Service Module Sector 1

[StevieA]

Sector 1 of the SM wasn't used for the first few missions, later missions (15-17?) had a science experiment module installed. Was there a reason why this space wasn't used initially? Surely space was so tight when designing it that they wouldn't have left an unused area like this, or was it originally intended for a system that wasn't needed?

Ref:
http://www.hq.nasa.gov/alsj/CSM07_Service_Module_Overview_pp53-60.pdf

[Glom]

It was designed for the SIM.

Minor correction, it was used on Apollo 14 for the third oxygen tank introduced from the lessons learnt from Apollo 13.

[StevieA]

Ok, so why wasn't the SIM flown on apollos 8-13?

[darren r]

Presumably NASA had a planned schedule of tasks and experiments to be performed on each mission and each Apollo only carried the equipment required for those particular tasks. Obviously the earlier missions didn't need to utilise the space. Each module was built to a standard design though, so the space was there if the plans were amended (or for ballast, like it says in the pdf). 

I'm only guessing though! I'm sure there are other people here who can give a better answer.

[Peter B]

Sector 1 of the SM wasn't used for the first few missions, later missions (15-17?) had a science experiment module installed. Was there a reason why this space wasn't used initially? Surely space was so tight when designing it that they wouldn't have left an unused area like this, or was it originally intended for a system that wasn't needed?

Ref:
http://www.hq.nasa.gov/alsj/CSM07_Service_Module_Overview_pp53-60.pdf

Space wasn't nearly as much of an issue as mass.

Also, science was a much lower priority than engineering. NASA's objective was to land a man on the Moon and return him safely to the Earth. Kennedy said nothing about science. NASA was happy to allow science to play a part in Apollo, but only once they were sure the SM actually worked as designed. That's why Apollo 11 had no SIM pod and had a much simpler surface science package than later missions.

[ka9q]

The interesting thing about SM bay 1 is that, despite mass being precious, ballast had to be put there to keep the CSM's center of mass controlled. I don't know how much, but obviously it made much more sense to replace it with extra oxygen, a spare battery, and scientific equipment.

[smartcooky]

Presumably NASA had a planned schedule of tasks and experiments to be performed on each mission and each Apollo only carried the equipment required for those particular tasks. Obviously the earlier missions didn't need to utilise the space. Each module was built to a standard design though, so the space was there if the plans were amended (or for ballast, like it says in the pdf). 

I'm only guessing though! I'm sure there are other people here who can give a better answer.

Well, what would be the alternative?

If they knew that later missions were going to have to carry additional equipment, the only option open to them would be to have a different design of CSM. The cost and logistics of that would be immense.

Now I'm just guessing here, but IMO there is also the issue of weight & balance.

Apollo 15, 16 and 17 were the only ones to carry the lunar rover. It was installed in the descent stage of the LM and that additional weight would have needed balancing on the "other side" of the Centre of Mass, which would put it right about the forward end Sector 1 of the CSM



______________________FWD___________________ROVER

 

[Glom]

is that diagram right? The HGA is on the opposite side of the SM (its by bay 4 hence the communications loss when the panel was blown out on Apollo 13) so shouldn't be visible.

Edit: I was right before I first modified my post thinking it was wrong. The LM hatch and the CM aren't directly above each other. Just take a look at photos from the Apollo 9 EVA.

[smartcooky]

is that diagram right? The HGA is on the opposite side of the SM (its by bay 4 hence the communications loss when the panel was blown out on Apollo 13) so shouldn't be visible.

Edit: I was right before I first modified my post thinking it was wrong. The LM hatch and the CM aren't directly above each other. Just take a look at photos from the Apollo 9 EVA.

I don't know. I just picked the first assembly I came to in order to illustrate the C of M issue!

[ka9q]

The centers of mass would have to be controlled individually for the CSM and LM since they were required to fly independently. You can get these numbers in great detail from the individual mission reports from the "Mass Properties" section, usually in an appendix. For each major point in the mission, all the way from liftoff to splashdown, the following was calculated for each vehicle or connected combination of vehicles:

Mass (weight)
Center of mass
Moment of inertia around X axis
Moment of inertia around Y axis
Moment of inertia around Z axis
Product of inertia for X/Y axes
Product of inertia for Y/Z axes
Product of inertia for Z/X axes

[smartcooky]

AIUI the LM was installed in Stage 3 "behind" the CSM until it separated and turned around to dock with the LM.

The LM was then extracted and the whole vehicle CSM/LM was transposed so that it travelled to the moon LM first.

I'm no engineer but I would have thought adding something like the Rover to Apollo 15, 16 and 17 would change the whole assembly's centre of mass unless some mass/ballast was added on the "other side". Having no compensating ballast would change the flight characteristics when manoeuvring.

I'm not sure where the centre of mass actually was, but I would not have thought it would be very far from the docking point of the two spacecraft.

[ka9q]

Yes, everything else the same I would think that adding the LRV moved the LM's center of mass.

But why would you assume that everything else was kept the same? Major changes were made to the LMs for the J-missions to enable them to stay three days on the moon: extra batteries, extra water, extra food, extra oxygen. And then there's the extra propellant needed to land all that stuff on the moon and to get the ascent stage with its large load of samples back off again. There would be plenty of opportunities to move these things around to keep the c.g. in the right place after the LRV was added.

Check the mission report for each mission to see the precise masses and c.g. locations of the LM at each major point in the mission.