The future of the ISS

International Space Station science officer Don Pettit (top) and Commander Ken Bowersox (left) outside the orbiting laboratory on January 15, 2003. - REUTERS

Should the space station be left unmanned after the present three-man crew returns and for how long? Some experts believe that a delay of a year or more in linking up with the ISS could result in it falling back to Earth.

WITH the grounding of space shuttles Atlantis, Discovery and Endeavour there is a big question mark over the operations of the International Space Station (ISS), a 16-nation collaborative effort under construction since 1998. Indeed, the coincidental launch of the Russian Proton 10 rocket, carrying supplies to the ISS, on the very day disaster struck Columbia (February 2 by GMT) drew attention to the potential impact of the tragedy on the ISS.

Shuttle launches since 1999 - barring those of Columbia, the oldest and the heaviest - have been largely dedicated to ISS assembly missions, ferrying astronaut crews and equipment. With the grounding of the shuttle, the scheduled launches of the shuttle to the ISS during 2003 and 2004 are in total disarray. And if, following the investigation into the Columbia burn-up, the shuttle fleet is not back to flying in the next few months or so, the future of the ISS may well be in jeopardy. Some experts even think that a delay of a year or more would result in the station falling into the earth's atmosphere and being destroyed. But NASA spokesman Rob Navias ruled this out.

The expanding ISS, which is at present 46 m across and weighs 200 tonnes, has completed 1,540 days in orbit, and is subject to a heavy drag caused by the friction of the huge frame with diffuse air molecules even at the 390 km altitude where the station is. This can result in a loss of altitude and, unless periodically corrected, prove to be calamitous. One of the crucial operations during every shuttle mission to the ISS - either to rotate the ISS crew or deliver trusses to be added to the assembly - is to boost the station altitude by 10-12 km upward with the extra fuel that the shuttle carries. This is perhaps the main reason for the intimate shuttle-ISS link that has evolved in the recent years.

Russia, the other major space technology provider to the ISS, may not be able to fill in with its Soyuz and Proton launchers - for manned and unmanned flights respectively. The Russian cargo launch Proton can, in principle, carry fuel to boost the ISS but enough Proton launches are not scheduled this year to compensate for the grounded shuttle fleet. Indeed, the cash-strapped Russian economy finds it hard to finance, build and launch the six or so Progress fuel tankers needed each year to keep the station at safe altitude. The shuttle reboost of the ISS was not in the original plans. The fuel thus supplied by the shuttle already is equivalent to at least two Progress tankers worth of propellant, a NASA spokesman observed.

According to the NASA shuttle launch schedule, updated on January 30, seven shuttle missions to the ISS - STS-114 (March 2003) through to STS-120 (February 2004) - had been planned, three of which - STS-114 in March, STS-116 in July and STS-119 in January 2004 - were ISS crew exchange launches. These seven missions were also planned to be a series of five truss/solar array assembly flights following a multi-purpose logistics module (MPLM) flight leading to the establishment of Node 2 in February 2004 for attaching four more laboratories. Clearly, these important crew rotation operations as well as assembly flights would be reviewed and, already, NASA and the ISS international partners have commenced discussions on the status and future plans for the ISS.

There is currently a three-member crew (ISS Crew No. 6) on-board - Commander Kenneth Bowersox and science officer Donald Petit of NASA and flight engineer Nikolai Budarin of the Russian Space Agency - in the third month of their mission. They were delivered to the ISS by Endeavour (STS-113) on November 24, 2002. Their original schedule of return in March 2003 will, in all likelihood, get postponed. The question is how long? A Russian Progress supply vehicle, which was launched last June and had been docked with ISS loading material to be junked, de-docked from the station on January 1 and the resupply craft Progress 10 had successfully docked and delivered fresh supplies of fuel and other cargo. Sufficient supplies of food, water, fuel, and so on, are supposed to be there on-board the ISS for at least six months of nominal activities. Besides, the rocket also delivered components for an important research experiment that had experienced power supply problems.

The venerable Russian space capsule Soyuz, which has been flying since the 1960s, is capable of transporting people into space and bringing them back but is currently being used only as a taxi flight to the ISS. Currently, one Soyuz (flight 5S) is in orbit, docked to the ISS as the station's lifeboat, and is scheduled to be there until May. The Soyuz can have only three people on-board and can remain in space for a maximum of six months. The next Soyuz flight (6S), which will dock with the ISS in place of 5S, is planned for April 26 soon after the crew rotation in March. Soyuz 6S is meant to be a taxi flight carrying an astronaut of the European Space Agency (ESA), but this plan is now under active review, according to the ESA. Similarly, Soyuz 7S, scheduled for a taxi flight carrying another ESA astronaut in October, is also up for review.

In an emergency situation such as this, Soyuz 5S can be used to bring back the on-board crew No.6. But the question is: can the station be left unmanned after that or should the crew remain for some more time? The current view among the ISS partners, according to the ESA, is that they should strive to ensure that the ISS is permanently manned. Proposals on how the Soyuz and Progress vehicles could best support the station are being studied, as are other options.

These discussions have yet not ruled out the ESA astronauts' trips aboard Soyuz in April and October. Russia is committed to launching a fresh Soyuz escape capsule every six months until April 2006 and ISS partners were in the process of negotiating (as well as finding ways of financing its continued production) to extend the deal through 2008. Given the present situation, altered proposals may be made to the Russians to deal with the current emergency aboard the ISS.

The Columbia burn-up has also revived the debate within the U.S. of resurrecting projects held in abeyance due to budgetary cuts over the last couple of years, which would have eased reliance on the Russian launchers Proton and Soyuz. NASA's $100-million project for the development of a propulsion module, on which work had begun and which would have served to replace the Progress cargo trips and fuel tankers, appears to have been shelved for good. The ESA's refuelling craft called ATV is also only under development and is some time away. The work on the X-38 emergency Crew Return Vehicle (CRV) - also known as the Orbital Space Plane - which can be launched by any of the modern expendable launch vehicles like Atlas or Delta and is capable of bringing back a crew of up to seven in one go in an emergency, is also in jeopardy. It was supposed to be ready by 2006. The disaster is bound to give a fresh impetus to all these proposals unless the international community decides to abandon the ISS. Having spent so much on it already, that option is unlikely to be voted for by the ISS partners.