1. The payload subsystem interconnection diagram is shown in Fig. 40. This subsystem provides the primary mission functionality for the spacecraft. For the FireSat IImission, thisis asensor capableof detecting fires bydetecting temperaturevarianceontheEarth.Inadditiontothissensor,thePayloadincludesaSignal Processor which post processes the observation data that are later downlinked to the ground. The Payload SW controls the Payload Sensor and provides Payload telemetry.
2. The Communications Subsystem interconnection diagram is shown in Fig. 41. This subsystem provides capability to communicate with the FireSat II Ground Station and supports uplink of vehicle commands, downlink of telemetry data and downlink of Payload Sensor observation data. The Spacecraft must Fig.40 Thepayloadsubsystemsensesandprocessesthethermalemissions,andincludesa Payload Sensor, Signal Processor and optional Sensor Pointing Mechanism as well as Payload SW to control the sensor. communicatetwodifferentkindsofdatawiththegroundeachwithdifferingdata rate requirements. As such, this requires two data channels within the communications subsystem-one low rate for commands and telemetry and one high rate for observation data.
3. The structure comprises a Spacecraft Frame, a number of Panels, and a mechanical interface to the Launch Vehicle and its faring. The number of Frames is influenced by the internal volume required for components and the size of the Launch Vehicle faring [Pegasus Launch Vehicle Users Guide, 2010]. TheSeparationMechanismandLaunchVehicleinterfacedependsontheselection oftheLaunchVehicle.Thestructureandotheraspectsofthemechanicaldesignof the Spacecraft are captured in a 3D CAD modeling tool.
4. Figures 52-54 show three representative activity diagrams for selected Spacecraft functions to Provide Power, Control Attitude, and Collect and Downlink Observation Data. The Provide Power activity shows the high-level actions that Avionics, the Power Subsystem, and the Power Harness perform to deliver power to the subsystems. The inputs include solar radiation to the Solar Array and the Electrical Power provided by the Launch Vehicle before Spacecraft separation. The Control Attitude activity shows the high-level actions that Avionics, GN&C,andthePropulsionSubsystemperformtocontroltheattitudeoftheSpacecraft. This is accomplished by sensors that measure the Sun angle, Earth horizon angle,and theSpacecraft angular rateto control theReaction Wheel spin rateand the thrust. The Collect and Download Observation Data activity shows the highlevel actions that the Payload, Avionics, and Communication Subsystem perform to sense the thermal emissions from the Earth, store the data, and then downlink the data to the ground.