Category Soviet Robots in the Solar System

FIRST ON THE MOON, FIRST ON VENUS, AND FIRST ON MARS

The latter hall’ of the 20th Century will forever be known as the time when the human race broke its Earth-bound chains and began to explore the boundless reaches of interplanetary space. The Soviet Union initiated this enterprise with its Earth orbiting satellite ‘Sputnik’, meaning ‘fellow traveler’, in 1957, and shortly thereafter Soviet scientists made the first attempts to send spacecraft to the Moon and to the planets. What followed were 38 years of triumph and tragedy in one of the most cxcitmg adventures in recent human history.

The first pioneers of space flight lived in the first half of the 20th Century. Tsiolkovsky, Tsander and Kondratyuk in Russia, Obcrth in Germany, Goddard in the US, and later Korolev and Glushko in the Soviet Union, von Braun in the US, and Esnault-Pcltcrie in France, all believed that humankind could travel to other planets in the Solar System using new developments in rocket propulsion. These early visionaries established the notion that it was in fact possible to fly to the planets, but their dreams became reality only after the intervention of World War II created the technological catalyst for accomplishing deep space propulsion. By the end of the 20th Century, humans had set foot on the Moon and had sent robotic spacecraft to most of the planets, as well as to some comets and asteroids.

Most of the history of space exploration in the 20th Century is characterized by intense competition for dominance between the USSR and USA. At the dawn of the ‘space age’ the two nations were developing TCBMs to drop nuclear warheads on each other’s cities. Europe and Japan were preoccupied with rebuilding after the devastation of World War II. The USSR launched the first artificial satellite, Sputnik on October 4, 1957, using a modified version of their first operational ICBM. The first human space flight was also Soviet; Yuri Gagarin’s orbital flight of April 12, 1961. These events shocked Americans, who had difficulty imagining how they could not have been first into space. The Americans also immediately recognized the implications of these events for their national defense. The USA mobilized a massive space development program of its own in 1958, and on May 25, 1961 President

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies >

and Discoveries, Springer Praxis Books 1, DOl 10.1007/978-1-4419-7898-1 1,

© Springer Science 4-Business Media, LLC 2011 4 Space race

Kennedy formulated a national goal to land a man on the Moon before the decade was оul implicitly meaning that this man should be American, not Russian.

The Soviet Union was slow to respond to the challenge, but in 1964 initiated a national program to send a cosmonaut to the Moon ahead of the Americans. The Americans won the ‘race’ on July 20, 1969. with Apollo 1 Us touchdown on the Sea of Tranquility. The Soviet program stalled after a series of failures of the N-l heavy rocket, their equivalent to the American Saturn V, but the USSR produced dramatic results with robotic lunar rover and sample return missions through 1976. The Americans shut down their Apollo lunar program in 1972 after six successful flights to the lunar surface.

The space race’ was a Cold War phenomenon, but just like the international air races in the first half of the 20th Century, the space race resulted in an explosion of research and technological development. While competition in space exploration between the USSR and the USA originally focused principally on flying humans to the Moon, there w as also competition to fly robotic spacecraft to the Moon and beyond, and this yielded remarkable feats of engineering and enormous scientific progress in understanding our Solar System and technological progress for Earth applications. If it had not been for the political imperatives of the Cold War, it is highly unlikely that the national investments required for this progress would have been made. After the fall of the Soviet Union in 1991, the Russian robotic space exploration program withered aw’ay.

This book provides the technical details of the Soviet Union’s robotic space exploration missions, beginning with the attempted launch of a lunar impaetor on September 23, 1958. and concluding with the final launch in the Russian national scientific space program in the 20th Century, the Mars-96 mission, on November 16. 1996. Each flight campaign is placed into the political and historical context in which the entire endeavor occurred, chronicling the boldness of the program, the daring spirit of its creators, the genius of its implementation, and the successes and in some cases the tragic failures in its execution. The book is in two parts. Part I describes the pieces that must be combined to make up a space program: the key players who make things happen; the institutions that design, build and operate the hardware; the rockets that offer access to space; and the spacecraft that carry out the enterprise. Part II is a chronological account of how the pieces are put together to undertake space flight and mission campaigns. Each chapter covers a particular period, usually several years, when specific mission campaigns were undertaken during launch windows determined by celestial mechanics. Each chapter in Part 11 gives a short overview of the flight missions that occurred during the time period and the political and historical context for the flight mission campaigns, including what the Americans were doing at the time. The bulk of each chapter is devoted to the scientific and engineering details of each flight campaign, and in each case the spacecraft and payloads are described in as much technical detail as is available at the time of writing this book, the progress of the flight is described, and a synopsis of the scientific results is given.

The Soviet robotic space program was dramatic, and was driven by a thirst for technological achievement and a desire for international recognition and respect. It achieved all these things. Soviet robotic spacecraft were first on the Moon, first on Venus, and first on Mars.

In early 1958 Korolev began planning for planetary missions. His original intention w as to use the 8K73, a version of the 8K72 with a more capable third stage. During that summer OKB-1 began w ork on spacecraft for launch to Venus in June 1959 and Mars in September 1960. However, the 8K73 project and the 1959 Venus mission were abandoned w’hen Glushko’s engines for the new’ third stage had development problems. Korolev turned to Kosberg again and decided to adapt the second stage of the new’ silo-based ICBM under development, the R-9A. also know n as the 8K75. as the third stage for his planetary launcher. Kosberg fitted the stage with larger tanks to sustain the longer engine burn times. In the meantime, the R-7 w as still in its final development phases in preparation for operational deployment.

During 1958 an improved version of the basic tw o-stage R-7. the R-7A or 8K74.

was being developed for easier operational servicing and greater performance. The 8K74 had all-inertial guidance with the original radio guidance system retained only as a backup, improved engines for reliability, redesigned verniers for simpler control and increased performance, a new ignition system, and some portions of the engines were moved nearer to service hatches. The first launch of the 8K74 on December 24. 1959, was a success. The 8K74 became the basic two-stage booster for generations of launchers to the present day. The only 8K71-based vehicles used after this 8K74 test were two 8K72 Luna launches on April 12 and 18. 1960. both of which failed.

In all this rush of rocket development in 1958 59, Keldysh*s mathematicians had determined that continuous burn of all stages was an inefficient use of energy to reach interplanetary velocities. Continuous burn also required precise timing without margin for launch delays. Instead they recommended a scheme in which the booster placed an escape stage into low Earth orbit. This would be ignited when the orbital phasing was optimum for launch towards the Moon or planetary target, and once on course it would release its payload.

Abandoning the three-stage approach for lunar and planetary launches, in early 1959 Korolev began w ork on a four-stage approach. The airframe of the 8K74 core vehicle w as strengthened to support the mass of the new upper stages, modifications w ere made to the operating pressures and burn programs to increase the thrust of the core vehicle, a stronger open truss was provided between the suStainer and third stage, and new guidance and control systems were supplied for the upper stages. The К os berg third stage was modified further with an increased propellant load and an upgraded 8D715K four-chamber engine and designated Block I. The 8K74 III two – stage core vehicle w ith the new Block I third stage and a first burn by a new fourth stage. Block L. built by OKB-1. would put the Block L and spacecraft combination in Earth orbit. The Block L was made res tart able, so that its second burn would put the spacecraft on an interplanetary trajectory. It would be capable of sending 1,600 kg to the Moon or 1,200 kg to either Venus or Mars. This four-stage 8K78 is known as the ‘Molniya* launcher. A prototype with a dummy fourth stage w7as successfully tested on January 20. 1960, with a second successful test 10 days later. The Block L completed its ground tests in the summer of 1960. and Korolev rushed preparations for three Mars launches on the first tests of this new launcher. 1 he spacecraft were also built in a great rush before the launch window7 closed in mid-October. Only two rockets made it to the launch pad on time.

The first flight test of the complete 8K78 occurred on October 10, 1960, w ith a 1M Mars spacecraft at the top of the stack. The spacecraft had to be stripped down in order to provide sufficient mass for rocket test instrumentation. The launch failed when resonant vibrations in the upper stages damaged the avionics during third stage burn and the rocket veered off course. A second attempt on October 14 also failed when the third stage engine did not ignite because a LOX leak on the pad had frozen kerosene in the fuel lines. The first test of the Block L did not come until the third flight on Kebruary 4, 1961, which attempted to launch a 1 VA Venus spacecraft. The first three stages performed perfectly, but the Block L was stranded in Earth orbit by a primary powder failure.

The Block L stage was a challenging design because it had to coast unpowered for

almost 2 hours in Earth orbit without losing volatile propellant, orient itself to the proper firing attitude at a programmed time, and ignite its engine in a zero-G state. The engine used a more efficient ‘closed-cycle’ technology which US rocket makers deemed unworkable, and used gimbals for yaw and pitch control and a pair of small verniers for roll control. The stage used, a cold gas attitude control system and solid rockets to provide ullage control before engine ignition in zero-G. The challenges of perfecting this planetary injection stage proved difficult. The Block L succeeded on its second opportunity on February 12, I960, deploying Venera 1. But it failed many times thereafter, including the final planetary mission to use the Molniya launcher on March 31, 1972, when the Block L stage failed to put another spacecraft intended for Venus on an escape trajectory.

In 1962 an extended shroud was introduced to accommodate the next generation

2MV Mars and Venus spacecraft and the sustainer engines were upgraded. In 1964 a new version of the 8K78 was introduced, with improved versions of Glushko’s RD – 107/8 engines and an improved engine in the Block L fourth stage. This vehicle was designated 8K.78M, and was known in the West variously as SL-6 and А-2-е. Tt was first used for the test launch of a 3MV Venera spacecraft on March 19, 1964, then used consistently for Venus missions until the introduction of the Proton-launched spacecraft in 1975. Mars launches used the 8K78 until switching to the Proton in 1969. The Ye-6 Luna probes used both the 8K78 and 8K78M vehicles until Luna 9 on January 31, 1966, when the SK78M came into exclusive use. A variant of this vehicle was created for the Luna soft landing missions, in which the avionics were deleted from the upper stages to save mass and the Ye-6 spacecraft controlled the functioning of the third and fourth stages. This vehicle was designated with a / Ye-6 suffix. The 8K78 vehicle was completely replaced by the 8K78M after December 1965. ‘

The 8K78M received another upgrade in 1966-67 when the core and strap-ons were replaced by those of the three-stage LSoyuz’ version used in the manned space program. In 1965, responsibility lor the Block L stage was transferred from OKB-1 to NPO-Lavochkin, which introduced improvements in 1968 including upgraded avionics and a new third stage interface and fairing design. Lavochkin produced two versions of this new Block L, one for lunar and planetary missions and the other to place ‘Molniya’ communications satellites into highly elliptical Earth orbits. Further improvements to the 8K78M were made in 1974 and again in 1980. In its various forms the Molniya launcher was the workhorse for the lunar and planetary program in the 1960s and early 1970s, successfully deploying the Luna 4 to 14 missions from 1963-1968, Mars missions from 1960-1965 including Mars 1, and Venera 1 to 8 from 1961-1972. The versatility of the ‘Semyorka’ rocket is demonstrated by its continued

use up to the present day, particularly in its three-stage Soyuz* variant. It resumed its utility for planetary launches on June 2, 2003, with the successful launch of the Mars Express spacecraft for the European Space Agency using a Soyuz fitted with the new Fregal fourth stage.

Of the six Ye-1 spacecraft launched, only two survived the process. A seventh was returned to the barn after its launcher failed to lift off. Aware from press reports that the Americans were to try for the Moon on August 17, Korolev managed with great effort to prepare a vehicle for the same day. There were a number of malfunctions during pre-launch preparations, but he knew that his flight path to the Moon was shorter than the Americans so he waited before risking a launch to see if the Florida launch succeeded. When the US rocket blew up after only 77 seconds of flight, he stood down in order to perform more careful preparations and additional testing. How ever, the launch on September 23 failed when the strap-on boosters of the first stage developed resonant longitudinal vibrations in the second minute of flight. The various stages separated at 93 seconds, fell back and exploded. Reacting to pressure to beat the US to the Moon, Korolev is said to have lost his temper and replied "Do you think only American rockets explode? ‘ Indeed not, and he could not know that the Soviet lunar program w ould be plagued w ith rocket failures for years to come.

The second American attempt at the Moon was scheduled for October 11, amid a flurry of press coverage. Korolev w’as again ready that same day. The wdiole world w as aware of events in Florida, but only a few in the USSR were aw are of Korolev with his linger on the launch button at Baikonur, ready to beat the Americans to the Moon using a faster trajectory. News of the US launch was relayed to Korolev. But the third stage failed, preventing Pioneer 1 from reaching the Moon. Sitting now in the catbird seat, Korolev proceeded with his launch. Later the same day, the second Luna 8K72 launcher blew up 104 seconds into its flight due to the same vibrations wiiich had destroyed the first vehicle.

The two failures in row w’ere demoralizing. It w’as discovered from analyzing the w reckage that the additional mass of the third stage was creating resonant vibration in the basic R-7 booster wThich had not been present before. The problem was solved with minor design changes, but it would take two months and Korolev had to watch over his shoulders as America made a third attempt on November 8. but this too fell short.

The third launch on December 4 failed yet again, this time caused by a different problem. The rocket sailed through the period wdien vibrations broke up the previous two rockets, but after 4 minutes of flight the thrust of the second stage engine began to diminish and then the engine shut dow n due to a gear box failure in the hydrogen peroxide turbine pump. Frustrated, but relieved by the fourth American failure two days later on December 6, Korolev prepared for another

attempt. The fourth launch was a success and on January 2, 1959, put Ye-1 No.4 on a trajectory to the Moon. The spent third stage released a 1 kg cloud of sodium gas on January 3, some 113,000 km from Earth, producing a glowing orange trail visible over the Indian Ocean with the brightness of a sixth-magnitude star. The experiment provided data on the behavior of ionized gas in near-Earth space, and was used for tracking. Luna 1 (as the probe was later named) missed its target and passed within 5,965 km of the lunar surface on January 4 after 34 hours of flight. The miss was caused by a late second-stage shutdown command from the ground radio guidance. Nevertheless, Luna 1 holds three cosmic ‘firsts’, being the first spacecraft to achieve escape velocity, the first spacecraft to fly close by the Moon, and the first spacecraft to enter an independent heliocentric orbit. Contact was lost on January 5, after 62 hours of flight, possibly when its battery drained.

Luna 1 was a major success and feather in the cap of Soviet space exploration, but it failed to impact the Moon as planned and the program goal was not yet fulfilled. After further problems with the R-7 in the beginning of 1959, another spacecraft was readied that incorporated modifications to the magnetometer, Geiger counters and micrometeoroid detectors resulting from the successful m-flight measurements of both Luna 1 in January 1959 and the American Pioneer 4 lunar flyby in March. The modifications earned it a new Ye-IA designation. The first attempt to launch a fifth spacecraft, Yc-IA No.5, was aborted on June 16, 1959, when it was discovered that the third stage tank had been filled with the standard kerosene instead of the higher density type required for this mission. The tanks were emptied, refilled with the proper fuel, and a second launch attempt made two days later. All went awry when the launch vehicle deviated from the planned trajectory after 153 seconds. One of the gyroscopes in the inertial guidance system had failed, and the launcher was destroyed by ground command.

An aborted launch of a sixth spacecraft occurred on September 9, 1959, when the core sustainer engine failed to reach full thrust upon ignition. ‘Hie launcher remained on its mount, and all the engines were shut down after 20 seconds. The rocket was replaced by a backup. The spacecraft on the aborted rocket was probably the Ye-1A Ко.6 model. Three days later Luna 2 (Ye-IA Ко.7) was successfully launched on a lunar trajectory. On 13 September, at a distance of 156,000 km, the spent third stage released its sodium cloud. Luna 2 impacted the Moon at 23:02:23 UT September 14. after 33.5 hours of flight, near the Autolycus crater in the Marsh of Decay region at about 29. Г N 0.0 E. Some 30 minutes later, the third stage of the Luna launcher also impacted the Moon.

Luna 2 was the first spacecraft to impact another celestial body. The Soviets had announced their transmission frequencies and Jodrcll Bank in hngland tracked the spacecraft through its the final plunge to silence. There had been some claims in the West that Luna 1 was a fraud, but Sir Bernard Lovell’s tracking and radio recordings provided all the proof needed that Luna 2 had hit the Moon. Nikita Khrushchev celebrated the achievement by presenting President Eisenhower with duplicates of the Soviet emblems that had been carried to the Moon at a United Nations meeting in Kew York on September 15, 1959.

Results:

Luna 1 was the first spacecraft to reach the vicinity of the Moon. The measurements obtained provided new data on the Earth’s radiation belt, and discovered the solar wind – a thin, energetic ioni/cd plasma flowing outward from the Sun past the Earth and Moon. It established that the micrometeoroid flux between Earth and Moon was small, and placed an upper limit on the strength of any magnetic field that the Moon may possess at no more than 1/10.000th that of Earth.

Luna 2 was the first spacecraft to impact on the Moon. It verified at much closer distance that the Moon had no appreciable magnetic field, and found no evidence of radiation belts around the Moon.

Campaign objectives:

By the end of 1965 the Soviets had failed in a total of sixteen launches to Venus and Mars. Ten of these failed attempts were aimed at Venus, including the most recent Venera 2 and 3 missions that had come so close to achieving their goals. Adding to the frustration was the fact that by this time the US had succeeded with close flybys at Venus in 1962 and at Mars in 1964. Nevertheless, the Soviets were encouraged by their near successes, and were determined to push on. Realizing that the US was to attempt another Venus flyby mission in 1967. the Soviets wanted to outdo them with two missions to pierce the cloudy veil of the planet and obtain new information on its mysterious atmosphere and surface.

After Venera 2 and 3 the robotic planetary program was transferred from OKB-1 to NPO-Lavochkin. Beginning in April 1965 Babakin decided not to send any more llyby missions to Venus after the 1965 campaign and Lavochkin began to revise the 3MV spacecraft for the 1967 window for this planet, concentrating heavily on entry and landing. Working from 3MV blueprints supplied by OKB-1 and insight drawn from the Venera 2 and 3 experience. Babakin’s engineers devised improvements to the thermal control and other systems. Lavochkin did more ground testing and built two new test facilities, one a thermal vacuum chamber completed in January 1967 to test the spacecraft under simulated flight conditions and the other a centrifuge rated at 500 G to test the entry and descent system. The first test of an entry probe in this chamber at the 350-450 G load expected for high angle Venus entries near 11 krn/s destroyed its internal components. As the earlier descent capsules would certainly not have worked, the design had to be modified. This revitalized effort was rewarded immediately with the USSR’s first truly successful planetary mission in 8 years of trying, with Venera 4 yielding in-situ data on the atmosphere of Venus. It began a new and much more fruitful era in the Soviet investigation of this planet.

Spacecraft:

Carney spacecraft:

These spacecraft were the first 3MV for Venera missions built by NPO-Lavochkin which, in particular, greatly improved the thermal control system that had caused so much trouble with Venera 2 and 3. The hemispherical fluid radiators on the ends of the solar panels were deleted and a new system of heat transfer pipes located behind the parabolic antenna, which itself served as a radiator since it faced in the opposite direction to the solar panels. Liquid coolant was abandoned in favor of gas coolant. The communication system was also improved and the omnidirectional antenna was replaced by low gain spiral cone antennas mounted on booms connected to the solar panels and angled in flight to keep Earth in the radiation pattern. As previously, the spacecraft had to be turned to aim its high gain antenna at Earth, but this was only during scheduled communications sessions and operations at Venus.

Like its predecessors. Venera 4 w? as 3.5 meters tall, the solar panels had a span of 4 meters and the parabolic high gain antenna w as 2.3 meters in diameter. The panels measured 2.5 square meters but. as previously, were sparsely populated with cells. The noticeable difference between Venera 4 and its predecessors in the 3MV series were the change in the solar panels to a more rectangular shape and the absence of the hemispherical radiators.

Entry vehicle:

For the 1967 mission the entry capsule was strengthened to resist stresses as high as 350 G and given an internal damper to reduce shock effects during entry and landing. At 1 meter in diameter it was 10 cm larger than the previous probes and nearly spherical with an ablative surface and a covered opening in the rear hemisphere for deployment of the parachute and antennas. It was the first of a series of entry probes which would be progressively better suited to survive the descent down to the surface. The internal mass distribution was bottom heavy to ensure the proper pointing on entry and aerodynamic stability during the descent. It was pre­cooled to -10 C by a system in the main module prior to separation, and operated a re-circulating fan thereafter. The capsule was intended to transmit atmospheric data

and radar data on descent, survive the impact and make measurements on the surface. The 28 amp-hour battery, which was rechargeable by the spacecraft during the cruise, could sustain 100 minutes of independent operation. The capsule design pressure was 10 bar with a margin up to about 18 bar, and the maximum survivable temperature for the parachute was 400°C.

The Venera probes were targeted to the center of the planetary disk as seen from Earth for optimum communications directly back to home. A helical antenna on top of the descending capsule was used to direct a radiation pattern to the zenith, and the telemetry was sent at 1 bit/s on 922,8 MHz using a pair of redundant transmitters. Measurements were sent back every 48 seconds. If the capsule w’ere to splash down in an ocean, which few people believed was likely, it would float and a ‘sugar seal’ would release a semaphore signal to signify this fact.

Figure 10.15 (left) show’s the entry vehicle without its upper insulation layers. The two ports arc for testing the insulation system on this engineering model. Inside the thick, porous and lightweight ablative material is ihe descent capsule itself shown in Figure 10.15 (right). Hanging out over the side are the radio altimeter antennas that spring out when the parachute deploys. In accordance with international regulations, the capsule was sterilized prior to launch.

Five levels of redundancy w’ere provided to ensure separation from the spacecraft. First by direct command from Earth, second by the on board sequencer, third by the triggering of a G switch on atmospheric entry, fourth by a sensor activated if Earth communications were interrupted by reorientation on entry and, as a last resort, the bands attaching the capsule to the spacecraft would burn through during initial entry.

Launch mass: 1,106 kg

Entry vehicle mass: 383 kg

Payload:

Carrier spacecraft:

1. Triaxial fluxgatc magnetometer

2. Solar wind charged particle detector

3. Lyman-alpha and atomic oxygen photometers

4. Cosmic ray gas discharge and solid state detectors

It had the same instruments as the Venera 2 and 3 cruise modules, except that the cosmic ray instrument included a second gas discharge counter of a different type.

Descent I landing capsule:

1. Temperature, pressure and density sensors

2. Atmospheric chemical gas analyzers

3. Radio altimeter

4. Doppler experiment

The temperature, pressure and density sensors were the same as on Venera 3. The gas analyzers used eleven cells to measure carbon dioxide, molecular nitrogen.

molecular oxygen and water vapor. The composition was identified by how the atmosphere reacted with the material in each cell, such as by the electrical conductivity of chemically absorbing surfaces; or by reactive heated filaments; or by how the internal pressure varied with specific absorptive materials. The experiment was to take a set of readings at parachute deployment and then again 347 seconds later. The instrument wras the same as flown on Venera 3 but included a hydrometer Гог water vapor measurement. A radio altimeter was carried for the first time to obtain absolute altitudes and confirm landing on the surface. The system w:as built by the Research Institute for Space Device Engineering and adapted from one used in aircraft. To conserve bandwidth, it did not issue continuous data, but only a semaphore to indicate falling through the altitude of 26 km. The Doppler experiment required no hardware on the capsule, utilizing the frequency shift of the carrier wave of the transmitter to determine the line of sight velocity of the probe as it descended through the atmosphere.

Some of the instruments carried by previous probes had to be deleted in order to release mass for the radio altimeter and the structural strengthening. The gamma-ray instrument, wave motion sensor, and photometer were sacrificed. But, as always, it carried a medallion with the coat of arms of the USSR and a bas relief of Lenin.

Mission description:

The first spacecraft was launched successfully towards Venus on June 12. 1967, and became Venera 4. The second was stranded in parking orbit on June 17, when the fourth stage did not ignite because the turbopump had not been pre-cooled. It was named Cosmos 167 by the Soviets and re-entered 8 days later. Venera 4 performed well during cruise, reorienting itself every few days to point its high gain antenna at Earth for a communication session. A midcourse correction was made on July 29 at a range of 12 million km from Earth. It arrived at Venus on October 18 and released the entry capsule at 04:34 IJT, at which time it was 44,800 km over the night side. The carrier spacecraft sent measurements on the upper atmosphere and ionosphere until it broke up in the atmosphere. The capsule entered the atmosphere at 10.7 kiu/s and slowed through a peak deceleration of 350 G. At a pressure level of 0.6 bar and a speed of 300 m s it shed the rear cover and deployed the 2.5 square meter drogue parachute. Several seconds later it deployed the 55 square meter main parachute and radio altimeter antennas. The instruments were turned on at 55 km altitude, at w hich time the rate of descent was 10 m/s. The mechanical commutator interrogated each instrument in turn and fed the data to the transmitter. It transmitted for 93 minutes on its parachute descent before falling silent. It reached the surface at 19 N 38 E, in darkness near the morning tenninator. It was 4:40 Venus solar time and the solar zenith angle was 110 degrees. Including three intended test flights, this was the first successful Soviet planetary mission after twenty attempts, and the first successful entry probe by either spacefaring nation.

Jodrell Bank reported receiving signals from the surface, not realizing that these had been sent during the descent. Thinking the capsule had reached the surface in an

operational slate, the Soviets reported that it had landed. But it slowly became clear that this could not be the case. The data from Mariner 5, which flew by Venus a day after Venera 4 arrived, indicated that the surface temperature was much higher than the final measurement reported by the entry probe. A series of meetings by Soviet and American scientists conducted over the next 2 years decided that the probe had succumbed to the increasingly hostile environment and had been disabled while still far above the ground. Nevertheless, as the first mission to transmit data from within a planetary atmosphere it achieved a major scientific milestone. The data return was significant and demonstrated just how hostile was the environment of Venus. It was evident that future probes would have to be further strengthened.

Results:

During its descent the Venera 4 entry probe returned more than 23 sets of readings by the atmospheric structure experiment. They began at an altitude of 55 km, and the atmospheric temperature was measured over the entire 93 minute descent. The initial temperature was 33nC and it increased to 262nC. The initial pressure reading was 0.75 bar, and the instrument reached its limit of 7.3 bar long before the probe ceased to transmit. Using atmospheric models constructed from the data at the time, it was concluded that the signal was lost at an altitude of 24 km. Atmospheric density
was obtained by plugging the temperature and pressure data into the hydrostatic equation and the result tested against the parachute descent characteristics. Doppler data (i. e. changes in received master oscillator frequency) provided altitude profiles of wind speed and direction, both horizontal and vertical, but the measurement errors were large.

The atmospheric composition experiment showed the atmosphere to be composed mainly of carbon dioxide:

carbon dioxide molecular nitrogen molecular oxygen water vapor

The percentage of carbon dioxide was initially disputed because the expectation was that at least 50% of the atmosphere would be molecular nitrogen, and American scientists were skeptical. But later missions would prove Venera 4 correct. The arid nature of the atmosphere was also unexpected. The model of Venus as a watery world had to be completely scrapped.

The aircraft-derived radio altimeter was designed to send a signal semaphore at an altitude of 26 km, but it had not been adequately adapted for the Venus mission and actually sent its signal at twice that altitude, 52 km. This was a principal cause of the confusion over whether Venera 4 had reached the surface or not. Atmospheric data and Doppler measurements showed that the probe had descended through about 28 km during transmission and the altimeter semaphore indicated that the top level was 26 km. The last measured temperature of 262 C and the derived pressure of 18 bar were about what was expected at the surface at the time. However, measurements of the planet’s microwave brightness made by terrestrial radio telescopes had indicated values of about 325 C. The chemical analysis by Venera 4 showing the dominance of carbon dioxide required a reanalysis of the radio-telescope microwave brightness based on atmospheric models with less carbon dioxide. A new analysis in 1967 explained some of the unusual features of the microwave spectrum of Venus as due to carbon dioxide, and resulted in surface conditions of about 427 C and 75 bar that were inconsistent with the Venera 4 probe having reached the surface. Atmospheric models based on Mariner 5 data also showed far higher temperatures and pressures at the surface. One suggestion was that Venera 4 had landed on a large mountain, but Carl Sagan pointed out that radar studies of the planet had found no such large edifice. Extrapolation of the Venera 4 atmospheric profile indicated conditions at the surface at the impact site to be 500°C and 75 bar. Eventually the data wns reconciled by Avduevskv, Marov, and Rozhdestvensky (1969) using an adiabatic model of the Venusian atmosphere which confirmed loss of signal at 18 + 2.5 bar at an altitude of about 24 km and extrapolated conditions at the surface as 442 C and 90 bar.

The signal ceased near the pressure limit of the capsule, but it is possible that the probe exhausted its battery near the 18 bar level after 93 minutes of operation. In any case the capsule would have been crushed and thereafter the parachute would have burned, leaving the capsule to free fall to the surface.

Prior to breaking up, the main spacecraft provided the first in-situ measure­
ments of the close-in magnetic field, thermosphere, ionosphere, and solar wind interaction. In 1962 Mariner 2 had flown past Venus at 34,773 km. which was too great a range to detect a magnetic field or magnetospheric signature. Venera 4 found no intrinsic planetary magnetic Held. The low fields detected were due to interaction of the solar wind with the ionosphere. No radiation belts were found, and an extended corona of atomic hydrogen was discovered reaching 10,000 km into space from the planet.

TIMELINE: MAR 1972-DEC 1973

The year 1972 opened with the last launch of a 3MV spacecraft, Venera 8, marking the final use of the Molniya launcher for a Soviet lunar or planetary mission. Using Venera 7’s measurement of the temperature at ihe surface, and an inferred pressure, the over-engineered descent capsule was simplified to enable Venera 8 to carry more instruments. It was dispatched on March 27 and the lander operated successfully on the surface of Venus. Two other significant closeouts were in 1972, the launch of the fourth N-l rocket in November whose failure led to that project being canceled, and the final Apollo landing in December.

The second and final robotic lunar rover, Lunokhod 2, was delivered to the Moon by the Luna 21 mission in January 1973. Apart from this, the year 1973 witnessed perhaps the most frustrating campaign in the history of robotic planetary flight. The Soviets were acutely aware of US plans to launch sophisticated orbiter/landers to Mars in 1975. Encouraged by the near-success of the Mars 3 lander, they devised an audacious campaign for 1973. This opportunity was less favorable than that of 1971, which precluded sending orbiter/landers, so instead they launched four spacecraft in July and August: Mars 4 and 5 were orbiters, and Mars 6 and 7 carried landers to be released during flybys. During the development of these spacecraft, the Soviets had incorporated a new transistor into many spacecraft systems. These were discovered before launch to be faulty, with limited lifetimes due to technological “innovations’’ in their manufacture. They could not be trusted to last for the duration of the flight to Mars, yet they could not be replaced in time to achieve the launch window. It was a terrible dilemma. Rather than stand down and wait for the next Mars opportunity in 1975, when the US missions would be launched, the Soviets decided to proceed and hope that at least one of the landers would succeed. But the transistor lifetime tests proved to be accurate, and there were failures in all four spacecraft which ultimately resulted in disaster for this campaign.

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer Praxis Hooks 1, DOl 10.1007/978-1-4419-7898-1 13,

© Springer Science+Business Media, LLC 2011

Launch date

Crippled by ailing systems. Mars 4 was unable to enter Mars orbit and sailed past the planet. Mars 5 achieved orbit, but fell silent after only 22 orbits. After an early failure in its telemetry system, the Mars 6 flyby spacecraft had to be commanded in the blind. It miraculously made automated midcourse maneuvers, optical navigation on approaching Mars, and dispatched its entry system on the correct trajectory. The entry system entered the atmosphere, descended by parachute, and sent back mostly garbled data on its compromised communications system. Contact was lost when the lander was released near the surface. The Mars 7 flyby spacecraft released its entry system as planned, but this failed to function and missed the planet. The lack of any real results from this massive campaign was not explained until after the collapse of the USSR.

Meanwhile the US launched Pioneer 10 on March 2, 1972, for the first mission to the outer Solar System. It went on to make a flyby of Jupiter, the largest of planets. In November 1973 Mariner 10 was launched lo use a flyby of Venus for a gravily – assist to reach Mercury. *And Pioneer 11, launched in April 1973, went on to use this same technique at Jupiter lo reach Saturn.

The Mars-96 mission was designed to use an orbiter, two small soft landers, and two penetrators to undertake a comprehensive investigation of the current state and past evolution of Mars by studying physical and chemical processes in the atmosphere, on the surface, and in the interior.

The scientific objectives of the orbiter included obtaining high resolution mapping and spectral imagery of the surface to study its geology, mineralogy and topography, to investigate the gravity field and crustal structure, and to monitor the climate. The spacecraft was also equipped to study the magnetic field, plasma characteristics, and magnetospheric structure. And it had instruments for astrophysieal investigations of gamma-ray bursts, and both stellar and solar oscillations. The penetrators were to obtain images of the surface, undertake meteorological measurements, examine the physical, chemical, magnetic, and mechanical properties of the near-surface regolith. measure the water content of the soil, and measure seismic activity and the heat flow7 from the interior of the planet through the crust. The small landers were to study the vertical structure of the atmosphere and obtain images during the descent to assist in interpreting images taken on the surface, measure elemental, magnetic and oxidant composition of the soil, measure seismic activity, and monitor the local weather for its diurnal, seasonal, and annual variability.

The delays and problems w ith development had been extremely frustrating for the international participants, whose own budgets and schedules were heavily impacted. The failure of the launch and breakup of the spacecraft over the west coast of South America was the final straw for a Russian planetary exploration program that had been struggling against diminishing resources since the Phobos failures in 1988 1989 and the demise of the Soviet bmpire in 1991.

The failures of the Phobos and Mars-96 missions were a heavy loss for planetary exploration. They w’ere ambitious and complex missions aimed at comprehensively studying Mars and the larger of its two moons. They had more engineering systems, more observation platforms, more scientific instrumentation, and more subsidiary
vehicles than any other missions in the history of planetary exploration. The array of measurements they were to have made was simply enormous. If these missions had been successful, the knowledge produced would have been astounding. They were also very international, complex, and expensive. They are missions the like of which will not be experienced in planetary exploration for a long time to come.

Spacecraft:

Orbiter:

The Mars-96 orbiter was a З-axis stabilized spacecraft based on the Phobos design. A pressurized toroid at the base held the computer and most of the avionics, thermal regulation, communications, batteries and electronics for scientific instruments. The equipment tower was replaced with a flat deck on which equipment and instruments were mounted, including the solar panels and the entry systems for the two landers. The solar panels were larger, and extended out from opposite sides of the deck. They also carried low gain antennas and attitude control nozzles. Many subsystems and scientific apparatus were on the toroid below7 the deck level, including a pair of scan platforms for accurate and stable pointing of cameras and spectrometers. The high gain dish antenna extended off one side of the toroid, oriented perpendicular to the solar panels, and the medium gain antenna w7as on the opposite side. In this case the high gain was not steerable, and provided a communications rate of 130 kbits/s. The thermal control radiators, navigation and Sun and star sensors for the attitude control system were attached to the toroid, including the onboard propulsion system with its propellant tanks and thrusters, as for the Phobos spacecraft. The separable ADU propulsion system (now7 named the Fregat stage) was attached underneath, as before. The two penetrators were mounted on the ADU propellant tanks. The computers were more advanced and supplied by the Europeans who did not trust the Phobos computers after their poor performance. The orbiter carried more than two dozen instruments in addition to the landers and penetrators. Owing to the massive weight of the spacecraft, the Proton could not quite provide sufficient energy for the escape maneuver. After the Block D had released the spacecraft, the Fregat would fire to provide the final increment. The Fregat would perform the midcourse corrections, orbit insertion at Mars, and in-orbit maneuvers before being jettisoned.

Scan platforms were fairly new7 to Russian spacecraft. The 220.7 kg TPS 3-axis platform had its own computer control system, memory, thermal control, navigation camera, and a 53.5 kg payload of remote sensing instruments. The developers had difficulty achieving the stringent pointing and stability requirements, and when the Russians suggested deleting the platform and mounting the instruments on the body of the spacecraft, w hich would have severely limited the science objectives, German engineers were brought in to help to resolve the problems. The 74.2 kg PAIS 2-axis scan platform was simpler, and it carried instruments that had less stringent pointing requirements. The orbiter was to have deployed its landers on approach and then
performed a deflection maneuver to reach the insertion point, whereupon it would put itself into an elliptical orbit. This would be shaped over the first month using several maneuvers to achieve an orbit in which the spacecraft would make four revolutions around the planet while Mars rotated seven times on its axis, because such orbits arc generally quite stable. Once it had achieved an orbit with a periapsis of 300 km and a period of 43.09 hours, it would deploy the penelrators.

The Mars-96 spacecraft was 3.5 meters tall and 2,7 meters wide; 11.5 meters wide with its solar panels deployed.

6,824 kg 2,614 kg 176 kg (2)

241 kg (2)

283 kg (for landers and penetrators) 490 kg

Fuel: 2,832 kg

Hydrazine: 188 kg

Landers:

The two landers or ‘small stations’ were similar to those used on the M-71 and M-73 missions but much smaller. They were about the same size as, but lighter than those of Luna 9 and 13. Each lander was approximately 60 cm in diameter and, including the 8 kg payload, was 30.6 kg. For entry, each was contained within a blurt-ended conical ablative aeroshell approximately 1 meter in diameter (Figure 20.3). The total mass of the lander and its entry system was 120.5 kg. Separation was to occur 4 or 5 days prior to orbit insertion, after being given a spin of 12 revolutions per minute for stability. Entry would begin at an altitude of about 100 km at 5.75 km/s and an angle of 11 to 21 degrees. After about 3 minutes, at an altitude in the range 19 to 44 km and a velocity of 200 to 320 m s. the parachute w’ould deploy. The aeroshell would be jettisoned 10 seconds later, and a 130 meter harness would unreel the lander. At about 18 to 4 km and a velocity of 20 to 40 m/s an airbag would inflate around the lander. This was designed to survive an impact at vertical and horizontal rates of about 20 m/s. Immediately upon contact after a descent lasting anything from 6 to 17 minutes, the lander would discard its parachute, and after rolling to a stop the airbag

would split open at the seam and he discarded. In a manner similar to the Mars 3 lander four triangular petals would open, each extending about 30 cm from the central base. Three of these petals had springs to deploy instruments away from the lander.

On the surface the lander would draw power from two coffee-cup-sized 220 mW RTGs, a technology that had not previously been used in a Soviet mission but was intended for the rovers, supplemented by NiCd batteries. A lithium battery was used for the descent phase. The uplink and downlink at 2 and 8 kbits/s would use a UHF relay through the orbiter. There was no command capability; downlink was only to initiate transmission. The internal temperature of the lander would be maintained by a combination of insulation and heat from the RTGs and dedicated RHUs; 8.5 W of heater power was available. The expected operating life was about a local year.

In addition to the scientific payload, the landers carried a compact disk provided by The Planetary Society entitled ‘Visions of Mars’ which contained a compendium of knowledge about Mars.

Entry mass: 120.5 kg

Lander mass: 30.6 kg

Payload: 8 kg (~ 5 kg of science)

Figure 20.5 ‘Small Station’ lander.

Figure 20.6 Test lander in a ‘sandbox’.

The penetrators were cylinders 2 meters long with a pointed 12 ail diameter fore­body and a 17 cm diameter after-body that included a funnel-shaped tail section that broadened to 78 cm diameter. They drew power from a 0.5 W RTG and a 150 watt- hour lithium battery. A total of 4.5 kg of science instruments were distributed in the two sections. Each penetrator was to be released from orbit near apoapsis by pointing the spacecraft in the proper direction and spinning the entry system to 75 revolutions per minute for stabilization prior to release. At a safe distance the orbiter was to make a small diversion maneuver. The penetrator would then fire a solid rocket to reduce its velocity by 30 m/s, jettison this de-orbit motor, and inflate the ballute that was to decelerate the initial phase of its entry when it fell into the atmosphere about 21.5 hours later. Entry would be at a speed of 4.6 to 4.9 km/s and an angle of 12 degrees.

The penetrator would be slowed aerodynamically, then inflate an extension to the ballute in the after-body (Figure 20.8). After a 6 minute descent, it would hit the

2. Transfer to the

descent trajectory

i. Initiating inflation M’ of brakititr device J

4. r. ntry into the
atmosphere

5. Descent through

the atmosphere

6. Contact with the surface

7. Penetration and separation of two petretrator pans

Figure 20.8 Penetrator entry, descent and landing scheme.

surface at about 75 m/s. The 500 G shock was to be cushioned by a fluid reservoir. The wide after-body was designed to stop at the surface as the fore-bod у separated and penetrated up to 6 meters into the ground, remaining attached by a coiled wire. The aft mast with the antenna, camera, magnetometer, and mcteorologieal sensors was then to extend, and thermal probes would protrude into the soil.

One penetrator was to be sent to a site near one of the landers, and the other to a location at least 90 degrees away to facilitate the triangulation of seismic signals. Communications at 8 kbits/s would be feasible for about 5 to 6 minutes every 7 days through the transmitter on the after-body and would use the relay through the orbiter for uplink and downlink. The expected lifetime was a local year.

Penetrator mass w і engine: 88 kg

Entry mass: 45 kg

Science payload: 4.5 kg

Payload:

Or hi ter:

The orbiter had twelve instruments to study the surface and atmosphere of Mars, seven instruments for plasma, fields, particles and ionospheric composition, and five instruments for solar and asirophysical research. And radio occultalions during limb crossings would give data about the atmosphere. The instruments were on the sides of the spacecraft, on one or other of the two scan platforms, and on the solar panels. The three optical instruments of the ARGOS package were on the З-axis I PS scan platform along with the navigation camera, and the SPICAM, EVRIS and PHOTON instruments were on the simpler 2-axis PAIS scan platform.

Remote sensing of the surface and atmosphere:

1. Multifunctional stereoscopic high resolution TV camera (ARGOS HRSC. Germany-Russia)

2. Wide-angle stereoscopic TV camera (ARGOS WAOSS, Germany-Russia)

3. Visible and infrared mapping spectrometer (ARGOS OMEGA, Eranee – Russia-Italy)

4. Planetary infrared Fourier spectrometer (PFS, Italy-Russia-Poland-France – Germany-Spain)

5. Mapping radiometer (TERMOSKAN, Russia)

6. High resolution mapping spectrophotometer (SVET, Russia-USA)

7. Multi-channel optical spectrometer (SPICAM, Belgium-France-Russia)

8. Ultraviolet spectrophotometer (UVS-M, Russia-Germany-France)

9. Long wave radar (LWR, Russia-Cermany-USA-Austria)

10. Gamma-ray spectrometer (PHOTON, Russia)

11. Neutron spectrometer (NElJ I RON-S, Russia)

12. Quadrupole mass spectrometer (MAK, Russia-Finland)

The West Germans supplied the 21.4 kg high resolution HRSC camera and the hast Germans the 8.4 kg wide angle WAOSS camera. After the reunification of that nation the instruments were combined into a single project. Each was a push-broom scanner using parallel linear arrays of 5,184 pixel CCDs. The narrow angle camera had nine arrays for multispectrak photometric, and stereoscopic imaging. The wide angle camera had three arrays for stereoscopic imaging. The best resolution would be 12 meters for the narrow angle camera and 100 meters for the wide angle camera. Because the altitude and velocity of the spacecraft would vary during the periapsis encounters in an elliptical orbit, the CCD integration times could be tailored over the long scans. The cameras on the TPS platform had an extensive 25.3 kg MORION-S onboard processing unit which incorporated a 21 kg solid-state memory system built in cooperation with ESA with a capacity of 1.5 gigabits to reduce the transmission requirements. These data acquisition resources were shared with other instruments. Also on the TPS platform was the 23.7 kg OMEGA visible and infrared mapping spectrometer to measure atmospheric composition and map surface composition.

The 28 kg TERMOSKAK instrument from Phobos was re-flown to measure the thermal properties of the regolilh. The 12 kg SVET mapping spectrophotometer was to analyze the spectrum of the surface and aerosols. The 20 kg PHOTON gamma – ray spectrometer would map the elemental composition of the surface, and the 8 kg NEUTRON-S neutron spectrometer would determine ice and water abundances. The 35 kg LWR would probe the near-surface layer to measure vertical structure and ice deposits. The 25.6 kg PES was to make atmospheric profiles of carbon dioxide, and measure atmospheric temperatures, winds, and aerosols. The 46 kg SPICAM would use solar and stellar occultations to produce vertical profiles of water vapor, ozone, oxygen, and carbon monoxide. The 9.5 kg UVS-M was to map atomic hydrogen, deuterium, oxygen and helium in the upper atmosphere of Mars and the interstellar medium. The 10 kg MAK mass spectrometer was to measure the composition and distribution of ions and neutrals in the upper atmosphere.

Space plasma and ionosphere:

1. Energy-mass ion spectrograph and neutral particle imager (ASPERA-C. Sweden-Russia-Finland-Poland-USA-Norway-Germany).

2. Fast omni-directional non-scanning energy-mass ion analyzer (EON EM A. UK-Russia-Czech Republic-France-Ireland).

3. Omnidirectional ionospheric energy-mass-spectrometer (DYMIO, France – Russia-Cermany-USA).

4. Ionospheric plasma spectrometers (MARIPROB, Austria-Belgium-Bulgaria – Czech Republic-Germany-Hungary-1 reland-Russia-USA).

5. Electron analyzer and magnetometer (MAREMF. Austria-Belgium-France – Germany-Great Britain-Hungary-Ireland-Russia-USA).

6. Plasma wave instrument (ELISMA, France-Bulgaria-Great Britain-ESA – Poland-Russia – Ukraine).

7. Low-energy charged particle spectrometer (SLED-2, Ircland-Czcch Repub – lic-Cermany-IIungary-Russia-Slovakia).

The 12.2 kg ASPERA instrument was to measure the energy distribution of ions and fast neutrals. The 10.7 kg EON EM A ion analy/er would measure the dynamics and structure of the upper atmosphere plasma. The 7.9 kg MARIPROB and 7.2 kg DYMIO instruments would complement these instruments. The 12.2 kg MAREMF instrument would analyze plasma electrons and it carried two lluxgate magnetometers to measure magnetic fields in interplanetary space and in orbit of Mars. The 12 kg EL-ISM A instrument was to measure plasma waves in the Martian environment. It consisted of three Langmuir probes and three search coil magnetometers. In addition to probing the surface of the planet the LWR radar was also to be used to measure the distribution of electrons in the ionosphere and how this interacted with the solar wind. The 3.3 kg SLED-2 instrument was to measure low energy cosmic rays during the interplanetary cruise and in the Mars environment.

Solar physics and astrophysics:

1. Precision gannna-ray spectrometer (PCS, Russia-USA).

2. Cosmic and solar gannna-ray burst spectrometer (LILAS-2, Russia-France).

3. Stellar oscillations photometer (EVRIS, France-Russia-Austria)

4. Solar oscillation photometer (SOYA. Ukraine-Russia-France-Switzerland)

5. Radiation dosage monitor (RADIUS-M, Russia-Bulgaria-Greece-USA – France-Czech Republic-Slovakia)

The 25.6 kg PCS gamma-ray spectrometer was intended to examine solar flares during the interplanetary cruise and then measure gannna-ray emission when in orbit around Mars. The 5 kg LILAS-2 instrument would locate celestial gamma-ray bursts in conjunction w’ith several spacecraft in Earth orbit and Ulysses in deep space. The celestial sources were also to be examined by using Mars occultation observations. The 1 kg SOYA and 7.4 kg EVRIS photometers were to make helioseismology and astroseismology measurements respectively. SOYA was body mounted but EVRIS was on the 2-axis scan platform. The RADIUS-M radiation dosimeter was carried to obtain data pertinent to prospective future human Mars missions.

Landers:

Entry and descent:

1. Descent imager (DESCAM, France-Finland-Russia)

2. Three-axis accelerometer plus sensors for temperature and pressure (DPT Russia)

The lander had a suite of sensors and a descent imager. DESCAM was mounted on the bottom of the lander to obtain imagery to provide context for the panorama that would be taken following landing. It had a 400 x 500 pixel CCD and was to be detached 2 minutes after landing, just before the airbag was discarded. The DPI had an accelerometer and temperature and pressure sensors to provide vertical profiles of temperature, pressure and density during entry and descent, and the dynamics of the landing. It was mounted outside the lander bay under one of the petal covers, so that descent data was convoluted with flow dynamics during descent.

Surface:

1. Panoramic camera on a central mast (PANCAM. Russia-France-Finland)

2. Meteorology instrument system on a 1-meter tall mast for temperature, pressure, humidity, wind, and optical depth (MIS, Finland-France-Russia)

3. Seismometer, magnetometer and inclinometer (OPTIMISM, Francc-Ger – many – Russia)

4. Alpha, proton and x-ray spectrometer for soil elemental analysis (APX. Germany-Russia-USA)

5. Oxidant sensor (MOX, USA-Russia)

At the top of the station shell, the lander carried a PANCAM scanning photometer camera similar to those on the earlier Mars landers to provide a 360 x 60 degree panorama composed of 6,000 x 1,024 pixels. A deployable overhead mast supported the MIS meteorology package with sensors for temperature, pressure and humidity, an ion anemometer for wind, plus an optical-depth sensor. The ODS optical sensor in this package was supplied by the French and measured direct Sun and scattered light at the zenith in three narrow bands at 270, 350. and 550 nm, and one broad band from 250 to 750 nm. The DPI package measured temperatures and wind velocities on the surface. Three of the petals contained instruments for deployment to the surface: the OPTIMISM instrument containing a seismometer, inclinometer and З-axis lluxgate magnetometer; the APX backseat ter analyzer to determine elemental abundances in the soil; and the MOX experiment. The latter was a colorimetric soil analyzer that had reactant spots sensitive to different types of oxidants. Supplied by the IJS it was developed in less than a year, weighed only 0.Я5 kg, and had its own power supply and data storage. Its function was to test the inference from the Viking landers that the soil was rich in oxidants and hence inimical to life.

Penetvatovs:

After-body above surface:

1. Television Camera (TVS, Russia)

2. Meteorological sensors for temperature, pressure, humidity, wind and opacity (MEKOM, Russia-Finland-USA)

3. Magnetometer (IMAP-6, Russia-Bulgaria)

After-body below surface:

1. Gamma-ray spectrometer for soil analysis (PEGAS, Russia)

2. Temperature sensor for heat flow (TERMOZOND Part 1, Russia)

Fore-body:

1. Seismometer for interior structure (KAMERTON, Russia-Great Britain)

2. Accelerometers for soil mechanics (GRUNT, UK-Russia)

3. Temperature sensor for heat flow (TERMOZOND Part 2, Russia)

4. Neutron detector for water detection (NEUTRON-P, Russia)

5. Alpha-proton spectrometer for soil analysis (ALPHA, Russia-Cermany)

6. X-ray fluorescence spectrometer for soil analysis (ANGSTREM, Russia)

The GRUNT accelerometer in the fore-body was to measure the properties of the surface during impact and penetration. The KAMERTON seismometer would search for Martian activity. The TERMOZOND thermal probes would measure heat flowr and provide data for thermal diffusivity and heat capacity. The gamma – ray, alpha, proton, neutron, and x-ray spectrometers would analyze the soil chemistry including its water content. Remaining above the surface on the after­body, the TVS 2,048 pixel linear camera would take a panoramic image of the site, the MEKOM package would monitor the temperatures and winds, and the IMAP-6 magnetometer would measure the local magnetic field.

Mission description:

Mars-96 was to have arrived at Mars in September 1997 on a direct trajectory about 10 months after launch. The small surface stations were to have been released 4 or 5 days out from the planet for direct atmospheric entry. The spacecraft would execute a deflection maneuver for its orbital insertion point. By this time the Mars ephemeris was very well know7n, so the complex optical navigation and close-in release of the M-71 and M-73 missions was not required. Three landing sites were selected for the landers, the two primary ones being at 41.31CN 153.77:W in Arcadia and at 32.48CN 163.32;W in Amazonia, with the backup at 3.65:,N 193 W.

At insertion the spacecraft would perform a braking maneuver into an initial orbit of 500 x 52,000 km, and this would be reduced in stages to a 43.09 hour 7:4 Mars synchronous orbit at 106.4 degrees inclination with a 300 km periapsis.

The two penetrators were to have been deployed within 7 to 28 days, one targeted for Arcadia and the other at least 90 degrees away in Utopia Planitia to provide a good baseline for seismometry. The Eregat would be jettisoned after the deployment of the penetrators. Orbit maintenance would then be the task of the smaller onboard propulsion system.

At the start of the orbital mission communications sessions with the landers and penetrators were expected to be through the orbiter approximately once per day for 20 minutes each. One small orbit correction of about 1 to 2 m s w ould be required each month to maintain visibility with the surface elements, w’hose nominal lifetime was to have been one local year or roughly two terrestrial years.

The spacecraft was launched on the optimal day of the window’, November 16, 1996, and reached Earth orbit after the first firing of the Block D. If this stage had fired properly to initiate the escape maneuver, the Eregat propulsion system on the spacecraft would have provided the final increment required to reach Mars. It seems that cither the Block D-2 did not fire or it shut down after only 20 seconds, perhaps owing to an inappropriate command from the spacecraft, which was in control of it. The logic of the situation then caused the spacecraft to separate and fire its Hregat as if to complete the escape maneuver. However, this burn left it in an 87 x 1.500 km elliptical orbit. With its periapsis inside the atmosphere the spacecraft was doomed. The Block D-2 stage entered the atmosphere at some time between 00:45 to 01:30 IJT on November 17 and crashed into the Pacific between the Chilean coast and Easter Island. A day later, the spacecraft was spotted re-entering the atmosphere as a fireball over southern Chile, and is believed to have crashed in the Andes mountains of Chile near the border with Bolivia. It was carrying 270 grams of plutonium-238 in 18 pellets as part of the landers and pcnctrators. Designed to withstand heat and impact, these probably survived re-entry. Searches were made but the spacecraft was never found.

The failure occurred at the second ignition of the Block D-2 upper stage w hile the spacecraft was out of range of Russian ground stations. Owning to budget limitations the Russians had no tracking ships in the Pacific. The lack of telemetry data during critical parts of the escape phase of the mission precluded identification of the cause of the failure, and in particular w hether it w as due to failure of the Block D-2 upper stage or to a malfunction of the controlling spacecraft. It was an abysmal situation.

Results:

None.