Messenger En Route To Mercury

Soft writes "NASA's Messenger space probe has lifted off on its second try on a Delta 2-Heavy rocket. As mentioned earlier on Slashdot, it is poised to orbit Mercury in 2011 after three flybys, as well as two flybys of Venus and one of Earth for course corrections. It will be the first probe to visit the innermost planet since Mariner 10 in 1974 and 1975. Stories on the BBC and SpaceflightNow."

Comments

I thought we knew this bit already . . .

[StateOfTheUnion]

From the Spaceflight Now

How did Mercury, believed to be 60 percent iron, end up with an oversize core, a thin shell of a crust and the highest density in the solar system? Was its crust blasted away in the distant past by a cataclysmic impact? Was it boiled away in the extreme heat of the young, nearby sun? Or were metals for some reason concentrated in the inner region of the solar nebula that coalesced to form the sun and planets?

Perhaps my knowledge is a little dated, but I thought that the inner four planets have higher density because the sun stripped the inner solar system of light gasses like hydrogen due to the larger mass and higher gravitational field of the sun during the formation of the sun and the solar system. Outer planets are gas giants because the Sun's (or the pre-sun center of the accretion disk ) gravitational field was not strong enough to grab the light elements from the portion of the solar system that would become the gas giants (further from the center of the pre solar system accretion disk). Also, this was thought to be why Pluto is an oddball (far away from the sun, but a frozen rock of a planet) that might be an escaped moon or oort cloud refugee.

Can anyone confirm this? Or am I citing stone age planetary science that is no longer valid?

Re:I thought we knew this bit already . . .

[el-spectre]

I think your science is right... what the article seems to be emphasizing is the massive iron content... Earth, whilst having an iron core, is still mostly silicon and oxygen (the mantle & crust). For some reason Mercury has more than it's fair share of iron core, compared to other inner planets. 'tis puzzling.

Re:I thought we knew this bit already . . .

[Anonymous Coward]

According to the Messenger website you are largely correct, the absence of lighter gpI&II metals is down to them simply boiling away from the crust. However it goes on to say that this is unconfirmed _theory_ and one purpose of the mission is to collect more evidence to confirm/deny this. The other theory is that physical activity (impacts) have blasted away most of these elements from the early crust.

On a sceptical note, I question the value of such a mission. Mercury is going to remain beyond our reach for many centuries so whatever we find there is of theoretical value only, and I wonder whether advances in spectroscopy and remote analysis will soon overtake the value of a probe mission.

Re:I thought we knew this bit already . . .

[CheshireCatCO]

Not quite, no.

The inner planets are rocky/metallic because it was too hot for ices to form. Most of the proto-solar disk would have been in the form of hydrogen and helium. The next most abundant elements are oxygen, carbon, and nitrogen. With so my of these and hydrogen, hydrogen compounds (water, ammonia, methane) can do a lot of planet building if they can form solids. Near the proto-Sun, it would habe been too hot for this to happen. Somewhere around 5 AU, water ice could first freeze out. Not surprisingly, you find jovian planets starting around that point. (They have the gases because they were able to get large enough fast enough to trap some of the gas in the disk before the disk dissipated. The terrestrial planets are too small to accomplish this because they never had enough solid materials around to build themselves with.)

You would have found that the composition of the proto-solar disk was probably pretty uniform. The acceration of gravity is higher near the center thanks to the proto-Sun, but that's a red herring. The acceleration is balanced by the orbital motion. The mass of the orbiting object doesn't factor into the motion, so hydrogen gas orbits the same as rock particles. (Well, almost. Gases are subject to gas pressures, but that wouldn't make them move inward or outward, it just slows their orbital speed some.)

planet inside mercury orbit

[ch-chuck]

maybe now they'll finally find Planet Vulcan

2011? How long with ion drives?

[adeyadey]

I dont understand why solar-powered ion drives are not used on missions like this. Probes like the ESA SMART-1 has shown that such craft can be small & economical, and there is an abundance of solar power available for free. I understand that final orbital insertion can be a problem - could a solar ion drive deliver enough "punch", or would a supplemental booster be needed? Otherwise I understand that solar would be way more fuel/time efficient over a few years compared to carrying rocket fuel & hanging around for gravity slingshots. Am I right?

I have even read of deep-space solar-powered mission designs that head in inside mercurys orbit, grab loads of power and then head out beyond Jupiter..

Why arnt ion drives used more?

Re:2011? How long with ion drives?

[Rei]

What calculations are you looking for, in particular? There are a lot of them, you know ;) Here's a page that has a good number of them:

http://members.axion.net/~enrique/rocket.html

As for myself, there is only one problem in orbital mechanics that I have been unable to track down a solution to, which has been holding up the addition of the effects of torques (and consequently, realistic effects of RCS thrusters, control surfaces, and gimballing) to my rocket simulator:

Does anyone know how to, given a number of forces applied in arbirary positions with arbitrary angles to an object for a given amount of time, determine the rotational and linear accelerations on the object? I've checked a number of physics texts, and none of them address this problem.

For example, picture an object in which there is a heavy, dense ball in the middle, with a long, thin, lightweight bar passing through its center. At the end of the bar on one side, you apply a force. Due to the low moment of inertia, almost all of the energy goes into rotational acceleration instead of linear acceleration. If you were to apply the force on the center of the ball, it would all go to linear motion. So, it would seem that the further out the force is applied, the larger the percent of energy goes into rotational acceleration instead of linear acceleration. However, if you apply force to *both* ends of the bar in the same direction, *all* of the energy goes into linear acceleration.

Does anyone know the formulae related to this?

Re:2011? How long with ion drives?

[adeyadey]

Yes I remember that impulse was rated in seconds - I should have said per Kg of propellant - ie, I understand that an ion drive can generate 10x the thrust per Kg of propellant, it just does it slower..

The SMART-1 mission cost $100 million in *total*, not too much in terms of space exploration. The thrusters will operate for 18 months & I think newer designs allow for multiple replacement anodes to replace old ones..

Ion drive missions have spiral paths, in this case decellerating towards the sun. An ion drive mission could also exploit slingshot slowdowns, no?

At points where the craft is nearer the sun, more power is available - lots more power..

So, has anyone done the calculation for a mission profile with solar-ion propulsion?

Mercury, messenger of the Gods?

[Airw0lf]

As another poster has pointed out, officially the name is derived thus: MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. I was looking at this information and thought that it was a rather contrived name - kind of like the laws that the US Congress passes (PATRIOT Act, etc...) And then it occurred to me, they probably called it Messenger because in Greek mythology, Mercury was the messenger of the Gods. Or I could be completely wrong...

Re:2011?

[essreenim]

Yeah. I _KNOW_ my grandmother could get there before then. I know orbital mechanics is tricky because trying to enter orbit around Mercury is difficult with the immense speed generated by travelling towards the sun ... but come on.
What this is like everything is a money dictated project i.e the Messenger guys have none and have had to come up with a low cost lengthy gravity controlled trip ..blah blah blah.
Come on Nasa, start working on cutting down your mission times..

Re:So many fly by's

[Anonymous Coward]

There's no doubt that a direct flight to Mercury could have been made in theory, but it would have required a MASSIVE amount of fuel to prevent it from being sucked into the giant gravity well of the sun. There's a remarkable grace in the use of planetary fly-by's to achieve the same result much more efficiently. I actually work with the rocket scientists responsible for this planning.

Stupid rockets... :)

[JCMay]

We were, of course, some of the first people to know that the Messenger launch had occurred; with TS Alex to our northeast we had winds out of the north and the noise of the launch was exceptionally clear at our house. Woke me up with rattling windows and a low rumble.

Re:So many fly by's

[thbigr]

I am sorry I must not have phrased the question well. I do understand using a fly by to increase Velocity, but this guy is going around the sun quite few times. Mercury is inside those orbits. I am assuming it is more of a case of placement rather then speed? Right?

Re:Useful tip for the NASA engineers ....

[unknowns]

It's no joke kids.

At an AAS (American Astronomical Society) meeting two years ago,I picked up a neat little reference card from the NGST (now the James Web space telescope) booth. I still have it. There's this great image of the telescope with Ball Aerospace, Northrup Grumman, and Kodak corporate logos plastered around it. On the back was a reference table with star magnitudes, colors, etc as well as some useful distance conversions; including the distance from the earth to the sun:

"AU - Astronomical Unit - Mean distance between the Sun and Earth: 149,599,000km. 190,236,576 miles."

Take a good hard look. Now look again with the knowledge that there are about .62 miles per kilometer! Whoops!

Now I'm not saying that this is an apples to apples comparison. I'm sure (I hope, for the love of god) that they do a few more checks on a spacecraft propulsion system than a cheap promo. But still!

Solar Flare strike

[random coward]

When is next solar max? What are the odds of a solar
flare hitting it before it orbits mercury? What ar ethe odds of a solar
Flare hitting it early on in its orbit of mercury? Isn't mercury struck by solar flares
from time to time?