Environmental Engineering Reference
In-Depth Information
agent, which prepares the SI, as necessary, for the upcoming observation uti-
lizing plans generated by the planning-and-scheduling agent, would command
execution of these plans at the proper time. The data generated would then
be processed by the SI data processing agent for storage and later transmis-
sion to the ground by that agent. By this means, immediate onboard response
removes the need for scheduling revisits at a later date.
6.3 Spacecraft Enabling Technologies
To support the Remote Agent functionality described in the previous subsec-
tions, a series of enabling technologies will be required. Many of these technol-
ogy elements have already been flown on NASA missions, but have not as yet
achieved mainstream status. Others are proposed for use on upcoming NASA
missions, but are not as yet flight-proven. And others are still purely in the
“talking” stage, but could reasonably be expected to be available in the next
decade. The following is the list of technology items:
1.
Modern “Lost-in-Space” star trackers
2.
Onboard orbit determination
3.
Advanced flight processors
4.
Cheap onboard mass storage devices
5.
Advanced operating system
6.
Decoupling of scheduling from communications
7.
Onboard data trending and analysis
8.
Ecient algorithms for look-ahead modeling
The following subsection discuss these in more detail.
6.3.1 Modern CCD Star Trackers
The Wilkinson Microwave Anisotropy Probe (WMAP) mission (launched in
2000) utilized CCD star trackers containing both calibration and star catalog
information, permitting the star tracker itself to output a direct measure-
ment of its orientation relative to the celestial sphere. A simple multiplication
(within the attitude control subsystem (ACS) FSW) by the device's alignment
matrix relative to the spacecraft body yields the spacecraft's attitude quater-
nion. This capability enables fine attitude determination “on the fly” without
a priori initialization, an important autonomy feature supporting calibrations,
target acquisitions, communications, target of opportunity (TOO) response,
and smart FDC.
6.3.2 Onboard Orbit Determination
Onboard orbit measurement via GPS is widely in use on commercial satel-
lites and is planned for use on the Global Precipitation Measurement (GPM)
