Peter Nachtwey
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OP
Now that this thread is active
Dennis came back and filled me in. I was wrong about some of my facts. Dennis told me that they dropped the simulate probe 78 times. I thought it was only 8 times. They also found problems with the radar by doing these test but they obviously corrected the problem. Dennis told me that the real trick was the radar and when ditch the parachutes and make the transition to thrusters and radar control. Apparently they got a star fix just before the descent. From there inertial guidance was used to estimate elevation, speed and x,y position. If you think about it any external gear would have been ripped off and burned away by the friction of retry. When the inertial guidance system said they were close then the parachutes were released and the thruster/radar mode begins. A lot dependent on the inertial guidance system. The inertial guidance system has accelerometers for the x, y, z and perhap rotational modes too. The acceleration is integrated to provide velocity and position. These have got to be very fine accelerometers because any offset will result in significant error in the position. If the position, velocity and acceleration wasn't calculated right the Phoenix would go into thruster/radar mode to soon and possibly run out of fuel. If it goes into thruster and radar to too late there is yet another crater on Mars. Dennis told me the Phoenix had plenty of fuel left.
Dennis was disappointed he didn't get a chance to meet the people that did the thruster control.
Dennis came back and filled me in. I was wrong about some of my facts. Dennis told me that they dropped the simulate probe 78 times. I thought it was only 8 times. They also found problems with the radar by doing these test but they obviously corrected the problem. Dennis told me that the real trick was the radar and when ditch the parachutes and make the transition to thrusters and radar control. Apparently they got a star fix just before the descent. From there inertial guidance was used to estimate elevation, speed and x,y position. If you think about it any external gear would have been ripped off and burned away by the friction of retry. When the inertial guidance system said they were close then the parachutes were released and the thruster/radar mode begins. A lot dependent on the inertial guidance system. The inertial guidance system has accelerometers for the x, y, z and perhap rotational modes too. The acceleration is integrated to provide velocity and position. These have got to be very fine accelerometers because any offset will result in significant error in the position. If the position, velocity and acceleration wasn't calculated right the Phoenix would go into thruster/radar mode to soon and possibly run out of fuel. If it goes into thruster and radar to too late there is yet another crater on Mars. Dennis told me the Phoenix had plenty of fuel left.
Dennis was disappointed he didn't get a chance to meet the people that did the thruster control.
