It had the right stuff - where did it go wrong?: Tom Wilkie says America's ambitious space programme has become stuck in a time warp

SPACE. The final frontier. The ultimate aspiration for clean-cut heroes boldly going where no man has gone before.

And yet. While the fictional Captain Kirk and his crew of the starship Enterprise appear virtually immortal, the real US space agency, Nasa, is showing signs of mortal frailty.

Yesterday, the first Nasa craft since 1976 to venture to Mars approached the Red Planet. In itself that is striking: the world's wealthiest space research agency has not been near our most interesting planetary neighbour for 17 years. But even this visit is in peril, for the Mars Observer has fallen silent, prompting controllers on Earth to frenzied activity to restore communication.

This may be merely a setback. Space probes are complex pieces of technology operating in a fiercely hostile environment. There is a lot that can go wrong with them. Nasa's designers, naturally sensitive to this, have equipped the craft with back-up systems that may yet wake it up and set it talking to ground control again.

But even if the craft is resurrected, this week's hitch in yet another high-profile space mission will add to the agency's troubles and further dent its once-proud 'can do' image.

The Mars Observer was a troubled mission right from the start. It should have been launched from the space shuttle in August 1990, but the Challenger explosion delayed that for two years. So the probe began its dollars 980m ( pounds 662m) voyage last September, when it was launched from Cape Canaveral, not on the reusable shuttle but on a Titan III rocket. Even then, the launch was delayed, because the space probe was accidentally contaminated while staff tried to protect it from damage by Hurricane Andrew.

Mars Observer carries seven instruments to explore the mysteries of the Red Planet. If ground control can be re-established, its primary mission will begin in about four months' time and will last one Martian year (687 Earth days). From an orbit some 240 miles (390km) above the planet, the satellite's camera will photograph and map the entire planet. Most of this will be fairly low-resolution stuff, but interesting areas, melting ice caps, for example, or shifting sand dunes, will be reproduced using high-resolution photography.

Unlike the Viking 1 unmanned probe that landed on Mars on 20 July 1976, or Viking 2 on 3 September the same year, Mars Observer is not designed to descend to the surface. According to George Bush's ambitious Space Exploration Initiative, announced in July 1989, Mars Observer was to be followed by a flotilla of robot craft, which would crawl over the planet's rocks and dust. Before the end of the century an unmanned probe was to have gone out and returned to Earth carrying a sample of Martian rock. And then, on 20 July 2019, on the 50th anniversary of Neil Armstrong's stepping on to the surface of the Moon, another all-American hero with 'the right stuff' was to walk out under an alien sky and tread the red dust.

Four years on, such a programme appears a fantasy. Nasa has been plagued by a string of technical failures. The most conspicuous, which happened before President Bush announced his plans, was the explosion of the space shuttle Challenger and the deaths of all seven crew members on 28 January 1986.

The publicity surrounding the disaster distracted attention from the shuttle programme's fundamental deficiency. Nasa had touted the system as a fleet of reusable 'space-trucks', capable of cheap and frequent round trips into low Earth orbit. Instead, the shuttle became an instrument of baroque complexity incapable of fulfilling its basic specification. Nasa envisaged sending a shuttle aloft every fortnight - 24 trips a year - but although it now has four shuttle orbiters, Nasa managed only five missions in 1989, and six each in 1990 and 1991.

As serious a deficiency is the fact that the shuttle's maximum attainable altitude is only about 500 miles - much lower than the orbits required by most satellites. To attain their usable orbits, of up to 22,375 miles, satellites had to carry their own (disposable) rocket booster within the Shuttle's cargo hold - an arrangement that somewhat undermines the system's 'reusability'.

Manned spacecraft such as the shuttle system are inherently more complex than unmanned probes, not least because they have to be far more reliable when human life is at stake than when the loss would be only financial. But Nasa has always believed that only high-prestige manned space trips will catch and retain the interest of the American public and thus ensure an ungrudging flow of tax dollars into the organisation's coffers.

While Nasa has been struggling with maintaining prestige through manned space missions, the Europeans have developed the unmanned Ariane system into a relatively cheap, and certainly more reliable, launch vehicle, thus capturing a considerable slice of the lucrative commercial market in launching communications and Earth observation satellites.

Even Nasa's unmanned space programme has been having difficulties. Possibly the most embarrassing display of technological incompetence was the failure of the Hubble Space Telescope in 1990. This behemoth, weighing 11.25 metric tonnes, is the size of a city bus, and carries a telescope mirror 7.9 feet in diameter, whose total cost will exceed dollars 3bn, and which was supposed to probe the astronomical secrets of the stars and galaxies at the universe's outermost edge. But it cannot focus properly. Not only that, it shakes.

Underlying the technical faults lies a failure of vision. Nasa no longer knows what it is for. Space has lost its glamour. Where once, in the Sixties, the entire world would crowd round television sets to watch the launch of the Apollo Moonshots, now when the space shuttle lifts off, it merits barely a mention on the foreign pages.

The space race of the Sixties was the continuation of the Cold War by other means. Those were the heady days when Star Trek was created. But during the Seventies, detente and disarmament were the themes and attention focused not on other worlds but on the mess that humanity was making of its own.

When President Reagan decided to step up the pressure on the Evil Empire, he also turned to space, not only with the military fantasy of the 'Star Wars' Strategic Defence Initiative, but by dreaming up the grandiose space station project. It was to be named 'Freedom' and it was to show all the world what could be achieved by free enterprise in the land of the free (admittedly under lucrative contract to the government).

President Reagan willed the end, but the mess that Reaganomics made of the US economy denied Nasa the means. Outer space was once the celestial stage upon which the US industrial superpower could display a technological ingenuity to match the 'right stuff' of its youth. Now, as President Clinton struggles with the legacy of debt from Reagan and Bush, the space programme has become a costly and near-pointless exercise.

A partially sighted space telescope and a little probe wheeling endlessly around Mars, mute in the immensity of the void: how appropriate are these as icons of our time.