• THE ELECTRONIC SWITCHING SPHERICAL ARRAY (ESSA) ANTENNA FOR THE EARTH RADIATION BUDGET SPACECRAFT (ERBS)

      Kudrna, Ken; Hockensmith, Richard P.; Ball Aerospace Systems Division; Goddard Space Flight Center (International Foundation for Telemetering, 1982-09)
      The ESSA is a microprocessor controlled antenna for low orbiting spacecraft for telemetry and command relay through the Tracking and Data Relay Satellite (TDRS) System. The array is a hemispherical shape which is covered with disk radiating elements. A group of radiating elements are continuously selected by the microprocessor controller to form a beam in the direction of a TDRS. A radial switching power divider uses PIN diodes to select the desired radiating elements. The antenna gain is a function of the size of the hemispherical dome. A 30-inch diameter dome is presently being built for the Earth Radiation Budget Spacecraft (ERBS). Gain of this antenna over a hemisphere is 14 dBi and polarization is left hand circular. There are 145 radiating elements with 12 being used at one time to form a beam. The ESSA subsystem weighs 74 pounds and power consumption is 20 watts. R. F. power handling capability is 30 watts. The S-Band radiating elements have a 10 percent bandwidth which allows simultaneous transmission and reception.
    • ELECTRONICALLY STEERABLE SPHERICAL ARRAY CAPABILITIES AND INTERFACES

      Taylor, Taliaferro H.; Ball Aerospace Systems Division (International Foundation for Telemetering, 1982-09)
      For antenna applications which require gains of 7 to 23 dBic over very large solid angle coverage regions, the Electronically Steerable Spherical Array (ESSA) is an antenna which has significant benefits. This paper describes these benefits along with the ESSA’s key performance parameters and its electrical and mechanical interfaces. As extensions of the basic ESSA design, this paper also describes alternate configurations which allow multiple beam operation and integrated packaging of RF electronics. Basically a simple antenna, the ESSA forms its beams by selecting N elements which point in the desired direction. Selection of these elements is performed by a multipole PIN diode switch. This switch sums together the N desired elements from the M elements located on the ESSA’s spherical surface upon receipt of the appropriate commands from the ESSA’s dedicated microprocessor. The ESSA may be either Phase Compensated, or Non-Phase Compensated. In the Phase Compensated ESSA, a 1 or 2 bit phase shifter is used to correct the spherical phase front produced by the array shape. That correction results in higher gain. The most important ESSA benefits are its characteristics of constant phase and gain which are independent of beam pointing angle. These characteristics free the system from the gain and phase perturbations caused by other types of antennas. As a mature technology, the ESSA has been successfully tested with the NASA standard transponder and is presently being fabricated as a 14 dBic gain protoflight unit for a NASA-Goddard Space Flight Center program.
    • PLANETARY SOIL WATER ANALYZER (PSWA) PROTOTYPE

      Cashin, William F.; Anderson, Duwayne M.; Ball Aerospace Systems Division; State University of New York (International Foundation for Telemetering, 1982-09)
      A microprocessor-based differential scanning calorimeter is being designed for eventual use in planetary soil water analysis. The uniqueness of this effort is in the use of the microprocessor as an integral section of the system control loops, instead of as merely an auxilary processor of output data. The use of differential scanning calorimetry is advantageous in determining water content of soil samples. The basic idea is to use two matched ovens, one with a soil sample included. The average temperature of the ovens is forced to track a desired programmed temperature (normally a slow ramp) with one control loop, while a second control loop forces the oven temperatures to be equal, even during a transition. The power necessary to keep the temperatures equal is monitored, containing information as to the transition energy, and thus the water content at programmed water transition temperatures. This approach uses the microprocessor to close both of the loops, taking oven sensor temperatures as an input, and providing power duty cycles as outputs. In actuality, two microprocessors are used - a slave to accumulate and process sensor information, and a master to generate the loop control, output data control, and temperature program control. The PSWA performance is compared to a state-of-the-art commercial instrument using analog loop control. The major advantage of the microprocessor loop control utilized in the PSWA is the capability of remote operation, including remote alignment and adjustment. Further advantages include accommodation of oven changes with software reprogramming, a flexible single oven capability, correction for system nonlinearities using software, and auto gain and auto zero control for the sensor circuitry. The analog loop control approach has somewhat better sensitivity, resolution, and noise performance. The current phase of the development of the PSWA is a feasibility study and circuit design, performed for the Planetary Geology Program Office, NASA Headquarters. The next developmental phases would include breadboarding, software design, testing, and evaluation. In conclusion, this instrument is a significant advance in the state-of-the-art for automatic water measurements, and will be of great value in further planetary exploration.