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FACT SHEET: PHOBOS DYNAMICS EXPERIMENT SUMMARY American space scientists and NASA's Deep Space Network (DSN) are participating in scientific activities of the USSR's Phobos mission to study Mars and its satellite Phobos in 1989. Two Soviet Phobos spacecraft were launched in July 1988 and scheduled to arrive at Mars in January 1989. Contact with one spacecraft was lost in early September. The other was put in an equatorial orbit, to be carefully stepped down toward the orbit of Phobos, the inner moon of Mars, to permit a very slow and close flyby encounter with that body. The rendezvous and deployment of landers on the moon are planned for March/April 1989. The Phobos orbiter carries a lander and a mobile "hopper" which can make measurements at several sites on the moon's surface. The DSN, which is operated by the California Institute of Technology's Jet Propulsion Laboratory for NASA, will help Soviet ground stations maintain radio contact with the lander on the surface of Phobos, and will help measure Phobos's positions and motions. This supports the Phobos Dynamics Experiment, in which U.S. scientists have a major role. Making these measurements with sufficient precision, over an extended period, can help scientists working on several different problems: the rotation and internal makeup of the moon Phobos itself, the gravitational field and interior of Mars, the relation of Mars and other planets to a precise and distant frame of reference based on quasars, the masses of passing asteroids, and aspects of gravity itself. Using a transponder aboard the lander, the DSN will conduct two-way doppler, ranging, and very long baseline interferometry (VLBI) passes to permit precise calculation of the orbit and its location in space, working with scientists from France and the Soviet Union. In addition to the Dynamics Experiment measurements, the DSN will help collect lander telemetry for other experimenters and has helped provide navigation information on the way to Phobos. Radio contact with the Phobos lander is complicated by the fact that it and its radio antenna will be fixed to the moon, which is rotating and orbiting rapidly. The need to conserve the lander's electric power also limits communication periods. Engineers estimate that one or more Earth stations will be able to communicate with the Phobos lander for only about 17 minutes out of each 7-1/2-hour rotation period. In the framework of the 1987 U.S./USSR space cooperation agreement, a number of U.S. scientists are participating in scientific experiments of the mission. The two orbiters and three landers were launched carrying instruments supporting about 35 experiments in all, and scientists from about a dozen nations are working on them. PHOBOS, DEIMOS AND MARS Phobos is the larger and inner of the two satellites of the planet Mars. Deimos, the other satellite, is one-fifth as massive and orbits more than twice as far from Mars as Phobos. Both satellites are irregular in shape, dark gray in color and rather low in density; both are covered with impact craters. They have nearly circular, equatorial orbits, and their rotations are locked to their orbital motions, so that each always turns the same face to Mars, as the Moon does to Earth. Phobos's orbit is slowly decaying, spiraling in towards Mars, so that Martian tidal forces may overcome the satellite's own gravity and break Phobos up into rings like Saturn's, perhaps within 50 million years. Deimos may, like our Moon, be slowly spiraling outward. Their densities, color and size suggest that Phobos and Deimos may be similar to carbonaceous chondrites, perhaps the most primitive type in the asteroid belt. The Martian moons may be asteroids captured long ago by Mars's gravitational field. Mars is the outermost, coldest, next-to-smallest, least dense and (except for Earth) most explored of the four terrestrial planets of the solar system. Its surface is highly diverse, with impact craters, inactive volcanoes, lava flows, polar caps which change with the seasons, and features suggesting wind and water erosion. Mars has a thin, relatively clear atmosphere, composed mostly of carbon dioxide, with a surface pressure less than one percent of Earth's. From time to time, as in mid-1988, gigantic dust storms rage across its deserts. Mars has the largest known extinct volcano (Olympus Mons), and the largest known canyon (Valles Marineris) in the solar system. Variations in its gravitational field indicate irregularities in density within the planet. The surface composition appears to be dominated by quartz (common sand) and iron-oxide minerals. Water cannot long exist in liquid form (depending on temperature at the low pressure, it would either freeze or evaporate at once) and appears to be rare in any form. The orbital motions of Mars and the Earth interact in such a way that Mars passes close to the Earth, and in opposition relative to the Sun, every 780 days or about 26 months. Because of the eccentricity of Mars's orbit, the distance at opposition varies from more than 60 million miles to less than 37 million miles, as occurred in September 1988. PREVIOUS MISSIONS TO MARS Exploration of Mars with unmanned spacecraft began with the 1964-65 flight of Mariner 4, which sent back some 20 close-up images of the cratered surface, together with atmospheric density measurements and other planetary data, during and after its July 15, 1965 flyby encounter. The eleventh of these images, which showed Moon-like craters, forever ended the romantic myth of Mars as an Earthlike, fully developed but dying planet. Instead it revealed at least a part of Mars's surface to be primordial, little changed since early in solar system history. In August 1969 Mariner 6 and 7 flew past Mars, collecting two series of global images during the approach phase as well as wide- and narrow-angle close-ups, mostly of cratered regions, and data on atmospheric and polar-cap composition and surface temperature. Minimum-energy opportunities to fly to Mars occur about every 26 months; the launch opportunity occurs a few months before, and the corresponding arrival at Mars a few months after, each opposition, the point when Mars is approximately opposite the Sun in our skies. During the 1971 opportunity Mariner 9, the first Mars orbiter, began its global investigation of the planet, while the Soviet Union sent Mars 2 and Mars 3, each consisting of an orbiter and a lander. However, a planet-wide dust storm obscured nearly all the surface for several weeks after the spacecraft arrived, and Mars 2 and 3 obtained very little useful scientific data from orbit or surface. Mariner 9 was able to wait out the storm, and continued operations until late October 1972. It mapped the whole globe, most of it at about 2- to 4-kilometer (approximately 1- to 2- mile) resolution, and obtained images of Phobos and Deimos from as close as 5,600 kilometers (about 3,500 miles). Mariner 9's 12-hour, elliptical orbit had a closest point 1,300 to 1,600 kilometers (about 800 to 1,000 miles) above the surface and was tilted 64 degrees from the equator, permitting global and especially polar coverage, but limiting satellite opportunities. The 7,300 images collected by Mariner 9 revealed the variety of terrain types on Mars, going far beyond the impact craters which dominate the regions observed earlier. The pictures show Deimos and Phobos to be small, irregular and dark, as expected, and marked with many craters. In the 1973 opportunity the USSR sent four more spacecraft, two orbiters and two landers; the Mars 5 orbiter acquired about 70 images comparable to those of Mariner 9, and the Mars 6 lander sent atmospheric descent data and reached the surface. Viking 1 and Viking 2, launched in August and September 1975, entered inclined, near-synchronous elliptical orbits in June and August 1976. Their surface stations landed on Mars on July 20 and September 3 of that year. The two orbiters and two landers supported comprehensive research and observation programs, lasting until April 1980 in the case of Viking Orbiter 2 and November 1982 in the case of Viking Lander 1. The landers completed extensive visual, physical, chemical and biochemical analyses of the surrounding areas and weather, and of materials within reach. The orbiters re-surveyed Mariner 9's territory at higher resolution, with extensive use of color, and observed changes since Mariner 9 in 1972 and within the 1976- 80 Viking survey period. Their orbits were altered at various times after the landings in order to "walk" around the equator, to fly closer to the surface for improved resolution, and to bring Viking Orbiter 1 within about 90 kilometers (55 miles) of Phobos and Viking Orbiter 2 within 25 kilometers (15 miles) of Deimos. The Mariner projects and large parts of the Viking project were managed or carried out for NASA by the Jet Propulsion Laboratory. Project Viking was managed by NASA's Langley Research Center. Scientific data from the Mariner and Viking explorations of Mars were shared with the international scientific community and especially with Soviet space scientists as they undertook the planning and development of the 1988 Phobos mission. This included the latest ephemeris of Phobos, which locates the moon relative to Mars within about 10 kilometers (6 miles), based on Mariner and Viking images. The Phobos project will improve this accuracy tenfold, using new spacecraft images, before attempting rendezvous and landings. Future Mars missions include the U.S. Mars Observer, scheduled for launch in August 1992 and Mars orbital operations from August 1993 through July 1995, and a planned USSR lander mission in the 1994 opportunity. PHOBOS MISSION On July 7 and July 12, 1988, the Soviet Union launched two nearly identical 13,700-pound Phobos spacecraft aboard four-stage Proton launch vehicles from Baikonur Cosmodrome near Tyuratam in the southern part of the USSR. The Phobos spacecraft were scheduled to arrive at Mars on January 25 and 29, 1989, after 480-million-kilometer (300- million-mile) flights taking them two-fifths of the way around the Sun. During the interplanetary cruise phase they were to observe and measure the Sun and the space environment, communicating results to Earth about every five days. In late September, the first spacecraft was found to be out of communication with Earth, apparently the result of a command error. It has not been recovered. The other, duplicating most of the sensors and carrying a lander and the hopper, was put in Mars orbit January 29. The initial Mars orbit, swinging in to 875 kilometers 540 miles) above the surface and back out to about 80,000 kilometers (50,000 miles) every 77 hours, was maintained for about ten days. Then, at intervals of several weeks, giving time for observation and study of Mars and the local environment and careful tracking of Phobos, the spacecraft was to be maneuvered through three more orbits, the last of which is circular, equatorial, and only about 30 kilometers (20 miles) beyond that of the tiny moon. Throughout the orbital phase, the spacecraft will record its scientific and engineering data for transmission to Earth about every three days. From this close circle, armed with precise observations and calculations of the relative positions and motions of the moon and the spacecraft Phobos, controllers will fly the craft down for a contour-following close flyby about 50 meters (approximately 150 feet) from the surface, at about 7 to 15 kilometers per hour (5 to 10 miles per hour). At the end of this 20-minute survey, the Phobos spacecraft will deploy a 110-pound Long-Duration Lander (expected to operate for about a year), and the 112-pound "hopper" (limited by its battery life of a few hours). Then it will return to its 6,000-kilometer (3,700-mile) circular orbit above Mars. The "hopper" is a mobile instrument package which uses spring-loaded legs to jump 20 yards at a time to examine several surface locations. PHOBOS SPACECRAFT Weighing nearly seven tons at launch and spanning about 9 meters (30 feet) when solar panels are unfolded, the Phobos spacecraft is the newest generation of the Soviet planetary series used in previous Mars and Venus missions. The design is built around a large toroid or doughnut shape topped by a cylinder containing most of the electronics, with antennas, solar panels and scientific sensors mounted outside. Much of the initial mass is devoted to the orbital rocket system which propels it into Mars orbit, does subsequent maneuvers, and then is separated. The spacecraft is normally stabilized relative to the Sun and the star Canopus, and is gyro-controlled during maneuvers. Electric power is supplied by solar cells and rechargeable batteries. SCIENTIFIC EXPERIMENTS Eleven European nations, the European Space Agency, the United States and the Soviet Union are participating in 37 experiments as part of the Phobos mission. The experiments are designed to study Phobos, Mars, the Sun and the interplanetary environment. In addition to remote sensing devices such as imaging, spectrometers, radiometers and radar, Phobos will use lasers and ion beams to analyze surface materials. The landers and the "hopper" will perform various on-site analyses; radiation and particle detectors, plasma instruments, and magnetometers will monitor the space environment; and the Dynamics Experiment, in which the U.S. scientists play a major role, will use the lander- to-Earth radio link to examine the motion of Phobos for gravitational effects. NASA/JPL PARTICIPATION AND SUPPORT As part of the U.S./USSR cooperation in solar system exploration under the 1987 U.S./USSR space cooperation agreement, NASA participates in the Phobos mission in a number of ways. A major investigation called the Dynamics Experiment, developed largely by a U.S. scientist, will use precision ranging and very long baseline interferometry (VLBI) with the Phobos lander, together with data from the lander's sun sensor. A team of U.S. scientists will participate in this experiment, which represents the major U.S. involvement in the Phobos mission. To conduct this experiment and provide supplementary support to the other lander experiments, the Deep Space Network, operated for NASA by the Jet Propulsion Laboratory, will conduct more than 200 telemetry, ranging and VLBI passes with the lander during the mission's lifetime. The compatibility of lander communications equipment with the DSN was verified on the ground before launch, and the system was tested in flight as well. Under the same agreement, NASA has named ten U.S. scientists to participate as guest investigators or interdisciplinary investigators in the Phobos science activities; a like number of Soviet scientists will participate in the U.S. Mars Observer mission. NASA and JPL scientists and engineers also support the Phobos mission by providing navigational data and analyses, providing preflight and inflight data analysis to improve knowledge of the ephemeris of the Martian satellite, helping the Soviet scientists and specialists to achieve the Phobos rendezvous and landings. DEEP SPACE NETWORK The NASA/JPL Deep Space Network (DSN) was established nearly 30 years ago, soon after the Jet Propulsion Laboratory became an element of NASA. The network was designed to be, and has become, a general spacecraft tracking facility for all NASA spacecraft missions beyond Earth orbit, and for some Earth satellites as well. NASA's Office of Space Operations is responsible for the tracking and data acquisition for NASA spacecraft, and has delegated DSN implementation and operations to JPL. The DSN participated in the Pioneer, Ranger, Surveyor, Lunar Orbiter, Apollo and Mariner series of flights, supported the Viking Mars orbital and landing operations, and has been a part of the continuing Voyager outer planets mission for more than a decade. International cooperation is a significant activity of the DSN as well, exemplified by support to such missions as Helios, AMPTE, the Vega/Venus balloons and the Halley's Comet investigations conducted by the European Space Agency, the Soviet Union and Japan. The DSN has large tracking antennas situated around the world to assure continuous communication with spacecraft en route to the Moon and beyond. It is the only such sensitive, world- wide facility in existence. Deep-space communication complexes are located in Australia, 40 kilometers (25 miles) southwest of Canberra; in Spain, 60 kilometers (37 miles) west of Madrid; and in the California desert 72 kilometers (45 miles) northeast of Barstow. Each complex includes four large parabolic dish antennas: a 70-meter (230-foot) dish, two 34-meter (111-foot), and a 26-meter (85-foot) antenna. They are equipped with sensitive receivers and precise computer controls, and are capable of sending and receiving signals at a number of frequency bands used for spacecraft. These stations are tied together and to the Network Control Center at JPL in Pasadena and mission controllers in the U.S. and overseas by a NASA ground communications facility of cable, microwave and satellite links. A total of about 1,100 people are employed by NASA, the responsible agencies of Australia and Spain, and their contractors to operate and maintain the DSN 24 hours per day, 365 days per year. DYNAMICS EXPERIMENT Planetary spacecraft carry sophisticated two-way radio equipment to transmit their scientific observations to Earth and receive commands from their mission controllers. These systems also include navigation transponders for measuring the range and velocity between spacecraft and Earth, permitting controllers to calculate precisely where the craft is and where it is going and to change course as needed. This utilitarian system can also function as a huge scientific instrument. Perturbations in the flight path, or in the spacecraft's orbit around a planet, enable scientists to chart the gravitational fields through which it flies. For centuries, astronomers have used perturbations to discover new planets through their influence on known ones, and to weigh them by tracking their satellites. A spacecraft, which can be located and tracked with great precision, makes an excellent probe for this kind of research. A radio astronomy technique called very long baseline interferometry (VLBI) improves the navigation and scientific value of the results by adding precise angular data and linking the positions to a stable reference frame. Using two widely separated radio telescopes linked and calibrated together, scientists count radio wavelengths to measure the difference in the distances from the spacecraft to the two stations; a trigonometric calculation then gives the angle. Repeating the measurement with a quasar (a natural, very distant radio source whose position has been precisely determined), scientists can precisely pin the spacecraft data to an absolute map of space. In the Phobos mission, the lander, anchored to the Martian moon Phobos, will do the probing. Scientists will be able to chart three kinds of motion: that of Phobos around its own center, Phobos's orbital motion around Mars, and the motion of Mars in solar orbit, relative to the motions of the Earth stations. They will measure the libration, or wobbling, in the moon's synchronous rotation as it orbits Mars with one end always pointing down at the planet. For this part of the study, the lander's sun-sensor data will be combined with the radio data. The scientists will continue charting the global gravity field of Mars, work begun by Mariner and Viking. They will also look for tiny perturbations in the planet's orbit caused by close-passing asteroids, to weigh those asteroids. The accumulated data should also provide a test of the theory that the universal gravitational constant is slightly and slowly changing as the universe expands. Finally, they will measure the gradual speeding-up and dropping-down motion of Phobos as it falls toward Mars, a slow and inevitable decay that may take 50 million years. This Phobos Dynamics Experiment is led by Dr. Robert Preston of JPL in collaboration with a team of investigators from JPL, MIT, the French space agency CNES and the Soviet Union. The experiment is supported by the Deep Space Network, whose individual stations will do radio doppler and ranging and receive telemetry from the landers, and pairs of whose ground stations (for example, Madrid, Spain, and Goldstone, California) will make VLBI measurements. The large 70-meter (230-foot) antennas will maintain the links to the Phobos lander. In order to test the system in flight, the Phobos project installed transponders on the Phobos orbiters to simulate lander radio systems, which will not be powered until after landing. This additional weight reduced spacecraft propellant reserves slightly, and in compensation NASA and JPL agreed to provide VLBI and other navigation data support and analysis to the spacecraft in flight, reducing the uncertainty in the Mars orbit-insertion maneuvers and saving fuel. JPL is also helping six other teams in Europe and the USSR to calculate and update the ephemeris of Phobos from Earth-based and spacecraft observations, further assisting the delicate operation of meeting and overflying the tiny moon. At JPL, the Phobos project manager is Dr. James A. Dunne, and the tracking and data system manager is Marvin R. Traxler. CHARACTERISTICS OF MARS, PHOBOS AND DEIMOS Mars Phobos Deimos Av. orbital radius (km) 227 mill 9,400 24,200 (mi) 141 mill 5,800 15,000 Orbital period 687 days 7hr 37m 30hr 18m Rotation period 24hr 37m 7hr 37m 30hr 18m Density (water = 1.0) 3.9 1.9 1.4 Mass, million million tons 600 mill 9 2 Diameter (maximum), km 6800 27 12 Albedo (sunlight reflected) 9-43% 6% 6% Color reddish dark gray dark gray PHOBOS SCIENTIFIC PAYLOAD Orbiter Multichannel CCD Cameras Bulgaria, E. Germany, USSR Low-frequency Radar Sounder USSR Gamma-Ray Spectrometer USSR Neutron Spectrometer* USSR Infrared Spectrometer France, USSR Thermal IR Radiometer France, USSR Infrared Spec/Radiometer USSR Ion-Beam-Aided Analyzer Austria, Finland, France, USSR Laser-Aided Mass Spectrometer Austria, Bulgaria, Czecho- slovakia, E. and W. Germany, Finland, USSR Atmosphere Spectrometer France, USSR Radar Ionosphere Analyzer USSR Ion/Electron Mass Spec Finland, Sweden, USSR Magnetometers (2) E. Germany, USSR Austria, USSR Plasma-Wave Analyzer Czechoslovakia, ESA, Poland, USSR Solar Wind Mass Spectrometer Austria, Hungary, W. Germany, USSR Proton/Alpha Spectrometer Austrua, Hungary, W. Germany, USSR High-E Solar Cosmic-Ray ESA, Hungary, W. Germany, USSR Low-E Solar Cosmic-Ray Hungary, W. Germany, USSR High-E Gamma-Ray Burst France, USSR Low-E Gamma-Ray Burst France, USSR Solar X-Ray/Coronagraph* Czechoslovakia, USSR Solar X-Ray Spectrometer Czechoslovakia, USSR Solar Extreme Ultraviolet* USSR Solar-Constant Photometer ESA, France, Switzerland Lander TV Camera France, USSR Penetrometer Sensors USSR Seismometer USSR X-Ray Fluorescence/Alpha W. Germany, USSR Scattering Spectrometer Celestial Mechanics/Dynamics USA, France, USSR Libration monitor France, USSR "Hopper" X-Ray Fluorescence Spec USSR Magnetometer USSR Penetrometer, Dynamograph, USSR Gravimeter __________________ *Phobos 1 only (apparently no longer operating) U.S. PHOBOS SCIENTISTS Dynamics Experiment: Robert A. Preston, JPL (Principal Investigator) John D. Anderson, JPL John M. Davidson, JPL Ronald W. Hellings, JPL Robert D. Reasenberg, Harvard-Smithsonian Center for Astrophysics Irwin I.Shapiro, Harvard-Smithsonian Center James G. Williams, JPL Charles F. Yoder, JPL Guest Investigators and Interdisciplinary Scientists: William V. Boynton, University of Arizona Dale Cruikshank, Ames Research Center Thomas C. Duxbury, JPL Frazer Fanale, University of Hawaii James W. Head, Brown University Bruce C. Murray, California Institute of Technology Andrew F. Nagy, University of Michigan Norman F. Ness, Bartol Res. Inst., University of Delaware Gary Olhoeft, U. S. Geological Survey Bradford A. Smith, University of Arizona ##### 2-89 JW