Environmental Engineering Reference
In-Depth Information
data volume will be restricted to avoid potential interference with critical
backbone processing. Should any or all Remote Agents “fall off” the bus or
simply cease to operate, the backbone will not be impacted, though science
observations could well be temporarily degraded or terminated.
The FSW backbone processing is time-driven. Each function within the
backbone receives a well-defined “slice” of processing time. All backbone
functionalities are scheduled to begin at a fixed time relative to the start
of a processing cycle and will complete within one or more time cycles. A
list of backbone functions is provided below, with more detailed descriptions
following:
1.
Safemode
2.
Inertial fixed pointing
3.
Ground commanded thruster firing
4.
Ground commanded attitude slewing
5.
Electrical power management
6.
Thermal management
7.
H&S communications
8.
Basic fault detection and correction (FDC)
9.
Diagnostic science instrument (SI) commanding
10.
Engineering data storage
6.1.1 Safemode
Safemode is the key enabler of higher-level FSW functions. Safemode guaran-
tees that no matter what may happen during the conduct of the mission, be it
a hardware malfunction (for redundant H/W components) or a FSW abnor-
mality, as a last resort (provided the problem is detected), the spacecraft can
enter a state where no further permanent damage will be done and spacecraft
H&S can be maintained. The allocation of this function to the FSW backbone
is clearly essential.
Return from safemode is contingent on diagnosing the underlying cause
of the problem and implementation of corrective action, either selection of
a “canned” solution or creation of a new solution. Currently, return from
safemode is within the purview of the flight operations team (FOT), but, with
a suciently advanced onboard FDC, the capability could be shared. Some
spacecraft are provided with multiple levels of safemode, but nearly all God-
dard Space Flight Center (GSFC) spacecraft have a sun-pointing safemode to
guarantee power and SI safemodes to protect delicate SIs. In the past, most
GSFC spacecraft also had a hardware safemode in case the onboard computer
(OBC) went down.
6.1.2 Inertial Fixed Pointing
Although the safemode function discussed above guarantees maintenance
of spacecraft H&S, recovery from safemode and interception of the science
