Venera 4 (), also designated 4V-1 No.310, was a probe in the Soviet Venera program for the exploration of Venus. The probe comprised a lander, designed to enter the Venusian atmosphere and parachute to the surface, and a carrier/flyby spacecraft, which carried the lander to Venus and served as a communications relay for it. In 1967, it was the first successful probe to perform in-place analysis of the environment of another planet. Venera 4 provided the first chemical analysis of the Venusian atmosphere, showing it to be primarily carbon dioxide with a few percents of nitrogen and below one percent of oxygen and water vapors. While entering the atmosphere it became the first spacecraft to survive entry into another planet's atmosphere. The station detected a weak magnetic field and no radiation field. The outer atmospheric layer contained very little hydrogen and no atomic oxygen. The probe sent the first direct measurements proving that Venus was extremely hot, that its atmosphere was far denser than expected, and that it had lost most of its water long ago. Spacecraft The main carrier spacecraft 4 stood high, its solar panels spanned and had an area of . The carrier spacecraft included a 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 carrier spacecraft 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 carrier spacecraft contained a nearly spherical landing capsule in diameter and weighing . Compared to previous (failed) Venera probes, the capsule contained an improved heat shield that could withstand temperatures up to . 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 pressurized up to 25 atmospheres. (The surface pressure on Venus was unknown at the