The Soviet Union loses both Phobos probes
Phobos 1 died in September 1988 to a flawed command sequence. Phobos 2 reached Mars orbit and failed in March 1989, weeks before dropping its landers.
Phobos 1 left Baikonur on 7 July 1988, Phobos 2 five days later. They were the most ambitious machines the Soviet Union ever aimed at Mars: six-tonne spacecraft carrying instruments contributed by a dozen countries, built not merely to orbit the planet but to creep up on its inner moon and set two landers on it — a long-lived station bolted to the surface by harpoon, and a hopper called PROP-F that would travel by jumping.
Phobos 1 was killed by a command sequence. On 29–30 August a set of instructions was uplinked without the usual ground verification step, because the software that did the checking was unavailable. A single wrong character switched off the attitude-control system. The spacecraft drifted, its solar panels slid off the Sun, the batteries ran flat, and the scheduled contact on 2 September never came.
Phobos 2 worked at Mars longer than any Soviet spacecraft before it. It entered orbit on 29 January 1989, worked its way inward to match Phobos's 9,400-kilometre orbit, and returned 37 images of the moon, the sharpest resolving detail about 40 metres across, along with infrared spectra of its surface. Its ASPERA instrument measured ions streaming off the top of the Martian atmosphere — early direct evidence that the solar wind was actively stripping the planet's air away. The same team flew a successor, ASPERA-3, on Mars Express fifteen years later, but nobody put a firm number on the loss rate until MAVEN.
Then, on 27 March 1989, shortly before the final phase — in which the spacecraft was to close to within 50 metres of Phobos's surface and release the landers — the on-board computer failed. Controllers received one weak, garbled transmission — the spacecraft was tumbling — and nothing afterwards. The landers stayed bolted to their dead carrier.
That was the end of it. The Soviet Union dissolved in 1991 without launching anything else toward Mars, and Russia's successor attempt, Mars 96, came back down on 17 November 1996 after its upper stage misfired in Earth parking orbit, scattering debris across the Pacific and the Andes and taking two surface stations and two penetrators with it. Viking 1's lander had gone quiet in November 1982. Nothing worked on the surface of Mars again until July 1997, and in that fifteen-year gap the only spacecraft to return anything at all from Martian orbit was Phobos 2, for two months, before it stopped answering.