Russia remembered two unlikely national heroes Thursday — a pair of skinny street mutts who moved the Soviet Union into the lead of the space race when they became the first living creatures to circle the Earth and come back alive.

The Aug. 19, 1960 mission by Belka and Strelka was a key step in preparations for the flight of Yuri Gagarin, who became the first human in space about a year later.

It showcased the Soviet lead in space exploration and turned the two dogs into global celebrities. Celebrations of the mission's 50th anniversary topped national newscasts on Thursday.

By 1960, Soviet space engineers had designed a returnable spacecraft capable of carrying a human into orbit, but they needed to run an extensive program of animal tests first and many of the dogs died during tests. Only stray mutts were picked up for such flights — doctors believed they were able to adapt quicker to harsh conditions — and they were all very small so they could fit into the tiny capsules.

Laika became the first dog to orbit Earth in a non-returnable capsule but died of overheating after her 1957 launch. Two other dogs died in a July 1960 launch when their rocket exploded seconds after blastoff.

Boris Chertok, a top engineer in the Soviet space program at the time, recalled the sense of relief space engineers felt when they heard Belka and Strelka barking in orbit and realized they were in good shape.

"They aren't howling, they are barking — that means they will return," Chertok quoted a colleague as saying.

Belka (Squirrel) and Strelka (Little Arrow) were accompanied by mice, rats, flies and some plants and fungi. The spacecraft landed successfully a day after making 17 orbits in more than 25 hours.

"These dogs acted like real pros," said Vladimir Tsvetov, an engineer who took part in the mission, said on Rossiya state television.

Soviet official reports claimed that the dogs felt well throughout the flight, but a participant in the program recalled later that it wasn't completely trouble-free. Dr. Vladimir Yazdovsky, who prepared the experiment, said that Belka was very nervous during the flight.

"She was very restless, tossing about and trying to get rid of the belts fixing her and barking," Yazdovsky wrote in his book chronicling the story of Soviet space medicine. However, post-flight medical checkups showed that both dogs were in fine condition without any adverse effects from the flight.

Strelka later had six puppies, one of which, Pushinka (Fluffy), was sent by Soviet leader Nikita Khrushchev to President John F. Kennedy's daughter Caroline.

Earlier this year, the dogs' story came to the screen in Russia's first 3D computer-animated movie, "Belka and Strelka: Star Dogs."