Attitude Reference Devices for Space Vehicles

As the avenues of space travel broaden, the problem of determining the attitude of the space vehicle becomes more difficult; hence, the need for a compact, reliable sensing device is becoming increasingly important. This paper presents the design features of an attitude sensing device which is quite compact and should prove to be reliable. The original objective in the design of the device was to provide a simple means´ of establishing a vertical reference line from an orbiting space vehicle to a planet under observation. It has been accomplished through the use of two narrow infrared scanning beams. The center line of each beam rotates at constant angular velocity in a plane, the plane of one beam being perpendicular to that of the other. The active portion of the scan is 270° for each beam. When the scanner intersects the planet, a step in the signal level occurs. Position of the beam when the half width of the signal step occurs establishes a plane which contains the center of the planet. Intersection of the two such planes generated by the dual scanner is the direction to the planet local vertical. The assembly is described in detail. Further, by using analog computer techniques, it is shown that pitch and roll angles about this vertical reference line can be generated. A single degree of freedom gyro can be added to the equipment to produce yaw information in the case of an orbiting vehicle. Finally, a method for measuring altitude is discussed.