Question: Roll During LM Ascent

One aspect of an STS launch is the roll program early in the ascent to
bring the vehicle to the correct inclination for its eventual orbit. I
can't recall hearing of any discussion of the LM rolling after
liftoff to find the correct orbital inclination to rendevous with the
CM.

I am guessing that the initial inclination of the LM's descent would
have been similar to the CM's orbit, but it seems that the LM may
change its heading during final descent, especially if there is a
crater full of boulders in the way as there was on Apollo 11. As a
result, the LM may have come to rest facing a different direction
relative to the Moon's north then it would have if no end-game
maneuvering was required. If that was the case, would the LM need to
roll during its initial ascent prior to pitch over to find the correct
orbital inclination to complete the rendevous?

Since the Moon has no global magnetic field, how was heading determined
in the LM? The Lunar Roving Vehicle used bearing to the last point of
its navigation system's initialization (usually the LM) to determine
heading on the moon, which would be fine in that frame of reference. I
guess it might have been the LM's internal guidance, but was that
system accurate enough without some measurement against an external
reference? What method and what datum did the LM and its crew use to
navigate to the correct orbital inclination.

Does anyone know where I could read more to learn more about this?
(Rusty probably has THE .pdf file).

Thanks in advance. Take care . . .

John

In article .com,
John wrote:
...the LM may have come to rest facing a different direction
relative to the Moon's north then it would have if no end-game
maneuvering was required. If that was the case, would the LM need to
roll during its initial ascent prior to pitch over to find the correct
orbital inclination to complete the rendevous?

Yes, there was a yaw maneuver -- the LM coordinate system was based on the
crew looking forward rather than upward, so rotation around the engine
axis was yaw, not roll -- just after takeoff. It's not really mentioned
much, but you can find allusions to it if you go hunting. The takeoff
trajectory included a brief vertical rise before pitching over, and that
provided the opportunity to yaw to point the LM the right way.

Since the Moon has no global magnetic field, how was heading determined
in the LM?

The LM had an inertial guidance system -- in fact, two -- which were
aligned by star sightings before takeoff.
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spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Henry Spencer wrote:

Yes, there was a yaw maneuver -- the LM coordinate system was based on the
crew looking forward rather than upward, so rotation around the engine
axis was yaw, not roll -- just after takeoff. It's not really mentioned
much, but you can find allusions to it if you go hunting. The takeoff
trajectory included a brief vertical rise before pitching over, and that
provided the opportunity to yaw to point the LM the right way.


IIRC, you could actually see that on the Apollo 17 LM ascent films from
inside the LM.

Pat

Pat Flannery wrote:
Henry Spencer wrote:

Yes, there was a yaw maneuver -- the LM coordinate system was based on the
crew looking forward rather than upward, so rotation around the engine
axis was yaw, not roll -- just after takeoff. It's not really mentioned
much, but you can find allusions to it if you go hunting. The takeoff
trajectory included a brief vertical rise before pitching over, and that
provided the opportunity to yaw to point the LM the right way.


IIRC, you could actually see that on the Apollo 17 LM ascent films from
inside the LM.

Pat

Thank you Henry and Pat.

John

John wrote:


Thank you Henry and Pat.

John



What is fascinating about the LM ascent films is watching how the LM
maneuvers without a gimbaling ascent rocket.
It goes up, then suddenly changes direction as the RCS changes its
course to bring it onto true for its intended trajectory, then ascends
again.
Nothing smooth about it, very rapid trajectory changes by several
degrees in a very short timeframe.
The astronauts must have been getting bounced all over the place as
this all occurred.
It's very notable in the ascent films.

Pat

Pat Flannery wrote:


John wrote:


Thank you Henry and Pat.

John



What is fascinating about the LM ascent films is watching how the LM
maneuvers without a gimbaling ascent rocket.
It goes up, then suddenly changes direction as the RCS changes its
course to bring it onto true for its intended trajectory, then ascends
again.
Nothing smooth about it, very rapid trajectory changes by several
degrees in a very short timeframe.
The astronauts must have been getting bounced all over the place as
this all occurred.
It's very notable in the ascent films.

Are you talking about that one where it looks like it's doing some kind
of weird corkscrew manuver -- traveling generally straight, but still
twirling tightly around its x axis? Check out how the scenery below
looks as if it's wobbling in little circles in the window from liftoff
up until pitch-over...


--

..

"Though I could not caution all, I yet may warn a few:
Don't lend your hand to raise no flag atop no ship of fools!"

--grateful dead.
__________________________________________________ _____________
Mike Flugennock, flugennock at sinkers dot org
"Mikey'zine": dubya dubya dubya dot sinkers dot org

In article ,
Pat Flannery wrote:
What is fascinating about the LM ascent films is watching how the LM
maneuvers without a gimbaling ascent rocket...
Nothing smooth about it, very rapid trajectory changes by several
degrees in a very short timeframe.
The astronauts must have been getting bounced all over the place...

The Apollo 10 and 11 LM crews both described ascent steering as a sort of
wallowing motion, and compared it to "Dutch roll" in an aircraft, but said
that it was not violent or unpleasant.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

mike flugennock wrote:


Are you talking about that one where it looks like it's doing some
kind of weird corkscrew manuver -- traveling generally straight, but
still twirling tightly around its x axis? Check out how the scenery
below looks as if it's wobbling in little circles in the window from
liftoff up until pitch-over...


Without seeing the film again I wouldn't know; the one that would have
made an interesting view is when the Apollo 10 LM went berserk on
separation from its descent stage in lunar orbit.

Pat

Henry Spencer wrote:


The Apollo 10 and 11 LM crews both described ascent steering as a sort of
wallowing motion, and compared it to "Dutch roll" in an aircraft, but said
that it was not violent or unpleasant.


It looks like it would make you seasick from the video; what exact level
of G's did they experience during the ascent?

Pat

In article ,
Pat Flannery wrote:
The Apollo 10 and 11 LM crews both described ascent steering as a sort of
wallowing motion, and compared it to "Dutch roll" in an aircraft, but said
that it was not violent or unpleasant.

It looks like it would make you seasick from the video; what exact level
of G's did they experience during the ascent?

If memory serves -- references aren't handy and it's time to go to bed --
it was about 1/3 G at takeoff, and close to double that at insertion.
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spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |