The Beagle has landed

Early Christmas morning, the Beagle 2 spacecraft landed on the surface of Mars at the end of a 250 million mile (400 million km), six-month trek to the Red Planet. Launched with the European Space Agency's Mars Express orbiter on 2 June 2003, the Beagle 2 was named to commemorate Charles Darwin's five-year voyage around the world in HMS Beagle (1831-36). Its main objective is to search for signs of life -- past or present -- on the Red Planet.

Although the first attempt to use NASA's Mars Odyssey orbiter to communicate with the lander three hours after touchdown was unsuccessful, scientists and engineers are still awaiting the best Christmas present possible -- the first faint signal to tell them that Beagle 2 has become only the fourth spacecraft to make a successful landing on Mars.

And what exactly was the signal they were waiting for? Well, believe it or not, it was a cell phone ring tone.

The lack of immediate communication wasn’t totally unexpected, but the continued failure to make contact is starting to become worrisome.

"This is a bit disappointing, but it's not the end of the world," said Professor Colin Pillinger, lead scientist for the Beagle 2 project.

"We still have 14 contacts with Odyssey programmed into our computer and we also have the opportunity to communicate through Mars Express after 4 January."

There are several possible explanations for the failure of Odyssey to pick up Beagle 2's signal. Perhaps the most likely is that Beagle 2 landed off course, in an area where communication with Mars Odyssey was difficult, if not impossible. Another possibility is that the lander's antenna was not pointing in the direction of the orbiter during its brief passage over the landing site. If the onboard computer had suffered a glitch and reset Beagle 2's clock, the two spacecraft could be hailing each other at the wrong times.

The Beagle 2 lander entered the thin Martian atmosphere at 2:47 GMT Christmas day. Travelling at a speed of more than 12,500 mph (20,000 km per hour), the probe was protected from external temperatures that soared to 1,700 C by a heat shield made of cork-like material.

As friction with the thin upper atmosphere slowed its descent, onboard accelerometers were used to monitor the spacecraft's progress. At an altitude of about 4.5 miles (7.1 km), Beagle's software was to order the firing of a mortar to deploy a pilot parachute, followed one minute later by deployment of the 33 ft (10 m) diameter main parachute and separation of the heat shield.

At a few hundred metres above the surface, a radar altimeter was to trigger the inflation of three gas-filled bags. Cocooned inside this protective cushion, Beagle 2 was expected to hit the rust-red surface at a speed of about 38 mph (60 km/h). As soon as the bags made contact with the surface, the main parachute was to be released so that the lander could bounce away unhindered. Like a giant beach ball, the gas bag assembly was expected to bounce along the surface for several minutes before coming to rest at 2:54 GMT.

Finally, a system of laces holding the three gas-bags onto the lander was to be cut, allowing them to roll away and drop Beagle 2 about 3 ft (1 m) onto the surface. The whole descent sequence from the top of the atmosphere to impact was to take less than seven minutes.

Beagle 2 was targeted to land within an ellipse, 30 km long and 5 km wide, on Isidis Planitia, a large lowland basin near the Martian equator. However, the exact location of the landing site depended on factors such as the angle of descent and wind speed.

The landing site was chosen for its low elevation, since a greater depth of atmosphere would assist the parachute in braking the lander's descent. Its equatorial location also means that temperatures are warmer, minimising the amount of insulation (and hence mass) needed to protect the lander from the cold Martian night. The relatively flat site was also thought to be neither too dusty nor too rocky to threaten a safe landing (but rocky enough to be interesting for the experiments).

For further details on Mars Express and Beagle 2 see the following websites, check out these websites:

Beagle 2 lander homepage
Mars Express overview
Christmas on Mars: be there with ESA
PPARC News Updates
ESA's Mars page
Europe goes to Mars

Posted by Ted at December 26, 2003 01:08 AM
Category: Space Program