MAXIMA Attitude Control System

Documentation for the MAX ACS System:

The purpose of the ACS system is to control the pointing of the gondola. Most of the hardware resides in the Italian side Electronics Box, located on the right hand side of the gondola when one views the sky along the telescope beam.

Below is an itemized list of the components, and documentation location:

ACS system outside the E-box.

A. Elevation Drive
(Desc: The purpose of the elevation drive is to move the inner frame of the gondola which points the telescope at different elevation angles. The drive consists of a motor and gearbox attached to a ball-screw mechanism which in turn moves the inner frame.) B. Flywheels
(Desc: The azimuth pointing is achieved by conservation of angular momentum; using a set of two flywheels located at the apex of the gondola. These flyweels are spun by direct torque motors which use a Pulse-Width-Modulated input signal)

Electronics Box Components

A. CCD Camera System
(Desc: For fine azimuth and elevation pointing, a CCD Camera system is used. The image from the camera is processed by a computer with a Digital Signal Processing board, which locks onto and tracks the location of a bright object, such as a star) B. FLC Computer
(Desc: The FLC computer receives input from a variety of sensors and calculates the control ouput to the respective motors based on a trajectory sent by the FP computer (see below). The sensors are read by A/D boards such as the RTD and MESA cards) C. FP Computer
(Desc: The FP computer's primary purpose is to receive telecommands from the RX/TX box and relay them to the respective computers, and to send trajectories to the FLC computer. The FP also receives longtitude and latitude position through a Global Positioning System antenna) D. Power Electronics
(Desc: The motor outputs of the FLC computer is sent to the Power Electronics which amplify the PWM signal and send them to the motors) E. RX/TX Box
(Desc: The RX/TX box is electrically isolated from the entire Electronics Box, by way of plastic washers and optical fibers. Its purpose is to receive radio transmissions from ground, decode them into useful telecommands, and send them to the FP. The box also sends the downlink and answerback signals to the CIP) F. Magnetometer
(Desc: The magnetometer gives coarse azimuthal coordinates for pointing; the magnetometer must be calibrated through a messy look-up table) G. Relay/Serial Concentrator Box
(Desc: The serial concentrator collects useful data from all the computers and packs them into a single downlink signal which is sent to the RX/TX box. The Optical Fiber Drivers convert serial lines into optical signals which are sent to the SIM on the Berkeley side and to the RX/TX box. The Relay box receives discrete telecommands from the CIP and turns on or off the appropriate electronics) H. Ground Station
(Desc: The ground station computer is used to send telecommands and discrete telecommands to the gondola during flight; it also receives downlink data. The communcations equipment includes a radio transmitter and a packet modem to convert and send the signals) I. Misc. Documents