NASA mission discussed at scientific gathering here

By Ann McCreary

NASA’s Dawn spacecraft, launched nine years ago, is now orbiting a dwarf planet on the far side of the sun — the first spacecraft to orbit two objects in the solar system.

Dawn’s mission to the far reaches of the solar system has turned “science fiction into science fact,” said Marc Rayman, chief engineer and Dawn Mission director.

Rayman and Tom McCord, director of Bear Fight Institute, a planetary research center near Winthrop, gave a public presentation last Thursday (June 2) about Dawn during an international gathering of scientists involved in the space mission.

Dawn uses a futuristic, hyper-efficient ion propulsion system to carry it through space. Without that propulsion system, Rayman said, the spacecraft could not have accomplished its goal of orbiting Vesta, a massive asteroid, and Ceres, a dwarf planet — the two most massive objects in an asteroid belt lying between Mars and Saturn.

The Dawn Mission is producing science and new knowledge “that extends mankind’s vision of our environment out to the solar system,” said McCord, who is a founding member of the Dawn Mission team.

“Like Lewis and Clark … we too feel excited when we get an image of something nobody has ever seen before,” he said.

Dawn carries technology that produces color photographs, analyzes mineral and elemental composition of the surface of the objects, measures gravity fields, and searches for moons.

“Dawn represents some of humankind’s most advanced technology,” Rayman said.

The information transmitted by Dawn will help scientists better understand how our solar system was formed.

In 58 years of space exploration, most spacecraft have not gone beyond low Earth orbit — a distance from Earth’s surface that is about the same as from the Methow Valley to Seattle, Rayman said.

Dawn, on the other hand, “passed the orbit of the moon on the day it launched” and is now “four times as far away as the sun” is from Earth, Rayman said.

Now in low orbit around the dwarf planet Ceres, Dawn has traveled 3.1 million miles since it left Earth.

“We have a spacecraft on the far side of the sun. To me, everyone who has ever looked up at the night sky and wondered is part of a mission like this,” Rayman said.

Ion propulsion

The ion propulsion system, which uses xenon gas, is the key to Dawn’s ability to travel so far. At maximum thrust, the engines produce about the amount of force exerted by a piece of notebook paper resting on the open palm of your hand, Rayman said.

In the zero-gravity, frictionless conditions of spaceflight, the effect of this tiny amount of thrust has accumulated for more than five years.  Ion propulsion is “acceleration with patience,” Rayman said. The engines emit a cool blue glow, he said.

To help boost Dawn on its travels, NASA used Mars’ gravity to slingshot the spacecraft past the planet, robbing Mars of a tiny bit of its own orbital energy, Rayman said.

McCord said images and readings transmitted through radio signals from Dawn are providing valuable information about Vesta and Ceres.

Dawn orbited Vesta in 2011-2012 and produced images of impact craters from asteroids, with some impacts so intense they “nearly fractured Vesta,” McCord said.  Carbon-rich meteorite material has been found on the surface of impact sites, and readings indicate the asteroid has an iron core, he said.

Ceres, now being orbited by Dawn, has a surface marked by “bumps and lumps, that indicate the surface is moving,” McCord said.

Bright reflective spots inside craters are thought to be salt deposits “perhaps left over from an early ocean” and there may be water in the form of ice beneath the planet surface, he said.

Dawn’s primary mission is scheduled to end this month, but the spacecraft has not used all its xenon gas, which could allow Dawn to conduct additional work if authorized by NASA, the scientists said. Dawn will remain in orbit around Ceres long after it has run out of fuel and NASA has finished with it.