The 6.5-ton satellite that crashed to Earth sometime late Friday or early Saturday morning is missing, according to NASA officials.

Launched 20 years ago, the defunct spacecraft housed an Ann Arbor invention called the High Resolution Doppler Imager.

Associated Press

The imager, the brainchild of University of Michigan researchers and engineers at Ann Arbor-based company KMS Aerospace, was one of 10 instruments aboard the bus-sized Upper Atmosphere Research Satellite.

Although most of the craft burned up when it passed through Earth’s atmosphere, some 26 pieces that weigh a total of 1,200 pounds are expected to have landed somewhere on Earth.

But where is anybody’s guess.

NASA has narrowed the satellite’s crash time to a roughly two-hour time period between 11:23 p.m. Friday and 1:09 a.m. Saturday.

“The precise re-entry time and location of debris impacts have not been determined,” NASA wrote in a news release issued Saturday.

NASA says that during its re-entry, the satellite passed over the east coast of Africa, the Indian Ocean, the Pacific Ocean, northern Canada, the northern Atlantic Ocean and West Africa.

But NASA still is investigating where the spacecraft landed.

“This was not an easy re-entry to predict,” said NASA Chief Scientist for Orbital Debris Nick Johnson.

The U-M-built imager conducted scientific measurements of emissions and the atmospheric makeup over the course of 78,000 orbits of Earth. But after more than 5,200 mission days, the satellite was deactivated in winter 2005.

The imager is one of the largest objects ever built by U-M’s Atmospheric, Oceanic and Space Sciences discipline.

Kellie Woodhouse covers higher education for AnnArbor.com. Reach her at kelliewoodhouse@annarbor.com or 734-623-4602 and follow her on twitter.