Venera 4
Template:Infobox Spacecraft Venera 4 (Russian: Венера-4, Венера meaning Venus; manufacturer's designation: 1V (V-67)) was a probe in the Soviet Venera program for the exploration of Venus. Venera-4 was the first successful probe to perform in-place analysis of the environment of another planet. It was also the first probe to land on another planet.[1] Venera 4 provided the first chemical analysis of the Venusian atmosphere, showing it to be primarily carbon dioxide with a few percent of nitrogen and below one percent of oxygen and water vapors. The station detected a very 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 the atmosphere was far denser than expected, and that Venus had lost most of its water long ago.
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 to detect hydrogen and oxygen gases. The devices were intended to operate during the flight up to the descent into the Venusian atmosphere. Upon descent, 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.[2]
The front part of the hub contained a nearly spherical landing capsule of 1 meter diameter and 383 kg weight. 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.[3] The durability of the capsule was tested for temperature, pressure and acceleration/deceleration using three unique testing installations: temperature durability was checked in a high-temperature vacuum system emulating the upper layers of the atmosphere.[4] The capsule was also pressurized up to 100 atmospheres (the surface pressures on Venus were though to be 72 atm.). Finally, it was run in a centrifuge up to accelerations of 450 G. The centrifuge test revealed cracking of electronic components and cable brackets, which were all replaced shortly before the launch. The timing for launch was rather tight, so as not to miss the "launch window" - days of the year when the destination planet is closest to the Earth.
The capsule could float in case of an oceanic landing. Considering a possibility of such landing, its designers made the lock of the capsule using sugar;[2][4] it was meant to dissolve in a 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.[4]
The capsule contained an altimeter, thermal control, a parachute and a measurement set. The latter included a thermometer, barometer, hydrometer, altimeter and a gas analysis set. The data were sent by two transmitters at a frequency of 922 MHz and a rate of 1 bit/s that is the data 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.[2][3]
The capsule was equipped with a rechargeable battery with a capacity sufficient for 100 minutes of powering the measurement and transmitter systems. To avoid self-discharge 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.[3]
The mission
Two nominally identical Venera 4-type probes were launched in June 1967. The second, one launched on 17 June, experienced a failure of one of the rocket stages; it only managed to reach Earth orbit and re-entered Earth's atmosphere 8 days later. This probe was renamed Cosmos 167. The first probe reached Venus. [2]
The first probe, Venera 4, was launched on 12 June from a Tyazheliy Sputnik (67-058B). A course correction was performed on 29 July when it was 12 million km far from Earth; otherwise the probe would have missed Venus. Although two such corrections had been planned, the first one was accurate enough and therefore the second correction was canceled. On October 18, 1967, the spacecraft entered the Venusian atmosphere with an estimated landing place near 19°N 38°E / 19°N 38°E.[2]
During entry into the Venusian atmosphere, the temperature rose to 11000 °C and at one point the cabin acceleration reached 300 G.[3] The descent lasted 93 minutes. The capsule was released at an altitude about 52 km, and deployed its parachute and started sending data on pressure, temperature and gas composition back to Earth. The temperature control kept the inside of the capsule at -8 °C. The temperature at 52 km was recorded as 33 °C, and the pressure as less than 1 atm. At the end of the 26-km descent, the temperature reached 262 °C and pressure increased to 22 atmospheres, and the signal transmission terminated. The atmospheric composition was measured as 90-93% carbon dioxide, 0.4-0.8% oxygen, 7% nitrogen and 0.1-1.6% water vapor.[2]
Misbehavior of the altimeter resulted in the value of initial altitude (deployment of the capsule's parachute and start of the measurements) being transmitted as 26 km. Therefore, some Earth observers interpreted the descent as having continued to the surface of Venus, which was quickly dismissed as inconsistent with other data. In particular, the pressure readings by the capsule were much too low for the Venusian surface.[4][3]
Achievements
For the first time, in situ analysis of the atmosphere of another planet was performed and the data sent back to Earth; the analysis included chemical composition, temperature and pressure. The measured ratio of carbon dioxide to nitrogen of about 13 corrected the previous estimates so much (an inverse ratio was expected in some quarters) that some scientists contested the observations. The main station detected no radiation belts; relative to Earth, the measured magnetic field was 3000 times weaker, and the hydrogen corona was 1000 times less dense. No atomic oxygen was detected. All the data suggested that water, if present, had leaked from the planet long time ago. This conclusion was unexpected considering the thick Venusian clouds. Because of this negligible humidity, the sugar lock system, employed on Venera 4 in case of a water landing, was abandoned in the subsequent Venus probes.[2][3]
The mission was a complete success, which was a relief after several previous failures of Venera probes. Although the Venera 4 design did allow for data transmission after landing, the Venera 3-6 probes were not built to withstand the pressures at the Venusian surface. The first successful landing on Venus was achieved by Venera 7 in 1970.
References
- ^ David Leverington (2000). New cosmic horizons. Cambridge University Press. pp. 74–74. ISBN 0521658330.
- ^ a b c d e f g Brian Harvey (2007). Russian planetary exploration. Springer. pp. 98–101. ISBN 0387463437.
- ^ a b c d e f "Venera 4 (in Russian)". Retrieved 2009-07-07.
- ^ a b c d Paolo Ulivi, David Michael Harland (2007). Robotic Exploration of the Solar System: The golden age 1957-1982. Springer. pp. 55–56. ISBN 0387493263.
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