A Sunny Outlook for NASA Kepler's Second Light
You may have thought that NASA's Kepler spacecraft was finished. Well, think
again. A repurposed Kepler Space telescope may soon start searching the sky
again.
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.
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
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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.
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
NASA
Guillermo Gonzalo Sánchez Achutegui
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