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Effect of gimbal friction modeling technique on control stability and performance for centaur upper-stage
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Graham, Ronald E. |
| Copyright Year | 1987 |
| Description | The powered-phase autopilot for the Centaur upper stage rocket uses an autopilot forward loop gain scheduler that decreases the proportional gain as propellant mass is depleted. Nonlinear time response simulation studies revealed that Centaur vehicles with low-gain autopilots would have large attitude error limit cycles. These limit cycles were due to the assumed presence of Coulomb friction in the engine gimbals. This situation could be corrected through the use of an harmonic dither, programmed into the on-board digital computer and added to the engine command signal. This would introduce impending motion to the engines, allowing control of the engines even under small commands. Control authority was found to be restored when dither was used. A concern arose that the Centaur could be unacceptably excited at resonances near the dither frequency, if the dither amplitude was to be chosen on the basis of friction level present, a test was conducted to measure this level. Dither characteristics were to be based on the test results. The test results showed that the gimbal friction characteristic was actually hysteretic rather than the assumed Coulomb friction. The simulation results showed that, using this new model of gimbal friction, dither would no longer be necessary. |
| File Size | 400410 |
| Page Count | 10 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19870013322 |
| Archival Resource Key | ark:/13960/t9k40pf01 |
| Language | English |
| Publisher Date | 1987-01-01 |
| Access Restriction | Open |
| Subject Keyword | Launch Vehicles And Space Vehicles Dynamic Response Centaur Launch Vehicle Vibration Friction Gimbals Automatic Pilots Control Stability Control Theory Hysteresis Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Technical Report |
