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Exective summary

The Science of SCOPE

The SCOPE mission strategy

SCOPE in the Roadmap

SCOPE and the simulation studies

Link to Cross-Scale (ESA)

Observation supporting bus system elements

In order to realize the plasma wave correlation measurements among the mother and daughter satellites, the spacecraft’s clock should be synchronized and the relative positions between the spacecraft should be obtained during the observations. The required accuracy is shown in the Table.

image largeimage small Inter-satellite time synchronization and ranging accuracy.

The requirements necessary for scientific observation are as follows.

(1) The clock must be synchronized with the accuracy indicated in Table 1 throughout the observation.

(2) The relative ranges should be obtained onboard the spacecraft with the accuracy indicated in Table 1, so that onboard data selection can be made.

(3) The 3-dimensional relative position should be obtained with the accuracy indicated in Table 1. Since real time determination is not required, the positions are calculated on the ground.

(4) Concerning the absolute positions with reference to the Earth, only the ordinary accuracy of orbit determination is required.

Since the conventional ground based orbit determination can achieve the accuracy of about 1km for SCOPE orbit, these requirements (1) - (4) lead to the need for onboard relative ranging and time synchronization system via inter-satellite communication link.

The three dimensional formation, is obtained by a filtering process on the ground. In order to know the orientation of the formation from the relative ranges, time domain history of the range data is required. Table 1 shows that the formation orientation must be determined within 1/100 rad. According to our analysis, the relative range measurement for a few hours per 3.7days orbital period is sufficient to achieve the required accuracy.

SCOPE adopts nominally a tetrahedron formation at apogee, with its size varying depending on the mission phase. The mission phase is mainly divided into two phases. In the “Phase-1”, all the daughters fly within 100km from mother. In this phase, the inter-satellite ranging and clock synchronization are fully utilized to satisfy the required accuracy shown in the Table. Additionally, the daughters are designed to be commanded from the ground station via mother satellite. This enables a concentrated operation of all the SCOPE satellites, using the mother as a gateway, to simplify the operation and mission management. In the “Phase-2”, daughters fly up to 5000km from mother. As they are too far from mother, and the accuracy requirement is looser in this range, each satellite is operated independently from the ground.

So far, BBM (Bread Board Model) of the inter-satellite ranging and clock synchronization system has been developed. This system is named ICORASS(Inersatellite Communication and RAnging, Synchoronization System). Figure shows the picture of the BBM including one mother spacecraft and two daughter spacecraft.

image largeimage small Bread Board Model of the the inter-satellite ranging and clock synchronization system (ICORASS).