Messenger Spacecraft Prepared for Mercury

An anonymous reader writes "NASA's first orbiter to the planet Mercury is shown today in cut-away, revealing the parasol design that will protect it from intense heat. Twenty layers of aluminized Kapton will be its sunshade. Curiously since the innermost planet is so close to the Sun, the Mercury mission itself will look for (cometary) water-ice preserved on the less baked north pole."

Comments

Ice?

[seanmcelroy]

Being the closest planet to the Sun you would expect Mercury to be the hottest but this is not true. Mercurys maximum temperature falls 50C short of that of Venus. The reason for this is that Mercury has very little atmosphere so there is no 'greenhouse' effect on the environment. The 430C daytime temperature is dictated purely by the Suns radiation. The Mercurian day is 176 terrestrial days long, the night is 88 terrestrial days long with a minimum temperature of -180C.

Re:Is that even possible?

[Anonymous Coward]

Here's the key concepts: Stefan's Law states that the net power of radiated heat absorbed is proportional to the surface area, the emmissivity (black = 1, white = 0), and the temperature difference to the fourth power (T_you ^ 4 - T_them ^ 4). Since them is the Sun in one case, you aren't going to win so you put up the Parasol to block off the Sun. In the second case, them is just space, so all you have to do is adjust your emmissivity to have the power created by your electronic components equal the power radiated into space.

Re:Is that even possible?

[Detritus]

There are three modes of heat transfer:

• Conduction
• Convection
• Radiation

Conduction and convection are not going to work in a vacuum, but radiation works just fine. This is electromagnetic radiation, like light and radio waves, so it does not need a medium.

Re:Ion drive

[physicsnerd]

Sorry, I keep seeing this misconception about Ion engines and it's bugging me. Ion drives do not have exit velocities anywhere near the speed of light. The absolute best Ion engines on the drawing board have a maximum Isp below 10,000s. The conversion between exit velocity and Isp is simple Ve=Isp*g so the best engines even on the drawing board have exit velocities no greater then 100,000 m/s while the speed of light is roughly 30,000,000 m/s. Production engines like the one on Deep Space One have Isps closer to 3,000s.

For comparison purposes the best Isp from a chemical rocket system in use is pretty much Lox/H2 which gives you an Ispvac in the 460s range.

More info here: http://nmp.jpl.nasa.gov/ds1/tech/ionpropfaq.html

And yes, I am a rocket scientist.