NASA’s Dawn spacecraft begins approach around dwarf planet

Chuck Bednar for – Your Universe Online

After a journey that lasted more than seven years, NASA’s Dawn spacecraft has entered its approach phase around Ceres as it prepares to become the first spacecraft ever to visit the Texas-sized dwarf planet, the US space agency announced on Monday.

However, as Mashable points out, the approach phase will be a lengthy one. Dawn is still more than 400,000 miles away from Ceres, and even though it is travelling at speeds of over 450 miles per hour, it is not expected to enter orbit around the dwarf planet until March 2015.

Dawn, which launched in 2007, recently emerged from the opposite side of the sun (a status known as solar conjunction) that limited communication with antennas on Earth. Now that the probe has established contact with NASA officials, mission controllers have programmed the maneuvers required for the next stage of its rendezvous with the distant dwarf planet.

The vehicle navigates using special ion thrusters, according to Mashable. As Marc Rayman, Dawn Chief Engineer and Mission Director at NASA’s Jet Propulsion Laboratory, explained in a recent video, they give xenon gas a slight electric charge, then use higher voltage to accelerate the resulting ions through a metal grid and out of the engine at speeds topping 90,000 mph.

Dawn’s arrival at Ceres will mark the first time that a spacecraft has ever orbited two solar system targets, NASA claimed. Previously, the spacecraft spend 14 months exploring, capturing images and collecting data from the protoplanet Vesta in 2011 and 2012.

“Ceres is almost a complete mystery to us,” said Christopher Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles, said in a statement. “Ceres, unlike Vesta, has no meteorites linked to it to help reveal its secrets. All we can predict with confidence is that we will be surprised.”

“The two planetary bodies are thought to be different in a few important ways,” NASA added. “Ceres may have formed later than Vesta, and with a cooler interior. Current evidence suggests that Vesta only retained a small amount of water because it formed earlier, when radioactive material was more abundant, which would have produced more heat.”

In contrast, Ceres, has a thick ice mantle and could even have an ocean beneath its icy crust. With an average diameter of 590 miles (950 km), the dwarf planet is also the largest body located in the asteroid belt between Mars and Jupiter. Vesta, by comparison, has an average diameter of 326 miles (525 km) and is the second most massive body in this region of space.

“Orbiting both Vesta and Ceres would be truly impossible with conventional propulsion. Thanks to ion propulsion, we’re about to make history as the first spaceship ever to orbit two unexplored alien worlds,” said Rayman.

“The next couple of months promise continually improving views of Ceres, prior to Dawn’s arrival,” NASA added. “By the end of January, the spacecraft’s images and other data will be the best ever taken of the dwarf planet.”


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