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An Atlas 5 rocket rises from its fog-shrouded launch pad at Vandenberg Air Force Base in California, sending NASA’s Mars InSight lander toward the Red Planet. (GeekWire Photo/Kevin Lisota)

NASA’s Mars InSight lander and two piggyback probes were lofted through California’s coastal fog into space before dawn today, beginning a six-month, 300 million-mile journey to study the Red Planet’s mysterious interior.

It marked the first interplanetary mission to be launched from the U.S. West Coast.

The launch pad at Vandenberg Air Force Base was shrouded in murk when the United Launch Alliance Atlas 5 rocket lifted off at 4:05 a.m. PT. Near the pad, the typically foggy weather blocked the view, but not the sound.

“We really heard it,” NASA chief scientist Jim Green said after liftoff. “Car alarms went off in the parking lot.”

Spectators across a wide swath of the Southern California coast got a good look at the rocket’s red glare as the Atlas ascended to orbit.

After going into a pole-to-pole orbit, the Atlas’ Centaur upper stage boosted NASA’s car-sized lander through a “left turn” and onward to Mars.

Vandenberg was selected for today’s launch because NASA’s traditional interplanetary launch site in Florida was facing a space traffic jam, Scott Messer, ULA’s program manager for NASA missions, said during a pre-launch briefing. The Atlas 5 provided more than enough oomph to get its payload into deep space.

Just after the lander was sent on its way, the upper stage deployed two nanosatellites, each the size of a cereal box, which will make parallel trips to Mars and test miniaturized systems for spacecraft propulsion and communications during a flyby.

NASA Administrator Jim Bridenstine, who was sworn in less than two weeks ago, passed along his thanks to the Mars InSight team in a congratulatory phone call. “This is a big day,” he said. “We’re going back to Mars.”

Previously: Here’s what Mars InSight and its piggyback probes will do

At the end of its long cruise, InSight is due to light up its thrusters and land on a Martian plain known as Elysium Planitia on Nov. 26.

That happens to be right after Thanksgiving, on Cyber Monday, said Tom Hoffman, InSight project manager at NASA’s Jet Propulsion Laboratory. “If you’re shopping online … and you want to see something else, you can put that on your other screen,” he joked.

The lander will deploy a super-sensitive seismometer as well as a heat probe that’s designed to hammer its way as much as 16 feet beneath the Martian surface. It will also use its radio antenna system to make precise measurements of Mars’ wobble on its axis.

All those readings are expected to give scientists unprecedented insights into the planet’s “Marsquakes,” its interior structure and the composition of its crust, mantle and metallic core. That could help them flesh out their understanding of the solar system’s origins, and help NASA anticipate what its astronauts will eventually face.

The $1 billion mission is a joint effort involving NASA as well as partners in France, Germany and elsewhere in Europe.

Today’s launch was originally supposed to take place in 2016, but problems with the French-built seismometer forced a 26-month delay.

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