A Tribute to the Philae Lander Science does not always come out as expected. Twenty five years ago engineers/scientists/technicians at the European Space Agency (ESA) began planning for the mission to fly to a comet, insert into an orbit, and launch a lander towards its surface that ultimately became the Rosetta/Philae Comet Mission. Comet 67P/Churyumov-Gerasimenko (67P/C-G) was discovered by Ukranian astronomers Klim Ivanovich Churyumov and Svetlana Ivanovna Gerasimenko on September 20, 1969 on photographic plates obtained at the Alma-Ata Astrophysical Institute using a 20-inch (50-cm) Schmidt camera. Comet 67P/C-G has an orbital period of 6.44 years, rotation period of 12.4 hours, and its closest approach to the Sun (perihelion) is 1.2432 AU (115,587,321 miles (185,980,000 km) and furthest distance form the Sun (aphelion) at 5.6829 AU (520,371,639 miles (850,150,000 km). Comet 67P/C-G will reach perihelion on August 13, 2015 (it may reach an apparent magnitude of 11 at that time requiring the use of a telescope). The Rosetta Orbiter/Philae Lander was launched on March 2, 2004 on an Ariane 5 rocket and after three Earth flybys (March 4, 2005/November 13, 2007/November 12, 2009), a Mars flyby (February 25, 2007 (distance form the surface of Mars at 160 miles (250 km). Rosetta also flew by asteroids 2867 Steins on September 5, 2007 (500 miles (800 km) and 21 Lutetia on July 10, 2010 (1,965 miles (3,162 km). The spacecraft finally arrived to its destination (67P/C-G) on August 6, 2014. The Rosetta Orbiter has obtained impressive images of the bi-lobed nucleus. The Philae lander is named for the Philae Obelisk discovered on Philae (an island on Lake Nasser, Egypt) in 1815. The tablet was later translated by the English Explorer/Egyptologist William John Bankes (1786-1855) as it contained Egyptian Hieroglyphics and Ancient Greek. The lander contains ten instruments contributed by ten countries that will study the nucleus in detail (including 3 spectrometers, 1 radar instrument, a Magnetometer and Plasma Monitor, a Sounding and Acoustic Monitor, and 1 Drill). The European Space Agency (ESA) announced the landing site (initially labeled Site J) on September 15, 2014 and named it Agilkia (after an island located upon the Nile containing the Ancient Egyptian temple complex of Philae at the present). After a series of Go/NoGO checks performed on November 11-12, 2014 it was decided to deploy the Philae lander even thought the cold-gas thruster (to provide downward thrust in order to keep the lander upon the surface of the comet) was not working correctly. The lander was deployed on November 12, 2014 at 08:35 UTC along a ballistic trajectory 14 miles (22.5 km) below the Rosetta orbiter. and was supposed to land upon the surface seven hours later at 15:35 UTC. The Philae lander was supposed to touch down upon the surface of the comet at 1 meter per second (2.2 mph or 3.6 km/h). The lander legs were designed to dampen the initial impact to avoid bouncing along with ice screws and two (2 ) harpoons (firing at 70 meters/second (160 mph or 250 km/h) that were supposed to fix the lander to the surface of the comet. The cold-gas thruster on top of the lander was supposed to fire and lessen the bounce upon impact and reduce the recoil from the harpoon firing. The lander initially touched down at 15:33 UTC at the original landing site (Site# 1), but due to the failure of the harpoons and cold-gas thruster the lander bounced upwards into space up to 1 kilometer (1.6 miles) and fell back down again for a second landing (Site# 2) at 17:26 UTC then bouncing a smaller amount for seven minutes. The Philae lander finally touched down permanently at 17:33 UTC adjacent to a cliff wall and at a tilt up to 1 kilometer (1.6 miles) from the original landing site. The lander appeared to be within the shadow of the cliff and only one panel was partially receiving sunlight to power the lander. The landers batteries (primary and secondary) had a maximum of 64 hours. The limited sunlight at the landing site of 1.5 hours (during a 12-hour comet day) was insufficient to maintain Philaes scientific activities. Fortunately 80% of the initial science observations, MUPUS (MUlti Purpose Composition) soil penetrator and SD2 drill data were able to be uploaded before the batteries died at 00:36 UTC on November 15, 2014 just before the Rosetta orbiter orbited below the horizon. It is theoretically possible in the following months that the landers computer may be rebooted if sufficient sunlight powers the various lander systems. I have produced a digital painting of the Philae lander adjacent to a cliff upon the surface of Comet 67P/Churyumov-Gerasimenko and mostly positioned within the cliffs shadow. A jet is visible towards the far horizon. I congratulate all of the talented engineers, scientists, and technicians that have created and supported the Rosetta/Philae mission since its inception to the present time. A job well done!
Posted on: Sat, 15 Nov 2014 05:56:11 +0000
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