Missions to Venus

Ballistic Interplanetary Trajectories

Venera-5 Flight Plan

To first approximation, the optimum trajectory is an elliptical Hohmann Orbit, tangent to the Earth's orbit at aphelion and tangent to Venus' orbit at perihelion. Every 583.92 days (the synodic period of Venus) a launch window occurs, during which nearly optimal paths can begin at Earth and arrive at Venus. The diagram above illustrates the flight plan of Venera-5.

1967, Jun 11 142 days 3.2 megajoules/kilogram
1969, Jan 12 127 days 3.8 megajoules/kilogram
1970, Aug 17 117 days 4.2 megajoules/kilogram
1972, Mar 27 112 days 6.1 megajoules/kilogram
1973, Nov 9 107 days 6.7 megajoules/kilogram

Every 5 synodic cycles, the relative configuration of Earth and Venus repeats almost exactly. This is called the metonic cycle. Because planetary orbits are not coplanar or perfectly circular, launch windows have different associated flight durations and payload costs.

Energy for 1972 Venus mission

The orbit of Venus is nearly circular, but its large angle of inclination primarily accounts for differing mission costs (for Mars, the major issue is the eccentricity of its elliptical orbit). The plot of launch date versus arrival date, sometimes called a pork-chop plot, shows payload costs during the 1972 opportunity. The optimum launch date was March 27, requiring 112 days and 6.1 megajoules per kilogram of payload. The Soviet Union made two Venus launches that year, on March 27 and March 31.

As seen above, two local optima exist, a shorter Type I trajectory, which goes less than halfway around the Sun, and a longer (Type II) trajectory. In 1972, a cheaper Type II trajectory left on April 4, took 170 days and cost 4.1 megajoules per kilogram. Type I trips result in communications distances of around 60 million kilometers between Venus and Earth, upon probe arrival. Type II trajectories were not used for fly-by or impactor missions because the communications distance would be several times greater.

When saving energy is important or launch scheduling is constrained, longer orbits may be used. For long-term orbiter missions, it is also less critical to optimize for arrival distance. For example, Pioneer-13 was send on a Type II path and required a large solid-fuel retro rocket to slow it to orbital speed, during that year's energetically unfavorable trajectory. Magellan reached Venus via a Type IV trajectory, going one and a half times around the Sun.

Venus Missions

Launch Date Spacecraft Mission Origin Outcome
1959, Jun 13       Unused Type I window
1961, Feb 4 1VA No. 1 impactor USSR Stranded in parking orbit
1961, Feb 12 Venera 1 impactor USSR Attitude control sensor overheated
1962, Jul 22 Mariner 1 flyby USA Crashed in North Atlantic
1962, Aug 25 2MV-1 No.1 lander USSR Stranded in parking orbit
1962, Aug 27 Mariner 2 flyby USA First successful planetary mission
Venus has small magnetic field
1962, Sep 1 2MV-1 No.2 lander USSR Stranded in parking orbit
1962, Sep 12 2MV-2 No.1 photo-flyby USSR Stranded in parking orbit
1964, Mar 27 3MV-1 No.5 lander USSR Stranded in parking orbit
1964, Apr 2 Zond 1 lander USSR Pressure loss/corona discharge
1965, Nov 12 Venera 2 flyby USSR Thermal control failure
1965, Nov 16 Venera 3 lander USSR Thermal failure
First impact on another planet
1965, Nov 23 3MV-4 No. 6 flyby USSR Explosion in parking orbit

1967, Jun 12 Venera 4 lander USSR First planetary-atmosphere probe
Crushed at attitude of 25 km
1967, Jun 14 Mariner 5 flyby USA Fly-by, radio occultation
1967, Jun 17 V-67 No. 2 lander USSR Stranded in parking orbit
1969, Jan 5 Venera 5 lander USSR Successful, but crushed at 18 km
1969, Jan 10 Venera 6 lander USSR Successful, but crushed at 18 km
1970, Aug 17 Venera 7 lander USSR First successful planetary landing
1970, Aug 22 V-70 No. ? lander USSR Stranded in parking orbit
1972, Mar 27 Venera 8 lander USSR Measured surface illumination
1972, Mar 31 3V lander USSR Stranded in parking orbit
1973, Nov 3 Mariner 10 photo-flyby USA First good pictures of Venus
Gravity assist to Mercury

1975, Jun 8 Venera 9 lander/orbiter USSR First pictures of surface, 4-month
orbital photo study of clouds
1975, Jun 14 Venera 10 lander/orbiter USSR Same as Venera 9, one of two
cameras failed on each lander
1977, Jan 9       Unused Type I window
1978, May 20 Pioneer 12 orbiter USA Radar mapping, photo study of
clouds, operated 14 years
1978, Aug 8 Pioneer 13 impactors USA Cluster of 5 atmosphere probes
1978, Sep 9 Venera 11 lander/flyby USSR Spectra from clouds to surface,
atmosphere chemical analysis
1978, Sep 14 Venera 12 lander/flyby USSR Both color cameras, rock analysis
failed on both 11 and 12
1980, Mar 25       Unused Type I window
1981, Oct 30 Venera 13 lander/flyby USSR Color images, rock analysis
1981, Nov 4 Venera 14 lander/flyby USSR Color images, rock analysis

1983, Jun 2 Venera 15 orbiter USSR High resolution radar mapping
1983, Jun 7 Venera 16 orbiter USSR High resolution radar mapping
1984, Dec 15 Vega 1 lander/flyby USSR Night landing, balloon probe
Halley's comet encounter
1984, Dec 21 Vega 2 lander/flyby USSR Same as Vega 1
1986, Oct 11       Unused Type I window
1988, Mar 22       Unused Type I window
1989, May 4 Magellan orbiter USA High resolution radar mapping
1989, Oct 18 Galileo flyby USA Images, gravity assist to Jupiter

1991, Jun 5       Unused Type I window
1993, Jan 5       Unused Type I window
1994, Aug 9       Unused Type I window
1996, Mar 20       Unused Type I window
1997, Oct 15 Cassini flyby USA Images, gravity assist to Saturn

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Copyright © 2003,2004 Don P. Mitchell. All rights reserved.