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ESA Launches GOCE To Map Earth's Gravity

Posted by kdawson on Tue Mar 17, 2009 04:10 PM
from the go-see dept.
Space Science
DSG2 sends in an ESA press release which reads in part: "This afternoon, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite developed by the European Space Agency was lofted into a near-Sun-synchronous, low Earth orbit by a Rockot launcher lifting off from the Plesetsk cosmodrome in northern Russia. GOCE is the first of a new family of ESA satellites designed to study our planet and its environment in order to enhance our knowledge and understanding of Earth-system processes and their evolution, to enable us to address the challenges of global climate change. In particular, GOCE will measure the minute differences in the Earth's gravity field around the globe." One consequence of mapping the planet's geoid in finer detail is that ocean currents can be limned more accurately. This BBC article from 2007 goes into some detail about this application.
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Submission: ESA launches first Earth Explorer mission GOCE by DSG2 (1436395)
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  • Whoa, this is heavy (Score:5, Funny)

    by MrEricSir (398214) on Tuesday March 17 2009, @04:16PM (#27232801) Homepage

    There's that word again; "heavy." Why are things so heavy in the future? Is there a problem with the earth's gravitational pull?

    • Why not use a unfeasibly massive cloud of Internet grid connected next generation aspect oriented sensors instead? Spam everyone on the Internet, and ask them in which direction gravity is manifesting itself in their part of the world. I think most respondents will reply "down."

      On the serious side, serious scientists have proposed using laptop accelerometers to detect earthquakes: http://www.wired.com/science/planetearth/news/2008/03/quake_network [wired.com]

      Maybe something free on the iPhone App Store could help

      • Speaking of earthquakes, we had a small tremor a week or so ago here in Melbourne, Australia. We just had another one a short while ago. I'm sure there are people on here who live where they get earth tremors all the time but it's unusual to have two in a short space of time down here.

  • height (Score:3, Interesting)

    by Silm (1135973) on Tuesday March 17 2009, @04:18PM (#27232843)
    what really interests me is the fact that this satellite in such a low orbit that it actually has wings and an aerodynamic body to cope with the small amounts of air on that height. Those wings combined with the ion motor's onboard make it almost a plane/ satellite hybrid.

    • Re:height (Score:5, Informative)

      by TorKlingberg (599697) on Tuesday March 17 2009, @04:40PM (#27233233)

      It actually flies "sideways" though. The upper side of the two big wings always face the sun. The two smaller wings at the back are for aerodynamic stability.

      While I'm here, there is more information at the ESA [esa.int] GOCE [esa.int] sites [esa.int].

    • The atmosphere remains a fairly significant factor in satellite design up to altitudes of about 1000km (depending on where you are in the solar cycle; as Sun activity increases, the atmosphere expands). However, your premise remains.. 250km is a VLEO (Very Low Earth Orbit).

      Aikon-

  • this and that (Score:4, Interesting)

    by girlintraining (1395911) on Tuesday March 17 2009, @04:27PM (#27233013)

    Article title: ESA Launches GOCE To Map Earth's Gravity
    Article quote: ...to enable us to address the challenges of global climate change.

    Great. Now we're going to have to start ejecting people into orbit because they stayed under their carbon credits quota, but they had too much gravitational pull and that's damaging the environment. I can just see the green movement in five years: "Stop warping spacetime! Excercise! And screw the whales."

      • The PR filters are obligated to affix some mention of "climate change" to many things. The physicists attempting to (re)measure minute changes in Earth's gravity field are probably oblivious to whatever state the atmosphere might be

        No, rather the non-minute changes in water/ice distribution causes significant differences in the created geoid model.

  • Truly an amazing machine (Score:5, Informative)

    by Thagg (9904) <thadbeier@gmail.com> on Tuesday March 17 2009, @04:34PM (#27233125) Journal

    GOCE is a gravity measuring satellite -- the spiritual successor to the amazing GRACE pair of satellites from a few years ago.

    GRACE works by flying two satellites in the same orbit, one a few dozen miles ahead of the other. By monitoring the distance between the satellites with laser rangefinders, one can measure how strong gravity is -- the more gravity, the faster the satellite goes, so the distance between the satellites grows until the second one reaches the same area. This was the state-of-the-art, and GRACE made some amazing measurements. It was able, for instance, to measure the amount of extra groundwater during flooding along the Mississippi.

    But GOCE does it all with one satellite. Where the baseline for GRACE was many miles, for GOCE it is just 50 cm.

    Now, if you think about it, in any satellite, the amount of gravity you would feel is zero...or at least, very very close to zero, as you are orbiting inertially. But, really, gravity is only zero right at the center of mass of the satellite. You'd feel a tiny amount of acceleration the further you go. As you go toward the center of the earth, you would be in a lower orbit, and you would be pulled down with respect to the satellite.

    GOCE measures this microgravity to rediculous precision. By measuring the difference in gravity affecting two test masses 50 cm apart, it can measure how strong gravity is at that point. It should have much better accuracy, and far better resolution, than GRACE.

    GOCE is amazing in other ways, too. It flies very low, to get better resolution. So, it has fins! A satellite with fins, to keep it pointing along the direction of travel. Because there is some tiny amount of air drag at the altitude it is flying, GOCE has a tiny xenon ion engine pushing it along to keep it at the same altitude, and to keep the air drag on the satellite from overwhelming the gravity measurement.

    Hats off to ESA, this is an amazing machine!

    • >Now, if you think about it, in any satellite, the amount of gravity you would feel is zero...or at least, very very close to zero, as you are orbiting inertially.

      There is plenty of gravity, if there wasn't, the sat would be flying off into deep space.

      • The amount of gravity you would feel

        • I would argue that "feel" in the sense of human nerves saying "this way is down" is irrelevant, given that we are talking about a satellite, and the satellite most certainly "feels" the effects of gravity by staying in orbit.

    • > GOCE is a gravity measuring satellite -- the spiritual successor to the amazing GRACE pair of satellites from a few years ago.

      Technically it is not measuring gravity: it measures *variations* in the gravitational field: basically from it's known orbit it detects incredibly small delta-Vs in it's path.

    • Re:Truly an amazing machine (Score:5, Informative)

      by khayman80 (824400) on Tuesday March 17 2009, @07:37PM (#27235503) Homepage

      I am a physicist working with GRACE data, and I feel the need to nitpick. GRACE uses a microwave ranging system, not a laser ranging system. The increased accuracy of a laser ranging system wouldn't be useful because there are so many other sources of noise, but it is being considered for GRACE 2.

      Also, the baseline between the GRACE satellites is more than a couple dozen miles. On average, GRACE A and B are 220 km apart.

      GOCE is an amazing satellite, and its low altitude combined with its ion engine (to precisely compensate for drag) will increase the resolution of our STATIC (i.e. not time dependent) gravity field maps. But it can't replace GRACE's measurements of the changing gravity field. GRACE has provided independent measurements [colorado.edu] of the Greenland ice sheet melt and helped to correct water storage models, which underestimated [harvard.edu] the 2005 Amazon drought.

      My research involves pushing GRACE's temporal resolution even further down. Rather than detecting annual signals or slowly varying linear mass changes (like ice sheet melt), I'm trying to measure the gravity changes from ocean tides. My preliminary results show that GRACE can detect gravity fluctuations from twice-daily tides, which means that it can be used to improve our ocean tide models. This helps oceanographers, but indirectly helps all gravimetry because tides are a source of noise even for static measurements of the earth's gravity field. Modelling the tides better can help to reduce this noise.

      GRACE isn't dead yet.

      • Thanks...I suppose I was in GOCE rapture this morning when I read about it, and I was more harsh than I should have been. It's good to hear about the work that you're doing, and that you're possibly going to do a GRACE2. What are the other new features of GRACE2 over GRACE?

        I love the apparent simplicity of GRACE -- I say apparent because I know there's a mountain of math between the distance measurements and the geoid data. Congratulations on your work, and keep it up!

        • What are the other new features of GRACE2 over GRACE?

          The "drag-free" concept that GOCE is using has been popular at the GRACE Science Team Meetings [utexas.edu]. This would allow GRACE's altitude to be lowered from its current ~500km (starting) altitude to something more like 200km. Lowering the altitude increases the spatial resolution because from very far away the Earth's gravity field looks exactly like a point mass's. The closer to the surface the satellite gets, the more of the extra features are revealed.

          A laser

        • First, it's in a sun-synchronous orbit. That means that it only passes over a certain spot on the earth's surface at a particular time of day, which never changes from day to day. As a result, it can't tell if gravity is different at that spot at a different time of day. Secondly, the GOCE mission is expected to fall out of the sky in 20 months (and that's if the ion engine works well). It just won't be up there long enough to measure a long enough time series for any serious analysis.
    • By measuring the difference in gravity affecting two test masses 50 cm apart, it can measure how strong gravity is at that point.

      If the two masses are separated by 50 cm, as you say, gravity will pull on the nearer one very, very slightly stronger than it does on the farther one. If the masses were free to move, they'd be in separate orbits, with the outer one moving away from the inner one. As they are (I presume) tethered, there will be a force acting on that tether. This is, in fact, the same thing

  • From the ESA website:.. (Score:3, Informative)

    by Star Particle (1409451) on Tuesday March 17 2009, @04:37PM (#27233195)
    For 24 months, GOCE will collect three-dimensional gravity data all over the globe. The raw data will be processed on the ground to produce the most accurate map of the Earth's gravitational field to date and to refine the geoid: the actual reference shape of our planet. Precise knowledge of the geoid, which can be considered as the surface of an ideal global ocean at rest, will play a very important role in further study of our planet and, with any luck, by detecting subtle changes in gravitational potential, it will be able to provide mankind with its first indirect measurement of your girlfriend's mass.

  • ...knowledge and understanding of Earth-system processes and their evolution,...

    We all know that Evolution and Gravity are just theories and there's no concrete evidence that they exist. Okay? We also need to teach "Intelligent Downward Pull". There may be some intelligent force that really loves us and doesn't want us flying off into space - upon which we'd hit the Sun because it revolves around the Earth.

  • Glad they managed to get GOCE to orbit in one piece.

    Cut-price Russian satellite launches don't seem to work out all that often. Probably a good thing for American cities in the case of a nuclear war...

  • Now if only we could launch a satellite to keep an eye on carbon...we did? What happened?

  • Would it be possible to pin-point the location of impact to the Earth that formed our Moon? I would think the impacted site would be more dense from compression.

    Then again, I'm no geologist.

    • Re: (Score:3, Interesting)

      by khayman80 (824400)

      GRACE has found what many believe to be an ancient impact crater [agu.org] in Antarctica. It might have been responsible for splitting Antarctica away from Australia, and might have been responsible for the Permian extinction. The researchers note that it formed 260 million years ago- around the right time, and it was directly opposite to the usual culprit- the Siberian traps. It's possible that the impact sent shockwaves around the world, which converged on the antipodal point and triggered the Siberian traps.

      But th

      • When talking about a Mars sized impact, there would be no crater. It would pretty much liquify the crust and homogenize the rock structure planet wide. The moon was probably formed before the earths surface was completely solidified anyway, if you take an impact as the likely formation method. The fact of the moons low density does give credence to the impact theory as it is composed of the less dense rocks that might have been knocked off the earth. The denser stuff like iron was already deeper in the eart

  • Half of the word in the name are ignored. They just picked a few letters that could make a sound.

    It's a crapronym! (c) 2009 Apeiron

    Crapronym - a kludge of an acronym that ignores the rules of abbreviation

    Look, if you can't give a project a name like, Percy or "The Gravity Observation Thing", at least go with an honest unpronounceable abbreviation. You can leave out the articles and prepositions if helps. But this is just laziness.

    • When did "Global Warming" become politically incorrect and "Climate Change" became politically correct?

      When they realized they might be wrong.

      • Re:Yeah... (Score:4, Insightful)

        by khayman80 (824400) on Tuesday March 17 2009, @08:40PM (#27236115) Homepage

        As a climate scientist, I've seen that shift in wording too. I think it was largely a PR move, designed to combat fundamental misconceptions that laymen have regarding "Abrupt Climate Change" (the officially accepted title).

        1. Most people don't understand the difference between weather (purely local phenomena, hard to predict because it requires extremely complex vector-valued numerical models of the motion of the atmosphere) and climate (purely global phenomenon, easier to predict because it just requires summing energy input and subtracting energy output). They stuck the word "climate" in there to emphasize that today's cold temperatures in Joe Schmoe's town don't "disprove" climate change.
        2. Global warming is a little simplistic. A more accurate description is that our addition of greenhouse gasses has reduced the volume of energy leaving the planet while leaving the energy input constant. As a result, the average energy in the atmosphere is increasing, which allows the system to "explore more of its phase space". More energy means more opportunities for extreme weather- even weather that involves colder temperatures! (Again, note that weather is local.)
        3. The word "abrupt" was added to emphasize that what we're experiencing isn't a natural process. The ice core from Vostok shows that CO2 hasn't risen above 300 ppm in the last half million years. It's at 380 ppm now, which is almost certainly due to human activities. This rapid increase hasn't happened in the hundreds of thousands of years over which we have records. The consequences aren't likely to be pretty. Hence, "abrupt".

        I'm embarrassed to admit it, but climate change has me pretty scared. I might live to see some of the effects (drought, famine, extreme weather) and I wonder if my life will be as comfortable as my parents was. I used to assume that advancing technology would make my life much better, and I'm just now coming to grips with the possibility that it won't.

        But what really scares me is the ostrich-like manner with which people react to the problem. They seem to be in denial, which is understandable. Scientists aren't bringing good news, so it's natural to be resentful. But I figured that some deep survival mechanism would kick in eventually as people looked at the rigorous nature of the modeling, the diverse data sets all leading to the same conclusions, and the myriad positive feedback effects that makes climate change accelerate on its own.

        Instead, people seem to react as though the existence of climate change is somehow a political question rather than a scientific question. They don't seem to be looking at that evidence [www.ipcc.ch]. Instead, they seem to decide that their political party's position on climate change is "X", so they believe "X". (Note that I'm talking about the existence of anthropogenic abrupt climate change. I realize that our response to climate change is a legitimate political question.)

        • Global warming is a consequence of climate change. Global cooling is a consequence of climate change.

          I am not a denier, but I am not about to be told we must halt climate change. This is a phenomenon that is as old as the earth, and to think we can just stop it when we want to is ludicrous. If you want to limit our impact on that change, fair enough. But don't tell me it has to stop, because you make yourselves look like idiots. The climate has changed in cycles, and despite the CO2 lobbys best propoganda,

          • Re: (Score:3, Informative)

            by khayman80 (824400)

            Global warming is a consequence of climate change. Global cooling is a consequence of climate change.

            I think the term global dimming [wikipedia.org] more accurately describes a separate problem that is sometimes referred to as global cooling. Aerosols decrease the size of cloud droplets, thus increasing the albedo (whiteness) of the clouds. This reflects more sunlight back into space. Its effects have been seen in long-term sunlight brightness studies (in Israel) and in long term evaporation rate measurements (amazingly, e

        • IPCC is run by a political origination with an axe to grind. Al Gore, a Politician won a peace prize for little movie campaign. Can you blame people that they say its all politics these days.

          Hell even ask about model details and your slammed with a global warming denier label. You don't get your question answered.

          The science is now so obscured with media and other groups agenda bias that its pretty hard to claim its not all politics. Really what does your emotional state ("I'm pretty scared") have to

          • Re:Yeah... (Score:4, Informative)

            by khayman80 (824400) on Wednesday March 18 2009, @09:43AM (#27241267) Homepage

            IPCC is run by a political origination with an axe to grind. ...

            I've read through their reports and rebuttals, and I've not seen any difference between the science they're reviewing and my own work (or the work of my colleagues or my advisor). In fact, some of my personal research results support their conclusions. I guess that means that my dissertation research is just politically motivated claptrap?

            Hell even ask about model details and your slammed with a global warming denier label. You don't get your question answered.

            Wow. If you politely asked a climate scientist for details of their model, and got that reaction then you were talking to a pretty bad scientist. Alas, PhDs cannot be revoked...

            The science is now so obscured with media and other groups agenda bias that its pretty hard to claim its not all politics.

            The science isn't obscured from where I'm sitting, and it isn't for anyone within driving distance of a university library. Those biases you're talking about don't make it into the peer reviewed journals like Geophysical Research Letters. I'd recommend those sources over the secondhand sources that you're reading. They sound like horrible sources of information.

            Really what does your emotional state ("I'm pretty scared") have to do with the science?

            Umm... I'm not writing a scientific journal article right now. It's just an online forum. I definitely wouldn't include statements like that in my article submissions.

            I was in fact working with climate scientists for a while, and i was quite shocked that most think its appropriate to misrepresent the certainty of the models because they "know" best.

            What a coincidence! I, too, work with climate scientists. And my experience with scientists in general is that they're much less likely to overstate their case than other people. Scientists are more likely to add caveats to their statements, and less likely to make statements of certainty when all that the evidence supports is "strong probability". What you're describing is just the normal way scientists act.

            Now tell me again why people shouldn't think that the science is just as politicized as the rest of the debate?

            Show me an experiment from a peer reviewed journal article that you think is politicized. I'll review it and get back to you. On the other hand, if you were talking about Rush Limbaugh's editorial about climate science, then I think we mean different things when we use the word "science".

            • I was in fact working with climate scientists for a while, and i was quite shocked that most think its appropriate to misrepresent the certainty of the models because they "know" best.

              What a coincidence! I, too, work with climate scientists. And my experience with scientists in general is that they're much less likely to overstate their case than other people. Scientists are more likely to add caveats to their statements, and less likely to make statements of certainty when all that the evidence supports

              • My experience is "anecdotal" evidence. But it is however my experience. They won't put in a journal. But when a reporter is asking....

        • Instead, people seem to react as though the existence of climate change is somehow a political question rather than a scientific question.

          It became political the moment it became obvious that it would cost something to fix. The evidence may not be in doubt, but like all finite resources, the mindset today is "take what you can now" -- not plan for tomorrow. The collapse of the social security system, medicaid, the global recession, all point to a fundamental lack of interest in the future. Politics globally has aquired a hedonistic taint. The evidence could be indisputable and as solid and proven as gravity but it wouldn't change people's rea

      • No when they realized that stupid people were getting confused when they got hit by a big winter storm. "Dang it's cold! Guess we don't have none of that librul warmin here." /Cletus the slack-jawed yokel. The idea that destabilizing an equilibrium leads to extremes in both directions is too big a concept for people who can't correctly say how long it takes the earth to go around the sun.

    • Re: (Score:3, Informative)

      by vadim_t (324782)

      You can have both global warming and local cooling.

      For instance, one possible effect is that while the average temperature over the whole planet does rise (global warming), the melting of the ice will shutdown the gulf stream and make some countries like Britain colder.

    • The average global temperature has been going up, much more so in recent years. Thus the term "global warming." When some scientists predicted that if the earth gets hot enough there might be a catastrophic rebound and another ice age the term "climate change" began to be used. It's more accurate, since the warming may lead to extreme cooling.

    • No. Currently ICBM's are accurate anywhere from 1 to 100 cm. It doesn't really matter if it's off even 5x that amount, the target will get hit or be incinerated.

      • Currently ICBM's are accurate anywhere from 1 to 100 cm.

        American and Russian ones, because these nations have their own gravity mapping satellites. (and I believe the number was somewhere around 100m, i.e. the payload has a 50% chance of landing in a circle with 100m diameter of the target).

        Can you say the same about French and British ICBMs? Do the US share all of the significant digits of their gravity maps? Do they keep them up to date, too?

      • Last time I had data on ICBMs (80s?) a miss of 50 or 100 miles by an ICBM was considered a "near miss". /shrug

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