[meteorite-list] Rosetta Awakens from Hibernation for Asteroid Encounter (2867 Steins)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat, 5 Jul 2008 22:00:25 -0700 (PDT)
Message-ID: <200807060500.WAA14851_at_zagami.jpl.nasa.gov>

http://www.esa.int/SPECIALS/Rosetta/SEMQPDSHKHF_0.html

Rosetta awakes from hibernation for asteroid encounter
European Space Agency
3 July 2008

Spacecraft controllers have just awoken Rosetta from hibernation to prepare
for its encounter with asteroid (2867) Steins on 5 September. ESA's comet
chaser will study the relatively rare asteroid as it flies by on its way to
comet 67/P Churyumov-Gerasimenko.
 
Launched in March 2004, Rosetta will reach its final destination only in
2014, after travelling a total of about 6500 million km. The distance
between the spacecraft and the Sun as it approaches the comet will be about
600 million or 4 AU (1 AU or 1 Astronomical Unit is equal to 150 million km,
the mean distance between Earth and the Sun).

Rosetta has swung by Earth twice and Mars once, performing gravity-assist
manoeuvres, that gave it the necessary boost to continue on its journey. The
third and last Earth swing-by is scheduled for November 2009. The spacecraft
will also fly by two asteroids and study them on the way: (2867) Steins in
September this year and (21) Lutetia in June 2010. As it closes in on (2867)
Steins in September, Rosetta will have travelled about 3700 million km and
will be 2.1 AU from the Sun.

After its last planetary swing-by on 13 November last year, Rosetta headed
towards the asteroid belt located between the orbits of Mars and Jupiter. On
27 March 2008, the spacecraft switched to its near-Sun hibernation mode for
a period of three months. During this phase, a few subsystems were put into
a dormant state to optimise their lifetime (as this is only the beginning of
the mission's science phase).

Next stop, Steins
 
Rosetta will be closest to (2867) Steins at 20:37 CEST on 5 September, at a
distance of 800 km. The spacecraft will zoom past at a relative speed of 8.6
km/s.

In preparation for the fly-by, all the instruments will be checked and
tested through the month of July. Between 4 August and 4 September,
spacecraft operators will conduct an optical navigation campaign: Steins
will be tracked by the on-board cameras and the observations will be used to
refine the knowledge of its orbit which has been derived only from
ground-based measurements so far.

Asteroids are samples of the Solar System's material at different stages of
evolution, and studying them helps scientists understand the origin and
evolution of Earth and of our planetary neighbourhood.

(2867) Steins is a relatively rare type of asteroid. Based on ground-based
observations it has been classified as an E-type asteroid, composed mainly
of silicates and basalts, but its properties are not known in detail. For
these reasons, it has been selected as one of the two asteroids that Rosetta
will study, from among those that were within reach of the mission. The
knowledge gained from the measurements will add to our knowledge of the
composition and evolution of E-type asteroids and will also supplement and
help interpret future ground-based data on asteroids.

Making most of the fly-by
 
The observations will be used to characterise the asteroid and its
environment and to test Rosetta's instruments, most of which will be active
during the fly-by.

The science objectives of the fly-by observations are as follows:

* To characterise the asteroid by studying its physical and chemical
properties
* To study its kinematic properties (its rotation, for example)
* To study the asteroid's surface and to perform comparative studies with
surfaces of other asteroids in order to understand differences between
asteroid types
* To study the interaction between the solar wind and the asteroid
* To study the asteroid's environment, including the presence of natural
satellites, the magnetic and electrical properties of the immediate
environment, and gas or dust orbiting the asteroid

The fly-by will push Rosetta to its design limits, especially owing to the
fast rotation of the spacecraft around the time of closest approach. The
manoeuvre is necessary to ensure that the asteroid will stay in the field of
view of the instruments. In view of this, a full in-flight simulation of the
fly-by was performed on 24 March 2008. The tests were successful, confirming
the spacecraft's robustness.

Major journey milestones
 
Launch: 2 March 2004
First Earth swing-by: 4 March 2005
Mars swing-by: 25 February 2007
Second Earth swing-by: 13 November 2007
Third Earth swing-by: 13 November 2009
Comet 67/P Churyumov-Gerasimenko rendezvous: May 2014
Landing on the comet: November 2014
Escorting the comet: until end 2015

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 suporting this release are available at
http://www.esa.int/SPECIALS/Rosetta/SEMQPDSHKHF_1.html ]
Received on Sun 06 Jul 2008 01:00:25 AM PDT