Long March 4B lofts CBERS-04A and Ethiopia’s first satellite

by Rui C. Barbosa

China launched a new remote sensing satellite on the CBERS program. Launch of CBERS-04A took place on December 20 from the Taiyuan Satellite Launch Center, Shanxi Province, at 03:21 UTC from the LC9 launch complex using the Long March-4B (Y44) – Chang Zheng-4B – rocket. The launch included other payloads, including Ethiopia’s first satellite.

CBERS-04A:

CBERS (China-Brazil Earth Resources Satellite) is a cooperative program between China and Brazil.

In China, the CBERS satellites are referred to as Ziyuan-1 (“Resource-1”). The agreement for the development of first-generation satellites was signed in July 1988 to establish a complete remote sensing system (space and ground segment) to supply both countries with multi-spectral remotely sensed imagery.

The overall objective is the observation and monitoring of the Earth’s resources and environment with a multi-sensor imaging payload providing different spatial resolutions.

With the same configuration as the CBERS-3 and CBERS-4 satellites, CBERS-04A is a remote sensing satellite medium resolution provided optical payloads operating in the visible spectrum with resolutions in the range of 2 to 60 meters.

The new satellites have improvements to accommodate the new Chinese Imager camera that has superior quality in geometric and spectral resolution.

Total mass for CBERS-04A is 1,730 kg and its dimensions are 1.8 x 2.0 x 2.6 meters, with solar panels dimensions 6.3 x 2.6 meters. The satellite will operate for 5 years in a 628.6 km orbit with 97.89 degrees inclination. Orbital Period will be 97.25 minutes.

The orbital characteristics of CBERS-04A are important for the missions achieving the sol-synchronicity for CBERS-04A, which ensures uniform illumination during imaging since the angle between the plane of the orbit and the line joining the center of the Earth to the Sun is kept constant throughout the mission.

Another important feature is the almost circularity of the orbit, which maintains regularity in the imaging range, making objects in the scene in any orbital positions are comparable in its dimensions. The local time for crossing the equator was set at 10: 30h, which establishes a compromise between a satisfactory amount of solar radiation, the contrast between targets and the presence of clouds. The repetition cycle set for 31 days with an interval between adjacent tracks of 3 days.

The fixed distance between tracks on the equator aims to ensure an overlap between tracks of two imagers will be described below so that imaging no risks are avoided at any point on the Earth’s surface.

The interval of three days between adjacent strips remains the same pattern as the previous imaging CBERS and allows phenomena occurring in areas adjacent two imaging ranges that may be viewed in a short time. Although it is an operating parameter set in two and a half kilometers the maximum acceptable range for the satellite deviates from the expected imaging range, which will ensure the regularity and consistency of imaging all the imaging ranges.

The division of responsibilities between Brazil and China will remain 50% for each country, as well as the division of responsibilities regarding the provision of equipment and subsystems. In the service module, Brazil was responsible for the structure, power supply and S-band communication TTCS. For its side, China was responsible for the thermal control system, attitude and orbit control system, monitoring board (with CTU RTUs and equipment provided by Brazil) and wiring.
For the payload Brazil is responsible for the Multispectral Camera (MUX), the Wide Field Imaging Camera (WFI), the Digital Data Recorder (DDR) and the Subsystem Data Collection (DCS), while China is responsible for the Data Transmitter System (DTS), Space Environment Monitor (SEM), Multispectral and Panchromatic Wide-Scan Camera (WPM) and Wiring (SYCS).

In addition to the subsystems that make up the satellite, each country is responsible for providing a set of test equipment used to test the satellite during the assembly phase, Integration and Test (AIT). Brazil was responsible the Mechanical Support Solo equipment – MGSE (for AIT in Brazil) and for the Solo Equipment Electrical Support – EGSE (SCOE for Brazilian and OCOE subsystems), while China was responsible for Solo Equipment Electrical Support – EGSE (SCOE for Chinese subsystems) and Mechanical Support Solo equipment – MGSE (to launch campaign in China).

CBERS-04A is equipped with cameras to optical observations from around the globe, as well as a data collection and environmental monitoring system. Payloads on the satellite are all instruments directly related to the acquisition of scientific data or related to satellite mission, as follows.

The instruments on CBERS-04A are the Multispectral and Panchromatic Wide-Scan Camera (WPM); Multispectral Camera (MUX), Wide Field Imaging Camera (WFI), Image Data Transmitter (DTS) to the MUX cameras (the WFI and WPM) Digital recorder (DDR), Data Collection System (DCS) and the Space Environment Monitor (SEM).

On imaging systems, it is Brazil’s responsibility to the MUX and WFI cameras, while China is responsible for the WPM camera.

The camera MUX for use in the CBERS-04A is the same as the CBERS-3 and CBERS-4, with a resolution increased to 16 meters in nadir due to reduced operating altitude CBERS 04A.

As the MUX camera, the camera WFI to be used in CBERS-04A is the same as the CBERS-3 and CBERS-4, with a resolution increased to 55 meters in nadir due to reduced altitude of the satellite. The WFI camera has as the main characteristic of their ability to perform return visits in a short period of time (up to 5 days), allowing activities such as monitoring and surveillance are well executed. The WFI camera has true character and multispectral resolution passed for 55 meters at nadir, due to reduction of the satellite operating altitude without losing the ability to revisit fast, as it kept a large target field.
The WPM camera is the main payload of the CBERS-04A is Chinese-made. It aims to provide images with a widescreen resolution of 2m and 8m multispectral resolution simultaneously in the orbit of the satellite. It has a width range imaged of 92 km, with 2 meter resolution in panchromatic mode and 8 meter resolution in multispectral mode.

The spacecraft consists of a hexahedron shaped structure divided into service and payload modules. In the orbital configuration, the Z axis is pointed to the Earth’s surface. The cameras and antennas are mounted on the +Z side panel. The solar panel is mounted on the -Y side panel and rotates around the Y axis. The antennas, thrusters and attitude sensors – such as sun sensors and infrared Earth sensors – are mounted on other panels.

The spacecraft is 3-axis stabilized keeping the imager pointed toward nadir. The AOCS (Attitude and Orbit Control Subsystem) includes sensors, gyros, GPS receiver, a control computer, momentum wheels and a hydrazine propulsion system.

Thermal control is achieved mainly by passive means using thermal coating and multi-layer insulation blankets. Heat pipes and heaters are also used. The EPS (Electrical Power Subsystem) uses triple-junction GaAs solar panels, a shunt regulator, battery charge control, a battery discharge regulator, DC/DC converters and NiCd (Nickel Cadmium) batteries. The EPS can provide 2.30 kW to the spacecraft.

The OBDH (On-Board Data Handling) subsystem consists of a main computer and 7 remote terminal units to provide onboard data handling and the spacecraft monitoring and control functions. The S-band is used for the TT&C functions providing two-way communications with the ground. The S-band antenna offers a near omnidirectional coverage.

The payload image data is downlinked in X-band by two TWTA transmitters. One of them has three carriers modulated in QPSK (Quadra-Phase Shift Keying): The on-board recorder has a capacity of 274 Gbit and is capable of recording data from all cameras.
The MUXCam is an INPE instrument designed and developed at Opto Eletrônica S. A., of São Carlos, São Paulo, Brazil. The objective is to provide imagery for cartographic applications. MUXCam is a multispectral camera with four spectral bands covering the wavelength range from blue to near-infrared (from 450 nm to 890 nm) with a ground resolution of 20 m and a ground swath width of 120 km. The MUXCam instrument consists of three devices: RBNA, RBNB and RBNC. The RBNA provides image acquisition and is composed of the optical system (entrance mirror and lens assembly), optical housing and the focal plane assembly.

The RBNC subsystem is responsible for generating the CCD reading clocks, processing the CCD analog outputs to a digital signal, and then encoding the signal into a serial data stream. This data is transmitted to the satellite.

The CCD detector is a 4-line array, each line having 6000 pixels of size: 13 µm x 13 µm. Spectral thin films, deposited over a window that covers the photosensitive elements of the CCD, are responsible for the separation of the four spectral bands.

Provided by China, the PanMUX (Panchromatic and Multispectral Camera) is a CCD pushbroom camera that provides panchromatic images with 5m GSD (Ground Sample Distance) and three-band multispectral images with 10 m GSD. The camera has a swath width of 60 km and a side-viewing capability of ±32º. The PanMUX has focal plane adjustment and on-orbit calibration capabilities.

Also provided by China and developed on the heritage of the Infrared Multispectral Scanner used on previous missions, the IRS (Infrared System) or IRMSS-2 (Infrared Multispectral Scanner-2) is an imager with 4 spectral bands. The spatial resolution is halved concerning IRMSS.

The WFI (Wide-Field Imager) (also referred to as WFI-2) is an advanced version of the INPE instrument flown on CBERS-1, and CBERS-2, featuring 4 spectral bands with a ground resolution of 64 m at nadir and a ground swath of 866 km.

The WFI instrument on CBERS-04A provides also an improved spatial resolution in comparison with the previous WFI sensors on board of the CBERS-1 and CBERS-2 satellites (260 m on previous missions), maintaining, however, its high temporal resolution of 5 days.

This camera will be used for remote sensing of the Earth and it is aimed to work at an altitude of 778 km. The optical system is designed for four spectral bands covering the range of wavelengths from blue to near-infrared and its FOV (Field of View) is ±28.63º, which covers 866 km, with a ground resolution of 64 m at nadir.

WFI has been developed through a consortium formed by Opto Electrônica S. A. and Equatorial Sistemas. The optical system development and the performance analyses (including optical system MTF, distortion, polarization sensitivity and stray-light) were executed using ZEMAX software.

Besides the cameras, CBERS-4 is equipped with the DCS (Data Collection System) and the SEM (Space Environment Monitor). The DCS is provided by INPE and the SEM is provided by CAST (Chinese Academy of Space Technology).

The FloripaSat small satellite

FloripaSat-1 is a technology demonstration mission entirely developed by SpaceLab students at the Federal University of Santa Catarina (UFSC), Brazil.

It is a cube-shaped satellite made of 5 modules. There the core modules for the mission control and the payloads. The core modules developed at UFSC are the On-Board Data Handling (OBDH), Telemetry, Tracking, and Control (TT&C), the Electric Power System (EPS), and the passive Attitude Control System (ACS). The payload is an amateur radio repeater, which can be used all over the globe in emergency and rescue situations.

Mission objectives are to introduce to the community the “new space” concept, which enables a more efficient and lower-cost development if compared with processes used in traditional satellites; In-orbit validation of a multi-mission platform that can be reused on satellites developed by other academia and industry groups; and to provide amateur radio relay station service to respond to emergency events in areas without coverage of the cellular network (oceans, rivers, forests, deserts).

Payloads onboard are the Payload-X and the Payload Rush. Payload-X has an FPGA made to resist radiation. This component will be tested for the first time in a space environment onboard FloripaSat. Payload RUSH was developed at UNSW University, Australia. First developed to validate a new approach to reconfiguring unique disturbance events due to solar radiation in reconfigurable logic circuits. This payload has an FPGA as the test circuit due to the ratio of logical density to power consumption.

ETRSS-1 Ethiopia first satellite

The 70 kg multi-spectral Ethiopian Remote Sensing Satellite was developed by the China Academy of Space Technology (CAST), as the prime contractor, after an agreement with the Ethiopian Space Science Technology Institute (ESSTI). Developed in collaboration with Ethiopian scientists, trained on the project as part of the technology transfer agreement, the development of the satellite had an estimated cost of USD 8 million (with the Chinese Government providing USD 6 million grant to cover the cost of the development).

ETRSS-1 satellite will provide data to monitor the environment and weather patterns for better agricultural planning, early warning for drought, mining activities and forestry management.

ESSTI will operate the ETRSS-1 via a ground receiving, control and command station located in Ethiopia at the Entoto Observatory and Research Centre.

Launch Vehicle and Launch Site:

The feasibility study of the CZ-4 Chang Zheng-4 began in 1982 based on the FB-1 Feng Bao-1 launch vehicle. Engineering development was initiated in the following year. Initially, the Chang Zheng-4 served as a backup launch vehicle for Chang Zheng-3 to launch China’s communications satellites.

After the successful launch of China’s first DFH-2 communications satellites by Chang Zheng-3, the main mission of the Chang Zheng-4 was shifted to launch sun-synchronous orbit meteorological satellites. On the other hand, the Chang Zheng-4B launch vehicle was first introduced in May 1999 and also developed by the Shanghai Academy of Space Flight Technology (SAST), based on the Chang Zheng-4.
The rocket is capable of launching a 2,800 kg satellite into low Earth orbit, developing 2,971 kN at launch. With a mass of 248,470 kg, the CZ-4B is 45.58 meters long and has a diameter of 3.35 meters.

SAST began to develop the Chang Zheng-4B in February 1989. Originally, it was scheduled to be commissioned in 1997, but the first launch didn’t take place until late 1999. The modifications introduced on the Chang Zheng-4B included a larger satellite fairing and the replacement of the original mechanical-electrical control on the Chang Zheng-4 with electronic control.

Other modifications were an improved telemetry, tracking, control, and self-destruction systems with smaller size and lighter weight; a revised nozzle design in the second stage for better high-altitude performance; a propellant management system for the second stage to reduce the spare propellant amount, thus increasing the vehicle’s payload capability and a propellant jettison system on the third-stage.

The first stage has a 24.65 meter length with a 3.35 meter diameter, consuming 183,340 kg of N2O4/UDMH (gross mass of the first stage is 193.330 kg). The vehicle is equipped with a YF-21B engine capable of a ground thrust of 2,971 kN and a ground specific impulse of 2,550 Ns/kg. The second stage has a 10.40 meter length with a 3.35 meter diameter and 38,326 kg, consuming 35,374 kg of N2O4/UDMH.

The vehicle is equipped with a YF-22B main engine capable of a vacuum thrust of 742 kN and four YF-23B vernier engines with a vacuum thrust of 47.1 kN (specific impulses of 2,922 Ns/kg and 2,834 Ns/kg, respectively).

The third stage has a 4.93 meter length with a 2.9 meter diameter, consuming 12,814 kg of N2O4/UDMH. Having a gross mass of 14,560 kg, it is equipped with a YF-40 engine capable of a vacuum thrust of 100.8 kN and a specific impulse in a vacuum of 2,971 Ns/kg.

Situated in the Kelan County in the northwest part of the Shanxi Province, the Taiyuan Satellite Launch Center (TSLC) is also known by the Wuzhai designation. It is used mainly for polar launches (meteorological, Earth resources and scientific satellites).
The launch center has two single-pad launch complexes, a technical area for rocket and spacecraft preparations, a communications center, mission command and control center, and a space tracking center.

The stages of the rocket are transported to the launch center by railway and offloaded at a transit station south of the launch complex. They were then transported by road to the technical area for checkout procedures.

The launch vehicles were assembled on the launch pad by using a crane at the top of the umbilical tower to hoist each stage of the vehicle in place. Satellites were airlifted to the Taiyuan Wusu Airport about 300km away and then transported to the center by road.

The TT&C Centre, also known as Lüliang Command Post, is headquartered in the city of Taiyuan, It has four subordinate radar tracking stations in Yangqu (Shanxi), Lishi (Shanxi), Yulin (Shaanxi), and Hancheng (Shaanxi).

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