LUNA 16

The first of the new batch of Ye-8-5 spacecraft was not available until the following month. Luna 16 was launched on 12th September 1970, and it headed out moonwards on a slow four-day coast. In contrast to the great media interest which Luna 15 had attracted, Luna 16 went virtually unremarked by the Western media. This was a pity,

for Luna 16 was a remarkable technical achievement by any standard. Its flight coincided with what became known to the world as Black September. Four airliners were seized in the space of a few hours by Palestinian fighters; the aircraft were hijacked to a remote airstrip called Dawson’s Field in Jordan; King Hussein’s army moved in to crush the Palestinians. The world looked on, mesmerized.

Luna 16 carried, like Luna 15 before it, the new KTDU-417 main engine built by the Isayev design bureau. The KTDU-417 had a throttleable engine ranging from

750 kg to 1,920 kg. At highest thrust, it had a specific impulse of 310 sec, able to burn for 10 min 50 sec using up to four tonnes of propellant. This engine was built to perform mid-course correction, lunar orbit insertion, pre-descent burn, the ‘dead – stop’ burn to take it out of lunar orbit and the final burn 600 m above the moon. There was also scope for further manoeuvres in lunar orbit, as had proved necessary on Luna 15 and the engine could be fired up to eleven times. It could also be used at lowest thrust with a specific impulse of 250 sec [1]. The engines for the final stages of landing had a thrust of 210 and 350 kg.

Luna 16 burned its engine on the first day for 6.4 sec to make a course correction. Luna 16 entered moon orbit on 17th September at an altitude of 110 km to 119 km, 71°, 1 hr 59min. The aim was to achieve a circular lunar orbit around 100km.

After two days, Luna 16 fired its engine to make a 20-m/sec velocity change and brake into an elliptical course of 106 km by 15.1 km, with the perilune over the landing site. Its final path before descent was 15 km by 9 km, so low as to only barely scrape the peaks of the moon’s highest mountains. At this stage, the four 75 kg large propellant tanks that had been used for mid-course correction, lunar orbit injection and orbital change were jettisoned.

As Luna 16 skimmed over the eastern highlands of the moon on the 20th, the retrorocket of the 1,880 kg craft blasted and Luna 16 began to fall. First, the main engines blasted for 267 sec, using about 75% of fuel remaining, to kill all forward motion. This was a big burn, 1,700 m/sec. The critical stage had begun. Luna 16 was now over flat lowlands. Sophisticated radar and electronic gear scanned the surface, measuring the distance and the rate of descent. After the ‘dead stop’ engine burn, Luna 16 was in free fall, coming down at 215 m/sec, until six minutes later it was at 600 m. Then the main engine blasted again. At 20 m, a point detected by Doppler – sounding gamma rays, the retrorocket cut off and small vernier engines came into play. At 2 m, sensing the nearness of the surface, these too cut out, the intention being to achieve a landing speed of 2.5 m/sec or 9km/hr. Luna 16 dropped silently to the airless surface, bouncing gently on its four landing pads. It was down, safe and sound, on the Sea of Fertility, 100 km from crater Webb. The flat and stony ground was marked only by a few small craters, even if they were not visible during the descent, because Luna 16 had landed in darkness. This and subsequent soil-sampling missions carried stereo cameras of the type carried by Luna 13, so the quality of images should have been very good. The purpose of the cameras was to help to guide the operators of the drill and for such night landings floodlights were carried.

Strong signals were picked up by Western tracking stations. Within hours, the USSR had announced its third soft-landing on the moon – but said no more. The Russians had still not admitted that the intention of the probe was to collect samples.

Meantime, a quarter of a million miles away a 90 cm drill arm swung out from Luna 16 like a dentist’s drill on a support. It swung well clear of the base of the spacecraft, free from any area that might have been contaminated by gases of landing engines. The wrist of the drill had a flexibility of 110° elevation, 180° rotation and was able to drill to 35 cm. The drill head bored into the lunar surface at 500 r. p.m. using electric motors for 7 min and then scooped the grains of soil down to 35 cm deep. There it began to hit rock and, rather than risk damaging the drill, the boring was

terminated and the sample collected and put into the container attached to the drill head. Like a robot in a backyard assembly shop, the drill head jerked upwards, brought itself alongside the small 39 kg spherical recovery capsule, turned it round and pressed the grains into the sealed cabin, which was then slapped shut.