Moon

"There are no resources on this airless rock."

- Zofia, detailing the worst aspect of Luna

A moon is a type of naturally-occurring satellite that's within orbit of a planetary body where the barycenter is still within the larger body. Earth itself has only one such satellite, Luna, which is typically, in English, simply called "the Moon".

Background
Luna is far smaller than Earth, though it is larger relative to its parent planet compared to other moons in the Solar System and is the 5th largest. Having a smaller mass than Earth means the Moon has lower gravity. This means that the Moon lacks an atmosphere, making it uninhabitable, without a contained air supply.

Within the Red Alert storyline, the Moon is depicted as possessing a very hostile environment (in keeping with its real-life status). There is no air on the Moon, so most infantry units cannot function there - only retrofitted vehicles, or infantry equipped with hazard suits (converted Tesla Trooper armor and Desolators). A special Cosmonaut version of the Rocketeer, armed with LASER weaponry, is developed by the Soviets for lunar combat operations. Still, this means it is impossible to use Engineers on the Moon to capture enemy bases (or to capture them then sell them for resources). The worst aspect of the Moon, however, is that there are absolutely no resources. There is no ore (much less gems) or oil derricks. The only credits you get is what you bring with you, which will soon run out. The only reason for going to the Moon is that, due to its extreme isolation from Earth, bases there are ostensibly free from observation/attack from Earth.

Third World War (second iteration)
During the Psychic Dominator Disaster, Yuri had a base established on the Moon. A Soviet Commander had hijacked one of Yuri's spacecraft, becoming his nation's first Cosmonaut to reach Luna. Soon after the landing, Operation: "To the Moon" commenced, and a battle raged on the moon, its outcome affecting the future of the "Space Race". Using certain vehicles and infantry with airtight breathing apparatus, the Commander destroyed Yuri's moon base. The Commander's base presumably remained as a Soviet lunar colony after the war.

How this event influenced Soviet space exploration remains to be seen.

Third World War (third iteration)
In the final Allied mission, The Moon Shall Never Have Them, the player has to stop Anatoly Cherdenko and Nikolai Krukov from escaping into space. References to the Moon are made in this mission, including the name of the mission itself, and Commander Warren Fuller finds himself questioning if “we should just let them go to the Moon”.

It’s clear that the Soviets have a presence in space in this timeline, including space probes, satellites and space stations that could be decommissioned and turned into weapons, and a space base that the Premier and his aides could escape to. However, any presence on the Moon is not seen in game and simply implied in the story.

Trivia
In real life, the Moon was the goal of both the Allies and the Soviets in the Space Race, which is a literal race against time and competition. July 20, 1969 is the date the United States, with its Apollo 11 mission, had beaten the Soviets to the Moon. As Neil Armstrong, the first to walk on Luna, once said: "That's one small step for man, one giant leap for Mankind."