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Rosetta, the Comet Hunter
Roland Piquepaille writes: "After being delayed for about a year because of a failure of the Ariane-5 rocket, the Rosetta spacecraft is scheduled to be launched on February 26. Rosetta is a special spacecraft, including an orbiter and a lander. And it will take up to 2014 before landing on Comet 67P/Churyumov-Gerasimenko -- with the help of a harpoon. Then, as says the European Space Agency (ESA), Rosetta will help to solve planetary mysteries. This news release looks at the goals of Rosetta's mission and explains why it will take more than ten years to reach the comet. But here the 'funny' part of the story: the landing. 'In November 2014, the lander will be ejected from the spacecraft from a height which could be as low as one kilometre. Touchdown will be at walking speed, about one metre per second. Immediately after touchdown, the lander will fire a harpoon into the ground to avoid bouncing off the surface back into space, since the comet's extremely weak gravity alone would not hold onto the lander.' This overview contains more details and includes illustrations of the Rosetta's spacecraft and its landing on the comet."
Harpoon... check
Name I can't pronounce... check
10 years before getting some... check
I just have the class not to make a big deal out of it.
Is this truly the only Earth I can live on?
The timeline states that in 2014, Rosetta will orbit the comet for six months before it lands, mapping the comet to find a suitable landing spot. Then it goes on to say:
Immediately after touchdown, the lander will fire a harpoon into the ground to avoid bouncing off the surface back into space, since the comet's extremely weak gravity alone would not hold onto the lander..
My question is, if the comet's gravity is so weak, how is the Rosetta supposed to orbit this thing for six months?
The World is Yours.
...given that we probably know little about the surface of the comet.
Given that it could be porous (or even lots of shatterable ice), I hope that the harpoon has the force to bury itself deeply enough to actually anchor itself in something solid.
libertarianswag.com
I know that landing on Mars is a very tough thing, lots of variables to consider.
But this seems like it would be exponentially harder.
Ya know, landing on something that doesn't have gravity and they don't know what it's made of.
I'm curious. How big does an object have to be to have gravity that'll hold say, a person to it?
I'm thinking say, if I were standing on a rock the size of NYC out in space, would I just drift away from its surface without any noticeable gravity, or could it hold me there? How about something the size of a state like Oregon? or something only 2miles in diameter?
And it will take up to 2014 before landing on Comet 67P/Churyumov-Gerasimenko -- with the help of a harpoon.
What makes them think they'll be able to land an unmanned probe on a small rock in deep space that way when here on earth, countless bigger, manned ships have tried the same feat on whales for decades and failed?
They're just gonna kill that poor little comet. For nothing. Just like that. Somebody calls green-piss ferchrissake!
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
The French had a very reliable launch vehicle, the Arianne IV, which they decided to "upgrade" with the Arianne V. After failing on 4 of the first 13 missions, they introduced an upgraded version with an extended nozzle. The failure of that launch led to the (highly justified) delay of the Rosetta launch on a similar Arianne V because of the failure investigation. Turns out that the nozzle had a design flaw which led to the failure.
ESA did pretty well on their 1st trip to Mars, as the Mars Express is an unqualified success, but the Beagle II didn't work for whatever reason. All this is just to reiterate that space is hard, and there will be successes and failures. No one's at 100% (Russians have a worse track record on Mars than anyone, and NASA lost Contour--not a JPL mission-- last year due to an obvious design flaw).
Whenever a new technique is tried in space for the 1st time, the odds increase. That Pathfinder worked on its first attempt at a bouncy landing, and Sojourner roved Mars without a hitch speaks to the talent & luck of the JPL crew. Hopefully the Europeans will do as well with their harpoon, and hopefully they haven't made obvious mistakes like those made by NASA and the APL did in the Contour comet mission.
As mentioned, you have to be moving slower than the escape velocity to be in orbit around something. The formula is v = sqrt(2GM/r). G is 6.67x10^-11 m^3/s^2kg everywhere.
For Earth, M is 6x10^24 kg, and the highest relevent velocity as at the surface, so r = 6x10^6 m. That's 11.2 km/s. Very fast. Which is why it's hard just to get into orbit.
Now for the comet. If it's 4 km across, r = 2000 m. I can't find a value for the mass, but based on the common description of comets as dirty snowballs let's guess the density is about that of water, or 1000 kg/m^3. The volume of a sphere is 4/3 r^3 so our guess for M is 3.35x10^13 kg.
That makes the escape velocity for 67P/Churyumov-Gerasimenko at 1.5 m/s which pretty much the same brisk walking-speed which which the lander is expected to hit the comet, especially if our guess at the density is high. Thus, the lander could easily bounce off, and a person could with some effort jump off, fast enough that the comet's gravity wouldn't bring them back. On the other hand, an rocky asteroid (denser) the size of Manhattan (bigger) would probably be hard to get away from under your own power. This comet is right on the edge.
The so-called great voyages of discovery of the past were never undertaken for the sake of idle science all. Always there was that search for the elusive El Dorado or that secret shortcut to the spice capital of the world. While most voyages failed to recoup the wood and slave labor invested on them, enough returned with if not the silver and gold then things that would prove more valuable, like coffee, cannabis or the claims to a "New" World.
The pure science mission ("Is there life on Mars?") is a modern invention. While the altruism is admirable, the only way to justify to taxpayers the continued exploration of space is to turn these missions into hunts for precious metals and minerals. Follow not just the water (a valuable space resource in its own right) but also the platinum.