Monday, December 17, 2012

A Jones for MOL #6: Not Quite a Vacuum.

If you have read any of my preceding “A Jones for MOL” blog posts, you might have been wondering where all of this hypertrivial analysis of a defunct spaceflight project was leading. Your patience will now be rewarded, and if your response is, “That was the blockbuster?” I will also tell you why it is so interesting that it motivated these six blog posts and a few more yet to come.

The Revelation

Here it is: during their 30-day mission, while the two MOL pilots were to have been evaluating space reconnaissance techniques as well as being guinea pigs for space biomedical research, their Gemini-B capsule would have been sealed off and depressurized to 0.1 psi (5 mm. Hg, 0.7 kPa, 0.007 atm)—the same as atmospheric pressure at 42 km (26 miles) above Earth’s surface (ref. 1). Humans need supplemental oxygen above about 3 km (10,000 feet) altitude, and space suits above 19 km (12 miles), so the cabin pressure would have been just a smidge better than a vacuum, uninhabitable for the duration of the mission.

I stumbled upon this surprising and unexpected aspect of the MOL’s human factors plan while re-reviewing some declassified MOL documents at NASA’s Technical Reports Server (  As far as I know, this has not been reported anywhere since 1968. I do not remember ever having seen it reported, or even mentioned, anywhere else, certainly not among the rote, repetitive assertions that accompany any new discussion of MOL on the Internet.

Powered Down

It has long been known that the 90 ft3 (2.6 m3) Gemini-B capsule (ref. 2) was to be powered down, that is, many of its electrical systems were to be turned off, during the 30-day operational mission of the MOL reconnaissance station. Such a power-down has been, and continues to be, common practice in space station missions. It was not even unprecedented during the MOL planning period, although the single time it had happened before was unplanned. In August 1965, Gemini 5, the third manned capsule in the series, was testing electricity-producing fuel cells in flight for the first time. These were required for future long-duration missions, including the Apollo moon flights. According to NASA (ref. 3), “About [2 ½ hours after launch], the crew [command pilot Gordon Cooper and co-pilot Charles Conrad] noticed the pressure in the oxygen supply tank of the fuel cell system was dropping. At some point earlier in the flight the oxygen supply heater element had failed, and the pressure dropped from nominal pressure of 850 psia to a low of 65 psia 4 hours and 22 minutes into the flight. This was still above the 22.2 psia minimum but it was decided to […] power the spacecraft down. An analysis was carried out on the ground and a powering up procedure was started on the seventh revolution. Over the rest of the mission the pressure slowly rose in the fuel cells and sufficient power was available at all times.”

After entering the lab module, an early task of the Gemini-B co-pilot would have been to activate the lab’s systems so the command pilot could then shut down most of the Gemini-B’s systems for long-term quiescence. All guidance and navigation and communications systems would be off or on stand-by. Spacecraft power from the laboratory would preserve the capsule’s non-rechargeable batteries for re-entry. During the month-long mission, the Gemini-B would remain quiescent, and the pilots in the lab would monitor 10 parameters of its systems, including the pressure in two gaseous oxygen and two nitrogen tanks, in two fuel and two oxidizer tanks for the maneuvering engines, and the status of two coolant pumps. Meanwhile, 73 Gemini-B parameters would be monitored from Earth via the lab’s communication system whenever its orbit passed over a tracking station (ref. 4).

The phrase “powering down a spacecraft” brings to mind the images of the inert command module in Apollo 13 (both the movie and the actual spaceflight). The cabin would not be continually heated by its electronics, and would get cool. Then it would get damp, too, as the pilots’ warm, moist breath diffused throughout the open tunnel from the laboratory module into the capsule. This had been a problem on Gordon Cooper’s 34-hour Mercury flight in 1963: the short-circuiting of critical re-entry control systems led to improved packaging for electronics on the Gemini spacecraft, as well as relocating much of those systems outside the crew cabin, in the vacuum of space. Ironically, Cooper faced the challenge of a power-down on his second spaceflight on Gemini 5.

Closed and Depressurized

After its power-down, the Gemini-B was to be sealed off for its long dormancy and then depressurized. The MOL pilots would have lived in the 400 ft3 (11.3 m3) pressurized laboratory module (ref. 5) for all but the first and last few hours of the flight. This plan for the isolation and prolonged decompression of a portion of a manned spacecraft during flight was and is unprecedented in the annals of human spaceflight, but reflects the knowledge, experience and concerns of the manned spaceflight community of the day, 1964.

Of course, the Gemini capsule was designed to be depressurized because space walking, or extravehicular activity, was a goal of the Gemini program. The capsule needed to be opened to the vacuum of space so an astronaut could exit it and perform useful tasks outside. But these were episodic, rare and brief events, not continuous for weeks at a time.

In other spaceflight experience, during Skylab missions, the unpowered Apollo command module was accessible continuously and was used for privacy by the astronauts because temporary ducts circulated fresh, dry air through the capsule. The Russian Soyuz was also accessible during Salyut and Mir missions—and remains so during International Space Station (ISS) missions. Ditto for the Chinese Shenzhou-9 while docked with Tiangong-1. Of course, the Space Shuttle was open to the Mir and ISS on all of its docking missions, and was fully powered the whole time, even drawing current from the ISS’s solar panels to extend its own orbital lifetime.

However, the depressurization is mentioned specifically in only one document (ref. 4), a report produced by Bellcom, Inc., a Washington-based contractor which analyzed Apollo program technical decisions for NASA Headquarters. Early in 1968, Bellcom’s R.K. McFarland met with representatives of McDonnell–Douglas to learn how the Gemini-B capsule was being modified for long-duration quiescence, in a mode comparable to that planned for the Apollo command-service modules during upcoming NASA space station missions. Among other things, McFarland was told that the Gemini-B would be depressurized to 0.1 psia, with the crew not re-entering the capsule until the end of the 30-day mission.

Independent, albeit indirect, evidence for the long-term isolation of the Gemini-B is found in a fire safety report (ref. 6) by The Aerospace Corporation, the systems engineering contractor for MOL, in mid 1967, before McFarland’s visit. This report documented the responses of the MOL Program to the recommendations of the review boards for the Apollo 1 fire and the Brooks AFB chamber fire (ref. 7), both of which occurred within a period of four days at the end of January 1967.

The report noted that, “[u]nder the original baseline, the Gemini B was [to be] repressurized with 100 percent oxygen prior to crew transfer from the Laboratory. In case of a fire emergency in the Laboratory requiring the crew to abort to the Gemini, this pure oxygen atmosphere would have made a hazardous situation worse. A capability is being added to permit repressurization of the Gemini B with a two-gas atmosphere from the laboratory atmosphere supply source to minimize this hazard. In addition Gemini B emergency repressurization time is being sharply reduced.”

This is a telling comment: a repressurization of the Gemini-B capsule would have been necessary only if it had been depressurized earlier in the mission.


As originally designed, the Gemini-B’s life support system would have required remote control—either from Earth or from the MOL—to repressurize its cabin by releasing pure oxygen from on-board storage tanks. The added capability mentioned in the Aerospace report might have been as simple as a valve in the hatch between the MOL and the Gemini-B which would allow MOL atmosphere to flow into the Gemini-B.

There is another indication that the Gemini-B would have been left unattended, if not actually sealed and depressurized, for the 30-day MOL mission. In a memo reporting the results of a visit by MOL engineers to the GE space simulation facility in Valley Forge, Pa., astronaut Scott Carpenter is quoted as saying he wouldn’t leave the Gemini unattended for 30 days without several checks on its condition (ref. 8). The fact that he was saying anything of the sort is evidence that someone, either GE or the Air Force, must have asked his opinion about leaving the Gemini unattended for 30 days. In a vehicle with only 400 cubic feet of volume, if the secluded the Gemini cabin plus the attraction of its two windows were available, it would undoubtedly have prompted frequent visits from off-duty MOL pilots, who could then almost casually have checked on its systems—unless they were physically blocked from such visits.

In the absence of any explicit contemporary reports to the contrary, the two contractor reports from Bellcom and The Aerospace Corporation establish that the Gemini-B was indeed to be depressurized while in quiescent in-flight storage. All of the other primary and secondary sources are silent on the pressurized state of the Gemini-B during the MOL mission. Judging from discussions on some authoritative listservs, this plan to isolate and decompress the Gemini-B capsule during the MOL missions is literally unknown by space history buffs today.

Why the Depressurization?

The available documents don’t mention the reason or reasons for the prolonged depressurization, but I can suggest a couple. First, as previously mentioned, the pilots would have been the source of substantial humidity. The unpowered Gemini-B capsule would have been a natural cold-trap for that humidity, and would probably have become quite damp quite quickly. This subsequently happened on Apollo 13, whose astronauts actually experience a bit of a rain shower as their damp command module entered the Earth’s atmosphere and the condensation dripped onto them from the control panel and other overhead structures.

Sealing off the Gemini-B would also have reduced the air leakage that was an inevitable feature of any manned spacecraft, especially one with two large crewmember hatches.

As I said, I have not seen any documentation of the reasons for the decompression, but these may have been contributing factors.

How the Depressurization?

But how would the Gemini-B capsule have been sealed off? There were hatches between the Gemini-B cabin and the MOL’s pressurized laboratory—surely they were used for that purpose. In my next post I will describe how it might have been done, or not.

  1. Calculated using the equations at (accessed 16 Dec. 2012).
  2. Cohen, M., “Testing the Celentano Curve: An Empirical Survey of Predictions for Human Spacecraft Pressurized Volume,” 38th International Conference on Environmental Systems, San Francisco, California, June 29-July 2, 2008, SAE TECHNICAL PAPER SERIES 2008-01-2027, (accessed 28 Aug. 2012).
  3.  __, “Gemini 5,” National Space Science Data Center, (accessed 16 Dec. 2012).
  4. McFarland, R.K., , Bellcom, Inc. “Subsystem Modification to Develop Quiescent Operation for Gemini B, Case 620”, February 28, 1968, (accessed 6 Aug. 2012). McFarland briefed C.W. Matthews, Director, Apollo Applications Program, on Feb. 15.
  5. Wade, M., “MOL,” Encyclopedia Astronautica, (accessed 28 Aug. 2012).
  6. __, “MOL safety evaluation based on Apollo 204 Review Board findings and recommendations and Brooks Air Force Base Accident Investigation Board Conclusions,” Aerospace Corporation, AD-856687L, 58p., September 1967.
  7. __, “Apollo-1 (204),” (accessed 17 Dec. 2012).
  8. Anderson, J.J., Col., AFRMO, “Memorandum for the Record, Trip Report to Valley Forge, GE, Simulation Tests,” 20 Aug. 1964, courtesy of Dr. Dwayne Day.


  1. Serving as the most trusted supplier of test chambers, walk-in chambers, climatic chambers, and environmental chambers are the areas we specialize in.

    For more info : Vacuum Altitude Chamber

    1. I allowed this comment because it was on-topic (sort of) and because it was the only comment I received on this post (sigh).


Please feel free to suggest topics or comment on anything. Let's keep it on topic, and cite your sources whenever possible!