NASA
Kepler's Second Light.
This image by NASA's Kepler spacecraft shows the telescope's full field
of view taken in a new demonstration mode in late October. A new mission
concept, dubbed K2, would continue Kepler's search for other worlds,
and introduce new science observation opportunities. Image Credit: NASA Ames
This conception illustration depicts how solar pressure can be used to
balance NASA's Kepler spacecraft, keeping the telescope stable enough to
continue searching for transiting planets around distant stars.Image Credit: NASA Ames/W Stenzel
A new mission concept, dubbed K2, would continue Kepler's search for
other worlds, and introduce new opportunities to observe star clusters,
young and old stars, active galaxies and supernovae.
In May, the Kepler spacecraft lost the second of four gyroscope-like
reaction wheels, which are used to precisely point the spacecraft,
ending new data collection for the original mission. The spacecraft
required three functioning wheels to maintain the precision pointing
necessary to detect the signal of small Earth-sized exoplanets, which
are planets outside our solar system, orbiting stars like our sun in
what's known as the habitable zone -- the range of distances from a star
where the surface temperature of a planet might be suitable for liquid
water.
With the failure of a second reaction wheel, the spacecraft can no
longer precisely point at the mission's original field of view. The
culprit is none other than our own sun.
The very body that provides Kepler with its energy needs also pushes
the spacecraft around by the pressure exerted when the photons of
sunlight strike the spacecraft. Without a third wheel to help counteract
the solar pressure, the spacecraft's ultra-precise pointing capability
cannot be controlled in all directions.
However, Kepler mission and Ball Aerospace engineers have developed
an innovative way of recovering pointing stability by maneuvering the
spacecraft so that the solar pressure is evenly distributed across the
surfaces of the spacecraft.
To achieve this level of stability, the orientation of the spacecraft
must be nearly parallel to its orbital path around the sun, which is
slightly offset from the ecliptic, the orbital plane of Earth. The
ecliptic plane defines the band of sky in which lie the constellations
of the zodiac.
This technique of using the sun as the 'third wheel' to control
pointing is currently being tested on the spacecraft and early results
are already coming in. During a pointing performance test in late
October, a full frame image of the space telescope's full field of view
was captured showing part of the constellation Sagittarius.
Photons of light from a distant star field were collected over a
30-minute period and produced an image quality within five percent of
the primary mission image quality, which used four reaction wheels to
control pointing stability. Additional testing is underway to
demonstrate the ability to maintain this level of pointing control for
days and weeks.
To capture the telltale signature of a distant planet as it crosses
the face of its host star and temporarily blocks the amount of starlight
collected by Kepler, the spacecraft must maintain pointing stability
over these longer periods.
"This 'second light' image provides a successful first step in a
process that may yet result in new observations and continued
discoveries from the Kepler space telescope," said Charlie Sobeck,
Kepler deputy project manager at NASA Ames Research Center in Moffett
Field, CA.
The K2 mission concept has been presented to NASA Headquarters. A
decision to proceed to the 2014 Senior Review – a biannual assessment of
operating missions – and propose for budget to fly K2 is expected by
the end of 2013.
Kepler's original mission, which is still in progress to fully
process the wealth of data collected, is to determine what percentage of
stars like the sun harbor small planets the approximate size and
surface temperature of Earth. For four years, the space telescope
simultaneously and continuously monitored the brightness of more than
150,000 stars, recording a measurement every 30 minutes.
More than a year of the data collected by Kepler remains to be fully reviewed and analyzed.
Ames Research Center, Moffett Field, Calif.
michele.johnson@nasa.gov
