Info

Need to isolate magnetometer from electromagnets, either physically or by duty-cycling the magnets.

We assume we also need a yaw sensor capable of 0.1 deg, and this choice is less obvious. (Often, it is useful to question a tight yaw requirement. Many payloads, e.g., antennas, some cameras, radars, are not sensitive to rotations around their pointing axis. For this discussion, we will assume the requirement is firm.) We could use sun sensors, but their data needs to be replaced during eclipses. Magnetometers don't have the necessary accuracy on their own, but with our momentum-bias system, roll-yaw coupling, and some yaw filtering, a magnetometer-Sun sensor system should work.

At this point, we consider the value of an inertial reference package. Such packages, although heavy and expensive, provide a short-term attitude reference which would permit the Earth vector data to be used for full 3-axis knowledge over an orbit A gyro package would also reduce the single-measurement accuracy required of the horizon sensors, simplifying their selection and processing. Such packages are also useful in the control system if fast slews are required. Although nice to have, an inertial package does not seem warranted for FireSat Table 11-15 summarizes our hardware selections.

Once the hardware selection is complete, it must be documented for use by other system and subsystem designers as follows:

• Specify the power levels and weights for each assembly

• Establish the electrical interface to the outside world

• Describe requirements for mounting, alignment heating, or coding

• Determine what telemetry data we must process

• Document how much software we need to support equations of motion

Specific numbers depend on the vendors selected. A typical list for FireSat might look like Table 11-16, but the numbers could vary considerably with only slight changes in subsystem accuracies or slewing requirements.

ADCS Vendors. Typical suppliers for ADCS components are listed in Table 11-17.

TABLE 11-17. ADCS Component Suppliers. Aerospace mergers can result In sudden name changes.

Company

Sensors

Actuators

Sun

Earth

Magnetometers

Star

Inertial (Gyros)

Momentum/ Reaction Wheels

CMGs

Electromagnets

Thrus-ters

Adcole Corporation

0 0

Post a comment