First Probe To Orbit Mercury May Help Us Learn How Planets Form 88
An anonymous reader writes "Next month, the first space probe in nearly 40 years will approach the planet Mercury, with an array of instruments that could help answer fundamental questions about how planets form. The mission is called MESSENGER, for Mercury Surface, Space ENvironment, GEochemistry and Ranging. On March 17 it will pull into orbit around mercury, after more than six years of maneuvering between the Earth, Venus and Mercury itself."
shoutout to NASA! (Score:4, Informative)
http://www.nasa.gov/mission_pages/messenger/main/index.html [nasa.gov]
Re:Why six years? (Score:5, Informative)
A lot of gravity assist maneuvers. It is (energy wise) very difficult to get to put a probe in mercury's orbit, first you have to do a lot of braking to put it into an elliptical orbit to reach mercury's orbit then another lot of braking to make it match mercury's orbit then more braking to put it into (some sort) of elliptical orbit AROUND mercury then (optional) more braking to "circularize" your orbit around mercury!
I think energetically speaking it's about as difficult to send a probe to Mercury as it is to Jupiter even though Jupiter is much farther away. So in order to not have to use a huge (expensive booster), the probe does a bunch of gravity assists by sling-shotting near Venus, Mercury and maybe even the earth. This saves a LOT of fuel but adds a LOT of time (otherwise as you probably guessed it would've gotten there years earlier).
Re:Movie "Sunshine" (Score:5, Informative)
Just a note. Oxygen transport in your body isn't based on the oxygen being dissolved in your blood. It combines chemically with the hemoglobin. So, suddenly exposed to a vacuum, you still might have some gases come out of solution in your body, so maybe the bends, and your body would swell a bit quite possibly accompanied with some discomfort. I'm not sure what would happen with sinuses and eardrums and so forth. Also, if your lungs were full, you probably wouldn't be able to contain the pressure. I'm pretty sure it wouldn't be able to blow out your chest or anything, but there could be internal rupturing, or maybe the air would just force itself out of your mouth and nose. In any case, if you had enough oxygen in your blood to stay conscious for two minutes, then it looks like you'd stay conscious for two minutes regardless of the pressure (as long as you don't pass out from the pain of your ear drums bursting, etc.)
Hmmm. Before posting, something just occurred to me about how good a pressure vessel your lungs might actually be. I looked up the PSI trumpet players manage, because I've heard about how professionals manage to rupture their lungs sometimes and end up with air directly entering their body cavities. I found this [abel.hive.no] which says that student trumpet players were able to manage 35-50 PSI and professionals between 75-95 PSI. The question there is how much of that pressure is actually found in the lungs and how much is produced by clever use of the lungs as a lower pressure air supply, producing the pressure mostly in the mouth and feeding it with careful work? I'm not sure, but it makes it seem that it's quite possible that a healthy adult may very well be able to hold air at around 14.5 PSI without even being forced to breath out. For that matter, if they're in space in the first place, they probably weren't even breathing air at 1 atmosphere to begin with. The US space program uses a mostly oxygen atmosphere at only about 5 PSI.
So, it looks like you wouldn't want to just take a stroll out into the hard vacuum of space on a regular basis, but it looks like it's actually pretty survivable in most of our solar system.
Re:Why six years? (Score:4, Informative)
An object orbiting the sun could point the sail 45 degrees away from the sun so that sun light is reflected ahead in the orbit. That way pressure from sun light would slow the object down and move it into a lower orbit. Mercury is very difficult to reach because you need to dump a lot of kinetic and potential energy to match orbits with the planet. In other words you have to go a long way down the sun's gravitational well.