Parallels of the BIS Lunar Space Suit and Apollo Extravehicular Mobility Unit
Evan Champney, Spring 2025
In the late 1940s, long before the eventual Apollo program was developed across the pond, a group of space enthusiasts gather in a small house in London to discuss a new design for a space suit designed to allow an individual to live and work on the moon. Members of the British Interplanetary Society, their organization serves to educate and inspire members of the public on the matters of space travel. Whether it be on the use of rockets to reach space to the establishment of lunar colonies and beyond, it would seem that no topic could be idealistic for their considerations. Among their members is Harry Ross, whose new design for a Lunar Space Suit would closely parallel the eventual development of NASA’s Extravehicular Mobility Unit or EMU (consisting of the Personal Life Support System or PLSS and Pressure Garment Assembly or PGA) used in the Apollo Program some 20 years later.
Mr. Ross’ design considers chiefly two issues that would be present for any would-be lunar explorer, those being the management of heat and air. On the surface of the moon, surface temperatures would regularly move between 250 °F and -140 °F throughout the lunar day and night. Seeing this wide range of fluctuation, much of the Lunar Space Suit’s design is influenced by heat regulation. The ability to store heat during the night and to reject it under the sun is of paramount importance to Ross’ considerations, and numerous clever solutions are employed to this end. Most noticeable at first glance is the bright metallic finish on the surface of the suit. This finish was chosen to reject the heat added by the sun and by radiation from the hot lunar surface. The silvered exterior of the suit would reflect much of this energy, providing some measure of protection against the added heat. The one exception to this is the notably dark chest area, which is painted black to allow for its easier emission of heat to the environment.
Also present for the matter of heat rejection is a refrigeration system included in the backpack of the suit. In this module the internal atmosphere of the suit would be continually passed through a heat exchanger, in which its thermal energy would be transferred to a working fluid such as ammonia. The temperature of the suit would actuate a thermostatic valve, which would expose the ammonia to the vacuum of space, causing it to evaporate and thereby removing heat from the interior of the suit.
This system almost exactly parallels the similar subsystem of the PLSS. Here the working fluid chosen was water, which would pass by a porous plate on the exterior of the suit. Upon reaching the holes in the plate the liquid water would evaporate and absorb energy from the device, freezing the porous plate shut and preventing further cooling. Should the temperature of the water rise too far however, the frozen plug would then melt allowing for further evaporation and thereby cooling the suit only when its temperature exceeded a specified threshold. By specifically sizing the holes in the porous plate, the exact activation temperature could be controlled and automatic temperature regulation could be achieved with no moving parts. This type of cooling device, known as a porous plate sublimator, was first developed for the Apollo program but sees continued use to this day aboard the International Space Station.
By using the combined effects of the ammonia vapor refrigeration and clever placement of reflective materials, Ross claims that his system would be capable of rejecting 60 calories per second or about 250 watts from the suit. The actual standard that NASA specified for the PLSS started at 500 BTU/ hour or about 150 watts, later being increased after physical testing to 1200 BTU/ hour or about 350 watts. This puts Ross’ design within the realm of feasibility for having only very rough estimates for what the requirements for such a cooling system would be.
As for the issue of the internal atmosphere of the suit, three key factors must be controlled, those being the concentrations of oxygen, carbon dioxide, and humidity. Having too little or too much of any of these could result in, at the best case, severe discomfort or, in the worst, death. Both NASA and Ross suggest storing oxygen as a compressed gas, however Ross notes that storing it as a liquid may be worth consideration. The issue with this format is again heat retention, as any heat absorbed by the liquid oxygen would cause it to evaporate and possibly overpressure the system. NASA’s initial designs for the PLSS store oxygen in an onboard tank at a pressure of 1,110 psi, allowing for a runtime of around 4-6 hours for the Apollo 11-14 missions. With the introduction of the lunar rover however it was desirable for the duration to be extended. This necessitated moving the storage pressure up to 1,500 psi, allowing for run times of up to 8 hours. Ross claims an operational capacity of up to 12 hours with up to 43% reduction in oxygen storage capacity by using a clever trick with regards to the exhaled carbon dioxide.
The Apollo PLSS and Lunar Modules both used the same method for removing carbon dioxide from the atmosphere, that being canisters of lithium hydroxide. The reaction of lithium hydroxide sequesters the carbon in a physical state as lithium carbonate, and generates water as a byproduct. Ross however suggests using sodium peroxide, the reaction of which generates a similar sodium carbonate solid but importantly oxygen as its byproduct, rereleasing some of the previously inhaled oxygen to be used once again. This allows Ross’ Lunar Space Suit to carry significantly less oxygen while allowing for longer mission durations. The sodium peroxide also serves to absorb excess moisture from the internal atmosphere, a job carried out by the liquid water refrigeration system in the Apollo PLSS. While NASA did investigate the use of sodium peroxide and other related chemicals for this purpose, ultimately they ruled in favor of using lithium hydroxide instead. It is possible that NASA rejected the use of Sodium Peroxide due to its effects as a very strong oxidizing agent, making the risks associated with fires much more severe, or due to concerns regarding the synthesis of such a large amount of a relatively obscure compound.
The construction of the physical suit in both instances are also remarkably similar. Ross suggests in order from inside out a soft inner lining, an airtight layer of fabric backed rubber, a thick layer of heat retaining insulation, and the outer metallized fabric. Ross correctly identified from previous research into diving and stratospheric suits that the pressurized rubber layer should be fabric backed to prevent it from stretching like a balloon under pressure. Were this to be the case it would significantly hinder the movement of the astronaut within. NASA’s design for the PGA shares all of these layers sans the reflective outer layer and includes several extra layers for protection from micrometeoroids and lunar dust.
Overall the details explained in Ross’ 1949 pamphlet show a remarkable understanding of the types of problems likely to be encountered by potential lunar astronauts, and his clever solutions to many of these issues parallel the eventual designs of NASA’s Apollo mission some 2 decades later. Ross’ thermal management system bears an uncanny resemblance to the mechanism and construction of the eventual porous plate cooling system that would be developed for the Apollo PLSS. His suggestion to use chemical filtration of the exhaled carbon dioxide mirrored the method eventually chosen for use within the PLSS and on the Lunar Module, and his choice of sodium peroxide for this purpose was at one point considered as well. Construction of the suit from a multi-layered composite proved a sound method to allow for the numerous design constraints that would be required by such a mission, and the issues of comfort, air retention, and stability are factored into both Ross’ and NASA’s designs. The fact that a group of space enthusiasts could, with little more than idle speculation, reach similar conclusions as those resulting from the largest space forward initiative yet seen deserves nothing more than the highest of commendations, and speaks wonders to the merits of such a simple thing as the curiosity of the human mind
Bibliography
“Apollo’s Second Generation PLSS.” United Technologies Aerospace Systems via Thomas, Kenneth S. “The Apollo Portable Life Support System.” Accessed 2025-04-28 https://www.nasa.gov/wp-content/uploads/static/history/alsj/ALSJ-FlightPLSS.pdf
“Astronaut Edwin Aldrin walks on lunar surface near leg of Lunar Module.” 1969-07-20. https://images.nasa.gov/details-as11-40-5903 Accessed 2024-04-28
“British Interplanetary Society Lunar Space Suit.” British Interplanetary Society Lunar Spacesuit. The National Space Centre. Exploration Drive, SPACE CITY, Leicester LE4 5NS. Accessed 2024-04-28 https://www.spacecentre.co.uk/collections/categories/spacesuits-and-clothing/british-interplanetary-society-lunar-spacesuit/
Capotosto, A. Jr., Marriott J. A., Petrocelli, A. W., Uno, R., “The Synthesis And Utilization Of Low Molecular Weight Ozonides For Air Revitalization.” 1966-6-14. NASA Technical Reports Server. Document ID, 19670018175. Accessed 2025-04-28.
Carson, Maurice A., Lutz, Charles C., McBarron, James W. II., Rouen, Michael N. “Extravehicular Mobility Unit.” 1975. NASA Technical Reports Server. Document ID, 19760005607. Accessed 2025-04-28.
“Extravehicular Configuration of Torso Limb Suit Assembly (TLSA).” “Extravehicular Mobility Unit.” 1975. NASA Technical Reports Server. Document ID, 19760005607. Accessed 2025-04-28.
Gillen, R. J., Brady, J. C., Collier, F. “Apollo Experience Report: Lunar Module Environmental Control Subsystem.” NASA Technical Reports Server. Document ID, 19720013195. Accessed 2025-04-14.
The Lunar Space Suit. The British Interplanetary Society. 2020-11-29. https://www.bis-space.com/the-lunar-space-suit/ Accessed 2025-04-14.
Parkinson, Bob. Interplanetary: A History of the British Interplanetary Society. London, British Interplanetary Society, 2024.
Ross, H. E. “Lunar Spacesuit.” Journal of the British Interplanetary Society, 1949, pp. 23 - 37
Smith, Ralph A. “Sectional View of Space Suit.” “Lunar Space Suit.” Journal of the British Interplanetary Society, 1949, pp. 26. British Interplanetary Society, London.
Thomas, Kenneth S. “The Apollo Portable Life Support System.” https://www.nasa.gov/wp-content/uploads/static/history/alsj/ALSJ-FlightPLSS.pdf Accessed 2025-04-28