1. International Space Cooperation in Asia-Pacific Region

During early 1990s of the 20th century, several Asian and Pacific countries had realized that it's very importance for them to use space technology in environmental monitoring and disaster management, and it's necessary to conduct such applications by the manner of international cooperation in Asia-Pacific Region, because it's economically affordable / efficient and technologically sound. Inspired by this idea, starting from 1992 and based on a consensus, more than 10 Asian-Pacific countries have involved in the multilateral cooperation activities in the field of space technology and its applications. Guided by the mechanism of multilateral cooperation in space technology and applications in light of the consensus, so far Asian and Pacific countries have organized seven sessions of Asia-Pacific Space Cooperation Conference respectively in Bahrain, China, Iran, Korea, and Thailand, etc. These activities have strongly promoted the information exchanges and human resources cooperation on space science, space technology and their applications in Asia-Pacific Region. As the space cooperation increasingly expands in this region, participated by Bangladesh, China, Iran, Korea, Mongolia, Pakistan, and Thailand, the program of Small Multilateral Mission Satellites (hereafter referred as the SMMS) began from late 1990s of last century. As part of the efforts of international space cooperation in Asian Pacific Region, the SMMS has been aimed to combine itself with other space programs of Asia-Pacific countries, so as to constitute a constellation of the SMMS for civilian purposes, especially for environmental and disaster monitoring; and the first optical satellite of the SMMS has been scheduled to be launched by China either in late 2007or early 2008.

2. Introduction to the Program of the SMMS (the SMMS)

It has been broadly known that environment pollution, ecological destruction and natural disasters have seriously affected the sustainable developments of economies and societies around the world. Thus some effective solutions to prevent or cure them are urgently needed by all the countries in the world. Bearing this need in mind, a constellation of the SMMS can play a very important role in generating the conditions to help find the solutions to the problems caused by them. While within the family of a constellation of the SMMS, the remote sensing satellites, technologies and its applications stand in a significant position in environment protection and disaster mitigation both in China and around the world. When we dive a bit deeply into the SMMS, the conditions for solving the problems caused by the individual adverse events mentioned-above have to be carefully figured out based on the knowledge of the events; while recognizing, differentiating and classifying the situations and status of the events accurately, serve as the premise to monitor and manage them. To achieve these, some specific system requirements have been determined comprehensively for the SMMS and for the constellation of it as well. In sum, a spatial resolution range of 3 to 100m, from hours to many days revisiting time, multi-spectral bands with high resolution and wide swath will be needed for most of the applications in environmental monitoring and disaster mitigation, especially for getting the clear images of these negative events first. As for the all-weather and all-time observations, microwave and infrared remote sensing technologies will be very useful. To get the images out of the negative happenings from the receiving areas of ground stations, it is a better way to reach this via a constellation of SMMS rather than by individual satellites, because existing satellites themselves alone can not meet all the requirements of applications. So a set of correlated satellites is necessary to be built to meet the comprehensive requirements among Asian-Pacific countries. As the SMMS among the mentioned-above Asian-Pacific countries is specified, we could say that it is mainly proposed by the stakeholders for the purpose of monitoring environmental changes and natural disasters in Asia-Pacific Region.

The current environmental and disaster monitoring system with the SMMS can be divided into two segments: space segment and ground segment. As to the space segment, it involves two stages: the first stage (baseline) is arranged to make three satellites, and its second stage to produce eight satellites (four optical satellites and four SAR satellites). While its ground Segment includes data receiving, pre-procession, and application systems, and so on. Optical satellites are also an indispensable part of the SMMS, though they seem not that striking as remote sensing satellites do in the family of the SMMS. They have 650km/ 10:45AM sun synchronous orbits, and four of them are 90°phase distributed in the same orbit plane. Another indispensable part of the SMMS is the group of SAR satellites. The SAR satellites normally have 500km/ 6:00AM sun synchronous orbits, and four of them are also 90°phase distributed in the same orbit plane like the optical satellites. As we have known that the first stage (baseline) of the SMMS includes three satellites and their ground systems. The baseline system will begin to establish no later than 2008, and it is expected to expand into its second stage of eight satellites as soon as possible. The satellites of the second stage have been proposed to be constructed through an international cooperation among Asian Pacific Countries. To make the SMMS work well for us, certain kinds of Payloads have to be chosen and identified to fix on the satellites of the SMMS. They could be wide field multi-spectrum cameras, infrared scanners on the optical satellite 1, and hyper-spectrum imagers on the optical satellite 2, data collection systems on all the satellites, and the synthetic aperture radars on the SAR satellites, etc. Specific platforms, such as the platforms based on the CAST 968 platform, which was once used for several small satellites developed by Chinese Academy of Space Technology (CAST), could be considered here to apply in the SMMS. They normally include structure mechanism, attitude and orbit control system (AOCS), electronic power supply subsystem (EPSS), TT&C, OBDH, system circuit, etc. Besides the space segments, in the purpose of the SMMS, its ground segment is even more important, because it's where we can derive out our civilian applications from. In this regard, it is integrant for us to have a rough idea about how the ground segment or say the ground application systems (the name sounds fit better for the SMMS in the sense of applications than the ground segment) constitute and operate. We should know that the ground application systems are mainly composed of ground receiving, pre-processing systems, and application systems. While a so-called ground receiving and pre-processing system further embrace ground receiving subsystem, pre-processing subsystem, operational management subsystem, and data transmission / communication subsystem. While an application system mainly includes national environmental monitoring & forecasting center, and application center for national disaster mitigation. The ground receiving and pre-processing systems of the SMMS can be viewed as a three-station network being able to cover all Chinese territories, receiving and recording large-volume data (the data volume received by the three stations will be up to several hundreds of G-bytes each day) of multiple satellites, multiple sensors, and different data rates at a real-time mode. It can also conduct real time resolution-decreasing processing of optical and SAR data at each station, with the system capabilities of generating high production, near real time & high speed, and all resolution pre-processing products; while at the same time it can perform data transmission and communication tasks as well.

Now let's come to the issue of the environmental application system of the SMMS. The core of the environment application system is the national center of satellite disaster mitigation and environmental monitoring & forecasting. It is composed of following four parts:
-- Environmental remote sensing and GIS;
-- Special application sub-system;
-- Environmental remote sensing decision-making support sub-system;
-- Data network environment.

While a disaster mitigation application system of the SMMS is dominantly composed of image analysis application sub-system, and disaster decision-making support sub-system. The core of disaster mitigation application system is a disaster mitigation application system at national level, which further consists of disaster information sub-system, information processing sub-system, disaster forecasting and evaluation sub-system, aided by the decision-making sub-system, emergency management sub-system, disaster study, and training sub-system,etc.

Finally, the overall performance of the SMMS can be judged and measured by the payload features of its component satellites, such as Revisit time intervals of the satellites, coverage scales of the CCD Cameras and Infrared Scanners, and the Observation opportunities (in equatorial region). As we stated in the very beginning of this paper, international cooperation in peaceful use of space is a common request upon environmental protection and disaster mitigation issues. Sun synchronous orbit satellites are a practically feasible global resource for all the countries, but the construction of a satellite constellation demands very huge financial input and strong technological supports. It is often unaffordable for quite a lot of countries alone, and this holds to Asian Pacific countries too. Thus to form a joint effort to accomplish the SMMS, so as to reach the goal of completing the Constellation of the SMMS and to share the data acquired from the constellation in Asia-Pacific Region, is an efficient approach to realize the goals above, and a good example for other parts of the world. The SMMS will definitely benefit all the Asian-Pacific countries participating in the program, and make major contributions to them in their affairs of disaster mitigation and environment protection.