Zond 2

By 1964 the Soviet planetary programme had moved to a third-generation bus, the 3MV, and had settled into a naming convention that has confused people ever since. Craft that Moscow wanted credit for were announced as Mars or Venera. Craft flown mainly to shake down hardware were announced as Zond, Russian for probe, with the destination simply omitted from the communique. Zond 2 was one of these. A letter from Leonid Smirnov, chairman of the Military Industrial Commission, to the Central Committee dated 28 November 1964, two days before launch, sets out what the flight was actually for: a single 3MV-4A spacecraft to test elements of the 3MV design and carry out scientific work in interplanetary space, and, if everything functioned normally, to be steered into Mars to deliver commemorative pennants to the surface. The TASS communique of 2 December described only systems testing and interplanetary research, and did not mention Mars. Zond 2 left Site 1 at Baikonur on 30 November 1964 on a four-stage 8K78, went into a 153 by 219 km parking orbit, and was pushed onto a trans-Mars trajectory by the Blok L stage. Even the basic numbers are unsettled: the launch time is published as 13:12 or 13:25 UTC, and the mass as 890, 950, 960 or 996 kg.

The trouble began within hours of separation. Antennas deployed and the panels were commanded open, but the first communication session showed onboard power at roughly half what it should have been. One of the two solar wings had not unfolded. The cause is given as a broken tug cord meant to pull the panel free at separation from Blok L, or as a protective shroud that failed to retract, depending on which reconstruction you read. Controllers spent a fortnight manoeuvring the spacecraft to shake the panel loose, and on 15 December 1964 it finally opened. By then the date for the first midcourse correction had passed, and with it any realistic chance of steering the craft into Mars as Smirnov's letter had envisaged. Weeks of running on reduced power had also left the spacecraft in poor thermal condition, and Russian accounts add that the onboard programme timer had failed shortly after injection onto the interplanetary trajectory, which put the thermal regime further out of shape. Whatever the exact chain, Zond 2 was already a wounded spacecraft by the middle of December, three weeks into a journey meant to last eight months. Perminov's summary, written by a designer rather than a historian, runs to a single sentence: Zond 2 did not fulfil its mission because the solar panels did not open entirely.

The part that worked was the part that had never flown to another planet before. Zond 2 carried six ablative pulsed plasma thrusters designed by A. M. Andrianov at the Institute of Atomic Energy, where Lev Artsimovich's department ran the Soviet plasma work. They were not gridded ion engines, though a great deal of what is written about them calls them ion engines. Each one discharged a capacitor bank of about 100 microfarads at roughly a kilovolt across two coaxial electrodes separated by a fluoroplast insulator, vaporising and ionising a sliver of the plastic and flinging it out at up to 16 km/s at a temperature near 30,000 K. Their job was attitude control: they could be commanded from the ground to act in place of the compressed nitrogen jets, which is exactly the failure mode that had killed Mars 1 two years earlier. Accounts of the test differ in detail. NSSDCA places it across 8 to 18 December 1964, English Wikipedia gives 14 December with 70 minutes of running at 4.2 million km from Earth, Russian sources give a total of 70 minutes, and Siddiqi records a double firing of all six on 18 December, just before contact began to deteriorate. All agree they ran, and that firing them is what shook the stuck panel open.

After December the record thins out and the sources stop agreeing. NSSDCA records a putative but unconfirmed midcourse manoeuvre on 17 February 1965. A declassified United States weekly intelligence review from 1965 gives 7 April 1965 as the date of the last communication session. The Russian Academy of Sciences space council says May 1965, and Soviet authorities announced the loss publicly on 5 May 1965. Andrew LePage, who has worked through the Soviet documents most carefully, notes that communications were already erratic by 18 December 1964. The honest reading is a range: contact went some time between the middle of December 1964 and the beginning of May 1965, and nothing we consulted narrows it further. Zond 2 then coasted, silent, and reached Mars on 6 August 1965. The distance is disputed too. The figure normally quoted is 1,500 km at a relative speed of 5.62 km/s, which would have been an extraordinarily close pass for an uncorrected trajectory; some later reconstructions put the miss near 650,000 km. Since nothing was tracking the spacecraft by then, both numbers are trajectory propagations rather than measurements. Zond 2 is in a solar orbit of roughly 0.98 by 1.52 astronomical units, period near 508 days.

What Zond 2 is worth remembering for is not its arrival. It is that a crippled spacecraft three weeks out from Earth, running on half power, fired a set of experimental plasma thrusters that had never been operated on an interplanetary trajectory, and used their recoil to unjam a stuck solar panel. That is a good deal more interesting than the flyby it did not manage. It was not, however, the first electric thruster to work in space: NASA's SERT-1 ran a mercury electron-bombardment ion engine successfully on a suborbital flight to about 1,000 km on 20 July 1964, four months earlier. As far as the published record goes, Zond 2 was the first to operate on a spacecraft that had left Earth orbit, and the first flown as a working attitude control actuator rather than as a pure demonstration. Three months after its last confirmed signal, the question the whole 1M and 2MV effort had been built around was answered from somewhere else entirely, when Mariner 4 returned twenty-one close-up frames of a cratered, apparently lifeless surface in July 1965. The Soviet Union would not put a working spacecraft into Mars orbit until 1971.