Voyager Seeks the Answer Blowin' in the Wind

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

News release: 2011-069 March 8, 2011

Voyager Seeks the Answer Blowin' in the Wind

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-069&cid=release_2011-069

PASADENA, Calif. -- In which direction is the sun's stream of charged particles banking
when it nears the edge of the solar system? The answer, scientists know, is blowing in the
wind. It's just a matter of getting NASA's Voyager 1 spacecraft in the right orientation to
detect it.

To enable Voyager 1's Low Energy Charged Particle instrument to gather these data, the
spacecraft performed a maneuver on March 7 that it hadn't done for 21 years, except in a
preparatory test last month.

At 9:10 a.m. PST (12:10 p.m. EST), humanity's most distant spacecraft rolled 70 degrees
counterclockwise as seen from Earth from its normal orientation and held the position by
spinning gyroscopes for two hours, 33 minutes. The last time either of the two Voyager
spacecraft rolled and stopped in a gyro-controlled orientation was Feb. 14, 1990, when
Voyager 1 snapped a family portrait of the planets strewn like tiny gems around our sun
(http://photojournal.jpl.nasa.gov/catalog/PIA00451).

"Even though Voyager 1 has been traveling through the solar system for 33 years, it is still
a limber enough gymnast to do acrobatics we haven't asked it to do in 21 years," said
Suzanne Dodd, Voyager project manager, based at NASA's Jet Propulsion Laboratory in
Pasadena, Calif. "It executed the maneuver without a hitch, and we look forward to
doing it a few more times to allow the scientists to gather the data they need."

The two Voyager spacecraft are traveling through a turbulent area known as the
heliosheath. The heliosheath is the outer shell of a bubble around our solar system created
by the solar wind, a stream of ions blowing radially outward from the sun at a million
miles per hour. The wind must turn as it approaches the outer edge of the bubble where it
makes contact with the interstellar wind, which originates in the region between stars and
blows by our solar bubble.

In June 2010, when Voyager 1 was about 17 billion kilometers (about 11 billion miles)
away from the sun, data from the Low Energy Charged Particle instrument began to show
that the net outward flow of the solar wind was zero. That zero reading has continued
since. The Voyager science team doesn't think the wind has disappeared in that area. It
has likely just turned a corner. But does it go up, down or to the side?

"Because the direction of the solar wind has changed and its radial speed has dropped to
zero, we have to change the orientation of Voyager 1 so the Low Energy Charged
Particle instrument can act like a kind of weather vane to see which way the wind is now
blowing," said Edward Stone, Voyager project manager, based at the California Institute
of Technology, Pasadena. "Knowing the strength and direction of the wind is critical to
understanding the shape of our solar bubble and estimating how much farther it is to the
edge of interstellar space."

Voyager engineers performed a test roll and hold on Feb. 2 for two hours, 15 minutes.
When data from Voyager 1 were received on Earth some 16 hours later, the mission team
verified the test was successful and the spacecraft had no problem in reorienting itself
and locking back onto its guide star, Alpha Centauri.

The Low Energy Charged Particle instrument science team confirmed that the spacecraft
had acquired the kind of information it needed, and mission planners gave Voyager 1 the
green light to do more rolls and longer holds. There will be five more of these maneuvers
over the next seven days, with the longest hold lasting three hours 50 minutes. The
Voyager team plans to execute a series of weekly rolls for this purpose every three
months.

The success of the March 7 roll and hold was received at JPL at 1:21 a.m. PST (4:21 a.m.
EST) on March 8. But it will take a few months longer for scientists to analyze the data.
"We do whatever we can to make sure the scientists get exactly the kinds of data they
need, because only the Voyager spacecraft are still active in this exotic region of space,"
said Jefferson Hall, Voyager mission operations manager at JPL. "We were delighted to
see Voyager still has the capability to acquire unique science data in an area that won't
likely be traveled by other spacecraft for decades to come."

Voyager 2 was launched on Aug. 20, 1977. Voyager 1 was launched on Sept. 5, 1977.
On March 7, Voyager 1 was 17.4 billion kilometers (10.8 billion miles) away from the
sun. Voyager 2 was 14.2 billion kilometers (8.8 billion miles) away from the sun, on a
different trajectory.

The solar wind's outward flow has not yet diminished to zero where Voyager 2 is
exploring, but that may happen as the spacecraft approaches the edge of the bubble in the
years ahead.

The Voyagers were built by NASA's Jet Propulsion Laboratory in Pasadena, Calif., which
continues to operate both spacecraft. JPL is a division of the California Institute of
Technology in Pasadena. The Voyager missions are a part of the NASA Heliophysics
System Observatory, sponsored by the Heliophysics Division of the Science Mission
Directorate. For more information about the Voyager spacecraft, visit:
http://www.nasa.gov/voyager.

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