The first stage was the RS-27 powered Extended Long Tank Thor, flown on several earlier Delta rockets.

Its goals were to investigate the cosmic microwave background radiation (CMB or CMBR) of the universe and provide measurements that would help shape the understanding of the cosmos.

COBE's measurements provided two key pieces of evidence that supported the Big Bang theory of the universe: that the CMB has a near-perfect black-body spectrum, and that it has very faint anisotropies.

Two of COBE's principal investigators, George F. Smoot III and John C. Mather, received the Nobel Prize in Physics in 2006 for their work on the project.

According to the Nobel Prize committee, "the COBE project can also be regarded as the starting point for cosmology as a precision science".