Mon, Aug 15, 2011
Survey Phase Planned To Last 20 Days
The Dawn spacecraft has completed a graceful spiral into the
first of four planned science orbits during the spacecraft's
yearlong visit to Vesta. The spacecraft started taking detailed
observations on Aug. 11 at 0013 EDT, which marks the official start
of the first science-collecting orbit phase at Vesta, also known as
the survey orbit.
NASA/JPL Composite Image
Survey orbit is the initial and highest
orbit, at roughly 1700 miles above the surface, which will provide
an overview or "big picture" perspective of the giant
asteroid.
The primary objective of survey orbit is to image the surface with
near-global coverage in visible and infrared wavelengths with the
mapping spectrometer, also known as VIR. Dawn also will be using
its framing camera to collect image mosaics that complement the VIR
spectral data to produce geologic and compositional maps of Vesta's
surface. Ultrasensitive measurements of the spacecraft's motion
using radio signals will allow improved understanding of the giant
asteroid's gravity field. Dawn's gamma ray and neutron detector
will continue to collect background data.
The survey phase is planned to last 20 days. Each orbit takes
almost three days, which will provide the spacecraft seven trips
around Vesta. After survey orbit, Dawn will resume thrusting,
taking about a month to spiral down gently to its next science
orbit for an even closer view. That orbit, known as High Altitude
Mapping Orbit, or HAMO, begins in late September. Dawn will spend
about a month in HAMO, circling around Vesta in half a day, rather
than three. Dawn will orbit more than 60 times during HAMO,
allowing the camera to fully map the illuminated portion of Vesta
at even higher resolution, and enable the science team to generate
stereo images.
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