31 August 2015

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Image credit: NASA
On 28 July 1973, the Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off from Launch Pad 39B at Kennedy Space Center, Florida, bound for the Skylab Orbital Workshop in low-Earth orbit. Despite their mission's numerical designation, they were the second crew to visit Skylab; in a move guaranteed to generate confusion for decades to come, NASA had designated as Skylab 1 the unmanned Workshop launched on 14 May 1973, and had dubbed the first crew to visit it Skylab 2.

The Skylab 3 Apollo Command and Service Module (CSM) separated from the S-IVB second stage of its Saturn IB launch vehicle and began maneuvering to catch up with Skylab. During final approach to the Workshop, one of the four steering thruster quads on the CSM began to leak nitrogen tetroxide oxidizer from its forward-firing engine. The crew dutifully shut off the quad and used the three quads remaining to complete docking without further incident.

On 2 August, a second thruster quad began to leak, raising fears that tainted nitrogen tetroxide might have damaged both quads. If this were the case, then the Skylab 3 CSM's remaining two quads and Service Propulsion System (SPS) main engine might also have been compromised; though the individual quads and the SPS had independent plumbing, all contained oxidizer from the same batch. If the leaks continued and spread, moreover, nitrogen tetroxide might contaminate the inside of the CSM's drum-shaped Service Module, potentially damaging other spacecraft systems.

The leaks did not catch NASA off guard. As was common in the 1960s and early 1970s, NASA had considered potential Apollo and Skylab failures - however unlikely - and had planned ahead. Within hours of the second leak, The U.S. civilian space agency put into motion a variant of a plan Kenneth Kleinknecht, Skylab Program Manager, and Lawrence Williams, Apollo Spacecraft Program Office, had described less than a year earlier at the Fifth Annual Space Rescue Symposium in Vienna, Austria.

In their paper, Kleinknecht and Williams explained that Skylab would provide the first true opportunity for space rescue in the U.S. space program. One-seat Mercury and two-seat Gemini spacecraft had been too small and limited in capability to serve as rescue spacecraft. Apollo lunar CSMs were much more capable; even so, they each carried only a little more breathing oxygen, fuel cell reactants, and food than were needed to support a three-man crew for the duration of a lunar mission (about 10 days). If an Apollo CSM had become stranded in lunar orbit – by an SPS failure, say – then its crew would have perished long before NASA could have attempted a rescue.

The Skylab Orbital Workshop. The red arrow points to the Multiple Docking Adapter's radial port. Image credit: NASA
If astronauts needed to evacuate Skylab, they could board their CSM docked at Skylab's front port, undock from the Workshop, and splash down in the ocean in less than a day. If, on the other hand, a crew's CSM became unusable while they lived and worked on board Skylab, then the astronauts could await rescue.

Stranded astronauts were unlikely to run out of supplies. Kleinknecht and Williams noted that the Orbital Workshop would be launched with enough oxygen, food, water, and other supplies on board to support three men for eight months. At the time they presented their paper, NASA planned three three-man Skylab visits lasting 28, 56, and 56 days - that is, a total of a little less than five months.

NASA, meanwhile, would prepare and launch a rescue CSM with a crew of two. Skylab, Kleinknecht and Williams explained, had a second, radial docking port on its Multiple Docking Adapter. The rescue CSM would dock at the radial port to pick up the stranded crew.

They proposed that the CSM intended for the next Skylab crew should become the rescue CSM. This would presumably reduce by one the number of long-duration Skylab missions that could be flown. A fourth CSM, which would serve as the backup CSM throughout the Skylab program, would serve as the rescue CSM for Skylab 4, the third and final planned Skylab crew.

Image credit: NASA
Kleinknecht and Williams estimated that stripping out the rescue CSM's aft bulkhead lockers to make room for a "rescue kit" would require about a day. The rescue kit would include a pair of special astronaut couches, connectors and hoses for linking two additional space-suited astronauts to the rescue CSM's life support and communications systems, and an experiment-return pallet for bringing home a select few of the stranded crew's science results. The rescue CSM's two-man crew would recline in the left and right CSM couches; the three rescued Skylab crewmen would return to Earth in the center couch and in the two special couches mounted below the others in place of the lockers.

The rescue CSM would bring along a special Apollo probe-and-drogue docking unit that would enable astronauts inside Skylab to manually undock and cast off the crippled CSM. This would clear the Workshop's front port for any future CSM dockings. Kleinknecht and Williams did not explain what would happen to the unmanned CSM after it was discarded.

Though the time needed to install the rescue kit was minimal, the time needed to refurbish Pad 39B and prepare the rescue CSM and Saturn IB rocket for launch would depend upon when NASA declared that a rescue was necessary. After each Skylab Saturn IB launch, ground crews would need about 48 days to refurbish Pad 39B and prepare the next Skylab CSM and Saturn IB.

If a rescue were judged to be necessary at the beginning of the 28-day first manned Skylab mission (Skylab 2), then the mission would be extended by 20 days, making the total duration about 48 days. If a rescue were declared to be necessary late in Skylab 2 - say at the time of planned return to Earth - then preparations for the next Skylab CSM launch would be farther along, but would have started later. The rescue CSM and Saturn IB would thus need 28 days before they could lift off, bringing the total Skylab 2 mission duration to about 56 days, or double the duration planned at launch.

Activation of the Skylab rescue capability early in the Skylab 3 or Skylab 4 mission might permit a rescue before the return time planned when the stranded crew left Earth, Kleinknecht and Williams found. A failure near the planned conclusion of Skylab 3 or Skylab 4 would see a rescue CSM launched as little as 10 days after the rescue plan was activated.

Skylab rescue crewmen Vance Brand (left) and Don Lind. Though he never flew to Skylab, Brand would reach space as part of the Apollo-Soyuz Test Project in July 1975 and as Commander of Space Shuttle missions STS-5 (November 1982), STS-41-B (February 1984), and STS-35 (December 1990). Lind would reach space as a Mission Specialist on Shuttle mission STS-51-B (April-May 1985). Image credit: NASA
The 2 August 1973 failure of the second Skylab 3 CSM thruster quad unleashed a storm of activity. NASA prepared the backup Skylab CSM, not the Skylab 4 CSM, as its rescue vehicle, and tapped Skylab 3 backup crewmen Vance Brand and Don Lind to pilot it.

NASA had made other changes to Kleinknecht and Williams' rescue plan. The special probe-and-drogue docking unit for casting off the malfunctioning CSM had become a concave drogue unit that would be installed over the front port. It was launched with Skylab, not in the rescue CSM. After they installed it, the stranded astronauts would "trigger" the drogue to manually release their balky CSM. The rescue CSM would then dock at the front port, not the radial port.

Almost as soon as NASA activated the rescue plan, laboratory analysis on Earth showed that the batch from which the nitrogen tetroxide in the Skylab 3 CSM's propulsion systems had been taken was not tainted. As unlikely as it might seem, the two thruster quad malfunctions lacked a common cause.

Working in the CSM simulator in Houston, astronaut Brand demonstrated that the Skylab 3 crew could maneuver their spacecraft adequately even if they lost a third thruster quad. That is, if they were left with only one functioning quad when time came for them to return home, they could still safely deorbit their CSM.

Though rescue preparations continued as a precaution, by 10 August NASA managers had cleared the Skylab 3 crew for the full duration of their planned 59-day mission on board the Workshop. On 25 September 1973, Bean, Lousma, and Garriot returned to Earth as originally planned, in the CSM that had launched them to Skylab.


"Skylab Rescue Capability," Kenneth S. Kleinknecht and Lawrence G. Williams; paper presented at the Fifth Annual Space Rescue Symposium Organized by the Space Rescue Studies Committee of the International Academy of Astronautics, 23rd Congress of the International Astronautical Federation, Vienna, Austria, 9-12 October 1972

Skylab News Reference, NASA Office of Public Affairs, March 1973, pp. IV-6 - IV-8

"Skylab: Outpost on the Frontier of Space," T. Canby, National Geographic, October 1974, p. 460

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)

What If An Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)


  1. Hi David,

    Vance Brand first made it into orbit during ASTP where, ironically enough, a nitrogen tetroxide leak incapacitated the crew after splashdown.

  2. Oops! Can't believe I forgot that! Thanks for the correction.


  3. Could the Apollo 13 astronauts have retrieved the nuclear powered experiment from the LM equipment bay and harnessed its electrical output to benefit their crippled CSM? Charge batteries? Turn heaters on?

  4. The nuclear power source was kept in a holder outside the LM. The astronaut would remove it with a special tool stored outside the pressurized cabin. Getting to that tool through an unrehearsed spacewalk without adequate handholds/footholds and using it to move the nuclear source would have been a non-trivial challenge and probably very dangerous given its high temperature (it could easily melt through space suit material). Once inside, it would have produced a dangerous radiation dose. There'd be no way to get electricity from it.

    Putting it into the ALSEP central station would be impossible given the way the central station was packed in the LM descent stage. Even if one could, there'd be no way to get the central station into the spacecraft or to tie it electrically to the CSM or LM systems. I'm not sure whether the electrical systems were even compatible. I would guess not.

    Is this question inspired by THE MARTIAN? As I recall, Watney recovered the MAV nuclear source that had been removed and buried some distance away from the habitat. That was a fictional nuclear source, so author Weir could make it work to fit his plot.


    1. Thank you for a complete and thorough answer to my question. Came up with the idea on my own. I knew Apollo 13 carried some kind of nuclear powered experiment, and it is now on the bottom of the ocean, having survived atmosphere burn up (unlike the Apollo 13 LM).
      The Skylab 2 astronauts had to do an EVA, with little rehearsal/training to fix the damaged Skylab module. And latter Apollo moon missions had an astronaut spacewalk to retrieve film from the SM on the trans earth glide home. And Apollo 9 astronauts did a little bit of spacewalking out of the LM in earth orbit just as a test in case that ever became necessary. So I figured maybe it could be done.
      On latter moon missions, the astronauts said they could feel the heat right through their suits as they set up the ALSEP!! I always wondered if there was an ingenious way to tap that electricity--even with a jury rigged set of jumper cables; somehow penetrate the electrical system and recharge the LM main batteries. Yes radiation would be a huge issue. The heat would have been nice, as Apollo 13 was cruising home at about 40 degrees F. Brrr.
      I wonder if Apollo planners ever thought to configure the ALSEP power as a life boat; much like the LM lifeboat scenario on 13. Or even considered a trickle solar cell re charger for those CM batteries they drew so heavily on right after the explosion. I know electrical was reconfigured after Apollo 13; still they barely made it back with no battery power to spare!!
      One more off the wall scenario: Could the SIVB have carried emergency supplies (water. battery, air, propulsion, etc) and simply have flown, at a safe distance away from the CSM, as an emergency supply ship? What a waste to slam it into the moon; perhaps it could even propel a stranded CSM in lunar orbit, homebound!! Was there anyway to hold those stages in lunar orbit on standby for the next mission?

    2. The nuclear power source was Plutonium 238 which emits alpha particles during radioactive decay. Alpha particles are easily stopped by something as thin as a piece of paper. Since alpha particles are so easy to stop, they don't travel very far resulting in a concentrated source of heat. The heat is a far greater hazard than the radiation.

  5. Typically NASA just wanted to be rid of the S-IVB so it wouldn't create a collision hazard or a navigational distraction. Slamming the S-IVB into the moon was an experiment - it rattled the moon, producing seismic waves which reached the seismometers left by previous expeditions. That gave geophysicists inight into the moon's internal structure. There was a scheme to use the S-IVB as a relay for Farside missions - as it flew past the moon, it would have had much of the Farside and Earth in line of sight at the same time. There was also a plan to land an S-IVB on the moon to use as a habitat. Nothing came of these plans, of course.



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