1 / 21

Launching, Orbital Effects & Satellite Subsystems Joe Montana IT 488 - Fall 2003

Launching, Orbital Effects & Satellite Subsystems Joe Montana IT 488 - Fall 2003. Agenda. Satellite Subsystems. SPACECRAFT SUBSYSTEMS. Attitude and Orbital Control System (AOCS) Telemetry Tracking and Command (TT&C) Power System Communications System Antennas.

benjamin-guerra
Download Presentation

Launching, Orbital Effects & Satellite Subsystems Joe Montana IT 488 - Fall 2003

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Launching, Orbital Effects & Satellite Subsystems Joe Montana IT 488 - Fall 2003

  2. Agenda • Satellite Subsystems

  3. SPACECRAFT SUBSYSTEMS • Attitude and Orbital Control System (AOCS) • Telemetry Tracking and Command (TT&C) • Power System • Communications System • Antennas More usually TTC&M - Telemetry, Tracking, Command, and Monitoring We will look at each in turn

  4. AOCS • AOCS is needed to get the satellite into the correct orbit and keep it there • Orbit insertion • Orbit maintenance • Fine pointing • Major parts • Attitude Control System • Orbit Control System Look at these next

  5. ORBIT INSERTION - GEO TWO BASIC TYPES OF GEO INSERTION: • High-Energy Apogee Kick Motor firing • A few minutes, symmetrical about apogee • Low-Energy AOCS burn • Tens of minutes to > one hour burns, symmetrical about apogee • Uses Dual-Mode thrusters; i.e. thrusters used for both orbit raising and attitude control

  6. ORBIT MAINTENANCE - 1 • MUST CONTROL LOCATION IN GEO & POSITION WITHIN CONSTELLATION • SATELLITES NEED IN-PLANE (E-W) & OUT-OF-PLANE (N-S) MANEUVERS TO MAINTAIN THE CORRECT ORBIT • LEO SYSTEMS LESS AFFECTED BY SUN AND MOON BUT MAY NEED MORE ORBIT-PHASING CONTROL

  7. ORBIT MAINTENANCE - 2 • GEO STATION-KEEPING BURNS ABOUT EVERY 4 WEEKS FOR  0.05o • DO N-S AND E-W ALTERNATELY • N-S REQUIRES  10  E-W ENERGY • RECENT APPROACH USES DIFFERENT THRUSTERS FOR E-W AND N-S

  8. FINE POINTING • SATELLITE MUST BE STABILIZED TO PREVENT NUTATION (WOBBLE) • THERE ARE TWO PRINCIPAL FORMS OF ATTITUDE STABILIZATION • BODY STABILIZED (SPINNERS, SUCH AS INTELSAT VI) • THREE-AXIS STABILIZED (SUCH AS THE ACTS, GPS, ETC.)

  9. DEFINITION OF AXES - 1 • ROLL AXIS • Rotates around the axis tangent to the orbital plane (N-S on the earth) • PITCH AXIS • Moves around the axis perpendicular to the orbital plane (E-W on the earth) • YAW AXIS • Moves around the axis of the subsatellite point

  10. DEFINITION OF AXES - 2 Earth o Equator s Yaw Axis Roll Axis Pitch Axis

  11. TTC&M TTC&M is often a battle between Operations (who want every little thing monitored and Engineering who want to hold data channels to a minimum • MAJOR FUNCTIONS • Reporting spacecraft health • Monitoring command actions • Determining orbital elements • Launch sequence deployment • Control of thrusters • Control of payload (communications, etc.)

  12. TELEMETRY - 1 • MONITOR ALL IMPORTANT • TEMPERATURE • VOLTAGES • CURRENTS • SENSORS • TRANSMIT DATA TO EARTH • RECORD DATA AT TTC&M STATIONS NOTE: Data are usually multiplexed with a priority rating. There are usually two telemetry modes.

  13. TELEMETRY - 2 • TWO TELEMETRY PHASES OR MODES • Non-earth pointing • During the launch phase • During “Safe Mode” operations when the spacecraft loses tracking data • Earth-pointing • During parts of the launch phase • During routine operations NOTE: for critical telemetry channels

  14. TRACKING • MEASURE RANGE REPEATEDLY • CAN MEASURE BEACON DOPPLER OR THE COMMUNICATION CHANNEL • COMPUTE ORBITAL ELEMENTS • PLAN STATION-KEEPING MANEUVERS • COMMUNICATE WITH MAIN CONTROL STATION AND USERS

  15. COMMAND • DURING LAUNCH SEQUENCE • SWITCH ON POWER • DEPLOY ANTENNAS AND SOLAR PANELS • POINT ANTENNAS TO DESIRED LOCATION • IN ORBIT • MAINTAIN SPACECRAFT THERMAL BALANCE • CONTROL PAYLOAD, THRUSTERS, ETC.

  16. POWER SYSTEMS - 1 • SOLAR CELLS • 1.39kW/m2 available from sun • Cells 10 - 15% efficient (BOL=Beginning Of Life) • Cells 7 - 10% efficient (EOL=End of Life) • SOLAR CELL OUTPUT FALLS WHEN TEMPERATURE RISES • 2mV/degree C; Three-Axis hotter (less efficient) than a spinner

  17. POWER SYSTEMS - 2 • BATTERIES NEEDED • DURING LAUNCH • DURING ECLIPSE (<70mins) • BATTERY LIMITS • NiCd 50% (DOD=depth of discharge) • NiH2 70% DOD NOTE: ISS uses 110V bus and will need 110 kW; 30 minute eclipses per day; 55 kW required from batteries Solution: using Fuel Cells

  18. POWER SYSTEMS - 3 • BATTERIES ARE “CONDITIONED” BEFORE EACH ECLIPSE SEASON • BATTERIES DISCHARGED TO LIMIT • BATTERIES THEN RECHARGED • TYPICAL NiH2 BATTERY CAN WITHSTAND 30,000 CYCLES (AMPLE FOR GEO; WOULD BE 5 YEARS IN LEO)

  19. COMMUNICATIONS SUB-SYSTEMS • Primary function of a communications satellite (all other subsystems are to support this one). • Only source of revenue • Design to maximize traffic capacity • Downlink usually most critical (limited output power, limited antenna sizes). • Early satellites were power limited • Most satellites are now bandwidth limited.

  20. SPACECRAFT ANTENNAS • SIMPLE:GLOBAL BEAM, ~17O WID LOW GAIN, LOW CAPACITY • REGIONAL: NARROW BEAM FROM REFLECTOR ANTENNA, TYPICALLY 3o  3o OR 3o  6o • ADVANCED: MULTIPLE NARROW BEAMS STATIONARY, SCANNED, OR “HOPPED”

  21. ANTENNA TYPES • HORN • Efficient, Low Gain, Wide Beam • REFLECTOR • High Gain, Narrow Beam, May have to be deployed in space • PHASED ARRAY • Complex • Electronically steered

More Related