Manned Mars mission communication and data management systems

A manned Mars mission will involve a small crew and many complex tasks. The productivity of the crew and the entire mission will depend significantly on effective automation of these tasks and the ease with which the crew can interface with them. The technology to support a manned Mars mission is available today; however, evolving software and electronic technology are enabling many interesting possibilities for increasing productivity and safety while reducing life cycle cost. Some of these advanced technologies are identified

Effect of Gimbal friction modeling technique on control stability and performance for Centaur upper-stage

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