 IOCS (Inter-Orbital Communication Subsystem) transmits observation data via ETS-VI (Engineering Test Satellite-VI) and COMETS (Communications and Broadcast Engineering Test Satellite).
The ADEOS spacecraft was developed by the Mitsubishi Electric Corporation, Tokyo. NEC Corporation and Toshiba Corporation were subcontractors to Mitsubishi Electric Corporation.
Table 1: Some spacecraft parameters of ADEOS
Launch: The launch of ADEOS took place on August 17, 1996 with the H-II launch vehicle from TNSC (Tanegashima Space Center), Japan.
Orbit: Sun-synchronous sub-recurrent polar orbit; apogee = 804.6 km; perigee = 789.0 km; orbital period = 100.8 min, 10:30 AM local sun orbit (on descending node). Ground repeat cycle=41 days (subcycle = 3 days), inclination = 98.625º.
RF communications: ADEOS provides onboard recording (MDR=Mission Data Recorder (three instruments) and LMDR = Low Speed Mission Data Recorder). Observation data rates: AVNIR (M): 60 Mbit/s, AVNIR (P): 60 Mbit/s, OCTS: 3.0 Mbit/s. Polder: 0.882 Mbit/s. IMG: 0.9 Mbit/s. ILAS: 0.517 Mbit/s. NSCAT: 2.9 kbit/s. TOMS: 0.7 kbit/s.
RF comuunications: TT&C: Uplink frequency (S-band) = 2.0 GHz (CMD and ranging), downlink frequency = 2.2 GHz (TLM and ranging), command bit rate = 500 bit/s.
IOCS frequencies: S-band (low rate mission data), Ka-band (120 Mbit/s max).
Figure 2: Artist's rendition of the ADEOS spacecraft (image credit: JAXA)
• The ADEOS spacecraft operations were terminated: ADEOS operated nominally for some period (10 months), but then suffered several malfunctions and stopped functioning on June 30, 1997 after an apparent loss of power due to structural damage in its solar array. This loss of an observatory like ADEOS was definitely a great blow, particularly for all involved in the mission and of course the data user community. 9)
Immediately after this great loss of the spacecraft, Jaxa established a Task Team to investigate the cause. The investigation lasted about three months and focused on the solar paddle subsystem (PDL) and the attitude orbit control system (AOCS).
• JAXA completed the on-orbit initial checkout of all equipment aboard ADEOS as planned. The satellite began the routine operational phase on November 26, 1996, and the project began providing OCTS and AVNIR standard products for the ADEOS PIs on January 1, 1997. 10)
• The critical phase of ADEOS ended after the 22nd revolution on August 19, 1996. JAXA started verifying the functions of the bus system and the mission instruments on that date. The initial mission checkout of ADEOS will continue for 90 days (until the middle of November 1996). 11)
Sensor complement: (OCTS, AVNIR, NSCAT, TOMS, POLDER, IMG, ILAS, RIS)
OCTS (Ocean Color Temperature Scanner):
OCTS is a mechanical scanning (whiskbroom) radiometer, and a JAXA (NASDA) core sensor. Objectives: Ocean color and sea surface temperature measurements (ocean primary productivity, interaction between the ocean and the atmosphere and environmental studies). OCTS offers 12 measurement bands from 0.402 - 12.5 µm. Swath width = 1400 km; ±20º along-track tilting. Spatial resolution: approx. 700 m. Operation requirements: global observation of the Earth during daytime (TIR channel during night if required). 12)
Table 2: Definition of OCTS parameters
The OCTS sensor consists of a scanning radiometer with an optical system, a detector module and an electrical unit. OCTS employs a catoptric optical system and a mechanical rotating scanning method with a mirror (due to wide spectral coverage). OCTS can be tilted about the along-track axis to prevent sea surface sun glitter. The IR detectors are cooled to 100 K by a large radiant cooler facing deep space. Calibration: solar and internal lamp for VNIR, deep space and black body for IR. 13) 14) 15) 16)
Figure 3: The observation concept of the OCTS instrument
Figure 4: Internal configuration of the SRU (SCanning Radiometer Unit) of OCTS (image credit: NASDA)
Figure 5: First ocean color image of the Sea of Japan and the East China Sea taken by OCTS on October 1, 1996 (image credit: JAXA) 17)
AVNIR (Adv