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

The probe's slogan

[Anonymous Coward]

"My future's so bright, I've got to wear shades."

Is that even possible?

[mindless4210]

The outside of this 6-foot solar umbrella will rise to 680F (360C), while its special insulating properties will keep its inside surface below 212F (100C) - and the spacecraft operating at room temperature.

How can you keep the spacecraft at room temperature if everything around it is at least 212F? I need to get some of those fans for my computer.

Re:Is that even possible?

[Xandu]

How can you keep the spacecraft at room temperature if everything around it is at least 212F? I need to get some of those fans for my computer.

It would be amazing if it was true that everything around the spacecraft was at 100C. But the side which doesn't face the sun A) doesn't need the sun shields, and B) sees the cold vacuum of space, a great place to passivly radiate unwanted heat to.

Check out this page from the MESSENGER site showing the sun shields only on the side facing the sun.

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?

[Overzeetop]

Yes, it seems infeasable, since you lack both convective and conductive heat sinks, but you do get to radiate your excess heat to a 3K (-270C) heatsink.

It's still an annoying problem, as radiators take up valuable surface area / FOV space which would preferable used for observational instrumentation.

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:Is that even possible?

[StateOfTheUnion]

BTW: Stefan's law has nothing to do with the color of an object. A perfect blackbody has a emissivity of 1 but this has nothing to do with color.

If an object only gets rid of heat only through electromagentic radiation, it's emissivity is one (this is a perfect blackbody), if it gets rid of heat through other means, the emissivity will be something less than one. Color is not relevent . . . radiation of heat is.

Note that for very hot objects, other methods of getting rid of heat can be assumed to be negligible (e.g. stars) and one may assume an emmisivity of one.

Re:Is that even possible?

[StateOfTheUnion]

Actually, there is no heatsink . . . space may be cold, but it also has no heat capacity. Heatsinks rely on conduction (which requires heat capacity). Stefan's law states that radiating heat in the form of electromagnetic radiation has nothing to do with the ambient temperature, only the temperature of the radiant object.

Re:Is that even possible?

[jerde]

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

Which is why vacuum flasks also use silvered glass, to help reflect the infrared radiation back into your hot soup. :)

- Peter

Re:Is that even possible?

[InfiniteWisdom]

Of course, I'm not a science guy, so what do I know, right?

Apparently. I thought the energy from the sun reaching the earth through 150 million miles of hard vaccum might have been some clue.

Re:Is that even possible?

[barakn]

150 million miles

150 million kilometers, or 93 million miles.

Re:Is that even possible?

[InfiniteWisdom]

I work for Nasa, you insensitive clod.

I do'nt kneed on dman pvriev buton!

Ion drive

[Geoffd1]

At first glance, I thought they were using an ion drive, or something - classic design for such a thing is to have a giant "sail" at the back, powered by the "wind" generated by an ion drive... slow at first, then gets very fast.

Re:Ion drive

[cbiffle]

You're thinking of a solar sail. Ion drives derive thrust directly from the force of the escaping gas (lightweight but high energy), generally xenon.

Trying to ride the 'wind' from your own ion drive is very similar to trying to windsurf by blowing into your own sail -- or, to use a more familiar analogy, pulling one's self up by one's own bootstraps.

Re:Ion drive

[Bandman]

when I was about 3 years old, I took my matchbox cars, and mounted a magnet on the front of one. Then I took a metal beam from my erector set, taped it to the top of my car, and put one end way out in front, on which I taped another magnet, opposite poles facing each other. It took me a couple of seconds to realize why it wasn't going to work :-) It sounds pretty similer to an ion drive pushing it's own sail.

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.

Re:Ion drive

[physicsnerd]

It's little g, 9.8m/s^2. Isp is defined as the total impulse per unit of propellant weight on Earth. It's basically a rating system to tell us how efficent a particular rocket system is with respect to it's fuel. We use weight because that's what you get when you stick something on a scale on Earth.

Let me define a few things real quick
It=total Impulse=Thrust*Time [N-s]
F=Thrust [N]
t= time [s]
Mp=Propellant Mass [kg]
dMp/dt=Propllant mass flow rate [kg/s]
Wp=Propellant weight [N]

Isp=It/Wp=F*t/(Mp*g)
which if you solve for F in terms of Isp you get:
F=Isp*Mp*g/t

Then, you have Newton's law: F=dP/dt=d(mv)/dt which for a constat exit velocity you get:

F=Ve*dMp/dt
which for a constant mass flow can be written as:
F=Ve*Mp/t

Setting the two equations for thrust together you get:
F=Isp*Mp*g/t=Ve*Mp/t
which if you cancel out the Mp/t on both sides of the equation you get that:

Ve=Isp*g.

One of the real nice things about using Isp is that it's one of the few things that is the same in both EE and metric because it's units are seconds. For more info on this I recomend Chapter 2 from 'Rocket Propulsion Elements' by George Sutton and for a more advanced look at this stuff check out 'Space Propulsion Analysis and Design' By Humble, Henry and Larson. Both books can be purchased through Amazon or other large book sellers.

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:Ice?

[internewt]

Quick google search reveals this too:
http://nssdc.gsfc.nasa.gov/planetary/ice/ice_mercu ry.html

Re:Ice?

[uujjj]

I belive what you are missing here is "the obvious"

Re:Ice?

[calyxa]

Mercury's rotation

-calyxa

Bottom of the (gravity) well

[maggard]

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.

Curiously? One of the best places to look for anything is at or near the bottom of a well (gravity well in this case.)

Sure there are lotsa other places to look too but this is a tidally-locked object not far from where many inner-system comets end up, ie the Sun. It'd be curiouser if Mercury hadn't intercepted a few comets over the eons and there weren't some traces of those collisions left on the benign parts of the planet.

Re:Bottom of the (gravity) well

[DudeG]

It's worth mentioning that although it's true that Mercury is tidal-locked with the sun, it's in a 3:2 lock, not 1:1.

This means that it does rotate relative to the sun, so there's no permanent "dark side".

(For comparison, the moon is tidal-locked 1:1 with Earth, so we never see the far side.)

Is it hot or is it me?

[malia8888]

From the article: the spacecraft's temperature would climb to unmanageable levels without special protection. The outside of this 6-foot solar umbrella will rise to 680F (360C), while its special insulating properties will keep its inside surface below 212F (100C) - and the spacecraft operating at room temperature.

Then in the case of Mercury, I guess it really is the heat, not the humidity that gets to you :P

Re:Looking for water...

[Overzeetop]

Dubya's new space initiative to look for extraterrestrial oil hasn't filtered through to the mission planners yet...

(Just proof that any dumb @$$ can get elected in America...ooooh, pretty shiney!)

Re:Looking for water...

[guile*fr]

since oil is organic matter more or less fossilized, in facts it would be interresting to look for extraterrestrial oil :D

Looks like crap to me

[bperkins]

This image beautifully illustrates the multilayered approach the team devised to fend off the excess heat while the spacecraft is near Mercury

Are we looking a the same picture?

This is not an informative image.

It could just as well be Fruit Fucker Prime with a tarp over it.

Impressive technology. Abysmal photography.

Send a rover!

[qualico]

They should send a rover on over.

Mercury must have some interesting elements collected from solar winds.

A good landing site would be on the dark side obviously to avoid overheating.
However, if I remember correctly, Mercury also sports the coldest temps in the solar system due to its rapid evaporation.
Kind of like the cooling effect one gets when a wind blows on wet skin.
But I somehow doubt those rumors with it being so close to the sun.

So how about playing on the transitional areas of light and dark areas.
This planet was thought to be like our moon in that the same face points towards the Sun, leaving a perpetual dark and light side. However, it was shown to have a strange rotation of three rotations every two of its years.

What I would like to see from a rover is a video showing the sunsets and sunrises.

Its suppose to be really bizarre.
The sun rises and picks up speed as it grows in size! Then it pauses at the top and reverses the process.

If they did find ice water on the planet, do you think huddling some poor humans in a crater there would be beneficial or sacrificial?

Just some musings.

Re:Send a rover!

[panurge]

OK, I'll bite.

The rover would have to move continuously to stay in the correct temperature zone. So you would need to know in advance that you could travel round a significant part of the circumference without encountering obstacles.

It would obviously have to stay in the dark because any level of sunshine would overheat it. So it would never see a sunrise or sunset. It would just crawl sadly around staying in the zone that current electronics and motors can handle (say -25 to 70C) until the batteries ran down (no solar power, you see.)

Who modded this interesting?

Re:Send a rover!

[qualico]

Actually, the sunrise and settings last over many months. So it would be boring to watch unless you time lapsed it.

Further, with such a slow procession, there would be no need to worry about getting caught in the sun. Mapping would take place with the current messanger anyway.

As for overheating, just give the thing 20 Kapton Umbrellas. :-)

Here is a short movie I created in StaryNight Pro to give a good visualization of a sun rise and set:

spacecanada.org/mercuryrising.mov

Re:Send a rover!

[VanillaCoke420]

The Bepi-Colombo project was meant to carry to orbiters and one lander, but the lander was scrapped. I think that they should have sent a rover or two... I mean, someone will do that some day anyway. Why wait? Also a sample return or two would be nice, one from the nightside, one from the dayside, or something.

Re:Send a rover!

[VanillaCoke420]

You're absolutely right, thanks for correcting me!

Re:Send a rover!

[VanillaCoke420]

True, I wasn't aware that Mercury did not face the same side to the sun at all times... Anyway, the landing is a bit more difficult, but it could be done of course. A rover would be nice... but the lander was scrapped because of budget restrictions. If they get more funding quickly, they might be able to throw in one, but it wont happen. I do agree though that a core sample return would be very valuable.

Metalized Kapton Film

[StateOfTheUnion]

I figured that Kapton had to be some new fangled high tech insulating product but . . .

Kapton is a polyamide film duPont product that's been around for some 30 years . . .

I wonder if its the same metalized film used in some automobile window heat shields (or might that be metalized biaxially oriented nylon film)?

Re:Metalized Kapton Film

[wass]

I've been using Kapton tape for years in electronics in the lab. It's a great insulator, and coming on a roll of tape with adhesive it's really easy to use.

And recently I've been using it in my cryogenic experiments. In the dilution fridge in my lab we can get to temperatures as low as 20 mK. Kapton tape is stable at these low temps, and provides a good way to ensure insulation between two conductors while still being 'removable'.

Good Lord, how stupid!

[winkydink]

Everybody knows that if you want to avoid pesky problems with being so close to the sun, you go at night.

Sheesh.

I HATE that attitude.

[dmaxwell]

There will NEVER be a day when there is a utopian heaven on Earth. There will always be corruption, war, famine, greed and every other problem that is born from human failings. Earth's persistant failure to become a paradise is not a valid reason to postpone space exploration. And in 200 years, your great-great-great-great grandchildren will be saying "There is no reason to explore the Oort clouds until all problems on Earth have been solved....." With that attitude, we needn't have even bothered climbing out of the ocean. "There is no use exploring the land until there is enough plankton for everybody...." And it isn't as though vast amounts of money are being spent on space exploration. We spend a hell of a lot more on porkbarrel projects and foreign misadventures that won't have any sort of meaningful return at all. At least we get some knowledge and wonderment out of the deal.

Re:What bright future?

[zero_offset]

you may ponder what the carpenter said a couple thousand years back

"I'm so frigging tire of sawing logs. I wonder if I could run one of those prophet scams without the Romans catching on?"

Federal budget vetoed Messenger mission

[peter303]

April Physics Today reports the Bush administration cut Messenger from the budget. This in order to concentrate on remaining missions like the Kuiper Pluto mission, Kepler planetary dectection, New Technology Space Telescope, and a few others. This is an advisory to Congress, which occasionally restores programs over administration objections.