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TOPIC: Rosetta mission
Blobrana


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RE: Rosetta mission
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ESA mission controllers have confirmed Rosetta is on track for a critical 250-km Mars swingby on 25 February. Engineers have started final preparations for the delicate operation, which includes an eclipse, a signal blackout, precise navigation and complex ground tracking.
Rosetta is scheduled to make its closest approach to Mars at 02:57 CET on Sunday, 25 February, using the Red Planet as a gravitational brake to reduce speed and alter trajectory as part of the spacecraft's complex, 10-year, 7.1-thousand-million-kilometre journey to comet 67P/Churyumov-Gerasimenko.

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Blobrana


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During its long trek to final destination (comet 67P Churyumov-Gerasimenko), Rosetta is planned to study two asteroids – 2867-Steins and 21-Lutetia, both lying in the asteroid belt between the orbits of Mars and Jupiter. Asteroids, as well as comets, carry important information about the origin of the Solar System – a better understanding of which is one of the primary goals of Rosetta.
The two asteroids will be visited at close range in September 2008 and July 2010, respectively, but the Rosetta scientists have already taken the opportunity to collect preliminary data about them. This opportunity will help scientists to better prepare for the broader observation campaigns of the two asteroids to come at later stage.

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rosettae1 rosettae3



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Blobrana


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Asteroid 21 Lutetia
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Sequence of images obtained by the OSIRIS Instrument, during a 36-hour remote observation campaign of asteroid 21 Lutetia, on the 2-3 January 2007.
 Rosetta was at 245 million kilometres from the asteroid.
Together with 2867 Steins, 21 Lutetia is one of the two target asteroids that Rosetta will study during its long trek to comet 67P/Churyumov-Gersimenko. The two asteroids will be visited at close range in September 2008 and July 2010, respectively.

The Mars swing-by phase formally started on 28 July 2006. The actual swing-by will take place on 25 February 2007, followed by a Deep Space Manoeuvre in April 2007.

Video  (114kb, avi)
Credit ESA

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Blobrana


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RE: Rosetta mission
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Earlier this month ESA's Rosetta had a first look at asteroid 21-Lutetia, one of the targets of its long mission. The onboard camera OSIRIS imaged the asteroid passing through its field of view during the spacecraft's gradual approach to Mars. The planet will be reached on 25 February 2007 for the mission's next gravity assist.

RosettaMars
Expand (1184kb, 1024 x 1024)
Credits: ESA/MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

This view of Mars (visible towards the top of the image) and of the Milky Way was taken by the OSRIS camera on board the Rosetta orbiter on 3 December 2006, during the last series of instrument check-outs. In this image Mars is heavily overexposed and therefore surrounded by a halo of scattered light.

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Blobrana


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Title: Determination of the light curve of the Rosetta target Asteroid (2867) Steins by the OSIRIS cameras onboard Rosetta
Authors: M. Kueppers, S. Mottola, S. C. Lowry, M. F. A'Hearn, C. Barbieri, M. A. Barucci, S. Fornasier, O. Groussin, P. Gutierrez, S. F. Hviid, H. U. Keller, P. Lamy

Context: In 2004 asteroid (2867) Steins has been selected as a flyby target for the Rosetta mission. Determination of its spin period and the orientation of its rotation axis are essential for optimisation of the flyby planning.
Aim: Measurement of the rotation period and light curve of asteroid (2867) Steins at a phase angle larger than achievable from ground based observations, providing a high quality data set to contribute to the determination of the orientation of the spin axis and of the pole direction.
Methods: On March 11, 2006, asteroid (2867) Steins was observed continuously for 24 hours with the scientific camera system OSIRIS onboard Rosetta. The phase angle was 41.7 degrees, larger than the maximum phase angle of 30 degrees when Steins is observed from Earth. A total of 238 images, covering four rotation periods without interruption, were acquired.
Results: The light curve of (2867) Steins is double peaked with an amplitude of ~ 0.23 mag. The rotation period is 6.052 ± 0.007 hours. The continuous observations over four rotation periods exclude the possibility of period ambiguities. There is no indication of deviation from a principal axis rotation state. Assuming a slope parameter of G = 0.15, the absolute visual magnitude of Steins is 13.05 ± 0.03.

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Blobrana


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This month the team working on ESA's Rosetta mission have been particularly busy. Activities are underway to set the spacecraft's trajectory and prepare the on-board instruments ready for the next major mission milestone: the swing-by of planet Mars in February 2007.
Since its launch in March 2004, Rosetta has been bouncing around the inner solar system on a trajectory that will eventually lead it to its final destination in the first half of 2014 – comet 67P Churyumov-Gerasimenko. As the three-tonne spacecraft could not be set by its launcher onto a trajectory that would take it directly to the comet, a series of four planetary gravity-assisted manoeuvres were introduced into the mission design.
Swing-bys allow a spacecraft to gain energy in a 'natural' way by exploiting the gravitational energy of massive planetary bodies such as planets, similar to the way in which a slingshot is used to release a stone.

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-- Edited by Blobrana at 18:56, 2006-11-29

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Blobrana


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Report for Period 30 June to 28 July

The reporting period covers four weeks of passive cruise, in which the spacecraft remained in Near Sun Hibernation Mode (NSHM). The mode performance during the reporting period has been nominal.

On 26 July, the spacecraft was reconfigured to Active Cruise Mode. This system-level transition involved a reconfiguration of the AOCS subsystem to Normal Mode, a reconfiguration of the thermal subsystem hardware, and a reconfiguration of the telecommunications subsystem to High Gain Antenna and maximum bit rates. The mode performance is being closely monitored on a weekly basis using real-time housekeeping telemetry and radiometric data.
The Rosetta Plasma Consortium (RPC) was activated for five days on 4 July as the spacecraft crossed the tail of comet Honda. As this operation took place with the spacecraft in Near Sun Hibernation Mode, science and housekeeping telemetry were stored on-board and will be dumped at the next opportunity in August. In addition, SREM was kept active in the background for the entire period.

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Blobrana


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2867 Steins
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Title: First albedo determination of 2867 Steins, target of the Rosetta mission
Authors: S. Fornasier, I. Belskaya, M. Fulchignoni, M. A. Barucci, C. Barbieri

Researchers present the first albedo determination of 2867 Steins, the asteroid target o f the Rosetta space mission together with 21 Lutetia.
The data were obtained in polarimetric mode at the ESO-VLT telescope with the FORS1 instrument in the V and R filters. Observations were carried out from June to August 2005 covering the phase angle range from 10.3 deg. to 28.3 deg., allowing the determination of the asteroid albedo by the well known experimental relationship between the albedo and the slope of the polarimetric curve at the inversion angle. The measured polarisation values of Steins are small, confirming an E-type classification for this asteroid, as already suggested from its spectral properties.
The inversion angle of the polarisation curve in the V and R filters is respectively of 17.3 ±1.5deg. and 18.4±1.0 deg., and the corresponding slope parameter is of 0.037±0.003 %/deg and 0.032±0.003 %/deg.

Their polarimetric investigation shows that 2867 Steins is a high albedo asteroid (pv = 0.45±0.1) with an estimated diameter of approximately 4.6 km, assuming an absolute V magnitude of 13.18 mag. The high albedo, together with the peculiar polarimetric properties typical of E-type asteroids, lead to the conclusion that 2867 Steins is an E-type object, as already suggested on the basis of its spectral behaviour .
Rosetta will be the first space mission to fly by an E-type asteroid, and its results will be very important in the understanding the physical properties of this peculiar class.

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Blobrana


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Rosetta
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A major unexpected event from a solar flare on 8 and 9 September, which hit the Rosetta spacecraft, put the space craft onboard Star Tracker computer into safe mode, at the beginning of the weekly non-coverage period.

When the signal was acquired for the weekly contact on 15 September the spacecraft was found with the active Star Tracker crashed in INIT mode, and the second Star Tracker (not used for attitude control) in Standby mode.
The Attitude and Orbit Control System (AOCS) had determined the attitude over a period of 6 days using gyroscopes only, and accumulated therefore a drift of about 0.7 degrees, of which 0.3 degrees offset in the High Gain Antenna pointing direction, small enough to allow the RF signal to be received on ground.
The recovery activities took most of the ground station pass on 15 September. At the end both Star Trackers were back in Tracking mode and the nominal attitude reacquired.

Apart for this and routine monitoring activities and the upload of a software patch to the Star Tracker B (on 8 September), every thing is normal

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Blobrana


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ESA’s Rosetta comet-chaser spacecraft has acquired its first view of the Deep Impact target, Comet 9P/Tempel 1.

This first Rosetta image of the Deep Impact campaign was taken by its Navigation Camera (NAVCAM) between 08:45 and 09:15 CEST on 28 June 2005.
The image shows that the spacecraft now points towards Comet 9P/Tempel 1 in the correct orientation.
The NAVCAM is pointing purposely slightly off-target to give the best view to the science instrumentation.


The comet is the fuzzy object with the tail in the lower left of the image. The faintest stars visible in this image are about 13th magnitude, the bright star in the upper left is about 8th magnitude. The image covers about 0.5 degrees square, and celestial north is to the right.

The NAVCAM system on board Rosetta was activated for the first time on 25 July 2004. This system, comprising two separate independent camera units (for back-up), will help to navigate the spacecraft near the nucleus of Comet 67P/Churyumov-Gerasimenko in ten years time.
In the meantime though, the cameras can also be used to track other objects, such as Comet Tempel 1, and the two asteroids that Rosetta will be visiting during its long cruise, Steins and Lutetia.

The cameras perform both as star sensors and imaging cameras (but not with the same high resolution as some of its other instruments), and switch functions by means of a refocusing system in front of the first lens.

The magnitude of Comet Tempel 1 is at the detection limit of the camera: it is not as easily visible in the raw image and the image here is a composite of 20 exposures of 30 seconds each.




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