Pioneering Soviet-era cosmonaut Valery Bykovsky, who made the first of his three flights to space in 1963, has died at age 84, Russia’s space agency said.

Roscosmos said Mr Bykovsky died on Wednesday, but a cause of death wasn't specified.

Mr Bykovsky was one of 20 Soviet military pilots in the first group selected to voyage into space. He first blasted into outer space in June 1963 as the pilot of the Vostok-5 crew.

Once in orbit, he radioed to ground control that he was 'feeling fine'.

He underwent training for a moon mission before the United States won the race to the moon and the Soviet Union cancelled its plans to go there.

Mr Bykovsky was one of 20 Soviet military pilots in the first group selected to voyage into space. He first blasted into outer space in June 1963 as the pilot of the Vostok-5 crew

Soviet cosmonaut Valery Bykovsky (left) prior to a space trip aboard Soviet rocket Soyuz 31 to the Salyut 6 space station in 1978

'Bykovsky belonged to the first generation of Soviet cosmonauts, who wrote many bright pages in the glorious history of Russian manned cosmonauts,' officials at the Gagarin Cosmonaut Training Center in Star City said in a statement.

Bykovsky spent his time in space conducting scientific experiments, and even recorded himself exercising in zero-gravity, studying his body's reaction to the environment.

During his first mission, Bykovsky planned to stay in orbit of the Earth for eight days, but increased solar flare activity brought his voyage to an end after four days, 23 hours and 17 minutes.

The mission remains the longest solo spaceflight in history.

He landed back down to Earth on June 19, 1963, three hours after Valentina Tereshkova, the first woman in space.

Bykovsky spent his time in space conducting scientific experiments, and even recording himself exercising in zero-gravity

Born in Pavlovsky Posad, in August 1934, Bykovsky spent 20 days, 17 hours and 47 minutes in Earth's orbit

Bykovsky's solo voyage of four days, 23 hours and 17 minutes, remains the longest solo spaceflight in history.

Mr Bykovsky made his second space flight 14 years later, in 1976.

Flying as the commander of Soyuz 22, Bykovsky spent a nearly seven days taking more than 2,400 photographs of Earth's horizon, and images of the moon rising and setting through the planet's atmosphere.

Bykovsky's third and final trip came in 1978, with Germany's first citizen in space, Sigmund Jahn.

Born in Pavlovsky Posad, in August 1934, Bykovsky spent 20 days, 17 hours and 47 minutes in Earth's orbit.

He also served as a backup to the Vostok 3 and Soyuz 37 missions. Bykovsky was primed to enter orbit with the Soyuz 2 crew, but the mission was cancelled after its predecessor, Soyuz 1, ended in tragedy.

27 марта на 85 году ушел из жизни летчик-космонавт, дважды Герой Советского Союза, полковник Валерий Быковский — https://t.co/MVhoiXN1hF



Роскосмос соболезнуют родным и близким Валерия Федоровича... pic.twitter.com/bIkHmALyUB — РОСКОСМОС (@roscosmos) March 27, 2019

For his service to his Russia's space program, Bykovsky was named a Hero of the Soviet Union and awarded the Order of Lenin and the Order of the Red Star, am amassing numerous other Russian and international accolades along the way.

Bykovsky was married to Valentina Sukhova, with whom he had two children.

He is survived by his son Sergei. His daughter Valery died in 1986.

'The leadership of the Cosmonaut Training Center, pilot-cosmonauts of the USSR and Russia and the whole team offer their condolences to the families and friends of Valery Fyodorovich,' Gagarin Cosmonaut Training Center said in a statement.