Apollo 13 movie question

[Emilio]

In the movie, when they are going back to earth, Ground Control says than they are too light because they should have some Moon rocks.

But instead of having Mun rocks, they had the LEM, that was a LOT more than moon rocks, so shouldn\'t they have been too heavy instead ?

It\'s maybe a movie mistake...

[Joshua21B]

They may have been referring to the weight of the capsul, once it separated from LM, for reentry purposes.

[RC1062]

That would make sense... The LEM wouldn\'t make much difference in space...

*EDIT* Well it would... But the reserves of fuel would cover it...

[thorfinn]

I think that it was an oversimplification for normal audiences of a center-of-gravity problem.

The small lift force that allowed to steer an Apollo CM during reentry and to avoid untolerable deceleration was produced by tilting the capsule. This required shifting some mass to a side, so that the dynamically stable attitude wasn\'t exactly blunt side first. The sixty kilograms of moon rocks were included in the calculation. I don\'t think that it was really critical, but with all the other problems, why letting yet another one be when you can fix it?

[RC1062]

60 kg is about a person. I suppose it would be spread in certain places though?

[VincentMcConnell]

At first, it was assumed that moon rocks were the reason for the shallowing reentry corridor, but it was later determined that vapors being given off from the Lunar Module were acting as a weak propulsion system, slowly venting the spacecraft off course, despite an initial reentry angle of 6.24 degrees. (6.5 is considered perfect).

Because none of the other Apollo spacecraft had their LM attached during Trans Earth Coast from the Moon, this was the first time this problem had been encountered.

[Johno]

Vincent\'s got it.

Plus, with all the stuff that the crew had no control over (the typhoon, the heat shield, the lack of electricity), it was nice to give them an actual procedure they could follow.

[Emilio]

Vapors ? Why vapor whas coming out of the LEM ?? ?

Edited May 13, 2015 by Emilio

[VincentMcConnell]

Vapors ? Why vapor whas coming out of the LEM ?? ?

Theses are the consequences of playing KSP almost everyday....

I believe -- not 100% sure -- that the LM emits some sort of gases from it\'s systems.

[Johno]

The vapour in question was steam from the Aquarius\' cooling system (a steam sublimator). Simple and obvious in retrospect, but there was a lot of balls for Mission Control to keep in the air.