Destination Mars (2 page)

J
uly 20, 1976: The Viking 1 orbiter instructed its lander to begin the separation sequence to start the long journey to the Martian surface. It was just after midnight at the Jet Propulsion Laboratory (JPL) in Pasadena, but as the probe was automated, no commands had been exchanged for some time. The onboard computer initiated a final round of systems checks. The explosives that joined the lander to the orbiter were armed…

Anxious flight controllers, largely powerless at this distance, could only watch the time-delayed data as the onboard computers made their own decisions. At 00:00 onboard computers fired the pyrotechnics, separating the Viking lander, which soon fired its own braking thrusters to begin the slow fall out of Martian orbit. In the dusky skies above, the orbiter from which it had recently separated continued on its mission. Below spread the ruddy expanse of Mars: dusty, cold, unexplored…and in about three and a half increasingly turbulent hours,
home.

The Viking 1 lander, at ten feet wide by seven feet tall, was part of the largest and most expensive US unmanned mission to date. The orbiter, eight feet wide and ten tall, with a solar-panel span of thirty-two feet, shared the distinction. In a few weeks, Viking 2, a virtual twin, would arrive on Mars on an identical mission, but within a different landing zone on the opposite side of the planet.

The people who had sent Viking to this dangerous rendezvous waited out the landing confirmation signal in tense quiet. Only
the most necessary words were spoken. There was an eighteen-minute delay between Earth and Mars at this distance; whatever happened to Viking now would be of its own doing. Many scientists on this program estimated a 50-50 chance of success, even with two landers. It was, in essence, a blind landing on a rocky, undulating landscape.

The Viking 1 lander was, for the first time in its short life, completely alone.

The tiny craft plummeted into the thin Martian atmosphere at 10,000 mph, still firing its braking thrusters. These rockets were models of simplicity. The fuel was a monopropellant and needed no ignition source and no other chemical mixed with it to explode into thrust. Further, instead of using complex pumps to feed the engine, the propellants were pressurized by stored helium gas. There was little to go wrong once they fired.

The lander was encased by a heat-resistant aeroshell, a dish-shaped structure that protected it from the heat of entry but also placed more demands upon its small digital brain. For as it plummeted through the upper reaches of the tenuous Martian atmosphere, Viking's computer was focused not just on a successful landing but also on conducting research in this wispy environment. Nothing is wasted in space exploration, and this early descent phase was no exception. As the computer labored to steer the craft, data began flowing in from sensors mounted on the aeroshell, providing data about charged particles surrounding the descending craft. Within the parade of arcane obsessions in the mind of the planetary scientist, understanding how the solar wind—high-energy particles streaming forth from the sun—interacts with the upper reaches of the Martian atmosphere is a thrill. The measurements now being recorded on the onboard tape drives should shed some light on this question. But Viking cared not; it simply stored the data for eventual delivery to Earth. Recording data was its raison d'être, and to this task it applied itself from its first moments.

At about 180 miles in altitude, another instrument switched
on: the mass spectrometer. This would measure the makeup of the upper atmosphere, analyzing the thin gasses present to provide a more detailed accounting of the “air” to augment the painstakingly gathered information already gleaned from Earth-bound telescopes. This first US spacecraft to enter another planet's atmosphere would accomplish multiple objectives, but primary among them was searching for one capable of supporting life as we understood it in 1976.

At about sixty miles high, this group of instruments switched off and another set became active. These performed an elegant analysis of the pressure, density, and temperature of the lower atmosphere by measuring the slowing of the craft. It was a bit like a waltz with a nonexistent partner, where one's success is measured via self-observation rather than direct feedback from the surroundings. But it was enough.

At about seventeen miles, the trajectory shifted: the aeroshell was sufficiently aerodynamic that it began to generate some lift, and Viking began to glide across the Martian sky. All this was by design; it was another way to scrub off excess velocity. Eventually, weight and drag took their toll and the craft began its steep descent once more.

The continual hiss of the rockets was joined by the roar of the thickening atmosphere, which, while thin, would soon be enough for the single parachute, set to deploy at nineteen thousand feet, to slow the machine sufficiently to land in one piece. This slowing to a sane rate of descent would be aided by more rocket engines. These were ingeniously designed as three clusters of eighteen tiny nozzles that would provide adequate braking propulsion without disturbing the surface upon which it alighted. All this, plus the fanatical sterilization of the spacecraft, was critical to preserving the sanctity of the ground below. For this was central to its primary mission—the search for life.

The onboard radar was scanning the ground, providing excellent data for range to the surface. What it was
not
providing was
any idea of how rough that surface might be. The Viking team back on Earth had searched for the best landing place it could find with Mariner 6 and 7 photographic surveys, and later with results from Mariner 9, but it was barely better than a rough guess. At the Mariner 9 camera resolutions, the best images heretofore available, items smaller than the Rose Bowl were nearly invisible. Anything smaller than that had to be inferred from the analysis of surrounding terrain, and this was more alchemy than science, based on Earth-bound geological assumptions. Teams had agonized over these images for years. Then, data from the just-arrived Viking orbiter cameras resulted in more eleventh-hour angst about the landing area and a new site was selected at the last moment. Now all JPL controllers could do was aim the gun, close their eyes, and squeeze the trigger. In short, Viking was what lab folk later referred to as a BDL—a Big, Dumb Lander. Much of what happened from now on was based on luck. Viking could crash and mission control would be blissfully unaware until eighteen minutes after the fact, when the signal would simply vanish.

Soon the lander unhooked from the parachute, now relying only on its tiny landing rockets to control the final descent. At three hundred feet up, low-level radar kicked in to give a last set of readings. At sixty feet, the computer worked to cancel any horizontal motion and the lander settled into a strictly downward mode. It would now land directly below, no matter what. So said the simple instructions burnt into its primitive memory, saved in tiny magnetic cores that lived at the intersection of minute, hair-thin wires. While brutishly dumb by today's standards (your toaster probably holds more data), it was an elegant and almost bombproof method of storing data.

Slowly, Viking descended the final few feet. The rockets would not shut off until the lander made ground contact. But what lay below? The Viking lander had a scant 8.5 inches of ground clearance; any rock larger than that would likely end the mission. Falling in the weak gravity at a leisurely 6 mph, about the speed a
person can walk, Viking 1 settled onto Chryse Planitia, Greek for “Golden Plain,” a large and relatively flat expanse not far from the Tharsis volcanic region.

Touchdown. Silence returned to Mars. The Viking 1 lander was down, alive and well, after a 440,000,000-mile journey.

The date was July 20, 1976, the seventh anniversary of the landing of Apollo 11 on the moon. It was the first US soft landing on another planet (a moon is a satellite), and the first probe to function for more than a minute on another planetary body (an earlier Soviet probe had landed, but failed upon touchdown).
¹
In fact, it would perform well beyond its builders' wildest expectations.

As the lander began surface operations, the Viking orbiter continued overhead, entering a new phase of its own science program. Armed with high-resolution cameras, it continued its observations while also acting as a relay station between the lander below and Earth, a blue star barely visible over the horizon.

Lander 1 went through a deliberate cycle of making sure that the descent engines and associated systems were shut down. It would not do to drip anything caustic or polluting onto the ground below. Hydrazine, the craft's volatile and corrosive fuel, would not be friendly to any microorganisms lurking about and would be a terrible way of saying hello. In fact, not so much as a microbe of Earth biota had been knowingly allowed to fester on Viking either; it had been baked, purged, and sterilized better than any surgeon's tool before launch. Nothing could be allowed to pollute the virgin Martian soil.
²
As the engines were “safed,” the computer queried the navigation system, or inertial guidance unit. This simple system, while no longer needed for steering the craft, would help to supply altitude and directional information, so it was run for another five minutes. This information was critical to aiming the radio dish toward Earth, so the more accurate the data, the better.

At the same time, the first postcard to home was being assembled. The Viking landers used a new type of imaging camera. Previous
space probes had used state-of-the-art TV cameras, but at the time, the images were not up to what the designers had yearned for. For Viking, the camera stared upward into a mirror that swung vertically, “nodding” up and down. Between each nod the mirror would rotate a small amount. In this way, a series of strips were assembled over time, and these resulted in what was, for the day, a very high-resolution image. Two of these ingenious devices were mounted on each lander, allowing three-dimensional imaging, and the first job of the day was to send an image home.

But this first snapshot of another planet was not to be a splendid panoramic of the landing area; rather, it was a somewhat mundane image of the nearest footpad. This would accomplish multiple goals instantaneously: the safety (or lack thereof) of the landing site would be demonstrated by the placement of the footpad. The amount of sinking into the sandy soil (properly called
regolith
, as the word
soil
implies life within) would be shown, and this, along with other measurements such as the amount of slowing at contact and the designed-in collapsing of the lander's legs upon touchdown would supply information about the compactibility of the ground. Remember, nothing is wasted in space exploration.

Back on Earth, strips of the first picture from Mars began to come in. It was innocuous enough: a shot of footpad 3. If the probe had failed then and there, a lot of folks would have been very upset to have nothing more to show for the billion-dollar effort. But this shot was needed to ensure that the craft was stable. Cheers rang out at JPL and Caltech as the proof of a successful landing were made visible. But from Mars, the lander could not hear, nor would it have cared. It merely carried on in its eighteen kilobytes of programmed duties with dogged and ruthless determination.

Next on the lander's to-do list were the pyrotechnic events, known to most of us as explosions. In spaceflight, whether manned or unmanned, small explosives had long had a leading role. Then as now, they were used to separate the stages of rockets as they ascended away from Earth. They released spacecraft once in orbit. They opened and closed valves. And, in Viking's case, they were critical to beginning Mars-based activities. These are, by their nature, one-shot operations—as in, they work or they don't. Their duties included releasing safeties for the life-science experiments and opening the meteorology boom—an arm with instruments to measure wind speed, temperature, and the like. These performed without a hitch.

Now a second photo was taken, and this was the money shot: the first picture of the horizon of Chryse Planitia. As the lander went about its business, breath was again held in mission control. What would we see? What did the surface of Mars look like at ground level? Remember that these were the days of rotary telephones, bias-ply tires, and such state-of-the-art things as
The Eagles: Greatest Hits
via vinyl records. An image from the surface of Mars was heady stuff. And with the Viking orbiter disappearing over the horizon in about twelve minutes, and with it, the best link to home, this had to be done
now.