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Aviation History
1961
1961 - 1045.PDF
Above, Ranger I in the launch position, with solar panels upright and parabolic antenna tucked beneath the body of the spacecraft. Above right, extension of the solar panels cold gas jets and the gyroscopes. The gyros first act to cancel outthe residual movements resulting from separation. There are ten Sun sensors on the spacecraft, located so that, nomatter how the craft is positioned in space, some of the sensors will see the Sun. There are three sensors located on the backs of eachof the two solar panels, and four located on the legs of the space- craft. The Sun sensors are light-sensitive diodes which inform thegas jets and the gyros when they see the Sun. The attitude control system responds to these signals by turning the spacecraft in such amanner that the longitudinal or roll axis points toward the Sun. This is accomplished by ten cold gas jets which are fed from an 8indiameter bottle containing 2^1^ of nitrogen under 3,000lb/sq in pressure. This is calculated to be sufficient to operate the gas jetsto maintain attitude control for 50-100 days. The gyros have first acted to cancel out the residual separationrates which affected Ranger 1 after it left Agena B. The Sun sensors, working on the valves controlling the gas jets, thenmanoeuvre the spacecraft so that its long axis is pointed at the Sun. Both the gyros and the Sun sensors can activate the gas jetvalves. In order to conserve gas, the attitude control system permits a pointing error towards the Sun of ^ 0.5 . The mixing network inthe attitude control system is calibrated to keep the spacecraft slowly swinging through this I of arc pointed at the Sun.This swing takes approximately 60min. As Ranger 1 nears the 0.5 limit on one side, the sensors signal the gas jets and they fireagain. It is calculated that the gas jets will fire for 0.1 sec each 60min to keep the spacecraft's solar panels aimed at the Sun. Approximately 15-3Omin will be required initially to lock on tothe Sun. While this is taking place, the 4ft directional antenna is extended to a pre-set angle. This is accomplished by the same Above right, spacecraft with solar panels com- pletely extended (elec- trostatic-analyser boom on right). Left, the operation of the 4ft parabolic directional an- tenna is checked command from the controller which initiated the Sun acquisition. When the Sun is acquired, the power system recognizes that itis receiving electric power from the solar panels through the con- verter, and so it switches off the large silver zinc battery and startsto use power from the Sun. After Ranger 1 has been locked on to the Sun, the spacecraftcontroller turns off the six Sun sensors located on the under-sides of the solar panels. This is done to prevent the possibility of thesesensors seeing the Earth and perhaps confusing it with the Sun, which would cause them to give commands to the gyros and gasjets. Fifth Command. This occurs at 90min. In effect, the spacecraftcontroller tells Ranger 1, "Okay, you've locked on to the Sun; now start looking for the Earth w ith your directional antenna but don'tlose your lock on the Sun." So. keeping its long axis pointed at the Sun, Ranger starts looking for the Earth with three Earth sensors,which are photomultiplier tubes mounted co-axially with the direc- tional antenna. The spacecraft then starts to roll on its long axis,with the directional antenna extended. During the roll, the Earth sensors will see the Earth and inform the gas jets. The jets will fireto keep the Earth in view of the sensors, and thus to lock on to the Earth. The spacecraft now is stabilized on two axes, the solar-panel/Sun axis, and the Earth/directional-antenna axis. There is some danger that the Earth sensors may see the Moon and lock onto it, but telemetry will inform ground stations if that error occurs, and Goldstone has the ability to send an override command. Sixth Command. This occurs at 118min 20 sec. This command changes the scale factor of a telemetry measurement which
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