Environmental Engineering Reference
In-Depth Information
B.2 Space-to-Ground Dialog Scenario
The dialog in this scenario is initiated by the spacecraft and driven by the
following assumptions:
1.
The mission type is a 1-AU (i.e., 1
astronomical unit
) drift-orbit survey
mission.
2.
The mission goal is to map out the entire celestial sphere to chart the
microwave structure of space. Each mapping will take 6 months, so four
mappings will be performed during the 2 year mission lifetime.
3.
As the onboard antenna size is quite small and transmitting power is highly
limited, the deep space network (DSN) must be used for data capture. To
reduce transmission costs by reducing downlink volume, the spacecraft
will process all raw science data onboard and only downlink science end-
products. The spacecraft will utilize beacon mode and will burst-transmit
its processed science data on a low priority basis.
4.
In the event of major anomalies that the autonomous SFDDIC Agent can-
not handle, the spacecraft will notify the ground, downlinking a diagnostic
file whose contents characterize the problems encountered.
Relative to these assumptions, consider this scenario for space-ground com-
munications. As the survey work continues, the SI data processing agent pro-
cesses SI output and forwards the end-product to the SI data-storage agent.
In addition, raw SI data are stored in buffers (a precaution against the event
of an SI anomaly). When the SFDDIC Agent (in conjunction with the data
monitoring and trending agent) validates a given subset of data and declares
it to be acceptable, and also verifies nominal SI performance during that time
period, the storage locations associated with the raw SI data are designated
as available to be over-written.
When sucient processed survey data have been accumulated to warrant
scheduling a downlink, the SI data-storage and communications agent for-
wards to the executive agent a request to turn on the transmitter to contact
the DSN and request a downlink opportunity. This request is then relayed
to the FSW backbone, which activates the transmitter, establishing contact
with DSN. The DSN informs the spacecraft of its telemetry window. After
the start of the window, the onboard agent then downlinks all available, val-
idated SI end-products. The lights-out ground system automatically verifies
that all data received from the spacecraft in this pass are intact (i.e., have
not been corrupted in transmission) and notifies the onboard SI data-storage
agent that the memory areas used for storage of the telemetered science data
may now be overwritten.
Sometime later, after this conversation has terminated, the spacecraft loses
(at least temporarily) one of its four reaction wheels. The FSW backbone
responds by transitioning both the platform and payload to safemode. While
in safemode, the SFDDIC (in conjunction with data monitoring and trending,
as well as look-ahead modeling) evaluates the situation, both with respect to
