Multi-functional Transport Satellites

Multi-functional Transport Satellites (MTSAT) is a series of geostationary weather satellites operated by the Japan Meteorological Agency (JMA). MTSAT carries an aeronautical mission to assist air navigation, plus a meteorological mission to provide imagery over the Asia-Pacific region. The meteorological mission includes an imager giving nominal hourly full Earth disk images in five spectral bands (one visible, four infrared). The satellites also have the capability to relay weather data from remote Automatic Weather Stations.

MTSAT is a box-like structure, 2.4m x 2.6m x 2.6m. The overall deployed length is about 33 meters and a launch mass of the spacecraft is about 2900 kg (dry mass is 1250 kg). It has a 2.7 KW Gallium Arsenide (Ga As) solar array with 3 panels, each 2.4m x 2.6m, mounted on the South pointing side. The array rotates to track the Sun and charges the Ni-Cd batteries. The use of a single solar array allows the emager's north-facing passive radiation cooler to view cold space. There is a 3.3m solar sail on a 15.1m boom on the North side. The solar sail counteracts the torque produced by sunlight pressure on the solar array. The trim tab on the solar array makes small adjustments to the torque balance. Two aeronautical L-band antennas (spot and global) are mounted on the East and West sides. The Image Sensor, the S-band Receive and Transmit antennas, the UHF antenna for the meteorological mission, and the Ku and Ka spot antennas for the aeronautical mission are all mounted on the Earth facing side. Also First IR MTSAT-1R Image showing Australia mounted on this side is the Earth Sensor which is next to the attitude control system which maintains the spacecraft's position in space using 12 small thrusters.

The MTSAT series of satellites are three axis stabilised satellites which use momentum wheels in the two horizontal axes and two reaction wheels in the vertical axis. The motion of the satellite can then be managed by increasing or decreasing the rotational speed of any of the "wheels" to provide corrections to the satellite's orbital path or to correct for roll, pitch and yaw of the satellite.

The imagery from the Earth is collected using the Japanese Advanced Meteorological Imager (JAMI) on board the satellite. The JAMI scans the Earth using a gimballed two axis scan mirror which relays the input scene to an off axis focal telescope. This telescope is focussed onto two focal planes which spatially sample the Earth at 4 km for the infrared channels and 1 km for the visible channel. The image sizes for a full Earth scan are then equivalent to an image of 121 million pixels for the visible image and 7.5 million pixels for the infrared images. The scan function of the imager is completely flexible but to scan the whole Earth from pole to pole takes about 20 minutes.

The first direct broadcast test transmissions to all ground stations in the Asia-Pacific region from MTSAT-1R occurred on 9 May 2005. The Bureau received its first images then, as shown above.

Summary

Imager characteristics

  • Imager hardware:
    • sensor module with 311 mm telescope
    • a servo-driven, two axis gimbaled scan mirror assembly
    • dual detector array
    • thermal louver
    • 94 K to 104 K passive radiant cooler
    • power supply module
    • electronics module
  • Imager wavebands and response functions for MTSAT-1R and MTSAT-2
    • Visible (VIS): 0.55 - 0.80 µm, Silicon (Si) photovoltaic detector
    • Infrared (IR1): 10.3 - 11.3 µm, Mercury Cadmium Telluride (HgCdTe) photoconductive detector
    • Infrared (IR2): 11.5 - 12.5 µm, Mercury Cadmium Telluride (HgCdTe) photoconductive detector
    • Water Vapour (IR3): 6.5 - 7.0 µm, Mercury Cadmium Telluride (HgCdTe) photoconductive detector
    • Near Infrared (IR4): 3.5 - 4.0 µm, Indium Antimonide (InSb) photovoltaic detector
  • Imager resolution:
    • Visible: 28 µ radian IFOV, 1 km nadir
    • IR 1-4: 112 µ radian IFOV, 4 km nadir
  • Imager quantization levels:
    • Visible: 10 bits
    • IR 1-4: 10 bits
  • Imager data is sent directly to the CDAS, processed and re-transmitted to users in HRIT and LRIT formats

MTSAT Transmission Parameters

  • HRIT:
    • Frequency: 1687.1 MHz
    • Modulation: 3.5 Msps PCM/NRZ-M/QPSK 50% RRC
    • Coding: Convolution (R=1/2, k=7) + Reed Solomon (255,223,4)
    • Bandwidth: 5.2 MHz
    • EIRP: 55 ±1.5 dBm
  • LRIT:
    • Frequency: 1691.0 MHz
    • Modulation: 150 ksps PCM/NRZ-M/BPSK, 50% RRC
    • Coding: Convolution (R=1/2, k=7) and Reed Solomon (225,223,4)
    • Bandwidth: 250 kHz
    • EIRP: 55 ±1.5 dBm

Operations Notices

  • 04 - 08 MAR: 02:30 UTC image cancelled due to sun interference.
  • 05 MAR: 20:30 UTC image cancelled due to scheduled JMA system maintenance.
  • 09-10 MAR: 02:30 UTC image affected by stray sunlight.
  • 01-10 APR: 02:30 UTC image may be affected by solar interference at ground station.