Converting imperial measurements into metric units may not be rocket science, but it was clearly beyond the wits of Nasa scientists building the Mars space probe, which disappeared moments after reaching its destination. Nasa yesterday had the embarrassing task of admitting that the disastrous loss of its $193 million Mars Climate Orbiter last week was due to faulty flight calculations based on the simple failure to convert imperial measurements into their metric equivalents.

The probe had successfully flown 416m miles (670m km) in nine-and-a-half months without the error coming to light, only to vanish minutes after it began to circle Mars on September 23.

The metric mistake apparently caused the interplanetary weather satellite to fly too close to Mars, where it either burned up or broke apart in the atmosphere.

Astronomer Patrick Moore described the mistake as the worst space gaffe since the Hubble telescope, adding: "But while the Hubble could be put right, this very sadly is lost forever."

In an understatement of galactic proportions, Tom Gavin of Nasa's jet propulsion laboratory admitted: "It does not make us feel good that this happened. This mix-up has caused us to look at our entire end-to-end process. We will get to the bottom of this." By way of explanation he added: "In our previous Mars missions, we have always used metric."

The 629kg (1,387lb) Orbiter was carrying a British-designed radiometer to probe the temperature, dust, water vapour and clouds in the thin Martian atmosphere for 687 days - a Martian year - to find evidence of water in the hope of discovering whether life ever existed there.

The crucial metric mistake occurred with the numbers used to calculate the force of the probe's thruster firings used to adjust its position.

In a preliminary report, Nasa said the spacecraft's American builder, Lockheed Martin Astronautics in Denver, submitted acceleration data to Nasa in units of pounds of force instead of the metric unit of newtons. While most of America has steadfastly refused metrification, Nasa has made the leap. So, when the numbers were entered into a Nasa computer, it was assumed they were metric measurements.

Although the faulty numbers had been used since the spacecraft's launch last December, the effect was so small that it went unnoticed over the months as the spacecraft journeyed toward Mars.