The suicide plunge will bust up Compton, with flaming wreckage slicing through the sky and slamming into an uninhabited part of the Pacific Ocean. That debris "footprint" is about 2,500 miles (4,025 kilometers) southeast of Hawaii.
Earlier, Compton had fired its thrusters on two different days -- May 30 and May 31 -- dropping it into lower and lower altitudes over Earth.
"Everything has been right on the mark," said Alan Bunner, a NASA science program director. "I have full confidence that everything is going to be by the book. Compton will fall exactly where the footprint is predicted," he told SPACE.com.
In the midnight hour
Ground controllers at the space agency's Goddard Space Flight Center in Greenbelt, Maryland are prepared to command Compton's thrusters for a third time. That engine burn, lasting some 26 minutes, is set for Sunday, June 4 at 12 a.m. Eastern Daylight Time (04:00 GMT).
Video animation of Compton Observatory fiery reentry.
Compton will then slip through space at just 93 miles (150 kilometers) above Earth. A fourth and final burn of the spacecraft's engines for 30 minutes will start at 1:30 a.m. EDT (05:30 GMT), pushing the satellite toward Earth, with pieces hitting the ocean at around 2:20 a.m. EDT (06:20 GMT).
This controlled reentry brings to an end the spacecraft's nine-year tour of duty in collecting valuable science data. TRW of Redondo Beach, California built the NASA satellite.
"We're ready for the main event," said Martin Frederick, a Goddard associate chief engineer and consultant to the team bringing down Compton. "Now that we've done the two burns, we're ready to nail this thing," he said.
Breaking up is so hard to do
As Compton makes its suicide plunge, an Air Force aircraft dispatched from Hawaii is expected to be in position to record the event.
Similarly, SPACE.com has learned that several classified satellites are to eye Compton's fall from grace. Knowing firsthand the weight, size and physical makeup of the science satellite offers a unique chance to study the breakup process of a spacecraft during reentry.
"Within a matter of hours we will be able to confirm that the spacecraft came down in the right place. We want to be able to tell the public that Compton did go down where we said it did, and the matter is settled," said Bunner.
Edward Tagliaferri, a consultant to The Aerospace Corporation in El Segundo, California, said monitoring the reentry of a satellite is of great value.
"The [computer] models we have for satellite breakups are relatively crude. We don't have a lot of data to go with them," Tagliaferri said.
A good percentage of Compton leftovers are expected to rain down through the atmosphere, striking the sea, including: pieces of science gear, a set of heavy nickel batteries, propulsion tanks and aluminum I-beams used in constructing the satellite.
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