You have to hand it to the Apollo Spacecraft Project Office: They tried to imagine and equip for many, many scenarios as the two spacecraft were in development in 1964.

Here’s one obscure idea. Your two newest moonwalkers are done and ready to leave the lunar surface for rendezvous with the Command/Service Module.

Sometime before liftoff, the Command Module Pilot passes out, or bites off too much of his corned beef sammich and dies.

The CSM is the only way home for everyone.

Now what?

The question was put to the floor in a couple of letters between the Manned Spacecraft Center, the ASPO and the prime contractors of the CSM and LM.

August 25

At a Contractor Coordination Meeting on June 9-10, the point had been made that there existed a single- point failure that would preclude the crew’s safe return – a disabled crewman in the CM during LEM operations. MSC demanded unequivocally that, even under these circumstances, the two crewmen in the LEM must be able to complete the mission. Therefore, the CSM must be designed for such a contingency; and to limit hardware impact, this must be done by using onboard equipment as much as possible.

Accordingly William F. Rector III, the LEM Project Officer in ASPO, advised Grumman of two operational requirements:

The radar transponder in the CSM must be turned on before the LEM’s ascent from the moon and must be pointed toward the LEM during ascent and rendezvous.

The CSM’s attitude had to be stabilized during this phase of the mission.

The two prime contractors, Rector said, should decide on some means of controlling remotely the CSM’s transponder and its stabilization and control system. The contractors should, however, use the simplest and most reliable arrangement. To initiate these two functions, the CSM would receive commands from the ground. Finally, Rector informed Grumman of a new ground rule on CSM communications: continuous communications, both telemetry and voice, must be maintained whenever the spacecraft was in view of the earth.

Letter, Rector, MSC, to GAEC, Attn: R. S. Mullaney, “Contract NAS 9-1100, Operations Groundrule for Disabled CSM Astronaut,” August 25, 1964.

October 16

In a letter on August 25, 1964, the LEM Project Office had requested Grumman to define the means by which CSM stabilization and rendezvous radar transponder operation could be provided remotely in the event the CSM crewman was disabled.
In another letter on October 16, the Project Office notified Grumman that no requirement existed for remote operation of either the rendezvous radar transponder or the stabilization and control system. The letter added, however, that the possibility of an incapacitated CSM astronaut must be considered and that for design purposes Grumman should assume that the astronaut would perform certain functions prior to becoming completely disabled. These functions could include turning on the transponder and the SCS. No CSM maneuvers would be required during the period in which the CSM astronaut was disabled but the CSM must remain stabilized during LEM ascent coast and rendezvous and docking phases.

Letter, W. F. Rector III to GAEC, “Contract NAS 9-1100, Operations Groundrule for Disabled CSM Astronaut,” October 16, 1964.

Thankfully, this idea never had to be used. But what might have happened in such a scenario?

What the LM Needed for Rendezvous

The Lunar Module had a few dependencies to ensure that they met with the mothership. They needed to encounter the CSM at a specific point in lunar orbit to minimize sun angles that could blind the astronauts as they attempted to find each other and dock.

The great news is that both the LM and CSM used very similar systems for navigation. The LM crew also had data from Mission Control, through their Real Time Computer Complex (RTCC). In short, once the LM knew where the CSM was, the LM would do the bulk of the work for rendezvous.

Houston preferred to make their navigation calculations the default means for both CSM and LM navigation, while using the features of the Apollo Guidance Computers in each spacecraft for the short times while the vehicles were behind the moon and out of earth contact. To verify all calculations, however, both crew and ground would make navigational checks and then compare notes. In Apollo’s history, the onboard computers were highly accurate, relative to the ground calculations. So NASA could relay liftoff information to the LM about the CM even without CMP communication.

The most important bit of data for the lunar ascent is the location of the Command Module in orbit. The position of the CSM determined when the LM was take off as part of the rendezvous calculations. Else, the limited fuel aboard the LM ascent stage might be exhausted from too many course corrections.

Unless there was a very serious issue with the CM’s communications systems, NASA would know of the CMP’s fate immediately. Every astronaut wears biomedical sensors at all times, as part of their constant-wear garment. This telemetry is sent to the flight surgeon.

So if the CMP is dead, the biomed sensors would show this. If the CMP was alive but periodically unresponsive, NASA would likely do what it could to get the CMP to activate a handful of switches that would give Mission Control the ability to run the DAP, or digital autopilot, which could stabilize the CSM.

A CSM with a dead or disabled Command Module Pilot would still be transmitting enough telemetry that could be used as part of rendezvous calculations. Optimally, the CSM would have its rendezvous transponder active. That is part of the unified S-band (USB) system. Even if the transponder weren’t powered on, the basic ranging functionality of the S-band would give enough information for Mission Control to relay to the LM for rendezvous calculations.

The LM’s ascent to a rendezvous in the original flight plans were based on what was called the concentric or co-elliptic rendezvous plan. Later Apollo missions, starting with Apollo 14, would experiment with other plans that would use a more direct rendezvous trajectory and thus leave a shorter time for the the LM to be in orbit. If the CSM was believed to be disabled but still alive, time for the other crew to reach him would be of the essence.

If you want the full story on the co-elliptic plan, here’s a great film from NASA’s Mission Planning and Analysis Division.

These guys and gals were probably the biggest nerds in the whole program and they deserve every accolade. Their calculations made all space travel possible, and they nailed the calculations that made lunar orbit rendezvous work.

Plus, they made some of the coolest, hip films that NASA ever had.

Time would be critical for more than the CMP’s life. Orbiting the moon wasn’t a steady process. The moon had strange mass concentrations of material all around it. This tended to alter things as they moved in lunar orbit. Without a CMP on station, the CSM’s course and altitude may be altered, affecting rendezvous calculations and eventually causing orbital decay over time.

As said before, standard procedure for the LM crew is that they are the active spacecraft in the rendezvous, using their reaction control jets for course corrections. This conserved the reaction control jet propellants in the CSM.

To Dock or Not to Dock

Let’s say that the LM makes it to the CSM. Their mothership could be stable, or tumbling. With a disabled Command Module Pilot, the tumbling situation is more dire, although not impossible.

With a stable CSM, the LM would normally align its docking port and make a slow approach to connect with the CSM docking probe.

But the docking probe isn’t a passive system. There are several latches on the end of the docking probe that must be armed by the CMP for use. If the CSM had rearmed the system after the LM first separated for the powered descent, then it would be possible for the LM to push its drogue against the probe and cause the probe to latch–a “soft” docking.

Normally, after a soft docking, the CMP would command the probe to retract, pulling the LM closer to activate 12 latches that form the hard dock, the pressurized seal where crew could move through the tunnel.

If the probe latches wouldn’t latch, the LM would simply have to get as close as possible–unless the CSM was tumbling. In that situation, they’d have to match the tumble for both spacecraft to appear relatively still to each other.

Returning to the Command Module, the Hard Way

Either soft dock or stationkeeping scenario would have to be enough for the second, more harrowing step: EVT, or emergency vehicle transfer.

NASA planned for EVT and astronauts trained and were equipped for it. Early Apollo equipment included at least one Portable Life Support System (PLSS) backpack inside the CSM, along with the two used for the moonwalk in the LM.

With weight reductions, the CM PLSS was cut, but they did keep a smaller square emergency oxygen pack, found atop each PLSS, called the Oxygen Purge System (OPS), onboard.

Apollo OPS s69-38496
Buzz Aldrin’s Oxygen Purge System from Apollo 11. (NASA)

The OPS was also worn on later Apollo J-missions (15, 16 and 17) by the CMP as backup air while outside on an EVA to get the film from the Science Instrument Module’s camera on the side of the Service Module.

Apollo 9 as09-20-3064-orig
David Scott on Apollo 9. The LM handrail is in the right foreground, extending up. Note also the handholds on the outside of the CM, left of Scott. (NASA)

A test of emergency vehicle transfer was scheduled on the Apollo 9 earth-orbital test of the LM. But the test was cut because Rusty “Upchuck” Schweickart’s space-adaptation syndrome (then a new thing because Apollo’s spacecraft were more roomy and likely to generate the situation) made NASA worried. Also, time was short due to the delay to let Rusty’s body adjust to space so as to carry on with the rest of the mission objectives.


After the last moonwalk, the LM crews would jettison a bunch of things out to the lunar surface that would be unneeded, including the PLSS backpacks. But the crews kept their OPS packs onboard the ascent stage in case EVT was needed.

Typically, emergency crew transfer was primarily for when the docking tunnel was blocked or normal docking failed.  In that case, the LM astronauts would don their suits, connect their suits to the LM umbilical life support hoses (which were designed to be long enough to reach the CM hatch), put on their OPS (which gave about 30 minutes of life support) and exit through the LM egress hatch used for the moonwalk.

One astronaut at time would leave and crawl to the CSM using a series of handrails on both the LM and CM. (See the photo of Apollo 9 above with astronaut David Scott.)

In a normal EVT, the CMP would also be suited up and had depressurized the CM and opened the CM side hatch to help out.

Apollo OPS Fig1-46OPS
The Oxygen Purge System was a backup for the PLSS during a moonwalk. With an emergency vehicle transfer, the OPS would be mounted in front. An umbilical from the LM would also be used for normal life support. (NASA)

With a disabled CMP and without docking, things would get weird. The LM crew would have to get inside themselves.

Carried on every LM was a tool simply named “Tool B.”

It was basically an oversized type of Allen wrench, compatible with a space-suited hand.

Tool B had several uses. One use was removing a drogue and probe inside the docking tunnel from the LM side. This assumed that docking was otherwise normal and all hard latches along the docking ring had sealed the tunnel to make pressurization possible, but that the CMP couldn’t open the CM tunnel hatch or remove the drogue himself.

(The late Neil Armstrong kept a small cache of mementos from Apollo 11. One of them was his Tool B (item #16, the “wrench”).)

Tool B could also remove the Command Module tunnel hatch using recesses on the LM side of the hatch.

Apollo CM hatches
The LM-side view of the CM tunnel hatch (left) and the external side of the CM hatch (right). Both can be opened using Tool B. (NASA)


So, let’s play the worst scenario. The CSM is in a minor tumble. The CMP is dead. The LM has matched the tumble so they are relatively stationary to each other.

After the LM crew donned their suits, they appear to attach a lifeline tether that’s connected to each other (much like what mountain climbers would do). After umbilicals and the OPS are attached and the cabin is depressurized, the EVT procedures went something like this for “Undocked, Unstable” EVT:

  1. CDR (commander) leaves the LM through the forward hatch, feet first.
  2. The LMP (Lunar Module pilot) tends to the CDR umbilical, then follows.
  3. Both CDR and LMP shimmy up to the top of the LM.
  4. On cue, both jump off the LM at the same time, grabbing for the CM probe apex to slow.
  5. Using handholds, CDR and LMP move to the CM side hatch.
  6. CDR uses Tool B to vent the CM using the controls on the side hatch.
  7. CDR uses Tool B to release the latches on the CM hatch to unlock the hatch.
  8. CDR and LMP enter the CM.
  9. CDR and LMP activate their OPS for life support, isolate connections to the LM umbilicals and disconnect them.

From here the hatch is closed and the crew work on repressurization.

I have no idea how the LM would be kept stable as the two crewmen moved about, much less jumped from it. They could leave the LM in autopilot mode and Mission Control would manage it.

If the CMP wasn’t dead before they entered, he’d be dead now, for sure. In fact, all that the LMP and CDR could do on reaching the CM is to knock loudly in hopes of waking up the CMP. If the CMP could at least get into his suit and pressurize, he could survive. But in this disabled-CMP scenario, unconsciousness would spell death for the CMP as well. The returning crew simply has very little time to survive outside of the LM and must depressurize the CM cabin before entering.

Details aren’t available as to what the surviving crew would do with the CMP’s body. Odds are, the CMP is still suited and they need only put on his helmet and gloves to basically pickle him for the trip home. Despite the morbid idea, this is a serious concern. The crew could be ordered to depressurize and give the CMP a Viking funeral to let him float away into space, but this isn’t likely.

Why? For one, the Command Module is meant to come home with a specific weight and center-of-gravity. There were scenarios for the CMP to come home alone if the LM crew didn’t survive, which meant that, with the missing mass of lunar samples and two crew, the re-entry angles could be adjusted. Dead or alive, the CMP has some value for making the re-entry calculations easier.

Let’s mention the fact that the CMP’s families and the nation might want to have their loved one to bury if keeping him aboard didn’t jeopardize the lives of the surviving crew.

On the bright side: Remember the contingency sample that the CDR retrieves just after stepping foot on the moon, stuffing it into a pouch on his space suit? This scenario is one reason why it’s retrieved. EVT would leave all other lunar samples behind; there’s no safe way to retrieve them.

Emergency vehicle transfer in a tumbling scenario would make for one hell of a movie. Thank goodness it would be wholly fictional.