space probe, space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is placed in more or less permanent orbit around the earth, a space probe is launched with enough energy to escape the gravitational field of the earth and navigate among the planets. Radio-transmitted commands and on-board computers provide the means for midcourse corrections in the space probe's trajectory; some advanced craft have executed complex maneuvers on command from earth when many millions of miles away in space. Radio contact between the control station on earth and the space probe also provides a channel for transmitting data recorded by on-board instruments back to earth. Instruments carried by space probes include radiometers, magnetometers, and television cameras sensitive to infrared, visible, and ultraviolet light; there also may be special detectors for micrometeors, cosmic rays, gamma rays, and solar wind. A probe may be directed to orbit a planet, to soft-land instrument packages on a planetary surface, or to fly by as close as a few thousand miles from one or more planets. The particulars of trajectory and instrumentation of each space probe are tailored around the mission's scientific and technological objectives; the data provided by a single space probe may require months or even years of analysis. Much has been learned from probes about the origins, composition, and structure of various bodies in the solar system. Scientists trying to understand the earth's weather by constructing theoretical models of global weather systems make use of the knowledge that is gained concerning the atmospheres and meteorology of the planets. Because conditions on other planets are simpler than on earth, scientists can check each of their hypotheses separately in isolation from complicating factors.

The earliest space probes in the U.S. space program were the Mariner series, which investigated Mars, Venus, and Mercury, and the Pioneer series, which explored the outer planets. Pioneer 10 was the first human-made object to entirely escape the solar system. Several Viking space probes voyaged to Mars in the late 1970s, mapping the planet and searching for life. The Voyager probes, launched in 1977, returned spectacular photos and data from brushes by Jupiter, Saturn, Uranus, Neptune, and their moons. The Magellan spacecraft succeeded in orbiting Venus in 1990, returning a radar map of the planet's hidden surface. The Japanese probes Sakigake and Suisei and the European Space Agency's (ESA) probe Giotto both rendezvoused with Halley's comet in 1986, and Giotto also came within 125 mi (200 km) of the nucleus of the comet Grigg-Skjellerup in 1992. The U.S. probe Ulysses returned data about the poles of the sun in 1994, and the ESA Solar and Heliospheric Observatory (SOHO) was orbited in 1995. Launched in 1989, the Galileo spacecraft followed a circuitous route that returned data about Venus (1990), the moon (1992), and the asteroids 951 Gaspra (1991) and 243 Ida (1993) before it reached Jupiter in 1995 and sent a small probe into the Jovian atmosphere to study its composition. Over the next eight years it orbited Jupiter 35 times, returning data about the planet's atmosphere and also about Jupiter's largest moons, Io, Ganymede, Europa, and Callisto. The joint U.S.-ESA mission Cassini, launched in 1997, began exploring Saturn and some of its moons in 2004 and deployed the lander Huygens on the surface of Saturn's moom Titan. The Mars Pathfinder and Mars Global Surveyor, both of which arrived at the red planet in 1997, were highly successful, the former in analyzing the Martian surface and the latter in mapping it. Both the Mars Climate Orbiter and Mars Polar Lander, however, were lost upon their arrival at Mars in 1999, setting NASA's Mars exploration program back by at least two years. The NEAR (for Near Earth Asteroid Rendezvous)-Shoemaker probe returned data about the asteroid Mathilde as it flew by in 1997 and the asteroid Eros as it orbited it in 1999 and 2000 and then landed on its surface in 2001, returning unparalleled data about a minor planet. In 2003 the ESA's Mars Express achieved orbit around Mars, and although its Beagle 2 lander proved unsuccessful, the orbiter returned data on the planet. NASA's Spirit and Opportunity rovers landed on the planet shortly afterward in early 2004.

Rosetta is a space probe aiming to rendezvous with the comet 67P/Churyumov-Gerasimenko. This page records a detailed timeline of this mission.

Timeline

2004

February

• February 16 — Rosetta was placed on top of an Ariane 5 rocket at the Guiana Space Centre, Kourou. This put the mission on track for a timely launch.
• February 26 — Scheduled launch was stopped 20 minutes and 40 seconds before scheduled lift off and was delayed one day due to heavy winds in the upper atmosphere.
• February 27 — Before rescheduled launch, a piece of detached foam was discovered, which prompted a round of technical inspections (image of defect from ESA). Launch was rescheduled to very early March.

March

• March 2 — ESA's Rosetta mission is successfully launched at 07:17 GMT (08:17 Central European Time). The launcher successfully placed its upper stage and payload into an eccentric coast orbit (200 x 4000 km). About two hours later, at 09:14 GMT, the upper stage ignited its own engine to reach an escape velocity in order to leave the Earth’s gravity field and enter heliocentric orbit. The Rosetta probe was released 18 minutes later. ESA’s Operations Centre (ESOC) in Darmstadt, Germany, established contact with the probe shortly after that.
• March 3 — "S-Band" communication commenced with Rosetta on this day. Both low- and high-gain antenna configurations worked successfully. Also, for the first time, all reaction wheels were in operation. They are compensating for large disturbances due to outgassing from the space craft, which is expected to last for a few days in the vacuum of space.
• March 4 — The power subsystem of Rosetta was commissioned and performed as expected.
• March 5 — The "X-Band" communication was commissioned successfully for Rosetta.
• March 10 — The first three instruments (Cosima, Consert and Osiris) were activated and their initial commissioning activities successfully completed in the last three days. Also, the Consert antenna was deployed.
• March 11 — The Rosetta Science Working Team announces that the accuracy of the launch made it possible to select two asteroids as targets for a rendezvous fly-by of the probe. "Comets and asteroids are the building blocks of our Earth and the other planets in the Solar System. Rosetta will conduct the most thorough analysis so far of three of these objects," said Prof. David Southwood, Director of ESA’s Science Programme in a press release.
• March 17 — Over the last five days, starting on March 12, the commissioning of the lander was successfully completed. Only one step was rescheduled due to the early release of the launch locks during the first mission day.
• March 19 — The Rosetta Plasma Consortium (RPC) instruments were successfully commissioned during the previous two days. A redundant power supply seem to have failed during a repeat check of the RPC instruments. Further investigations are under way. The spacecraft booms carrying the RPC MIP (Mutual Impedance Probe) and LAP (Langmuir Probe) instruments were successfully deployed using the primary systems.
• March 26 — Three instruments successfully checked out during commissioning: ROSINA, ALICE, and VIRTIS. Each activity took two days and was well within or ahead of schedule. The High Gain Antenna (HGA) emission pattern was calibrated by performing spiral maneuvers. The gain was measured by the earth-side radio station at New Norcia.
• March 30 — The RSI (Radio Science Instrument) completed five days of commissioning.

April

• April 3 — After three passes of MIRO commissioning through more spiral maneuvers, scanning the planet Venus, this instrument checks out well.
• April 4 — The Rosetta spacecraft was pointed into its attitude towards Earth that is planned for the remainder of the year. Periodically, slight adjustments are planned to avoid to have sunlight hit Rosetta head-on. (Also called "+X" axis). The GIADA instrument was activated and commissioned.
• April 9 — The last instrument on board Rosetta (MIDAS) was turned on during April 4 and 5 days of commissioning concluded. At this point all science and engineering subsystems have been activated at least once.
• Use of the radio station at New Norcia was reduced from 11 hours to 7 hours, so that the Mars Express mission can use more communication time slots.

• April 15 — Five days of checkout procedures for the lander concluded successfully. This second lander activity was focussing on the lander's payload. The ALICE instrument was activated again and high voltage operations were executed. All other activities were performed as planned, including an adjustment of the internal heater system due to the decreasing distance to the Sun.
• April 17 — Rosetta commissioning hit a snag, today. A pyro did not fire, that was designed to allow the opening of the ALICE detector.
• April 21 — After some investigation, a backup pyro was successfully fired to release the ALICE detector door.
• April 25 — During a test sequence using an Earth pointing attitude, the thruster temperature (heated by the sun) caused an unplanned "slew" to occur. This mechanism is used to prevent the thrusters to overheat. Due to this maneuver, a planned imaging activity of the Earth-Moon system was cancelled, but all other commissioning activities were successfully completed.

May

• May 1 — The first scientific observations were performed at this date. The instruments were pointed towards comet currently close to the sun (discovered by LINEAR.)
• May 6 — In preparation for the first deep space maneuver of Rosetta a total of 12 pyro valves were fired, and the pressure in the reaction control system started to build up as expected.
• May 10 — The most critical deep space maneuver was successfully executed. The four thrusters on board of Rosetta were fired for about 3.5 hours, and a velocity change (delta v) of 152.8 metre per second was imparted to the spacecraft.
• May 16 — A planned "touch-up" deep space maneuver was successfully executed. A burn of just under 17 minutes was performed with high accuracy. Then Rosetta pointed its instruments again towards Comet LINEAR for observation.
• May 28 — ESA released the first pictures taken with the OSIRIS camera during the April 30 observation tests pointed at comet LINEAR. The camera produced high-resolution images of the comet from a distance of about 95 million kilometres.

June

• June 7 — Rosetta switched into "Cruise Mode" after completing all steps for commissioning the instruments.

July

• July 25 — A week of increased activities during the "Cruise 1" phase included the commissioning of the two navigation cameras by taking pictures of the Earth and the Moon.

2005

March

• March 4 — The first planned flyby of Earth was executed successfully. ESA asks amateur astronomers that took pictures of the spacecraft to submit them. Also, tests with the Moon as target standing in for a comet or asteroid, produced pictures and other data as expected.
• March 24 — Rosetta transitioned back into "cruise mode".

April

• April 15 — A test of the Near Sun Hibernation Mode (NSHM) was successfully concluded. It started on April 11 and tested a special low activity mode of Rosetta. In this state the gyroscopes and reaction wheels are inactive, and the craft is using the star tracker and the thrusters to control its attitude, only.

July

• July 18 — ESA reported that the observation of the Deep Impact encounter with comet Tempel 1 was very successful. Science data was recorded and down-linked to Earth during the period from June 28 until July 14, and the data is currently being analysed.

August

• August 8 — Mission members performed an unplanned monitor pass to investigate anomalies in the spacecraft's dynamic behavior. On mission day 213 and 216 a total of 20 grams of fuel were spent and a delta-v of 2.5 mm per second were added unexpectedly.

September

• September 15 — Telemetry received showed that a solar flare had hit the spacecraft around September 8 or 9. The star tracker subsytem was left in an abnormal state and needed to be fixed.

2006

March

• March 12 — The OSIRIS instrument was trained on the future flyby target asteroid Steins for science observation, and the data was downlinked to Earth over three days just before solar conjunction.

July

• July 6 — The spacecraft comes within 0.06 AU of the ion trail of comet 45P/Honda-Mrkos-Pajdusakova and scientific observations are planned for this event.

2007

February

• February 25 — The spacecraft approaches Mars up to 250 km.

November

• November 14 — Second Earth swing-by for Rosetta passing within 5295 km from the surface.

2008

September

• September 5 — Rosetta flies by asteroid 2867 Šteins at a distance of c. 800 km.

See also

• Rosetta mission
• Comet
• Unmanned spacecraft

References