[meteorite-list] Rosetta Starts Tracking Asteroid 2867 Steins

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 6 Aug 2008 09:32:53 -0700 (PDT)
Message-ID: <200808061632.JAA26429_at_zagami.jpl.nasa.gov>

http://www.esa.int/esaCP/SEMF0B8N9JF_index_0.html

Rosetta starts tracking asteroid Steins
European Space Agency
4 August 2008

Heading toward its first target-asteroid, (2867) Steins, ESA's Rosetta
spacecraft has started using its cameras to visually track the asteroid and
eventually determine its orbit with more accuracy.

Rosetta started the optical navigation campaign on 4 August 2008, at a
distance of about 24 million km from Steins; the campaign will continue
until 4 September, when the spacecraft will be approximately 950 000 km from
the asteroid.

"The orbit of Steins, with which Rosetta will rendezvous on 5 September,
closing to a distance of 800 km, is only known thanks to ground
observations, but not yet with the accuracy we would like for the close
fly-by," said Gerhard Schwehm, Rosetta Mission Manager based at ESA's
European Space Astronomy Centre (ESAC), near Madrid, Spain.

Optical tracking to better understand Steins' orbit
 
The purpose of the tracking campaign is to reduce the error in our knowledge
of Steins' orbit from about 100 km to only within 2 km (in the direction
perpendicular to the flight direction of the asteroid, called
'cross-track'), so as to allow Rosetta an optimal approach to this celestial
body.

Both Rosetta's navigation cameras and the OSIRIS (Optical, Spectroscopic,
and Infrared Remote Imaging System) imaging system will be used to track
Steins.

"For the first three weeks of the campaign, however, only the powerful eyes
of OSIRIS will actually be able to spot the asteroid, which will look only
like a dot in the sky," said Andrea Accomazzo, Rosetta Spacecraft Operations
Manager at ESA's European Space Operations Centre (ESOC), Darmstadt,
Germany.

"Starting 11 days before closest approach, as the distance with Steins
decreases, the two Rosetta navigation cameras will finally be able to see
and track the asteroid, too," he added.

For the first three weeks of the campaign, Rosetta will image Steins twice a
week and then, starting on 25 August, it will take images daily until 4
September.

The Steins orbital information gathered during the tracking campaign will be
used to adjust Rosetta's trajectory for the 5 September fly-by. "We will
already be able to use the first data set for the trajectory correction
manoeuvre planned for mid-August," said Sylvain Lodiot, from the Rosetta
Flight Control Team at ESOC.

"As Rosetta's distance from Steins decreases, the precision of the
measurements for Steins' orbit will increase even further, allowing us the
best possible trajectory corrections later on before closest approach,
especially in early September."

OSIRIS to obtain Steins' 'light curves'
 
Rita Schulz, Rosetta Project Scientist based at ESA's European Space
Research and Technology Centre (ESTEC), Noordwijk, the Netherlands,
explained that this is the first time in the Rosetta mission that the OSIRIS
scientific instrument is being used for tracking purposes.

"But OSIRIS will also take this opportunity to obtain 'light curves' of
Steins. Light curves tell us how the asteroid brightness varies with time,
providing us with additional preparatory information about the asteroid,
such as better knowledge of its shape and rotation characteristics," she
said.

The optical navigation campaign follows a series of active check-outs of
Rosetta's scientific instrumentation, which lasted from 5 July to 3 August
this year. A mission milestone for Rosetta, these activities also verified
the instruments' readiness for the fly-by observations, and allowed on-board
software modifications to be implemented for several of them.

For more information:
 
Gerhard Schwehm, ESA Rosetta Mission Manager
Email: Gerhard.Schwehm _at_ esa.int

Rita Schulz, ESA Rosetta Project Scientist
Email: Rita.Schulz _at_ esa.int

Andrea Accomazzo, ESA Rosetta Spacecraft Operations Manager
Email: Andrea.Accomazzo _at_ esa.int

[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaCP/SEMF0B8N9JF_index_1.html ]
Received on Wed 06 Aug 2008 12:32:53 PM PDT