The Russian Post has issued a stamp commemorating the 50th anniversary of the space trip of famous Soviet dogs Belka and Strelka.
From Wikipedia:Belka (Белка, literally, "squirrel") and Strelka (Стрелка, "Arrow") spent a day in space aboard Korabl-Sputnik-2 (Sputnik 5) on August 19, 1960 before safely returning to Earth.
They were accompanied by a grey rabbit, 42 mice, 2 rats, flies and a number of plants and fungi. All passengers survived. They were the first Earth-born creatures to go into orbit and return alive.Strelka went on to have six puppies with a male dog named Pushok who participated in many ground-based space experiments, but never made it into space. One of the pups was named Pushinka (Пушинка, "Fluffy") and was presented to President John F. Kennedy's daughter Caroline by Nikita Khrushchev in 1961.
The stamp features a portrait of the scientist, the first artificial Earth satellite and Keldysh's formula (on the completeness of the eigenfunction).
Mstislav Keldysh was a Soviet scientist in the field of mathematics and mechanics. He was one of the key figures behind Soviet space program. Among scientific circles of USSR Keldysh was known with epithet "the Chief Theoretician".
The crater Keldysh on the Moon, and a research vessel Akademik Mstislav Keldysh are named after him. A minor planet, 2186 Keldysh discovered in 1973 by Soviet astronomer Lyudmila Chernykh, is also named in his honor.