Historical Lunar Exploration
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Space FAQ 08/13 - Planetary Probe History

Larry Klaes

U.S. Planetary Missions

Mariner (Venus, Mars, & Mercury Flybys and Orbiters)

MARINER 1, the first U.S. attempt to send a spacecraft to Venus, failed minutes after launch in 1962. The guidance instructions from the ground stopped reaching the rocket due to a problem with its antenna, so the onboard computer took control. However, there turned out to be a bug in the guidance software, and the rocket promptly went off course, so the Range Safety Officer destroyed it. Although the bug is sometimes claimed to have been an incorrect FORTRAN DO statement, it was actually a transcription error in which the bar (indicating smoothing) was omitted from the expression "R-dot-bar sub n" (nth smoothed value of derivative of radius). This error led the software to treat normal minor variations of velocity as if they were serious, leading to incorrect compensation.

MARINER 2 became the first successful probe to flyby Venus in December of 1962, and it returned information which confirmed that Venus is a very hot (800oF, now revised to 900oF) world with a cloud-covered atmosphere composed primarily of carbon dioxide (sulfuric acid was later confirmed in 1978).

MARINER 3, launched on November 5, 1964, was lost when its protective shroud failed to eject as the craft was placed into interplanetary space. Unable to collect the Sun's energy for power from its solar panels, the probe soon died when its batteries ran out and is now in solar orbit. It was intended for a Mars flyby with MARINER 4.

MARINER 4, the sister probe to MARINER 3, did reach Mars in 1965 and took the first close-up images of the Martian surface (22 in all) as it flew by the planet. The probe found a cratered world with an atmosphere much thinner than previously thought. Many scientists concluded from this preliminary scan that Mars was a "dead" world in both the geological and biological sense.

MARINER 5 was sent to Venus in 1967. It reconfirmed the data on that planet collected five years earlier by MARINER 2, plus the information that Venus' atmospheric pressure at its surface is at least 90 times that of Earth's, or the equivalent of being 3,300 feet under the surface of an ocean.

MARINER 6 and 7 were sent to Mars in 1969 and expanded upon the work done by MARINER 4 four years earlier. However, they failed to take away the concept of Mars as a "dead" planet, first made from the basic measurements of MARINER 4.

MARINER 8 ended up in the Atlantic Ocean in 1971 when the rocket launcher autopilot failed.

MARINER 9, the sister probe to MARINER 8, became the first craft to orbit Mars in 1971. It returned information on the Red Planet that no other probe had, revealing huge volcanoes on the Martian surface, as well as giant canyon systems, and evidence that water once flowed across the planet. The probe also took the first detailed closeup images of Mars' two small moons, Phobos and Deimos.

MARINER 10 used Venus as a gravity assist to Mercury in 1974. The probe did return the first close-up images of the Venusian atmosphere in ultraviolet, revealing previously unseen details in the cloud cover, plus the fact that the entire cloud system circles the planet in four Earth days. MARINER 10 eventually made three flybys of Mercury from 1974 to 1975 before running out of attitude control gas. The probe revealed Mercury as a heavily cratered world with a mass much greater than thought. This would seem to indicate that Mercury has an iron core which makes up 75 percent of the entire planet.

Pioneer (Moon, Sun, Venus, Jupiter, and Saturn Flybys and Orbiters)

PIONEER 1 through 3 failed to meet their main objective - to photograph the moon close-up - but they did reach far enough into space to provide new information on the area between Earth and the moon, including new data on the Van Allen radiation belts circling Earth. All three craft had failures with their rocket launchers. PIONEER 1 was launched on October 11, 1958, PIONEER 2 on November 8, and PIONEER 3 on December 6.

PIONEER 4 was a Moon probe which missed the moon and became the first U.S. spacecraft to orbit the Sun in 1959. PIONEER 5 was originally designed to flyby Venus, but the mission was scaled down and it instead studied the interplanetary environment between Venus and Earth out to 36.2 million kilometers in 1960, a record until MARINER 2. PIONEER 6 through 9 were placed into solar orbit from 1965 to 1968: PIONEER 6, 7, and 8 are still transmitting information at this time. PIONEER E (would have been number 10) suffered a launch failure in 1969.

PIONEER 10 became the first spacecraft to flyby Jupiter in 1973. PIONEER 11 followed it in 1974, and then went on to become the first probe to study Saturn in 1979. Both vehicles should continue to function through 1995 and are heading off into interstellar space, the first craft ever to do so.

PIONEER Venus 1 (1978) (also known as PIONEER Venus Orbiter, or PIONEER 12) burned up in the Venusian atmosphere on October 8, 1992. PVO made the first radar studies of the planet's surface via probe. PIONEER Venus 2 (also known as PIONEER 13) sent four small probes into the atmosphere in December of 1978. The main spacecraft bus burned up high in the atmosphere, while the four probes descended by parachute towards the surface. Though none were expected to survive to the surface, the Day probe did make it and transmitted for 67.5 minutes on the ground before its batteries failed.

Ranger (Lunar Lander and Impact Missions)

RANGER 1 and 2 were test probes for the RANGER lunar impact series. They were meant for high Earth orbit testing in 1961, but rocket problems left them in useless low orbits which quickly decayed.

RANGER 3, launched on January 26, 1962, was intended to land an instrument capsule on the surface of the moon, but problems during the launch caused the probe to miss the moon and head into solar orbit. RANGER 3 did try to take some images of the moon as it flew by, but the camera was unfortunately aimed at deep space during the attempt.

RANGER 4, launched April 23, 1962, had the same purpose as RANGER 3, but suffered technical problems enroute and crashed on the lunar farside, the first U.S. probe to reach the moon, albeit without returning data.

RANGER 5, launched October 18, 1962 and similar to RANGER 3 and 4, lost all solar panel and battery power enroute and eventually missed the moon and drifted off into solar orbit.

RANGER 6 through 9 had more modified lunar missions: They were to send back live images of the lunar surface as they headed towards an impact with the moon. RANGER 6 failed this objective in 1964 when its cameras did not operate. RANGER 7 through 9 performed well, becoming the first U.S. lunar probes to return thousands of lunar images through 1965.

Lunar Orbiter (Lunar Surface Photography)

LUNAR ORBITER 1 through 5 were designed to orbit the moon and image various sites being studied as landing areas for the manned APOLLO missions of 1969-1972. The probes also contributed greatly to our understanding of lunar surface features, particularly the lunar farside. All five probes of the series, launched from 1966 to 1967, were essentially successful in their missions. They were the first U.S. probes to orbit the moon. All LOs were eventually crashed into the lunar surface to avoid interference with the manned APOLLO missions.

Surveyor (Lunar Soft Landers)

The SURVEYOR series were designed primarily to see if an APOLLO lunar module could land on the surface of the moon without sinking into the soil (before this time, it was feared by some that the moon was covered in great layers of dust, which would not support a heavy landing vehicle). SURVEYOR was successful in proving that the lunar surface was strong enough to hold up a spacecraft from 1966 to 1968.

Only SURVEYOR 2 and 4 were unsuccessful missions. The rest became the first U.S. probes to soft land on the moon, taking thousands of images and scooping the soil for analysis. APOLLO 12 landed 600 feet from SURVEYOR 3 in 1969 and returned parts of the craft to Earth. SURVEYOR 7, the last of the series, was a purely scientific mission which explored the Tycho crater region in 1968.

Viking (Mars Orbiters and Landers)

VIKING 1 was launched from Cape Canaveral, Florida on August 20, 1975 on a TITAN 3E-CENTAUR D1 rocket. The probe went into Martian orbit on June 19, 1976, and the lander set down on the western slopes of Chryse Planitia on July 20, 1976. It soon began its programmed search for Martian micro-organisms (there is still debate as to whether the probes found life there or not), and sent back incredible color panoramas of its surroundings. One thing scientists learned was that Mars' sky was pinkish in color, not dark blue as they originally thought (the sky is pink due to sunlight reflecting off the reddish dust particles in the thin atmosphere). The lander set down among a field of red sand and boulders stretching out as far as its cameras could image.

The VIKING 1 orbiter kept functioning until August 7, 1980, when it ran out of attitude-control propellant. The lander was switched into a weather-reporting mode, where it had been hoped it would keep functioning through 1994; but after November 13, 1982, an errant command had been sent to the lander accidentally telling it to shut down until further orders. Communication was never regained again, despite the engineers' efforts through May of 1983.

An interesting side note: VIKING 1's lander has been designated the Thomas A. Mutch Memorial Station in honor of the late leader of the lander imaging team. The National Air and Space Museum in Washington, DC is entrusted with the safekeeping of the Mutch Station Plaque until it can be attached to the lander by a manned expedition.

VIKING 2 was launched on September 9, 1975, and arrived in Martian orbit on August 7, 1976. The lander touched down on September 3, 1976 in Utopia Planitia. It accomplished essentially the same tasks as its sister lander, with the exception that its seismometer worked, recording one marsquake. The orbiter had a series of attitude-control gas leaks in 1978, which prompted it being shut down that July. The lander was shut down on April 12, 1980.

The orbits of both VIKING orbiters should decay around 2025.

Voyager (Outer Planet Flybys)

VOYAGER 1 was launched September 5, 1977, and flew past Jupiter on March 5, 1979 and by Saturn on November 13, 1980. VOYAGER 2 was launched August 20, 1977 (before VOYAGER 1), and flew by Jupiter on August 7, 1979, by Saturn on August 26, 1981, by Uranus on January 24, 1986, and by Neptune on August 8, 1989. VOYAGER 2 took advantage of a rare once-every-189-years alignment to slingshot its way from outer planet to outer planet. VOYAGER 1 could, in principle, have headed towards Pluto, but JPL opted for the sure thing of a Titan close up.

Between the two probes, our knowledge of the 4 giant planets, their satellites, and their rings has become immense. VOYAGER 1&2 discovered that Jupiter has complicated atmospheric dynamics, lightning and aurorae. Three new satellites were discovered. Two of the major surprises were that Jupiter has rings and that Io has active sulfurous volcanoes, with major effects on the Jovian magnetosphere.

When the two probes reached Saturn, they discovered over 1000 ringlets and 7 satellites, including the predicted shepherd satellites that keep the rings stable. The weather was tame compared with Jupiter: massive jet streams with minimal variance (a 33-year great white spot/band cycle is known). Titan's atmosphere was smoggy. Mimas' appearance was startling: one massive impact crater gave it the Death Star appearance. The big surprise here was the stranger aspects of the rings. Braids, kinks, and spokes were both unexpected and difficult to explain.

VOYAGER 2, thanks to heroic engineering and programming efforts, continued the mission to Uranus and Neptune. Uranus itself was highly monochromatic in appearance. One oddity was that its magnetic axis was found to be highly skewed from the already completely skewed rotational axis, giving Uranus a peculiar magnetosphere. Icy channels were found on Ariel, and Miranda was a bizarre patchwork of different terrains. Ten satellites and one more ring were discovered.

In contrast to Uranus, Neptune was found to have rather active weather, including numerous cloud features. The ring arcs turned out to be bright patches on one ring. Two other rings, and six other satellites, were discovered. Neptune's magnetic axis was also skewed. Triton had a canteloupe appearance and geysers. (What's liquid at 38K?)

The two VOYAGERs are expected to last for about two more decades. Their on-target journeying gives negative evidence about possible planets beyond Pluto. Their next major scientific discovery should be the location of the heliopause. Low-frequency radio emissions believed to originate at the heliopause have been detected by both VOYAGERs.

Soviet Planetary Missions

Since there have been so many Soviet probes to the moon, Venus, and Mars, I will highlight only the primary missions:

Soviet Lunar Probes

Soviet Venus Probes

Soviet Mars Probes

While there has been talk of Soviet Jupiter, Saturn, and even interstellar probes within the next thirty years, no major steps have yet been taken with these projects. More intensive studies of the moon, Mars, Venus, and various comets have been planned for the 1990s, and a Mercury mission to orbit and land probes on the tiny world has been planned for 2003. How the many changes in the former Soviet Union (now the Commonwealth of Independent States) will affect the future of their space program remains to be seen.

European Planetary Missions

GIOTTO was launched by an Ariane-1 by ESA on July 2, 1985, and approached within 540 km +/- 40 km of the nucleus of Comet Halley on March 13, 1986. The spacecraft carried 10 instruments including a multicolor camera, and returned data until shortly before closest approach, when the downlink was temporarily lost. Giotto was severely damaged by high-speed dust encounters during the flyby and was placed into hibernation shortly afterwards.

In April, 1990, Giotto was reactivated. Three of the instruments proved fully operational, 4 partially damaged but usable, and the remainder, including the camera, were unusable. On July 2, 1990, Giotto made a close encounter with Earth and was retargeted to a successful flyby of comet Grigg-Skjellerup on July 10, 1992.

Japanese Planetary Missions

SAKIGAKE (MS-T5) was launched from the Kagoshima Space Center by ISAS on January 8, 1985, and approached Halley's Comet within about 7 million km on March 11, 1986. The spacecraft is carrying three instruments to measure interplanetary magnetic field/plasma waves/solar wind, all of which work normally now, so ISAS made an Earth swingby by Sakigake on January 8, 1992 into an orbit similar to the Earth's. The closest approach was at 23h08m47s (JST=UTC+9h) on January 8, 1992. The geocentric distance was 88,997 km. This is the first planet-swingby for a Japanese spacecraft.

During the approach, Sakigake observed the geotail. Some geotail passages will be scheduled in some years hence. The second Earth-swingby will be on June 14, 1993 (at 40 Re (Earth's radius)), and the third October 28, 1994 (at 86 Re).

HITEN, a small lunar probe, was launched into Earth orbit on January 24, 1990. The spacecraft was then known as MUSES-A, but was renamed to Hiten once in orbit. The 430 lb probe looped out from Earth and made its first lunar flyby on March 19, where it dropped off its 26-pound midget satellite, HAGOROMO. Japan at this point became the third nation to orbit a satellite around the moon, joining the Unites States and USSR.

The smaller spacecraft, Hagoromo, remained in orbit around the moon. An apparently broken transistor radio caused the Japanese space scientists to lose track of it. Hagoromo's rocket motor fired on schedule on March 19, but the spacecraft's tracking transmitter failed immediately. The rocket firing of Hagoromo was optically confirmed using the Schmidt camera (105-cm, F3.1) at the Kiso Observatory in Japan.

Hiten made multiple lunar flybys at approximately monthly intervals and performed aerobraking experiments using Earth's atmosphere. Hiten made a close approach to the moon at 22:33 JST (UTC+9h) on February 15, 1992, at the height of 423 km from the moon's surface (35.3oN, 9.7oE) and fired its propulsion system for about ten minutes to put the craft into lunar orbit. The following is the orbital calculation results after the approach:

Planetary Mission References

I also recommend reading the following works, categorized in three groups: General overviews, specific books on particular space missions, and periodical sources on space probes. This list is by no means complete; it is primarily designed to give you places to start your research through generally available works on the subject. If anyone can add pertinent works to the list, it would be greatly appreciated.

Though naturally I recommend all the books listed below, I think it would be best if you started out with the general overview books, in order to give you a clear idea of the history of space exploration in this area. I also recommend that you pick up some good, up-to-date general works on astronomy and the Sol system, to give you some extra background. Most of these books and periodicals can be found in any good public and university library. Some of the more recently published works can also be purchased in and/or ordered through any good mass-market bookstore.

General Overviews (in alphabetical order by author):

Specific Mission References:

Other works and periodicals:

NASA has published very detailed and technical books on every space probe mission it has launched. Good university libraries will carry these books, and they are easily found simply by knowing which mission you wish to read about. I recommend these works after you first study some of the books listed above.

Some periodicals recommended for reading on space probes are National Geographic, which has written articles on the PIONEER probes to Earth's Moon, Luna and the Jovian planets Jupiter and Saturn, the RANGER, SURVEYOR, LUNAR ORBITER, and APOLLO missions to Luna, the MARINER missions to Mercury, Venus, and Mars, the VIKING probes to Mars, and the VOYAGER missions to Jupiter, Saturn, Uranus, and Neptune.

More details on American, Soviet, European, and Japanese probe missions can be found in Sky and Telescope, Astronomy, Science, Nature, and Scientific American magazines. Time, Newsweek, and various major newspapers can supply not only general information on certain missions, but also show you what else was going on with Earth at the time events were unfolding, if that is of interest to you. Space missions are affected by numerous political, economic, and climatic factors.

Depending on just how far your interest in space probes will go, you might also wish to join The Planetary Society, one of the largest space groups in the world dedicated to planetary exploration. Their periodical, The Planetary Report, details the latest space probe missions. Write to The Planetary Society, 65 North Catalina Avenue, Pasadena, CA 91106 USA.

Good luck with your studies in this area of space exploration. I personally find planetary missions to be one of the more exciting areas in this field, and the benefits human society has and will receive from it are incredible, with many yet to be realized.

Larry Klaes

(From Larry Klaes's Planetary Probe History section of the FAQ, with permission. Content by Larry Klaes <>)

Compilation copyright (c) 1994 by Jonathan P. Leech. This document may be redistributed in its complete and unmodified form. Other use requires written permission of the author.

The section on U.S. Planetary Missions was lightly adapted from an original posting by Larry Klaes, mostly minor formatting changes. Matthew Wiener contributed the section on Voyager, and the section on Sakigake was obtained from ISAS material posted by Yoshiro Yamada

Historical Lunar Exploration

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