Introduction

The Earth Observing 1 (EO-1) spacecraft has been one of the most trouble-free spacecraft that NASA has launched. A NASA New Millennium Program (NMP) mission dedicated to validating revolutionary technologies that will be used in future government and commercial missions, EO-1 was launched in November 2000 and flies in formation with Landsat 7. As the prime contractor, Swales Aerospace designed and built the spacecraft bus, integrated and tested the EO-1 observatory, and performed launch-site operations.

The EO-1 spacecraft was launched from Vandenberg Air Force Base on November 21, 2000, into a circular, sun-synchronous polar orbit at an altitude of 705 kilometers. It was co-manifested on the Boeing Delta II (7920-10C) launch vehicle with the SAC-C satellite developed by Argentina. The EO-1 orbital inclination (98.2 degrees) and descending nodal crossing time (10:01 a.m.) put it in "formation flight" with Landsat 7 and EOS AM-1 (Terra). With all three satellites following the same ground track, EO-1 flies "behind" Landsat 7 but "ahead of" Terra.

NMP, as a technology-driven mission, accepts a greater level of risk than the level considered acceptable for many other missions. Nevertheless, EO-1’s design sought to minimize risk to the extent possible given cost constraints that dictated a single-string design and which limited redundancy to key areas where risk mitigation was important. These areas of redundancy included mechanisms, e.g., solar array release; the power harness; portions of the command and data handling processor (two separate programmable read-only memories (PROMs) where each contained the full flight code); and an attitude control system safe-hold mode installed on a separate processor.

Table 1 lists the EO-1 Spacecraft bus salient specifications.

Table 1. EO-1 Spacecraft Specifications