SHENZHOU 4: LAST TRIAL

With the return of Shenzhou 3, Chinese space experts let it be known that only one more flight would be necessary before a manned spaceflight. This would be the dress rehearsal for the real mission in which two astronauts would spend three days in space. During the summer, 52 experiments weighing 300 kg were selected to fly on the Shenzhou 4 mission, some having taken part in earlier missions. With none of the delays that held back the launching the previous year, Shenzhou 4 soared into the cold night skies of northern China at 00:40 am on 30th December. They were indeed cold, for launch temperature was -18.5°C, rising from a previous -27°C. Present were Shenzhou designer Qi Faren and the 12 men of the yuhangyuan squad, each of whom hoped he would be chosen to fly the next one. Several days before the launch, the yuhangyuan had each entered the cabin on the pad to test entry and exit procedures. The scene echoed the events of 25th March 1961, when Yuri Gagarin and his five colleagues of the final training group went to Baikonour to watch the launch of Korabl Sputnik 5, the final dress rehearsal before the mission of Yostok.

The orbit was spot on: 331-337 km, 91.2 min, 42.41°, tweaked to the perfect orbit on the fifth circuit. Two maneuvers were made to raise the orbit, on 31st December and 3rd January. On each occasion, when the orbit dropped to 91.088 min, engine firings pushed Shenzhou back up to 91.102 min and there was a further set of two thruster firings on 4th January. An important function of the mission was to improve the air supply system, which had left excessive harmful gases on the previous missions.

Shenzhou 4 blasted its retrorockets over Africa, making a giant curved descent over the horn of Africa, Arabia, and Pakistan. In the cold and shghtly foggy recovery region, Mil helicopters, transfer cabins, and recovery vehicles with direction finders on their roof moved in. The cabin came to rest in the dark in the middle of the 60 x 36-km landing zone, targeted 40 km from Hohhot, the capital of Inner Mongolia. Teams in orange suits rushed forward to the silvery descent cabin, which lay on its side, and retrieved the two dummies inside. The descent cabin returned to Beijing three days after it touched down. The experimental section was opened and the yuhangyuan climbed inside to examine its condition. The biological experiments were recovered: the Institute for Plant Physiology and Ecology in the Shanghai Institute for Biological Sciences had devised a complex set of experiments for fusing

cells in animals (mice) and plants (tobacco), so sensitive that they could not be loaded on board until eight hours before take-off. Among the plants and seeds to be flown were vegetables, grain, flowers, medicinal herbs, Pinellia tuber, and goldthread. Peony seeds from Luoyang, Henan, were subsequently exhibited at its next spring show. Ground crews recovered the cell electrofusion unit for life and materials sciences experiments.

As was the case with previous missions, Shenzhou 4 left its orbital module behind. The module maneuvered first on 5th January to 354-366 km. A month later, its altitude had declined to 331-346 km, so the rockets on board fired on 9th February to raise its orbit to 359-366 km. The third maneuver raised the orbit to 359-373 km on 1st April, with additional corrections on 17th and 22nd April to restore the orbital altitude. The module finally decayed on 9th September 2003 after the longest orbital module mission so far.

On board were 11 experiments, including an upper atmosphere detector, high – energy radiation and low-energy radiation detector, biological module, and microgravity fluid tester. Shenzhou 4 continued fluid physics experiments begun on Shi Jian 5 and Mir, this time using drops of inert liquids and silicon oil. The first electrophoresis separation experiment was performed, the outcome of research initiated under project 863 in the early 1990s. The cabin also carried ion and proton detectors.

Shenzhou 4 carried a multi-mode microwave remote sensor system first developed by Li Jing, also under project 863. This combined a radar altimeter, radar scatter meter, and multichannel microwave radiometer, called a Multimode Microwave Sensor (MMS), to observe in five bands the atmosphere and ocean, specifically their temperature and winds through clouds. There was a laser microwave altimeter to measure the altitude of the module from the ground to 10-cm accuracy (e. g. 331.25631 km). The altimeter was only 20 cm across and 800 g in weight and was installed on the bottom of the spacecraft. Over 2,000 measurements were taken over three days both to test out its accuracy and to infer information about changes in the Earth’s oceans. The quadruple mass spectrometer atmospheric composition detector took readings from January to March 2003 over the southern hemisphere summer. During geomagnetic disturbances, the level of nitrogen in the atmosphere rose and the level of oxygen declined, more so closer to the South Pole, possibly as a result of the heating of the upper atmosphere. Shenzhou 4’s orbital module was the third in the series to carry an atmospheric density detector and, several years later, their accumulated outcomes were published. They showed that, during quiet solar periods, atmospheric density had a diurnal pattern, falling at night and rising during the daytime. During a strong magnetic disturbance, air density could rise as much as 56% within 7 hr, falling back to its original value in not more than three days [8].