Tim Furniss/LONDON

John Glenn has made it in the nick of time. The STS95/Discovery mission due to launch the 77-year-old former astronaut into orbit on 29 October, it turns out, is his last realistic chance to return to space.

The fifth Shuttle launch this year, STS88, is scheduled for 3 December, will kick off NASA's launches for the International Space Station (ISS), but could be delayed. Just five specialist Shuttle missions have been scheduled for 1999, as NASA wrestles with various difficulties. Glenn would not have got a look-in next year.

Technical problems have pushed back the launch of the Advanced X-Ray Astrophysics Facility by at least two months from January 1999. Furthermore, because Russia is going to be late delivering its ISS Service Module in 1999, the Space Station assembly schedule has been shuffled yet again. It is likely that the STS88 mission will be delayed to 1999.

The first operations crew will not board the ISS until January 2000 at the earliest, and it is unlikely that the Space Station will be completed before 2004, 10 years later than planned when the project was initiated in 1984 by then US President Ronald Reagan.

Another flight, the Shuttle Radar Topography Mission, is also due in 1999, but as it is manifested for orbiter Atlantis, which is one of the vehicles assigned to ISS flights, it may also be delayed to fit in with assembly requirements.

All this uncertainty over further Shuttle missions will be pushed into the background as Glenn, the first US national to orbit the earth, aboard Mercury capsule Friendship 7 in 1962, prepares to spend nine days in space studying the effects of microgravity on the ageing process. Glenn will become the oldest person in space, the previous oldest being Story Musgrave, who was then a mere stripling of 61.

The STS95 crew also has six other members, including two former medical surgeons and the first Spanish astronaut, Pedro Duque of the European Space Agency. Glenn's research is jointly sponsored by NASA and the National Institute on Ageing. The planned investigations focus on bone and muscle loss, and balance and sleep disorders, conditions experienced both by astronauts in the near-weightless conditions of space and by the elderly on earth.

The payloads for mission STS95 include a single Spacehab mid-deck augmentation module packed with international experiments; the Spartan 201-5 deployable solar science satellite; the Hubble Orbital Systems Test (HOST); the International Extreme Ultraviolet Hitchhiker-3 package of astronomical instruments and numerous secondary experiments.

The $10 million Spartan observatory is being flown on STS95 to collect the solar data missed during its last mission in November. During that flight, the spacecraft did not activate after being released from the Shuttle's robot arm because the pre-release procedures overlooked a vital step. A Petite Amateur Navy Satellite will also be deployed from the Discovery to transmit digital communications to specific ground stations.

The HOST experiment is intended to provide Hubble officials with the opportunity to test hardware that may be installed on the orbiting telescope during a planned servicing mission in May 2000.

Source: Flight International