What the best-dressed astronaut is wearing

A mission to find out what suits the modern spaceman is about to be launched. Peter Bond looks at the competing designs

Later this month, providing Nasa can repair faults that forced a launch postponement last Saturday, two American astronauts will don their bulky pressure suits, enter the airlock and float out into the cargo bay of the space shuttle Endeavor. But they will have little time to admire the view. One of their tasks will be to evaluate modifications to the life-protecting suits as part of the preparations for assembling the international Alpha space station later this decade.

Space fashions have come a long way since March 1965, when Alexei Leonov became the first human to step into the emptiness of space. Leonov's life was threatened when his primitive garment ballooned outwards, preventing him from returning inside his capsule until he lowered the suit's internal pressure.

Thirty years on, spacewalking, or extravehicular activity (EVA) as it is officially known, is relatively commonplace. Well over 100 such excursions have been successfully completed. Politics have also changed. Americans and Russians are no longer competitors in a hard-fought space race but colleagues in a new co-operative venture to build Alpha.

The end of the Cold War has enabled spacesuit designers from both East and West to compare notes. Although the design of all EVA suits is determined by a number of constraints, including durability, flexibility, comfort and cost, the requirements of space travellers have been met in rather different ways by the engineers of the two space powers. Nasa favours a mix-and-match approach, with five sizes of upper torsos; Russian cosmonauts are simply selected to fit the available suits.

One of the few Westerners to have worn both Hamilton Standard's shuttle suit and the Orlan suit of the Russian Zvezda company is James Asker of Aviation Week & Space Technology. He found that it was quite straightforward to push his legs into the soft "trouser" section of the US suit, but inserting the head and upper body into a tight-fitting upper section was much more complicated. It involved raising his arms above his head and inserting them into the sleeves while pushing his head into place. Joining the two pieces of the suit was even more difficult.

In contrast, getting into the Orlan suit was simple. With the suit hanging from a rack, he swung open a door at the back of the aluminium casing on the upper torso and worked his legs down into the pants. He then put his arms down the sleeves and worked his fingers into the gloves. The rear door was closed and sealed using a lever at his waist.

Once inside the suit, the astronaut is protected from the hostile environment by the equivalent of a $10m personal spacecraft. Designed to operate in the vacuum of space, the suit has an impermeable inner lining that envelops the entire body and maintains air pressure at a constant level.

Russian designers have always favoured a suit that contains oxygen at a pressure of 5.8psi (pounds per square inch) compared with 4psi for the American suit. This means that American suits are more flexible and hand movements less tiring, but this is offset by the astronauts spending a lot more time purging their bloodstreams of nitrogen before they can venture outside so that they do not suffer from the bends.

Differing mission requirements have also influenced the final design. Russian EVAs are often shorter and centred around maintenance tasks outside the Mir space station. The suits remain on the station for long periods, so on-orbit servicing must be easy. As a result, many of the "frills" such as a drink bag, food and a urine collector have been omitted from the Orlan suit. American astronauts only fly for up to two weeks, but they are expected to carry out a wider range of tasks, including satellite repair and scientific experiments.

Both suits have an excellent safety record, although this has been achieved through radically different approaches. "While the US suit is designed to be failsafe," says Mr Asker, "the Russians designed the Orlan suit with a redundant approach for all life-critical systems. For example, it has dual pressure bladders, except in the gloves, where two bladders would diminish tactile sensing too severely."

Creating the perfect glove for EVA has proved extremely difficult. One astronaut described his experience in repairing a satellite as "surgery in boxing gloves". Providing adequate manual dexterity is only half of the problem. Spacesuits must be capable of protecting the wearer from extreme heat in direct sunlight and bitter cold in shadow or darkness. Last February, frozen fingers forced the astronauts Bernard Harris and Michael Foale to curtail their spacewalk as outside temperatures plunged to minus 87C.

Further improvements will obviously be required before assembly of Alpha begins. Two methods of fighting the cold will tested on Endeavor's next mission. One involves a bypass in the suit's liquid cooling system. "At present, the crew member anticipates when he will be working less hard and turns down his cooling system," says Richard Wilde, EVA systems engineering manager with Hamilton Standard. "The bypass will allow the fluid flow to stagnate so that it no longer takes out body heat."

The other innovation involves a battery-powered heater located just outside the pressure portion of the glove. "It will raise the temperature only a few degrees and add only a few watts of heat, but it should improve the comfort there significantly," says Mr Wilde.

Since both sides will be working side by side during the shuttle-Mir programme and the construction of Alpha, it would clearly be advantageous for US and Russian EVA suits to use as much common hardware as possible. Earlier this year, Hamilton Standard suggested upgrading its suit so that it could operate at the same high pressure as the Orlan, but this is unlikely to be funded in the current financial situation. "It's not necessary to get the station built," says Mr Wilde. "There will be two sets of suits and two sets of airlocks on board Alpha, one for US or Russian use and one solely for the Russians."

Nevertheless, some changes are going ahead to bring both suits into line. Nasa has budgeted about $5m over the next two years to develop compatible radio systems, foot restraints, safety tethers and tool carriers.

Looking further ahead, a new generation of suits is on the drawing board. Although they resemble the "Michelin man", the intention is to make them lighter, less bulky, more flexible and longer-lasting than existing suits. Minimal effort will be needed for movement since the hard suit maintains a constant volume, so the internal pressure remains constant no matter how much the wearer changes posture. Arm and leg movements will be eased by construction of extra sections in the sleeves and trousers, each mated to free-moving rotary joints. It may eventually be possible to replace the bulky thermal overgarment with thermal coatings applied directly on to the metallic structure.

Whether the suits will ever become operational remains in doubt. "There has been a lot of encouragement from the highest levels," says Mr Wilde, "but the money has not yet been authorised."