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

No, no, no...didn't they read the book?

[Sunburnt]

They'll have to land and go inside the caves if they want to find the harmoniums.

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 . . .

[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.)

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[mr_mischief]

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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)."

Re:Orbital Mechanics FTW

[Nyeerrmm]

Probably doing some rough calculations with spheres of influence, and then putting those rough trajectories into an optimization scheme, probably with a non-linear programming problems. Do this same method with a number of different schemes (direct Hohman transfer, Venus flyby, out to Mars and back) and see what gets you to Mercury orbit with as little fuel required and with minimal risk of accidentally smashing your spacecraft.

While its impossible to calculate these trajectories exactly by hand, its easy enough for a computer to do so, and if you can give a rough starting place, optimization techniques will find solution. Trade studies are done to find the best method overall, as in any other engineering practice.

Hope that helps some... it sounds like a fun problem to work out.

Trail blazed by Mariner 10

[Lincolnshire Poacher]

> is the first NASA mission sent to orbit Mercury

Well it may be the first to technically orbit Mercury, but
Mariner 10 used a Solar orbit to swing-past Mercury three
times.

http://nssdc.gsfc.nasa.gov/nmc/masterCatalog.do?sc=1973-085A

It was also the first probe to use plentary gravity assistance,
in this case Venus, to change course. La plus ca change...

Imagery here:

http://nssdc.gsfc.nasa.gov/imgcat/html/mission_page/MC_Mariner_10_page1.html

Re:Of course they've never been seen.

[Peter Lake]

Well, their dramatic wording is very correct - only about 45% of Mercury's surface has been imaged in detail. This was done 33 years ago by Mariner 10. So over half of the map of Mercury is still blank. It's the biggest unimaged planetary area in our solar system! Next week Messenger will image some of these never-before -seen/imaged areas of the planet (about 30% of it IIRC).

Here's a current map of Mercury.

There has been some interesting Earth-based radar observations using Arecibo's radio telescope. These observations give us an idea what to expect to see in the blank areas. Here's a map combined with radar observations. There are also various recent Earth-based optical observations using lucky-imaging techniques, but the images lack detail for accurate mapping.

So to be pedantic the Messenger will take detailed never-before-seen images of never-before-imaged-in-detail and never-before-imaged-at-all -areas of Mercury. In few weeks we'll get a new map of Mercury!