Radio astronomers are to try again to pick up signals from the Mars Polar Lander (MPL) spacecraft after their most recent observations last week produced an inconclusive result.

The Westerbork Telescope array in the Netherlands and the University of Manchester's Lovell telescope at Jodrell Bank, UK, are preparing for a second set of observations on Tuesday.

Ian Morison of Jodrell Bank told BBC News Online that a second set of observations were required in order to eliminate remaining uncertainty on the operational status of the batteries of the Lander.

Like last week, Nasa's Deep Space Network (DSN) array of radio telescopes has sent commands to MPL ordering the craft to get in touch.

Assuming MPL was able to receive and act on those commands, faint signals from the lander will head towards Earth. Astronomers are expecting MPL's transmissions to last half an hour each, with a two-hour cooling-down period in between.

Different method

Nasa mission managers speculate that MPL may not have been able to receive last week's commands, in which case a slightly different method has been used this time.

Ian Morison of Jodrell Bank told BBC News Online that last Friday's observations went very well and data of high quality was obtained - all 60 gigabits of it!

It was the tentative detection in December and January by scientists at Stanford University that sparked off this current flurry of activity and revived hopes that the MPL might not have been completely destroyed when it attempted a soft-landing on Mars on 3 December.

The Standford team detected what could have been a signal from MPL on two, possibly three, occasions.

Independent team

MPL made its last definitive contact with Earth just before it turned to enter the Martian atmosphere on 3 December last year. When it failed to report in, Nasa tried every trick in the book to find out what had happened to the lander.

The agency even got the orbiting Mars Global Surveyor to take pictures of the planet's surface in the hope of finding the probe's entry parachute, the one piece of debris that might be visible from space.

An independent assessment team, appointed by Nasa chief Dan Goldin, is currently investigating what went wrong with the mission. Its findings, which will not be available until mid-March at the very earliest, will shape future robotic missions to Mars.