GB flag iconENCN flag iconZH

Footwear in space

Reporting on how NASA designed astronaut boots when its space programme began, and the special problems created by the Moon landings.

by Stuart Morgan

Image © NASA

As head of advanced development, Joe Kosmo worked on the design of a number of space suits used by the National Aeronautics and Space Administration (NASA), beginning with the Mercury programme in the 1960s – including the boots used by astronauts for spacewalks and during the Moon landings. Originally an aeronautical engineer, Mr Kosmo was approached in the early days with an interesting proposition – to help develop life support systems for space suits. At first, he was unsure about how his skills could be put to use, saying: “I don’t know much about space suits.”

“Well, no-one else does, either,” came the reply “We’re all going to learn.”

The team gained knowledge quickly, and set to work designing a complete suit for the United States’ first step into space. With no experience of such high-altitude flight, educated guesses about the actual conditions an astronaut would encounter once he was free of the Earth’s atmosphere resulted in the adaptation of the closest equipment available – air suits worn by American pilots on the edge of space.

Despite NASA’s best efforts, the first human in space was actually a Russian – Air Force pilot Yuri Alekseyevich Gagarin – who travelled a single orbit of Earth on 12th April 1961. Just three weeks later, the USA followed by launching its first astronaut Alan Shepherd on a suborbital flight as part of the Mercury programme. The initial orbital flight took place on 20th February 1962, when John Glenn was thrust into space by an Atlas rocket.

Some of the Mercury suit components from 1961

A new design for boots was needed for the first ‘extra-vehicular activity’ (EVA) ‘spacewalk’. Because of the astronaut being in free space, NASA had to produce a thermal cover for the existing Gemini footwear, to take account of the extreme environment the equipment would now be expected to cope with.

Ed White was the first NASA astronaut to leave the protection of his spacecraft when he ‘walked’ in space for 22 minutes in June 1965. The boots he wore did all that was expected of them and proved a valuable stepping-stone to achieving the stated goal of putting a man on the Moon before the end of the 1960s.

Walking on the Moon

This new adventure required a programme – called Apollo – that would be so much bigger and require far more redesigns than anything NASA had done before. The obvious evidence of such effort and ingenuity was the giant Saturn V rocket used to power three men to the Moon, as well as a smaller craft which allowed two of its astronauts to land and then return the crew safely to Earth. However, NASA also needed a new generation of space suits and boots that could provide a combination of protection and mobility in what was, basically, an unknown environment.

Because NASA did not really know what the surface of the Moon was like, there was a fear that the Lunar Module or the astronauts themselves would sink into the dust. However, as with the Mercury and Gemini programmes, the organisation had some smart people working for it, and their judgment of the Moon’s surface was right, so there was a reasonably firm surface on which to stand.

Prototypes for the Apollo boots were first designed in 1962 and, within six years, a definitive design had been forged. During the Apollo programme, this footwear gradually evolved, with the last changes made in 1972.

Temperature extremes on the Moon can vary between -233°C and +123°C (-387°F to +253°F ), and astronauts also have to contend with the hazard of rocks lying just under the lunar dust. The great day when a man finally walked on the Moon arrived in 1969, when Neil Armstrong secured his place in history on 20th July as a member of the Apollo XI crew.

As can be expected, the boots that he and fellow astronaut Edwin ‘Buzz’ Aldrin wore that day had to meet the most stringent safety and performance specifications. These consisted of two main parts – an inner ‘pressure boot’ with a flexible sole which was worn by the crew during their time in space, and a galosh that was strapped on over the inner boot prior to stepping onto the Moon.

The inner boot’s sole was constructed from a non-flammable elastomer and ‘honeycomb’ material – a reaction to the tragic fire in the cabin of the Apollo I craft during a preliminary test and launch rehearsal on January 27th 1967, which cost the lives of Gus Grissom, Ed White and Roger Chaffee.

The outer boot consisted of 12 layers of biaxially-oriented polyethylene terephthalate (boPET) – a polyester film (commonly called ‘Mylar’) made from stretched polyethylene terephthalate (PET). This was selected for its high tensile strength, chemical and dimensional stability, reflectivity, gas barrier and electrical insulation properties. This footwear also included a nonwoven PET product and a fibreglass/ polytetrafluoroethylene (PTFE) inner liner material.

Requiring good flexibility under very low temperatures, the ‘RTV630’ sole was manufactured from silicon by the General Electric Company, and featured a ¼ inch tread. A fabric incorporating stainless steel was selected for the covering of the outer boot, as this provided good abrasion resistance.

Testing times

Most live testing of the spacesuits and boots took place in environmental chambers, although a limited amount of testing ‘in the field’ did take place in the USA’s closest representation of the lunar surface – Arizona.

The major complaint raised by the astronauts during their EVAs was the amount of dust which found its way between the inner and outer boots.

They described walking on the surface of the Moon as being ‘like a dirty camping trip’, so better dust-excluding materials were sourced. Certain materials broke down under the extreme conditions, so they were replaced. However, the RTV630 soles and the thermal insulation held up well.

Staying attached


Astronaut Piers Sellers on a 2002 Shuttle mission spacewalk with his boots secured in a restraint

After lunar surface exploration had been performed by six pairs of American astronauts, the programme ended in 1972. All manned NASA space missions after 1981 flew in the reusable Shuttle, often to launch or recover satellites or work on the International Space Station (ISS). Outer boots worn during spacewalks did not need to be as flexible as those used on the Moon’s surface or when inside the craft. A rigid sole was utilised and a heel clip fitted, which could locate and secure into foot restraints on the exterior of the ISS and on the robotic arm.

To accommodate the number of female astronauts in the Shuttle programme, NASA suits were modularised, with only the gloves being custom-made. Two sizes of boot were made available: large and small, with several bootie inserts available to create a comfortable and correct fit. There was also a provision for wearing extra socks of a special wicking material.

Different concepts


Mission specialist Nicholas Patrick being helped with his boots in preparation for a Shuttle flight in 2006

There are currently three nations which have manned space programmes – the USA, Russia and China, although a number of other countries have announced plans for limited goals for the future. China became the third nation to achieve independent human spaceflight capability by sending Yang Liwei on a 21-hour flight on 15th October 2003.

NASA uses a suit called an ‘Extravehicular Mobility Unit’ (EMU) while Russia’s cosmonauts wear an ‘Orlan’ suit (Russian for ‘eagle’). Both of these suits and their corresponding boots are functionally very similar – they are designed to allow a crew member to perform operations in the vacuum of space while in the immediate vicinity of a spacecraft, although neither is designed for use on the surface of a body like the Moon or Mars. The current Chinese spacesuit was based on the Russian Orlan-M design and was worn by astronaut Zhai Zhigang during China's first-ever spacewalk on September 27th 2008.

The biggest difference between the suits is how they are donned. The EMU is a modular suit, with the torso, legs, arms and helmet all being separate pieces that connect together. This modular system permits a substantial variation in astronaut size, because longer or shorter arms and legs can be used. By contrast, the Russian Orlan is a single component. As a result, the acceptable size of a cosmonaut is more limited than for the US programme.

Heading to Mars?

According to the NASA website, the Administration is now planning to build up its deep space capabilities before ultimately sending humans to our closest planetary neighbour – Mars. As with the Moon landings, any men or women who step on the surface of the ‘Red Planet’ will need very different boots than those used for space travel during recent decades.

Because there are so many unknown factors about the exploration of Mars, it is difficult to accurately plan the exact nature of the work clothes the astronauts will need to wear. However, what is obvious is that footwear will need to be pressurised, as the Martian atmosphere is so thin.

It is also important to consider that dust found on the surface of Mars contains hexavalent chromium (Cr VI), which can be harmful to humans. To solve this problem, the boots will either have to remain outside at all times, or they will need a removable layer that can be cleaned after each planetary excursion. If hexavalent chromium is inhaled in high concentrations, it can prove to be carcinogenic. It is also possible to develop an allergy to Cr VI that can cause asthma symptoms. If an allergic skin reaction develops, exposure can cause swelling and rashes that may worsen over time. Direct skin contact can result in non-allergic skin irritation and contact with damaged skin can cause ‘chrome ulcers’.

With temperatures on Mars ranging from a low of -176°C (-284°F) to a high of +30°C (+86°F), the boots will have to be designed with a proactive heating/cooling system. An ideal system to maintain foot temperature would use a liquid, especially if it has a high specific heat capacity.

Because the footwear will need to be pressurised (and, therefore, hermetically sealed), it cannot be breathable to atmosphere in the traditional sense. The material layers close to the skin will have to be absorbent and wicking in nature. This wicking will draw the moisture produced by the feet away and the absorbent material will allow the wearer to function for extended periods of time. It will be important for any sweat produced to be removed from the foot to avoid the risk of a number of immersion foot syndromes, such as the so-called ‘trench foot’. In the event of an emergency, it is not outside the realms of possibility that an astronaut may have to live inside a pressure suit for an extended period of time. It would only require a time period of 48 hours before he or she would run the risk of severe foot damage if the moisture could not be managed.

Additionally, if a semi-permeable membrane is used between an insulating liquid layer and the inner parts of the footwear, unwanted moisture could move from the inner parts of the footwear to the insulating liquid layer. The positive aspect of incorporating a semi-permeable membrane would be the reclamation of any water normally lost as a result of sweating. The negative outlook of using such a method is that all the other substances contained within sweat would be left in the inner parts of the footwear, requiring the boots to be cleaned out on a regular basis.

Adjusting the boots is likely to call for a ratchet and line closure system involving metal wire, as this does not require knots to be tied. Such a system would allow the boots to be loosened and tightened while the wearer is still in a pressurised suit, which will likely be quite restrictive in nature. Using metal wire as opposed to more traditional materials will cut down on ultraviolet (UV) degradation and improve resistance to wear.

With regards to UV, the boots will need to be made from highly resistive materials, as the thin atmosphere on Mars allows significantly more UV through to ground level than on Earth. In addition, Mars lacks a magnetosphere that would block out most cosmic radiation. The boots will therefore have to contain a material with a high level of radiation resistance. In addition, careful use of insulation will be necessary to avoid creating boots that will be too hot to wear at the higher temperatures found on Mars.

Much of what is necessary for boots to be suitable for exploration on Mars is therefore similar to that required for the missions to the Moon. The sole of the boots will need to be quite stiff to accommodate any uneven ground that the astronauts will need to traverse. Having said that, there are additional types of terrain on Mars that were not found during the Apollo missions. For instance, while it is unlikely that the astronauts would be expected to climb, much of the Martian surface is mountainous, so specific equipment – such as crampons – could feasibly be required, and footwear for exploration may have to accommodate such accessories.

As a progressive scientific organisation, NASA is leading the way among the ‘big three’ of space-going nations, and has great plans for future exploration of space. If these goals are achieved, footwear will definitely play a key role in such off-world voyages of discovery. With the experience the Administration has gained over the past 50 years, and the technical leadership of people like Joe Kosmo, the design of astronauts’ boots will undoubtedly continue to progress as new materials become available.

Publishing Data

This article was originally published on page 18 of the November 2019 issue of SATRA Bulletin.

Other articles from this issue ยป