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.

The Mariner 2 spacecraft was the second of a series of spacecraft used for planetary exploration in the flyby, or nonlanding, mode and the first spacecraft to successfully encounter another planet. Mariner 2 was a backup for the Mariner 1 mission which failed shortly after launch to Venus. The objective of the Mariner 2 mission was to fly by Venus and return data on the planet's atmosphere, magnetic field, charged particle environment, and mass. It also made measurements of the interplanetary medium during its cruise to Venus and after the flyby.

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 attitude control, and the power control, battery, and battery charger, as well as the attitude 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 scientific experiments were mounted on the instrument mast and base. A 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. A cosmic dust detector and solar plasma spectrometer detector were attached to the top edges of the spacecraft base. A microwave radiometer and an 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.

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 attitude 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 1962. 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. Mariner 2 remains in heliocentric orbit.

Scientific discoveries made by Mariner 2 included a slow retrograde rotation rate for Venus, hot surface temperatures and high surface pressures, a predominantly carbon dioxide atmosphere, continuous cloud cover with a top altitude of about 60 km, and no detectable magnetic field. It was also shown that in interplanetary space the solar wind streams continuously and the cosmic dust density is much lower than the near-Earth region. Improved estimates of Venus' mass and the value of the astronomical unit were made. Total research, development, launch, and support costs for the Mariner series of spacecraft (Mariners 1 through 10) was approximately $554 million.

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 done before, 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 cone-shaped probe 51 cm high and 23 cm in diameter at its base. The cone was composed of a thin fiberglass shell coated with a gold wash to make it electrically conducting and painted with white stripes to maintain the temperature between 10 and 50 degrees C. At the tip of the cone was a small probe which combined with the cone itself to act as an antenna. At the base of the cone a ring of mercury batteries provided power. A photoelectric sensor protruded from the center of the ring. The sensor was designed with two photocells which would be triggered by the light of the Moon when the probe was within about 30,000 km of the Moon. At the center of the cone was a voltage supply tube and two Geiger-Mueller tubes. It passed within 60,000 km of the Moon's surface. However, Pioneer 4 did not come close enough to trigger the photoelectric sensor. No lunar radiation was detected. The spacecraft was still in solar orbit as of 1999.

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 2001 and are heading off into interstellar space, the first craft ever to do so.

The spacecraft was 2.9 m long and contained a 2.74-m diameter high-gain antenna of aluminum honeycomb sandwich material whose feed was topped with a medium-gain antenna. A low-gain, omnidirectional antenna was mounted below the high-gain dish. The spacecraft contained two nuclear electric-power generators, which generated 144 W at Jupiter, but decreased to 100 W at Saturn. There were three reference sensors: a star (Canopus) sensor, and two sun sensors. Attitude position could be calculated from the reference direction to the earth and the sun, with the known direction to Canopus as backup. Pioneer 11's star sensor gain and threshold settings were modified, based on experience gained from the settings used on Pioneer 10. Three pairs of rocket thrusters provided spin-axis control (maintained at 4.8 rpm) and change of the spacecraft velocity. The thrusters could be either fired steadily or pulsed, by command.

Communications were maintained via the omnidirectional and medium-gain antennas, which operated together, connected to one receiver, while the high-gain antenna was connected to the other receiver. The receivers could be interchanged by command. Two radio transmitters, coupled to two traveling-wave tube amplifiers, produced 8 W power each in S-band. Communication uplink (earth to spacecraft) operated at 2110 MHz, and downlink (spacecraft to earth) at 2292 MHz. At Jupiter's distance, round-trip communication time took 92 min. Data were received at the Deep Space Network (DSN). The spacecraft was temperature-controlled to between -23 and +38 deg C (-10 to +100 deg F). An additional experiment, a low-sensitivity fluxgate magnetometer, was added to the Pioneer 11 payload.

Instruments studied the interplanetary and planetary magnetic fields; solar wind properties; cosmic rays; transition region of the heliosphere; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves; the atmospheres of planets and satellites; and the surfaces of Jupiter, Saturn, and some of their satellites. Instruments carried for these experiments were magnetometer, plasma analyzer (for solar wind), charged-particle detector, ionizing detector, non-imaging telescopes with overlapping fields of view to detect sunlight reflected from passing meteoroids, sealed pressurized cells of argon and nitrogen gas for measuring penetration of meteoroids, UV photometer, IR radiometer, and an imaging photopolarimeter, which produced photographs and measured the polarization. Further scientific information was obtained from celestial mechanics and occultation phenomena.


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 was designed to transmit pictures of the lunar surface to Earth stations during a period of 10 minutes of flight prior to impacting on the Moon, to rough-land a seismometer capsule on the Moon, to collect gamma-ray data in flight, to study radar reflectivity of the lunar surface, and to continue testing of the Ranger program for development of lunar and interplanetary spacecraft. Due to a series of malfunctions the spacecraft missed the Moon and headed 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 was designed to achieve a lunar impact trajectory and to transmit high-resolution photographs of the lunar surface during the final minutes of flight up to impact. The spacecraft carried six television vidicon cameras, 2 wide angle (channel F, cameras A and B) and 4 narrow angle (channel P) to accomplish these objectives. The cameras were arranged in two separate chains, or channels, each self-contained with separate power supplies, timers, and transmitters so as to afford the greatest reliability and probability of obtaining high-quality video pictures. No other experiments were carried on the spacecraft. Ranger 6 was launched into an Earth parking orbit and injected on a lunar trajectory by a second Agena burn. The midcourse trajectory correction was accomplished early in the flight by ground control. On February 2, 1964, 65.5 hours after launch, Ranger 6 impacted the Moon on the eastern edge of Mare Tranquillitatis (Sea of Tranquility). The orientation of the spacecraft to the surface during descent was correct, but no video signal was received and no camera data obtained. A review board determined the most likely cause of failure was due to an arc-over in the TV power system when it inadvertently turned on for 67 seconds approximately 2 minutes after launch during the period of booster-engine separation.

Ranger 7 through 9 performed well, becoming the first U.S. lunar probes to return thousands of lunar images through 1965. Ranger 7 reached the Moon on 31 July. The F-channel began its one minute warm up 18 minutes before impact. The first image was taken at 13:08:45 UT at an altitude of 2110 km. Transmission of 4,308 photographs of excellent quality occurred over the final 17 minutes of flight. The final image taken before impact has a resolution of 0.5 meters. The spacecraft encountered the lunar surface in direct motion along a hyperbolic trajectory, with an incoming asymptotic direction at an angle of -5.57 degrees from the lunar equator. The orbit plane was inclined 26.84 degrees to the lunar equator. After 68.6 hours of flight, Ranger 7 impacted in an area between Mare Nubium and Oceanus Procellarum (subsequently named Mare Cognitum) at approximately 10.35 S latitude, 339.42 E longitude. (The impact site is listed as 10.63 S, 339.34 E in the initial report "Ranger 7 Photographs of the Moon".) Impact occurred at 13:25:48.82 UT at a velocity of 2.62 km/s. The spacecraft performance was excellent.

Ranger 8 reached the Moon on 20 February 1965. The first image was taken at 9:34:32 UT at an altitude of 2510 km. Transmission of 7,137 photographs of good quality occurred over the final 23 minutes of flight. The final image taken before impact has a resolution of 1.5 meters. The spacecraft encountered the lunar surface in a direct hyperbolic trajectory, with incoming asymptotic direction at an angle of -13.6 degrees from the lunar equator. The orbit plane was inclined 16.5 degreesto the lunar equator. After 64.9 hours of flight, impact occurred at 09:57:36.756 UT on 20 February 1965 in Mare Tranquillitatis at approximately 2.67 degrees N, 24.65 degrees E. (The impact site is listed as about 2.72 N, 24.61 E in the initial report "Ranger 8 Photographs of the Moon".) Impact velocity was slightly less than 2.68 km/s. The spacecraft performance was excellent.

Ranger 9 reached the Moon on 24 March 1965. At 13:31 UT a terminal maneuver was executed to orient the spacecraft so the cameras were more in line with the flight direction to improve the resolution of the pictures. Twenty minutes before impact the one-minute camera system warm-up began. The first image was taken at 13:49:41 at an altitude of 2363 km. Transmission of 5,814 good contrast photographs was made during the final 19 minutes of flight. The final image taken before impact has a resolution of 0.3 meters. The spacecraft encountered the lunar surface with an incoming asymptotic direction at an angle of -5.6 degrees from the lunar equator. The orbit plane was inclined 15.6 degrees to the lunar equator. After 64.5 hours of flight, impact occurred at 14:08:19.994 UT at approximately 12.83 S latitude, 357.63 E longitude in the crater Alphonsus. Impact velocity was 2.67 km/s. The spacecraft performance was excellent. Real time television coverage with live network broadcasts of many of the F-channel images (primarily camera B but also some camera A pictures) were provided for this flight.

Total research, development, launch, and support costs for the Ranger series of spacecraft (Rangers 1 through 9) was approximately $170 million.


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.

The main bus of the Lunar Orbiter had the general shape of a truncated cone, 1.65 meters tall and 1.5 meters in diameter at the base. The spacecraft was comprised of three decks supported by trusses and an arch. The equipment deck at the base of the craft held the battery, transponder, flight progammer, inertial reference unit (IRU), Canopus star tracker, command decoder, multiplex encoder, traveling wave tube amplifier (TWTA), and the photographic system. Four solar panels were mounted to extend out from this deck with a total span across of 3.72 meters. Also extending out from the base of the spacecraft were a high gain antenna on a 1.32 meter boom and a low gain antenna on a 2.08 meter boom. Above the equipment deck, the middle deck held the velocity control engine, propellant, oxidizer and pressurization tanks, Sun sensors, and micrometeoroid detectors. The third deck consisted of a heat shield to protect the spacecraft from the firing of the velocity control engine. The nozzle of the engine protruded through the center of the shield. Mounted on the perimeter of the top deck were four attitude control thrusters.

The Lunar Orbiter program consisted of 5 Lunar Orbiters which returned photography of 99% of the surface of the Moon (near and far side) with resolution down to 1 meter. Altogether the Orbiters returned 2180 high resolution and 882 medium resolution frames. The micrometeoroid experiments recorded 22 impacts showing the average micrometeoroid flux near the Moon was about two orders of magnitude greater than in interplanetary space but slightly less than the near Earth environment. The radiation experiments confirmed that the design of Apollo hardware would protect the astronauts from average and greater-than-average short term exposure to solar particle events. The use of Lunar Orbiters for tracking to evaluate the Manned Space Flight Network tracking stations and Apollo Orbit Determination Program was successful, with three Lunar Orbiters (2, 3, and 5) being tracked simultaneously from August to October 1967. The Lunar Orbiters were all eventually commanded to crash on the Moon before their attitude control gas ran out so they would not present navigational or communications hazards to later Apollo flights. The Lunar Orbiter program was managed by NASA Langley Research Center at a total cost of roughly $200 million.


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.

The Surveyor spacecraft was designed to attain the engineering objectives of the Surveyor program, which included the first lunar soft landing. No instrumentation was carried specifically for scientific experiments, but considerable scientific information was obtained. The spacecraft carried two television cameras -- one for approach, which was not used, and one for operations on the lunar surface. Over 100 engineering sensors were on board. The television system transmitted pictures of the spacecraft footpad and surrounding lunar terrain and surface materials.

The spacecraft also acquired data on the radar reflectivity of the lunar surface, bearing strength of the lunar surface, and spacecraft temperatures for use in the analysis of the lunar surface temperatures. The spacecraft was launched May 30, 1966, directly into a lunar impact trajectory. Engines were turned off at a height of 3.4 m above the lunar surface. The spacecraft fell freely from this height, landing on the lunar surface on June 2, 1966, in Oceanus Procellarum -- 2.45 deg s latitude, 43.22 deg w longitude (selenographic coordinates). The spacecraft transmitted data from shortly after touchdown until July 14, 1966, with an interval of no operation during lunar night (June 14 to July 7, 1966). Engineering interrogations continued until January 7, 1967.


Luna

Luna 3, an automatic interplanetary station, was the third spacecraft successfully launched to the Moon and the first to return images of the lunar far side. The spacecraft returned very indistinct pictures, but, through computer enhancement, a tentative atlas of the lunar farside was produced. These first views of the lunar far side showed mountainous terrain, very different from the near side, and only two dark regions which were named Mare Moscovrae (Sea of Moscow) and Mare Desiderii (Sea of Dreams).

The spacecraft was a cylindrically shaped cannister with hemispherical ends and a wide flange near the top end. The probe was 130 cm long and 120 cm at its maximum diameter at the flange. Most of the cylindrical section was roughly 95 cm in diameter. The cannister was hermetically sealed and pressurized at 0.23 atmospheres. Solar cells were mounted along the outside of the cylinder and provided power to the chemical batteries stored inside the spacecraft. Jalousies for thermal control were also positioned along the cylinder and would open to expose a radiating surface when the interior temperature exceeded 25 degrees C. The upper hemisphere of the probe held the covered opening for the cameras. Four antennae protruded from the top of the probe and two from the bottom. Other scientific apparatus (micrometeoroid and cosmic ray detectors) was mounted on the outside of the probe. Gas jets for attitude control were mounted on the outside of the lower end of the spacecraft. Photoelectric cells were used to maintain orientation with respect to the Sun and Moon. The spacecraft had no rockets for course adjustment. The interior of the spacecraft held the cameras and film processing system, radio equipment, propulsion systems, batteries, gyroscopic units for attitude control, and circulating fans for temperature control. The spacecraft was spin stabilized and was directly radio-controlled from Earth.

After launch on an 8K72 (number I1-8) on a course over the Earth's north pole the Blok-E escape stage was shut down by radio control from Earth at the proper velocity to put the Luna 3 on a trajectory to the Moon. Initial radio contact showed the signal from the probe was only about half as strong as expected and the interior temperature was increasing. The spacecraft spin axis was reoriented and some equipment shut down resulting in a drop in temperature from 40 C to about 30 C. At a distance of 60,000 to 70,000 km from the Moon, the orientation system was turned on and the spacecraft rotation was stopped. The lower end of the station was oriented towards the Sun, which was shining on the far side of the Moon. The spacecraft passed within 6,200 km of the Moon near the south pole at its closest approach at 14:16 UT on 6 October 1959 and continued on to the far side. On 7 October the photocell on the upper end of the spacecraft detected the sunlit far side of the Moon and the photography sequence started. The first image was taken at 03:30 UT at a distance of 63,500 km from the Moon's surface and the last 40 minutes later from 66,700 km. A total of 29 photographs were taken, covering 70% of the far side. After the photography was complete the spacecraft resumed spinning, passed over the north pole of the Moon and returned towards the Earth. Attempts to transmit the photographs to Earth began on 8 October but were believed to be unsuccessful due to the low signal strength. As Luna 3 got closer to Earth a total of 17 resolvable but noisy photographs were transmitted by 18 October. Contact with the probe was lost on 22 October. The probe was believed to have burned up in the Earth's atmosphere in March or April of 1960, but may have survived in orbit until after 1962.

The Luna 9 spacecraft was the first spacecraft to achieve a lunar soft landing and to transmit photographic data to Earth. The automatic lunar station that achieved the soft landing weighed 99 Kg. It was a hermetically sealed container with radio equipment, a program timing device, heat control systems, scientific apparatus, power sources, and a television system. The Luna 9 payload was carried to Earth orbit by an A-2-E vehicle and then conveyed toward the Moon by a fourth stage rocket that separated itself from the payload. Flight apparatus separated from the payload shortly before Luna 9 landed. After landing in the Ocean of Storms on February 3, 1966, the four petals, which formed the spacecraft, opened outward and stabilized the spacecraft on the lunar surface. Spring-controlled antennas assumed operating positions, and the television camera rotatable mirror system, which operated by revolving and tilting, began a photographic survey of the lunar environment. Seven radio sessions, totaling 8 hours and 5 minutes, were transmitted as were three series of TV pictures. When assembled, the photographs provided a panoramic view of the nearby lunar surface. The pictures included views of nearby rocks and of the horizon 1.4 Km away from the spacecraft.

Luna 16 was the first robotic probe to land on the Moon and return a sample to Earth and represented the first lunar sample return mission by the Soviet Union and the third overall, following the Apollo 11 and 12 missions. The spacecraft consisted of two attached stages, an ascent stage mounted on top of a descent stage. The descent stage was a cylindrical body with four protruding landing legs, fuel tanks, a landing radar, and a dual descent engine complex. A main descent engine was used to slow the craft until it reached a cutoff point which was determined by the onboard computer based on altitude and velocity. After cutoff a bank of lower thrust jets was used for the final landing. The descent stage also acted as a launch pad for the ascent stage. The ascent stage was a smaller cylinder with a rounded top. It carried a cylindrical hermetically sealed soil sample container inside a re-entry capsule. The spacecraft descent stage was equipped with a television camera, radiation and temperature monitors, telecommunications equipment, and an extendable arm with a drilling rig for the collection of a lunar soil sample.

The Luna 16 automatic station was launched toward the Moon from a preliminary Earth orbit and after one mid-course correction on 13 September it entered a circular 111 km lunar orbit on 17 September 1970. The lunar gravity was studied from this orbit, and then the spacecraft was fired into an elliptical orbit with a perilune of 15.1 km. The main braking engine was fired on 20 September, initiating the descent to the lunar surface. The main descent engine cut off at an altitude of 20 m and the landing jets cut off at 2 m height at a velocity less than 2.4 m/s, followed by vertical free-fall. At 05:18 UT, the spacecraft soft landed on the lunar surface in Mare Foecunditatis (the Sea of Fertility) as planned, approximately 100 km west of Webb crater. This was the first landing made in the dark on the Moon, as the Sun had set about 60 hours earlier. According to the Bochum Radio Space Observatory in the Federal Republic of Germany, strong and good quality television pictures were returned by the spacecraft. However, such pictures were not made available to the U.S. by any sources so there is question as to the reliability of the Bochum report. The drill was deployed and penetrated to a depth of 35 cm before encountering hard rock or large fragments of rock. The column of regolith in the drill tube was then transferred to the soil sample container. After 26 hours and 25 minutes on the lunar surface, the ascent stage, with the hermetically sealed soil sample container, lifted off from the Moon carrying 101 grams of collected material at 07:43 UT on 21 September. The lower stage of Luna 16 remained on the lunar surface and continued transmission of lunar temperature and radiation data. The Luna 16 re-entry capsule returned directly to Earth without any mid-course corrections, made a ballistic entry into the Earth's atmosphere on 24 September and deployed parachutes. The capsule landed approximately 80 km SE of the city of Dzhezkazgan in Kazakhstan at 03:26 UT.


Venera

Venera 4 was launched from a Tyazheliy Sputnik (67-058B) towards the planet Venus with the announced mission of direct atmospheric studies. On October 18, 1967, the spacecraft entered the Venusian atmosphere and released two thermometers, a barometer, a radio altimeter, and atmospheric density gauge, 11 gas analyzers, and two radio transmitters operating in the DM waveband.

The main bus, which had carried the capsule to Venus, carried a magnetometer, cosmic ray detectors, hydrogen and oxygen indicators, and charged particle traps. Signals were returned by the spacecraft, which braked and then deployed a parachute system after entering the Venusian atmosphere, until it reached an altitude of 24.96 km.

This spacecraft entered Venus orbit and was separated from the lander on October 20, 1975, after about 4.5 months of flight. The orbiter mission was to act as a communications relay for the lander and to explore cloud layers and atmospheric parameters with instruments including a French 3500 angstrom UV photometer, a 4000-7000 angstrom photo-polarimeter, a 1.5 to 3 micron infrared spectrometer, and a 8 - 30 micron infrared radiometer. The orbiter also carried a magnetometer and charged particle traps. Some reports indicated a camera system was also aboard. The orbiter consisted of a cylinder with two solar panel wings and a high gain parabolic antenna attached to the curved surface. A bell-shaped unit holding propulsion systems was attached to the bottom of the cylinder, and mounted on top was a 2.4 meter sphere which held the landers. At launch the Venera 9 spacecraft, including the lander, had a mass of 4936 kg.

On October 20, 1975, this spacecraft was separated from the Orbiter, and landing was made with the sun near zenith at 0513 UT on October 22. A system of circulating fluid was used to distribute the heat load. This system, plus precooling prior to entry, permitted operation of the spacecraft for 53 min after landing. During descent, heat dissipation and deceleration were accomplished sequentially by protective hemispheric shells, three parachutes, a disk-shaped drag brake, and a compressible, metal, doughnut-shaped, landing cushion. The landing was about 2,200 km from the Venera 10 landing site. Preliminary results indicated: (A) clouds 30-40 km thick with bases at 30-35 km altitude, (B) atmospheric constituents including HCl, HF, Br, and I, (C) surface pressure about 90 (earth) atmospheres, (D) surface temperature 485 deg C, (E) light levels comparable to those at earth midlatitudes on a cloudy summer day, and (F) successful TV photography showing shadows, no apparent dust in the air, and a variety of 30-40 cm rocks which were not eroded.


Mars

The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with a bus/orbiter module and an attached descent/lander module. The primary scientific objectives of the Mars 2 orbiter were to image the martian surface and clouds, determine the temperature on Mars, study the topography, composition and physical properties of the surface, measure properties of the atmosphere, monitor the solar wind and the interplanetary and martian magnetic fields, and act as a communications relay to send signals from the lander to Earth.

The attached orbiter/bus and descent module had a mass of approximately 4650 kg at launch (including fuel) and was 4.1 meters high, 5.9 meters across the two solar panel wings, and had a base diameter of 2 meters. The mass of the orbiter/bus was about 3440 kg fully fueled, and the fueled mass of the descent/lander module was about 1210 kg. The propulsion system was situated at the bottom of the cylindrical spacecraft body and was the main structural element of the orbiter. It consisted of a cylindrical fuel tank divided into separate compartments for fuel and oxidizer. The central part of the main body was composed primarily of this fuel tank. The engine was mounted on a gimbal on the lower surface of the tank. The descent module was mounted on top of the orbiter bus. The two solar arrays extended from the sides of the cylinder and a 2.5 meter diameter parabolic high-gain communications antenna and radiators were also mounted on the side. Telemetry was transmitted by the spacecraft at 928.4 MHz. The instruments and navigation system were located around the bottom of the craft. Antennae for communications with the lander were affixed to the solar panels. Three low power directional antennae extended from the main body near the parabolic antenna.

Mars 2 was launched towards Mars from a Tyazheliy Sputnik (71-045C) Earth orbiting platform. Mid-course corrections were made on 17 June and 20 November. Mars 2 released the descent module (71-045D) 4.5 hours before reaching Mars on 27 November 1971. The descent module entered the martian atmosphere at roughly 6.0 km/s at a steeper angle than planned. The descent system malfunctioned and the lander crashed at 45 deg S, 302 deg W, delivering the Soviet Union coat of arms to the surface. Meanwhile, the orbiter engine performed a burn to put the spacecraft into a 1380 x 24,940 km, 18 hour orbit about Mars with an inclination of 48.9 degrees. Scientific instruments were generally turned on for about 30 minutes near periapsis. The Mars 2 and 3 orbiters sent back a large volume of data covering the period from December 1971 to March 1972, although transmissions continued through August. It was announced that Mars 2 and 3 had completed their missions by 22 August 1972, after 362 orbits completed by Mars 2 and 20 orbits by Mars 3. The probes sent back a total of 60 pictures. The images and data revealed mountains as high as 22 km, atomic hydrogen and oxygen in the upper atmosphere, surface temperatures ranging from -110 C to +13 C, surface pressures of 5.5 to 6 mb, water vapor concentrations 5000 times less than in Earth's atmosphere, the base of the ionosphere starting at 80 to 110 km altitude, and grains from dust storms as high as 7 km in the atmosphere. The data enabled creation of surface relief maps, and gave information on the martian gravity and magnetic fields.

The Mars 2 descent module was mounted on the bus/orbiter opposite the propulsion system. It consisted of a spherical 1.2 m diameter landing capsule, a 2.9 m diameter conical aerodynamic braking shield, a parachute system and retro-rockets. The entire descent module had a fueled mass of 1210 kg, the spherical landing capsule accounted for 358 kg of this. An automatic control system consisting of gas micro-engines and pressurized nitrogen containers provided attitude control. Four "gunpowder" engines were mounted to the outer edge of the cone to control pitch and yaw. The main and auxiliary parachutes, the engine to initiate the landing, and the radar altimeter were mounted on the top section of the lander. Foam was used to absorb shock within the descent module. The landing capsule had four triangular petals which would open after landing, righting the spacecraft and exposing the instrumentation.