Mission controllers at the Beijing Aerospace Command and Control Centre (BACCC) said that the SZ-3 Orbital Module had been operating smoothly and the experiments aboard had returned enormous amount of data.

A Changzheng-2F (Long March-2F) launcher delivered SZ-3 to space on March 25. The 7-day, 108-orbit primary mission ended when the Descent Module separated from the Orbital Module and returned successfully to the designated landing site in Inner Mongolia on April 1.

The Orbital Module remains in space to continue its extended mission, which space officials have said would last about six months.

After 93 days in space, the SZ-3 Orbital Module is in an orbit of 373.7 x 381.1 km with an inclination of 42.4 deg and a period of 92.1 minutes.

Since the beginning of the extended mission BACCC controllers have issued more than 2,000 commands for mission operation, including several maneuvers for orbit and attitude maintenance, and flight plan commanding.

CSN reported that BACCC had gained valuable experience in commanding the Shenzhou manned spacecraft for an extended period last year when the SZ-2 Orbital Module stayed in space for 260 days. Mission operation data gathered on this flight allows controllers to improve their skills in managing an extended mission of the Shenzhou Orbital Module.

For example controllers have made key breakthroughs in low-orbit spacecraft decay research, observation and control factors analysis, Sun-pointing/Earth-pointing model research, support control research, micrometeoroid impact analysis, propellant optimal distribution analysis, and contingency failure handling.

SZ-3 carried 44 science and utility payloads into space. The science experiments involved material and life sciences studies, Earth and atmospheric observations, and space environment monitoring. Chinese Academy of Sciences (CAS) led its affiliated research institutions in many of the experiments.

The payloads include: medium-resolution imaging spectroradiometer, cirrus [cloud] sounder, Earth radiation budget sensor, solar ultraviolet spectral monitor, solar constant monitor, atmospheric composition detector, atmospheric density detector, spacecraft Orbital Module optical window module, multi-chamber space crystallization furnace, space protein crystal equipment, cell bioreactor, solid matter tracking detector, microgravity gauge, and payload common facilities.

Among all the SZ-3 payloads, the microgravity gauge and the Descent Module payload common facility had made the third trip into space.

Payloads that had made the two flights were the multi-chamber space crystallization furnace, the space protein crystal equipment, and the Orbital Module payload common facility. The rest of the payloads made their inaugural flight in space on this mission.

The material and life sciences investigation payloads had returned to Earth in the SZ-3 Descent Module. Scientists involved in these experiments have been busy examining the returned samples after a weeklong exposure in a microgravity environment.

The rest of the science payloads remain aboard the SZ-3 Orbital Module to continue data collection for another half a year. Space officials also indicate that some of these payloads are housed in the "appendage section", whose nature other than housing payloads is unclear.

As the material and life sciences experiments were planned to return to Earth with the Descent Module, they received a higher operational priority. Science Times reported on Apr. 2 that when the automated experiments were completed more than halfway through the mission on orbit 68, mission controllers started experiments with terrestrial and atmospheric observations. Interspersed among these observations was test operation of the medium-resolution imaging spectroradiometer (MRIS).

According to Chinese space officials MRIS, which the Shanghai Institute of Technical Physics of CAS designed and built, is among the most advanced of such instrument in the world. The imaging spectroradiometer operates in 34 spectral bands, including shortwave infrared and thermal infrared. The spectral sensitivity of the instrument is only two wavebands less than that of the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites.

MRIS is installed in the appendage section of the SZ-3 Orbital Module.

In the extended mission, the imaging spectroradiometer is being assessed on the technologies of imaging spectroradiometry, infrared focal plane assemblies, and mechanical cooling of the instrument.

The mass, volume and power consumption of MRIS is smaller than comparable instruments of other nations. The testing and assessment of MRIS will help design subsequent versions with longer operational lives.

Looking At Oceans, Atmosphere And Land
China Space News reported in the March 27 issue that MRIS would make observations of the atmosphere, land, and ocean.

In ocean observations, the focus is on water colour and temperature as well as surveying sea ice and coastal zones. The emphasis in ocean colour observations is on chlorophyll concentration, suspended silt content, and pollutant survey. Scientists also make ocean colour observations in the sounding of water depth and shallow water topography.

Observations on the atmosphere are primarily in studying water vapour, aerosols, and cirrus clouds.

Large-scale soil and vegetation distribution is the main concern in land observations. Other areas of studies include large-scale geological structure, desertification, and soil water content.

In an interview with the China Central Television (CCTV) on Apr. 3, researcher Sun Huixian of CAS Center for Space Science and Applied Research (CSSAR) explained the application of the imaging spectroradiometer: "Through these images, conditions of atmospheric and oceanic pollution, crop growth, land vegetation and desertification can be analyzed."

Sun showed the CCTV reporter an image of the estuary of Chang Jiang (Yangtze River). "From the analysis of this image, a lot of information can be obtained on the formation of low beaches, sedimentation, and pollution of the ocean.

"With this instrument, we would know the land resources, pollution of the atmospheric environment, and conditions of waters. This is of great significance to the development of remote sensing technologies and land resources in our country," said Sun

Another suite of three sensors is dedicated to examine the interaction of the Earth's atmosphere with solar radiation. The Earth radiation budget sensor, the solar ultraviolet spectral monitor, and the solar constant monitor collectively gather data on the total amount of solar radiation that the Earth receives and the amount that the planet reflects and emits into space.

Atmospheric scientists use the solar constant monitor to measure the amount of solar radiation at the orbiting altitude of SZ-3, and the solar ultraviolet spectral monitor to determine the absolute irradiance of the solar ultraviolet radiation spectrum.

Data obtained with the three sensors will allow scientists to determine how much the Earth reflects solar radiation in short wavelengths and emits long-wave thermal radiation, as well as the concentration, distribution and vertical structure variation of atmospheric ozone.

Conclusion drawn from analysis of the data would lend support to formulate government policies on environmental protection.

Scientists also hope that the experiments with the three sensors would bring China on par with the international community in this field of study and offer opportunities for China to participate in world-class research.

Monitoring Space Weather And Environment
The final set of major experiments on the SZ-3 Orbital Module check the space environment in low-Earth orbit where the module traverses.

Three detectors -- atmospheric composition detector, atmospheric density detector, and heavy particle solid matter tracking detector -- continuously collect data on the space environment and presence of particles at Shenzhou's orbital altitude.

Qin Guotai, Manager of the SZ-3 space environment monitoring experiments at CAS Space Environment Prediction Center (SEPC), told Science Times on Apr. 3 that the experiments were part of the monitoring and forecasting system to ensure the safety of the Shenzhou spacecraft and its occupants.

Qin explained, "Under solar ultraviolet irradiation, gas molecules are ionized to an atomic state in the upper atmosphere. At the 343-km orbit of SZ-3, oxygen, nitrogen and helium in their atomic states predominate.

"Atomic oxygen is reactive. Collision with oxygen atoms would erode spacecraft surfaces such as the thermal control layers, and accelerate surface material oxidizing reaction that results in roughening of the material and reduction in mass."

Qin added that reaction with atomic oxygen might contaminate and significantly reduce efficiencies of critical spacecraft components such as the solar arrays and optical sensors; thus seriously jeopardizing the safety of the vehicle.

The quantity and density of atomic oxygen in the upper atmosphere varies depending on solar activities. According to Qin strong magnetic activities on the Sun, for example flares and proton events, can change the atomic oxygen density by up to three orders of magnitude.

The increased atmospheric density would create greater drag on the spacecraft, causing a change in the spacecraft attitude and an orbit decay typically of tens of meters daily. But during a severe solar storm the orbit decay can be as high as several kilometers per day.

Qin said, "Atmospheric density variation is random. Therefore it is necessary to monitor the atmospheric density in realtime and continuously, and to provide timely forecast and adjustment in the spacecraft orbital altitude and attitude. This would provide normal spacecraft operation realtime space environment warnings and contingency measures."

Both the atmospheric composition detector and the atmospheric density detector began operation on orbit 68. The detectors have been returning data on the mass spectrum and density of the upper atmosphere.

Scientists at the Space Environment Prediction Center were delighted to obtain valuable data on the upper atmosphere from these detectors in April during strong solar storms.

Xinhua News Agency reported on Apr. 26 that the SZ-3 Orbital Module had encountered severe solar storms on April 17, 19 and 22. The spacecraft survived the onslaught of energetic solar radiation. The two detectors collected precious information on the relations between solar storms and the ensuing disturbances in the near-Earth space environment.

Qin disclosed that similar experiments to monitor the space environment would continue on the SZ-4 mission later this year.

Data obtained from the space environment monitoring experiments will help scientists at SEPC to improve their forecast accuracy.

Combining data from the domestic Fengyun metsats (Fengyun means "Wind and Cloud"), foreign satellites and ground-based observations, SEPC scientists issue short-, medium- and long-range forecast on space environment conditions for Shenzhou launch and on-orbit operation.

The forecast reports include information on solar activities, solar radio emission, space radiation, geomagnetic activities, atmospheric parameters at the spacecraft orbiting altitude, meteoroid bodies, space debris environment and collision risks, and spacecraft orbital lifetime and decay rate.

The medium-range forecast offers decision-makers timely information and an effective reference opinion to choose a tentative "safe launch window" and mission duration period.

The center was pressed into service for the inaugural Shenzhou flight SZ-1 in Nov. 1999. Scientists at the center recalled that SZ-1 was originally planned to go into space on Nov. 18, 1999. But the center forecast a Leonid meteor storm at the planned launch time. The historic liftoff was postponed for two days to avoid any impact from the meteors.

On the SZ-2 mission the center had proposed two sets of mission dates.

Scientists eventually settled for the mission dates between Jan. 10 and 18, 2001 when they had forecast adverse space environment conditions on the 19th. However, the scientists did not provide details of how "adverse" the conditions were.

For the SZ-3 mission, as soon as the launch date was set SEPC scientists began long-term forecasting three months ahead of the blastoff. They issued monthly reports with a corrected launch time and mission duration based on the latest space environment conditions.

During the critical 8-day period from one hour before the SZ-3 launch to one day after the landing, teams of three forecasters provided round-the-clock monitoring of the changing conditions in space.

The forecast teams issued the last prelaunch forecast at T minus one hour. After SZ-3 achieved orbit, forecasters issued a report once every five orbits.

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