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

2011?

[Anonymous Coward]

Not exactly Instant Messenger, is it?

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 Or am I citing stone age planetary science that is no longer valid?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 . . .

[pedroloco]

Mercury is real hard to observe from Earth-based telescopes since it is so close to the Sun. In the near future, the only way to get higher resolution data is to send the telescopes to Mercury. Even the most fervent remote sensing advocate will have to admit that data quality generally improves with decreasing distance to the target.

Using martian studies as an analogy for mercurian (hermitian?) observations, one can see how spacecraft data provide much more detailed observations over ground-based observations. Earth-based data of Mars obtained during the last opposition last summer (when Mars was closer to Earth than Mercury ever gets) does not compare to spacecraft data in terms of resolution. Earth-based (visible-wavelength) observers of Mars have to content themselves with seeing albedo variations. The geology which caused those albedo variations was largely unknown prior to our sending spacecraft. (Please note that tha "canals" reported by Lowell were likely optical illusions - Lowell's canal maps do not correspond to locations of known martian dry channels.)

Similarly, Earth-based spectroscopic observations of Mars have poor spatial resolutions. I remember one paper from '96 which reported 300 km/pixel resolutions. Two spectrometers currently in orbit around Mars get far better spatialresolution (Thermal Emission Spectrometer gets 3 km/pixel; THEMIS-IR gets 100 m/pixel - although, granted, that's with a low spectral resolution).

Two advantages that Earth-based observations have over spacecraft data are: 1) Earth-based observations are a lot cheaper to obtain and 2) a network of Earth-based observers can look for changes in the target with better time continuity than a singe spacecraft (since the spacecraft may be looking at some other part of the planet).

The true value of a Mercury mission is two-fold. Most obviously, new spacecraft observations will provide geologic context for current ground based observations (Mariner 10 only imaged ~40% of the planet). Additionally, Mercury is considered an end-member planet - a planet that likely formed close to the Sun in the solar nebula from which the solar system formed. As such, understanding how Mercury formed will provide a calibration point for models of solar system formation, which could have implications for formation in other portions of the solar nebula or the early solar system or of other planetary systems.

No, we aren't going to be sending people to Mercury anytime soon, but neither are we going to be sending people to Mars in the near future. (Even Bush's space initiative doesn't plan a Mars landing for at least 20 years - plenty of time to get distracted by other problems.) However, even if people aren't going to those placed, there are still useful things to learn regarding the solar system in which we live.

Messenger's telemetry log...

[vudufixit]

8-2-3004 2:15:56.537 EST: Departure Scan, Cape Canaveral 9-5-2005 Scan Venus gravitational assist 4-22-2008 Scan First flyby 12-14-2009 Scan Second flyby 6-12-2010 Scan Third flyby 2-01-2011 Scan Orbital Insertion ADDRESSEE NOT HOME, SIGNATURE WAIVED

Re:Second try?

[Kiryat Malachi]

When a launch is canceled due to mechanical failures, weather, or any other reason, it's considered a try as long as the launch procedure has been started. Since launch procedures can range from 6 hours to 6 days, there are a lot more tries than launches.

Yoda wisdom or no Yoda wisdom, you're still wrong.

(With rockets, if you try and don't succeed, its pretty much SOP - most things don't launch on the first attempt. Now, if you were to say "ignite" instead of try, you'd be correct - most rockets don't do too well on a second ignition.)

Re:that long?

[ufoman]

The spacecraft cannot fly straight to Mercury; it does not carry nearly enough fuel. So it will fly once past Earth, twice past Venus and three times past Mercury and make 15 loops around the sun before slowing enough to slip into orbit around the small, hot planet.

What Messenger Really Stands For . . .

[StateOfTheUnion]

According to JPL

MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging

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:that long?

[LooseChanj]

Also, remember the Earth is in orbit around the sun, so to get to the orbit of Mercury you need to lose a lot of the energy Earth's higher 'altitude' gives you to start with. Plus you need to slow down enough to where you don't need an ungodly amount of fuel to slow down into orbiting Mercury itself.

Lot of activity on ion engines at NASA too

[Morgaine]

Why aren't ion drives used more?

That's actually quite a good question, given the huge amount of power available from sunlight in the inner solar system. A continuous-burn trajectory to Mercury would probably be very much shorter than the current one; the thrust may be small, but craft speed builds up rapidly under such continuous acceleration. You'd only need to carry enough conventional chemical propellant for the final orbital insertion.

NASA has been very active on the ion-engine front -- last year it successfully completed a pretty advanced test: http://www.sciencedaily.com/releases/2003/11/03112 1072826.htm. (And enter "ion engine" at NASA's main site for a huge number of links.) So, it's not only ESA that have their fingers in this pie.

Maybe the answer is that ion engines still need a few more years of development? Certainly not long though, since small ion thrusters are already in use, as you point out.