The COBE satellite, which stands for Cosmic Background Explorer, was not in orbit around Earth, but rather it was a free-flying spacecraft that traveled in a heliocentric orbit around the Sun.

Because it was in a heliocentric orbit rather than a geocentric one, its distance from Earth varied greatly.

However, the satellite was never designed to orbit Earth and its path was dictated by its mission to observe the cosmic microwave background radiation.

To answer your question more precisely, the COBE satellite was not at a specific altitude above Earth as it was traveling in space around the Sun.