Long March 2C lofts CFOSAT for CNES

by Rui C. Barbosa

China launched a cooperative mission with the French agency CNES when the CFOSAT oceanographic satellite was lofted place from the Jiuquan Satellite Launching Center at 00:43 UTC Monday. A Long March-2C (Chang Zhen-2C) rocket was used to launch the new satellite together with several small satellites.

Developed jointly by the China National Space Administration (CNSA) and the Centre National d’Études Spatiales (CNES), CFOSAT carries two radar instruments. The SWIM (Surface Waves Investigation and Monitoring), is a wave scatterometer supplied by CNES and the SCAT (wind SCAT terometer), a wind-field scatterometer supplied by CNSA.

SWIM’s 6 rotating beams will enable it to measure wave properties (direction, wavelength, etc.), while SCAT will measure wind intensity and direction. The data will be downlinked to French and Chinese receiving stations.

These data will allow scientists to achieve more accurate ocean forecasts and give earlier warning of severe weather events like storms and cyclones. CFOSAT will also help climatologists to learn more about exchanges between the oceans and atmosphere, which play a key role in climate.

Conceived by the LATMOS atmospheres, environments and space observations laboratory in Paris and Guyancourt, the SWIM instrument was developed by Thales Alenia Space with oversight and funding from CNES. Other mission partners include the French Institute of marine research and exploration IFREMER, the French national weather service Meteo-France, and SHOM, the French naval hydrographic and oceanographic office.

Both instruments are Ku-band radars (13.2 to 13.6 GHz) scanning around the vertical axis. SWIM is a 6-beam radar at small incidence (0 to 10°), SCAT is a rotating fan-beam radar with larger incidence angles (18~50°). This combination of incidence angles is necessary to measure the wind vector (from large incidence) and wave properties (from small incidence).

CFOSAT in action – via CNES

The interest for the combination of the two payloads is evident since surface wind is the energy source which creates the surface waves; the space and time evolution of these surface waves is dependent on both local and remote wind conditions. The combination of the two instruments will help to separate the different effects governing the evolution of the wave field.

CFOSAT is a pre-operational mission of joint measurements of winds and waves which aims is to supply wind/wave observations in near-real time to the meteorological agencies to improve their forecast and sea state models. These measurements will also be supplied to the scientific community for the oceanographic and climate research to improve sea models as well as our understanding of the influence of the sea state on surface fluxes.

Operating at an altitude of 519 km, CFOSAT’s data availability will be in near-real time (less than three hours after acquisition) for the meteorological agencies. Data distribution will be made on request through a server and an authentication for the scientists, and systematically through meteorological servers for the meteorological agencies. The satellite will have a global coverage at a 13-day scale for SWIM and at a 3-day scale for SCAT.

CFOSAT is based on the CAST2000 satellite bus provided by the DFH Satellite Corp. The spacecraft has a launch mass of 600 kg and the primary structure has a size of 1.4 m x 1.4 m x 1.2 m. Mission design life is 3 years.

These main objectives are the modeling and prediction of ocean surface wind and waves; to determine the physical processes of wind and waves; to determine the interactions between surface waves, atmosphere and ocean; to investigate the interactions between electromagnetic signals and the ocean surface; and to study the wave evolution in coastal regions.

The requirements for the two payloads on CFOSAT are to estimate directional spectra of ocean waves along the satellite track at scales ranging from 50 x 50 km² to 70 x 70 km²; to transmit data in near real-time within 3 hours after acquisition; to estimate wind speed and significant wave height from nadir-looking beam, in a way similar to altimeter missions, and to estimate the wind vector over a swath of about 900 km with a nominal resolution of 50 x 50 km² (goal 25 x 25 km²); to sample spectral wave properties with a global coverage at a temporal scale of 10 to 15 days; and to sample wind with a global coverage at a temporal scale of 1 to 2 days.

The accuracy for wave estimates is of a minimum detectable wavelength of about 70 m, maximum detectable wavelength about 500 m, accuracy in wave propagation direction of about 15°, accuracy in wavelength of 10 to 20%, accuracy in significant wave height of 10% or better than 40-50 cm (TBC); the accuracy on wind speed estimates of ±2 m/s or 10% (whichever is larger) and on wind direction of ±20° in the range 4-24 m/s.

The two instruments will also be able to estimate the radar cross-section dependence with incidence (from 0 to 10° and from 18 to 50° for SWIM and SCAT, respectively) and azimuth, in order to derive from properties on the statistics of the sea surface slope (mean square slope, shape of the slope probability density function), to estimate of wind direction and wind speed; in the polar ice sheet, the contribution of volume scattering with respect to surface scattering, and ice surface and snow pack characteristics; and the humidity and roughness of bare soils over land surface.

The CFOSAT ground segment is composed of several major components located in different countries. The Control Centre and the S-band station network are located in China, while the French Mission Centre, with its two X-band polar stations, is located in France, Canada, and Sweden. The Chinese Mission Centre and its three X-band stations are also located in China.

The Satellite Control Centre (located in Xi’an) and its Telemetry, Tracking, and Commanding (TT&C) S-band station network are in charge of operation, control and management of the CFOSAT satellite. The Centre will be used for reception and processing of satellite telemetry data and monitoring of satellite operation status; transmission of commands and uploading of command data in order to control and manage the satellite; and tracking, determination, and forecast of the satellite’s orbit (including injection orbit).

The Satellite Mission Centre is composed of two independent Mission Centres: the French Mission Centre, located in Toulouse and Brest, and the Chinese Mission Centre located in Beijing. Both Mission Centres are in charge of reception of both instruments’ (SWIM and SCAT) scientific telemetry; for processing of both instruments’ (SWIM and SCAT) scientific telemetry, as well as combined SWIM, SCAT, and other instruments’ telemetry; and to generating, archiving, and dispatching the CFOSAT scientific products to the end users.

The CAST2000 is a compact satellite platform characterized by its high performance, expandability and flexibility. It is fitted with an S-band TT&C sub-system, X-band data transmission sub-system and 3-axis attitude stabilization, and is able to offer highly precise control, large-range sway maneuver, flexible orbit maneuver, highly integrated housekeeping and highly effective power supply.

Together with the CFOSAT, the Long March-2C orbited five small satellites: the Xiaoxiang-1 (2), Zhaojin-1 (Tongchuan-1), Tianfuguoxing-1 (Xinghe), Changshagaoxin and the CubeBel-1 (BSUSat-1).

Xiaoxiang-1 (02) is a small satellite demonstration mission for the LaserFleet that aims to develop a 288 small laser communication satellite constellation to provide broadband Internet access.

Also designated Tongchuan-1, the Zhaojin-1 is a 6U CubeSat that is the first of a 24 satellite constellation developed by the Tsinghua University. The designated Gamma Ray Integrated Detectors (GRID) will try to detect the signatures of the gamma-ray bursts, trying also to identify and locate the electromagnetic counterparts to gravitational waves.

The Tianfuguoxing-1 (Xinghe) CubeSat will be used for technological demonstration. The mission is operated in conjunction with the Guoxing Yuhang Co. Ltd. (ADA Space).

CubeBel-1 (BSUSat-1) was developed by the Belarusian State University (BSU) and is a demonstration satellite to test satellite propulsion, communications systems, and data collection, among others. It will have a design life of 5 years and be placed in Low Earth Orbit (LEO) at an altitude of 500km and will transmit radio signals that students can access by using a USB flash drive. The agreement to launch BSUSat-1 was signed on February 7 between BSU and the China Great Wall Industry Corporation (CGWIC).

The 2U CubeSat will serve as a basis for various aspects of the aerospace educational and research programs at the university. In the context of practical courses, students will learn to receive and process telemetry and satellite imagery, to test various stabilization algorithms, calculate orbital elements, to study gamma spectra at low Earth orbit, etc. Students will study also the radio systems of amateur satellites and get an idea of amateur radio. The satellite has been equipped with a digital repeater for the purpose of amateur radio community.

The Chang Zheng 2C (Long March 2C) is a Low Earth Orbit (LEO) launch vehicle derived from DF-5 ICBM.
The rocket can be launched from the Jiuquan Satellite Launch Center or from the Taiyuan and Xichang Satellite Launch Centers.

Long March 2C from a previous launch

The launch vehicle has three configurations. The basic two stage Long March-2C and the Long March-2C/SMA and the Long March-2C/SM, using upper stages.

The rocket is a two stage hypergolic launch vehicle with a total length of 35.15 meters, a diameter of 3.35 meters and a total mass of 192,000 kg. The first stage is equipped with four YF-20A engines. It has a length of 20.52 meters and a burn time of 122 seconds.

The second stage is equipped with one YF-22A engine and has a length of 7.50 meters with a burn time of 130 seconds.

The Jiuquan Satellite Launch Center, in Ejin-Banner – a county in Alashan League of the Inner Mongolia Autonomous Region – was the first Chinese satellite launch center and is also known as the Shuang Cheng Tze launch center.

The site includes a Technical Centre, two Launch Complexes, Mission Command and Control Centre, Launch Control Centre, propellant fuelling systems, tracking and communication systems, gas supply systems, weather forecast systems, and logistic support systems.

The launch site photoed from the ISS

Jiuquan was originally used to launch scientific and recoverable satellites into medium or low earth orbits at high inclinations. It is also the place from where all the Chinese manned missions are launched.

The LC-43 launch complex, also known as South Launch Site (SLS) is equipped with two launch pads: 91 and 94. Launch Pad 91 is used for the manned program for the launch of the Long March-2F launch vehicle (Shenzhou and Tiangong). Launch Pad 94 is used for unmanned orbital launches by the Long March-2C, Long March-2D and Long March-4C launch vehicles.

Other launch zones at the launch site are used for launching the Kuaizhou, Kaituo, the Long March-11 solid propellant launch vehicles and other private solid launch vehicles, like the Zhuque-1.

The first orbital launch took place on April 24, 1970 when the Long March-1 rocket launched the first Chinese satellite, the Dongfanghong-1 (04382 1970-034A).

Next in line for China will be the launch of two new navigation satellites from the Xichang Satellite Launch Center schedule for November 1.

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