Mission and observations
The spacecraft carries sensors for observing the atmosphere and Earth's surface. Its route differs substantially from the nearly fixed apparent position of a GOES satellite: a polar orbiter moves over many latitudes while Earth turns beneath it.
How to read the orbital position
Track NORAD 54234 in CUPOLA to see a computed sub-satellite location and orbit. The calculation relies on available OMM/TLE orbital elements and SGP4 propagation. A currently shown orbit is not proof that the VIIRS imagery layer, or any other Earth imagery feed, comes from NOAA-21 at the same time.
Important distinction
Satellite location, sensor acquisition time and published image freshness are three independently verified quantities.
CUPOLA uses orbital elements and SGP4 to estimate position and ground track. These are mathematical predictions rather than directly measured real-time spacecraft coordinates. Old or unverified source data may prevent a current result from appearing.
Mission source
Read the spacecraft's scientific and operational background from the mission organization.
NASA — Joint Polar Satellite System ↗