SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 8 - April 21, 2006

17 SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
Includes space systems telemetry; space communications networks; astronavigation and guidance; and spacecraft radio blackout.

For related information see also 04 Aircraft Communications and Navigation; and 32 Communications and Radar.

20060011008 Indian Space Research Organization, Bangalore, India

Orbit Model Studies for Onboard Orbit Estimation

Akila, S.; Kumar, E. Krishna; Gopinath, N. S.; Journal of Spacecraft Technology, Volume 16, No. 1; January 2006, pp. 8-30;In English; See also 20060011004; Copyright; Avail.: Other Sources

Conventionally, Orbit Determination (OD) procedures were followed for spacecraft missions only on ground. Based onthese experiences over many years and the proficiency acquired following the advent of space borne GPS receivers, onboardOD using GPS data is realized to be presenting excellent scope for a new phase of development to support advancedrequirements of today as well as the futuristic missions. Better utilization of onboard radio receivers due to continuousavailability of tracking data and feasibility of frequent sampling has been the key driver for the current study. This study forselection of a suitable orbit dynamics model for onboard OD is carried out using various orbit models considering relativecontributions from different acceleration effects. The analysis presented includes individual effects of Central Force, ZonalHarmonics, Drag, and Luni-Solar gravitations. This study helps to logically judge the possible candidate models for onboardimplementation. Clear conclusion is drawn from the study and is substantiated with the position determination for a typicallow earth orbiting satellite using satellite state vector observations from GPS receivers.Author

Global Positioning System; Orbit Determination; Radio Receivers; Support Systems

20060011009 Indian Space Research Organization, Bangalore, India

Antenna Fine Pointing Mechanism (AFPM)

Viswanatha, Shamrao; Viswanatha, N.; Journal of Spacecraft Technology, Volume 16, No. 1; January 2006, pp. 36-40; InEnglish; See also 20060011004; Copyright; Avail.: Other Sources

Future communication satellites incorporating multi-beam RF system need very accurate pointing of the antenna beamsin the order of +/- 0.05deg or better. The pointing requirement that can be met directly by the satellite platform is limited to+/- 0.2deg hence, calls for a separate pointing mechanism to correct for spacecraft attitude and orbit control system pointingerrors. The objective is achieved by several methods, viz.; orthogonal mounting of two rotary drives, driving two axes gimbalmechanism using rotary drives or linear actuators etc. The drawbacks of these methods are, they use gear systems andbearings, which have backlash and wear problems associated with them respectively. The paper describes a novel andinnovative linear motor driven compliant (as the pointing range is small) mechanism, which has several advantages over theother alternative designs. The mechanism development model of compliant AFPM has been designed and the working of themechanism has been successfully demonstrated.Author

Antenna Radiation Patterns; Radio Frequencies; Communication Satellites; Attitude Control; Spacecraft Orbits; Actuators

Source: NASA