Mariner 2

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Mariner 2
Organization	NASA
Major contractors	Jet Propulsion Laboratory
Mission type	Flyby
Flyby of	Venus
Launch date	27 August 1962 at 06:53:14 UTC
Launch vehicle	Atlas-Agena B
NSSDC ID	1962-041A
Webpage	NASA NSSDC Master Catalog
Mass	202.8 kg

Mariner 2 (Mariner-Venus 1962), a space probe to Venus, was the first successful spacecraft in the NASA Mariner program. It was a simplified version of the Block I spacecraft of the Ranger program and an exact copy of Mariner 1. The missions of Mariner 1 and 2 spacecraft are together sometimes known as the Mariner R missions.

The Mariner probe consisted of a 100 cm (39.4 in) diameter hexagonal bus, to which solar panels, instrument booms, and antennas were attached. The scientific instruments on board the Mariner spacecraft were two radiometers (microwave and infrared), a micrometeorite sensor, a solar plasma sensor, a charged particle sensor, and a magnetometer. These instruments were designed to measure the temperature distribution on the surface of Venus, as well as making basic measurements of Venus' atmosphere. Due to the planet's thick, featureless cloud cover, no cameras were included in the Mariner unit. Mariner 10 later discovered that extensive cloud detail was visible in ultraviolet light.

The primary mission was to receive communications from the spacecraft in the vicinity of Venus and to perform a radiometric temperature measurement of the planet. A second objective was to measure the Interplanetary Magnetic Field and charged particle environment.^{[1] [2]}

The two-stage Atlas-Agena rocket carrying Mariner 1 veered off-course during its launch on July 22, 1962 due to a defective signal from the Atlas and a bug in the program equations of the ground-based guiding computer, and subsequently the spacecraft was destroyed by the Range Safety Officer. A month later, the identical Mariner 2 spacecraft was launched successfully on August 27, 1962, sending it on a 3½-month flight to Venus. On the way it measured the solar wind, a constant stream of charged particles flowing outwards from the Sun, confirming the measurements by Luna 1 in 1959. It also measured interplanetary dust, which turned out to be more scarce than predicted. In addition, Mariner 2 detected high-energy charged particles coming from the Sun, including several brief solar flares, as well as cosmic rays from outside the Solar system. As it flew by Venus on December 14, 1962, Mariner 2 scanned the planet with its pair of radiometers, revealing that Venus has cool clouds and an extremely hot surface.

The spacecraft is now defunct in a heliocentric orbit.

Contents 1 Detailed description 1.1 Spacecraft and subsystems 1.2 Objectives 1.3 Mission profile 1.4 Scientific observations 2 References 3 External links

[edit] Detailed description

The Mariner 2 spacecraft was the second of a series of spacecraft used for planetary exploration in the flyby mode and the first spacecraft to successfully encounter another planet.

[edit] Spacecraft and subsystems

Mariner 2 consisted of a hexagonal base, 1.04 meters across and 0.36 meters thick, which contained six magnesium chassis housing the electronics for the science experiments, communications, data encoding, computing, timing, and altitude control, and the power control, battery, and battery charger, as well as the altitude control gas bottles and the rocket engine. On top of the base was a tall pyramid-shaped mast on which the science experiments were mounted which brought the total height of the spacecraft to 3.66 meters. Attached to either side of the base were rectangular solar panel wings with a total span of 5.05 meters and width of 0.76 meters. Attached by an arm to one side of the base and extending below the spacecraft was a large directional dish antenna.

The Mariner 2 power system consisted of the two solar cell wings, one 183 cm by 76 cm and the other 152 cm by 76 cm (with a 31 cm dacron extension (a solar sail) to balance the solar pressure on the panels) which powered the craft directly or recharged a 1000 Watt-hour sealed silver-zinc cell battery, which was used before the panels were deployed, when the panels were not illuminated by the Sun, and when loads were heavy. A power-switching and booster regulator device controlled the power flow. Communications consisted of a 3 Watt transmitter capable of continuous telemetry operation, the large high gain directional dish antenna, a cylindrical omnidirectional antenna at the top of the instrument mast, and two command antennas, one on the end of either solar panel, which received instructions for midcourse maneuvers and other functions.

Propulsion for midcourse maneuvers was supplied by a monopropellant (anhydrous hydrazine) 225 N retro-rocket. The hydrazine was ignited using nitrogen tetroxide and aluminum oxide pellets, and thrust direction was controlled by four jet vanes situated below the thrust chamber. Attitude control with a 1 degree pointing error was maintained by a system of nitrogen gas jets. The Sun and Earth were used as references for attitude stabilization. Overall timing and control was performed by a digital Central Computer and Sequencer. Thermal control was achieved through the use of passive reflecting and absorbing surfaces, thermal shields, and movable louvers.

The following scientific instruments were mounted on the instrument mast and base:^[3]

1. A microwave radiometer to determine the absolute temperature of Venus' surface and details concerning its atmosphere through its microwave-radiation characteristics. Measurements were performed simultaneously in two frequency bands of 13.5 mm and 19 mm.
2. A two-channel infrared radiometer to measure the effective temperatures of small areas of Venus. The radiation that was received could originate from the planetary surface, clouds in the atmosphere, the atmosphere itself or a combination of these. The radiation was received in two spectral ranges: 8 μ to 9 μ (focused on 8.4 μ) and 10 μ to 10.8 μ (focused on 10.4 μ).
3. A three-axis fluxgate magnetometer to measure planetary and interplanetary magnetic fields. Three probes were incorporated in its sensors, so it could obtain three mutually orthogonal components of the field vector. Readings of these components were separated by 1.9 seconds. It had three analog outputs that had each two sensitivity scales: ± 64 γ and ± 320 γ (1 γ = 10^-5 gauss). These scales were automatically switched by the instrument. The field that the magnetometer observed was the super-position of a nearly constant spacecraft field and the interplanetary field. Thus, it effectively measured only the changes in the interplanetary field.^[4]
4. An ionization chamber with matched Geiger-Müller tubes (also known as a cosmic ray detector) to measure high-energy cosmic radiation.
5. A particle detector (by using an Anton special-purpose tube) to measure lower radiation (especially near Venus).
6. A cosmic dust detector to measure the flux of cosmic dust particles in space.
7. A solar plasma spectrometer to measure the spectrum of low-energy positively charged particles from the Sun, i.e. the solar wind.

The magnetometer was attached to the top of the mast below the omnidirectional antenna. Particle detectors were mounted halfway up the mast, along with the cosmic ray detector. The cosmic dust detector and solar plasma spectrometer were attached to the top edges of the spacecraft base. The microwave radiometer, the infrared radiometer and the radiometer reference horns were rigidly mounted to a 48 cm diameter parabolic radiometer antenna mounted near the bottom of the mast. All instruments were operated throughout the cruise and encounter modes except the radiometers, which were only used in the immediate vicinity of Venus.

[edit] Objectives

The objectives of both the Mariner 1 and 2 probe included engineering objectives and scientific objectives.^[1] The engineering objectives were:

1. Evaluation of the attitude control system.
2. Evaluation of the environmental control system.
3. Evaluation of the entire power system.
4. Evaluation of the communication system.

The scientific objectives were:

1. Radiometer experiment.
2. Infrared experiment.
3. Magnetometer experiment.
4. Charged particles experiment.
5. Plasma experiment.
6. Micrometeorite experiment.

[edit] Mission profile

Mariner 2 was launched from Cape Canaveral Air Force Station Launch Complex 12 at 06:53:14 UT on 27 August 1962.^[5] After launch and termination of the Agena first burn, the Agena-Mariner was in a 118 km altitude Earth parking orbit. The Agena second burn some 980 seconds later followed by Agena-Mariner separation injected the Mariner 2 spacecraft into a geocentric escape hyperbola at 26 minutes 3 seconds after lift-off. Solar panel extension was completed about 44 minutes after launch. On 29 August 1962 cruise science experiments were turned on. The midcourse maneuver was initiated at 22:49:00 UT on 4 September and completed at 2:45:25 UT 5 September. On 8 September at 17:50 UT the spacecraft suddenly lost its altitude control, which was restored by the gyroscopes 3 minutes later. The cause was unknown but may have been a collision with a small object. On October 31 the output from one solar panel deteriorated abruptly, and the science cruise instruments were turned off. A week later the panel resumed normal function and instruments were turned back on. The panel permanently failed on 15 November, but Mariner 2 was close enough to the Sun that one panel could supply adequate power. On December 14 the radiometers were turned on. Mariner 2 approached Venus from 30 degrees above the dark side of the planet, and passed below the planet at its closest distance of 34,773 km at 19:59:28 UT 14 December. After encounter, cruise mode resumed. Spacecraft perihelion occurred on 27 December at a distance of 105,464,560 km. The last transmission from Mariner 2 was received on 3 January 1963 at 07:00 UT, making the total time from launch to termination of the Mariner 2 mission 129 days.^[6] Mariner 2 remains in heliocentric orbit.

[edit] Scientific observations

The microwave radiometer made three scans of Venus in 35 minutes on 14 December 1962 starting at 18:59 GMT. The first scan was made on the dark side, the second near the terminator and the third was located on the light side. The scans with the 19 mm band revealed a temperature of 460 ± 69 K on the dark side, 570 ± 85 K near the terminator, and 400 ± 60 K on the light side. It was concluded that there is no significant difference in temperature across Venus. However, the results suggest a limb darkening, an effect which presents cooler temperatures near the edge of the planetary disk. This also supported the theory that the Venusian surface was extremely hot or the atmosphere optically thick.^[7][8][9]

The limb darkening effect was also present in the measurements by both channels of the Infrared Radiometer. The effect was only slightly present in the 10.4 μ channel, but is more pronounced in the 8.4 μ channel. The 8.4 μ channel also showed a slight phase effect. The phase effect indicated that if a greenhouse effect existed, heat was transported in an efficient manner from the light side to the dark side of the planet.^[8]

The magnetometer could detect changes of about 4 γ on any of the axes, but no trends above 10 γ were detected nor were fluctuations seen like those that appear at Earth's magnetospheric termination. This means Mariner 2 found no detectable magnetic field near Venus.^[8][10]

It was also shown that in interplanetary space the solar wind streams continuously^[5][11] and the cosmic dust density is much lower than the near-Earth region.^[12] Improved estimates of Venus' mass and the value of the astronomical unit were made. Also, research suggested (which was later confirmed by other explorations) that Venus rotates very slowly and in a direction opposite that of the Earth.^[13]

[edit] References

[edit] External links

• Mariner 2 Mission Profile by NASA's Solar System Exploration
• Full-scale engineering prototype of Mariner 2 in the Smithsonian Air and Space Museum, Washington, D.C.

v • d • e Mariner Program Mariner 1 · Mariner 2 · Mariner 3 · Mariner 4 · Mariner 5 · Mariner 6 and 7 · Mariner 8 · Mariner 9 · Mariner 10 Previous mission: Mariner 1 — Next mission: Mariner 3

v • d • e Spacecraft missions to Venus Flybys Venera 1 · Mariner 2 · Zond 1 · Venera 2 · Mariner 5 · 10 · Venera 11 · 12 · 13 · 14 · Vega 1 · 2 · Galileo · Cassini-Huygens · MESSENGER Orbiters Venera 9 · 10 · Pioneer Venus Orbiter · Venera 15 · 16 · Magellan · Venus Express Descent probes Venera 3 · 4 · 5 · 6 · Pioneer Venus Multiprobe Landers Venera 7 · 8 · 9 · 10 · 11 · 12 · 13 · 14 · Vega 1 · 2 Balloon probes Vega 1 · 2 Future missions PLANET-C (2010) · BepiColombo · Venus Entry Probe (2013) · Venera-D (2016) See also Colonization of Venus · List of artificial objects on Venus Bold italics indicates active missions