Vega Veneras Comet Program

solar system exploration

Although considerable concern was expressed by Western scientists about the breadth and pace of the Soviet solar system exploration program, the years 1983-1987 demonstrated the modest pace at which the Soviet planetary exploration program proceeded. Only two probes were launched, VEGA 1 and 2, for studies of Venus and Comet Halley. As noted earlier, the Phobos probes which were launched in July 1988 will also be incl uded here, even though the launch occurred outside the purview of this report, for the sake of completeness.

THE VEGA PROGRAM

The name VEGA reflects the dual nature of this program—VE for Venera, GA for the Cyrillic spelling of Halley—designating its mission as investigations of Venus and Comet Halley. Not only did the VEGA probes send back a wealth of scientific data about Venus and the comet, but because of the opening of the Soviet space science program to greater Western participation and review, it was a public relations bonanza for the Soviet Union.

The probes were international, including equipment not only from Soviet bloc countries (Czechoslovakia, Hungary, Bulgaria and Poland), but from four Western countries as well: France, West Germany, Austria and the United States (as discussed in more detail below, the U.S. contribution was provided by a university professor working through the West Germans, and was not a direct government-to-government cooperative effort). At the time of the Comet Halley intercept, IKI invited a large group of Western ob­servers to be on hand when the encounters occurred, an unprece­dented move for the Soviets. In addition, the Soviets actively par­ ticipated in an international group that coordinated Comet Halley observations. Called the Inter-Agency Consultative Group (IACG), it was composed of representatives of the Soviet Union, Japan, the European Space Agency, and the United States,

According to the Soviets, their VEGA program cost approximate­ ly 100 million rubles. 7

Event Summary

VEGA 1 was launched on December 15, 1984, and VEGA 2 fol­ lowed on December 21. Both were launched from Tyuratam using the Proton launch vehicle. The VEGA 1 entry probe was released on June 9, 1985, and entered Venus's atmosphere on June 11. The landing module touched down at 7 degrees 11 minutes north lati­tude, 177 degrees 48 minutes longitude. The VEGA 2 entry probe was released on June 13 and entered the atmosphere on June 15, the landing module touching down at 6 degrees 27 minutes south latitude, 181 degrees 5 minutes longitude. Both landed on the night side of the planet. The fly-by modules, using a gravity assist from Venus, continued on to intercept Comet Halley on March 6 and March 9, 1986, respectively.

Cooperation with the United States

Four days after the launch of VEGA 1 and one day before VEGA 2's launch, Dr. John Simpson of the University of Chicago an­ nounced that he had designed a comet dust analyzer that was aboard each of the spacecraft. 8 Dr. Simpson stated that he had been approached by Dr. Roald Sagdeyev, then director of IKI, about flying the instrument on the VEGA probes after he was unable to have it incorporated on the European Comet Halley spacecraft, Giotto. Dr. Simpson received approval from the U.S. State Depart­ment, Department of Defense, and NASA (which also funded the project) to accept the invitation. He worked through the Max Planck Institute in West Germany since the United States and Soviet Union did not have a formal cooperative space agreement at the time. The device recorded the impact of dust particles, provid­ing data on their mass and density. Other U.S. scientists also were involved with the VEGA project, including Dr. Bradford Smith of the University of Arizona who served as a member of the imaging analysis team, John Hseih, an Arizona physicist who designed the neutral mass spectrometer which was built by the Max Planck In­stitute, and Andrew Nagy of the University of Michigan who was a member of the plasma physics team, working with Hungarian sci­ entists. 9 A U.S. scientist developed one of the instruments carried on the balloon part of the mission, working with the French.

The participation of the U.S. scientists was not given high visibil­ ity by either country prior to the mission because of strained rela­tions. In 1982, President Reagan had chosen not to renew the bilat­eral space cooperation agreement because of concerns about Soviet activity in Poland. A new agreement was not signed until 1987, so at the time of the VEGA missions, government-to-government level cooperation was almost non-existent. 10 In official statements, the Soviet Union maintained that the United States was not participat­ing in the program. 11

In addition to the Comet Halley involvement, the United States also was very involved in tracking VEGA 1 and 2, using NASA's Deep Space Network to track the French/Soviet balloons in Venus's atmosphere and to track both spacecraft as they encoun­ tered Halley's Comet. The Soviets dealt with this cooperative aspect by mentioning all the countries that were involved in an international network to track the spacecraft (see below), stating that antennas in North and South America were included in the complement, but not specifically saying the United States was in­ volved.

Spacecraft Design

The two VEGA spacecraft, which were identical, are depicted in figures 1 and 2. The spherical object shown on the top in figure 1 is the entry module that housed the balloon and landing module for studies of Venus. The fly-by module, also shown in figure 1 and in more detail in figure 2 was used for the Comet Halley intercept. Figures 3 and 4 shown the trajectory profile of the entry probe and a more detailed view of the lander. 1 2

Vega Venera Comet Spacecraft

Vega Landing Operation

Vega Venera Lander

The Venus Entry Modules

The VEGA 1 and VEGA 2 entry modules each consisted of a landing module plus one balloon. The balloons were built coopera­ tively by the French and Soviets. Two-way communications with the probes were made using the 6 Gigahertz (GHz) band, while a different frequency (1.67 Ghz) was used for the balloons.

The Soviets decided to build the VEGA probes in 1980, revising their original plan to launch two probes only to Venus in 1984. 13 The original 1984 mission was to carry the French balloons, and when the Soviets changed the mission to include a Comet Halley encounter, they asked the French to design smaller balloons so the Comet Halley instruments could be accommodated. The French de­ termined that new balloons could not be delivered in time, so the balloon idea was dropped and the French role was renegotiated so that French scientists participated in building instruments for the lander and fly-by modules. 14 Then the Soviets decided to build the balloons themselves using a French design and the instruments they carried were built by the French. 1 5

The balloons were built of Teflon and automatically filled with helium at a predetermined altitude (54 kilometers) as they descend­ed towards the surface of Venus. Drop tests were conducted from helicopters and airplanes to ensure that the release mechanism worked. Each balloon was 3.4 meters in diameter, supporting a total mass of 21 kilograms (kg) including a 6.9 kg gondola suspend­ ed by a 13 meter tether. The balloons used lithium batteries for power, which could last 46-52 hours. Two watt transmitters operat­ ing at 1.67 Gigahertz sent back data in 5.5 minute bursts at a rate of 4 bits per second. 1 6

The Comet Intercept Fly-By Modules

The fly-by modules that intercepted Comet Halley carried a wide variety of scientific instruments. The module's total mass was 3,500 kg, including fuel. The science platform had a mass of 253 kg, of which experiments accounted for 85 kg. 17 The following experi­ments were carried:

• A two camera television system with an onboard microproces­ sor, built by the Soviet Union, France, and Hungary. The cameras produced both black and white and color images of the nucleus and central coma region. Focal lengths were 150 mm and 1,200 mm for the two cameras. By using both wide-angle and narrow-angle sys tems, images of the entire comet, with the coma and the tail, as well as high resolution images of the nucleus, were possible. Spa tial resolution of the long focal length camera was 180 meters;
• A three-channel spectrometer developed by the Soviet Union, Bulgaria and France which provided data on emissions in the ul traviolet, visible and infrared bands;
• An infrared spectrometer built by France with three optical channels, two of which operated in a spectroscope mode, and a third designed to construct an infrared nucleus image;
• A dust mass spectrometer built by the Soviet Union and West Germany;
• Two dust particle counters built by the Soviets. One was an acoustic type made of metal plates with detectors made from piezo­ electric elements on each plate. The other was a plasma detector;
• A neutral-gas mass spectrometer built by Hungary, West Ger­many, and the Soviet Union;
• An ion mass spectrometer and electron analyzer package con­ taining five detectors, built by the Soviet Union and Hungary;

(8)A high-energy particle counter built by Hungary, West Germa­ ny and the Soviet Union;

• Plasma wave analyzers built by Czechoslovakia, France, Poland and the Soviet Union; and
• Magnetometers that could measure the magnetic field to an accuracy of 10-6 Gauss built by Austria. 18

The VEGA 1 module was designed to fly as close as 10,000 kilo­ meters to the nucleus, and VEGA 2 even closer, 3,000 km. Inter­ cept velocity was 80 kilometers per second. It was difficult to con­ struct spacecraft able to withstand an encounter of this magnitude with particles from the comet impacting the spacecraft at such high velocity, so the spacecraft had a special "armor" of two and three layers of skin. 1 9

Operations and Results The Balloons

Details on the design of the balloons and analysis of the resulting data were published on March 21, 1986 in Science, a publication of the American Association for the Advancement of Science, from which much of the following material is extracted. 20 The balloons were released on the night side of the planet, then drifted with the clouds towards the Sun. 21 Instruments were designed to make me­teorological measurements (including temperature and pressure) as well as the frequency of lightning flashes, the vertical velocity of wind gusts, and the location and density of clouds.

Twenty antennas around the world were used to track the bal­ loons, including six in the Soviet Union whose operation was co­ ordinated by IKI, and fourteen around the world coordinated through the French space agency CNES and including NASA's three Deep Space Network antennas in the United States, Spain and Australia (the other 11 were radio astronomy observatories). 22 By using such a large number of antennas located at great dis­ tances from each other, the technique of very long baseline inter ferometry could be used, providing accuracy of 4 km per hour in the tracking area. Five antennas were used to actually receive te­ lemetry, and they then could direct the other antennas where to look. 23

Both balloons were deployed at a longitude of 180 degrees near Venus midnight. 24 VEGA 1 entered at 7 degrees north of the equa­ tor and VEGA 2 at 1 degrees south. Each was tracked over a dis­ tance of 11,500 km, encountering dawn at 33 hours after deploy­ment. The float time of each balloon was estimated at 46 hours and data were received for 22.5 hours from each. Each flew at approxi­ mately 54 km altitude. The speed of the balloon's movements, and therefore of Venus' cloud layer, was 200 kilometers an hour (60 meters per second). Descending and ascending currents were re­ corded at a speed of up to 4 km per hour, buffeting the VEGA 1 balloon by as much as 200-300 meters up and down. 25 VEGA 2 en­ countered even stronger vertical winds, up to 11 km per hour, when the balloon was over Aphrodite, one of the highest mountain­ous areas on the planet. 26

Results from the VEGA data showed that at altitudes from 63 to 48 km, there is an average of 1 milligram of sulfuric acid per cubic meter of atmosphere, and the clouds contains sulphur (some in free form), chlorine and phosphorous. 27 The lightning sensors detected no lightning around or beneath them.

The Landing Modules

Not much information has been published about the landing modules, possibly because the instruments they carried were simi­ lar to those on Venera 13 and 14 and more attention was focussed on the new experiments conducted with the balloons. 28 It is also possible that some of the experiments failed. The landing modules had instruments for atmospheric measurements during descent, and soil analysis equipment, including a drill. Data from the VEGA 2 landing site showed the soil to be soft and similar to loose andesite-basalt soils on Earth, different from the previous landing sites. 29 The VEGA 1 lander transmitted data for 21 minutes. 30

The landers carried gamma spectrometers which began operating at an altitude of 25 km. VEGA 1 produced 9 spectra before landing and eight afterwards. VEGA 2 produced 10 before landing and nine after. Results from these instruments reportedly showed that the Venusian rocks were similar to tholeitic basalts and gabborids. 31

The Encounter with Comet Halley

The VEGA 1 fly-by module passed Venus at a distance of 39,000 km, 32 while VEGA 2 passed the planet at a distance of 24,500 km. 33 Both received gravity assist boosts from Venus to enable them to reach Comet Halley.

On February 12, 1986, the fly-by probes were put into an oper­ ational mode and on February 14, the television cameras were tar­ geted on Jupiter as a systems test. 34 The first pictures of Comet Halley were received on March 4 when VEGA 1 was at a distance of 14 million km from the comet (and 171 million km from Earth). Pictures were taken for 90 minutes through various filters and sev­eral dozen pictures were returned. 35 Photos of the comet were also obtained on March 5 from a distance of 7 million km, and on March 6, at closest approach, which was 9,000 km from the nucle­ us, slightly closer than planned. Measurements were made during a three hour period and more than 500 television pictures were re­turned in total. 36

VEGA 2 reached its closest point, 8,200 km from the nucleus, on March 9. 37 Either a cosmic ray or a dust particle disabled the mi­ croprocessor system monitoring the exposure for the camera, causing the images to be somewhat overexposed. A total of about 700 pictures were taken with VEGA 2, however. 38

Both spacecraft were damaged during the encounter, VEGA 2 re­ceiving more damage for unknown reasons since it approached the comet from its quiet side. Power from the solar panels was reduced by 80 percent on VEGA 2, and 40-45 percent on VEGA I. 39 Two VEGA 1 experiments and three on VEGA 2 ceased functioning during closest approach, probably because of damage from the dust. 40 The spacecraft first detected gas sublimated from the comet's nucleus at a distance of 35 million km, and the first dust particles were encountered more than 200,000 km out. 41

Data from VEGA 1 showed the comet's magnetic field to have an intensity as high as 75 nanoteslas. Instruments recorded up to 3,000 dust particles per square decimeter each second at closest ap­ proach, and a large quantity of water vapor was detected, as well as the presence of all molecules with a weight of less than 28. Sci­ entists found that 30 tons of water vapor and 5-10 tons of dust evaporate from the surface of the nucleus every second. The shock wave boundary was at 1 million km. 42 Based on the VEGA data, Soviet scientists concluded that the nucleus was irregularly shaped, with a diameter of 14 km and height of 7 km, resembling either a peanut or a potato. 43 Temperature of the surface of the nucleus was deduced to be approximately 100 degrees C, higher than ex­ pected.

Both spacecraft survived the encounter with Comet Halley, de­ spite the damage. In January 1987, almost a year after the encoun­ter, the probes were reported to be in heliocentric orbit and regular radio communications sessions were being conducted. 44 References:

A . SOVIET SPACE PROGRAMS: 1981-87, SPACE SCIENCE, SPACE APPLICATIONS, MILITARY SPACE PROGRAMS, ADMINISTRATION, RESOURCE BURDEN, AND MASTER LOG OF SPACEFLIGHTS, Part 2, April 1989, Printed for the use of the Committee on Commerce, Science, and Transportation, U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON, D.C. 1989, Committee print 1981-87- part-2

7. Soviets to Aid Halley's Comet Observations. Aviation Week and Space Technology, Jan. 2, 1984. p. 20.

8. University of Chicago News Release, Dec. 20, 1984.

9. Wilford, John Noble. U.S. Device Riding Soviet Spacecraft. New York Times, Dec. 21, 1984, p. Al, 23.

10. Two programs started under the 1977-1982 agreement were allowed to continue despite the lack of the agreement's renewal. These were related to a biosatellite mission and a search and rescue satellite system. Thus, there was a small amount of governmental cooperation for exist­ ing projects.

11. Moscow Television Service in Russian, 1510 GMT, Jan. 12, 1985. Also see: Soviet Denies U.S. Participation in Soviet Halley Mission. Defense Daily, Jan. 6, 1985. p. 39,

13 Soviets Revise 1984 Venera Unmanned Mission Plan to Include 1986 Flyby of Halley's Comet. Aviation Week and Space Technology, Nov. 10, 1980. p. 18-19.

14. Le Monde, Feb. 12, 1981, p. 4.

15 Soviet VEGA Launches Set for Dec. 1984. Aerospace Daily, Dec. 21. 1982. p. 269.

16. Dornheim, Michael A. Soviets' VEGA 2 Balloon, Lander Transmit Data From Venus. Avia­ tion Week and Space Technology, June 24, 1985. p. 2H.

17. Clark, Phillip. The VEGA Missions. Spaceflight, May 1985. p. 219.

18. Seven Nations to Contribute to Soviet Comet Observations. Aviation Week and Space Tech nology, July 12, 1982. p. 72; also: Izvestiya, Dec. 16, 1984, p. 2.

19. Sovetskaya Estoniya, Dec. 16, 1984, p. 3.

20. The Jan. and Feb. 198B issues of the Soviet "Pisma v Astronomicheskiy Zhurnal" also de­ tailed results from the Venus part of the VEGA mission.

21. Izvestiya, Nov. 18, 1984, p. 8.

22. In total, facilities in ten countries were used: Australia, Brazil, Canada, England, West Ger­ many, South Africa, the Soviet Union, Spain, Sweden and the United States.

23. Dornheim, Michael A. Soviets' VEGA 2 Balloon, Lander Transmit Data from Venus. Avia­ tion Week and Space Technology, June 24, 1985. p. 24.

24. Sagdeyev, R. Z. et al. The VEGA Venus Balloon Experiment. Science, Mar. 21, 1986. p. 1407.

25 TASS, 1400 GMT, June 15, 1985.

26 Weather Balloons at Venus. Science, Mar. 21, 1986, p. 1369.

27. Pravda, Nov. 18, 1985, p. 8.

28. Of 23 articles about the VEGA missions in the Jan. and Feb. 1986 issues of Pisma v Astron omicheckiy Zhurnal, only 1 was on results from the experiments at the landing site.

29. Trud, June 16, 1985, p. 3.

30. Dornheim, Michael A. Soviets' VEGA 2 Balloon, Lander Transmit Data From Venus. Avia­ tion Week and Space Technology, June 24, 1985. p. 23.

31. Pisma v Astronomicheskiy Zhurnal, Feb. 1986, p. 114-119. English abstract in JPRS-USP- 86-006, Nov. 12, 1986. JPRS is the Joint Publication Research Service, a series of publications by the Foreign Broadcast Information Service (FBIS). FBIS publications are available from the U.S. Dept. of Commerce National Technical Information Service (NTIS).

32. TASS, 0813 GMT, June 11, 1985.
33. TASS, 0725 GMT, June 15 1985.

34. TASS, 1145 GMT, Feb. 17, 1986.

35. Leningradskaya Pravda, Mar. 5, 1986, p. 1.

36. Leningradskaya Pravda, Mar. 7, 1986, p. 11.

37. Izvestiya, Mar. 10, 1986, p. 1.

38. Bohlen, Celestine. Soviet VEGA 2 Passes Closer to Comet. Washington Post, Mar. 10, 1986, p. A 23.

39. Lenorovitz, Jeffrey M. Both Soviet VEGA Spacecraft Relay New Data From Halley. Avia tion Week and Space Technology, Mar. 17, 1986. p. 18.

40. VEGA's 1 and 2 Visit Halley. Science, Mar. 21, 1986. p. 1866.

41. VEGA's 1 and 2 Visit Halley. Science, Mar. 21, 1986. p. 1866.

42. Vestnik Akademii Nauk SSSR, Aug. 1986, p. 17

43 Balebanov, V. The Vega Project: the Concluding Stage. Sovremennyye Dostizheniya Kos-
monavtiki (Novoye v Zhizni, Nauke, Tekhnike: Seroya Kosmonavtika). Astronomiya, Dec. 1986.
p. 17-34. English Translation: JPRS-USP-87-003, Apr. 22, 1987.

44 Izvestiya, Jan. 16, 1987, p. 2.