Rosetta awakes from hibernation

The spacecraft prepares for an encounter with an asteroid.Provided by ESA, Noordwijk, Netherlands
By | Published: July 7, 2008 | Last updated on May 18, 2023
Rosetta goes into passive cruise mode on the way to the asteroid belt. It observes the asteroids from a distance of a few thousand kilometers. Data recorded on board is transmitted to Earth after the fly-by.
ESA/AOES Medialab
July 7, 2008
Spacecraft controllers have just awoken Rosetta from hibernation to prepare for its encounter with asteroid (2867) Steins on September 5. 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 traveling a total of about 6,500 million kilometers. 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 kilometers, the mean distance between Earth and the Sun).

Rosetta has swung by Earth twice and Mars once, performing gravity-assist maneuvers 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 traveled about 3,700 million kilometers and will be 2.1 AU from the Sun.

After its last planetary swing-by on November 13 last year, Rosetta headed towards the asteroid belt located between the orbits of Mars and Jupiter. On March 27 of this year, the spacecraft switched to its near-Sun hibernation mode for a period of 3 months. During this phase, a few subsystems were put into a dormant state to optimize their lifetime (as this is only the beginning of the mission’s science phase).

This is an artist’s rendition of Rosetta’s closest approach to Earth during its second swing-by of our planet on November 13, 2007. The image shows the fly-by configuration as seen from above.
ESA (Image by C. Carreau)
Rosetta will be closest to (2867) Steins at 1:12 P.M. CDT on September 5, at a distance of 800 kilometers. 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 August 4 and September 4, 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 neighborhood.

(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.

Rosetta’s 12-year expedition began in February 2004, with an Ariane-5 launch from Kourou in French Guiana. The 3 ton spacecraft was inserted into a parking orbit before being sent on its way towards the outer solar system.
ESA/AOES Medialab
The observations will be used to characterize 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 characterize 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 maneuver 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 March 24, 2008. The tests were successful, confirming the spacecraft’s robustness.