Zero Phase

by Gerald Brennan

  Another innocent sentence. Heavy with meaning. They are going to test the main engine with a quick burn. If it blows up, our decision will be made for us. Do they know what we’re thinking? Probably. It doesn’t take a rocket scientist to figure it out, although obviously we have plenty on hand.

  “I assume they’ve been discussing this in the back rooms.”

  “Roger, Jim. There was some talk about the risks of doing an extra burn. But we’ve looked at the telemetry and we think it’ll be best all around. And unless you have any objections, we’re gonna give it a go.”

  “If this is Flight’s best decision, I’m fine with it.”

  We go back to stowing gear. The mass must be precisely distributed for a successful liftoff. There is a hanging spring scale like you would use for weighing a fish. We’re supposed to be using it for boxes of moon rocks. We have none besides the contingency sample. But Houston also told us to keep our PLSS packs, which we ordinarily would have thrown out after the second EVA. We know the weights of some things already. But it is good to double-check. Maybe it’s busywork, but it’s something to do.

  We hear Ken talking through the lead-up to the burn: “…Main B, Auto…Main A, Auto…AC2, off. BMAGS to 1 ATT, Spacecraft controller to SCS.”

  Neither Freddo nor I acknowledge it, but we both stop working to listen a little better.

  “…getting some vibrations here,” Ken says, crackly. “…unstable pitch gimbal. And…Master Alarm.”

  “Shut it down, Ken. We’ll get as much data as we can before LOS.”

  “Fuel cell 1 is back offline. We’re back down to one…SPS just started oscillating.”

  “Roger, Ken. We might be able to do the burn with the secondary system.”

  “OK. Yaw 1’s off, Pitch 1’s off, Yaw 2’s off, Pitch 2’s off…ervos 1 and 2 are off…back to P00 so I can resolve the fuel cell issue.”

  “Aquarius is standing by,” I radio.

  “We copy, Jim,” Houston says. “We will get you revised liftoff times before LOS.”

  More packing. Houston works their tracking magic and gives us the new numbers.

  Things are settling down. Or maybe it just feels that way. It’s still a crisis, but we have our bearings. We are working off of a surface abort checklist now. They have dreamed up a fair number of off-nominal contingency scenarios, so we aren’t completely in the dark. This is what happens when thousands of people think about a particular set of problems for years on end.

  And then, a transmission that makes us listen up: “Houston, Odyssey…levels on Tank 1 are acting up. They dropped after the burn and plateaued…just saw another drop.”

  “Roger, Odyssey. We’re monitoring that. We’ll have to take a look after AOS.”

  Freddo and I trade glances.

  We get back to business as Ken heads behind the moon.

  •••

  Like much of science, space exploration is a numbers game. Large numbers, small numbers. 218,096 nautical miles—the distance from earth to moon. 235 cubic feet—the interior volume of the LM cabin. 9,200 ft/s—the max delta-v of the SPS engine. There are high probabilities that somehow avoid you. There are low probabilities that catch up with you because you hang around them for too long. There is a small but non-zero probability that the LM will be struck by a micrometeorite large enough to rupture the hull while we’re in it without our fishbowls on, in which case we’d be dead. And there is a large probability that the AGC will function without breaking for the entire course of a two-week mission. But it’s still a number less than one.

  The AGC handles large and small numbers much the same way you do when you use a slide rule. When you express a number in scientific notation you get two parts, the mantissa and the exponent. So 218,096 nautical miles becomes 2.18096 * 105. The mantissa is the 2.18 part. You express everything in scientific notation and you perform all operations on the mantissas and then you use the exponent parts to determine where to put the decimal in your result. And that, of course, determines the significance of the number.

  A key part of Kennedy’s pledge was getting a man back to earth safely. And several members of the Space Task Group (Bob Gilruth and Caldwell Johnson and Max Faget and a few others) had to determine what constituted “safely.” They decided on a .99 probability of mission success. So, theoretically, one mission in a hundred will fail. And they settled on a probability of .999 for getting the crew back safely. So, in theory, one crew in a thousand will die.

  The problem is you don’t know, statistically, the actual probabilities of system failure. You can draw all the probability trees you want, but you won’t know if the percentages are accurate unless you test each component thousands of times. And since that’s not going to happen, you won’t really know if the overall probability is correct unless you fly a thousand missions. And one in a thousand doesn’t sound like a lot, until you’re the one.

  I guess what I’m saying is: it’s all a question of significance. Move the decimal point too far one way and everything starts to look like nothing. Move it too much the other way and nothing becomes everything.

  Obviously no one knows what condition the CSM is in. Which systems are fine, which systems are just hanging on until the next vibration. What will happen if we do a full burn. The SPS might be fine except for a loose connection to the gimbal motor. Or it could be about to explode. They are working to get as complete a picture as possible, but we won’t be able to do much besides make better decisions. This isn’t like the movies where the hero can do a dramatic spacewalk and fix everything and save the mission. Our engines were designed for reliability, not maintenance. Simple, self-contained structures filled with extremely caustic propellants that would probably eat through our gloves. So we’re stuck with what we’ve got. The SPS will either give us enough delta-v to get us home, or it won’t. It’s up there in some indeterminate state. Like Schrödinger’s thought experiment where the cat is simultaneously alive and dead until you open the box. A cloud of probabilities ready to collapse into one reality. Only we’re the cat. And we won’t know our end state until we light the SPS again.

  I suppose I can understand, in a theoretical sense, why some people would choose to just stay on the moon in those circumstances. To spend a final day or so exploring, and say their goodbyes, and turn off the radios. But I wouldn’t be in this spot in the first place if I was that type of person. And I know the same goes for Freddo.

  During that last bit of work everything fades away except what is in front of us. Neither of us is looking out the window. The surface of the moon might be 99.999999% uninhabited and airless right now, but we are going to do what we can on our little slice of it.

  •••

  “Aquarius, Houston, you can take descent battery 2 off now.”

  “OK, Houston.” Freddo flips the switch.

  We are almost at liftoff. The way it works is the bottom part of the spacecraft, the descent stage, becomes the launch pad for the top half. We tested the ascent-stage batteries a while back but have been running down the descent batteries as long as possible because everything in that stage has to stay on the moon. There is a lot of oxygen in there that we can’t take with us. I am not complaining. They designed it the way it needed to be designed. I wouldn’t have done it any differently, even now.

  We’ve done what we can. We even topped off the PLSS packs with O2 from the descent stage. Given the overall consumables need for the three of us on the way home, it may not make a difference. (We’ll need the O2 from Tank 1 for the trip home, and we have no way of knowing if it’ll start leaking again once we fire the SPS. After AOS, Ken said it had plateaued again and stayed relatively steady, but it’s safe to say none of us is brimming with confidence on the issue.) Still, there’s a chance a few extra hours’ worth of oxygen will come in handy.

  In the meantime, Houston has been working through revised procedures for our TEI burn. Calculating probabilities for longer burns at lower thrust. Trying to change mantissas and lower exp
onents in a way that raises probabilities.

  “OK, Houston, we’re standing by to pressurize the ascent helium,” I say at last.

  The ascent engine and the RCS system are pressurized with helium that forces the hydrazine and nitrogen tetroxide down their respective pipes to the thrusters. Simple: no pumps. Very little to break. But you can only pressurize it right before launch. Otherwise the pressure will eventually bleed off and you will have no way to fire the ascent engine or steer. So this is it. Once we do this, we will not be able to delay the rest of it.

  I look over. Freddo is looking out the window at the bleak bright scene.

  I don’t think he’s thinking of anything other than getting one last look. Which is understandable. Still I say: “There’s nothing for us down here, Freddo.”

  He doesn’t say anything.

  Houston: “Go ahead, Aquarius. One at a time, please.”

  Freddo reaches for the switch. If he hesitates, I don’t see it. “There’s Number 1, Houston.”

  We watch the pressure gauges climb.

  Freddo flips another switch. “OK, there’s Number 2.”

  There is a pause while we wait for the final GO. Now we are both getting a last look. Neither of us says anything. What can you say at a moment like this?

  At last, a crackle. “Aquarius, this is Houston. You are GO for lift-off this pass. Direct rendezvous. Guidance control: PGNS. Over.”

  “Roger, Houston. Go for lift-off. Direct rendezvous. PGNS. Over.”

  A pause. Then: “Godspeed, Aquarius.”

  We have some final circuit breaker changes, per pages 8-16 and 8-17 of the surface checklist. And now we have to go to VHF for a comm check with Odyssey. Ken is nearly overhead. We will need to talk to him real-time to do the rendezvous.

  “Odyssey, Aquarius, how do you read?”

  I wait.

  “Odyssey, Aq…”

  A faint voice. “Jim, I read you. Not perfect, but it’ll have to do.”

  “OK, Ken, we have you about 3 by,” I respond. “Two minutes to liftoff…mark.”

  “Aquarius, Houston. Less than two minutes and we are GO.”

  More switches. There are pyrotechnic systems in the descent stage that fire guillotines that sever the electrical and plumbing connections between the two stages. “Master Arm is on. A and B lights are on.”

  From Houston: “Roger, Aquarius, we confirm both systems armed.” And to Ken: “Odyssey, Houston, Aquarius has ascent engine armed.”

  “Roger, Houston, I am reading them loud and clear now.”

  “OK, Ken, we’ll be up there shortly,” I say.

  A quick scan of the DSKY. Our clock’s counting down. Everything looks right. This is happening.

  “10, 9, 8…Abort Stage set. Engine Arm,” I call out, and the explosive bolts and guillotines fire and the DSKY is flashing 99 and Freddo pushes PRO. “Proceed,” he calls out, and I continue “…4, 3, 2, 1.”

  And the engine lights and Freddo calls: “Ignition.” And the floor presses against us and I look out the window in time to catch a quick glimpse of a flurry of torn Mylar skittering across the lunar surface, which is quickly falling away.

  “Velocity’s good, and we have pitchover,” I call out as the 8-balls roll again and the LM pitches forward.

  We have to build horizontal velocity to catch up to the CSM. So, unlike on the way in, we’re looking down at the moon. And we’re swaying a little as the RCS fires. And I am busy tracking values against printed cue cards, but it occurs to me how strange this is. And I keep scanning the instruments to make sure the computer’s doing what it’s supposed to do, but once or twice I look out at the craters below. And the dead landscape whips by, faster and faster and faster.

  •••

  On Apollo 11 and 12, they executed a conservative rendezvous technique. Coelliptic. Basically a slower ascent with several burns along the way to refine the LM’s trajectory. Rendezvous three and a half hours after liftoff.

  But Apollo means gradual improvements. New capabilities from mission to mission. Never getting too far ahead of yourself, but always going forward. So our planners pushed for a direct rendezvous. Fewer burns, faster link-up with the CSM. And given the current crisis, we have all the more reason to get up there quicker.

  The initial ascent places us in an orbit 9nm at its lowest point and 45nm at its highest. From there, it’s one big burn to close the gap.

  •••

  During the first hour after orbital insertion, we are flying through the moon’s shadow. Launched into lunar night. A bisected universe. Everything above: innumerable stars and galaxies. And nothing below but cold dark blankness. I saw it on Apollo 8 and it still gives me chills.

  In this phase, we can’t see Odyssey. We have to track him with the rendezvous radar. Making sure everyone’s where they’re supposed to be. Trusting in the unseen.

  Terminal Phase Insertion takes place after crossing the lunar terminator. Another crucial burn. Talking to Ken on the VHF but still out of contact with Houston. Now that we are out of the moon’s shadow and aligned properly I can see the cloud of oxygen around the CSM. It’s flecked with pieces of debris that hang suspended and glint as they catch the sun.

  “Oh, Lord, that’s quite a cloud,” I say.

  A crackling transmission. “…quarius, Odyssey, say again, over.”

  “That’s quite a cloud you’ve got around you, Ken. But I will say, it’s easy to get a visual on you when you’re surrounded by debris.”

  “Always look on the bright side, huh?” Ken says.

  I steal a glimpse at this bright slice of the far side. A much different view of the moon than most humans see. None of the dark lowlands. I will only see it twice more, and never after today. We are closing the gap.

  “Aquarius, Houston, how do you read, over?” Houston calls us up after AOS.

  “We’re here, Houston. TPI was nominal and everybody’s where they’re supposed to be.”

  A crackle. “…you have the numbers, Aquarius?”

  Freddo reads them off: “Noun 81, plus 62.1, plus 0.1, plus 63.1. The burn went on time. We nulled PGNS to 00 plus 0.1.”

  “We have sight of Odyssey and it is a fair-sized cloud orbiting with them,” I add.

  “Roger, Aquarius. Odyssey, how’s it working from your end?”

  “Well, the sextant was pretty much useless. But I was able to pick up a VHF range after TPI, and I saw their strobe once we were in range for that.”

  Ken wasn’t able to get a visual on us with the optics. No surprises there. But he could determine our range based on the VHF signals, and then he saw our strobe, so we’re still OK.

  “Roger, Odyssey,” Houston calls. Then: “Aquarius, take your time on the way in. We’d like to have Fred get some pictures of the CSM.”

  “We’ll see what we can do, Houston.”

  “And Odyssey, you were able to get the LM weight of 5600 pounds loaded into the DAP?”

  “Roger, Houston,” Ken answers. He had to get our weight entered into his computer so the autopilot functions properly once we’re docked. Despite the crisis, we still have to check all the boxes.

  The CSM is obviously in bad shape. We ease our way in close. Then Ken does a quick RCS rotation to put the damaged side of the spacecraft in front of us.

  Freddo and I both gasp.

  “Houston, Aquarius, there’s a side of the spacecraft missing. The entire panel appears to have been blown off. We can see in along that shelf, and Tank 2 is completely gone.”

  “Roger, Aquarius. What is the condition of the SPS, over?”

  “Houston, the SPS appears to be in good shape. I do see a streak along the engine bell that I didn’t see before.”

  “Roger, Aquarius.” Houston sounds more distant than ever. “Use your best judgment and get all the pictures you can.”

  Fred’s taking care of that, working the 70mm Hasselblad. He spends a roll shooting the side of the spacecraft. These photos should be a huge help to whatever accident
board they convene to determine what happened to us. Provided, of course, we can take them back to get developed.

  The docking itself is surprisingly uneventful. There was some talk of us taking the active role for the final link-up, but Ken has stabilized things to the point that he’s comfortable with Odyssey handling this. And we have to be careful so we don’t go into gimbal lock and lose our alignment.

  “Apollo 13, Houston, you are GO for docking,” Houston calls out. I watch through the overhead window as the CSM moves toward us for the last couple minutes. A smooth approach, particularly given the circumstances. Moving together so that speed and distance both go to zero at the same time.

  “We have capture,” Ken calls out before I’m sure I’ve even felt anything. And then: “We have a hard dock.”

  We hear the ripple of the latches engaging. It’s somewhat reassuring. Whatever our other problems, some things are working normally.

  •••

  After the docking, Ken has to remove the nose probe assembly and equalize the pressure so he can open up the tunnel between the two spacecraft.

  Ordinarily we would be unstowing boxes of moon rocks and getting ready to transfer them over. Instead, Houston reads a revised checklist. We are transferring over the PLSS packs so that, if worst comes to worst and Tank 1 fails, we’ll at least have a few more hours’ worth of oxygen. And we’re taking a few nylon tethers so we can stow the packs under the couches for the reentry we’re hoping to have three days from now. It goes without saying that none of us knows if any of this will make a difference. If we’re close to reentry, it might mean everything. If the tank fails now, we’re just delaying our deaths. Still, it beats doing nothing.

  Then we pull up some guidance numbers from the DSKY in Aquarius and read them through the tunnel to Ken so he can convert them and plug them in to Odyssey. Meanwhile Ken has reconfigured circuits and breakers to draw some power from Aquarius while we’re still attached.

  After that, a long burn with the LM attitude thrusters until they’re nearly spent. Something Houston cooked up to give us a touch more delta-v and cut down on the burden on the SPS later. It’s awkward flying, trying to steer the whole stack from the little LM. Like backing a boat trailer down a ramp. We’ve never simulated anything remotely like it.