The nomination of a collection task, the tasking and scheduling of the sensor, the processing of the mission data, and the distribution of the data can dramatically increase the complexity of the systems engineering challenge and decrease the final accuracy of the system. Not only can physical effects such as atmospheric correction, calibration, and rectification degrade system performance, but technical effects such as quantization and data compression errors can decrease the resolution of the system from the perspective of the end user. For additional information about technical aspects of the end-to-end throughput problem for spacecraft imagery, see Shott [1997].

The concept of operations for a spacecraft system such as FireSat needs to account for the full breadth of the operational mission, including different phases of the mission and alternate operating modes. See Sec. 2.1 and Chap. 14 for a description of a mission operations concept

For preliminary mission planning, we should pay particular attention to the projected sequence of events during each mission phase (see Activity Planning in Chap. 14). For the FireSat mission under normal operations, a sample mission timeline for normal operations includes the following steps:

1. Fire starts at some location

2. Sensor field-of-view passes over the fire

3. Signature from the fire introduced into the sensor data stream

4. Data is passed to the mission ground station for analysis (or processed on board)

5. Fire detection algorithm determines the possible presence of fire (this may be a multistage process with a preliminary, coarse fire detection process that triggers a more precise algorithm or set of measurements)

6. Generate appropriate messages indicating the presence of fire

7. Issue reports and notifications to appropriate authorities and research centers

8. Monitor the fire (this could involve switching to an alternate operating concept that tracks the progress of the existing fire and monitors surrounding areas for new outbreaks)

We should create a concept of operations for each phase of the mission and each operating mode of the spacecraft—including contingency and failure modes. This step will ensure mission success within the constraints of the operating environment (See Chap. 14.)

9.43 Required Payload Capability

Frequently there are several ways to meet mission requirements. How to sort through these multiple approaches is not always obvious. The general approach we outline provides a repeatable framework for choosing a payload to satisfy a remote sensing mission. Once we select a physical phenomenology (e.g., measuring thermal infrared radiance to detect forest fires), then two things need to be established. First the radiometric measurement levels that are needed to satisfy the information need; and second, the implications for a payload in terms of size and performance to be able to sense the required signature.

Categorizing remote sensing missions is complicated by the fact that sensors usually have multiple uses, and they can be categorized according to any number of different aspects, such as measurement technique (active or passive), event measured (such as fire or deforestation), and measurement resolution (spatial, spectral, radiometric, temporal). By way of example, however, Table 9-13 provides a small sampling of remote sensing payloads and corresponding spacecraft missions.

TABLE 9-13. Characteristics of Typical Payloads.
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