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Mercury Probe Delayed by Ten Weeks, and Two Years
Gogo Dodo writes "Spaceflight Now reports that NASA's MESSENGER probe launch has been delayed by 10 weeks. Unfortunately, this means MESSENGER will not arrive at Mercury until 2011, a two year delay."
Mercury goes around the sun in 87 days. Assuming that the orbits are circles (they're pretty close) it should never be more than 86 days for the planet to be in an optimal position to launch a probe. So, why would it be off by two years? What am I missing here?
Uh, maybe an in depth knowledge of how the gravity of all the planets affects trajectories?
This may answer your question. Either that or just confuse you more. ;P
Because they're planning to swing around Venus to get there, and more than once.
The links already posted answer the question, but the short, simple answer is "angular momentum". Specifically, the need to dump a lot of it (and, equivelently, a lot of energy). The energy changed needed to get to Mercury is actually greater than that needed to reach Pluto. This means that it's better to use the inner planets (Earth, Venus, and/or Mercury) in gravitational slingshots (but backwards of how we usually use them) to save fuel. In theory, if you jacked up NASA's budget, you could go straight there once a synodic (not sideral: it doesn't matter how often Mercury orbits, but how long it takes to get back to the same relative arrange with Earth) period. But NASA, alas, has a finite budget for this sort of thing, so slow and cheap is the way to go.
And since I'm in a good mood...no, you're not a moron. :)
Goo goo g'joob.
You're correct. It needs to loose about 62% of its angular momentum, which is a pretty significant amount of energy. This is in addition to the amount of energy needed to reach earth's escape velocity in the first place and to insert into an orbit around Mercury.