NASA Spacecraft Set to Shine Spotlight on Mercury

coondoggie writes to tell us Network World is reporting that NASA will this month see the realization of a mission launched in 2004, sent to explore the planet Mercury. "MESSENGER, launched in 2004, is the first NASA mission sent to orbit Mercury, the planet closest to the sun. But on Jan. 14 it will pass close by the planet and use Mercury's gravity for a critical assist needed to keep the spacecraft on track for its ultimate orbit around the planet three years from now. Still, the spacecraft is also expected to throw back some never-before -seen images, NASA said. The flyby also will gather essential data for planning the overall mission. After flybys of Earth, Venus, and Mercury, it will start a year-long orbital study of Mercury in March 2011, NASA said. "

Comments

Why so long . . .

[StefanJ]

It's hinted at in the story, but the reason the probe is taking its sweet time to actually achieve an orbit is Mercury's high orbital velocity.

It's pretty easy to get into an elliptical orbit which stretches from Earth's orbit around the Sun to Mercury's orbit around the sun. But getting into a circular orbit means matching Mercury's velocity, and doing so in a way that lets a "burn" be made to actually enter into an orbit around the planet. As I recall, you need a total velocity change of 40 kps to get into orbit around Mercury. That more than twice the change required to get into an orbit around Mars.

It's pretty impressive that NASA figured out a way to do this with a gravity assist. A proposed European probe would have used an ion rocket to make the velocity change.

Re:Why so long . . .

[Deadstick]

It's hinted at in the story, but the reason the probe is taking its sweet time to actually achieve an orbit is Mercury's high orbital velocity.

Well, actually, Mercury's low orbital velocity. It's more than Earth's, but when that elliptical transfer orbit reaches Mercury's orbit, the spacecraft is purely hauling ass. It actually takes a negative delta-V to match velocities.

To reach a superior planet (one outside your own orbit) you initiate the transfer orbit with a positive delta-V, then circularize it with another positive delta-V when you get there. For an inferior planet (inside your orbit), substitute "negative" for "positive" in both places.

rj

Re:Why so long . . .

[evanbd]

Well, delta-v is usually treated as a positive scalar value in orbital mechanics. The propellant needed to change your velocity by (say) 3 km/s is independent of whether you're speeding up, slowing down, or changing direction. So, while velocity is a vector quantity with direction and magnitude, delta-v is usually treated as a simple positive-valued scalar. (At least when the impulse comes from a high-thrust rocket engine; for very low thrust things like ion engines, or weird things like solar sails, the problem changes somewhat.)

Re:Why so long . . .

[Anonymous Coward]

I freaking LOVE slashdot comments like this. I'm a goddamn nerd and the only time I hear about orbital mechanics is here. At work it's a never ending stream of fart jokes and stories about people defecating, and shitting, and crapping their pants, and drinking and crapping their pants, or drinking and crapping on the shower curtains, or eating and crapping on tables. I kid you not.

Re:Why so long . . .

[mcmonkey]

I freaking LOVE slashdot comments like this. I'm a goddamn nerd and the only time I hear about orbital mechanics is here. At work it's a never ending stream of fart jokes and stories about people defecating, and shitting, and crapping their pants, and drinking and crapping their pants, or drinking and crapping on the shower curtains, or eating and crapping on tables. I kid you not.

And as a NASA employee, can you give us an insider's take on the mission?

Of course they've never been seen.

[techno-vampire]

"Still, the spacecraft is also expected to throw back some never-before -seen images, NASA said."

Am I the only Slashdotter who looked at this and thought, "Of course they've never been seen, they haven't even been taken yet." Yes, yes, I know what they meant, but couldn't they have said what they meant instead of something dramatic but wrong?

OK, folks, see if you can manage to mod me down with a -1 Pedant, now.

Bright light! Bright light!

[PhxBlue]

NASA Spacecraft Set to Shine Spotlight on Mercury

I can't imagine they'd need any more light on Mercury, what with the sun just 36 million miles off and all.

Nice alliteration, btw.

Oblig Hedberg

[Adambomb]

Here's a picture of me when I was younger......

ALL PICTURES OF YOU ARE OF YOU WHEN YOU WERE YOUNGER.

Heres a picture of me when i'm older....

You son of a bitch, where did you get that camera?

Ah, how i wish Mitch was still rambling.

Not the first mission to Mercury

[cusco]

This isn't the first mission to Mercury, just the first mission to ORBIT the planet. Mariner 10 swung by the planet several times.

"http://www.jpl.nasa.gov/missions/past/mariner10.html"

It was also the first mission to use a gravity assist. At the time of launch the rotation period of Mercury was unknown. By an amazing coincidence, every pass of the spacecraft photographed the SAME FACE of the planet, as its rotation period matched exactly the interval of Mariner 10's return.

Re:Refrence for Mecury day

[Technician]

Mercuries rotation is synchronized with its' orbit in such a fashion that the same portion always faces towards/away from the sun.

http://www.enchantedlearning.com/subjects/astronomy/planets/mercury/

"Until 1962 it was thought that Mercury's "day" was the same length as its "year" so as to keep that same face to the Sun much as the Moon does to the Earth. But this was shown to be false in 1965 by doppler radar observations. It is now known that Mercury rotates three times in two of its years. Mercury is the only body in the solar system known to have an orbital/rotational resonance with a ratio other than 1:1 (though many have no resonances at all)."