Countdown: Martian Traffic Jam

The early fiery entry of Beagle 2 probe into the thin Martian upper atmosphere at 12,000 miles per hour Credit: ESA

2003 is the best year to aim for Mars in the next two decades. Earth and Mars are on the same side of the Sun (around 93 million miles apart) and at nearest approach for the complex orbital paths needed to succeed from launch to landing. To take advantage of this opportunity, three landing missions are planned to take-off in June.

Recent reviews have given all three missions the greenlight for launch. This spectacular blitz on the red planet should begin in the next five weeks, culminating after a six month journey in the rovers’ expected January 2004 traffic jam. While the European and two American probes have different mission profiles, they all will be seeking out evidence for water in Mars’ ancient past.

Europe: Mars Express/Beagle 2

Mars Express is the first European spacecraft to visit the planet Mars. Just before midnight on June 2nd (23:45 local time, 19:45 CEST), a Soyuz rocket operated by Starsem will lift off from the Baikonur Cosmodrome, and Mars Express will ascend from its Russian launch stand. The spacecraft was approved to launch following a successful flight readiness review on May 3rd.

The Mars Express launch window opens on May 23rd and lasts only four weeks. However, just before the spacecraft was due to leave Toulouse, France, for its trip to Baikonur in Kazakhstan, engineers discovered a fault in one of the electronics modules. "Of course, it was the most difficult box to remove from the spacecraft," says Rudi Schmidt, the Mars Express Project Manager, with a smile.

In view of the estimated time needed to correct the fault, the launch date was initially put back from May 23rd to June 6th, still within the launch window. However, thanks to the skill and dedication of the engineering team, the job was completed sooner than expected and the launch date was brought forward.

Mars Express is currently being fuelled, an operation that takes about a week. It will then be attached to Fregat, the Soyuz upper stage rocket booster, and mated with the Soyuz rocket. The whole system will be rolled out to the pad four days before launch. The journey to Mars will take six months and the probe will be inserted into an elliptical quasi-polar orbit on the day after Christmas, December 26th.

The landing site for the European rover called Beagle 2 lies on the floor of a large impact basin in the northern hemisphere of Mars. The name of the site, Isidis Planitia, refers to the broad, relatively flat plain that covers the floor of an extremely ancient, large basin formed by an asteroid or comet impact perhaps more than 4 billion years ago.

Employing seven major instruments for its on-the-spot analyses, Mars Express will be able to identify signs of water in liquid, solid, or vapour form on Mars. Its lander will take a good chemical and morphological look at its landing site, looking for water in the soil, on rocks, and in the Martian atmosphere. It will investigate the existence of carbonate minerals and organic residues to detect possible signs of past or present life.

Delta launch rocket for MER mission.
Credit: NASA

USA: Mars Exploration Rovers

In the same launch window, the two Mars Exploration Rovers are scheduled to take off from Cape Canaveral Air Force Station on June 5th and 25th. A potentially risky communication cable problem has been corrected and both are on-plan for take-off. Like the European mission, the rovers will attempt to land on Mars also in January 2004.

Compared to previous Mars missions, each of the twin rovers weighs about 375 pounds on Earth–a much more ambitious payload than the 1997 Pathfinder [which was about 23 pounds upon landing].

On January 4th, after a six-month journey, the first rover will start its entry through Mars’ thin atmosphere. It will first encounter the atmosphere on the side of the planet opposite its chosen landing site: Gusev Crater. It will be flying at 14,000 miles per hour.

During the rapid descent through the atmosphere, an aero-shell capsule will shield the lander and rover from the heat of re-entry. The thin Martian atmosphere slows the spacecraft down ten-fold, from 14,000 mph to 1,000 mph. Six miles above the Martian surface, a polyester-nylon parachute will unfold. To compensate for the much greater weight of the MER probes, their new parachute designs are about 40 percent larger than the 1997 Pathfinder parachute.

A simulated image of the new Mars rover carrying its science instruments.
Credit: NASA

To assist the parachute in the thin atmosphere (about one percent of Earth’s sea-level pressure), a set of solid rockets on the craft’s underside will fire. As the capsules hit the surface and bounce to their resting places, airbags that surround the landers will cushion the blow. The new rovers could bounce as far as 0.6 miles in the course of their settling phase. The entire sequence will last 12 minutes.

Upon touchdown, their airbags will deflate and the rovers must venture out from their cocoon-like, landing shells. Instead of the single bladder used on Pathfinder, the new airbag designs have two airtight layers covered with protective cloth. That way, if a sharp rock or boulder punctures the outer layer, the inner layer will protect the rover.

To complete the deployment, the rovers and landers must go through 17 carefully-orchestrated steps — from rolling out exit ramps for the rovers, to unfolding the solar arrays and popping the camera masts up — just so the rover can venture out and explore the red soil.

The second Mars Exploration Rover should follow its twin lander and is scheduled currently for January 25th descent.

Each Mars Exploration Rover ( MER ) will roam its landing site for geological evidence of past liquid water activity and past environmental conditions hospitable to life. The landing sites were selected to be near the equator, low in elevation, not too steep, not too rocky and not too dusty, among other criteria; 155 potential sites were studied. Public reviews by more than a 100 Mars’ experts finally arrived at the two sites selected, one near an ancient lakebed and crater (Gusev) and another (called Meridiani) rich in potentially water-formed minerals (hematite).

"They are fabulous sites, and they complement each other because they’re so different," said Dr. Steve Squyres, principal investigator for the rovers’ science toolkit and a geologist at Cornell University, Ithaca, N.Y.

JPL manages the MER Project for NASA’s Office of Space Science, Washington. JPL is a division of the California Institute of Technology in Pasadena.