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Remote Sensing of the Ocean and Atmosphere: John Wilkin [email protected] IMCS Building Room 214C 732-932-6555 ext 251 Orbits and Measurement Geometry Johannes Kepler (1571 – 1630) German mathematician, astronomer and astrologer 1. Planets move in elliptical orbits with the sun as one focus 2. the radius vector from the sun to the planet sweeps out equals areas in equal times 3. T2 : R3 ratio is constant for all planets, where T is orbital period and R is semimajor axis of the orbit Epoch (UTC): 10:07:53 AM, Monday, January 28, 2008 Eccentricity: 0.0005362 Inclination: 51.6418° Perigee Height: 334 km Apogee Height: 341 km Right Ascension of Ascending Node: 22.2238° Orbit Number at Epoch: 52631 Revolutions per Day: 15.77540422 Nov 5, 2007 view from Space Shuttle Stewart, R. H., 1985, Methods of Satellite Oceanography, University of California Press, 360 pp. Stewart, R. H., 1985, Methods of Satellite Oceanography, University of California Press, 360 pp. http://spaceflight.nasa.gov/realdata/elements See graphics of orbital elements and data for ISS Jason-1 launch from Vandenburg Air Force Base, California Orbit: http://www.aviso.oceanobs.com/en/missions/current-missions/jason-1/orbit/index.html Launch: http://www.youtube.com/watch?v=Z4WHOSF2Ktg Other launches: Delta-II (Themis): http://www.youtube.com/watch?v=p_pAhPecto0 Ariane: http://www.youtube.com/watch?v=OfONuo3h3t0 http://www.youtube.com/watch?v=kYUrqdUyEpI Jason-2 OSTM http://www.youtube.com/watch?v=cf0loVEs_lo Topex/Poseidon launched with Ariane rocket http://sealevel.jpl.nasa.gov/gallery/tiffs/videos/launch.mov Pegasus vehicle aircraft launch http://www.youtube.com/watch?v=QRHiTvRHHd8 OSTM / Jason-2 Boost Profile Space craft separation: Hohmann Transfer Maneuver to different inclination http://en.wikipedia.org/wiki/Hohmann_transfer http://www.nytimes.com/2007/02/06/science/space/06orbi.html?emc=eta1 On Jan 11, 2007, China tested an antisatellite rocket. The initial collision added 800 to 1000 pieces of space junk to the current total of detectable objects. How many detectable objects (< 4 inches) are in orbit? Collisions between existing debris generate additional pieces of debris. There is concern that eventually a chain reaction will ensue (the Kessler syndrome) littering the low earth orbit (LEO) with debris making it almost impenetrable to new satellite launches for fear of collision. http://www.nytimes.com/2007/02/06/science/20070206_ORBIT_GRAPHIC.html Kessler, D. J., and Burton G. Cour-Palais. "Collision frequency of artificial satellites – The creation of a debris belt." Journal of Geophysical Research Vol. 83 (June 1978): 2637-2646. http://spaceflight.nasa.gov/realdata/elements See graphics of orbital elements and data for ISS Sidereal day = time it takes for Earth to rotate through 360o This is slightly shorter than a solar day (24 hours) There are 365.25 solar days in a year but 366.25 sidereal days Sidereal day = 365.25/366.25*24 = 29.93 hours solar sidereal http://en.wikipedia.org/wiki/Sidereal_time SeaWiFS daily coverage Terra satellite, MODIS instrument, coverage of all instrument swaths during a single day ( 01/28/2006 ) Jason altimeter satellite ENVISAT 35-day repeat Equatorial separation of Jason groundtracks is 315 km Scan geometry • zenith angle w.r.t. satellite nadir • look angle and solar zenith angle w.r.t local vertical • Fixed solid angle Field of View (FOV) such as for an optical lens, gives elliptical footprint off-nadir and varying spatial resolution in the scan View satellite orbits and ground tracks at: http://science.nasa.gov/realtime/jtrack/Spacecraft.html Internet resources on orbits and satellites • http://science.nasa.gov/realtime/jtrack/Spacecraft.html Shows ground tracks and 3-D orbits for all satellites – Notice the clusters of satellites in the major categories or orbits • • • • Geostationary Polar orbiting (NOAA, Topex, ERS, Envisat) Low Earth orbit (Iridium, HST, ISS) GPS – Unusual orbits (especially ground track) • Chandra • IMAGE • CRRES (in a geosynchronous transfer orbit) • http://heavens-above.com Shows predicted orbits and visibility magnitudes and star charts of pass trajectories for all satellites – See Homework 1 • http://tinyurl.com/11-670-451-homework-1 http://spaceflight.nasa.gov/realdata/elements – See graphics of orbital elements and data for ISS • Real-time satellite tracking at http://www.n2yo.com
