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Ratio of KE to binding energy mass ratio newton third law force Mass = 3 x 10^12 kg Density = 0. 1 -0. 4 !!!
Dust coma August 1
Past Missions to Comets (2) • Deep Impact – launched a 350 kg copper impactor into the nucleus of comet 9 P/Tempel 1, in July, 2005. – A 100 m x 25 m crater was created. • Visible and infrared spectrometers on the parent craft looked for the composition of the nucleus. – 250, 000 kg of water vapor were detected. 44
Current Missions to Comets • Stardust – sampled the coma of P Wild 2 from a distance of 236 km above the nucleus. • Returned comet particles back to the earth for microscopic examination and chemical testing. You can help with the microscopic work by signing up at the following website. http: //stardust. jpl. nasa. gov/home/index. html 48
Cometary Orbits & Comet Reservoirs • Members of the solar system in very eccentric orbits - Oort Cloud comet - long-periodic comet - short-periodic comet no interstellar comet • Comet reservoirs - Oort Cloud - Kuiper Belt (+Centaurs) with “graveyards” for - Jupiter family comets - dormant comets - main belt comets ?
Comets & Earth Ocean Water • • Earth after formation: hot, hence no water on Earth Clean-up of formation disk produced bombardment (most likely in 2 phases) import of water on terrestrial surface Problem: D/H ratio of ocean water differs from (barely known) D/H ratio of comets way-around: mixing of 2 or more sources with different D/H ratio, cometary source would have contributed about 30% early bombardment late bombardment (comets? )
Organics in Comets • Comets contain organic compounds both in volatile ices (simple organics) and solid dust (CHON, most likely more complex organics) long-term storage facility • CI chondrite meteorites are most likely related to comets 2 CI chondrites had amino acids with preference for left-handed enantiomer contribution to life formation on Earth (if cometary material can reach Earth surface reasonably intact)
The Latest Coup: Deep Impact Live Impact & Cratering Experiment • NASA mission to 9 P/Tempel 1 - impact: 4 July 2005, 05: 52 UT - impactor: 360 kg – speed: 10 km/s – vis. camera – fly-by S/C: vis. cameras & IR spectrometer – impact site visibility: 14 min
Deep Impact: Learning by Doing • impact: shot in the blind • shape of ejecta cloud indicates low strength dominated impact regime • DI impact crater not found cratering science suffers (now to be imaged by STARDUST in 2011) • surface: many natural craters occurence frequency consistent with expected cratering rate of inactive body but impact craters should not survive cometary activity for very long (erosion rate ~ 1 m/rev)
DI: The Expected & the Unexpected • low bulk density 0. 6 g/cm 3 Kuiper Belt objects are heavier (Pluto: 2 g/cm 3) • low thermal conductivity (100 W/K/m 2/s 1/2) very porous material • comet: very weak (~300 Pa) (weaker than powder snow) loosely bound, signature of soft aggregation process during formation, unclear whether planetesimal or impact formation 1 km
The ROSETTA S/C • ROSETTA Orbiter (ESA) Dimensions: Weight: 2. 8 x 2. 1 x 2. 0 m 3000 kg 1600 kg fuel 165 kg experiments Instrumente: 11 - close sensing (~ telescopes) - in-situ experiments (~ lab) • PHILAE Lander (DLR/CNES/ASI) Dimensions: Weight: 0. 7 x 0. 9 m 100 kg 15 kg experiments Instruments: 10 (telescope & lab & samples)
The Flight Schedule Duration: ~ 10 years 4 x planet swing-bys (Earth, Mars) Cruise science: 2 x asteroids Earth/Mars fly-bys Science at comet: > 1 ½ years in orbit lander delivery 1 Launch Earth 02. 03. 2004 2 Swing-by 1/Earth 04. 03. 2005 3 Swing-by 2/Mars 25. 02. 2007 4 Swing-by 3/Earth 13. 11. 2007 5 Fly-by Steins 05. 09. 2008 6 Swing-by 4/Earth 13. 11. 2009 7 Fly-by Lutetia 10. 07. 2010 8 Rendez-vous comet 22. 05. 2014 9 Landing on comet 10. 11. 2014
OSIRIS - The ROSETTA Eyes © OSIRIS team (close sensing) 2 cameras (wide & narrow angle + stereo) for vis. + UV wavelength region Science: nucleus mapping geology, activity (backbone inst. ) Orion nebula © DLR © NASA Resolution: 1 cm/pixel 100 x better than any existing comet image Komet Wild 2 mit STARDUST Farbe 100 x 1 x
ROSINA – COSIMA The Comet Chemistry Labs ROSETTA (in-situ) Science goal: original gas and dust chemistry cometary organics Isotope ratio in comets (ocean water from comets? ) Instrument type: mass spectrometers (lab exp. ) GIOTTO
Philae Lander Touchdown Dynamics Revisited L. Witte, S. Schröder, R. Roll, S. Ulamec, J. Biele, J. Block, T. van – Tests For The Upcoming Landing Zoest Preparations – 10 th International Planetary Probe Workshop, San Jose State University, June 2013
www. DLR. de • Chart 17 10 th International Planetary Probe Workshop, San Jose State University, June 2013 Understanding Philae‘s Landing Gear (1/2) The landing gear consists of a foldable tripod and a central damping mechanism. Its damping behavior can be simplified as linear velocity dependent damping force. •
www. DLR. de • Chart 18 10 th International Planetary Probe Workshop, San Jose State University, June 2013 Understanding Philae‘s Landing Gear (2/2) A cardanic joint between the tripod and the central damper unit allows the This range was reduced to +/-3° by LG to adapt to the installation of the tilt limiter (late design change). local terrain (+/-30°). Further elements (not shown): • 2 anchoring harpoons, • Active Descend System (ADS)
www. DLR. de • Chart 19 10 th International Planetary Probe Workshop, San Jose State University, June 2013 Test Results: A Fully Asymmetric T/D Condition Example: Spec_2 a , Vv=0. 8 m/s, Vh=0. 2 m/s, Robot han d position r/p/y=17/0/90°, surface: wood IRU Cardan angle data da ta
1 px = 1. 1 meters
2. 4 m per pixel
• • The computer processing power is about the same as that of a 1990 s hand calculator, however, the chips used were radiation hardened to survive space conditions. Philae’s systems will be watching and making navigation corrections throughout the descent. Nothing fancy, this is a simple and straightforward execution with a modest control system on board. Nevertheless, it has everything necessary to accomplish the soft landing on a comet. When studying the design, I first imagined that Philae would make a long descent and the comet would make a full rotation. But rather, Rosetta will be navigated to somewhere between 2 to 10 km above the comet surface then release Philae. Because of the comet’s odd shape, the probes could be 4 km above the surface at one time and then just 2 km at another, due to the rotation of the comet. The odd rotating shape means that the gravity field effecting the descent will be constantly changing. One might compare the effects of 67 P’s gravity on Philae as similar to the motion of a well thrown knuckleball (e. g. , Wakefield, Wilhelm). Catchers resort to using a larger catchers mitt and likewise, the landing zone (or ellipse) is 1 square kilometer, sizable considering 67 P’s dimensions are 3. 5 × 4 km (2. 2 × 2. 5 miles).
ilae towards the comet, 2) Descent: the comet is rotating and its gravity is weirdly pulling on
• 3) Touchdown is when the CDMS will earn its badge of honor. Upon touchdown, the control system will fire the cold thrusters to push Philae snugly onto the surface. At the same time, the two harpoons will be fired to, hopefully, pierce and latch onto the cometary surface. To further prevent bounce or tipping, the dampener will absorb energy of the touchdown. Philae is likely to have some transverse velocity on touchdown and this will translate into a torque and a tipping action which the Harpoons and cold thrusters will reckon with.