NASA DAWN: Spacecraft operating normally after safe mode triggered

Artist concept of NASA's Dawn spacecraft orbiting Ceres during an upcoming flyby. 

Credit: NASA/JPL-Caltech/UCLA

The Dawn spacecraft has resumed normal ion thrusting after the thrusting unexpectedly stopped and the spacecraft entered safe mode on September 11.

That anomaly occurred shortly before a planned communication with NASA's Deep Space Network that morning.

The spacecraft was not performing any special activities at the time.

Engineers immediately began working to restore the spacecraft to its normal operational state.

The team determined the source of the problems, corrected them, and then resumed normal ion thrusting on Monday night, Sept. 15.

"This anomaly presented the team with an intricate and elaborate puzzle to solve," said Robert Mase, Dawn project manager at NASA's Jet Propulsion Laboratory in Pasadena, California.

After investigating what caused the spacecraft to enter safe mode, the Dawn team determined that it was likely triggered by the same phenomenon that affected Dawn three years ago on approach to the protoplanet Vesta: An electrical component in the ion propulsion system was disabled by a high-energy particle of radiation.

"We followed the same strategy that we implemented three years ago to recover from a similar radiation strike, to swap to one of the other ion engines and a different electronic controller so we could resume thrusting quickly," said Dawn Mission Director and Chief Engineer Marc Rayman of JPL.

"We have a plan in place to revive this disabled component later this year."

Complicating the issue, the team discovered that the spacecraft had experienced not just one anomaly, but also a second one that affected the ability to point the main antenna at Earth to communicate.

Because the spacecraft could not communicate using its main antenna, the team had to utilize the weaker signals of another antenna, slowing their progress.

In addition, Dawn is so far from Earth that radio signals take 53 minutes to make the round trip.

Although they have not yet specifically pinpointed the cause of this issue, it could also be explained by a high-energy particle corrupting the software running in the main computer.

Ultimately the team reset the computer, which restored the pointing performance to normal.

As a result of the change in the thrust plan, Dawn will enter into orbit around dwarf planet Ceres in April 2015, about a month later than previously planned.

Ceres

The plans for exploring Ceres once the spacecraft is in orbit, however, are not affected.

Vesta

Dawn orbited Vesta, the second most massive object in the main asteroid belt, from July 2011 until September 2012.

The spacecraft's ion propulsion system enabled it to spiral away from Vesta and head toward Ceres, the most massive object in that region.

NASA NEOWISE: Asteroid 2014 HQ124 to Pass Earth Safely

This diagram shows the orbit of asteroid 2014 HQ124, and its location relative to Earth on June 8.

Image Credit: NASA/JPL-Caltech

A newfound asteroid will safely pass Earth on June 8 from a distance of about 777,000 miles (1.25 million kilometers), more than three times farther away than our moon.

Designated 2014 HQ124, the asteroid was discovered April 23, 2014, by NASA's NEOWISE mission, a space telescope adapted for scouting the skies for asteroids and comets.

The telescope sees infrared light, which allows it to pick up the infrared glow of asteroids and obtain better estimates of their true sizes.

The NEOWISE data estimate asteroid 2014 HQ124 to be between 800 and 1,300 feet (250 and 400 meters).

More than one hundred follow-up observations from NASA-funded, ground-based telescopes and amateur astronomers were used to pin down the orbit of the asteroid out to the year 2200, during which time it poses no risk to Earth.

Its trajectory will continue to be recalculated past that time frame as additional observations are received.

"There is zero chance of an impact," said Don Yeomans, manager of NASA's Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, California.

"In fact, it's fairly common for asteroids to pass near Earth. You'd expect an object about the size of 2014 HQ124 to pass this close every few years."

Yeomans said that 2014 HQ124 is a good target for radar observations using NASA's Deep Space Network antenna at Goldstone, California, and the Arecibo Observatory in Puerto Rico, shortly after the closest approach on June 8.

Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than otherwise known.

2014 HQ124 is designated a "potentially hazardous asteroid," or PHA, which refers to those asteroids 460 feet (140 meters) in size or larger that pass within 4.6 million miles (7.4 million kilometers) of Earth's orbit around the sun.

There are currently 1,484 known PHAs, but none pose a significant near-term risk of impacting Earth.

"Because NEOWISE is a space telescope observing the dawn and twilight sky at infrared wavelengths, it is particularly good at finding large NEOs that make relatively close passes to Earth," said Amy Mainzer, the principal investigator of NEOWISE at JPL.

"Using infrared light, we can estimate the object’s size, and we can tell that it reflects a fair amount of light. That means it’s most likely a stony object.”

NASA detects, tracks and characterizes asteroids and comets passing close to Earth using both ground- and space-based telescopes.

The Near-Earth Object Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them and identifies their orbits to determine if any could be potentially hazardous to our planet.

To date, U.S. assets have discovered more than 98 percent of the known near-Earth objects.

NASA's Deep Space Network (DSN): Goldstone's Antenna Tracks Spacecraft

Late night in the desert: Goldstone's 230-foot (70-meter) antenna tracks spacecraft day and night. 

This photograph was taken on Jan. 11, 2012.

The Goldstone Deep Space Communications Complex, located in the Mojave Desert in California, is one of three complexes that comprise NASA's Deep Space Network (DSN).

The DSN provides radio communications for all of NASA's interplanetary spacecraft and is also utilized for radio astronomy and radar observations of the solar system and the universe. 

DSN, the world's largest and most powerful communications system for "talking to" spacecraft, will reach a milestone on Dec. 24: the 50th anniversary of its official creation.

JPL, a division of the California Institute of Technology in Pasadena, manages the Deep Space Network for NASA. 

More information about the Deep Space Network is online at: www.jpl.nasa.gov/dsn50.

More information about NASA's Space Communications and Navigation program is at: www.spacecomm.nasa.gov.

Image Credit: NASA/JPL-Caltech