For NASA, these are indeed the nauseating nineties: four years and four partial or total mission failures. Following the six Apollo visits to the moon and the faultless performance of the Voyager vehicles, it seemed that NASA was master of its trade, that nothing was beyond reach. Building on these successes, its missions became more ambitious and its space vehicles more sophisticated. The on-board computers increased in power by leaps and bounds as the control functions for the new multi-task missions multiplied. But hand in hand with these developments went the increasing possibility of failure.
That possibility has become actuality. Starting with the horrid technical and managerial errors of the space shuttle Challenger explosion in January 1986. there has been a series of major disasters or malfunctions.
The first images from the Hubble Space Telescope, received May 20 1990, raised hopes that were soon to be dashed as tests showed that the main mirror had a manufacturing defect. Knowing precisely the nature of the problem. it has been possible to electronically massage the data transmitted back to earth and so recover high-definition images, but at the cost of a loss of light-gathering power.
In August 1990, the high-definition radar mapping of the cloud-covered surface of Venus from Magellan teetered on the edge of total failure. The attitude control computer developed a fault, and for 14 hours the spacecraft was pointing away from Earth, transmitting uselessly into space, before control could be regained. This problem happened five times, significantly reducing the amount of data recovered from the mission.
1992 saw the Galileo mission to Jupiter thrown into disarray when a locking pin on the main transmitter aerial failed to disengage, severely reducing the rate of data transmission.
But now comes the most savage blow of the decade: the Mars Observer has gone missing.
For 11 months, this spacecraft has been hurtling towards Mars—the first NASA mission to the red planet since the successful 1979 Viking landings. Everything went as planned until, as Observer was approaching Mars, the command to pressurise the fuel tanks was transmitted. This was the first step in the command sequence for firing the retro-rockets. But the result was silence. Observer’s transmitter did not switch on, and in spite of pleas, commands and screams from Earth there has been no other response.
Far beyond the reach of the most powerful radar, Observer is effectively lost. We do not know what has happened or where the spacecraft is. Did the retro-rockets fire and the craft go into orbit as planned, or did it just plunge on into the depths of space?
Either way, the mission is a total failure—a billion dollars lost, and years of design and construction gone for naught. What is more, subsequent missions which were to use not only data from this mission but also its transmitting facilities will have to be recast.
These failures constitute a major setback to our exploration of the solar system and of deep space. Whatever the contribution of other nations, the fact is that the US taxpayer has borne the brunt of the billion-dollar costs of off-Earth physics and astronomy. In the face of the continuing domestic economic troubles, NASA’s already reduced budget is likely to be cut yet further.
As if this tale of woe were not bad enough, there is the increasing likelihood of worse to come. During our 40-year spree of launching space vehicles, we have been treating our immediate neighbourhood as we have our oceans—as a rubbish dump. Any superfluous item on a voyage was jettisoned, and as a result, Earth is surrounded by a cloud of high-velocity debris. This material ranges in size from particles of aluminium oxide, the ejecta from solid fuel boosters, to dead satellites. Between these extremes is an assortment of parts and fragments either dumped or the result of accidental explosions or deliberate destructions.
All this material is in a wide variety of orbits, some highly elliptical with velocities of the order of 10,000 to 70,000 metres per second (36,000 to 250.000 kph).
The kinetic energy of a moving object is equal to half the product of its mass multiplied by the square of its velocity (K = 1/2mv2). Thus, at high speeds very light fragments can have counter-intuitively high energies. For example, the kinetic energy of a postage stamp moving at 10,000 metres per second is equal to that of a medium-calibre rifle bullet. So a fleck of paint probably only 10 mm across was able to crater, though not puncture, the windscreen of a space shuttle.
In 1987, US space flight centres were tracking more than 6000 objects the size of a softball or larger. Any collision with this material would completely destroy a space vehicle.
But these objects are only the tip of the iceberg, for as the size decreases, so does the number increase—dramatically. An estimated 30,000 fragments down to the size of a marble, millions upon millions of flakes of paint and slivers of metal and thousands of trillions of dust particles are all in circulation. These last are too small to do lethal damage at a blow, but their cumulative effect can be to destroy the solar panels which supply the power for satellites. They may also pit and erode optical surfaces of cameras and telescopes, rendering them useless.
So serious is the problem considered that in 1984, on only the eleventh shuttle flight, Challenger placed the Long Duration Exposure Facility in orbit to study the effect and frequency of impacts by natural and man-made space debris. Recovered after six years, the LDEF’s exposure panels had registered 40,000 impacts per square metre. man-made debris accounting for the great majority of these. Such results throw severe doubt on the projected life of observational instruments such as the Hubble Space Telescope. Moreover, the total number of orbiting particles is continually increasing as collisions further fragment the larger shards. Debris impacts are the suspected cause of several satellite failures, and may have contributed to the explosive disruption of spent booster stages which still contained fuel.
The effects of space debris are not limited to the hazards which they pose to existing and projected orbiters and space vehicles on their way to the planets. Of increasing concern is their interference with our view of the cosmos and the gathering of electromagnetic, particularly optical, data. This is the raw material upon which we build our theories of the universe, our galaxy and the solar system—the fundamental setting of human existence.
Large objects, spent boosters, jettisoned aerodynamic shrouds, reflective foil shields, redundant or failed satellites, together with the hundreds of functioning payloads, increasingly interfere with Earth-based astronomy. The hundreds of millions of dollars invested in the great telescopes, designed to detect those whispers of light coming from near the edge of the observable universe, are now continually threatened with the overloading of their ultra-sensitive detectors by light from the highly reflective orbiting objects crossing their field of view.
And the picture gets even worse. Added to the ever-increasing interference of light pollution are proposals to place giant reflectors in orbit about the Earth. During the last few years, a number of these projects have been floated. For the Russians, it was to be an attempt to mitigate the effects of the long arctic night in Siberia, for a Frenchman a piece of “space sculpture,” celebrating the centenary of the Eiffel Tower, and for the American Celestis Corporation a strictly commercial proposition to put the ashes of loved ones into low Earth orbit in shiny canisters.
With such schemes afoot, for all that they are presently blocked, the stage is being set for the last great act of environmental vandalism. The fashionable theory of market forces will doubtless see the attack renewed in the name of GNP. Designs for commercial and political space advertising are rumoured. Such celestial billboards will each have the brilliance of the full moon, blinding telescopes to far galaxies and our children to the glory of their own, the Milky Way.
In a world at last beginning to take seriously the damage we are doing to the surface and atmosphere of our planet it is already past time that our concern should also reach out towards the stars.