Tyazhely Sputnik, also known as Venera 1VA No.1, and in the West as Sputnik 7, was a Soviet

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 spacecraft, which was intended to be the first spacecraft to explore Venus

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

. Due to a problem with its upper stage it failed to leave low Earth orbit

Low Earth orbit

A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

. In order to avoid acknowledging the failure, the Soviet government instead announced that the entire spacecraft, including the upper stage, was a test of a "Heavy Satellite" which would serve as a launch platform for future missions. This resulted in the upper stage being considered a separate spacecraft, from which the probe was "launched", on several subsequent missions.

Tyazhely Sputnik was launched at 01:18:03 UTC on 4 February 1961, atop a Molniya

Molniya (rocket)

Molniya 8K78 was a modification of the well-known R-7 Semyorka rocket and had four stages.This derivative of the original three stage Vostok rocket was especially designed to bring high flying satellites into orbit or to launch probes to other planets. The first launch of this rocket was on...

 8K78 carrier rocket flying from Site 1/5

Gagarin's Start

Gagarin's Start is a launch site at Baikonur Cosmodrome in Kazakhstan, used for the Soviet space program and now managed by the Russian Federal Space Agency....

 at the Baikonur Cosmodrome

Baikonur Cosmodrome

The Baikonur Cosmodrome , also called Tyuratam, is the world's first and largest operational space launch facility. It is located in the desert steppe of Kazakhstan, about east of the Aral Sea, north of the Syr Darya river, near Tyuratam railway station, at 90 meters above sea level...

. When the upper stage ignited, cavitation

Cavitation

Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

 in the liquid oxygen

Liquid oxygen

Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

 flowing through the oxidiser pump caused the pump to fail, resulting in an engine failure eight tenths of a second after ignition. It reentered the atmosphere over Siberia

Siberia

Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

 on 26 February 1961.

The sister probe, Venera 1

Venera 1

On February 12, 1961, 00:34:36 UTC, was the first planetary probe launched to Venus by the Soviet Union. The Venus-1 Automatic Interplanetary Station, or Venera 1, was a 643.5 kg probe consisting of a cylindrical body 1.05 metres in diameter topped by a dome, totalling 2.035 metres...

, successfully launched and was injected into a heliocentric orbit toward Venus one week later, although telemetry on the mission failed a week into flight.