UPS

Universal Polar Stereographic, for the polar caps UTM does not cover.

Universal Polar Stereographic (UPS) is the grid for the polar caps, north of 84° N and south of 80° S, where UTM stops. Polar researchers, military users, and anyone mapping Antarctica or the high Arctic use it. Start with latitude and longitude to UPS. A pitfall is expecting a zone number: UPS has none, and in MGRS the polar areas use the letters A, B, Y, and Z instead.

I want to convert to or from UPS

Latitude and longitude to UPS
Converts polar coordinates (84° N and beyond, or 80° S and beyond) to Universal Polar Stereographic easting and northing.
UPS to latitude and longitude
Converts a Universal Polar Stereographic easting and northing back to latitude and longitude.