Dynamics Control Analysis
Analysis to show Spacecraft Avionics Works
Single Task
An independent Dynamics Control Analysis (DCA) consultant can provide services limited to a single task. Program management writes a focused Statement Of Work (SOW).
This is the shortest duration contract limited to a single task, usually less than 1 year. Often called Freelancing.
General Program Support
Here an independent DCA consultant would become a team member in an existing team of employees and other consultants. Program management writes a general SOW.
Typically, general program support would be for 1 or more years. Often called Staff Augmentation.
Subcontract Support
Independent consultants can also support a program indirectly through a subcontract. In this case, the SOW would be written by the direct contractor instead of the satellite company receiving the services. This can be a convenient way to add DCA support without increasing the number of contractor companies.
In each case, Dynamics Control Analysis provides services to the client on an as needed basis. No need for career development or other employee related overhead. After the task is completed, a new SOW can be arranged to continue low-level support to answer questions and remain aware of the program state. We move in, help out, move on, stay available. Client pays no tax or benefits in addition to the consulting fee. At the end of the year, the client submits a NEC-1099 form to report the payments.
TODAY’S TIP
A biquad filter is a filter of the form:
where are the numerator coefficients and are the denominator coefficients. This filter becomes a work horse in many controllers, because it can allow a classical PID controller to be used on spacecraft with significant flexiblity. It can be compiled as a unit, thoroughly tested (including the cases where ) and called as a function.
This filter is perhaps best known for implementing a 2nd order lowpass filter. This use-case is especially useful on relatively stiff spacecraft where the control bandwidth is below the first flexible mode frequency. Additional roll-off can be achieved by stringing together additional biquads.
The biquad can also be used as a band-limited differentiator, as we have done for nutation control. While this application is not directly related to the control of flexible structures, the nutation mode in spinning spacecraft is a similar problem. See Patent 6062512 or Patent 5794892.
Yet another application is to implement a notch filter to remove an unwanted band of frequencies (perhaps aliased frequencies) that might otherwise blow a smear budget. This might be a frequency well beyond the bandwidth of the control system, so the effect is indirect.
Perhaps the most interesting application is to provide phase compensation for a PID controller with the bandwidth above the first flexible mode. In this case, we use the filter to affect the frequency dependent delay rather than the magnitude. We’ve used the phase compensation technique to compensate stationkeeping controllers with bandwidths well above the first flexible mode using classical design techniques to provide sufficient stability margins using PID controllers.
