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Space Science

NASA Gravity Probe Set for Launch 250

Posted by michael
from the weighty-concepts dept.
The Real Dr John writes "NASA announced yesterday that its longest running program, Gravity Probe B, was ready and scheduled for launch on April 17th. The project has taken 44 years to complete, at a cost of approximately $700 million. The reason for the high cost is that the probe contains the most sensitive gyroscopic equipment ever created, which will be used to test Einstein's theory of gravity. Einstein predicted that the gravity created by a large body warped space-time, but he also predicted that if the large body was rotating it would create a drag effect on space-time known as frame dragging. Gravity Probe B will be able to test Einstein's theory using Earth's relatively small gravitational field because the instruments are so sensitive."
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NASA Gravity Probe Set for Launch

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  • by Anonymous Coward on Saturday April 03, 2004 @01:38PM (#8756816)
    Seems God plays roulette even if he doesn't play dice.
  • Too sensitive (Score:5, Interesting)

    by pholower (739868) <longwoodtrail AT yahoo DOT com> on Saturday April 03, 2004 @01:38PM (#8756818) Homepage Journal
    The slightest bit of interference could deem it unusable data with as much precision the gyroscopes will be operating. I have a feeling that even interference they are not thinking about (who am I kidding, this is nasa) such as solar radiation, and the magnetic north shift (which as of late, has been about 10 miles a year) will alter the results of this test dramaticly.
    • by David Hume (200499) on Saturday April 03, 2004 @02:02PM (#8756981) Homepage

      In addition to the sensitivity problem, I wonder if this could be an experiment whose time has passed.

      In 1995, the GP-B was described as the "only experiment ever devised to test [the existence of frame-dragging] [sfsu.edu]."

      However, in 1997 NASA announced that it had successfully tested frame dragging [sfsu.edu]. See also here [scienceweb.org].


      • Sorry to follow-up on my own post. Caught a link error. I stated:

        However, in 1997 NASA announced that

        it had successfully tested frame dragging [sfsu.edu]. See also here [scienceweb.org].

        That should instead read:

        However, in 1997 NASA announced that

        it had successfully tested frame dragging [nasa.gov]. See also here [scienceweb.org].

        • "If our interpretation is correct, it could demonstrate the presence of frame dragging near spinning black holes," said Cui."

          Not this is an observation, not a TEST. So the two statements are not in conflict. We an observe a thing, but to test for it is to demonstrate a higher order of understanding.
      • by Anonymous Coward
        Your 1997 NASA link actually goes to the previous 1995 statement.

        Anyway, while we do have astrophysical tests of frame-dragging, they're not direct. There's a big difference between trying to infer the effect by observing the orbits of matter outside a black hole, and actually putting a gyroscope into a frame-dragging field and seeing what happens to it. In particular, direct measurement is much more sensitive. Astrophysical tests can merely suggest the existence of frame dragging. GPB can quantitative
      • If you read the write-up on the 1997 discovery, it seems that they detected *evidence* of frame dragging, while GP-B is designed to *measure* frame dragging.

        Not quite the same thing.
    • Re:Too sensitive (Score:5, Informative)

      by QuantumET (54936) on Saturday April 03, 2004 @02:46PM (#8757237)
      Having worked on GP-B for a bit...

      Just about all of the engineering that's gone into the project is to eliminate interference from everything else; those gyros are going to be just about the best-isolated objects we've ever made.

      Yes, they need to account for solar wind, as well as atmospheric drag, as small as it is at that height. This is done by flying the satellite drag-free; one of the gyros free-floats inside its housing, and if it starts to drift off-center, the satellite fires its thrusters to reposition _the satellite_ so that the free-floating gyro is again in the center of its cavity.

      This way, any external force on the satellite can be removed, since the gyro is shielded from them by the bulk of the satellite, and the satellite then follows the gyro on a perfect gravitational orbit.

      Magnetic fields are filtered out to some ungodly factor; the leftover fields inside the science probe are on the of 10^-17 gauss.

      They also account for micrometeorites, electric noise, and many other error sources. There's a reason this has taken 40 years.

      • Re:Too sensitive (Score:3, Interesting)

        by jabberjaw (683624)
        Given that you have worked on this project, would you care to comment on the other projects such as SUMO [physicsweb.org] and LATOR [nasa.gov] which also aim to test Einstein's relativity?
        • Re:Too sensitive (Score:5, Informative)

          by QuantumET (54936) on Saturday April 03, 2004 @03:39PM (#8757530)
          Well, I'm not a physicist; I just played around on the hardware.

          But it looks like to me that LATOR is a very-high precision test of what's already been tested several times: the exact amount of curvature of spacetime that heavy objects create.

          GP-B tests the effects of frame dragging, which is a completely separate effect.

          As to SUMO, I wouldn't be able to say what kind of effect a Lorentz-transform symmetry breaking would cause, and whether GP-B's results could be affected by that. But the tests seem to be fundamentally about clock rates at various moving frames, which is more of a special relativity test (as the Loretz transform comes from special relativity). GP-B is about general relativity, and specifically about spin, which seems to be relatively untested ground.
      • Re:Too sensitive (Score:2, Interesting)

        by Anonymous Coward
        This is sooo cool! Very elegant. I notice from some of the numbers that it appears to be using superfluid helium (current cryostat temp ~1.77k)

        Will it be using a high or low, circular or elliptical, equatorial or inclined orbit?
        (i'm sure the info is at the GP-B site, i just missed it)

        The electrostatic suspension system also reminds me bit of a Stargate SG-1 episode, Serpent's Venom.

        kudos and good luck. You launch on my birthday.

        • Re:Too sensitive (Score:5, Informative)

          by QuantumET (54936) on Saturday April 03, 2004 @03:42PM (#8757547)
          Polar orbit, with satellite roll axis fixed on a guide star for a good reference frame. I think it's about as circular as they can make it.

          And yeah, it's superfluid helium, enough for about 18 months given the boil-off rate (it boils off continually to maintain dewar temperature; the boiled-off gas is actually used in the precision manouvering thrusters)

          And the suspension system is a rather scary system... it has to ramp from barely touching the gyros to making sure they don't impact the cavity walls when a micrometeorite hits almost instantaneously. And there's only about a millimeter of clearance there. And the gyros spin at 10,000 rpm. You don't want them touching the walls.

    • Behold! 700 million dollars an 40+ years worth of precise engineering is ripped apart on slashdot!

      I seriously don't think an arm-chair physicist can take this project down. Whatever you think of, they've already thought of it.
  • Gravity dragging? (Score:3, Informative)

    by AKAImBatman (238306) <akaimbatman@gma i l . c om> on Saturday April 03, 2004 @01:38PM (#8756819) Homepage Journal
    large body was rotating it would create a drag effect on space-time known as frame dragging.

    I think we're all familiar with time dialation (if you haven't read "The Elegent Universe", you're missing the best explanation of *why* time dislation occurs that I have ever heard), but what is frame dragging? What kind of effects does it have on the observer?

    • Re:Gravity dragging? (Score:5, Informative)

      by pholower (739868) * <longwoodtrail AT yahoo DOT com> on Saturday April 03, 2004 @01:42PM (#8756852) Homepage Journal
      The earth is a mass-energy. According to General Relativity, as a mass-energy, it should create a little dimple in the local space-time fabric. It is also theorized that the daily rotation of the earth causes a twisting of the local space-time fabric. This effect is known as frame dragging and it should manifest itself as a force that pushes a gyroscope's axis out of alignment as it orbits the Earth. [GP-B will be using four small, incredibly precise gyroscopes as its main tool for detection of relativistic effects on the local space-time fabric.] Gravity Probe B will attempt to measure the force, gravitomagnetism, giving scientists an important insight into how it might affect objects that are much larger than ping pong balls, such as black holes. At the same time, the gyroscopes will experience a much bigger force - the geodetic effect - which is a result of the warping of space-time predicted by Einstein. This force will tend to push their axes in a direction perpendicular to the frame-dragging effect which allow it to be measured separately. The geodetic effect is hundreds of times bigger than frame dragging and the experiment should measure its size with an accuracy of 0.01 per cent the most severe test of general relativity ever undertaken.
    • Re:Gravity dragging? (Score:5, Interesting)

      by Anonymous Coward on Saturday April 03, 2004 @01:53PM (#8756927)
      Frame dragging occurs when a massive object is rotating. It turns out that a when a body rotates, it 'pulls' the surroundng space around in the direction of rotation. This means that if you drop an object toward the rotating body, it will not just fall radially tooward the centre but will aquire a component of velocity tangental to the surface.

      Of course, this effect also applies to light rays, so the question of what one would actually see is a bit tricky.

      Another situation that 'frame dragging' alters from classical theory is orbits around the body. Imagine an observer fixed at a particular set of coordinates in orbit around a rotatng body. If they send photons in orbits around the body opposite directions, they will not be recieved at the same time; that which travels in the direction of rotation will arrive sooner than that travelling in the opposite direction. In extreme cases, it is possible that the photon opposing the direction of motion, although locally moving at the speed of light, won't appear to move at all from the point of view of a distant observer.
    • It sounds more complicated than it is because it is usually phrased in geometrical language.

      You may be aware that elctricity and magnetism are intimately connected. In one sense magnetism is an extra force that moving electrical charges exert on other moving electrical charges.

      Einstein discovered that gravity can work much the same way. Moving gravitational charges (i.e. masses) generate an extra force on other moving masses. This extra force is sometimes refered to a gravito-magnetism and is usually v
  • Interesting... (Score:2, Interesting)

    by Mr. Certainly (762748)
    It'll be interesting what the results would be -- was Albert right about all these theories?

    More interestingly enough, what can we use this for? No, this isn't sarcasm, but how can we apply these scientific principals to help our daily lives and to understand the universe better?

    Comments anyone?

    • If you look on the web site, you'll see they have already contributed to the technology sector. http://einstein.stanford.edu/content/spinoffs/tech nology.html
  • Gravity Probe A (Score:2, Interesting)

    by Anonymous Coward
    So what happend to Gravity Probe A?

    (sorry had to ask)
  • by spacepimp (664856) on Saturday April 03, 2004 @01:41PM (#8756845) Homepage
    i viewed the elegant universe, the other day by brian green, and am currently reading the text, much has changed in theory over the last 44 years, string theory for one, currently holds the possiblility that gravtiy strings are looped and therefore capable of jumping from our current brane/dimension. will this allow and or test for this theory or is the device antiquated before deployment? I guess thats a risk involved with such a long dev cycle. hopefully it will take this into account, or has the CERN project already made this redundant?
    • by Anonymous Coward on Saturday April 03, 2004 @02:27PM (#8757136)

      will [GPB] allow and or test for [braneworld] theory or is the device antiquated before deployment?


      No, it won't serve as a test of string theory braneworld scenarios, and no, that doesn't make it "antiquated", either. There are lots of reasons to do the experiment, other than its ability to verify somebody's speculative pet theory. (Heck, string theory doesn't even predict that our universe is confined to a brane; it's just a possibility within string theory.)

      The point of GPB is merely to test the accuracy of general relativity's predictions. If GR is wrong, there are many ways it could be wrong, and thus GPB might be able to tell us which way is correct, or rule out alternative theories that predict effects that aren't measured.
    • Well, as I understand it, string theory is incomplete and does not yet necessarily replace relativity, even though it aims to do that, since it's still untested/the math hasn't been worked out/something like that. So the device probably isn't antiquated. Yet, anyway.
      • From what little I understand of string theory, it's the other way around: the math works out perfectly, but there's no testable hypotheses, thus it isn't going to displace current theories among the majority of physicists until some such test can be devised.
  • Well if it doesn't work, I'll buy the gyroscopic equipment and use it to balance a cup of coffee inside my car, to avoid spills.

    Did I mention that my car is a Maybach 62, which costs $380,000? With an expensive car like that, you want to make sure the upholstery doesn't get dirty.

  • Eww! (Score:4, Funny)

    by tigress (48157) <rot13.fcnzgenc03@8in.net> on Saturday April 03, 2004 @01:44PM (#8756861)
    Einstein predicted that the gravity created by a large body warped space-time, but he also predicted that if the large body was rotating it would create a drag effect on space-time known as frame dragging.

    AAagh! Mental images of my ex dancing! *SHUDDER!*
  • Bureaucracy (Score:5, Funny)

    by slipgun (316092) on Saturday April 03, 2004 @01:47PM (#8756888)
    NASA announced yesterday that its longest running program, Wooden Block B, was ready and scheduled for dropping off the Empire State Building on April 17th. The project has taken 44 years to complete, at a cost of approximately $700 million. The reason for the high cost is that the probe contains the most expensive wood ever created, which will be used to test Newton's theory of gravity. Newton predicted that an attractive force known as 'gravity' will act between any two bodies. Wooden Block B will be able to test Newton's theory using Earth's gravitational field, and a very tall building.
  • Finally! (Score:4, Informative)

    by Animats (122034) on Saturday April 03, 2004 @01:48PM (#8756892) Homepage
    That project has been kicking around Stanford for decades. I saw that satellite under construction almost twenty years ago. It's basically a subsidy program for PhD students, not a satellite program. If that job had been outsourced to Hughes or Loral, it would have launched decades ago.
  • Pardon the ignorance but can somebody spell out what impact the findings of this probe will have Science in general?
    • Re:Ignoramus (Score:2, Informative)

      by gnuman99 (746007)
      General Relativity is one of the pillars of physics (ther other being the Quantum Theory).

      The impact on science is quite straightforward. as this is science. Science is about testing theories. Without that, science is just a religion.

      GR predicted that Newtonian mechanics are too simplistic. This is one of the tests that verifies this. Anyway, any applications of this test are another 50 or 500 years away. Just like the applications of discovery of electrons (typing away on my electron machine).

  • by rixstep (611236)
    Wow. That gravity probe is pretty heavy stuff. I remember them discussing it in that movie 'The Incredible Lightness of Being'. Far out.
  • by igrp (732252) on Saturday April 03, 2004 @02:02PM (#8756978)
    According to this BBC article [bbc.co.uk], the mission completion is supposed to be in 16 months.

    I found the following quote especially interesting:

    Francis Everitt, the principal investigator of the project, said: "Aren't Einstein's theories all established and confirmed? After all it was 50 years ago that Einstein himself died and it's 100 years next year when he developed his first theory of relativity. Don't we already know it all? The answer is no."

    I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified. And, quite frankly, I'm surprised that there isn't much more VC and grant money available to go and do research on stuff like this. Afterall, these projects are quite prestigious.

    • by Anonymous Coward on Saturday April 03, 2004 @02:41PM (#8757210)

      "Aren't Einstein's theories all established and confirmed? After all it was 50 years ago that Einstein himself died and it's 100 years next year when he developed his first theory of relativity. Don't we already know it all? The answer is no."

      I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified.


      All of them. It's not possible to perform every test of a theory that can be performed, nor is it possible to perform any given test to an arbitrarily high precision. There are tests of quantum electrodynamics that are accurate to 11 decimal places, but people still test QED, because we never know whether it goes wrong at the 12th place, or whether there's some new phenomenon that QED doesn't predict. Likewise, there are many tests of general relativity, many of which are very accurate, and nobody doubt's the theory's general validity --- but that doesn't mean that there might not be small deviations out there that point the way to an even better theory.
    • And, quite frankly, I'm surprised that there isn't much more VC and grant money available to go and do research on stuff like this. Afterall, these projects are quite prestigious.

      If it takes $100 million to find mistakes in the theory, there is very little practical incentive to research it, since more than likely it will take many times $100 million to exploit any of those newly discovered differences for practical gain. Put another way, if existing theories are good enough for all but the most precise
    • I thought frame drag was one of the last big tests.

      Einstein's theories have been heavily tested and IIRC, so far hasn't been found to be invalid. There are other theories that explain the way things are. Einstein's theories I think are most accepted because of how well it tested so far.

      VC money is much more about return on investment than prestige. Funding science projects doesn't normally bring much money or prestige, IMO.
    • I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified.

      Einstein also said that nothing could travel faster than light, maybe we will get to test that someday ?...
    • by UnrepentantHarlequin (766870) on Saturday April 03, 2004 @05:42PM (#8758270)
      I wonder what other theories that are generally accepted throughout the scientific community have not been completely tested and/or verified.

      All of them.

      It is not possible to completely test and verify anything. That's the nature of reality. A theory is defined as an explanation that has been thorougly tested and is widely accepted by people knowledgable in that field, but it's an essential part of science that nothing is ever proved beyond all doubt; there is always room for change if additional data comes to light, or a better explanation for existing data is devised.

      One of my pet peeves is the common misuse of "theory" to mean "hypothesis" -- an untested conjecture. This popular misconception then leads to scientific knowledge being dismissed as "it's only a theory" by people who don't understand what a theory actually is, and assume that the Theory of (fill in the blank) is a mere hypothesis.
    • I'm surprised that there isn't much more VC and grant money available to go and do research on stuff like this.

      VC money is all about ego and self. I don't think you'll see any VC money go to this.

      However, you'll certainly see VCs making money off of projects like this.
  • by Tablizer (95088) on Saturday April 03, 2004 @02:12PM (#8757047) Journal
    They should launch anti-gravity probes. Wouldn't even need rockets and save us taxpayers some bucks.
  • Is this a NASA thing or a Stanford thing?

    Every article I found about it on NASA ends with "For more information, visit http://einstein.stanford.edu/".

  • There was a test (Score:2, Insightful)

    by MrRuslan (767128)
    Someone setup an experiment about 10 years ago with 2 highly percise clocks one was set up on the top of a tall build and the other was set at the bottom...they ticked and stoped at the same exact and the clock on top of the building was very slightly behind the clock on the bottom...so I guess that should say something about his theory of relativaty.
  • by hak1du (761835) on Saturday April 03, 2004 @03:39PM (#8757523) Journal
    Many theories of gravity, even those disagreeing wildly with GR, have frame dragging. If there are no decent alternative hypotheses that make different predictions, is it really worth spending hundreds of millions of dollars on conducting this experiment?
  • by tinrobot (314936) on Saturday April 03, 2004 @03:44PM (#8757564)
    From the article :

    Since the project was conceived by three scientists after a naked midday swim at Stanford University's pool, more than 1,000 people have worked on the satellite. Two of its founders are dead. More than 90 people have earned their doctorates working on the project.

    Naked physicists... wow... with the current administration in charge, this project would have never been approved.
  • Very Cool Experiment (Score:3, Interesting)

    by QuantumFTL (197300) * <justin DOT wick AT gmail DOT com> on Saturday April 03, 2004 @03:45PM (#8757577)
    Very cool experiment (well worth the cash) however I think the LATOR [slashdot.org] relativity experiment would be much more interesting and scientifically useful.

    And probably not much more expensive.

    LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics. LATOR also seems to be much more accurate, and less likely to receive interference.

    I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.

    Cheers,
    Justin Wick
    • by Anonymous Coward

      LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics.

      Or rather, it might conceivably be capable of testing some rather speculative models within string theory; there are plenty of other string theory models that LATOR can't test, and no good reason to believe in one over the other. That's one of the problems with string theory: it's too flexible. People can cook up all sorts of artificial string models, but that doesn't mean that any

      • by QuantumFTL (197300) * <justin DOT wick AT gmail DOT com> on Saturday April 03, 2004 @09:49PM (#8759403)
        Wow, nice to see an anon-post that's insightful for once!

        Bold is me, italics is parent.

        LATOR is capable of testing string theory, an exciting but so far merely theoretical development in high energy physics.

        Or rather, it might conceivably be capable of testing some rather speculative models within string theory; there are plenty of other string theory models that LATOR can't test, and no good reason to believe in one over the other. That's one of the problems with string theory: it's too flexible. People can cook up all sorts of artificial string models, but that doesn't mean that any of those models are likely to be true, even if string theory itself is true.

        It will test some of the most reasonable/popular models, which is a big step up from having never been tested at all.

        LATOR also seems to be much more accurate,

        It is, but it's also a test of something that we've already measured extensively (albeit much more sensitively). Our existing measurements of frame-dragging are extremely crude.

        Quoting this page:
        Abstract: LATOR is a space-based experiment to accurately measure the gravitational deflectional deflection of light. The experiment uses two laser bearing spacecraft at the opposite side of the Sun and a very long baseline heterodyne interferometer to measure the angle at an accuracy of 0.2 uas. Combining this measurement with laser ranging from Earth to both spacecraft, gravitational deflection can be made with an accuracy 5000 times better than previously done and will allow measurements of the second order and frame dragging effects. !10


        As you can see, you were mistaken.

        and less likely to receive interference.

        Why? And, so what? (Unless you're suggesting that GPB will receive so much interference that it won't work.) All it takes is a little bit of interference and the whole thing doesn't work at all, it's so darn sensitive. LATOR is less mechnically intensive.

        I do hope that this experiment works out, however as other posters have mentioned, there only has to be one unexpected source of error to totally screw this up.

        The same is true of LATOR or of any other experiment, especially highly sensitive ones.

        LATOR's architecture is much different, and I believe by using a long baseline etc, it makes it difficult for interference at one end to screw up the entire experiment. Also remember that it's something that's fairly time invarient, whereas precession is not. The architecture of LATOR seems more likely to deal with sources of interference than something that's based primarily on mechnical components.

        But I haven't done the actual math for either, so what do I know? :)

        Cheers,
        Justin
  • Finally we're the ones doing the probing!
  • but why were the super-precise quartz balls made in Germany [stanford.edu] ?
    • because that's where the refinery plant was at? eh?

      yes you are sounding trollish because you don't bring up any reason for not using the german refinery which might very well have been the only one in the world capable of the job.

      -
  • by gilroy (155262) on Saturday April 03, 2004 @04:23PM (#8757820) Homepage Journal
    ... the project that ate Stanford.

    When I was a grad student there, we had a running joke that nobody could get an astrophysics degree without selling at least a piece of their soul to Francis Everett, the chief booster for this project.

    I was there when a rogue group suggested that, in the intervening four decades, technology had advanced enough to do the frame-dragging experiment with a laser-coordinated satellite net for half the cost.

    We also circulated the "fact" that the GP-B launch date slipped by about 1.05 days per day. A friend defined it as a new universal constant for project overruns... :)
  • Pray it doesn't blow up on the launch pad...
  • So 42 really is the answer? 42 milliarcs, that is....

  • Will this be able to test any of the small deviations in reletivity predicted by some of the theories of Quantum gravity such as string theory?
  • ThinkGeek (Score:2, Funny)

    by Denix (125207)
    Can I buy one of these satellites on ThinkGeek?
  • by Genda (560240) <mariet.got@net> on Saturday April 03, 2004 @09:17PM (#8759280) Journal
    Hubble has had a pretty good look at the spectra of supermassive black holes at the ceters of local galaxies. With a nice close look at those centers, there is turbulences, physical discontinuities in the acretion disks around the supermassive black holes, and the only good candidate for the phenomena is frame dragging...

    I mean it'll be cool to see if the numbers and the phenomena match, but it's not like there's going to be wild surprise.

    Genda
  • The earth doesn't like to be.....probed.

    It won't bend over, it won't spread-em, and it doesn't care how sensitive those damn machines are.

    I also want to know who's going to be up there pulling all of those strings on those gyros!

    (There! I feel much better now! I know it's stupid! I can hear you groaning out there - but I just had to post it!)
  • From the ESA website [esa.int]
    LISA
    LISA is an ESA-NASA mission involving three spacecraft flying approximately 5 million kilometres apart in an equilateral triangle formation. Together, they act as a Michelson interferometer to measure the distortion of space caused by passing gravitational waves. Lasers in each spacecraft will be used to measure minute changes in the separation distances of free-floating masses within each spacecraft.
    The LISA mission is designed to search for and detect gravitational radiation
    • Why so much emphasis on Einstein's Theory all of a sudden??

      First, I would not call it all of a sudden. Testing theories with experiments is one of the building blocks of science.

      So much as Einsten's theories are concerned, since the very day he published his theories, other scientists have analyzed and thought of ways to test them. They have done so where possible, as technology has permitted. One example is the atomic clock and moving bodies experiments that have been done in the past.

      It is necessary

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