NOW FOR LUNAR ORBIT

Orbiting the moon was as essential to a manned mission as a soft-landing. Good photographs were essential to determine landing sites and it was important to learn as much as possible about the lunar orbit environment to ensure there were no nasty surprises (there were).

The Soviet lunar orbiter programme was commissioned by OKB-1 at the same time as the Ye-6 programme. Called the Ye-7 programme, it made very slow progress in comparison. Two partially completed Ye-7 models were turned over by OKB-1 to OKB Lavochkin in summer 1965 during the move between the design bureaux. After the success of Luna 9, attention focused on the lunar-orbiting missions.

Luna 10

Although the Ye-7 photographic equipment was not ready, Russia still wanted to achieve a lunar orbit before the Americans did so with their upcoming lunar orbiter. There was also political pressure to mark the 23rd Communist Party Congress, opening at the end of March 1966 and the first congress of new Soviet leader Leonid Brezhnev. Georgi Babakin and Mstislav Keldysh proposed that the Ye-6 bus be used to fly a lunar orbit mission in time for the congress.

This hastily conceived lunar orbiter was called the Ye-6S. It used the Ye-6 bus, to which was attached not the normal lander, but a pressurized 245 kg cabin that would serve as a lunar orbiter. It is more than likely that the cabin was taken from what would have been an Earth-orbiting satellite in the Cosmos series. Its shape strongly suggests that it may have been one of the Cosmos series built by Mikhail Yangel’s design bureau in Dnepropetrovsk. It was equipped with seven scientific instruments originally planned for the Ye-7, including a magnetometer on a long boom. From the ground, scientists would also measure gases in the lunar environment by examining signal strengths as the probe appeared and reappeared behind the lunar limb, and watch for changes in the orbit due to the lunar gravitational field. Lunar orbit insertion would be performed by the Ye-6 bus. Instead of a 46 sec burn for soft – landing, a much smaller burn was required for orbit insertion. Once in orbit, the pressurized Cosmos cabin would separate for an independent mission.

The first Ye-6S was launched on 1st March 1966. The upper-stage problems reasserted themselves and block L failed to fire the probe – renamed Cosmos 111 — out of Earth orbit. The second Ye-6S eventually got away on 31st March 1966. No sooner was it streaking towards the moon than it was announced that it was directed towards an entirely new objective — lunar orbit. Eight thousand kilometers from the moon, Luna 10 was turned around in its path and its rockets blazed briefly but effectively. They knocked 0.64km/sec off its speed, just enough to let it be captured by the moon’s gravity field. The boiler-shaped instrument cabin separated on schedule 20 sec later. Luna 10 was pulled into an orbit of 349 by 1,015 km, 71.9°, 2 hr 58 min and became the first spacecraft to orbit the moon.

But, first things first, Luna 10 celebrated the latest Russian achievement in style. Celestial mechanics meant that Luna 10 would enter the first of its lunar orbits just as the Communist Party was assembling in Moscow for its morning congress session. As it rounded the eastern edge of the moon, Luna 10’s transmitter went full on and relayed the bars of the Internationale — in turn, broadcast live by loudspeaker direct to the party congress over the static of deep space. It was a triumphant moment and the 5,000 delegates had good reason to stand and cheer wildly. Thirty years later, it was learned that the ‘live’ broadcast was actually a prerecording taken from Luna 10 earlier in the mission. The radio engineers did not trust the live broadcast to work, but, as they later admitted, playing tricks on the Central Committee was a dangerous game and the truth could only be safely revealed in the 1990s when the Central Committee itself was no more.

Luna 10’s mission lasted way into the summer and did not end till 30th May after 56 days, 460 lunar revolutions and 219 communication sessions. Data were trans­mitted on 183 MHz aerials and also on 922 MHz aerials. A stream of data was sent back by its magnetometer, gamma ray spectrometer, infrared radiometer, cosmic ray detector and meteoroid counter. These found a very weak magnetic field around the moon, 0.001% that of Earth (probably a distortion of the interplanetary magnetic field); no lunar magnetic poles; cosmic radiation at 5 particles/cm2/sec; 198 meteoroid impacts, more in lunar orbit than in the flight to the moon; no gaseous atmosphere; and that there were anomalous zones of mass concentrations below the lunar surface disturbing the lunar orbit (mascons). Using its gamma ray spectrometer, Luna 10 began the first initial survey of the chemistry of the moon, enabling a preliminary map to be compiled. Lunar rocks gave a composition signature broadly similar to basalt, but other important clues to its composition were picked out. The gamma ray spec­trometer was used to measure the level of uranium, thorium and potassium in lunar rock. There were significant variations in radiation levels on the moon, being high in

the Sea of Clouds, for example. Luna 10’s magnetometer was put on the end of a 1.5 m boom and took measurements every 128 sec for two months. Designer Shmaia Dolginov – who had built the original magnetometer on the First Cosmic Ship – was able to refine the range to between —50 and +50 gammas.

Luna 10’s final orbit, as measured on 31st May, was 378-985 km, 72.2° – whether the changes were due to mascons or reflect more accurate measurement of the original orbit is not certain. Despite its hasty assembly, the Dnepropetrovsk Cosmos mission had presented a significant haul of science, significantly advancing the knowledge of the moon in only a couple of months.

Luna 10 instruments

Meteorite particle recorder. Gamma spectrometer. Magnetometer with three channels. Solar plasma experiment.

Infrared recorder.

Radiation detector.

Charged particle detector.

The discoveries of Luna 10

Weak magnetic field around the moon, 0.001%.

No lunar magnetic poles.

Cosmic radiation in lunar orbit.

Meteoroid impacts, more in lunar orbit than in the flight to the moon. No gaseous atmosphere.

Mascons.

Basaltic surface composition.