Welcome on Steins blog
By gaudonp | September 5, 2008
This blog is dedicated to a major step of Rosetta mission: its first scientific objective, the asteroid Steins. The nearest distance of the fly-by took place on Friday September 5, at 18h 38′ 16” Universal Time, meaning 20h 38′ 16” Paris local time. The minimal distance will be deduced from data received, but will be of the order of 800 km foreseen.
It outlines the major science activities planned during the fly-by:
- views of the asteroid surface executed by cameras of the Osiris instrument. They will allow to reconstruct the asteroid shape in 3 dimensions. Details of roughly 15m will be visible on the most resolved images, thanks to the Narrow Array Camera developed by LAM (Laboratoire d’Astrophysique de Marseille). Also these images will allow to look for Steins satellites, that is possibly small asteroids orbiting around Steins. Indeed a lot of asteroids of the main belt own 1 if not 2 smaller bodies orbiting around them,
- the Virtis spectroimager, whose the high resolution part was developed by LESIA (Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique) will allow to sharply analyse the surface composition and then characterise precisely the E-type asteroid Steins belongs to,
- other scientific instruments were switched on: Rosina to try to detect gases coming from the asteroid, Cosima and Giada to try to quantify dust coming from the asteroid, RPC to measure the asteroid influence on the solar wind. Finally Alice and Miro were switched on to observe Steins in the respectively UV and Microwaves wavelengths.
On the lander Philae currently fastened to the orbiter, 2 scientific instruments also were activated: Romap to measure the magnetic field, Sesame to count the dust impacts. Their data will be cross-analysed with data got by the orbiter.
All Rosetta orbiter instruments are located on the same face, face that is permanently and automatically directed to the asteroid center during the whole close fly-by. This implies that Rosetta has to rotate around its gravity center along its straight trajectory. Indeed Steins is too small, too light to interact on the probe trajectory. This fly-by orbiter attitude leads to interuptions in the data transmission towards the Earth because of the main antenna de-pointing. Thus during the close fly-by (nearly 1h 30) data are stored on board and sent later when Earth is back in the field of the antenna.
Here are Steins asteroid simulations as it should be observed by ROSETTA thanks to its high resolution camera OSIRIS/NAC These simulations were performed under the responsibility of the Laboratoire d’Astrophysique de Marseille (LAM-OAMP, CNRS, Université de Provence). A fractal terrain model as well as craters have been arbitrarily added to make the left image more realistic.
These two images are a digital re-construction of the three-dimensions shape of Steins determined after several observation campaigns. They took place between 2004 and 2007 with different means:Â Osiris imaging system on Rosetta, Spitzer satellite of NASA and numerous telescopes on Earth. These observation campaigns have notably enabled to estimate the diameter (about 5 km) and the aproximate spherical shape of Steins as well as its rotation period (6,05 hours). These observations also revealed that Steins reflects very highly light (albedo = 0.4) which is very rare for an asteroid and that we have to rank Steins in the E-type asteroide category.
Rosetta is one of the most ambitious mission of the European Space Agency (ESA). Its main objective is to study Churtumov-Gerasimenko comet that the probe will reach in August 2014.
The Centre National d’Etudes Spatiales (CNES, French space agency) is involved in The Rosetta mission at different responsibility levels: financing the ESA mandatory program in which the French industry intervenes to build the orbiter, national financing of French participations in the scientific instruments (of orbiter and lander), but also developing a ground segment to ensure the Philae mission. Besides this, CNES provided a technical expertise to the INSU laboratories when necessary. Finally they developed 2 critical Philae sub-systems: communication antennas to allow data transfers between orbiter and lander, primary and secondary batteries that will allow Philae an autonomous functioning once released by the orbiter.
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