STORY HIGHLIGHTS

(CNN) -- An unmanned NASA-contracted rocket exploded in midair early Tuesday evening, producing huge flames and loud booms along the eastern Virginia coast but no injuries or deaths.

Orbital Sciences Corp.'s Antares rocket and Cygnus cargo spacecraft had been set to launch at 6:22 p.m. ET from the Wallops Flight Facility along the Atlantic Ocean, carrying roughly 5,000 pounds of supplies and experiments to the International Space Station.

It exploded about six seconds after launch.

What was left of the spacecraft and rocket plummeted back to Earth, causing even more flames upon impact.

The rocket and spacecraft -- which together cost more than $200 million, according to Frank Culbertson, the general manager of Orbital's Advanced Programs Group -- are gone. And there's obvious damage beyond that, including to the launchpad, though the night skies made it hard to immediately gauge how much.

One thing officials do know is that rocket science is, in the words of NASA Administrator Bill Gerstenmaier, "a really tough business."

"Tonight's events really show the difficulty that it takes for us to do this task of delivering cargo to the space station," he said.

Witnesses: From 'breathtaking' to horrific

The Orbital rocket had been set to go up Monday, only to be scrubbed "because of a boat down range in the trajectory Antares would have flown had it lifted off," according to NASA. Coast Guard spokesman David Weydert said the boat that triggered the postponement was 40 miles offshore.

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NASA rocket explodes upon launch