Citation
Abstract
The Deep Space 3 (DS3) mission will demonstrate several elements of the technology required for optical space interferometry, including autonomous formation flying (AFF). It will consist of three spacecraft, each having a degree of autonomy but all composing a single instrument and constrained to move together at the vertices of an equilateral triangle with sides of 100 to 1000 m. In order to meet the mission’s goals, AFF must measure the distances between spacecraft within 1 cm and the relative orientations of the spacecraft within 1 arcmin per axis. This article proposes an implementation of AFF that borrows technology from the Global Positioning System (GPS), using measurements of both rf carrier phase and a ranging code. Each spacecraft will have at least one transmitting antenna and three receiving antennas, operating at 30 GHz with a code rate of 100 Mchips/s. To validate the proposed scheme, two sets of covariance analyses have been performed using batch and sequential processing. Both analyses suppose measurement errors of 1 cm on the ranges and 10 „m on the phases, but they process the data differently and make somewhat different assumptions about the nature of systematic errors. Nevertheless, the two analyses reach similar results, concluding that with careful calibration the mission requirements can be met by measurements of the specified accuracy. In general, AFF measurements adequate to meet the DS3 specifications will require an initialization period extending over several epochs separated by substantial spacecraft rotations. Because the spacecraft will be capable of only very slow angular acceleration, this initialization may take as long as 15 or 20 min. During normal operation, however, initialization should rarely be needed. The article also summarizes various aspects of the proposed implementation that have not been entirely worked out, indicating in general terms how each might be handled and what problems remain to be solved. These problems include initialization, the location and beam shape of the antennas, multipath, systematic measurement errors, and the effect of the local transmitter on received signals. 1Tracking Systems and Applications Section.
Keywords
Details
- Volume
- 42-134
- Published
- August 15, 1998
- Pages
- 1–21
- File Size
- 392.2 KB