1. Satellite platform

The platform uses an extension of the product that had been successfully used for the missions of Beidou, Tan and SVOM satellites, which has been proven high stability and high technical ready maturity. The launching status of the whole satellite is:

• Size: 3000mm×3605mm
• Weight: ≤1450kg
• Power: ≥1212 Watts in average
• Attitude: 3-axis stabilizing, inertial orientation during observation
• Manoeuvring capacity: better than 60 degree in 4 minutes
• Pointing accuracy: better than 0.05 degree
• Stability: better than 0.0005 degree/s

2. Scientific payloads alignment

The satellite aligns the 12 WXT models in a 1/9 spherical surface according to their combined FoV of 3600 square degree, with the FXT in the central position. The FXT optic axis is set to be a critical baseline for all the 12 WXT models' orientation and the star sensors that give pivotal knowledge for the satellite manoeuvring in-orbit. A preliminary layout of the platform is shown in Figure 1

　　Figure 1 A preliminary layout of the platform.

3. Satellite operating modes

EP Satellite includes the following operating modes: all-sky survey, burst observation mode, ToO mode, calibration mode, energy acquisition mode and security mode. In order to realize the variety of operating modes above, the satellite has been designed to adapt orientating strategy of solar orientation, attitude maneuvering, and target orientation (inertial orientation).

　　Figure 2 Operation mode and pointing strategy

4. Orbit

A low-earth circular orbit with a low inclination in an altitude of 550 to 650 km is preferred to be designed for the EP satellite, which should mainly satisfy the requirements of observing operations, near-real-time data downlink/uplink, and minimizing irradiation interference by energetic particles mostly concentrated in the radiation belts and South Atlantic Anomaly (SAA) areas. The lifetime of the EP satellite is required to be  3 years (5 years as a goal). The launch site will be in Xichang Satellite Launch Centre, which allows direct orbit injection with inclination lower than 30 degree.

Table 1 Operating Orbit Parameters