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Ion Rocket to Map Moon with X-Rays

jralls writes "The Guardian is reporting that a European ion-rocket has taken the last year to reach the moon and is about to enter lunar orbit. Once it slows and gets into a very low orbit, it will probe the surface with x-rays in an effort to solve the long standing puzzle of the moon's origin."

117 of 172 comments (clear)

  1. Visibile from Earth? by fembots · · Score: 3, Interesting

    I wonder if we are able to observe this interplanetary tortoise from earth? If it passes the bright side in full moon, we should have quite a clear view of it since it's going so slowly.

    Play iCLOD Virtual City Explorer and win Half-Life 2

    1. Re:Visibile from Earth? by bsharitt · · Score: 1

      Why did it take so long to get to the moon?

    2. Re:Visibile from Earth? by bhima · · Score: 1

      I wonder if we'll be able to see the four elephants too.

      --
      Nothing in the world is more dangerous than sincere ignorance and conscientious stupidity.
    3. Re:Visibile from Earth? by NetKraft · · Score: 5, Informative

      Ion rockets can't generate very high accelerations. They can, however, keep going for a long time.

      --
      I don't suffer from insanity. I enjoy every minute of it.
    4. Re:Visibile from Earth? by bsharitt · · Score: 1, Troll

      If we used some sort of higher powered rocket to generate the velocity, I wonder if ion rockets could hold that velocity for a long time.

    5. Re:Visibile from Earth? by wertarbyte · · Score: 4, Insightful

      If we used some sort of higher powered rocket to generate the velocity, I wonder if ion rockets could hold that velocity for a long time.

      Since we are using this space, I wonder what we would need the ion rocket for to hold that velocity. In space, there is not much that could slow you down.

      --
      Life is just nature's way of keeping meat fresh.
    6. Re:Visibile from Earth? by M1FCJ · · Score: 1

      I don't think there ever were any problems with holding the velocity. Acceleration, however...

    7. Re:Visibile from Earth? by Squarepusher · · Score: 1

      So the question is, if we used conventional rockets to quickly achieve a high speed, could the ion propulsion continue the excelleration after the rocket burns out?

      --
      Every hour wounds. The last one kills.
    8. Re:Visibile from Earth? by pe1rxq · · Score: 3, Interesting

      That is exactly what this thing does...Use a conventional rocket to get away from earth's surface and then continue with ion propulsion to the moon.

      Jeroen

      --
      Secure messaging: http://quickmsg.vreeken.net/
    9. Re:Visibile from Earth? by Anonymous Coward · · Score: 1, Informative

      >In space, there is not much that could slow you down.

      True. Unless you are somewhat near a large gravity source that the rocket would have to fight against. The Earth for instance.

    10. Re:Visibile from Earth? by Fyre2012 · · Score: 1

      My question is will they be able to see the American flag that *supposedly* resides up there...

      this is assuming that they really *did* land on the moon

      --
      This is not the greatest .sig in the world, no. This is just a tribute.
    11. Re:Visibile from Earth? by dmadole · · Score: 2, Informative

      I wonder if we are able to observe this interplanetary tortoise from earth? If it passes the bright side in full moon, we should have quite a clear view of it since it's going so slowly.

      I'm curious what make you think it will be going slowly? It will be orbiting the moon at exactly the same speed as any other craft at the same altitude would be orbiting the moon. The type of engine or thrust has nothing at all to do with orbital mechanics.

    12. Re:Visibile from Earth? by cjameshuff · · Score: 1

      It's not going slowly, it's going at the same speed anything else in the same orbit would be at. It's taking a long time to reach lunar orbit because it started out in Earth orbit and needs to accelerate quite a bit. It's using an ion engine, so it'll take longer to achieve a given change in velocity. A conventional rocket would achieve the same change in velocity more quickly, but the end result would be basically the same...except that the conventional rocket would be bigger and heavier, and thus more expensive to lift.

      In any case, it's too small to see from Earth, no matter how fast it's going.

    13. Re:Visibile from Earth? by Ash-Fox · · Score: 1

      That's a very good point.

      --
      Change is certain; progress is not obligatory.
    14. Re:Visibile from Earth? by Digemedi · · Score: 2, Informative

      The general idea of a ionization engine is obviously sustained impulse (as previously stated).

      Ionizations engines are typically attatched to probes which have initial combustion engines that give them the thrust required to escape the earth's gravity. Once the probes have escaped gravity, the ion engines allow continual thrust that allow (for extremely long range expeditions) extremely high velocity. It is a competing technology with solar sails - which also allows for huge velocities over long distances using continual (though very low) acceleration.

      This probe isnt making much use of the ionization engine, as the article says: "Smart was originally designed to test the feasibility of 'ion engines' which operate by shooting out streams of electrically-charged xenon." The duration of the mission isnt long enough to reap the benefits of a continual acceleration device.

      Theoretically, ionization engines and such drives are the only currently possible means of probing, say, the other side of the galaxy, within hundreds or thousands of years, instead of taking billions of years with a one-thrust coast - as they have the possibility of reaching fractions of the speed of light.

      But this is more about the moon's origins than the ion drive =)

    15. Re:Visibile from Earth? by M1FCJ · · Score: 1

      Exactly. Smart is to ESA as DS1 was to NASA, a good testbed. DS1 managed to return with good scientific data as well, so will do Smart. Overall two very good test beds. DS1 managed to encounter two asteroids using its ion engine and managed to wander far away compared to Smart but this is still good. Moon is a forgotten scientific target, it is no longer sexy enough. We've been back there (even with robotic exploration) only twice in 20 years. :(

  2. Where do you think the Moon came from? by mfh · · Score: 2, Funny

    Place your bets!

    I say the moon came from Uranus, what do you say? Here take a survey!

    Survey...

    Uranus
    Another Galaxy
    Mars-sized planet crashed into the earth
    Comet
    Meteor
    Microsoft
    Another Dimension
    It was a spaceship!
    Cowboy Neal

    --
    The dangers of knowledge trigger emotional distress in human beings.
    1. Re:Where do you think the Moon came from? by MrWim · · Score: 5, Funny
      It was a spaceship!
      AKA "Thats no moon"
    2. Re:Where do you think the Moon came from? by mfh · · Score: 1

      AKA "Thats no moon"

      ROFTLMAO!!!!!

      --
      The dangers of knowledge trigger emotional distress in human beings.
    3. Re:Where do you think the Moon came from? by A+Boy+and+His+Blob · · Score: 1
      I voted Microsoft, I imagine the EULA would go something like this:
      By viewing or using light relected from the moon you agree to be bound by the terms of this License Agreement. IF YOU DO NOT AGREE TO THE TERMS OF THIS LICENSE AGREEMENT, LEAVE THE PLANET IMMEDIATELY AND/OR KILL YOURSELF.
    4. Re:Where do you think the Moon came from? by ForestGrump · · Score: 1

      Its actually Darth Vader in his death star orbiting above us..

      --
      Is it true that more people vote for the winner of American Idol, than vote for the president? -Ali G.
    5. Re:Where do you think the Moon came from? by uberdave · · Score: 1

      The death star is in orbit around Saturn

    6. Re:Where do you think the Moon came from? by dabigpaybackski · · Score: 2, Interesting
      (Slightly off-topic, but fittingly placed among the Star Wars-related posts.)

      Anyway, now that this mode of propulsion is being deployed in (or above) the real world, and the private sector is building spaceships, how long, I wonder, will it be before some rich hobbyist builds a functioning TIE Fighter? All the parts are waiting to be assembled, with the possible exception of the small megawatt-class lasers.

      It'd be great; get a bunch of rich Star Wars reenactors together with their lovingly assembled spaceships and we could have the equivalent of SCA tournaments in low earth orbit. Probably collisions, too, but hey, that's what television's for.

      --
      "OH SHIT, THERE'S A HORSE IN THE HOSPITAL!"
  3. Great title by Chairboy · · Score: 4, Funny

    I expected the story to read "But when Flash Gordon approaches, will the moon people fight back with their electro-guns? Watch next week to find out!"

  4. Moon mining? by FiReaNGeL · · Score: 4, Interesting

    From the article :

    "The sun emits X-rays and these are reflected back into space by atoms on the Moon's surface. A magnesium atom will reflect an X-ray in a different way from an iron atom, and Grande's detector can detect these differences.

    Flying over the lunar poles, so that it covers the entire Moon as it revolves below, Smart will create strip maps of the surface - and eventually a global map of its composition."

    Look like useful data to me if we were in the 'mine the moon' business... maybe in a not so distant future?

    1. Re:Moon mining? by metlin · · Score: 1

      Cool!

      Now that GWB is back in office, someone send up a note quick that there is oil and wealth on the moon!

      Maybe something useful could come out of his re-election, afterall! ;)

    2. Re:Moon mining? by npross · · Score: 1

      That won't work! Tell GW that al Qaeda has a secret lunar base deep inside the moon and is using it as a terrorist training camp...

    3. Re:Moon mining? by dyscant · · Score: 1

      Taking matter off the moon seems like dangerous business to me. We rely on her mass for myriad geo-physical phenomena which support our ecology.

      Tides, anyone? Or how about stabilizing the earth's rotation and orbit?

  5. A year to reach the moon? by ravenspear · · Score: 2, Insightful

    I keep hearing that Ion propulsion is faster than what we currently use. What's with the incredibly slow travel time?

    1. Re:A year to reach the moon? by SpryGuy · · Score: 5, Informative

      The ultimate speed of ion propulsion is higher than that of chemical propulsion.

      But the mass being expelled at high speeds (the ions) is so low, that accelleration is VERY slow. So it takes a long time to get up to speed, but the maximum speed you can theoretically reach is much greater than that of chemical rockets.

      --

      - Spryguy
      There are three kinds of people in this world: those that can count and those that can't
    2. Re:A year to reach the moon? by Anonymous Coward · · Score: 3, Funny

      They are using euro ions, which require extended committee meetings and discussions before determining the appropriate direction in which to apply their force.

    3. Re:A year to reach the moon? by InternationalCow · · Score: 1

      What you heard is that the specific impulse is way larger than with chemical, meaning that the exhaust velocity is very high. That means that you have a very efficient means of propulsion, with each particle of exhaust producing more thrust/particle than chemical rockets do. The exhaust being a tenuous gas however, the actual THRUST is very low (and the thrust/weight ratio even more so). Because it works in the vacuum of space and can run for years on end, the eventual velocity that this low thrust can impart on the craft is pretty impressive.

      --
      ----- One learns to itch where one can scratch.
    4. Re:A year to reach the moon? by GileadGreene · · Score: 4, Informative
      Actually, the maximum speed that you could theoretically reach is the same in both cases: c

      The difference is that it will take a chemical rocket much more propellant to get there, because it is far less efficient in its use of propellant mass (i.e. it has a lower specific impulse).

    5. Re:A year to reach the moon? by plj · · Score: 2, Funny

      I think they should have used Twin Ion Engines to get a little better acceleration...

      --
      “Wait for Hurd if you want something real” –Linus
    6. Re:A year to reach the moon? by WindBourne · · Score: 4, Informative

      There was no extra weight margins on the launch vehicle to do so. However, if you have a more powerful booster (i.e. lots more money), you can then get higher intial speed.

      This mission was to prove to EU that their ion engine worked. So they wanted it to keep running for quit some time. NASA did this be creating deep space one, which ran around picking up steam via its ion engine.

      Down the road, you can bet that EU will launch a number of deep space probes based on ion engines with high initial speeds.

      In addition, their will be a real push for micro sats with ion engines to control them. Makes a lot of sense to send these to other planets. think of 100 small satillites going though out jupitor or saturn planets. Or better yet, small micro sats around Mars providing surface to space communication, pictures, glp, etc. Send about 100 of these to orbit mars and we would have a very through pic of mars, moon, etc.

      --
      I prefer the "u" in honour as it seems to be missing these days.
    7. Re:A year to reach the moon? by bpd1069 · · Score: 2, Interesting

      I bet when this technology becomes the norm for deep space probes they will use the gravitational sling shot effects rather than attach boosters. Its going to take a while for any deep space probe to get to its destination, so why not use free (as in mass) to help you get there?

      I wonder how much of a boost the Sun can give you? (ala Star Trek)

      --
      --
    8. Re:A year to reach the moon? by Lawrence_Bird · · Score: 1

      shouldnt this have had a fairly substantial speed to start? Ie, the space torch orbits about 29,000 Km/hr which is about the minimum for low earth orbit.

    9. Re:A year to reach the moon? by someme2 · · Score: 1
      You can attach boosters to anything. It just costs more.
      Bravo! Bravo! Encore!
      From now on this line shall be known as my personal motto! It shall be enscribed in the family coat of arms. It shall be engraved in the family ring. It shall greet the trespasser when approaching the gates of the family manor.

      A timeless truth to live by. Bold words to guide us.

      Ah yes, and my new signature, too.
      --
      You can attach boosters to anything. It just costs more. -
      Anonymous Coward on Sunday November 07, @12:26PM
    10. Re:A year to reach the moon? by Brett+Buck · · Score: 5, Informative

      > The ultimate speed of ion propulsion is higher than that of
      > chemical propulsion.

      Depending of course on the fixed mass of the spacecraft, vs it's propellant mass, of course. You get more momentum change from given amount of propellant, but if you only had a teaspoon full of propellant, or the spacecraft was exceptionally massive, you wouldn't get more velocity.

      > But the mass being expelled at high speeds (the ions) is so
      > low, that accelleration is VERY slow. So it takes a long
      > time to get up to speed, but the maximum speed you can
      > theoretically reach is much greater than that of chemical
      > rockets.

      To expand, the measure of efficiency of a rocket engine is the specific impulse or ISP. It's how much momentum change you get per unit of propellant mass, and the usual unit is seconds (lb-sec/lb). The highest actually-achievable ISP from a chemical rocket is somewhere in the 475 seconds. The Saturn 5 first stage was more like about 350, and monopropellant thrusters used for many satellite propulsion systems is more like 150-180! That means that if you want to change the velocity a lot, you need a whole lot of propellant.

      I'm not sure which engine this particular program uses, but the ISP of the typical Xenon ion thruster is something like 1800. So you have to carry fantastically less propellant for a given velocity change, meaning it can weight less at liftoff, meaning you can use a weaker/cheaper booster.

      The downside is that you don't get something for nothing. It takes, not surprisingly, a whole lot of electrical power to make it go. So you put in 4000-5000 watts of power, and it only generates .04 lb of thrust - .64 of an ounce, pushing a spacecraft weighing thousands of pounds on the ground. So the acceleration is very small, meaning takes a long time to get going. The other downside is that the Xenon ions, although chemically pretty neutral, shoot out at such high speeds that anything that gets in the exhaust gets eaten away. This may or may not be an issue depending on there you put it relative to the rest of the spacecraft.

      Brett

    11. Re:A year to reach the moon? by 216pi · · Score: 1

      I thought nithing with a mass could be accelerated to c since it would take an infinite ammount of energy to accelerate it to c since the mass of the object grows the more it reaches c.

    12. Re:A year to reach the moon? by marco0009 · · Score: 1

      You are correct, as an object approaches the speed of light, the object's mass increases, requiring exponential quantities of fuel as the object approaches c.

      --
      Physics makes the world go 'round.
  6. Re:A year?! by Garion+Maki · · Score: 5, Informative

    unlike in the 60s and 70s, they are using ion engines for this mission, which can run of solar power.
    they give less trust/second, but they can keep burning for allot longer, since the sun gives a constant supply of fuel (in the form of electricity from solar panels).
    so you've got a smaller probe, which means easier to get into orbit from where it can fly on it's own power, so even tho it takes longer to get where you want, it will be cheaper to get it into orbit.

    btw, they are planning on bigger engines in the future, so hopefully they will go faster someday.

    --
    All indicators show that the human race is selectively breeding itself for stupidity.
  7. This is insane! by Anonymous Coward · · Score: 2, Funny

    Anyone still using film up there is going to be pissed when their exposures are ruined.

  8. It's from Wisconsin. by bs_02_06_02 · · Score: 3, Funny

    Everyone learns that the moon is made of cheese in the cartoons. I bet they'll say it's from Wisconsin.

    --
    -- No sig for you!
  9. Choose your cheeze by Nomeko · · Score: 1, Funny

    Finally we can have proofs that the moon is made out of cheese..

    I do hope it's cheddar..

  10. Possible Resolution to US moon landing hoax theory by jeoin · · Score: 5, Funny

    Will these guys be able to snag some good shots of the trash we left on the moon? Exluding the flag of course, which can't be trash cuz its on a stick.

    --
    Jeoin
  11. New tourist slogan by macrom · · Score: 3, Funny

    "Come to the moon and smell our dairy air!"

    Doesn't quite have the same ring...

  12. A Space Odyssey by Toutatis · · Score: 2, Funny

    Isn't that the way the monolith will be found?

    1. Re:A Space Odyssey by StuckInSyrup · · Score: 1

      That's 3 years too late. Our civilisation is doomed.

      --
      Ni.
    2. Re:A Space Odyssey by rossdee · · Score: 1

      The first monolith was found in the crater Tycho, because of its strong magnetic field. Hence Tycho Magnetic Anomoly (TMA).

  13. Re:Possible Resolution to US moon landing hoax the by Garion+Maki · · Score: 1

    if you know what the trash looks like on x-ray, then you could try searching for it... I think they are more interested in the rocks below the trash tho, so the camera's are probably designed to see that and not the surface (with the trash).

    --
    All indicators show that the human race is selectively breeding itself for stupidity.
  14. wow by flacco · · Score: 4, Funny

    sobering thought that that headline sounds exactly like something you might hear in a pulp sci-fi movie from the 50's...

    --
    pr0n - keeping monitor glass spotless since 1981.
    1. Re: wow by Black+Parrot · · Score: 2, Funny


      > sobering thought that that headline sounds exactly like something you might hear in a pulp sci-fi movie from the 50's...

      Science has finally caught up with fiction!

      --
      Sheesh, evil *and* a jerk. -- Jade
    2. Re: wow by nobbin · · Score: 1

      Now all we need is silver jumpsuits and hover cars!

  15. Re:This begs the question: by marsonist · · Score: 4, Insightful
    ... the beagle2 is laughing at your post all the way from mars

    In all seriousness it's nice to see some other serious large-scale attempts being made by countries other than the US and Russia. As with all things scientific, the more head working together the more we all learn.

  16. Re:A year?! by GileadGreene · · Score: 5, Informative
    Ion engines still use propellant (typically Xenon, but I haven't looked at what this particular mission is doing), they simply accelerate the propellant using electrostatic fields (in the case of ion engines) instead of chemical combustion. The key to ion engines isn't so much the solar power, as the fact that they have a much greater specific impulse (a rocket engineering term that relates to the efficiency with which propellant is used). Where a chemical engine may top out at ~400 s of specific impulse, ion engines have hit around 4000 s, or an order of magnitude greater propellant efficiency. That translates into a much smaller amount of propellant to do the same mission.

    The tradeoff is betwen the extra time it takes to get to the destination (due to the low thrust of an ion engine), and the reduced cost created by being able to launch a much smaller amount of mass into space in order to do the mission.

    btw, they are planning on bigger engines in the future, so hopefully they will go faster someday.

    The issue with ion enginer thrust is not so much size, as it is power. The thrust you get is directly proportional to the amount of power you can generate. If you're using solar arrays, then you're limited to something between 15-20 kW (the Boeing 702 has solar arrays that produce ~15 kW at end-of-life).

  17. From the article -- galactic bowling physics? by jdkane · · Score: 4, Insightful
    Smart's map should provide that data and show if scientists are right in believing that the Moon coalesced from a vast ring of debris generated when an ancient planet the size of Mars destroyed itself after crashing into Earth. Understanding the origins of the Moon will therefore give insights into the nature of our planet.

    Doesn't this mean earth should have some huge dent in it, and not be so round? Look at the sizes of Mars and Earth. Are you surprised earth is still here after a crash of that magnitude? I am. Maybe earth was a lot bigger before a Mars-like planet destroyed itself crashing into earth, but then I go back to my question about the roundness of the earth.

    Maybe someone more knowledgeable wants to talk about that. The article doesn't go into any great detail on that, which causes a lot of questions to be raised.

    1. Re:From the article -- galactic bowling physics? by Anonymous Coward · · Score: 1, Informative

      The eart wasn't a solid mass 4 billion years ago. It was molten.

    2. Re:From the article -- galactic bowling physics? by Anonymous Coward · · Score: 1, Interesting

      Any planet (or asteroid, or whatever) above a certain mass will become spherical under its own gravity. I don't have the numbers at hand, but it is surprisingly low, if I recall correctly it would have to be roughly 30 miles wide to have enough mass.

    3. Re:From the article -- galactic bowling physics? by gnatman64 · · Score: 1

      I saw something on the Science Channel about this, and the illustration they had involved the two planets hitting each other and swirling around a bit. Since the earth is mostly moltent rock, I think during the collision, a lot of that came in to fill it in. Plus this was a long long time ago, so the Earth could have covered it up by now. Not the best explaination I know, I can't say I understand it all myself.

    4. Re:From the article -- galactic bowling physics? by jdkane · · Score: 3, Informative
      Thanks. Your information enabled me to do some googling.

      For anybody who is interested, here's a theory (bottom of the page): "one theory says the moon formed when a big, molten chunk of crust was knocked/blown off from the rest of the planet". And much more info about it.

    5. Re:From the article -- galactic bowling physics? by DarkKnightRadick · · Score: 1

      Don't forget that the Earth was molten at the time, and even if it wasn't, look at what is left of the Yuccatan crater due to the forces of erosion. Wind and water are very, very powerful forces.

      --
      "There is a way that seems right to a man, but its end is the way of death." Proverbs 16:25 (NKJV)
    6. Re:From the article -- galactic bowling physics? by Anonymous Coward · · Score: 3, Informative

      There was once a theory that the Pacific Ocean was the hole left when the moon was pulled out of the Earth, but...

      There is a reason why small objects, like asteroids, are often irregular in shape, while large objects, like planets, tend to be nearly spherical. All parts of an object are attracted to each other by gravity, this tends to pull the object into a spherical shape. Above a certain size (which depends on the materials involved) the object is not strong enough to maintain its shape and collapses into a sphere. Also, even now, the Earth is mostly liquid or softened by the heat, and the collision would have released so much energy that it probably re-melted any part of the Earth that had solidified by then. Add to that the effects of billiions of years of plate tectonics and you would not expect to see the hole.

    7. Re:From the article -- galactic bowling physics? by The+Mgt · · Score: 4, Informative

      The earth wasn't a solid mass 4 billion years ago.
      It's still not a solid mass now.

    8. Re:From the article -- galactic bowling physics? by barakn · · Score: 4, Interesting
      Take a look at the moon. Those dark spots are the sites of enormous ancient impacts. They may have been holes briefly, but they then filled up with lakes of lava. As far as the Earth goes, the impact was so devastating that the outer layers of the Earth had to reform by falling back down.

      The following contains some links to mostly non-technical explanations of planetary roundness. I'd like to point out that part of this explanation, by "Derek Sears, professor of cosmochemistry at the University of Arkansas and editor of the journal Meteoritics and Planetary Science," is wrong. He says "Planets are round because their gravitational field acts as though it originates from the center of the body and pulls everything toward it." But this is a circular argument (pardon the pun). Generally a non-spherically symmetric distribution of matter doesn't have a gravitational field that acts as if it originates from the center of the body (the "center" being the center of mass). Spherically symmetric mass distributions do have this special property, so what Sears really implied is that planets that are already round will have gravitational fields that point towards the object's center of mass. This does absolutely nothing to address cases of objects that deviate from perfect roundness, i.e. all celestial bodies. This explanation by Dr. Sten Odenwald suffers from the same argument, and there's even a hint of it here. Nonetheless, these explanations are approximately true, and require bizarre shapes to break them.

      For example, imagine a homogenous, perfectly shaped doughnut (a torus with a circular cross section). At the center of the doughnut hole we'd feel no gravitational field at all (a perfectly balanced tug-of-war). But deviate from the exact center just a tiny amount, and the closer side of the doughnut becomes more attractive than the other. One suddenly experiences a gravitational field that points away from the center of mass.

      --
      "I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
    9. Re:From the article -- galactic bowling physics? by goodEvans · · Score: 1

      It was Lister playing Planet Pool. "Played for and got!"

    10. Re:From the article -- galactic bowling physics? by another_henry · · Score: 1
      For example, imagine a homogenous, perfectly shaped doughnut (a torus with a circular cross section). At the center of the doughnut hole we'd feel no gravitational field at all (a perfectly balanced tug-of-war). But deviate from the exact center just a tiny amount, and the closer side of the doughnut becomes more attractive than the other. One suddenly experiences a gravitational field that points away from the center of mass.

      Do you have a link to a proof of this? I know that this is not the case for a point inside a hollow spherical shell. At the center there's no field at all as you describe. As you move away from the center you are closer to the side of the sphere you experience a greater attractive force to that side, BUT there is now more mass "behind" you, i.e. a greater fraction of the sphere. The two effects cancel out perfectly so that there is no gravitational field ANYWHERE inside a sphere.

      Is the torus different? If so, why? Do the integrations just work out differently that way?

      Cheers

      Henry

      --
      "Studies have shown that people who eat peanuts live longer than those who do not eat."
    11. Re: From the article -- galactic bowling physics? by gidds · · Score: 1
      I don't know the deep maths (didn't do anything like that in my maths degree...) but one issue occurs to me: are objects with very different gravitational fields stable? If a roughly spherical shape is deformed (plastic flow due to gravity, impact, fragmentation, accretion, whatever), then its gravitational field will maintain a roughly spherical shape; but is that true of toroidal objects, for example?

      I wouldn't be surprised if the majority of shapes with radically non-spherical gravitational fields are unstable, and that the sort of spherical symmetry we see becomes extremely probable after enough disturbances and deformations.

      --

      Ceterum censeo subscriptionem esse delendam.

    12. Re:From the article -- galactic bowling physics? by barakn · · Score: 1

      At the moment, this is all I can find.

      --
      "I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
    13. Re:From the article -- galactic bowling physics? by maxwell+demon · · Score: 1

      Well, maybe that explains why we have continents which do not cover all of Earth's surface? (Reminder: The sea floor is a different material than the continents!)

      --
      The Tao of math: The numbers you can count are not the real numbers.
    14. Re:From the article -- galactic bowling physics? by another_henry · · Score: 1

      Thanks for the link. Very interesting.

      --
      "Studies have shown that people who eat peanuts live longer than those who do not eat."
  18. It's George Bush's Moon Mandate. by eBayDoug · · Score: 2, Funny

    Free X-rays for all Moon residents. Take that Canada!

    --
    Learn About Outsourcing. http://www.pioutsource.com
    1. Re:It's George Bush's Moon Mandate. by Anonymous Coward · · Score: 1, Informative

      This is an EUROPEAN spacecraft.

  19. Keep in mind.... by WindBourne · · Score: 3, Insightful

    that it is not the whole moon. There are areas that light, and x-rays do not reach. Sadly, that is the most inteesting as it may contain ice.

    --
    I prefer the "u" in honour as it seems to be missing these days.
    1. Re:Keep in mind.... by uberdave · · Score: 3, Informative

      That is not so. The sun shines (at one time or another) over the whole surface of the Moon, just like it shines over the whole surface of the Earth.

    2. Re:Keep in mind.... by MarkRose · · Score: 1

      There are some craters on the south pole of the moon which never get sunlight inside, which makes them a potentially good spot to collect volatile minerals. See more at Space.com's article on the south pole.

      --
      Be relentless!
  20. Re:British-made detectors? (OT!) by TWX · · Score: 1

    You know why the British don't build computers, right?

    They haven't figured out how to make them leak oil yet...

    --
    Do not look into laser with remaining eye.
  21. Just remember... by boola-boola · · Score: 2, Funny

    ....what happened when they probed Mars with X-rays! Watchout! (is Gary Sinise piloting?)

  22. Opposed by GNAW&NPS by AndroidCat · · Score: 1
    Scientists believe nuclear-powered ion-drives are their only real hope of exploring deep space, and vigorously support their development. Not surprisingly, anti-nuclear protesters, like the Global Network Against Weapons and Nuclear Power in Space, have pledged opposition.
    Too much time on Slashdot. Any group that starts GNA... automaticly activates my mental filters. (No great loss in the case of Huggers In Space.)
    --
    One line blog. I hear that they're called Twitters now.
  23. Biq == Round by DumbSwede · · Score: 4, Insightful
    Beyond a certain size, gravity pulls things into a spherical shape. The immense pressure makes the insides molten and irregular structures eventually sink down in. Mars has Mons Olympus, the tallest volcano in the solar system, this is because Mars is smaller and has less gravity than Earth. The larger the planet the more regular it has to be. Asteroids can be highly irregular because they haven't the size and gravity to collapse them into spheres.

    The mountains on Earth may appear huge to us insects on the surface, but from a distance the earth appears as smooth as a billiard ball.

    Ironically this event was so big, that unlike latter smaller hits, all evidence in the way of dents will be gone as the entire globe virtually liquefied and coalesced again. Though I wouldn't rule out some exotic mass distributions that might lend evidence of it.

    1. Re:Biq == Round by cheekyboy · · Score: 1

      Isnt the centre of any object like a planet void of all gravity? since all mass is around it equally, it cancels out.

      So on the surface you have strong gravity, but down in the centre, if you could carve out an empty area, you would be free floating like in space. Does this mean the centre is very loose and gooey, and objects that fall towards it fall right through. Anyone done a massive simulation of the earths core as if it was a liquid, not an iron solid?

      --
      Liberty freedom are no1, not dicks in suits.
  24. NO by mosb1000 · · Score: 1

    The first ion-powered spacecraft, Deep Space 1, was launched in 1998 by NASA. That's a lead of 5 years.

    1. Re:NO by Zaiff+Urgulbunger · · Score: 1

      ..and Russia is part of Europe! :-D

    2. Re:NO by mosb1000 · · Score: 1

      There's a difference between testing something in space, and actually using it. If it were enough just to test it, there'd be no reason to do it in space.

  25. MOD DOWN PARENT by Anonymous Coward · · Score: 4, Informative

    At each pole, there are such deep caverans that sun never reaches it. That includes X-rays and normal sun light. That is why it is possible for ice to be there. And yes, it is considered part of the surface.

  26. Re:A year?! by Mr2cents · · Score: 4, Informative

    SMART-1 has been making bigger and bigger orbits around the earth, because of the smaller thrust explained above. It goes faster and faster, and because the craft gets further from the earth, it becomes easier to get into a bigger orbit. So at first the orbits became larger very slowly, but the last months it has grown faster than ever before.

    The last months the orbit was also synchronized with the moon. The highest part of SMART-1's orbit coincided with the lowest point of the moon's orbit. This helps the craft to get an extra boost every month. Take a look at a graph of the orbit here.

    Oh, and they do have normal propellant onboard, there's some 70kg left iirc. I think it was installed in case the ion engine failed, but I'm not sure of that. It could also be to correct the initial orbit if the launcher would have placed it in a wrong one. Anyway I *hope* it will be used to attempt a soft landing after the mission is over.

    --
    "It's too bad that stupidity isn't painful." - Anton LaVey
  27. from 'dept' topic by deunan_k · · Score: 2, Interesting

    Posted by CmdrTaco on 01:06 AM -- Monday November 08 2004
    from the dept.


    I've always read the 'from the so and so and whatever dept' cuz it's humourously funny and cynic at the same time.

    This time, it's just plain ol' from the dept. I just wonder, whether it is an oversight or CmdrTaco really does not have anything witty to say about it? :-P

    I know, I know it is off-topic, mod me down then.. I probably deserve it.


    --
    Will sys-admin for food
  28. The ion drive is the real story by SimURL · · Score: 5, Interesting

    Ion drive technology allows you to explore space in ways that chemical rockets simply can't.

    Quoting from the article,
    "We have shown that even a small ion engine like Smart's can get us across space. Now we are planning to build space telescopes and robot probes to planets such as Mercury, using bigger and more powerful ion engines. These will take years off space-travel times. Instead of decades-long missions, we will take only a couple of years to cross space for future projects."

    But,
    "Ion engines need electricity and only solar panels can provide enough at present. So ion engine missions will be restricted to planets and moons near the Sun."

    So the solution to deep space exploration is nuclear-powered ion-drives and NASA is working on it.

    1. Re:The ion drive is the real story by snake_dad · · Score: 1

      Specifically, the proposed Jupiter Icy Moons Orbiter mission. Browse the site if you're interested, lots of info there, and linked from there.

      --
      karma capped .sig seeking available Slashdot poster for long-term relationship.
    2. Re:The ion drive is the real story by Tsalg · · Score: 1

      What slows down the nuclear-powered reactors in space is not much the technological problem involved but the political issue related to the use of nuclear energy in space. For a good report on thermoionics read e.g. http://www.nap.edu/books/030908282X/html/ (Thermionics Quo Vadis?) Also keep an eye on the eccentric but pragmatic Nobel laureate Carlo Rubbia who brought up the novel concept of utilizing the highly energetic fragments produced by nuclear fission to heat a gas. Extremely high temperatures produced in this reaction would enable faster interplanetary travel. Though interestingly he also states that this technology is not suited for interstellar travel (see http://www.spacedaily.com/news/fuel-01a.html The Italian Space Agency has started feasability studies on this.

    3. Re:The ion drive is the real story by Brett+Buck · · Score: 1

      > Quoting from the article, "We have shown that even a small
      > ion engine like Smart's can get us across space. Now we are
      > planning to build space telescopes and robot probes to
      > planets such as Mercury, using bigger and more powerful ion
      > engines. These will take years off space-travel times.
      > Instead of decades-long missions, we will take only a
      > couple of years to cross space for future projects."

      Bear in mind ESA exceptionally strong tendency to claim credit for things that they have just done as breakthrough firsts - when in fact, several Western projects have used ion thrusters before now (Deep Space 2, and several commercial commsats), and that was because the Russians had developed it years ago. It's a "breakthrough" for them in several ways, but they have not advanced technology. They're FAR worse than NASA or the DoD in that respect.

      I get a kick out of all the breakthrough discoveries claimed for Mars Express - and also how they were lining up to take credit for Beagle 2 (and how much better it was than those redneck colonials and their crappy rovers), then dropped the entire topic like a hot potato when it crapped out. Then it became a "auxiliary package carried by Mars Express" (which in reality, it was the entire time).

      > But, "Ion engines need electricity and only solar panels
      > can provide enough at present. So ion engine missions will
      > be restricted to planets and moons near the Sun."
      >
      > So the solution to deep space exploration is
      > nuclear-powered ion-drives and NASA is working on it.

      Indeed. "Only solar panels prove enough at present". Right, if you intentionally restrict yourself based on ideology. The Russkies have flown MANY space-based fission reactors. And then there's this:

      http://www.jpl.nasa.gov/jimo/

      Brett

  29. Basic rocket physics makes it a bit clearer by Evil+Pete · · Score: 4, Informative

    Look up any reasonable book on mechanics and you will find a formula for the final velocity of rockets that have a empty mass M, mass of fuel m, and have an exhaust velocity v. The final velocity of the vehicle is ...

    V = v . ln( (M + m)/M )

    In other words ion rockets will beat chemical rockets because they eject their exhaust at a reasonable fraction of c, whereas chemical rockets have exhaust velocities more like velocities we see on earth (e.g. bullets). So chemical rockets need lots of mass, but that's ok because they throw out lots of mass. Trouble getting to space is expensive ... each kilo of fuel you put in orbit better be wisely used ... so in space ion rockets make sense (apart from the fact you can't use them on Earth anyway ... wouldn't be able to lift off even).

    Hope this makes things a bit clearer.

    --
    Bitter and proud of it.
  30. Re:This begs the question: by snake_dad · · Score: 1

    This is hardly a large scale attempt... It is an interesting project and new stuff about Ion propulsion will be learned, but a huge project it is not. If you want large-scale European space efforts, look up "Rosetta".

    --
    karma capped .sig seeking available Slashdot poster for long-term relationship.
  31. Ion vs. Chemical thrust by gtkuhn · · Score: 1

    Ion engines become more efficient the longer the distance travelled. The short hop to the moon may take longer with a 'slow' ion engine, but going to, say, Alpha-Centauri would allow enough time for that same little ion engine to appraoch a signifigant percentage of c. It would take more chemical fuel than the earth could provide to approach that (assuming you had to carry all that fuel with you).

  32. Re:Which reminds me.... by Dr.Knackerator · · Score: 1

    im sorry you lot have to chill your beer to very cold to take the taste of chemicals and/or general awfulness away.

    give me pint of theakstons old peculiar instead of chilled buttweiser anyday

  33. an entire year? by gandalphthegreen · · Score: 1

    A year to get to the moon? Come on, the U.S. got there in three days over 30 years ago.

    1. Re:an entire year? by maxwell+demon · · Score: 1

      Yes, but that did cost them a lot more money.

      --
      The Tao of math: The numbers you can count are not the real numbers.
  34. Re:Which reminds me.... by cheekyboy · · Score: 1

    I thought it was because it never gets WARM in most of britain, so just leave your KEG outside in the shade or in a water tank.

    --
    Liberty freedom are no1, not dicks in suits.
  35. Re:A year?! by matts-reign · · Score: 1

    The link to the orbit graph doesn't work for me

    Working link here
    you added a 1 to the end of the url

    --
    Waffles rock.
  36. Re:A year?! by Mr2cents · · Score: 1

    Oops! Thanks for the correction.

    --
    "It's too bad that stupidity isn't painful." - Anton LaVey
  37. Gooey, Hot, Weightless and EXTREME PRESSURE by DumbSwede · · Score: 3, Informative
    I no geologist or seismologist, but they believe the core is mostly iron of a taffy like consistency. The heat to keep it so comes from 2 sources: 1. The original condensation of the planet (miles of mantel and crust are good insulators keeping the heat in for billions of years). 2. The decay of heavy elements like uranium, which would offset the slow cooling process, mentioned in one.

    Recent speculation is that the very center has a high ratio of Uranium, enough so that the pressure actually creates a self-sustaining natural nuclear reactor. When it gets too hot it diffuses and shuts down, only to coalesce and restart again (never a big boom). This starting and stopping of the nuclear processes at the Earth's core may be responsible for our planets large magnetic field, and occasional shut downs and reversals of the magnetic field as this nuclear process fluctuates.

    You're right that the center would be weightless, but under more pressure than we can possible create in the lab with the best diamond anvils. It only takes a few miles of crust to crush carbon to diamonds, and here we are talking 8,000 miles of rock pressing down. Though the rock (iron) at the center isn't adding any additional pressure, it has thousands of miles of rock above it that is. Quite the hellish place.

    BTW, I don't know how I typed Biq in my rirst post when I meant to type Big (no one seems to have noticed)

    1. Re:Gooey, Hot, Weightless and EXTREME PRESSURE by barakn · · Score: 1

      You're confusing the Oklo natural reactor which occurred near the surface in Africa with the Earth's core. These are entirely separate. The core is iron, not uranium (for the most part). While radioactive materials are responsible for keeping the Earth's interior warm, there's no "reactor" involved (unstable isotopes really don't need help to decay).

      --
      "I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
    2. Re:Gooey, Hot, Weightless and EXTREME PRESSURE by meringuoid · · Score: 1
      Recent speculation is that the very center has a high ratio of Uranium, enough so that the pressure actually creates a self-sustaining natural nuclear reactor.

      I find this implausible. Surely SNO and Kamiokande should detect a massive neutrino flux from such a large reaction? Kamiokande can pick up neutrino fluxes from the nuclear reactors across east Asia, so the flux from a monster reaction in the Earth's core should also be detectable.

      A flux from the Earth's core would be easy to distinguish from others. Solar neutrinos change direction over a 24-hour period, cosmic neutrinos are evenly spread across the sky, but hypothetical Earth-core neutrinos would always come from directly below.

      --
      Real Daleks don't climb stairs - they level the building.
  38. Correction to the Correction by DumbSwede · · Score: 1
    Damn now I've typed "rirst" instead of first.

    Gotta learn to use that preview button.

    Sheesh, this is almost recursive.

  39. Re:MOD parent down by jmcmunn · · Score: 1

    J-O-K-E, ever heard of it?

  40. TIE (Twin Ion Engine) Fighter? by Orbital+Observer · · Score: 1

    Perhaps George Lucas had something to do with it...

    --
    ---- I have nothing more to add.
  41. ESA doesn't have a moon capable rocket by tjstork · · Score: 2, Interesting

    It's fairly simple. The ESA doesn't have a rocket capable of putting a payload on a lunar path. AFAIK Arianne is really only good for LEO stuff. The only two countries with lunar capable rockets are I believe the Russians and the USA. Of course, the ultimate lunar capable rocket, the Saturn V, is dead, so all we can do is cross our fingers and hope that NASA will come to its senses and bring back the big dumb booster.

    --
    This is my sig.
    1. Re:ESA doesn't have a moon capable rocket by catfry · · Score: 1

      Thre ariane 5 standard is able to put about a 3 metric tonne payload on a moon rendezvous. The reason the Smart-1 was put in orbit the way it was, was simply because the probe was one of three sattelites, two of which were destined for geostationary orbit (All of course in order to save cash).

  42. Accreted Rings by CowboyRobot · · Score: 1

    Can any astrogeologists explain why the assumption is that the Moon is a result of debris from a two-planet crash as opposed to regular accretion of debris the way moons were formed on the other planets? Billions of years ago, each planet was a gradually coalescing disc, and the jovian planets still have evidence of this in their rings. The closer planets instead have moons - I assume because the Sun's gravity is stronger at our closer distance from the Sun, and caused the rings of the closer planets to aggregate as the debris rotated around the Earth more quickly when approaching the Sun and more slowly when moving away. I know our Moon is rather large compared to many others, but the idea of a two-planet crash seems unlikely given how the planets seemed to have found their natural distances from each other without some missing rogue planet threatening to collide.

    --
    every stain tells a story
    1. Re:Accreted Rings by cjameshuff · · Score: 2, Insightful

      It's really freaking big. Mercury and Venus don't have any moons, and the moons of Mars appear to be captured asteroids...relatively tiny rocks not big enough to form themselves into spheres. The Earth-Moon system is nearly a double planet. Of the inner planets, Earth is the only one with a decent moon...and it's a monster compared to the planet.

      In any case, the planets you see now are just the ones that stayed in the system. Material didn't just cleanly accrete directly into the existing bodies. Most of the objects formed were kicked out of the system by interactions with other bodies, or were absorbed into other objects or the Sun itself. What you see is the final result of a great many collisions and near-miss interactions. (And the present orbits aren't truly stable, just stable enough not to worry about. I think the lifetime of the present orbits of the planets is greater than that of the sun itself. Maybe a little less for the Moon.)

      The rings of the gas giants are likely far younger than the planets themselves, they are almost certainly not leftover material from the accretion. And they do have moons, lots of them...each giant has dozens, while the entire inner system has 3. However, even taken together, the moons and rings of each giant aren't much compared to the planet itself.

  43. Not confusing Anything by DumbSwede · · Score: 2, Interesting
    Not confusing anything. I'm aware of the Oklo natural reactor, but I speak of a much more recent (and controversial) theory. When first proposed it was dismissed as total bunk, but it has gained support over the last five years. Much more respectable than cold-fusion, but hard to put odds on whether it will prove out or not. It is the inspiration for the movie "The Core"

    Here is a link to a Discovery article
    Nuclear Planet
    Is there a five-mile-wide ball of hellaciously hot uranium seething at the center of the Earth?

    Yes the core is mostly Iron, but it's not pure iron. I mentioned iron as a core material in my post.

  44. Re:Learn what?? by TheMeuge · · Score: 1

    I hate to sound like a cliche, but you are extremely shortsighted. Aside from the usual 'we explore because it's in our nature' explanation, there are a ton more reasons for space exploration. Largely, it is not even about the ends, but rather the means. The number of technologies that came out of the space program, including developments in electronics and materials science are probably of more benefit to the world than any direct findings that came out as the result of the space program.

  45. Re:British-made detectors? (OT!) by N+Monkey · · Score: 1

    OT I know but...

    You know why the British don't build computers, right?

    Have you ever heard of ARM? I've heard a rumour, apparently, that are one or two of these CPUs in the world.

  46. Cool by GoLLuM.no · · Score: 1

    Cool ! I hope the finished maps can be downloaded from their website :) I would like to make some flyby videos in 3dsmax or something. Since everything is grey on the moon we dont need no textures either I would guess.

  47. There are already 3 Bases on the moon! by guru512 · · Score: 1

    The Alien Moonbase as reported by Neil Armstrong. http://www.beyondtopsecret.com/UFO_Moon_Base.html

    The German Nazi Base on the Moon http://www.beyondtopsecret.com/UFO_German_Moon_Bas e.html

    and the Supreme Headquarters Alien Defence Organisation http://www.ufoseries.com/hardware/lunarLanding-M.j pg

  48. Re:British-made detectors? (OT!) by lisaparratt · · Score: 1

    I think the British Science Mueseum has a computer designed a couple of centuries ago that disagrees with you.

  49. I'll be damned by barakn · · Score: 1

    You're right. Its hard to find scientists who support the idea though. Mostly because its a solution looking for a problem. Field reversals have already been seen in computer models of the dynamo theory.

    --
    "I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show