13 more things that saved Apollo 13

[Glom]

Universe Today are doing another series on factors that helped make the accident survivable.

http://www.universetoday.com/119747/13-more-things-that-saved-apollo-13/

The first one how the failed quantity probe in tank 2 made them stir the tanks more often assuring that the explosion happened during TLC and not later when  the LM wouldn't have been there to save them.

[ka9q]

Of course it's quite likely that the quantity sensor failed from the same thermal abuse that damaged the wiring and set up the accident.

[Glom]

That's what I thought happened too. The article said different though.

[ka9q]

I see that Woodfill said that, but I don't see what he based it on. The heater assembly is right next to the quantity gauge/fill-drain tube assembly. They also shared a common wiring path through the wall of the tank. It's entirely possible that the very high temperatures produced by the heater during the improvised boil-off procedure damaged the quantity gauge.

Remember that because of problems in draining the tank normally after a test, a ground crew boiled off the O₂ by applying 65V to the tank heater. The thermostatic switch was only rated for 28V, so it fused closed and the heater was continuously on for many hours.

It's also possible that the quantity gauge was physically damaged by the same drop incident that damaged the fill/drain tube and hampered normal tank draining. The fill/drain tube forms part of the quantity gauge, which works by measuring the electrical capacitance between the tube and a larger, concentric tube insulated from it. Maybe that's what Woodfill is thinking of.

[ka9q]

And while we're discussing Apollo 13, don't forget the towing invoice that Grumman sent North American Rockwell. It's a hilarious read.

[BazBear]

And while we're discussing Apollo 13, don't forget the towing invoice that Grumman sent North American Rockwell. It's a hilarious read.

Thanks, I had completely forgotten about that!



http://www.spaceflightinsider.com/space-centers/kennedy-space-center/the-apollo-13-invoice/

[Echnaton]

Great read.   As a native Houstonian of a certain era, I saw Marooned at the same theater on Richmond Avenue mentioned in Part 11.  It was called the Windsor Theater and was a nice large movie house that typically had the big ticket heavily promoted films like that.  My parents also took me to 2001 and a bunch of other shows there.  I can't imagine that the NASA guys would normally come all the way from Clear Lake to see any old film, but if Marooned had an exclusive engagement there, I could certainly see them making the trip.

[Allan F]

I have wondered . . .

The Service Module - was it used for anything after the CM was powered down, or was it just dead weight?

[Echnaton]

At least to protect the heat shield from direct exposure to space.

[ka9q]

The Service Module - was it used for anything after the CM was powered down, or was it just dead weight?

Dead weight. The one thing I might have done differently, or at least very seriously considered, was jettisoning the SM once it was fully understood that there wasn't much left in it anyway. Even if the SPS could be trusted, which it wasn't, there probably wasn't any way to power it. The SPS gimbal motors require so much power that the entry batteries have to supplement the fuel cells during each burn and be recharged later -- and of course the fuel cells were no longer available for that role.

The usual reason given for not jettisoning the SM was concern about exposing the heat shield to space but I think this might have been manageable with the right BBQ roll. It certainly would have been easier to perform one with the LM without all that dead weight.

Of course, the fact that they made it back does suggest that they made the right call. But it was by no means obvious that their consumables would last that long.

[Allan F]

If they had jettisoned the SM, would the descent engine have enough fuel to effect a direct abort? I don't think it would be a good idea to jettison the descent stage after depletion and then use the ascent engine, because the huge batteries in the descent stage would be needed to power the LM and recharge the CM's batteries.

[ka9q]

Jettisoning the SM probably wouldn't have allowed a direct abort, but it would have made it possible to speed up the return with the LM descent engine after pericynthion.

And yes, the batteries and water in the descent stage were much more important than the propellant in the ascent stage, at least until shortly before re-entry when it didn't matter anyway.

Oh, by the way the APS propellants were not completely inaccessible with the descent stage attached. There is a cross-feed system between the APS tanks and the LM RCS. It let the RCS draw on the remaining APS propellants near the end of the lunar orbit insertion burn. I think it would have let the LM RCS use at least some of those propellants to make delta-V maneuvers during the A13 emergency if the RCS engines could stand being fired that much. I'm not sure how much of the tanks could have been emptied in zero-g, though.

[Echnaton]

It seems like keeping the SM was the conservative decision to make once it was determined the consumable were sufficient to make it back with the dead weight still attached.  An early jettison would just complicate things by adding more "no one has ever thought of this before" questions into the rescue program.

[Allan F]

What was the velocity at the time of the accident?

[johnbutcher]

And while we're discussing Apollo 13, don't forget the towing invoice that Grumman sent North American Rockwell. It's a hilarious read.

Thanks, I had completely forgotten about that!



http://www.spaceflightinsider.com/space-centers/kennedy-space-center/the-apollo-13-invoice/

So is this a prank, like I think?

Because currently I work with a guy who would do something like this, for real.

Sloop.