*

            Flight Day 3 dawns, if that’s the word, aboard Apollo 13.  Our Commander, Jim Lovell, contacts Houston.  “We’re awake and getting the spacecraft shipshape.”

            The capcom replies, “Roger. Spacecraft is in real good shape as far as we’re concerned, Jim. We’re bored to tears down here.”

            Not boring, but routine, our last day before making lunar orbit, filled with routine housekeeping chores in the Command Module we’ve named Odysseyand minor issues, such as trouble getting an accurate quantity reading from oxygen tank 2 of the Service Module.  We stir the cryos — turn on egg-beater-like fans to mix the stratified liquid oxygen. The reading goes off-scale high. Twice more in the afternoon we stir the cyros, but the reading remains off-scale high.  The quantity probe must have failed. 

            The highlight of our day comes when we enter our Lunar Module, Aquarius, for the first time, three hours early, at 8:38 p.m. EST, to check the pressure of a helium tank that read slightly high before launch.  The pressure looks fine.  And an hour later, we begin a TV show in which we show off the lunar module.  The show ends just before 10 p.m. with Jim Lovell signing off, “This is the crew of Apollo 13 wishing everyone there a nice evening.  We’re just about ready to close out our inspection of Aquariusand get back for a pleasant evening in Odyssey.”

            We’re putting away TV equipment, about to install the hatch between Odyssey and Aquarius, and a yellow caution light comes on indicating a low pressure in one of two hydrogen tanks in the service module.  We use hydrogen and oxygen to produce electricity in our three fuel cells, with a by product of water.  In addition, we draw our breathing oxygen from the same tanks used by the power systems. The caution is routine, and the ground calls, “Thirteen, we’ve got one more item for you, when you’ve got a chance.  We’d like you to stir up your cryo tanks.”  That should bring the pressure back to normal in the hydrogen tank. We are 205,000 miles from earth, nearing the point where the command ship’s big SPS engine could not make a direct abort to send us on a quick course to Earth.

            From the lefthand seat, we flip four switches and . . . Nothing happens that we can detect for 24 seconds.  Then we feel a shutter, and in the tunnel area between the two spacecraft, a metallic popping as the two ships flex against each other.

            A second later, the master alarm blares.  We call, “OK, we’ve had a problem.”

            Jim Lovell swims up to the instrument panel and radios, “Houston, we’ve had a problem. We’ve had a Main B Bus undervolt.

            Capcom Jack Lousma calls up, “Roger, Main B undervolt.”  And then, “OK, stand by 13, we’re looking at it.”

            We’re looking at it ourselves, scanning the readouts on electric systems on the righthand end of the instrument panel.  We’re looking for something that makes sense.  We’ve got two electrical distribution buses, Bus A currently is tied to fuel cells one and two.  Main B is tied to fuel cell three.  Three minutes after the incident, B’s voltage returns to normal.  “OK, Houston, the voltage — is looking good.  And we had a pretty large bang associated with the caution and warning.”  It could just be an instrumentation problem.  So we hope.

            But at next look, Main B is putting out zip.

            And Oxygen tank 2 is reading between 20 and 60 percent.  “The jolt must have rocked the sensor on.”  But when we look again, it’s back reading full-scale high.

            Four minutes after the incident, we see more bad news and report, “We got a Main Bus A undervolt now, too, showing.  It’s reading about 25 and a half.  Main B is reading zip right now.”  Main A’s power output levels off.  

            At the same time, problems multiply.  We’re having trouble communicating, the spacecraft antenna had switched from narrow to wide beam.  We’re having trouble controlling the spacecraft’s attitude.  Only half of the thrusters are tied to Main Bus A — so the others aren’t working.  What is going on?

            Six minutes have gone by since the incident.  We’re not hearing anything from Houston.  Jim Lovell calls, “OK, Houston are you still reading Apollo 13?”

            “That’s affirmative. We’re reading you.  We’re still still trying to come up with some good ideas for you.”

            More master alarms ring, caused by a high hydrogen flow to fuel cell 2.

            About fifteen minutes after the incident, Jim Lovell looks out the side window, and sees a fog-like spray spreading from the spacecraft.  He radios, “It looks like we are venting something.  We are venting something out into space.”

            We know what it must be. Oxygen from our remaining tank. The readings for oxygen tank 1 are steadily decreasing.   We see that fuel cell 1, like fuel cell 3, is not producing power.   Houston has us shut them down by tripping the reactant valves. Perhaps that will isolate the leak, if it is in one of those cells.   Alas, the oxygen level in tank 1 continues to decrease.  It’s only a matter of time before our last fuel cell runs out of oxygen.

            We begin thinking of getting in the Lunar Module and activating.  Forty minutes after the incident, we begin powering down some systems in the Command Module to save power.  Less than two hours after the accident, we enter the Lunar Module and begin powering it up, an emergency power up rather than the nominal one which can take a couple hours.  Soon after we start, Houston calls that Odyssey‘sfuel cell 2 only has 15 minutes of life in it.  It shuts down 2 hrs. 6 min. after the incident.  We run the Command Module on it’s three small re-entry batteries until the guidance information, the “platform” that tells us where we are in space, is transferred to the LM.  At 2 hrs. 46 min. after the incident, the Lunar module is powered up. And the Command Module is shutdown. Not dead, but in an induced coma. 

            We’ve achieved the first milestone in our new mission.  Our new mission is survival.

            The next task, a short burn of the LM’s Descent Propulsion system, which should have been used to land us on the moon.  Instead we will fire it to push us back on a free-return trajectory.  It is now April 14.  Not that we are aware of the date.