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Originally Posted by geolindon
i totally concur.....amazing exploration and science, plus? as far as i can discern a significant leap forward in man's ability to travel. i am having some difficulty finding out the maximum velocity the craft achieved or will achieve e.g. to calculate the hypothetical travel time to Proxima Centuri.
comet 67P G-C is travelling at as much as 135,000 km/h (from ESA www) = 375 km/sec = approximately 0.125% of speed of light, and Rosetta space craft is now orbiting it. As Rosetta approached 67P it did a series of burns to slow down to the comet's speed.
other space craft such as New Horizons, Voyager 1 and 2 seemed to all travel at about 16 km/sec and i was starting to wonder what was special about that speed?
is it correct to deduce there has just been a 20+ fold increase in our effective travel velocity/speed?
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Rosetta is not orbiting the comet, it's orbiting the Sun in an almost identical orbit as the comet, though it will enter orbit around the comet in a few months. The comet will reach it's maximum speed of 135,000 km/h at perihelion and so will Rosetta. Both the comet and spacecraft are travelling much slower than that now.
135,000 km/h is faster than the maximum speed of the Voyagers (Voyager 1 max speed was 62,136 km/h but it's comparing apples with oranges. The Voyagers are technically not in orbit around the Sun, having exceeded escape velocity.
If the Voyagers were moving a bit slower, so that they were still orbiting the Sun, and if they had a similar perihelion to Rosetta then they would be travelling significantly faster than Rosetta when they reached perihelion.
Likewise to raise Rosetta's speed at perihelion to escape velocity would require adding many km/s to it's velocity.
So while Rosetta will achieve a faster top speed, relative to the Sun, the Voyagers/Pioneers/New Horizon have more orbital energy.
This spaceflight is amazing and full of "firsts" but it really relies on tried-and-tested propulsion technology and gravitational assists.
P.S. I think 135,000 km/h is 37.5 km/s which I get as 0.000125 %c, however maths was never my strong suit
