NASA Spacecraft Breaks Speed Boost Record
NASA's Dawn spacecraft, illustrated in this artist's concept, is propelled by ion engines.
Credit: NASA/JPL

Zooming deep toward the heart of the asteroid belt, NASA's Dawn spacecraft has accelerated itself into the record books for the biggest single speed boost ever by a spacecraft engine.

The ion-propelled spacecraft set the new record while on its way to visit the asteroid belt's two biggest space rocks, Ceres and Vesta.

"We are using this amazing ion-engine technology as a stepping-stone to orbit and explore two of the asteroid belt's most mysterious objects, Vesta and Ceres," said Robert Mase, Dawn project manager from NASA's Jet Propulsion Laboratory (JPL), located in Pasadena, Calif.

The all-time velocity change record was previously held by NASA's Deep Space 1 probe, which was the first interplanetary spacecraft to use ion propulsion technology. Ion propulsion creates thrust by consistently accelerating ions through a nozzle using electrostatic force.

Deep Space 1's record fell on June 5, when the Dawn spacecraft's accumulated acceleration over the course of the mission sailed past the 9,600 mph (15,449 kph) mark.

A spacecraft's change in velocity refers to its ability to change its path through space using its own rocket engines. Measurements of this change begin only after the spacecraft exits the last stage of the launch vehicle that initially hurled it into space. NASA launched the Dawn mission on Sept. 27, 2007.

Since then, Dawn has had to fire each of its three engines, one at a time, for a cumulative total of 620 days in order to reach the asteroid belt and set the new velocity change record. In doing so, it has used less than 363 pounds (165 kg) of xenon propellant.

Over the course of its eight-plus-year mission, Dawn's three ion engines are expected to accumulate 2,000 days of operation ? equivalent to 5.5 years of thrusting ? for a total change in velocity of over 24,000 mph (38,000 kph).

"I am delighted that it will be Dawn that surpasses DS1's record," said Marc Rayman, chief engineer for the Dawn mission, and a previous project manager for Deep Space 1. "It is a tribute to all those involved in the design and operations of this remarkable spacecraft."

While Dawn's energy thrusts of 0-to-60 mph (0-to-97 kph) in four days may seem underwhelming, the spacecraft is incredibly efficient. In fact, it expends a mere 37 ounces of xenon propellant during that time.

Furthermore, after four days of full-throttle thrusting, it continues thrusting for two more four-day intervals. By the end of 12 days, Dawn will have increased its velocity by more than 180 mph (290 kph), with more days, weeks and months of continuous thrusting to come.

Over the course of a year, Dawn's ion propulsion system can increase the spacecraft's speed by a whopping 5,500 mph (8,850 kph), all the while consuming the equivalent of only 16 gallons of fuel.

"This is a special moment for the spacecraft team," said Dawn's principal investigator, Chris Russell of the University of California Los Angeles. "In only 407 days, our minds will be on another set of records, the data records that Dawn will transmit when we enter Vesta orbit."

Next stop: space rock

The Dawn spacecraft is expected to voyage across 3 billion miles (4.8 billion km) on an odyssey that will include explorations of asteroid Vesta in 2011 and 2012, and the dwarf planet Ceres in 2015. Both Vesta and Ceres have witnessed much of our solar system's history.

By using the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn's full suite of science instruments will measure shape, surface topography and tectonic history, elemental and mineral composition, as well as seek out water-bearing minerals.

Additionally, the way that the spacecraft orbits both Vesta and Ceres will be used to measure the mass and gravity fields of the celestial bodies.

And while Dawn surpassed Deep Space 1's record for velocity change, the older probe still holds the record for the longest-duration of powered spaceflight, and will continue to do so for another few months. Dawn is, however, expected to take over that record at around early August of this year.

As the Dawn probe streaks through the asteroid belt headed for a space rock rendezvous, another unmanned probe is returning home from one. Japan's Hayabusa spacecraft is flying ever closer to Earth and set to drop a sample return capsule that may contain pieces of its asteroid target Itokawa on Sunday, June 13. Japan's space agency launched the Hayabusa mission in 2003 and the probe arrived at its asteroid target in 2005, but suffered multiple malfunctions during its trip.

The Dawn mission to Vesta and Ceres is managed by NASA's JPL. The University of California, Los Angeles is responsible for overall Dawn mission science.