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Did Apollo really travel sideways?



 
 
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  #1  
Old June 2nd 07, 09:53 PM posted to sci.space.history
[email protected]
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Posts: 46
Default Did Apollo really travel sideways?

I just watched Man Moment Machine featuring Apollo 13. In most of the
animations, the LM/CSM was traveling to the side. Is this right?
I always assumed it traveled straight ahead with that big CSM engine
nozzle to the rear.
  #4  
Old June 3rd 07, 06:31 AM posted to sci.space.history
Henry Spencer
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Posts: 2,170
Default Did Apollo really travel sideways?

In article ,
David Findlay wrote:
...Many spacecraft do a bbq
roll which is basically keeping the vehicle rolling so that no side of the
vehicle gets too hot.


A "barbecue roll" in fact isn't *that* common; most spacecraft are
designed to handle being constantly one side to the Sun. Apollo did it
not to keep things from getting too hot, but to keep one specific thing
from getting too cold: it proved impossible to qualify the CM heatshield
material for prolonged "cold soak" conditions, so a slow rotation with the
spacecraft axis roughly perpendicular to the sunlight was needed to keep
it within its temperature limits.

Positioning the spacecraft axis roughly north-south -- which did indeed
imply traveling sideways -- and rolling around it was a simple way of
doing this, independent of the exact trajectory being followed and
satisfying some other arcane constraints.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #5  
Old June 3rd 07, 08:19 AM posted to sci.space.history
Rocky Top
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Default Did Apollo really travel sideways?


"Henry Spencer" wrote in message
...
In article ,
David Findlay wrote:
...Many spacecraft do a bbq
roll which is basically keeping the vehicle rolling so that no side of the
vehicle gets too hot.


A "barbecue roll" in fact isn't *that* common; most spacecraft are
designed to handle being constantly one side to the Sun. Apollo did it
not to keep things from getting too hot, but to keep one specific thing
from getting too cold: it proved impossible to qualify the CM heatshield
material for prolonged "cold soak" conditions, so a slow rotation with the
spacecraft axis roughly perpendicular to the sunlight was needed to keep
it within its temperature limits.

Positioning the spacecraft axis roughly north-south -- which did indeed
imply traveling sideways -- and rolling around it was a simple way of
doing this, independent of the exact trajectory being followed and
satisfying some other arcane constraints.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |


On April 14th, 1970 the moon was in quarter phase, so the sun would
have been at some angle less than 90 degrees from a north/south axis.

RT



  #6  
Old June 4th 07, 06:02 PM posted to sci.space.history
Rick Jones
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Default Did Apollo really travel sideways?

Henry Spencer wrote:
A "barbecue roll" in fact isn't *that* common; most spacecraft are
designed to handle being constantly one side to the Sun. Apollo did
it not to keep things from getting too hot, but to keep one specific
thing from getting too cold: it proved impossible to qualify the CM
heatshield material for prolonged "cold soak" conditions, so a slow
rotation with the spacecraft axis roughly perpendicular to the
sunlight was needed to keep it within its temperature limits.


Did Apollo 13 then give them that qual?

rick jones
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  #7  
Old June 4th 07, 07:53 PM posted to sci.space.history
robert casey
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Posts: 790
Default Did Apollo really travel sideways?



Did Apollo 13 then give them that qual?


I don't think so. Even though the service module was rendered dead (or
at least not trustworthy) anymore, they still held onto it to protect
the heat shield. And they still did the barbecue roll, as that didn't
cost battery power or other consumables.

On the ground tests probably showed that the heat shield would not
qualify for a cold soak, but the barbecue roll was a workaround to get
past that problem. We did have a deadline to meet....
  #8  
Old June 6th 07, 01:55 AM posted to sci.space.history
Henry Spencer
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Posts: 2,170
Default Did Apollo really travel sideways?

In article ,
Rick Jones wrote:
...it proved impossible to qualify the CM
heatshield material for prolonged "cold soak" conditions...


Did Apollo 13 then give them that qual?


No, even on Apollo 13, they made a point of putting the spacecraft into
the thermal roll before shutting down after maneuvers etc.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #9  
Old June 6th 07, 01:58 AM posted to sci.space.history
Henry Spencer
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Posts: 2,170
Default Did Apollo really travel sideways?

In article tYt8i.991$jW6.679@trnddc01,
Rocky Top wrote:
...a slow rotation with the
spacecraft axis roughly perpendicular to the sunlight was needed...
Positioning the spacecraft axis roughly north-south -- which did indeed
imply traveling sideways -- and rolling around it was a simple way...


On April 14th, 1970 the moon was in quarter phase, so the sun would
have been at some angle less than 90 degrees from a north/south axis.


Uh, the Sun is *always* at roughly a right angle to a north/south axis,
because that axis is roughly perpendicular to the Earth's orbital plane.
The position of the Moon is irrelevant.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #10  
Old June 8th 07, 01:32 PM posted to sci.space.history
mike flugennock
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Posts: 285
Default Did Apollo really travel sideways?

wrote:
I just watched Man Moment Machine featuring Apollo 13. In most of the
animations, the LM/CSM was traveling to the side. Is this right?
I always assumed it traveled straight ahead with that big CSM engine
nozzle to the rear.


Well, since you're in zero-g and vacuum, it doesn't really matter which
way your spacecraft is pointed, although most times, iirc, the Apollo
crews preferred traveling with the CSM nose pointed in the direction of
travel, as a matter of style, I guess. Obviously, they were also pointed
in the direction of travel when burning midcourse corrections, although,
of course, they pointed the SM engine "forward" when braking into orbit
around the Moon.

The "flying sideways" you saw is likely a depiction of the spacecraft
using "Passive Thermal Control" or "barbecue mode", in which the
spacecraft is traveling sideways relative to the direction of travel and
to the sun, and rolling at a very slow rate, in order to keep the sunlit
areas from getting too hot, and the shadowed areas from getting too cold.

--

..

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Don't lend your hand to raise no flag atop no ship of fools!"

--grateful dead.
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