Impactor Away: Deep Impact Probe En Route to Comet
Deep Impact's Flyby mothership releases the Impactor probe in this illustration.
Credit: ESA/NASA.

This story was updated at 3:58 a.m. EDT.

PASADENA -- The Deep Impact mission is now less than 24-hours and 500,000 miles from its final destination after the spacecraft's Impactor probe successfully separated from its Flyby mothership early Sunday morning.

The $333 million mission is slated to crash an 820-pound (371-kilogram) Impactor probe into Comet Tempel 1 and record the event via the Flyby mothership. The collision is expected to take place at 1:52 a.m. EDT (0552 GMT) on July 4. A cheer went up at 2:16 a.m. EDT (0616 GMT) when a mission controller announced when Deep Impact's mission control received confirmation that the Impactor had separated from the Flyby mothership at 2:07 a.m. EDT (0606 GMT).

"It went like clockwork. Very good, we're very excited." Deep Impact project manager Rick Grammier, of NASA's Jet Propulsion Laboratory (JPL) here, told reporters. "The systems were all nominal and we were within half a kilometer of our target point before release and the release went very well."

Researchers hope NASA's Deep Impact mission will not just succeed in ramming a comet, but will punch through Tempel 1's surface and reveal material that has not been seen since the formation of the solar system 4.6 billion years ago. They hope Deep Impact will not only yield information about the composition of comets, but also shed light on the make-up of the early solar system.

"The first look at the data indicates that things couldn't have gone better," said Monte Henderson, program manager for Ball Aerospace and Technologies Corp., the builders of NASA's Deep Impact spacecraft, via e-mail.

Following separation, Flyby completed its divert engine burn and moved safely out of the comet's path. After the initial separation, an alarm went off onboard the Flyby vehicle. Mission controllers ran through a systems check and concluded the spacecraft was on track and the alarm could be ignored.

Grammier said that Flyby did manage to capture and image of Impactor after the release.

"We didn't know if we would quite get that or not, so that was a good thing," Grammier said.

"We have been working on this program for five-and-a-half years, yet the major milestones are still ahead of us," Henderson said earlier Saturday evening, prior to the release.

In recent weeks, Comet Tempel 1 has surprised mission managers with a series of outbursts, the result of the comet's ever-closer proximity to the sun. The first outburst was observed on June 14. A second outburst occurred on June 22 and was photographed by the Hubble Space Telescope.

"We did not expect to see it," Henderson said. "Our science team is really excited about what they are finding."

The outbursts--sprays of water vapor and carbon dioxide--are a result of portions of a comet's icy crust heating up under the sun's light. According to Henderson, Tempel 1's outburst is at the moment, a singular, predictable event. The comet completes one rotation on its axis every 42 hours, with one outburst per rotation.

Henderson described the outbursts as fog-like, dispersing over the surface of the comet, not an explosive plume that could adversely affect the Impactor's ability to pinpoint the brightest spot on the comet's surface. The team is not concerned that the outburst will interfere with the impact. The last outburst is expected to occur four hours prior to the collision said Henderson, and because of the outbursts diffuse orientation, it disperses after about 30 minutes.

"I think we are seeing it at it's most active," Henderson said.

Today's successful spacecraft separation is just the opening act for the Deep Impact mission. The real fireworks begin tomorrow, when Impactor begins its end-run toward Tempel 1 while Flyby, and a myriad of orbital and ground-based telescopes, look on.

A pre-impact press conference is currently set for 2:00 p.m. (1800 GMT) on July 3. NASA TV will provide live commentary of Deep Impact's arrival and expected impact with Comet Tempel 1 beginning at 11:30 p.m. EDT (0330 July 4 GMT).

You can follow Deep Impact's comet crash live via's mission commentary available here. Staff Writer Tariq Malik contributed to this story from New York City.

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