Venera 15

Nation: USSR (100) Objective(s): Venus orbit Spacecraft: 4V-2 (no. 860) Spacecraft Mass: 5,250 kg Mission Design and Management: NPO imeni Lavochkina Launch Vehicle: Proton-K + Blok D-1 (8K82K no. 321-01 / 11S824M no. 8L) Launch Date and Time: 2 June 1983 / 02:38:39 UT Launch Site: NIIP-5 / Site 200/39

Scientific Instruments:

Polyus-V side-looking radar
Omega-V 4-channel radiometric system
Radio occultation experiment
FS-1/4 infrared spectrometer
cosmic ray detectors
solar wind detectors
KS-18-6V to measure galactic and solar protons

Results: Venera 15/16 were a pair of two dedicated radar mappers designed to extend the studies began by the American Pioneer Venus Orbiter in constructing a detailed map of the surface down to about 1–2-kilometer resolution. For these missions, Soviet designers lengthened the central bus of the earlier Veneras (by 1 meter), installed much larger solar batteries, and attached a large side-looking radar antenna in place of the descent lander module on the earlier spacecraft. The infrared spectrometer was provided by the German Democratic Republic. Venera 15 carried out two mid-course corrections on 10 June 1983 and 1 October 1983 before successfully entering orbit around Venus at 03:05 UT on 10 October. Initial orbital parameters were 904.5 × 64,687 kilometers at 87.5° inclination, i.e., a near polar orbit. Two more orbital corrections were carried out on 17 October and 2 November leaving the spacecraft in an 873 × 65,000-kilometer orbit. The spacecraft's mapping operations began six days after entering orbit, over the north pole.

About three months after entering Venusian orbit, it was discovered that the main omni-directional antennae on both Venera 15 and 16 were not naturally facing the direction of Earth (connected as they were by the need to have the solar panels constantly facing the direction of the Sun). Instead the solar panels were angled at 45° to direct sunlight. Using a special command to re-orient the antenna into proper orientation (using springs) in January 1984 proved successful on Venera 16 but not Venera 15. A subsequent engine firing on 9 April 1984 shook Venera 15 sufficiently that the antenna finally moved into proper orientation. Because of the nature of the spacecraft's orbit, the two orbiters mapped only the area from 30° N to the pole, about 115 million square kilometers. The official mission of both vehicles was to end on 10 March 1984 but was extended on account that both spacecraft were in excellent condition. The primary photography mission was completed on 10 July 1984. After that, an "optional program" of scientific work continued through the remainder of the year. On 30 December 1984, controllers found that the orientation system had exhausted its nitrogen. Last contact was made with the spacecraft on 5 January 1985.

Venera 16

Nation: USSR (101) Objective(s): Venus orbit Spacecraft: 4V-2 (no. 861) Spacecraft Mass: 5,300 kg Mission Design and Management: NPO imeni Lavochkina Launch Vehicle: Proton-K + Blok D-1 (8K82K no. 321-02 + 11S824M no. 9L) Launch Date and Time: 7 June 1983 / 02:32 UT Launch Site: NIIP-5 / Site 200/40

Scientific Instruments:

Polyus-V side-looking radar
Omega-V 4-channel radiometric system
Radio occultation experiment
KS-18-6V infrared spectrometer
cosmic ray detectors
solar wind detectors
KS-18-6V to measure galactic and solar protons

Results: Venera 16 arrived at Venus orbit at 06:22 UT on 14 October 1983 after en-route course corrections on 15 June and 5 October 1983. Its initial orbital parameters were 977.3 × 67,078 kilometers. It began its mapping operations six days later in its 24-hour, 34-minute period near-polar orbit. Its operational orbit, reached on 22 October was 944 × 65,336 kilometers, its orbital plane 4° 27′ inclined to that of its sister craft. Venera 16 typically followed Venera 15 over the same surface area after a three-day gap. Mapping resolution of both Venera 15 and 16 was comparable to that possible with the 300-meter dish at Arecibo in Puerto Rico although the Soviet orbiters provided coverage over latitudes higher than 30°, too far north for Earth-based observations. Both spacecraft also used an East German infrared spectrometer to map the planet in infrared wavelengths to provide a "heat atlas" of the atmosphere.

The original missions of both spacecraft were to end by 10 March 1984 but due to the excellent condition of the vehicles, ground controllers extended the primary mission into the summer. On 21 June 1984, controllers altered Venera 16's orbit, and less than a month later, on 10 July, both vehicles finished their main missions, to photograph the northern hemisphere of Venus at a resolution of 1–2 kilometers. Venera 16 ended its extended mission rather strangely: on 13 June 1985, controllers were faced with an emergency situation on the Vega 1 spacecraft related to loss of orientation. A command was sent to Vega 1 to activate the recovery mode (constant solar-stellar mode orientation). Because the operating frequency of Vega 1 and Venera 16 were identical, the command activated Venera 16's search for an appropriate star to orient itself. The process unfortunately exhausted all the remaining propellant on Venera 16 and controllers lost contact. Because it had already fulfilled its primary mission, controllers did not consider this a great loss. In 1988, the Main Directorate of Geodesy and Cartography published a full album entitled "Atlas of Venus" (Atlasa venery) of annotated images generated by the Venera 14 and 15 missions. A 2013 article in a Russian journal claimed that these two orbital missions—Venera 15 and 16—were the "most successful [missions] in the history of automated spaceflight in the 1970s–1980s."

Magellan

Nation: USA (63) Objective(s): Venus orbit Spacecraft: Magellan Spacecraft Mass: 3,445 kg Mission Design and Management: NASA / JPL Launch Vehicle: STS-30R Atlantis Launch Date and Time: 4 May 1989 / 18:47:00 UT Launch Site: Kennedy Space Center / Launch Complex 39B

Scientific Instruments:

synthetic aperture radar (RDRS)

Results: Magellan, named after the Portuguese explorer Ferdinand Magellan (1480–1521), was the first deep space probe launched by the United States in almost 11 years, and also the first launched by the Space Shuttle. The Challenger disaster in January 1986 profoundly impacted the Shuttle launch manifest into the 1990s, which included a number of planetary missions. Magellan, for example, was delayed by at least a year. The spacecraft was designed to use a Synthetic Aperture Radar (SAR) to map 70% of the Venusian surface down to a resolution of 120–300 meters. The basic bus was assembled using spare parts left over from various prior missions including Voyager, Galileo, Ulysses, and Mariner 9. Magellan was deployed by the STS-30R crew and released at 01:01 UT on 5 May 1989 from Atlantis' payload bay. One hour later, a two-stage Inertial Upper Stage (IUS) fired to send the spacecraft on a trajectory to rendezvous with Venus. After three en route trajectory corrections (the first two on 21 May 1989, 13 March 1990, and 25 July 1990), Magellan arrived in Venus orbit on 10 August 1990.

Orbital parameters were 297 × 8,463 kilometers at 85.5° inclination. Six days after entering orbit, Magellan suffered a communications outage lasting 15 hours. After a second 17 hour-interruption on 21 August, the ground sent up new preventative software to reset the system in case of such anomalies. Beginning 15 September 1990, the spacecraft began returning high-quality radar images of the Venusian terrain that showed evidence of volcanism, tectonic movement, turbulent surface winds, kilometers of lava channels, and pancake-shaped domes. Magellan completed its first 243-day cycle (i.e., the time it took for Venus to rotate once under Magellan's orbit) of radar mapping on 15 May 1991, providing the first clear views of 83.7% of the surface. The spacecraft returned 1,200 Gbits of data, far exceeding the 900 Gbits of data from all NASA planetary missions combined at the time. The spacecraft's second mapping cycle, already beyond the original goals of the mission, ended on 15 January 1992, raising coverage to 96%. A third cycle that focused on stereo imaging ended on 13 September 1992, finished coverage at 98%. Further cycles—a fourth (ending on 23 May 1993), a fifth (ending on 29 August 1994), and a sixth (ending on 13 October 1994)—focused on obtaining gravimetric data on the planet.

In the summer of 1993, controllers commanded the spacecraft to drop into the outermost regions of the Venusian atmosphere and then successfully used an aerobraking method to circularize its orbit. Contact was lost after 10:05 UT on 13 October 1994 as the spacecraft was commanded to plunge into the atmosphere to gather aerodynamic data. The spacecraft burned up in the Venusian atmosphere about 10 hours later after one of the most successful deep space missions. Magellan found that at least 85% of the Venusian surface is covered with volcanic flows. The spacecraft's data suggested that despite the high surface temperatures (475°C) and high atmospheric pressures (92 atmospheres), the complete lack of water makes erosion an extremely slow process on the planet. As a result, surface features can persist for hundreds of millions of years. In addition, the spacecraft found that such phenomena as continental drift are not evident on the planet. Its imagery contributed to the best high-resolution radar maps of Venus' surface to date, improving on the images returned by the Soviet Venera 15 and 16 in the 1980s.

This simulated color global view of the surface of Venus taken by Magellan is centered at 180° E longitude. Data gaps in Magellan's data were filled in by information from Pioneer Venus. Most notably, the simulated hues are based on color images from the Soviet Venera 13 and Venera 14 spacecraft. Credit: NASA/JPL

Galileo

Nation: USA (64) Objective(s): Jupiter orbit and atmospheric entry Spacecraft: Galileo (Orbiter and Entry Probe) Spacecraft Mass: 2,380 kg Mission Design and Management: NASA / JPL Launch Vehicle: STS-34R Atlantis Launch Date and Time: 18 October 1989 / 16:53:40 UT Launch Site: Kennedy Space Center / Launch Complex 39B

Scientific Instruments:

Orbiter:

solid state imager (SSI)
near-infrared mapping spectrometer (NIMS)
ultraviolet spectrometer / extreme ultraviolet spectrometer (UVS/EUV)
photopolarimeter-radiometer (PPR)
magnetometer (MAG)
energetic particles detector (EPD)
plasma subsystem (PLS)
plasma wave subsystem (PWS)
heavy ion counter (HIC)
dust detector subsystem (DDS)

Atmospheric Entry Probe:

atmospheric structure instrument
neutral mass spectrometer
helium abundance interferometer
net-flux radiometer
nephelometer
lightning/radio-emission instrument

Results: Galileo, one of NASA's most ambitious deep space exploration projects, was the result of plans dating back to the early 1980s to deploy a Jupiter orbiter and probe. In its final configuration, the orbiter was a 4.6-meter tall spacecraft designed to operate for 22 months in Jovian orbit using 10 instruments/experiments to study the planet's atmosphere, satellites, and magnetosphere. Galileo, named after the Italian astronomer Galileo Galilei (1564–1642), carried a 337-kilogram probe designed to return data as it entered the Jovian atmosphere (by parachute) to identify atmospheric materials and conditions that cannot be detected from outside. Because of limitations of a Space Shuttle/IUS combination, NASA decided to use a complex multiple gravity assist scheme that required three flybys (two of Earth and one of Venus) on its way to Jupiter. The STS-34R crew released the spacecraft 6.5 hours after launch; an hour later, the two-stage IUS fired to send Galileo on its way.

Galileo flew past Venus at 05:58:48 UT on 10 February 1990 at a range of 16,106 kilometers during which it conducted an extensive survey of the planet (including imaging). Having gained 8,030 kilometers/hour in velocity, the spacecraft flew by Earth twice, the first time at 960 kilometers range at 20:34:34 UT on 8 December 1990 when it detected chemical signatures associated with lifeform activity in atmospheric trace elements on our home planet. The spacecraft also conducted lunar observations. A major problem occurred on 11 April 1991 when the high-gain antenna failed to fully deploy, thus eliminating the possibility of data transmission during its flyby of the asteroid 951 Gaspra. A low-gain antenna was instead used for the remainder of the mission, augmented by ingenious strategies including the use of data compression software that allowed a higher data throughput than was originally possible with the low-gain antenna. Becoming the first human-made object to fly past an asteroid, Galileo approached the minor planet Gaspra to a distance of 1,604 kilometers at 22:37 UT on 29 October 1991. The encounter provided much data including 150 images of the asteroid. Galileo then sped to its second encounter with the Earth–Moon system, with a flyby of Earth at 303.1 kilometers at 15:09:25 UT on 8 December 1992, adding 3.7 kilometers/second to its cumulative velocity. Galileo flew by a second asteroid, 243 Ida, at 16:51:59 UT on 28 August 1993 at a range of 2,410 kilometers, providing further data on minor planets. Later in July 1994, as it was speeding towards Jupiter, Galileo provided astronomers' only direct observations of Comet D/1993 F2 (Shoemaker-Levy 9) as its fragments impacted into the Jovian atmosphere.

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