While landing on the Sun at night has obvious advantages1 I'm curious why Luna 16 landed on the Moon at night. It was a complex mission involving robotic sample retrieval and a sample return launch back to Earth, and with 1970's technology it seems that one would want to avoid exposure to extreme cold as just one more way that things could go wrong.

Question: Why did Luna 16 land on the Moon and carry out it's sample-return during the lunar night, despite the challenges that the extreme cold would present to this complex mission?

1I think there is an oft-cited joke about this, can't find a source yet though.

Wikipedia's Luna 16:

Six minutes later, at 05:18 UT, the spacecraft safely soft-landed in its target area at 0°41' south latitude and 56°18' east longitude, in the northeast area of Mare Fecunditatis (Sea of Fertility) approximately 100 kilometers west of Webb crater and 150 km north of Langrenus crater. This was the first landing made in the lunar night side, as the Sun had set about 60 hours earlier. [...] Less than an hour after landing, at 06:03 UT, an automatic drill penetrated the lunar surface to collect a soil sample. After drilling for seven minutes, the drill reached a stop at 35 centimeters depth and then withdrew its sample and lifted it in an arc to the top of the spacecraft, depositing the lunar material in a small spherical capsule mounted on the main spacecraft bus. [...] Finally, after 26 hours and 25 minutes on the lunar surface, at 07:43 UT on 21 September, the spacecraft's upper stage lifted off from the Moon. The lower stage of Luna 16 remained on the lunar surface and continued transmission of lunar temperature and radiation data.


Landing at night is a side effect of limited time and place options.

Возможности ракеты–носителя «Протон–К» позволяли доставить на поверхность Луны возвратную ракету массой не более 5 кг — этого было явно недостаточно для обеспечения перелета Луна–Земля, учитывая необходимость проведения коррекций траектории. В этой критической ситуации было найдено совершенно оригинальное решение: посадку на Луну надо было осуществить в ограниченный район восточной части экваториальной зоны Луны — в этом случае вертикальный старт с Луны в строго заданное время обеспечивал попадание на Землю без коррекций траектории!

The capabilities of the Proton-K launch vehicle made it possible to deliver a return rocket with a mass of no more than 5 kg to the lunar surface - this was clearly not enough to support the Moon-Earth flight, given the need for trajectory corrections. In this critical situation, a completely original solution was found: landing on the Moon had to be carried out in a limited area of ​​the eastern part of the equatorial zone of the Moon - in this case, a vertical start from the Moon at a strictly specified time ensured hitting the Earth without trajectory corrections!

Выбранные траектории перелета существенно сужали возможные даты запуска аппаратов и районы посадок на поверхности Луны, но задача доставки грунта с Луны была принципиально решена при существующих весовых ограничениях и возможностях бортовой аппаратуры.

The selected flight trajectories significantly narrowed the possible launch dates of the spacecraft and the landing areas on the lunar surface, but the problem of delivering soil from the moon was fundamentally solved with the existing weight restrictions and the capabilities of the onboard equipment.

Из-за недостаточной освещенности изображения места бурения получено не было. На двух изображениях видна Земля в виде светлого пятна.

Due to insufficient illumination, the image of the drilling site was not obtained. In two images, the Earth is visible as a bright spot.



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