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Space Science

Messenger Spacecraft Prepared for Mercury 142

Posted by michael from the spf-5000 dept.
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."
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Messenger Spacecraft Prepared for Mercury More

Messenger Spacecraft Prepared for Mercury

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  • The probe's slogan (Score:5, Funny)

    by Anonymous Coward on Sunday April 11, 2004 @01:10PM (#8830991)
    "My future's so bright, I've got to wear shades."

  • Is that even possible? (Score:5, Funny)

    by mindless4210 ( 768563 ) * on Sunday April 11, 2004 @01:11PM (#8831007) Homepage Journal
    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.
    • well, rooms on Mercury are slightly hotter than rooms here on Earth...

    • Re:Is that even possible? (Score:5, Informative)

      by Xandu ( 99419 ) * <matt&truch,net> on Sunday April 11, 2004 @01:23PM (#8831095) Homepage Journal
      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 [jhuapl.edu] from the MESSENGER site showing the sun shields only on the side facing the sun.
      • a great place to passivly radiate unwanted heat to.

        See, I always thought that vacum was a BAD place to try to radiate heat to... Heat being a property of how active the molecules were. Vaccum, having nothing in it, doesn't transfer heat - which is why we have vaccum flasks, which keep hot things hot and cold things cold.

        Of course, I'm not a science guy, so what do I know, right?
      • Radiation is one of the poorest means of cooling something down. That's why serious cooling is done with a conduction/convection system (the cooling in your car's engine, for instance). However, since the only heat the spacecraft will be receiving is by radiation, it is reasonable that it can radiate enough of the heat it absorbs to maintain a cool temperature, provided it doesn't absorb too much radiant heat--and that is precisely what the sunshield is for.

    • Re:Is that even possible? (Score:5, Informative)

      by Anonymous Coward on Sunday April 11, 2004 @01:23PM (#8831096)
      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.
      • 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 neg

    • 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? (Score:4, Informative)

        by StateOfTheUnion ( 762194 ) on Sunday April 11, 2004 @03:25PM (#8831891) Homepage
        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.
    • Reminds me of when I saw baked alaska being made when I was six years old.
    • what is room temperature in space?

  • Ion drive (Score:2, Interesting)

    by Geoffd1 ( 466931 )
    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 (Score:5, Informative)

      by cbiffle ( 211614 ) on Sunday April 11, 2004 @01:38PM (#8831203)
      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.

      • Ion drives derive thrust from ions (often caesium IIRC) escaping in the direction opposite to the required motion. That's why they are called ion drives. The ions don't have great mass, but they can be accelerated to very high speeds (close to the speed of light). This makes them very efficient, even though they only produce small amounts of thrust.

        • Re:Ion drive (Score:5, Informative)

          by physicsnerd ( 607860 ) on Sunday April 11, 2004 @02:36PM (#8831607)
          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 [nasa.gov]

          And yes, I am a rocket scientist.

          • speed of light is roughly 30,000,000 m/s.

            I believe you meant 300,000,000 m/s. Only off by an order of magnitude.

          • The conversion between exit velocity and Isp is simple Ve=Isp*g

            Is that g as in 9.8 ms^-2? Or is it the universal constant of gravitation? Either way I'd be interested if you could tell me how it relates to an ion drive in the middle of space? Thanks Henry

            • Re:Ion drive (Score:5, Informative)

              by physicsnerd ( 607860 ) on Sunday April 11, 2004 @04:55PM (#8832480)
              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.

              • Bravo! (Why is this model of a worthwhile /. post rated so LOW?)
              • Thanks! I've actually had Sutton's book on my to-read list for a while, been interested in learning more about rockets. I'll try and find a copy.
              • Oh god, SPAD. The frelling bane of my life now that I'm doing semesterlong design courses. (AIAA: God hates you.)

                Of course, since I'm trying mightily to focus on engines, I learned it as V-equivalent and not V_exit. (for those who dunno: V_eq=V_e if the pressure of the gas that's escaping your nozzle is at the same pressure as Whatever Surrounds Your Craft. Not actually possible in vacuum.)
                • Yea you are absolutely correct. I just figured that I'd leave out the pressure thrust correction. I didn't want to get into all of that and everything else I did was perfectly ideal anyways. Oh, and long live SPAD!

      • Re:Ion drive (Score:5, Funny)

        by Bandman ( 86149 ) <`bandman' `at' `gmail.com'> on Sunday April 11, 2004 @01:58PM (#8831359) Homepage
        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.

  • Ice? (Score:5, Informative)

    by seanmcelroy ( 207852 ) on Sunday April 11, 2004 @01:17PM (#8831053) Homepage Journal
    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.

  • Bottom of the (gravity) well (Score:5, Interesting)

    by maggard ( 5579 ) <michael@michaelmaggard.com> on Sunday April 11, 2004 @01:25PM (#8831108) Homepage Journal
    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 (Score:4, Informative)

      by DudeG ( 623373 ) on Sunday April 11, 2004 @03:22PM (#8831873)
      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.)
    • One of the best places to look for anything is at or near the bottom of a well

      Ha! Unless its helium you're looking for!

      Oh, wait..Crap! [yarchive.net]
    • The actual reason the scientists are looking for water-ice at the north pole of Mercury is because there are small regions of permanent shadow in craters at the poles.

      Permanent shadows = lower temperatures which could mean ice.

      Similar studies have been done for other celestial bodies (including our Moon).

  • Is it hot or is it me? (Score:3, Funny)

    by malia8888 ( 646496 ) on Sunday April 11, 2004 @01:29PM (#8831140)
    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

  • Maybe interesting... (Score:1, Redundant)

    by Tagren ( 715283 )
    from http://www.nineplanets.org/venus.html
    There are several layers of clouds many kilometers thick composed of sulfuric acid. These clouds completely obscure our view of the surface. This dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead).
    Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun.

    ---

  • Looks like crap to me (Score:5, Insightful)

    by bperkins ( 12056 ) * on Sunday April 11, 2004 @01:38PM (#8831198) Homepage Journal

    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 [astrobio.net] is not an informative image.

    It could just as well be Fruit Fucker Prime [penny-arcade.com] with a tarp over it.

    Impressive technology. Abysmal photography.

  • Send a rover! (Score:4, Interesting)

    by qualico ( 731143 ) <[moc.liamg] [ta] [refrushcuocdlrow]> on Sunday April 11, 2004 @01:40PM (#8831221) Journal
    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! (Score:3, Insightful)

      by panurge ( 573432 )
      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

      • Re:Send a rover! (Score:2, Informative)

        by qualico ( 731143 )
        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
    • 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.
      • Interesting, was not aware of the BEPICOLOMBO project setting sail in 2012.
        It has time to reactivate the rover deal.
        They should include the already proven Mars rover technology. Although, with little atmosphere its probably going to need different braking tactics.

        Since the night and day sides both get exposure to the Sun over a the year, I would imagine there to be no difference in samples, but you never know.
        http://sci.esa.int/science-e/www/object/in d ex.cfm? fobjectid=31273

        A core sample would be intere
        • 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.
          • Hmmm...wonder what the rocket payload is capable of?

            You could bundle the rover seperately and then use its onboard cameras to monitor Bepi during the voyage.
            Although you'd have to share the shielding or make another umbrella.

            The information would be far far more valuable with a rover.

            The landing should be no more difficult than the moon landing.

            Hey, I just figured something.

            Could you not deploy a big solar wind grabbing parasail to do the braking?
            This would greatly save on propellants.

            more musing.
      • There isn't a nightside and a dayside. All bits of mercury get sunlight at some point.
        • True, however, that cycle happens 3 times every two years because it rotates around its axis very slowly.

          Mercurian Year: about 90 Earth Days.

          So its one hell of a long night. (about 2 Earth months)
          Great for partys though!
          Imagine the money Rave clubs would pull in. :->
          • Yes, but I don't think it's long enough for rock samples from different sides to be all that different.
            • Well it is baking in the sun stripping rays enough to be exposed for a cyclic 2 earth months.

              Thats got to change the nature of things.

              Hmmmm...

              How about deploying a reflective blanket onto the surface or in orbit if you can keep it there?

              Then we could bounce lasers off it and use it to keep a probe protected like a bug under the rug.
        • You're absolutely right, thanks for correcting me!

  • Metalized Kapton Film (Score:5, Interesting)

    by StateOfTheUnion ( 762194 ) on Sunday April 11, 2004 @01:59PM (#8831368) Homepage
    I figured that Kapton had to be some new fangled high tech insulating product but . . .

    Kapton [dupont.com] 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 (Score:3, Interesting)

      by wass ( 72082 )
      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'.

  • Naming a probe to Mercury Messenger is fitting because Mercury was a god of messengers. Of course, that wasn't his only devine attribute, so I expect the next probe to be called Thief, Traveller, or Merchant.
    • Merchant has got to be for Venus (Merchant of Venus, 5 players, no worms, anyone?)
      • I think Mercury/Hermes has prior art on that IP, but there might be a compromise. Mercury is more a god of travelling merchants or traders. In a modern context perhaps the probe could be called Door-To-Door-Salesperson?
  • Ok, so we send Mercury Messenger, but will it use it? I've heard Mercury is a unix geek and prefers IRC.

  • Good Lord, how stupid! (Score:3, Funny)

    by winkydink ( 650484 ) * <sv.dude@gmail.com> on Sunday April 11, 2004 @03:19PM (#8831853) Homepage Journal
    Everybody knows that if you want to avoid pesky problems with being so close to the sun, you go at night.

    Sheesh.


  • Aren't they just getting too obsessed with finding ice and water? how about looking for something else?
    • You are pretty naive if you think that's the only science goal for such a space mission.
    • Seeing as we're water based life forms, mapping out the exact location of all the water deposits in the solar system seems like a pretty good idea to me, if we're ever going to explore it.

      I get your point though, where are the frozen alcohol deposits?! ;)
  • Nice to see Mercury getting some action these days.

    A rover is an interesting idea, but it's pretty complicated to actually achive. Mercury is not rorationally locked to the Sun, so if you land something on the shade side, it'll rotate into sunlight within a month, or so.

    The big difference between Mars and Mercury when it comes to rovers would be that a rover on Mars is facing towards Earth every 24 hours, or so. (One Mars day is just a little over 24 hours). But, the Mercury orbit and rotation period
    • Your missing the point, there is obviously no plan in the mission for retransmission..

      The whole point is to land send data and then make molten computer parts....short of interplanetary art.

  • Federal budget vetoed Messenger mission (Score:3, Informative)

    by peter303 ( 12292 ) on Monday April 12, 2004 @10:59AM (#8837549)
    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.

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