Венера: Миссия космического аппарата "Маринер-5" (1967)

NASA space probe launched in 1967 to study Venus

Mariner 5 (Mariner V or Mariner Venus 1967) was a spacecraft of the Mariner program that carried a complement of experiments to probe Venus' atmosphere by radio occultation, measure the hydrogen Lyman alpha (hard ultraviolet) spectrum, and sample the solar particles and magnetic field fluctuations above the planet. Its goals were to measure interplanetary and Venusian magnetic fields, charged particles, plasma, radio refractivity and UV emissions of the Venusian atmosphere.

Mariner 5 was built as a backup to Mariner 4, but after the success of the Mariner 4 mission, it was modified to be used for a Venus flyby mission to take place during the 1967 Venus launch window. Mariner 5 omitted several experiments from Mariner 4, including the TV camera, the ionization chamber/geiger counter, the cosmic ray detector, and the cosmic dust detector. It retained the helium vector magnetometer, solar plasma probe, and trapped radiation detector from Mariner 4. Unlike Mariner 4, Mariner 5 needed to face away from the Sun to keep its high gain antenna pointed at Earth because of its trajectory. As a result, the solar panels were reversed to be aft facing so they could remain pointed at the Sun. Additionally, since its mission to Venus brought it in closer proximity to the Sun, fewer solar cells were needed to achieve the necessary power generation, and as a result the solar panels were reduced in size to save mass as well as to make room for two 50 MHz dual frequency receiver (DFR) antennas that were mounted on the frame of two of the solar panels. Since the aft side of the spacecraft faced the Sun, the solar plasma probe was relocated to the aft facing side of Mariner 5. The mounting for the high gain antenna also needed modification. Unlike Mariner 4, where the geometry of the transfer orbit allowed for the high gain antenna to be inclined at a relatively simple 38 degrees from the bottom plane, Mariner 5's trajectory required the high gain antenna to be skewed at a more awkward angle. The high gain antenna also included a single use mechanism that allowed the high gain antenna to make a shift in its angle as part of the radio occultation experiment.

Liftoff took place on June 14, 1967, from Cape Canaveral Air Force Station Launch Complex 12 on Atlas vehicle 5401. Booster performance was normal through the Atlas portion of the launch and the first Agena burn, with all systems operating at the proper level. During the second Agena burn, abnormal fluctuations in the engine chamber pressure occurred, however they did not preclude successful interplanetary injection. There had been several occurrences of this behavior on previous NASA and Air Force launches and a program was initiated to correct it which led to a redesign of the Agena turbopump gearbox.

Mariner 5 flew by Venus on October 19, 1967, at an altitude of With more sensitive instruments than its predecessor Mariner 2, Mariner 5 was able to shed new light on the hot, cloud covered planet and on conditions in interplanetary space. Radio occultation data from Mariner 5 helped to understand the temperature and pressure data returned by the Venera 4 lander, which arrived at Venus shortly before it. The Venera 4 and Mariner 5 data was subsequently analysed together under a combined Soviet–American working group of COSPAR in 1969, an organization of early space cooperation. With the data of these missions, it was clear that Venus had a very hot surface and an atmosphere even denser than expected. The operations of Mariner 5 ended in November 1967 and it is now defunct in a heliocentric orbit.

Further communication attempts were tried, in a joint spacecraft solar wind / solar magnetic fields investigation with Mariner 4, back in communication with Earth after being out of telemetry for about a year or more around superior conjunction. During the experiment, both spacecraft were going to be on the same idealized magnetic field spiral carried out from the sun by the solar wind. Between April and November 1968 NASA tried to reacquire Mariner 5 to continue probing interplanetary conditions. Attempts to reacquire Mariner 5 during June, July, and early August 1968 yielded no spacecraft signal. On October 14, the receiver operator at DSS 14 obtained a lock on the Mariner 5 signal. A carrier wave was detected, but outside expected frequency limits and varying in wavelength. Signal strength changes indicated the spacecraft was in a slow roll. Nevertheless, it was possible to lock the spacecraft to an uplink signal, but no response was observed to any commands sent to it. Without telemetry and without any signal change in response to commands, there was no possibility to repair or continue to use the spacecraft. Operations were terminated at the end of the track from DSS 61 at 07:46 GMT on November 5, 1968.