The Giotto spacecraft eventually passed by Halley on 14 March 1986. Closest encounter was at a distance of 596 kilometers at 00:03:02 UT, the spacecraft being the only one among the large armada of spacecraft sent to investigate Halley that actually entered the ionosphere of the comet. At a range of 137.6 million kilometers from Earth, just 2 seconds before closest approach, telemetry stopped due to impact with a heavy concentration of dust that probably knocked the spacecraft's high gain antenna out of alignment with Earth. Fortunately, data transmission was restored within 21.75 seconds (with proper orientation of the antenna restored after 32 minutes). On average, Giotto had been hit 100 times a second by particles weighing up to 0.001 grams. By the end of its encounter with Halley, the spacecraft was covered in at least 26 kilograms of dust stemming from 12,000 impacts. Giotto returned 2,000 images of Halley.

After the encounter, ESA decided to redirect the vehicle for a flyby of Earth. The spacecraft was officially put in hibernation mode on 2 April 1986. Course corrections on 10, 20, and 21 March 1986, however, set it on a 22,000-kilometer flyby of Earth on 2 July 1990 for a gravity assist (the first time that Earth had been used for such a purpose) to visit a new target: Comet 26P/Grigg-Skjellerup, which Giotto flew by at 15:30 UT on 10 July 1992 at range of approximately 200 kilometers. Eight experiments provided extensive data on a wide variety of cometary phenomena during this closest ever flyby of a comet. After formal conclusion of the encounter, Giotto was put in hibernation on 23 July 1992. Later, in September 1999, ESA scientists revealed that a second comet or cometary fragment may have been accompanying Grigg-Skjellerup during the encounter in 1992. The spacecraft repeated a flyby of Earth at 02:40 UT on 1 July 1999 at range of 219,000 kilometers but was not reactivated.

Suisei

Nation: Japan (2) Objective(s): Halley’s Comet flyby Spacecraft: Planet-A Spacecraft Mass: 139.5 kg Mission Design and Management: ISAS Launch Vehicle: Mu-3S-II (no. 2) Launch Date and Time: 18 August 1985 / 23:33 UT Launch Site: Kagoshima / Launch Complex M1

Scientific Instruments:

ultraviolet imaging system
electrostatic analyzer

Results: Planet-A, named Suisei ("comet") after launch, was the second of two Japanese probes launched towards Halley during the 1986 Earth encounter. The cylindrical spacecraft was launched directly on a deep space trajectory without entering intermediate Earth orbit. The main payload of the spacecraft was an ultraviolet-based imaging system that could study the huge hydrogen corona around the comet. After a course correction on 14 November 1985, Suisei flew within 152,400 kilometers of the comet's nucleus on 8 March 1986 at 13:06 UT, returning ultraviolet images of the 20 million-kilometer diameter hydrogen gas coma. Even at that relatively large distance from the comet, the spacecraft was hit by at least two dust particles, each 1 millimeter in diameter.

After the Halley encounter, in 1987, ISAS decided to send the spacecraft through an elaborate trajectory for an encounter with Comet 21P/Giacobini-Zinner on 24 November 1998, 13 years after launch. Suisei performed a series of trajectory corrections on 5–10 April 1987 to send it on a gravity assist around Earth on 20 August 1992 at a range of 60,000 kilometers. Unfortunately, hydrazine for further corrections had been depleted by 22 February 1991. The planned encounter on 28 February 1998 with Giacobini-Zinner (as well as a far distance flyby of Comet 55P/Tempel-Tuttle) had to be cancelled, formally ending the mission.

Fobos 1

Nation: USSR (104) Objective(s): Mars flyby, Phobos encounter Spacecraft: 1F (no. 101) Spacecraft Mass: 6,220 kg Mission Design and Management: NPO imeni Lavochkina Launch Vehicle: Proton-K + Blok D-2 (8K82K no. 356-02 + 11S824F no. 2L) Launch Date and Time: 7 July 1988 / 17:38:04 UT Launch Site: NIIP-5 / Site 200/39

Scientific Instruments:

Orbiter:

Lima-D laser mass spectrometer analyzer
Dion secondary ion mass analyzer
radar system (RLK) (of which Plazma ionosphere study instrument only on Fobos 1)
videospectrometric system (VSK)
KRFM-ISM infrared spectrometer
Termoskan infrared spectrometer
IPNM-3 neutron detector (only on Fobos 1)
GS-14 STsF gamma-emission spectrometer
Ogyust optical radiation spectrometer (ISO)
scanning energy-mass spectrometer (ASPERA)
plasma spectrometer (MPK)
Ester electron spectrometer
plasma wave analyzer (APV-F / PWS)
flux gate magnetometer (FGMM)
magnetometer (MAGMA)
Terek solar telescope/coronograph (only on Fobos 1)
RF-15 x-ray photometer
ultrasound spectrometer (SUFR)
gamma-ray burst spectrometer (VGS)
Lilas gamma-ray burst spectrometer
solar photometer (IFIR)
Taus proton and alpha-particle spectrometer
Harp ion and electron spectrometer
Sovikoms energy, mass, and charge spectrometer
Sled charged-particle spectrometer

DAS:

Al'fa x-ray and alpha-particle backscattering spectrometer
Stenopee (Libratsiya) sun sensor to measure librations
2 cameras
vibration measurement instrument (VIK) + temperature sensor
transponder

Results: Fobos 1 and 2 were part of an ambitious mission to Mars and its 27-kilometer diameter moon Phobos that culminated a decade-long program of development. A truly multinational project that was the last hurrah for Soviet planetary exploration, the missions involved contributions from 14 other nations including Austria, Bulgaria, Czechoslovakia, Finland, France (undoubtedly the most active partner), East Germany, West Germany, Hungary, Ireland, Poland, Switzerland, Sweden, and the European Space Agency. NASA provided some tracking support through its Deep Space Network. Each spacecraft, with a newly designed standardized bus known as the UMVL, comprised a Mars orbiter for long-term studies of the planet and a 67-kilogram Long-Term Autonomous Station (DAS) which would land on Phobos, anchored by a harpoon driven into the soil, to study its geological and climactic conditions.

The core of the bus was an autonomous engine unit (using the S5.92 engine, later named Fregat) that essentially acted as the fifth stage of the Proton launch vehicle, boosting the spacecraft to Mars from a highly eccentric Earth orbit attained after a firing of the Blok D upper stage. After each spacecraft entered orbit around Mars, they were designed to make very close (c. 50 meters) flybys of Phobos (on 7 April 1989 for Fobos 1), and sample surface material using two innovative methods (using a laser and using a beam of krypton ions) that would actively disturb the soil of Phobos. Instruments would then measure and evaluate the response. After the Phobos flyby, it was planned for the spacecraft to continue science missions directed at Mars from Martian orbit. The spacecraft were loaded with an unprecedented array of experiments, making them probably the most highly instrumented deep space mission ever launched.

Fobos 1 performed a course correction en route to Mars on 16 July 1988. On 29 August 1988, instead of a routine command to switch on the GS-14STsF gamma-emission spectrometer, an erroneous command was issued as a result of a programming error, to turn off the orientation and stabilization system. As a result, the spacecraft lost proper solar orientation, i.e., the solar panels faced away from the Sun and thus began to lose power. There was no word from Fobos 1 at the next scheduled communications session on 2 September. Continuing attempts to establish contact failed, and on 3 November 1988, the Soviets officially announced that there would be no further attempts at contact. The engineer who sent the false command was apparently barred from working on the shift teams for Fobos 2. Fobos 1 meanwhile flew by Mars without entering orbit (scheduled for 23 January 1989) and eventually entered heliocentric orbit. The most significant scientific data from the mission came from the Terek solar telescope, which returned important information on some of the then-least studied layers of the solar atmosphere, the chromosphere, the corona, and the transition layer.

Fobos 2

Nation: USSR (105) Objective(s): Mars flyby, Phobos encounter Spacecraft: 1F (no. 102) Spacecraft Mass: 6,220 kg Mission Design and Management: NPO imeni Lavochkina Launch Vehicle: Proton-K + Blok D-2 (8K82K no. 356-01 + 11S824F no. 1L) Launch Date and Time: 12 July 1988 / 17:01:43 UT Launch Site: NIIP-5 / Site 200/40

Scientific Instruments:

Orbiter:

Lima-D laser mass spectrometer analyzer
Dion secondary ion mass analyzer
radar system (without Plazma ionosphere study instrument, only on Fobos 1) (RLK)
videospectrometric system (VSK)
KRFM-ISM infrared spectrometer
Termoskan infrared spectrometer
GS-14 STsF gamma-emission spectrometer
Ogyust optical radiation spectrometer (ISO)
scanning energy-mass spectrometer (ASPERA)
plasma spectrometer (MPK)
Ester electron spectrometer
plasma wave analyzer (APV-F / PWS)
flux gate magnetometer (FGMM)
magnetometer (MAGMA)
x-ray photometer (RF-15)
ultrasound spectrometer (SUFR)
gamma-ray burst spectrometer (VGS)
Lilas gamma-ray burst spectrometer
solar photometer (IFIR)
Termoskop
Taus proton and alpha-particle spectrometer
Harp ion and electron spectrometer
Sovikoms energy, mass, and charge spectrometer
Sled charged-particle spectrometer

DAS:

Alfa x-ray and alpha-particle backscattering spectrometer
Stenopee (Libratsiya) sun sensor to measure librations
2 cameras
vibration measurement instrument (VIK) + temperature sensor
transponder

PrOP-FP:

penetrometer with ground sampler
accelerometers
x-ray fluorescence spectrometer
magnetometer (MFP)
kappameter
gravimeter
surface temperature sensors
instrument to measure surface electrical resistance
instrument to measure position tilt

Results: Fobos 2 had the same mission as its twin Fobos 1, to orbit Mars and fly past Phobos (on 13 June 1989) but had an additional payload, a small 43-kilogram instrumented "hopper" known as PrOP-FP that would make 20-meter jumps across the surface of Phobos for about 4 hours. The orbiter also had a slightly different instrument complement—it did not carry the IPNM, Plazma, and Terek instruments carried on Fobos 1. PrOP-FP (Device to Evaluate Mobility—Phobos) had its own power supply system, radio transmitter, and a suite of scientific instruments. This "rover" was designed to perform hops ranging from 10 to 40 meters and take data measurements after each hop. Despite some onboard anomalies, Fobos 2 carried out two en route course corrections on 21 July 1988 and 23 January 1989. One of the two radio transmitters failed, while its Buk computer was acting erratically due to faulty capacitors in the computer's power supply, a fact that was known before launch.

At 12:55 UT on 29 January 1989, the spacecraft fired its engine to enter orbit around Mars. Initial orbital parameters were 819 × 81,214 kilometers at 1.5° inclination. In the initial months in orbit around Mars, the spacecraft conducted substantive investigations of the Red Planet and also photographed areas of its surface. During this period, controllers implemented four further orbital corrections in order to put its trajectory on an encounter course with Phobos. The spacecraft also jettisoned its Fregat upper stage (which had fired its engine to enter Mars orbit). Fobos 2 took high resolution photos of the moon on 23 February (at 860 kilometers range), 28 February (320 kilometers), and 25 March 1989 (191 kilometers), covering about 80% of its surface. Release of its lander was scheduled for 4–5 April 1989, but on 27 March during a regularly planned communications session at 15:58 UT, there was no word from the spacecraft. A weak signal was received between 17:51 and 18:03 UT, but there was no telemetry information. The nature of the signal indicated that the spacecraft had lost all orientation and was spinning. Future attempts to regain communication were unsuccessful and the mission was declared lost on 14 April 1989. The most probable cause was failure of the power supply for the Buk computer, something that had actually happened earlier in the mission (on 21 January 1989). On this occasion, controllers failed to revive the vehicle. Roald Sagdeev (1932– ), the director of the Institute of Space Research noted in the journal Priroda (Nature) in mid-1989 that "I think we should seek the cause of the failure in the very organization of the project, in its planning" adding that "the relationships between the customer [the science community] and contractor [Lavochkin] … are clearly abnormal."

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