WASHINGTON, July 3: Too bad Little Green Men don't live on Mars. If they did, and should they happen to peep from behind Martian rocks or from inside Martian caves, they would see right now a giant spacecraft hurtle towards them at 16,000 miles an hour, lose momentum in their atmosphere, slowdown by opening parachutes and retrorockets, dangle about 40 feet above their surface, and cushioned against sharp rocks by four big airbags, bounce several times like a beach ball before coming to a halt.

The Earthlings are at it again.

More than two decades after mankind last sent out spacecraft to the planet closest to us, it's Mars-time again. Last year at this time on July 4, Hollywood introduced an alien attack in the movie theatres with the film Independence Day. This July 4 on the American Independence Day, scientists at NASA are engineering a spectacular Martian touchdown. And this is for real.

After travelling near 120 million miles since its launch last December, the spacecraft Pathfinder is hours away from landing on Mars, amid high dudgeon among scientists here on Earth. At around 3 pm EST on Friday (0030 hrs IST on Saturday), the one-tonne craft will touchdown, or rather bounce down, in an area called Ares Vallis, it's hard landing cushioned by giant balloons. And with it, mankind will open a new chapter in space.

Exploration of Mars became distinctly ``unsexy'' after the last successful mission, the Viking touchdown in 1976, showed no traces of life on the planet. Since then, space budgets have been hacked by hard-headed politicians, helped furthermore by the failure of later missions: Two Mars-bound Russian spacecraft failed in 1988 and 1989, NASA's Mars Observer was lost in 1993 and another Russian Mars 96 mission went kaput and plunged back to the Earth.

But promising ``faster, cheaper and better'' results, NASA scientists are back at their old game again. And the evidence last August in a meteorite suggesting life may have existed on Mars millions of years ago had further ignited interest. Compared to the failed $1 billion Mars Observer mission in 1993, the Pathfinder mission costs a trifling $270 million, about the same amount it took to make the movie Titanic, the costliest film ever made.

In fact, the tight budget is the main reason Pathfinder is going in for a hard landing (cushioned by balloons) and keeping scientists on tenterhooks.

To keep costs down and win political and public-approval, scientists jettisoned all the fancy bells and whistles on the spacecraft and cut down its weight. And instead of going into orbit around Mars and then descending in a soft touchdown, Pathfinder will plunge directly towards the landing site at something like 40 miles an hour. Scientists are praying that it will survive the impact. So far, the news is good. ``Pathfinder is very, very healthy. So far she's done everything we have asked her to,'' said Brian Muirhead at the mission control center in Pasadena, California.

Once Pathfinder lands safely, the air bags will deflate and cables will drag them back to the craft to get them out of the way. Then the computer aboard the 600-pound, tetrahedron-shaped main craft will open three panels, each a yard long. If the spacecraft has landed in the area it was aimed at, close to the Mars Equator to ensure maximum sunshine at this time of the Martian year, each petal with solar cells will begin producing electricity to run the spacecraft and a rover (about which more shortly).

In fact, Pathfinder will be open for business by 4 pm, within an hour after landing. A stereo camera will pop up and locate the sun and enable the onboard computer to point its main antenna correctly. The camera will also transmit the first picture. Scientists say these may be quite different from those sent by Viking 21 years ago, when Mars had a red, dusty sky. With the planet further away from the Sun and the dust having settled, they say the sky could be deep blue with brilliant white clouds.

But the real star of the show will be Sojourner, a diminutive micro-rover which will roll out of the main lander and set off on its own to sniff around Martian surface. Now, not so fast. Don't visualise Sojourner as some man-like robot. Conditions on Mars don't permit that kind of luxury.

Sojourner is a more modest mechanical beast. At a mere 24 inches long and 19 inches wide, it is about the size of a microwave. But its functions are vital (already, a toy prototype produced by Mattel Hot Wheels for $4.99 is sold out in stores and has become a collectors' item) and its performance will be key to what comes out of this mission. The six-wheel, 22-pound Sojourner will be navigated from Earth and will literally inch out to explore the rough Martian surface, moving at less than a mile per hour.

Scientists expect it to go no further than 30 to 40 feet from the lander during the first week. If it survives, it may later be sent out to 100 feet. It's main scientific instrument will be an alpha proton X-ray spectrometer which will determine the chemical composition of rocks and soil. This, in fact, will be the central focus of the mission. Mars is now dry as a bone except for polar ice and permafrost. But scientists believe that millions of years ago, Areas Vallis, where the Pathfinder will land, was awash with water, and torrents washed tons of rocks from the highlands. As Sojourner goes sniffing, it will try and determine the rock type to see if water, and thus life, existed on the planet. If the rock is basalt, for example, it would mean it came from deep within the planet. If, on the other hand, it is, say, limestone with calcium carbonate deposit in it, it could confirm that bodies of water were present on the Martian surface for long periods and conditions were favourable for development of life forms. In fact, the rock could match the meteorite ALH 84001, the piece found last August to be carrying Microfossil traces of Martian life.

If that happens, the space exploration community will get a shot in the arm for going ahead with a calender which America's budget-conscious politicians are frowning at. As things stand, NASA hopes to send up two missions every two years when Mars and Earth are, to filch an expression from astrologers, ``in conjunction'' for a launch. If all the effort yields good results, NASA administrator Daniel Golden, says mankind could take The Gigantic Step in the year 2011.

Copyright © 1997 Indian Express Newspapers (Bombay) Ltd.