This month's repairs to the Hubble Space Telescope so dominated the attention of those who are interested in such things, that another significant space event went almost unnoticed.

On March 1, the Ames Research Center, which manages the Pioneer series of spacecraft for the National Aeronautical and Space Administration, sent a signal to a little spacecraft that is travelling away from Earth at a speed of 12.24 kilometres per second. For those of you who ride Mobylettes, that's 27,380 miles an hour.

Pioneer 10 was launched 35 years ago. It left the Solar System 24 years ago.

Radio messages travel at the speed of light. Twenty-two hours and ten minutes after the Ames scientists sent their message, the spacecraft answered.

It's fine - heading steadily farther out into the vast stretches of open space that lie between the Solar System and the area of the red star Aldebaran, which forms the eye of the star group we know as Taurus, or the Bull. Aldebaran is an awfully long way away - it takes 68 years for its light to reach us. Pioneer's not moving anything like that quickly - it will take the spacecraft a little longer than 2 million years to pass by that region.

Pioneer 10 was launched in March, 1972, not very many months after Sir Henry Tucker retired, and Sir Edward Richards became Bermuda's second Government Leader. When Pioneer's journey ends, the Earth will long before have disappeared, consumed by an expanding, dying Sun.

Pioneer was designed to fly to Jupiter, the planet on the other side of Mars, and to send pictures and data back to Earth from there. Its mission was a great success - Pioneer 10 gave us pictures of the planet that in those days left us open-mouthed, an impact that has now become dulled by the passage of time.

In its day, Pioneer 10 was the fastest man-made object to leave the Earth. It passed the Moon in 11 hours, and crossed the orbital path of Mars in 12 weeks.

Four months after it left Earth, it entered the Asteroid Belt, a doughnut-shaped area that is 280 million kilometres wide and 80 million kilometres thick. It consists of what might be called orbiting construction debris - particles ranging in size from dust mites to chunks of rock the size of Alaska. A little bad luck is not what you want to have in the Asteroid Belt. But Pioneer made it through just fine. It was the first spacecraft ever to do so.

Pioneer 10 passed over the tops of Jupiter's clouds in December, 1973, and as it did, took the first close-up pictures of the planet, charted Jupiter's intense radiation belts, located its magnetic field and made the discovery that Jupiter is predominantly a liquid planet. It took dramatic photographs of Jupiter's Red Spot, made the first observations of the immense polar regions, and determined the mass of Jupiter's moon, Callisto.

Partly as a result of this success, another in the Pioneer series of spacecraft, Pioneer 12, was sent to Jupiter a little more than three years later, and was put into orbit around the planet in December, 1978. There it stayed, circling, photographing and measuring, for nearly 14 years. In the end, the fuel for the jets that mission controllers used to maintain its height above the planet ran out, and it dropped out of orbit, falling as a burning meteor into Jupiter's atmosphere.

Pioneer 10 has had a fascinating life. In December, 1992, when it was well outside the solar system, it experienced what is known as a gravitational deflection - its position shifted slightly after it bumped into the gravitational field of what is thought to have been an object of some kind, a Kuiper Belt object.

The Kuiper belt is the area of space through which Pioneer is still travelling. It is a huge, flat, disk-shaped region of asteroids and comets.

Pioneer didn't hit the Kuiper Belt object ... probably didn't even get close. But the significance of Pioneer's encounter with this object is that the deflection proved the object's existence. It is only the second time that a Solar System object has been detected by gravitational effect alone. The first was the planet Neptune, which was discovered in 1846. Its position had been predicted because the planet Uranus was moving in an odd manner, which scientists thought was probably explained by the gravitational tug of another planet.

The spacecraft was also observed to have experienced a tiny acceleration towards the Sun. The same thing happened to the Pioneer 11 and Ulysses spacecraft. What causes this acceleration is still a mystery.

Ames scientists say: "After exhausting the list of explanations deemed most plausible, the researchers examined possible modification to the force of gravity as explained by Newton's law, with the Sun being the dominant gravitational force… The scientists expect the explanation, when found, will involve conventional physics." That is to be regretted … a demented Space Octopus of titanic dimensions, or something of that kind, would have made a much more satisfactory explanation for fans of Buck Rogers and Dan Dare.

Pioneer is not a big spaceship. It looks like a giant hat with outsized hatpins sticking out of it at three points of its circumference. It measures nine-and-a-half feet long, and about nine feet wide. It weighs 570 pounds. It is spin-stabilised, spinning around the axis of its high-gain dish antenna at five revolutions a minute. It is atomic-powered, heat from the decay of the plutonium 238 isotope (which has a 92-year half-life) being converted into electrical current. That current has been used to power Pioneer's radio transmitters up to now, but may not be sufficient to last much longer.

As is the case with all spaceships that travel beyond the Solar System, Pioneer 10 carries a plaque for the benefit of other intelligent life in the universe, bolted onto its main frame. The late Dr Carl Sagan and his colleague, Dr. Frank Drake, designed it.

The key to translating its images lies in understanding the breakdown of the most common element in the universe, hydrogen. This element is illustrated in the upper left-hand corner of the plaque in schematic form, showing the "hyperfine transition of neutral atomic hydrogen". Anyone from a scientifically-educated civilization having knowledge of hydrogen, the theory goes, would be able to translate the message ... a kind of useful greeting from the people of Earth.

Pioneer 10 is now nearly 7.5 billion miles from Earth. In March, 1997, when the spaceship was 6 billion miles from Earth, Pioneer was retired from active service, and allowed to sail on towards Aldebaran, mostly undisturbed.

And undisturbed it is likely to continue to be. All the wear and erosion it is likely to experience are behind it, in the Asteroid Belt and in the severe conditions near Jupiter. Now, the spaceship is in the vacuum of space, where the average spatial density of molecules is, if you can believe this, one trillionth the density of the best vacuum science is able to create on Earth.

Pioneer will almost surely outlast Mother Earth. When, in 5 billion years, the Sun becomes a red giant, and expands to the point of engulfing our blue planet, Pioneer will still be sailing serenely on.

It will be a testament, perhaps, to how well we built the slow spacecraft of the very early days of space travel.

Comments on this, or any column, may be sent to the writer at gshortoibl.bm.