FIREFLY TO MARS

It was hardly a surprise that Mars followed closely behind the Moon in Chinese deep-space ambitions. In summer 2003, China Academy of Sciences Centre for Space Science and Applied Research expert Liu Zhenxing reported that Mars had been examined as part of a project 863 planetary exploration study. The first phase in this study had been a look at the exploration of Mars to date by other countries and the results obtained. This had helped the researchers to draw up some initial possible objectives for Mars exploration science and some outline spacecraft designs. Liu Zhenxing ventured the opinion that China should now examine the key technologies for unmanned Mars exploration, such as the calculation of orbits, appropriate launch systems, and a deep-space tracking network. Again, this suggested an approach similar to the new Moon project: theoretical studies, followed by a debate about the range and scale of possibilities, followed by the hardening of decisions into a concrete project. A series of scientific papers on flights to the planets began to appear in the universities from the late 1990s [16]. The model of a small spacecraft to orbit Mars was pictured in the Shanghai Daily in May 2005.

Russia provided an early opportunity for China to send a small spacecraft to

Mars. Ever since Mars 8 had crashed into the Pacific in 1996, Russia had been trying to return to Mars exploration and, after many false starts (mainly due to financial problems), had prepared a mission to bring samples back from Mars’s tiny moon Phobos, called Phobos Sample Return. For the Russians, there was a big attraction if China were to join the project, for the Chinese would bring a cash contribution, smoothing out Russia’s financial problems and making the eventual departure of the mission much more certain. Although the Chinese involvement made the mission a little more complicated, this was outweighed by the scientific gain and their funding. At a late stage, speciahsts in the Hong Kong Polytechnic University in China also contributed a 400-g device to grind Phobos rock for in situ analysis by the Russian lander.

Thus, an agreement was signed on 26th March 2007: Phobos Sample Return would carry a 115-kg satellite attached to its side, called Yinghuo 1, “Yinghuo” being the ancient Chinese astronomical word for Mars, also known as the “glittering planet” and the Chinese word for “firefly”. The role of Yinghuo was carefully chosen. Its formal objectives were to investigate the Martian magnetosphere, plasma distribution, the interaction of the solar wind with Mars, and the gravity field, and make a determination as to why Mars lost its water. According to the director general of the National Space Science Centre, Wu Ji, most recent missions had concentrated on the follow-the-water-to-find-life approach, meaning that the Martian atmosphere had been neglected. The planned mission would fly well ahead of the small American Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, not due for launch until 2013. Yinghuo’s study of the atmosphere could give important clues as to the planet’s climatic history and why water had disappeared from the surface.

The mission profile was that, three orbits after Phobos Sample Return arrived in its initial Mars elliptical equatorial orbit of 800-80,000 km, 72.8 hr, 0.7°, it would detach Yinghuo at a separation speed of 2 m/sec. Phobos Sample Return would then maneuver to meet Phobos at 9,700-km altitude. Russia and China would calibrate their instruments together and receive reports on the ionosphere from their two spacecraft simultaneously in quite different orbits, giving them an additional scientific bonus. Yinghuo’s orbit was set to make an ellipse through the plasmasheet in the Martian tail, swing around the side of Mars, and pass through the bow shock and magnetosheath on the sunward side. Their joint mission would last two years. Yinghuo would remain in the orbit where it was detached (800-80,000 km) but it was one likely to be perturbed over time by solar radiation and the non-spherical shape of Mars to reach an inclination of between 21.7° and 36°. Wherever it went, it was intended to use ground stations in Shanghai, Beijing, Kunming, and Urumqi to follow its orbit to a precision of 100 m. China also obtained permission to use both the ESA and Russian deep-space tracking networks. Just as the Chinese used a communications satellite as the basis for their first lunar probe, this time they used a miniaturized version of the ocean observation satellite, Haiyang, adapted as a small spacecraft measuring 75 x 75 x 60 cm. Yinghuo had a 950-mm x-band dish for communications, a 12-W transmitter on 8.4 and 7.17 GHz with a data rate of 8­16 kps, and two solar arrays each of three sections and 5.6 m across, generating 90­180 W. The instruments are listed in Table 9.3.

Table 9.3. Yinghuo instruments.

Wide field-of-view camera: 200-m resolution, weight 1.3 kg Satellite-to-satellite radio occultation sounder, weight 3 kg Fluxgate magnetometer, range 256 nT, weight 2.5 kg Plasma package

Ion analyzer (two): range 20 eV to 15 keV Electron analyzer: range 20 eV to 15 keV

The camera was tested out extensively on the ground and images were taken of our own Moon to verify its capabilities. At 80,000 km out, Mars would fill most of the field, but, at close approach, it would image terrain of 525-729 km. The camera was not intended for mapping (the spacecraft would not have the capacity) but to monitor sandstorms and for “public outreach”. The magnetometer was located at the end of the solar panel, 3.2 m from the center of the spacecraft, with two sensors 45 cm apart. The plasma instruments comprised two identical ion analyzers in the range 0.02-10 keV, measuring both its present level and escape rate. The joint occultation experiment with Phobos Sample Return spacecraft was one of the most unusual. Here, Phobos Sample Return would transmit a signal on 416.5 MHz and 833 MHz to a receiver on Yinghuo: as the signals penetrated the Martian ionosphere, their frequency shift would make it possible to characterize its features and measure its electron density. Typically, the signaling sessions would take place when the two spacecraft were at opposite ends of their orbits behind Mars, so as to

Final preparations for Phobos Sample Return. Courtesy: Roscosmos.

get the flattest possible angle over the Martian atmosphere. Another experiment was designed to test the finding of the Soviet probe Phobos 2 that there was a dust ring around Mars, trailing behind the moon Phobos and, if so, its cause [17].

In advance of the mission, the spacecraft underwent a series of tests for vibration, noise, vacuum conditions, illumination, solar array deployment, and power systems. Yinghuo arrived in Moscow in time for its October 2009 launch. Although the Chinese satellite provided additional resources for the project, scientists became more and more nervous as they tried to integrate the two spacecraft in time for launch less than two months ahead. At the last team review of the project a month before launch, it was decided to delay the project until the next launch window two years later. This was not the only such project delayed, for America’s Mars Science Laboratory, Curiosity, was similarly postponed to 2011 while at an advanced stage.

Phobos Sample Return was eventually launched at night on 8th November on the Zenit 2SB, entering a parking orbit of 206-341 km, 51.4°. The solar orbit insertion burn did not take place and the 13,500-kg stage, the main part of which was fuel, remained stubbornly stuck in Earth orbit. Every day for two weeks, the spacecraft computer commanded preparations for the Mars insertion burn over South America, orientated the spacecraft, and made a pre-firing maneuver. Each time, though, the control system shut the system down just before the burn, which never took place, but the pre-bum maneuver had the effect of gradually raising its orbit while simultaneously exhausting its fuel. At one stage, ESA made contact with Phobos Sample Return through its tracking station in AustraUa, but Russian ground controllers were never able to do so and override the fault on their system. The spacecraft eventually crashed into the Pacific off the coast of Chile in January. An enquiry blamed a badly designed computer control system with poor components, compounded by a communications system that could only work in deep space (and not in low Earth orbit), exacerbated by the lack of marine tracking systems at the critical point of the Mars injection bum over South America. It was a sickening re­run of the earlier Mars 8 failure.

The Chinese did their best to hide their disappointment at this outcome to such a cleverly constructed mission, costing them their first chance to get data back from Mars. After the crash, the director general of the National Space Science Centre, Wu Ji, spoke of how China hoped to be able to contribute a mission four years later, during the 2015 window, but it would now have to follow objectives different from MAVEN. In reconsidering their plans, the Chinese indicated that they would go the three-step route of orbiter-lander/rover-sample return, much as they had on the Moon. Increasing numbers of planning papers were published, on the best trajectories to follow and course corrections, for example. Project 863 funding was made available to study trajectories, navigation, sensors, antennae, and long­distance communications. Aerobraking systems were simulated. The Beijing Institute for Mechanical and Space Engineering (institute §508) tested airbags, a six-bag system being favored. Work also began on the radars, indicating a preference for the more precise but sophisticated and difficult method of a powered descent [18].

The outcome was a proposal to government for a Mars 2015 mission, using a DFH communications satellite, with aerobraking to enter the desired pre-landing orbit. The proposal to government was for a 2,000-kg orbiter with a small demonstration lander, with a CZ-3B launch in 2015, arrival in 2016, and operations until 2018. Following aerobraking, the orbiter’s planned path was an elliptical polar one with a low point of 300 km. Its purpose would be to explore the environment of Mars and analyze the chemical composition of its surface. The planned payloads were a camera, surface – penetrating radar, infrared spectrometer, gamma-ray spectrometer, high-energy particle detector, and solar wind particle detector, transmitting information back on two x-band antennae. The demonstration lander, which was in the shape of an aeroshell, would be 50 kg and parachute a rocket down to a semi-soft landing at the southern fringes of the arctic with the intention of functioning three to five days on the surface sending back information on a UHF antenna [19]. Three landing sites were selected on the southern fringes of the Martian arctic.

Exploratory studies have already been made of other possible Mars missions. Yuan Yong and his colleagues in the Aerospace System Engineering Institute of Shanghai outlined the idea of a Mars penetrator. The idea was to use a satellite like Yinghuo, equip it with two 50-kg penetrators, 90-120 cm long and 15-20 cm wide, and launch it on a CZ-3B. A parachute would open at 17 km, slowing the spacecraft until it was dropped at 2 km. Although the penetrator would impact at between 80 and 100 m/sec, it should be possible to design it to withstand impact forces of up to 10,000 G. Its objective would be to, over 10 Mars sols, image the surface, provide meteorological data, probe the physical and mechanical characteristics of the regolith, and look for water and life. Landing sites were under consideration at both the arctic (better for water) and equator (better for life). The penetrator would carry a descent camera, panoramic camera, thermometer, and sound recorder. In anticipation of the mission, China commissioned another overseas tracking dish in Nequen, Patagonia, Argentina, in 2012.

Meantime, Yao Kerning and his colleagues at the Nanjing University of Aeronautics and Astronautics sketched an aircraft that would travel in Mars’s thin atmosphere. Aircraft designs and possible flight paths – 650 km straighthne and 100 km rectangular – were mapped in the region 28-36°S and longitude 187-191° [20]. American engineers had originally promoted such a mission as far back as the 1970s, but they had never managed to attract funding. Worse, by 2012, the American Mars program was in disarray, with budget cuts forcing NASA to abandon or delay future collaborative Mars missions.