Apollo 13 fails while in Lunar orbit?

Heres an interesting question; what if the oxygen tanks weren't stirred until after the CSM/LEM had entered Lunar orbit?

There are two scenarios here:

Scenario 1: The CSM explodes before the landing is attempted. This one is fairly simple and boils down to whether or not the LEM had enough ∆V and TWR to beak Lunar orbit with the CSM attached.

Scenario 2: The CSM explodes after the landing is attempted. This is slightly more interesting and I would imagine, very very very bad for the crew.

Heres how I would imagine that would play out;

Immediately after the oxygen tank explodes, mission control would order the guys on the surface to abort to orbit ASAP. Before they do so though, they rip off the insulation from the LEM descent stage and cut out the descent oxygen tank, which they will be taking to orbit with them.

The CSM has about 1 hour 40 minutes of life left. By the time the LEM rendezvouses with it, Swigert will probably be in his EVA suit while the CSM's life support has failed. Here comes the first problem: can the LEM dock to the CSM, since usually, it was the other way around.

When they dock, one of the astronauts will go on EVA, rip the batteries out from the LEM, and try to wire them into the SM's electrical system. The oxygen tanks, internal batteries, EVA suits, and other supplies will also be transferred to the CM.

At this point, all of the batteries and other supplies have been taken from the LEM and it is jettisoned. Meanwhile, the astronaut on EVA continues trying to asses the condition of the SPS and fix what he can. Once he's finished, its time to do the trans-Earth injection burn.

In order for the SPS to fire it needs power. The CM's dead, so the only source of energy is the LEM's batteries that were just wired into the SM's electrical grid. Presumably when jerry-rigging stuff to that extent, it's not possible to wire the batteries to accept commands from the control panels, since they weren't designed to have batteries in the SM.

As such, we reach the second problem: the astronaut on EVA is probably going to have to flick the switch to dump the batteries power into the SPS (or more likely, he's going to have to connect the wires between the batteries and the power grid) while outside the craft, meaning either he will have to scramble to get back in very quickly, or he will have to hold onto the side as hard as he can as the SPS fires.

Oh, and the burn will have to be flown by the seat of their pants since the guidance computer is probably offline.

Assuming this works, and the astronaut doesn't fall off the side, we now have a dead CSM slowly floating towards Earth. I image the crew could possibly use the LEM batteries to power the CO2 scrubbers, radio, and other stuff until its time for reentry. At that point, it proceeds as it did IOTL.

Overall I give scenario 2 a 0% chance of success, but its an interesting concept. What do you think? Could they have survived either of those scenarios?
 

SsgtC

Banned
In order for the SPS to fire it needs power. The CM's dead, so the only source of energy is the LEM's batteries that were just wired into the SM's electrical grid. Presumably when jerry-rigging stuff to that extent, it's not possible to wire the batteries to accept commands from the control panels, since they weren't designed to have batteries in the SM.
Except that's not how the SPS worked. It needs oxygen to fire. And the onboard supply is now gone. And what little is left in the LM's tank won't be enough to fire the SPS. At least not enough to fire it for long enough to break lunar orbit.

Then there's the fact that there is a ton of debris floating around out there. No way does NASA authorise an EVA in those conditions. Too much chance of debris tearing a hole in a suit.
 
Except that's not how the SPS worked. It needs oxygen to fire. And the onboard supply is now gone. And what little is left in the LM's tank won't be enough to fire the SPS. At least not enough to fire it for long enough to break lunar orbit.
That's not true. The oxygen it uses is chemically bound in the prop in the Nitrogen Tetroxide tanks, not the oxygen tanks used for the cabin and the fuel cells. The reason they didn't use it was worries about damage to the engine, not depletion of the contents of the prop tanks.

If the issue occurs in lunar orbit before descent of the LM, then my calculations show they have (just barely) enough prop to make a standard Trans-Earth Injection (TEI) burn. The CSM masses 28,800 kg at TLI, and burns about 13,200 kg of prop during Lunar Orbit Injection, leaving it with a wet mass of 15,587 kg. With the descent stage's initial wet mass of 15.2 metric tons for Apollo 13's LM, that totals just shy of 30.8 metric tons. The LM descent stage's 8,200 kg prop capacity can supply 944 m/s with that supply of prop, meaning it can perform the ~920 m/s TEI burn with ~300 kg of prop remaining for trajectory control on the way home.
 
Last edited:
That's not true. The oxygen it uses is in the Nitrogen Tetroxide tanks, not the oxygen tanks used for the cabin and the fuel cells. The reason they didn't use it was worries about damage to the engine, not depletion of the contents of the prop tanks.

If the issue occurs in lunar orbit before descent of the LM, then my calculations show they have (just barely) enough prop to make a standard Trans-Earth Injection (TEI) burn. The CSM masses 28,800 kg at TLI, and burns about 13,200 kg of prop during Lunar Orbit Injection, leaving it with a wet mass of 15,587 kg. With the descent stage's initial wet mass of 15.2 metric tons for Apollo 13's LM, that totals just shy of 30.8 metric tons. The LM descent stage's 8,200 kg prop capacity can supply 944 m/s with that supply of prop, meaning it can perform the ~920 m/s TEI burn with ~300 kg of prop remaining for trajectory control on the way home.

Thanks! So scenario 1 is fine, that’s good. What about scenario 2 - Does anyone know just how easy or difficult it would have been to get the SPS to fire if the SM’s fuel cells are dead and you’re Jerry-rigging batteries from the LEM? I would presume it would be difficult, but I’m no expert. A similar thing happened in https://www.alternatehistory.com/fo...imeline-of-a-scientific-america.418531/page-2 but that was a micrometeoroid hitting the CM, so it wasn’t quite as bad.
 
Thanks! So scenario 1 is fine, that’s good. What about scenario 2 - Does anyone know just how easy or difficult it would have been to get the SPS to fire if the SM’s fuel cells are dead and you’re Jerry-rigging batteries from the LEM? I would presume it would be difficult, but I’m no expert. A similar thing happened in https://www.alternatehistory.com/fo...imeline-of-a-scientific-america.418531/page-2 but that was a micrometeoroid hitting the CM, so it wasn’t quite as bad.
It's be very difficult, if it was even feasible at all. The tanks aren't plug-and-play--you can't just yank them out and swap them like LEGO elements, and while batteries at least don't leak if you clip the leads, doing wire cutting and splicing in space in gloves with is pretty close to impossible. Even if it weren't, that's a lot of EVA work to do in basically no time with basically no tools. Worse, there may not be enough battery capacity to sustain the capsule back to Earth even if you can splice it in--77% of the LM battery capacity is in the descent stage, and you'll deplete part of the remaining battery capacity in the ascent stage on the way to rendezvous.

Ironically, while an Apollo 13-style explosion probably leads to a dead crew, whether in LEO or on the way home, a failure in lunar orbit before separation is actually probably more survivable than the OTL accident. They're only about 72 hours away from return, instead of about 86 hours. The LM is already powered up or in the process of being powered up, and the residual 300 kg of prop after TEI give them about 40 m/s of margin, compared to the 3.5 m/s used in OTL.
 
Last edited:

marathag

Banned
If in Lunar Orbit when things go 'bang', would they risk undocking the LEM to examine the damage to the CSM engine and panels with a slow flyby and then redock?
 
If in Lunar Orbit when things go 'bang', would they risk undocking the LEM to examine the damage to the CSM engine and panels with a slow flyby and then redock?
I doubt it unless they're already separated for descent--it's a big risk for something that helps in the investigation post-flight but doesn't actually help get the crew home now.
 
The LM is already powered up or in the process of being powered up, and the residual 300 kg of prop after TEI give them about 40 m/s of margin, compared to the 3.5 m/s used in OTL.

It's actually better than that - the LM RCS jets can be used to trim velocity and orientation, and they can pull from the LM ascent tanks in addition to the descent prop. It would take a while to burn all of that prop (over an hour!), but it can be done.

As you note however, as soon as Powered Descent starts, all three astronauts are dead.
 
If in Lunar Orbit when things go 'bang', would they risk undocking the LEM to examine the damage to the CSM engine and panels with a slow flyby and then redock?

Extrem difficult if CSM becomes inoperative, first the SM RCS will fire automatic to stabilize the spacecraft until CSM Pilot intervene manually
also he has to deal with situation in CM alone while others are in LM. he will lose valuable Time and has to shut down the CSM
here The LM crew has to dock manually a inactive CSM and if the tanks still vent out, the CSM is spinning or moving...

back scenario LM dock CSM in lunar orbit as Lox tanks blowup
could crew jettison the SM in lunar orbit and just ETI with Capsule dock on LM ?
 
It's be very difficult, if it was even feasible at all. The tanks aren't plug-and-play--you can't just yank them out and swap them like LEGO elements, and while batteries at least don't leak if you clip the leads, doing wire cutting and splicing in space in gloves with is pretty close to impossible. Even if it weren't, that's a lot of EVA work to do in basically no time with basically no tools. Worse, there may not be enough battery capacity to sustain the capsule back to Earth even if you can splice it in--77% of the LM battery capacity is in the descent stage, and you'll deplete part of the remaining battery capacity in the ascent stage on the way to rendezvous.

Ironically, while an Apollo 13-style explosion probably leads to a dead crew, whether in LEO or on the way home, a failure in lunar orbit before separation is actually probably more survivable than the OTL accident. They're only about 72 hours away from return, instead of about 86 hours. The LM is already powered up or in the process of being powered up, and the residual 300 kg of prop after TEI give them about 40 m/s of margin, compared to the 3.5 m/s used in OTL.

Good points. It really all comes down to power.

The explosion in the SM probably didnt get the SPS, since if it had it would have also gotten the tanks that feed it, and those were fine. Also, we know at least a few of the SM's RCS quads were operational. So, that leaves up with the SPS, Lunar module ascent motor, and the RCS on the SM, CM, and LEM (could the use the CM's RCS while still attached to the SM?).

Now, power wise, as you said, they have a problem. Let's assume that the failure happened right before the CSM went around the far side of the Moon. Houston orders Lovell and Haise back to the LEM ASAP and to prep for abort. Houston also realizes the problem is power critical (the CSM has 160 minutes left) and tells them to rip the batteries out of Quadrant 4 on the LEM descent stage and bring them up to orbit.

They have about 60 minutes (give or take 10 minutes) before they need to launch. It takes 10 minutes to get back to the LEM, 20 minutes to grab the batteries, 10 minutes to get back inside the LEM, and another 20 minutes to prep for the rendezvous (too bad Buzz isn't with them). They launch and dock to the CSM on one orbit, 70 minutes later. They now have 30 minutes to get power back to the CSM before it dies.

Haise goes on EVA (the LEM was depressurized throughout the launch, and they're still in their suits) and starts assessing the damage, while Lovell transfers to the (also depressurized) CSM, and with the help of Swigert starts wiring the batteries from the LEM descent stage in series with the batteries in the CM. This gains them about 2000 amp-hours. Meanwhile, Haise reports that the damage to Sector 4 of the CSM was extensive, ripping off the entire panel, with shrapnel destroying the high-gain, which in turn ricocheted downwards and dented the SPS nozzle. The SPS would however still be operational, but the RCS and engine gimbal would be needed to correct the slight thrust imbalance. He also reports that the heat shield looks mostly intact, but it's difficult to tell for sure. After fixing anything he can (mostly reconnecting wires that had come loose) Haise travels over to the LEM and starts trying to grab the ascent batteries from it. 30 minutes after the LEM docked the descent batteries come online, and the CM's power is restored.

10 minutes later Haise re-enters the CM with the ascent batteries, which are also spliced into the CM's power grid. They also grab all of the oxygen tanks they can off of the LEM, including the main ECS tanks, the PLSS backpacks, and the PLSS refill tanks (they don't worry about connecting the oxygen tanks to the CM's ECS grid, they just open the valve and release oxygen into the CM manually). At this point, there repressurized the LEM and CM, and after using what's left of the LEM's propellant to raise there orbit as much as possible, they grab the remaining equipment of the LEM (carbon dioxide scrubbers, etc) and ditch it. At this point, about three hours have passed since the incident started.

So far in their current situation, for propulsion, they have a working SPS and RCS grid. For power, they have three 40 amp-hour Earth descent batteries, two 296 amp-hour LEM ascent batteries, and four 415 amp-hour LEM descent batteries. For oxygen, they have the CM tanks, two oxygen tanks from the LEM's ECS, two PLSS backpacks, and all the PLSS refill tanks. For water, they have 15 kg in the CM and two 19 kg water tanks from the LEM.

Once they are in the correct position relative to the Earth and Moon, the SPS is fired (using electricity from the batteries in the CM), and the vehicle is put on a trans-Earth trajectory. Using a bunch of supplies on the CM, they create an adapter to use the LEM's carbon dioxide filters in the CM. Halfway to Earth, they use the CSM's RCS to do a blind mid-course correction, similar to OTL. 4 hours from reentry the SM is jettisoned, and the rest is the same as OTL.

So far, the biggest problems for them to overcome are:

1 - How difficult would it have been for them to grab the 4 LEM descent batteries in under 20 minutes? (probably doable, but difficult)
2 - Could they rendezvous with the CSM in under 70 minutes? (maybe)
3 - Could the various EVA procedures I specified be accomplished? Could the spacecraft be repressurized afterward? (probably not)
4 - Could Lovell and Swigert splice in the LEM descent batteries in time, while wearing space suits inside the depressurized CM? (maybe)
5 - How difficult would it have been to get the LEM ascent batteries. (probably quite difficult, they were behind a bunch of panels, and one wrong move could rupture the pressure vessel)
6 - Could the power from the CM be used to ignite the SPS in the SM? (maybe)
7 - Would the SPS work? (probably, since the explosion didnt damage the hypergolic prop tanks, it probably didn't damage the SPS either)
8 - Did the LEM's batteries buy them enough power to get back, even with the CM in low power mode? (maybe)
9 - Did they have enough oxygen left after repressurizing the spacecraft (after the earlier EVA) to get back to Earth? (maybe)
10 - Could the mid-course correction using the RCS have worked? (probably, after all, it did OTL)

I don't know the answers to these for sure, but I would guess the chance of it working is below 50/50. Still, I would be interested in any of your thoughts on the matter. Does anyone actually know how much power they would have needed for the return?

Extrem difficult if CSM becomes inoperative, first the SM RCS will fire automatic to stabilize the spacecraft until CSM Pilot intervene manually
also he has to deal with situation in CM alone while others are in LM. he will lose valuable Time and has to shut down the CSM
here The LM crew has to dock manually a inactive CSM and if the tanks still vent out, the CSM is spinning or moving...

back scenario LM dock CSM in lunar orbit as Lox tanks blowup
could crew jettison the SM in lunar orbit and just ETI with Capsule dock on LM ?

In ether OTL or scenario 1 they wouldn't jettison the SM, they didnt know what prolonged exposure to micrometeoroids and radiation would do to the heat shield.
 
Slightly off topic but if you're ever taking I-10 east, you can pull off at a rest stop just past the Louisiana-Mississippi line and see an exact replica of a lunar module.
 
Top