MOS-1/1B Overview

MOS-1/1B
Mission
MOS-1 Overview

The Marine Observation Satellite (MOS - also known as MOMO) constellation consisted of MOS-1 and MOS-1B, Japan’s first satellites dedicated to marine observation. Both satellites housed the same instruments:

Multi-spectral Electronic Self-Scanning Radiometer (MESSR), designed to provide information on coastal zone dynamics, water resources, vegetation dynamics, and geological applications.
Microwave Scanning Radiometer (MSR), that provided information on sea ice, snowfall, and water vapour content at the ocean and in the atmosphere.
Visible and Thermal Infrared Radiometer (VTIR) that measured sea-surface temperature.

Mission Background

The constellation was developed by NASDA (National Space Development Agency of Japan), now part of JAXA (Japan Aerospace Exploration Agency) for natural resource utilisation and environmental protection. After 10 years of development, MOS-1 was launched in February 1987, followed by MOS-1B in February 1990, into an orbital plane only a few degrees away from MOS-1.

Satellite Design

The MOS spacecraft had dimensions of 1.26 x 1.48 x 2.40 m and a singular solar array of three 1.51 m wide panels with 1-axis articulation providing power. It was composed of two modules: a bus module and a mission module, on which the three instruments were mounted. Both satellites were nadir-pointing, three-axis stabilised and controlled by momentum wheels and four hydrazine thrusters. Communications consisted of S-, X-band downlink, and S-band uplink, with mission design lives of 2 years. MOS-1 and 1B had respective launch masses of 745 kg and 740 kg.

Mission Operations

MOS-1 was launched on 19 February 1987, at 01:23 UTC on the N-2 launch vehicle followed by MOS-1B on 7 February 1990, at 01:33 UTC on the H-2 launch vehicle. Both satellites were launched from Tanegashima Space Center, Japan. The two satellites were placed in sun-synchronous orbits at a height of 909 km with inclinations of 99.1° (MOS-1) and 99.0° (MOS-1B), and with an orbital period of 103 minutes. The initial revisit period of 17 days was halved following the launch of MOS-1B as the two satellites were in the same orbit, but were separated by 180°.

Payload data from the satellites were primarily transmitted in real-time to the NASDA (now JAXA) Earth Observation Center in Hatoyama, Japan.

MOS-1 ended operations on 29 November 1995 due to a degradation of the batteries, while MOS-1B ended operations on 17 April 1996. With mission durations of nine and six years respectively, MOS-1 and MOS-1B greatly exceeded their designed lifetime of two years.