The STS69 space-walk has paved the way for assembly of the international Space Station.

Tim Furniss/LONDON

A 6H 46MIN SPACE-WALK BY two astronauts on 16 September, during the STS69/Endeavour mission, has given NASA more confidence in the ability of crews to assemble the international Space Station during arduous space-walks.

James Voss and Mike Gernhardt assessed the performance of several power tools and restraints designed to help with Space Station assembly. The astronauts conducted typical Space Station chores, such as removing debris and insulation shields and working on equipment boxes, wires and an antenna boom. An arm-sleeve strap-on computer, with a touch-sensitive screen, designed to display construction checklists and other technical information, was also evaluated.


More importantly, however, modified Shuttle space-walking suits passed an important test. Space Station assembly will involve astronauts spending long periods in shadow, in temperatures as cold as -90¡C. Suit modifications to counter the low temperatures did not work during an earlier evaluation by the STS63 astronauts in February. They were ordered back inside the Discovery 3h short of a planned 6h sortie, suffering from cold. The modifications did not allow them to turn off their suits' liquid-cooling systems. Their fingertips grew uncomfortably cold, especially when they touched metal objects, such as handling fixtures, during planned long periods in shadow.

Voss and Gernhardt tested suit refinements, including battery-powered fingertip heaters in the spacesuit gloves and a system, which enabled them to close down totally the liquid-cooling system and rely on body heat to warm the suits. Voss and Gernhardt also assessed their suits while in shadow for 1h at the end of the Shuttle's remote-manipulator system.

Space Station assembly will begin in earnest in November 1997 and, by 1998, NASA astronauts will be conducting regular space-walks, as the pace quickens towards a Space Station completion date of June 2002. By then the station will span the size of a football field. Space-walks will not last longer than 6h.

NASA estimates that 650h of space-walking, will be required for the assembly job - 200h more than estimated originally - plus an additional 170h a year, for maintenance and operations after 2002. Russian cosmonauts will also need about 240h during assembly work. While Russian cosmonauts have exceeded this required experience level, both astronauts and cosmonauts lack experience of conducting tasks similar to those needed for Space Station assembly.

Of the 125 walks so far conducted since Alexei Leonov's first exploit on 18 March, 1965, 63 have been completed by the former Soviet Union and Russia, all of them in Earth orbit, amassing about 256h of space-walking time, or 518h man-hours. US astronauts have also performed 63 walks, including 14 lunar walks and three midway between the Earth and the Moon, gaining a total of 307h experience and 609 man-hours, but only 224h experience or 410h man-hours during the 46 Earth orbital space-walks, of which 30 were from the Space Shuttle. Shuttle space-walks account for only 176h, or 360 man-hours.

During Space Shuttle missions, early space-walks were seen as exercises to be conducted for specific tasks, such as satellite retrievals and repairs, and only recently have they been added to missions to give astronauts experience. To increase its cadre of experienced space-walkers, NASA is spreading space-walk assignments and planning sorties during several missions before 1998. Clearly, some of the Space Station assembly crew have already been selected.

The next walk, will be conducted by two STS72/Endeavour astronauts, in January 1996, while two more are planned for the STS76/Atlantis and STS79/Atlantis Shuttle Mir Missions (SMM) 3 and 4, in April and August 1996. The SMM 4 will be another demonstration of the vital Safer backpack which will enable a stranded astronaut to manoeuvre back to base if he or she were to lose physical contact. The SMM 5 and 7, involving STS81 and STS86 - both with the Atlantis - may also conduct walks. The SMM 5, in December 1996, may feature a US astronaut joining a routine Russian space-walk.


The SMM 7, in September 1997 - two months before the first US Space Station mission - could see the two US and two Russians walking together in the first four-person space-walk in history, possibly with one of each country's space-walkers wearing his counterpart country's suit. The STS82/Discovery mission in February 1997 will also involve four space-walking astronauts servicing the Hubble Space Telescope. In addition, every Shuttle mission carries two crew members trained to conduct contingency walks, if required.

Space-walking is not a glorious sightseeing trip in open space. It is grueling and tiring. One astronaut has likened working on the Hubble Space Telescope to hanging upside down over the engine of a car trying to change the spark plugs wearing mittens. That analogy does not include the effort it takes to counteract the tendency to float away from everything, especially the counter-force after touching a surface. Every movement has to be accompanied by the fixing of restraint anchors, like a mountaineer using crampons.

It did not take NASA long to realise the value of placing an astronaut at the end of a remote-manipulator system, which is clearly destined to play a major role in Space Station assembly. It will be equipped, with the necessary tools for the space walker, before an excursion is made.

Source: Flight International