Remote Sensing of the Oceanand Atmosphere:John Wilkin

Orbits and Measurement Geometry (2)

jwilkin@rutgers.eduIMCS Building Room 214C732-932-6555 ext 251

Nov 5, 2007 view from Space Shuttle

15.77540422

Revolutions per Day:

52631Orbit Number at Epoch:

022.2238°Right Ascension of Ascending Node:

341 kmApogee Height: 334 kmPerigee Height: 051.6418°Inclination: 0.0005362Eccentricity:

Hohmann Transferhttp://www.youtube.com/watch?v=p_pAhPecto0

On Jan 11, 2007, China tested an anti-satellite rocket. The initial collision added 800 to 1000 pieces of space junk to the current total of detectable objects.

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.

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.

How many detectable objects (< 4 inches) are in orbit?

http://www.nytimes.com/2007/02/06/science/space/06orbi.html?emc=eta1

http://www.nytimes.com/2007/02/06/science/20070206_ORBIT_GRAPHIC.html

Stewart, R. H., 1985, Methods of Satellite Oceanography, University of California Press, 360 pp.

http://spaceflight.nasa.gov/realdata/elementsSee 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

sidereal

solar

http://en.wikipedia.org/wiki/Sidereal_time

Jason altimeter satellite

Equatorial separation of groundtracksis 315 km

Terra satellite, MODIS instrument, coverage of all instrument swaths during a single day ( 01/28/2006 )

View satellite orbits and ground tracks at:http://science.nasa.gov/realtime/jtrack/Spacecraft.html

SeaWiFS daily coverage

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

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.comShows predicted orbits and visibility magnitudes and star charts of pass trajectories for all satellites

– See 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