Results: Helios 2 was the second spacecraft launched to investigate solar processes as part of a cooperative project between the Federal Republic of Germany and the United States in which the former provided the spacecraft and the latter the launch vehicle. Although similar to Helios 1, the second spacecraft had improved systems designed to help it survive longer. Like its twin, the spacecraft was put into heliocentric orbit; all communications with the spacecraft was directed from the German Space Operation Center near Munich. In contrast to Helios 1, Helios 2 flew three million kilometers closer to the Sun, achieving perihelion on 17 April 1976 at a distance of 0.29 AU (or 43.432 million kilometers), a distance that makes Helios 2 the record holder for the closest ever flyby of the Sun. As a result, the spacecraft was exposed to 10% more heat (or 20°C more) than its predecessor.
The spacecraft provided important information on solar plasma, the solar wind, cosmic rays, and cosmic dust, and also performed magnetic field and electrical field experiments. Besides its investigation of the Sun and solar environment, both Helios 1 and Helios 2 observed the dust and ion tails of at least three comets, C/1975V1 West, C/1978H1 Meier, and C/1979Y1 Bradfield. Helios 2's downlink transmitter, however, failed on 3 March 1980 and no further usable data was received from the spacecraft. Ground controllers shut down the spacecraft on 7 January 1981 to preclude any possible radio interference with other spacecraft in the future.
<!-- image -->A technician stands next to one of the twin Helios spacecraft. Credit: NASA/ Max Planck Institute for Solar System Research
Luna 24
Nation: USSR (95) Objective(s): lunar sample return Spacecraft: Ye-8-5M (no. 413) Spacecraft Mass: c. 5,800 kg Mission Design and Management: NPO imeni Lavochkina Launch Vehicle: Proton-K + Blok D (8K82K no. 288-02 + 11S824 no. 1501L) Launch Date and Time: 9 August 1976 / 15:04:12 UT Launch Site: NIIP-5 / Site 81/23
Scientific Instruments:
- stereo imaging system
- LB09 drill for sample collection
- radiation detector
- radio altimeter
Results: Luna 24 was the third attempt to recover a sample from the unexplored Mare Crisium (after Luna 23 and a subsequent launch failure in October 1975), the location of a large lunar mascon. After a trajectory correction on 11 August 1976, Luna 24 entered orbit around the Moon three days later. Initial orbital parameters were 115 × 115 kilometers at 120° inclination. After further changes to its orbit on 16 and 17 August, which brought the orbit down to an elliptical 120 × 12 kilometers, Luna 24 began its descent to the surface at perilune by firing its descent engine. Just 6 minutes later, the spacecraft set down safely on the lunar surface at 06:36 UT on 18 August 1976 at 12° 45′ N / 62° 12′ E (as announced at the time), not far from where Luna 23 had landed. Later analysis showed that the spacecraft landed just 10 meters from the rim of a 65-meter diameter impact crater.
After appropriate commands from ground control, within 15 minutes of landing, the lander deployed its sample arm and pushed its drilling head (using a rotary drilling mode) about 2.25 meters into the nearby soil. Because the drill entered at an angle, the probable surface depth of the sample was about 2 meters. The sample was safely stowed in the small return capsule, and after nearly a day on the Moon, Luna 24 lifted off successfully from the Moon at 05:25 UT on 19 August 1976. After an uneventful return trip lasting 84 hours, Luna 24's capsule entered Earth's atmosphere and parachuted down to Earth safely at 05:55 UT on 23 August 1976 about 200 kilometers southeast of Surgut in western Siberia. Study of the recovered 170.1 grams of soil indicated a laminated type structure, as if laid down in successive deposits. Tiny portions of the sample were exchanged with NASA in December 1976. At the time, the Luna 24 sample puzzled investigators because its titanium content and "maturity" (amount of time the sample was exposed to the space environment) were very different than expected at Mare Crisium. Images from NASA's Lunar Reconnaissance Orbiter (LRO) in 2012 showed that lander sampled impact ejecta from a nearby 64-meter diameter crater that brought up material from deeper lava flows that had not been previously exposed to the space environment. Thus, the Luna 24 sample probably represented subsurface materials only exposed to the space environment for a relatively short time. LRO images helped refine the landing target area as 12.7146° N / 62.2129° E, which was only 2.32 kilometers from the crashed Luna 23. Luna 24 remains the last Soviet or Russian probe to the Moon. A Japanese spacecraft (Hiten, page 179) returned to the Moon nearly 14 years later.
Voyager 2
Nation: USA (58) Objective(s): Jupiter flyby, Saturn flyby, Uranus flyby, Neptune flyby Spacecraft: Voyager-2 Spacecraft Mass: 721.9 kg Mission Design and Management: NASA / JPL Launch Vehicle: Titan IIIE-Centaur (TC-7 / Titan no. 23E-7 / Centaur D-1T) Launch Date and Time: 20 August 1977 / 14:29:44 UT Launch Site: Cape Canaveral / Launch Complex 41
Scientific Instruments:
- imaging science system (ISS)
- ultraviolet spectrometer (UVS)
- infrared interferometer spectrometer (IRIS)
- planetary radio astronomy experiment (PRA)
- photopolarimeter (PPS)
- triaxial fluxgate magnetometer (MAG)
- plasma spectrometer (PLS)
- low-energy charged particles experiment (LECP)
- plasma waves experiment (PWS)
- cosmic ray telescope (CRS)
- radio science system (RSS)
Results: The two-spacecraft Voyager missions were designed to replace original plans for a "Grand Tour" of the planets that would have used four highly complex spacecraft to explore the five outer planets during the late 1970s. NASA canceled the plan in January 1972 largely due to anticipated costs (projected at $1 billion) and instead proposed to launch only two spacecraft in 1977 to Jupiter and Saturn. The two spacecraft were designed to explore the two gas giants in more detail than the two Pioneers (Pioneers 10 and 11) that preceded them. In 1974, mission planners proposed a mission in which, if the first Voyager was successful, the second one could be redirected to Uranus and then Neptune using gravity assist maneuvers. Each of the two spacecraft were equipped with slow-scan color TV to take images of the planets and their moons and also carried an extensive suite of instruments to record magnetic, atmospheric, lunar, and other data about the planetary systems. The design of the two spacecraft was based on the older Mariners, and they were known as Mariner 11 and Mariner 12 until 7 March 1977 when NASA Administrator James C. Fletcher (1919–1991) announced that they would be renamed Voyager.
<!-- image -->One of the two Voyager Golden Records displayed with a Voyager spacecraft. Credit: NASA/JPL
Stunning image of Miranda taken by Voyager 2 on 24 January 1986 during the spacecraft's flyby of Uranus. This particular image was made from nine separate photos combined to obtain a full disc. Credit: NASA/JPL
<!-- image -->Power was provided by three plutonium dioxide radioisotope thermoelectric generators (RTGs) mounted at the end of a boom. Although launched after Voyager 1, Voyager 2 exited the asteroid belt after its twin and then followed it to Jupiter and Saturn. Its primary radio transmitter failed on 5 April 1978 and the spacecraft used its backup past that point. Voyager 2 began transmitting images of Jupiter on 24 April 1979 for time-lapse movies of atmospheric circulation. Unlike Voyager 1, Voyager 2 made close passes to the Jovian moons on its way into the system, with scientists especially interested in more information from Europa and Io (which necessitated a 10-hour long "volcano watch"). During its encounter, it relayed back spectacular photos of the entire Jovian system, including its moons Callisto, Ganymede, Europa (at 205,720-kilometer range, much closer than Voyager 1), Io, and Amalthea, all of which had already been surveyed by Voyager 1. Voyager 2's closest encounter to Jupiter was at 22:29 UT on 9 July 1979 at a range of 645,000 kilometers. It transmitted new data on the planet's clouds, its newly discovered four moons, and ring system as well as 17,000 new pictures. When the earlier Pioneers had flown by Jupiter, they noticed few atmospheric changes from one encounter to the second; in this case, Voyager 2 detected many significant changes, particular a drift in the Great Red Spot as well as changes in its shape and color. With the combined cameras of the two Voyagers, at least 80% of the surfaces of Ganymede and Callisto were mapped out to a resolution of 5 kilometers.
Following a mid-course correction 2 hours after its closest approach to Jupiter, Voyager 2 sped to Saturn, its trajectory determined to a large degree by the decision, taken in January 1981, to try and send the spacecraft to Uranus and Neptune later in the decade. Its encounter with the sixth planet began on 22 August 1981, two years after leaving the Jovian system, with imaging of the moon Iapetus. Once again, Voyager 2 repeated the photographic mission of its predecessor, although it actually flew 23,000 kilometers closer to Saturn. Closest encounter was at 01:21 UT on 26 August 1981 at 101,000 kilometer range. The spacecraft provided more detailed images of the ring "spokes" and kinks, and also the F-ring and its shepherding moons, all found by Voyager 1. Voyager 2's data suggested that Saturn's A-ring was perhaps only 300 meters thick. As it flew behind and up past Saturn, the probe passed through the plane of Saturn's rings at a speed of 13 kilometers/second; for several minutes during this phase, the spacecraft was hit by thousands of micron-sized dust grains that created "puff" plasma as they were vaporized. Because the vehicle's attitude was repeatedly shifted by the particles, attitude control jets automatically fired many times to stabilize the vehicle. During the encounter, Voyager 2 also photographed the Saturn moons Hyperion (the "hamburger moon"), Enceladus, Tethys, and Phoebe as well as the more recently discovered Helene, Telesto, and Calypso.
Although Voyager 2 had fulfilled its primary mission goals with the two planetary encounters, mission planners directed the veteran spacecraft to Uranus on a four-and-a-half-year-long journey during which it covered 33 AU's. In fact, its encounter with Jupiter was optimized in part to ensure that future planetary flybys would be possible. The Uranus encounter's geometry was also defined by the possibility of a future encounter with Neptune: Voyager 2 had only 5.5 hours of close study during its flyby, the first of any human-made spacecraft past the planet Uranus. Long-range observations of the planet began on
<!-- image -->High-altitude cloud streaks are visible in Neptune's atmosphere in a picture taken during Voyager 2's flyby of the gas giant in 1989. Credit: NASA/JPL
<!-- image -->The 34 meter High Efficiency Antenna in the foreground was nicknamed the "Uranus Antenna" because it was built in the 1980s to receive signals during Voyager 2's Uranus encounter. The antenna is located at the Goldstone Deep Space Communications Complex in California. Credit: NASA
<!-- image -->Pioneer Venus 1
Nation: USA (60) Objective(s): Venus orbit Spacecraft: Pioneer Venus Orbiter Spacecraft Mass: 582 kg Mission Design and Management: NASA / ARC Launch Vehicle: Atlas Centaur (AC-50 / Atlas no. 5030D) Launch Date and Time: 20 May 1978 / 13:13:00 UT Launch Site: Cape Canaveral / Launch Complex 36A
Scientific Instruments:
- charged particle retarding potential analyzer (ORPA)
- ion mass spectrometer (OIMS)
- thermal electron temperature Langmuir probe (OETP)
- neutral particle mass spectrometer (ONMS)
- cloud photopolarimeter (OCPP)
- temperature sounding infrared radiometer (OIR)
- magnetic field fluxgate magnetometer (OMAG)
- solar wind plasma analyzer (OPA)
- surface radar mapper (ORAD)
- electric field detector (OEFD)
- transient gamma ray burst detector (OGBD)
- radio occultation experiment
- atmospheric and solar corona turbulence experiment
- drag measurements experiment
- 2 radio science experiments to determine gravity field
- ultraviolet spectrometer (OUVS)