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Spacecraft Bus  



see the associated Validation Report,
Part 2

Related Sites
USGS/EO-1 website at

Questions and comments related to this document should be directed to:

Michael Flick
EO-1 Technology Transfer Manager
EO-1 Mission Office
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Phone: 301-286-8146
Fax: 301-286-1736
E-Mail: Michael Flick

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

Average Orbit Power

350 W

Spacecraft Bus Dry Mass

410 kg (including WARP and X-band phased array antenna (PAA)

Total Mass

588 kg


1.4 x 1.4 x 2 m high

Payload Attach Fitting


Pointing Stability (Jitter)

0.3 asec/sec

Slew Rate

15 deg/min


Zero Momentum 3-axis stabilized


1 receiver

Navigation Accuracy

60 m, each direction (3 sigma)

Science Data Downlink Capacity

105 Mb/s

Science Data Storage Capability

48 Gbits within WARP

C&DH Bus Architecture

Mongoose V, Rad Hard at 12 MHz
RISC Architecture

Downlink Formats/Network


Downlink Band

S-band (variable to 2 Mbps)
X-band (105 Mbps)

Uplink Band

S-band (2 Kbps)


Super NiCd/50 Ah


3 Panel/Si with GaAs/Articulating/5.25 m

Nominal Voltage

28 V


Hexagonal; aluminum honeycomb


1 tank/4 thrusters

Propellant Capacity

23 kg

Max delta V

85 m/s

Mission Design Life

1.5 years

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