit, IIRC.

So that if the ascent module would not work, then they would not
crash, but could perhaps be rescued by the CSM.

This must mean that the descent stage continued for a few more orbits
before crashing.

It had no electronics, so when the ascent stage was separated, it
couldn't do f.i. a reorbit burn or a TEI.

Why I'm interested in that ? Because I understand that there is an
advantage in having a crasher stage, i.e. use the last stage to slow
you down as much as possible before separation, then land in your
vehicle.

But I always thought that you'd invite a few failure modes doing that.
That the crasher stage works, releases you, but the landing modules
engine misfires, or the crasher stage denies to separate 500 ft above
the Moon, after slowing you down.

Also, I understand that the equipment should be reusable. Which is a
contradiction in terms with a crasher stage.

Regards

Carsten Nielsen
Denmark

18-7-2004 17:23:28

Carsten Nielsen wrote in message





Why I'm interested in that ? Because I understand that there is an

advantage in having a crasher stage, i.e. use the last stage to
slow

you down as much as possible before separation, then land in your

vehicle.

That's what the soviets were intending to do with their N1-L3 project,
using a separate stage which was first used for LOI (Lunar Orbit
Insertion) and afterwards to brake the lander to almost zero speed
low above the lunar surface.

The advantage is partly in the LOI manouvre, for LOI you have to slow
down the complete assembly (Lunar Lander and mothership) into lunar
orbit, but for TEI you are returning only the mothership, so you
could use a much smaller engine (and thus, a smaller mothership,
which then in turn saves launchweight, etc, etc). The Apollo CSM had
to have a big engine and plenty fuel mainly for LOI, and afterwards
you had to take most of this empty weight back to earth which you
could have saved by leaving it behind.

Furthermore, if you look at the typical moonlander flight profile,
you see that the first part of the landing is done at fuel power,
then you get a throttle back and the final part of the landing is
done at far less (and variable) power. If you use the crasher stage
for the 'full power' part (which doesn't require a throttleble
engine) your lunar lander itself can make do with a must smaller
engine, so once more you save weight. Finally if you forget about
separate descent and ascent stages (which you ONLY can do if you use
a crasher stage, otherwise the weight penalty will be too big) you
can once again save some weight by using the same engine(s) for both
descent and ascent (leaving only landing gear, landing radar, etc
below on the surface).

But I always thought that you'd invite a few failure modes doing
that.

That the crasher stage works, releases you, but the landing modules

engine misfires, or the crasher stage denies to separate 500 ft
above

the Moon, after slowing you down.



Sure, and apart from that the risk that the lander gets damaged by
the explosion of the crasher stage impacting the moon, OR that the
main engine of the mothership refuses to start for TEI...

You introduce a LOT more failure modes only to save a little bit of
weight...

Geert

In article ,
Carsten Nielsen wrote:
Why I'm interested in that ? Because I understand that there is an
advantage in having a crasher stage, i.e. use the last stage to slow
you down as much as possible before separation, then land in your
vehicle.

Yes, it has some practical advantages. In particular, it means that the
deceleration engine and the landing engine can be separate, which is
helpful because the thrust requirements are quite different, and
deeply-throttlable engines are hard to build. (You want to decelerate
as rapidly as possible, but a controlled soft landing requires thrust
equal to lunar gravity.)

The Surveyor unmanned landers effectively used a crasher stage, firing and
then jettisoning a big solid-fuel retrorocket.

But I always thought that you'd invite a few failure modes doing that.
That the crasher stage works, releases you, but the landing modules
engine misfires, or the crasher stage denies to separate 500 ft above
the Moon, after slowing you down.

Mind you, if you adopt an Apollo-style two-stage approach instead, the
analogous failures are just as deadly, because they make it impossible
to take off. About the only advantage is a little more time for
troubleshooting.

Also, I understand that the equipment should be reusable. Which is a
contradiction in terms with a crasher stage.

Indeed so. Reusability is pretty much incompatible with any form of
staging in a lunar lander. You really have to bring the whole vehicle
back up at least as far as lunar orbit.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Geert Sassen wrote:



Sure, and apart from that the risk that the lander gets damaged by
the explosion of the crasher stage impacting the moon, OR that the
main engine of the mothership refuses to start for TEI...

You introduce a LOT more failure modes only to save a little bit of
weight...


With the N-1 every pound counted, and they still weren't light enough by
the time the program ended.

Pat

Pat Flannery wrote...

With the N-1 every pound counted, and they still
weren't light enough by the time the program ended.

And they were alight a little too much

- Peter

(Henry Spencer) wrote in message ...
The Surveyor unmanned landers effectively used a crasher stage, firing and
then jettisoning a big solid-fuel retrorocket.

Hey, that was not a bad idea, I will think about a use of the LOI
stage to go to an Apollo 10 / Snoopy descent orbit, then use a solid
for final horizontal braking, then land with a vehicle.

Reuseability being a concern, the LOI stage must be recovered (to ISS
orbit ? ) but simple solids don't need that.

But I always thought that you'd invite a few failure modes doing that.
That the crasher stage works, releases you, but the landing modules
engine misfires, or the crasher stage denies to separate 500 ft above
the Moon, after slowing you down.

Mind you, if you adopt an Apollo-style two-stage approach instead, the
analogous failures are just as deadly, because they make it impossible
to take off. About the only advantage is a little more time for
troubleshooting.

A lot more time, because with the crasher stage, you only have
seconds, with Apollo, you have hours. OK, I don't quite know how
repairable a rocket engine is.

With a one stage approach, I think there is the failiure mode of
engine bell damage on landing, and that must be a danger for crasher
stage landings too.

Regards

Carsten Nielsen
Denmark