Four years seems a long time ago. Atal Behari Vajpayee was Prime Minister, BSE Sensex was at 5000 and Narayana Murthy was the Executive Chairman of Infosys. Yet, on that January morning, I thought very little of what was happening around me. I was glued to what was to take place that day on Mars.

It was Jan 3, 2004, and the first of the MER rovers were about to go through, as JPL folks refer to it, 12 minutes of hell, from the top of the Martian atmosphere to Gusev Crater, decelerating from 12,000 miles/hr to zero in this short interval. Would Spirit land safely on Mars? Beagle, the European rover, had been unsuccessful in landing on Mars barely a week back and two previous attempts by NASA to land on Mars had similarly ended in failure.

So, the third day of the New Year was shaping up to be a very tense day. I remember driving up to JPL, getting past security, going to a couple of briefings. We were then huddled in the Science Control Room. The descent through the Martian atmosphere started and finally after what seemed like eternity, Spirit called Earth to let us know that she had indeed survived the descent through the Martian atmosphere and was safely on the ground on Mars.

And, in three weeks, Opportunity would land successfully on Mars as well on Jan 24. So, we had not one, but two rovers, landing successfully on that planet.

That was four years ago. We thought that each rover would last 90 days, the warranty period that engineers had given and then it would all be over. What we did not know at that point, is that a very much longer voyage of discovery of Mars was about to unfold.

Achievements

Indeed, we have come up a long way. Spirit and Opportunity have driven far away from the landing sites: a distance of about 7 and 10 km respectively. Through more than 1400 sols (or Martian days), the science mission has progressed unfettered. Much like the early explorers of a virgin continent, Spirit and Opportunity have pressed on with discovery. In this they have been much like earth-based geologists of old, equipped with "backpacks”, “panoramic camera eyes" and a magnifying “hand-lens”. They also have had the ability to detect minerals from a distance and see in the infrared.

Their journeys across the landscapes of the Red Planet have given mankind its first experience of an overland expedition across another planet. Aside from the thrill of driving to a different location on Mars each day, Spirit and Opportunity have traversed significant milestones: in terms of science as well as “planetary firsts”.
Thus, Spirit and Opportunity were successful in finding evidence of past water and an environment that could have been suitable for sustaining microbial life. This was their main objective.

Our rovers have also chalked up many other pioneering feats in planetary exploration. Thus they are the first rovers to climb a hill on another planet and also the first to find meteorites, venture into craters and grind into rocks. The rovers also found frost on Mars and photographed clouds and sunsets on Mars.
Also, for the first time, they have conducted studies on Mars by coordinating observations with orbiting spacecrafts (like the Mars Odyssey and Express).

Problems

Were there bumps along the road? Yes, of course! Spirit went into an automatic cycle of reboots at the start of the mission, which could have killed the rover. A software patch fixed the problem. Then there was the dust storm earlier this year, which engulfed the whole planet and strained the energy budgets on Opportunity.

Spirit, after March 2006, lost use of one of her wheels. So, the rover drivers had to re-learn driving the rover with five wheels. Dust has accumulated over time over the solar panels that are the life-blood of the rovers. But, there have been nature sent “cleaning” events as well, where a burst of Martian wind, happened to come along and clear the obstructing dust off. Now, the worn out RAT (or the Rock Abrasion Tool) or the mini-drill for Spirit, seems to be losing its use.

Winters are tough, since the amount of sunlight on the solar panel decreases. Thus, the rovers often have to stay parked through the cold season because of energy constraints. Luckily, parking the rover at an angle on north-facing slopes, has given some badly needed energy to coast through the cold winters. The inclination of rovers towards the Sun results in the solar panels being closer to the normal incidence that results in greater power generation.

For Mars buffs, a bigger rover is being built to further the exploration of Mars: the Mars Science Laboratory is due to be launched in 2 years. This will be more powerful and well equipped, can drive longer distances and will have a new landing mechanism where a sky crane would be used to lower the rover onto the surface, in contrast to airbags used by Mars Exploration Rovers. Meanwhile, Spirit and Opportunity will press on with their extended missions to explore Mars.

(The writer is a member of NASA’s Mars Exploration Rover Mission Control).