00 · Orbit — 524 km, sun-synchronous
Same light over every place, every morning.
Tern flies twelve imaging satellites on a sun-synchronous orbit. Each one crosses every latitude at 10:30 local solar time, so the field you photographed last June and the field you see today are lit by the same sun, from the same angle.
01 · The instrument
A telescope that only looks down.
Tern-7 is the size of a washing machine and carries one thing that matters: a pushbroom telescope. Everything else on board exists to keep it pointed, powered and cold. Pick a part — on the bird or here.
Hover the rings on the satellite, or choose a part above.
A 0.7 m off-axis telescope that only ever looks straight down. Its pushbroom detector reads 32,000 pixels across the swath — a fresh line every 66 microseconds.
Two 1.2 kW wings. Because the bird crosses every latitude at 10:30 local time, the sun angle barely changes orbit to orbit, so the arrays almost never have to slew.
Two cameras match 4,000 catalogued stars ten times a second and hold pointing to 3 arcseconds — about eight metres on the ground from 524 km up.
A gimballed 14 cm dish that locks onto a ground antenna for the whole contact and moves 1.6 Gbit/s of imagery down while the station is in view.
02 · The swath
Sixteen kilometres wide, one line at a time.
A pushbroom sensor never takes a picture. It reads a single line of 32,000 pixels, again and again, and lets the orbit sweep that line across the ground at 7.6 km a second. The strip behind the bird is this morning's product.
Red, green and blue at 0.5 m — what your eye would see, with the haze taken out.
Red, green and blue at 0.5 m — what your eye would see, with the haze taken out.
Healthy leaves reflect infrared hard, so crops and forest burn red and water goes black.
Synthetic aperture radar sees through cloud and darkness. Calm water is a mirror; towns and ridges glitter.
- Ground sample
- 0.5 m
- Swath
- 16 km
- Bands
- 11
03 · Downlink
Eight minutes to empty the camera.
Over Svalbard, Inuvik or Punta Arenas the X-band dish swings onto a ground antenna and holds it for the whole pass. Imagery shot over Lisbon at 10:30 is calibrated, orthorectified and in your bucket before 11:15.
- Link rate
- 1.6 Gbit/s
- Stations
- 14
- To delivery
- < 45 min
04 · Constellation
Twelve birds, six planes, two looks a day.
The fleet is spaced across six orbital planes, so anywhere between the polar circles is seen twice daily — at 10:30 in sunlight by the telescopes, and again at 22:30 by radar on the night side.
- Satellites
- 12
- Planes
- 6
- Revisit
- 2× daily
05 · Task a pass