SVN 20 End-of-Life Frequency Standard Test Results
Abstract
In early 1989, the first Block II Global Positioning System (GPS) satellites were launched, marking the beginning of the second phase of the GPS program. The satellites were designed for a seven-and-one-half year lifespan and a six-year mean mission duration. Launched in March 1990, SVN 20 was the seventh of the Block II GPS satellites. On 11 May 1996, SVN 20 was set permanently unhealthy to users after being operational for just over six years. Due to degradation of the Attitude Velocity and Control Subsystem (AVCS), SVN 20 was no longer capable of maintaining the stable, earth-pointing platform necessary to perform the GPS navigation mission. However, through intensive maintenance by personnel at the Master Control Station (MCS) at Falcon AFB, it was possible to stabilize the vehicle long enough to perform extensive end-of-life testing on the four on-board atomic frequency standards. These tests on both the cesium and rubidium frequency standards varied in duration and complexity. Of the four frequency standards, one had been operational for five months, two had been used previously but were since off-line for two years and four years respectively, and one had never been initialized. Areas of interest for the rubidium clocks included determination of the temperature coefficient, voltage-controlled crystal oscillator (VCXO) open-loop operations, and measurement of the C-field and VCXO tune ranges. For the cesium frequency standards, the tests focused on Ramsey pattern generation, gain determination through loop time constant measurement, and C-field and VCXO performance degradation. All four clocks were still operational at various levels of performance and accuracy. The results of these tests were encouraging in that they supported conclusions made during the SVN 9 and SVN 10 (Block I) end-of-life testing. It is hoped these results will be useful to the GPS clock community as observations of performance characteristics of space-based atomic frequency standards.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1997
- Accession Number
- ADA500663
Entities
People
- Gary L. Dieter
- M. J. Van Melle
- Reeves E. Bower
Organizations
- 2d Space Operations Squadron