I find this image haunting. Philae, the mission lander, as photographed from mother-ship Rosetta after release and en route to the surface of comet.
Philae was simply dropped from Rosetta from a distance of 22.5 km from the surface; dropped at just the right time so it would hit a predetermined spot on comet CG 67P. And apparently the people at ESA did their job right because it did initially hit the right spot. It hit going about 1 metre per second (3.6 km/h; 2.2 mph). But it bounced a couple of times since the system to hold it to the comet surface failed. I wondered how Philae maintained its orientation after release and it did this by means of a kind of a flywheel arrangement sometimes referred to as a reaction-wheel. It’s just a spinning mass powered by a motor that keeps things like comet-landers and space telescopes and anything else in a low to no gravity environment oriented about its axis. I mean, if there’s no gravity, which way is up? Philae’s reaction wheel system weighed 6.4 lbs; but I couldn’t find anything else about it. It must have worked since Philae landed on its feet.
One of the instruments Philae had on board was a camera, ROLIS, and this is what comet CG 67P looked like as Philae was approaching:
Comet 67P/CG appears in an image taken by the ROLIS instrument on the Philae lander as it descended from Rosetta spacecraft on Nov. 12, 2014, from a distance of approximately 1.9 miles (3 km) from the surface.
So what was this little space craft lander thing doing out there in deep space; approaching what looks to me to be, shall we say, a tough neighborhood?
Philae was on a mission. That’s what. A mission to investigate what comets are made from exactly, to characterize the physical properties of the surface and subsurface material, and to explore the magnetic and plasma environment of the comet nucleus. What is the surface of a comet really like, and what goes on inside them.
To do this, Philae was armed with ten instrument packages:
APX Alpha: Alpha Particle X-ray Spectrometer
CIVA: Comet nucleus Infrared and Visible Analyser
CONSERT COmet Nucleus Sounding Experiment by Radiowave Transmission
COSAC: COmetary SAmpling and Composition
MUPUS: Multi-Purpose Sensors for Surface and Subsurface Science
PTOLEMY: gas chromatograph and medium resolution mass spectrometer
ROLIS: ROsetta Lander Imaging System
ROMAP: ROsetta lander MAgnetometer and Plasma monitor
SD2: Sample and Distribution Device
SESAME: Surface Electric Sounding and Acoustic Monitoring Experiment
For a complete description of Rosetta and Philae instruments: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Lander_Instruments
The descent took about seven hours and the target was the red square pictured below; but as I had mentioned, the harpoon anchors that were to attach Philae to the comet never fired and is bounced upon impact. “The first bounce (with a velocity of 0.38 m/s, compared to 1 m/s incoming) lasted two hours and may have been 1 km (0.62 mi) high, the second (at 0.03 m/s) lasted seven minutes. The initial bounce was the largest in history at 1 kilometer (0.62 mi), because of the very low gravity on the comet. Philae sits askew on all three legs, leaning on a rock in partial darkness as much as a kilometer from the first landing spot at an unknown location.” http://en.wikipedia.org/wiki/Philae
Gravity is so low on CG 67P that escape velocity is only about 1 mph (0.5 m/s)! Lucky Philae didn’t just bounce up and drift off into space!
Philae eventually landed somewhere inside the blue diamond – they think. Actually, no one is quite sure exactly where it is now. It is somewhere on the comet though, because it sent back this amazing photo:
As best as can be told, the final bounce found Philae in a spot mostly shaded from the sun rendering its solar panels useless. Oh for a nuclear battery as used on so many other missions!
Philae’s fate was sealed; with only 57 minutes of working time, the ESA ground crew ran as many scientific tests as they could before Philae ran out of battery power and went into hibernation mode. Evidently, most every instrument was used and results were communicated back to earth; so the mission is considered a success, even though an optimistic useful life for Philae was counted in months, not hours.
And maybe, just maybe as the comet approaches perihelion (closest approach to the sun) sometime in August, the solar panels will receive enough light to juice up the battery for a re-awakening – so no eulogy; yet.
Question for you readers: If comets are suppose to be made up of water and ice; so-called dirty snowballs; where’s the ice? I just see rocks. Where’s all the ice?