Venera 4 - Design

Design

The main hub of Venera 4 stood 3.5 meters high, its solar panels spanned 4 meters and had an area of 2.5 m². The hub included a 2 meter long magnetometer, an ion detector, a cosmic ray detector and an ultraviolet spectrometer capable of detecting hydrogen and oxygen gases. The devices were intended to operate until entry into the Venusian atmosphere. At that juncture, the station was designed to release the probe capsule and disintegrate. The rear part of the hub contained a liquid-fuel thruster capable of correcting the flight course. The flight program was planned to include two significant course corrections, for which purpose the station could receive and execute up to 127 different commands sent from the Earth.

The front part of the hub contained a nearly spherical landing capsule 1 meter in diameter and weighing 383 kg. Compared to previous (failed) Venera probes, the capsule contained an improved heat shield which could withstand temperatures up to 11000 °C. Instead of the previous liquid-based cooling design, a simpler and more reliable gas system was installed. The durability of the capsule was checked by exposing it to high temperatures, pressures and accelerations using three unique testing installations. The heat resistance was checked in a high-temperature vacuum system emulating the upper layers of the atmosphere. The capsule was also pressurized up to 25 atmospheres. (The surface pressure on Venus was unknown at the time. Estimates ranged from a few to hundreds of atmospheres). Finally, it was subjected to accelerations of up to 450 G in a centrifuge. The centrifuge test caused cracking of electronic components and cable brackets, which were all replaced shortly before launch. The timing for launch was rather tight, so as not to miss the "launch window" - the days of the year when the path to the destination planet from Earth is energetically least demanding.

The capsule could float in case of a water landing. Considering the possibility of such a landing, its designers made the lock of the capsule using sugar; it was meant to dissolve in liquid water, releasing the transmitter antennas. The capsule contained a newly developed vibration-damping system and its parachute could resist temperatures up to 450 °C.

The capsule contained an altimeter, thermal control, a parachute and equipment for making atmospheric measurements. The latter included a thermometer, barometer, hydrometer, altimeter and a set of gas analysis instruments. The data were sent by two transmitters at a frequency of 922 MHz and a rate of 1 bit/s; the measurements were sent every 48 seconds. The transmitters were activated by the parachute deployment as soon as the outside pressure increased to 0.6 atmospheres, which was thought to occur at the altitude about 26 km above the surface of Venus. The signals were received by several stations, including the Jodrell Bank Observatory.

The capsule was equipped with a rechargeable battery with a capacity sufficient for 100 minutes of powering the measurement and transmitter systems. To avoid becoming discharged during the flight to Venus, the battery was recharged using the solar panels of the hub. Before the launch, the entire Venera 4 station was sterilized to prevent possible biological contamination of Venus.