INTERAVIA, 1988, ¹6, ñ. 595-596.
The ambitious scope of the US Pathfinder program, outlined in the preceding article, could be viewed as a response to the Soviets' impressive plans for Mars missions in the 1990s. Soviet planners are not yet overtly concerned with manned expeditions to the Red Planet; but as reported in our initial report on Soviet Mars plans (Interavia 12/1987, page 1295), they are forging ahead towards the ultimate goal of a sample-return mission by the end of the century.
But a new report recently released by Moscow's Space Research Institute (IKI), covering the next phase after this July's departure of the twin Phobos/Mars probes, springs a few surprises. As Interavia suggested in December, the next mission will skip the 1992 launch window to allow time for full analysis of the Phobos results and instead head for Mars in October 1994.
A July's Phobos probes form the basis for 1994's orbiters.
A Mars-94's 500 kg descent section will use a combination of aerodynamics, parachute and rocket braking for landing. (Picture by NASA)
Target: Mars. Soviet landers are aiming for the more interesting polar regions where water supplier, and life are more likely (Picture by NASA)
A Mars-94's meteobeacons could be deposited on the more hazardous regions of the planet where the rovers dare not venture, such as the canyons seen here. (Picture by NASA)
A Earth-based operators would rely on stereo TV images for controlling the rover. (Picture by NASA)
The rovers must negotiate boulder and dune fields, as illustrated in this Viking 1 image. (Picture by NASA)
Trials on the Soviet Mars rover are believed to be under way. This is a prototype of the 1970s lunar vehicle.
The dual orbiters will not only deploy the expected rovers, balloons and penetrators but also eject a small sub-satellite and scatter up to ten hard-landing packages around the globe to return long-term meteorological information. But Mars-94 reserves its most novel surprise for mission end: a canister of high-resolution film wiil be blasted free of Mars towards Earth to aid selection of candidate landing sites for the sample-return missions.
The IKI document also reveals a change for the sampling venture. Soviet officials at last October's IAF Congress declared that a 1996 Earth departure was feasible, but 1998 is now being generally suggested as the earliest possible date, not least because Mars-94's photographs would take until August 1997 to arrive. It remains to be seen whether the 1996 window is used at all, should it simply be a repeat of the 1994 mission. Interestingly, the IKI report for the first time mentions a manned Mars expedition for 2010-2015, with, in the spirit of glasnost, extensive international cooperation.
Dr. Anders Hansson of London's Commercial Space Technologies learned from Soviet delegates at a recent NASA Mars conference that the broad thrust of Mars-94 has been approved. It is going ahead, he said, although the details remain to be settled.
Two spacecraft based on this July's generic seven-tonne Phobos vehicle will be launched by Protons from Tyuratam in October 1994 and given final 3.5km/sec boosts from their Earth parking orbits into Type II Mars trajectories. This route will take them more than half-way around the Sun before intercepting Mars after about 300 days, but this more economical approach permits a larger payload. It still seems that Energia's 27-tonne Mars capacity will not be called upon during the 1990s.
Mars-94 will demonstrate several vital techniques for the later sampling missions, such as an Earth return section and aerobraking on arrival at Mars in August 1995 to slot into orbit; no planetary spacecraft has ever attempted this. Onboard systems drawing on optical navigation data will guide the vehicle automatically through Mars' upper atmosphere to bleed off sufficient approach speed to establish a polar orbit and demonstrate a new level of sophistication in the Soviet planetary program. The Soviets estimate that deleting the conventional rocket braking system will in fact permit an extra 1.5 tonnes of useful payload.
The resulting orbit will be adjusted to a near-circular path some 200-500 km high over the poles, initially to reconnoitre landing sites by means of two stereo TV systems capable of 20 m resolution or better from their 50 kg steerable observation platform. Other instruments among the 400 kg science payload will look for evidence of sub-surface water, which is vital in the search for life and for future colonisation. They will also probe atmospheric conditions and measure the radiation, magnetic and dust fields surrounding the planet. The imminent Phobos probes will focus on their tiny namesake moon and observe Mars only from around 6,000 km out, but Mars-94 will conduct intensive high-resolution global investigations during its life of between one and four years.
After what one assumes will be several months of landing-site assessment, the 500 kg descent section will separate and fire a retrorocket to head for the surface with a small rover and a balloon. These elements remain much as outlined in Interavia 12/1987. The 150 kg six-wheeled nuclear-powered rover will cover about 100 km during its one-to-three-year life analysing the soil, drilling, looking for water and evidence of life. Its degree of autonomy is not clear, but the Soviets will possibly accept the inevitable communications lag of several minutes and keep it under direct Earth control rather like their two Moon Lunokhods of 1970 and 1973. By contrast, NASA is focusing on more complex rovers requiring minimal terrestrial input.
The 50 kg balloon will survive for 10-15 days and cover up to 2,000 km equipped with its tiny camera, meteorology and soil analysis package. The Planetary Society is still discussing the possibility of this being a US/European contribution.
Penetrators were briefly outlined in earlier IKI reports, but the inclusion of two per vehicle now seems certain. Each 100 kg device will be braked out of orbit to bury itself 1-5 m deep on impact. The 7 kg instrumentation package will detect "Mars-quakes", monitor heat flow, analyse the soil and return weather data for between one and two years. The four widely separated seismometers will permit modelling of Mars' internal structure. The penetrators might be battery— or nuclear-powered, but their data will certainly be transmitted in brief bursts up to the orbiter for relay to Earth.
For the first time, the Soviets have mentioned "meteobeacons", simple and robust packages "of several kilos" spread around Mars to provide the first comprehensive picture of surface weather conditions. Each will report on atmospheric pressure, temperatures and wind velocity, but some could include a seismometer, magnetometer, dust detector or even a small camera. Measuring the air's dust content would help to track Mars' vast dust storms.
Ten or so meteobeacons would deliver daily reports for at least a full Martian year (687 Earth days), but it has yet to be decided how they will be deposited. While dispatching them from the orbiter brings the entire planet within reach, the meteobeacons must survive all the rigours of atmospheric entry. Releasing them from the lander during descent or even as ballast would be far simpler but would give less geographic scope.
Again surprising Western analysts, each orbiter will eject a 50 kg sub-satellite into a slightly different path, with the aim of precisely radio-measuring their separation to map Mars' gravitational variations. This not only probes the planet's internal mass distribution but could be important for precise targeting of future landers. Lunar gravitational lumpiness had to be compensated for in the manned Apollo expeditions. If the measurements are sufficiently precise, it might even be possible to assess the amount of water locked in Mars' polar caps.
Although not mentioned in the IKI document, the sub-satellite will also probably sport magnetic field and radiation detectors, simply because two craft working jointly can better sort out the complex changing patterns around the planet. The Soviets have experience of this technique in Earth orbit, with the Prognoz satellite and its released Czech-built Magion sub-satellite; several such missions are imminent and it could be that the Czechs will be invited to provide the Mars equivalent.
If agreement is reached with the USA (and the growing spirit of cooperation, at least in data exchange, makes it highly likely), then NASA's 1992-94 Mars Observer orbiter could provide the Soviets with all the 1 m-resolution surface imaging they need for planning sample-return landings. If not, Mars-94 offers a novel solution to the problem.
Soviet scientists have estimated they need to study 30 per cent of the Mars surface at 1 m resolution, but the IKI report points out that returning these data at 128 kbit/sec (Phobos spacecraft data rate is 4 kbit/sec) for eight hours a day would require 258 years. Their solution is to photograph the surface, following the technique routinely used by Soviet spy satellites, and load the 30-40 kg film cassette into a 300 kg return vehicle.
An Earth return window opens in September 1996 for the small vehicle to accelerate out of Mars orbit. The film must be radiation-hardened and/or shielded throughout the mission and the return section must be able to adjust its trajectory on the way or it could miss Earth altogether in August 1997. The approach speed will be around 13 km/sec, but the Soviets have yet to indicate how the precious cargo wiil be captured. Aerobraking in the Earth's atmosphere is probably too complex for such a small vehicle and direct descent too risky, so it will most likely rocket-brake into a high orbit for recovery by space station Mir's successor.
Western observers now eagerly await the next batch of Soviet surprises.