For Rosetta, a comet up close

By Bonnie Berkowitz; Patterson Clark and Richard Johnson, Published: Nov. 11, 2014

Even before the Philae landing probe approaches the surface of Comet 67P/Churyumov-Gerasimenko today, scientists know the space rock is not what they imagined when the mission launched in 2004. Data collected by the Rosetta orbiter shows that the comet is warmer and shaped differently than expected, and the surface is porous and uneven rather than smooth. That increases the difficulty for today’s first-ever attempt to land a craft on a comet.

 gathering speed by slingshotting past Earth three times and Mars once.Propelled by its final pass by Earth, Rosetta began a five-year loop to align itself with the orbit of the comet, setting the stage for a rendevous this past August and a landing Wednesday.Rosetta’s journeyA tricky landing2.4 miles1.5 miles3.1 milesThe primary landing sitefor Rosetta’s lander Philaewas chosen from fiveoptions in September.ThrusterpushesPhilaedown.Ice screws oneach foot drillinto the cometsurface.Landinggear willabsorbthe impact.Harpoonswill lock Philaeto the surface.PRIMARY LANDING SITETHE SCALE OF THE COMETSideviewSideviewImperial Star DestroyerSmallendviewIf all goes well at the moment of touchdown on the comet (11 a.m. Wednesday), the landing gear will absorb the forces of landing, then ice screws in each of the probe’s feet and a harpoon system will lock Philae to the surface. At the same time a thruster on top of the lander will push down to counteract the impulse of the harpoon.2004, March 2Launch2005, March 4First Earth flyby2007, Nov. 13Second Earth flyby2009, Nov. 13Third Earth flyby2014, Nov. 12Scheduled landing on 67P/C-G2007, Feb. 24Mars flybySunSun2011, June 8 Placed in hibernation for 31 months2014, Aug. 6 Arrival at comet67P/C-G4:03 a.m. Wednesday Philae lander separatesfrom the Rosetta orbiter.

SOURCE: European Space Agency.