II.

Spacecraft

The USSR hid Vostok’s design from the rest of the world until 1965 because of the spacecraft’s origin as a spy satellite. The satellites, called Kosmos, used cameras to photograph military movements and installations around the world. When the satellite used up its film, the capsule containing the cameras and film would fall back to Earth. Shielding protected the capsule from burning up in Earth’s atmosphere and the film could be recovered and developed. Hundreds of these Kosmos satellites were in operation from the 1960s to the 1990s.

Vostok had two basic parts: the capsule and the equipment module. The capsule was the part of Vostok based on Kosmos spy satellites. It was a 2500-kg (5500-lb) sphere made of an aluminum alloy, and it had a diameter of 2.3 m (7.5 ft). A round hatch enabled cosmonauts to enter and exit, and another round hatch opposite it covered the parachute compartment. Four metal straps and a bundle of power and control cables joined the capsule to the equipment module, which was shaped like two blunt cones joined at their bases. Green spherical oxygen tanks ringed Vostok where the capsule joined the equipment module's top cone. The bottom cone held the craft’s retrorocket and was covered with metal plates that radiated heat.

Vostok had U-shaped communication antennas on its capsule and U-shaped telemetry antennas on its equipment module. These were essential parts of its control system, because Vostok flights were almost completely controlled by automatic systems and controllers on Earth. Compared to the Mercury astronauts, the Vostok cosmonauts were more passengers than pilots. This was in part because Soviet doctors feared that space flight might incapacitate humans. The cosmonauts could override the automatic orientation system (called Vzor) by typing in a code, but they were not given the code before the flight. The code was kept in an envelope on the capsule wall in case the cosmonaut needed it.

The Vostok spacecraft fired its retrorocket to drop out of orbit. The capsule’s weight distribution kept the heat shield pointed into the atmosphere. The equipment module had no heat shield, so when it detached and fell toward Earth, it burned up in the atmosphere. When the capsule reached the lower atmosphere, a small parachute opened to slow it down. The capsule landed hard, so in the test Korabl-Sputnik missions, the passenger dogs ejected in a cylindrical compartment that had its own parachute. For Vostok flights, the cosmonaut ejected about 4 km (about 2 mi) above the ground in an ejection seat, separated from the seat, and floated gently to the earth with a parachute.