Viking 1 and 2 land and refuse to die
Two orbiters, two landers and roughly a billion 1970s dollars. Designed for 90 days on the surface, Viking 1 kept transmitting from Chryse Planitia for over six years.
Viking 1 was to land on 4 July 1976, the American bicentennial. The orbiter arrived on 19 June and found the target site in Chryse Planitia a deeply incised channel bed, strewn with rock that could tip a lander over. Controllers spent three weeks hunting a new site from orbit, voted on 12 July for ground farther west, at 22.5°N, 47.5°W, and landed there on 20 July at 11:53:06 UTC, the seventh anniversary of Apollo 11. Viking 2 set down in Utopia Planitia on 3 September at nearly 48°N, far enough north to photograph winter frost.
Each Viking was two spacecraft: an orbiter of 2,328 kilograms fuelled at launch and a lander of 612 kilograms on the ground. The landers were sealed into a bioshield for launch and heat-sterilised against contaminating the search for life. Entry used an aeroshell, a parachute, then three throttleable hydrazine engines, each with eighteen small nozzles to spread the exhaust and spare the ground they would sample. Two radioisotope generators supplied about 70 watts. The programme cost roughly a billion dollars at the time and, adjusted for inflation, remains NASA's most expensive planetary science project.
The first pictures arrived 25 seconds after touchdown: a rock-strewn plain. Colour came on 21 July, released with a blue sky, then corrected to red. The meteorology stations ran for years: at Chryse the afternoon air reached about -33°C, predawn about -86°C. They tracked dust storms and recorded pressure rising and falling by roughly 30 percent over the martian year as carbon dioxide froze onto the winter pole and sublimed off again. Both landers carried a seismometer: Viking 1's never uncaged, and Viking 2's, bolted to the deck rather than the ground, recorded little but the wind shaking it.
The design life was 90 days; Viking 2's lander ran until 11 April 1980. Viking 1's last transmission reached Earth on 11 November 1982, after a faulty command cut communications: by the usual account a battery-charging sequence overwrote the memory holding the antenna-pointing parameters, leaving the dish aimed at nothing. Controllers kept calling for six months. The landers have names now, the Thomas Mutch Memorial Station in Chryse and the Gerald Soffen Memorial Station in Utopia, after the project's lander imaging lead and its project scientist.