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NASA Gravity Probe B mission enters science phase, ready to testEinstein's theory (Forwarded)
Don Savage
NASA Headquarters (202) 358-1547 Steve Roy Media Relations Dept. (256) 544-0034 Robert Kahn Stanford University, Stanford, Calif. (650) 723-2540 Buddy Nelson Lockheed Martin, Sunnyvale, Calif. (510) 797-0349 Status report no.: 04-228 For release: 09/07/04 NASA Gravity Probe B mission enters science phase, ready to test Einstein's theory Gravity Probe B (GP-B), a NASA spacecraft to test two predictions of Albert Einstein's general theory of relativity, achieved a major milestone this past week with the completion of the Initialization and Orbit Calibration (IOC) phase of its mission and the transition into the science phase. The GP-B mission is now one step closer to shedding new light on the fundamental properties of our universe. "This is the moment we have been waiting for," said Francis Everitt, GP-B science Principal Investigator at Stanford University. "It represents a magnificent effort by the entire Stanford-NASA-Lockheed Martin team." The GP-B spacecraft was launched on April 20, 2004 from Vandenberg Air Force Base, Calif., aboard a Boeing Delta II expendable launch vehicle. For the past four months, GP-B has been orbiting 400 miles above Earth, completing system checkouts and fine-tuning one of the most sophisticated science instruments ever put in orbit. On August 27 the spacecraft began science data collection. "It's been a long, amazing road to get to this point," said Rex Geveden, deputy director of NASA's Marshall Space Flight Center in Huntsville, AL. "When Gravity Probe B was first proposed more than 40 years ago, the technology required for this experiment did not yet exist. At least nine new technologies had to be invented and perfected, with the program's advances only possible through breakthroughs in cryogenics, drag-free satellite technology, and new manufacturing and measuring technologies." The spacecraft uses four ultra-precise gyroscopes to test two extraordinary predictions of Einstein's 1916 theory that space and time are distorted by the presence of massive objects. Specifically, it is testing two effects: 1) the geodetic effect -- the amount by which the Earth warps local spacetime in which it resides, and 2) the frame-dragging effect -- the amount by which the rotating Earth drags local spacetime around with it. "It's great to be in our science mode," said Gaylord Green, GP-B Program Manager at Stanford University. "The team is ecstatic that the demanding IOC phase is over and the science phase has begun. Most importantly, all systems are meeting or exceeding the requirements of the mission." At launch, the spacecraft's Dewar (the largest ever put in orbit) contained approximately 650 gallons of superfluid helium-enough to maintain the gyroscopes in a cryogenic state for an estimated 16 months. The GP-B mission time line originally specified two months for initialization, checkout, and instrument tuning, 13 months of relativity data collection, and one final month of instrument re-calibration. The IOC phase actually required a little over four months to complete. Although this results in a slightly shorter data collection period than originally planned, GP-B will significantly surpass its mission performance requirements. Tuning up the Attitude and Translation Control system to achieve the extraordinarily precise pointing and drag-free positioning requirements of the spacecraft, as well as refining the set-up up the science gyros, accounted for the IOC extension. "These are items that cannot be tested on the ground," said Gaylord Green. "Using the extra time required for the checkout phase, the team obtained invaluable information about the GP-B science instrument." The science phase is the heart of the GP-B mission. During this phase, at least twice a day, data is relayed from Earth-based ground stations or NASA's data relay satellites to the GP-B Mission Operations Center at Stanford University in Stanford, Calif. This data includes space vehicle and instrument performance information, as well as the very precise measurements of the gyroscopes' spin-axis alignment relative to its guide star, IM Pegasi. Over the course of a year, the anticipated spin axis drift for the geodetic effect is a minuscule angle of 6,614.4 milliarcseconds, and the anticipated spin axis drift for the frame-dragging effect is even smaller, only 40.9 milliarcseconds. This angle is so small that if someone were to climb a slope of 40.9 milliarcseconds for 100 miles, he would rise only one inch in altitude, measured to an accuracy of better than 1/100th of an inch. The GP-B mission has already achieved many extraordinary accomplishments: * GP-B is the first satellite ever to achieve both 3-axis attitude control (pitch, yaw, and roll), and 3-axis drag-free control (while orbiting the Earth, the whole spacecraft flies around one of the science gyros). * The GP-B gyros, which are performing perfectly in orbit, will be listed in the forthcoming edition of the Guinness Book of World Records as being the roundest objects ever manufactured. * The spin-down rates of all four gyros are considerably better than expected. GP-B's conservative requirement was a characteristic spin-down period (time required to slow down to ~37% of its initial speed) of 2,300 years. Recent measurements show that the actual characteristic spin-down period of the GP-B gyros exceeds 10,000 years-well beyond the requirement. * The magnetic field surrounding the gyros and SQUIDs (Super-conducting QUantum Interference Device) has been reduced to 10-7 gauss, less than one millionth of the Earth's magnetic field-the lowest ever achieved in space. * The gyro readout measurements from the SQUID magnetometers have unprecedented precision, detecting fields to 10-13 gauss, less than one trillionth of the strength of Earth's magnetic field. * The science telescope on board the spacecraft is tracking the guide star, IM Pegasi (HR 8703), to superb accuracy, and it is also collecting long-term brightness data on that star. The GP-B program will not release the scientific results obtained during the mission until after the science phase has concluded. It is critically important to thoroughly analyze the data to ensure its accuracy and integrity prior to releasing the results. NASA's Marshall Space Flight Center manages the GP-B program. NASA's prime contractor for the mission, Stanford University, conceived the experiment and is responsible for the design and integration of the science instrument, as well as for mission operations and data analysis. Lockheed Martin, a major subcontractor, designed, integrated and tested the space vehicle and built some of its major payload components. |
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Andrew Yee wrote in message m...
Don Savage NASA Headquarters (202) 358-1547 Steve Roy Media Relations Dept. (256) 544-0034 Robert Kahn Stanford University, Stanford, Calif. (650) 723-2540 Buddy Nelson Lockheed Martin, Sunnyvale, Calif. (510) 797-0349 Status report no.: 04-228 For release: 09/07/04 NASA Gravity Probe B mission enters science phase, ready to test Einstein's theory Gravity Probe B (GP-B), a NASA spacecraft to test two predictions of Albert Einstein's general theory of relativity, achieved a major milestone this past week with the completion of the Initialization and Orbit Calibration (IOC) phase of its mission and the transition into the science phase. The GP-B mission is now one step closer to shedding new light on the fundamental properties of our universe. "This is the moment we have been waiting for," said Francis Everitt, GP-B science Principal Investigator at Stanford University. "It represents a magnificent effort by the entire Stanford-NASA-Lockheed Martin team." The GP-B spacecraft was launched on April 20, 2004 from Vandenberg Air Force Base, Calif., aboard a Boeing Delta II expendable launch vehicle. For the past four months, GP-B has been orbiting 400 miles above Earth, completing system checkouts and fine-tuning one of the most sophisticated science instruments ever put in orbit. On August 27 the spacecraft began science data collection. "It's been a long, amazing road to get to this point," said Rex Geveden, deputy director of NASA's Marshall Space Flight Center in Huntsville, AL. "When Gravity Probe B was first proposed more than 40 years ago, the technology required for this experiment did not yet exist. At least nine new technologies had to be invented and perfected, with the program's advances only possible through breakthroughs in cryogenics, drag-free satellite technology, and new manufacturing and measuring technologies." The spacecraft uses four ultra-precise gyroscopes to test two extraordinary predictions of Einstein's 1916 theory that space and time are distorted by the presence of massive objects. Specifically, it is testing two effects: 1) the geodetic effect -- the amount by which the Earth warps local spacetime in which it resides, and 2) the frame-dragging effect -- the amount by which the rotating Earth drags local spacetime around with it. "It's great to be in our science mode," said Gaylord Green, GP-B Program Manager at Stanford University. "The team is ecstatic that the demanding IOC phase is over and the science phase has begun. Most importantly, all systems are meeting or exceeding the requirements of the mission." At launch, the spacecraft's Dewar (the largest ever put in orbit) contained approximately 650 gallons of superfluid helium-enough to maintain the gyroscopes in a cryogenic state for an estimated 16 months. The GP-B mission time line originally specified two months for initialization, checkout, and instrument tuning, 13 months of relativity data collection, and one final month of instrument re-calibration. The IOC phase actually required a little over four months to complete. Although this results in a slightly shorter data collection period than originally planned, GP-B will significantly surpass its mission performance requirements. Tuning up the Attitude and Translation Control system to achieve the extraordinarily precise pointing and drag-free positioning requirements of the spacecraft, as well as refining the set-up up the science gyros, accounted for the IOC extension. "These are items that cannot be tested on the ground," said Gaylord Green. "Using the extra time required for the checkout phase, the team obtained invaluable information about the GP-B science instrument." The science phase is the heart of the GP-B mission. During this phase, at least twice a day, data is relayed from Earth-based ground stations or NASA's data relay satellites to the GP-B Mission Operations Center at Stanford University in Stanford, Calif. This data includes space vehicle and instrument performance information, as well as the very precise measurements of the gyroscopes' spin-axis alignment relative to its guide star, IM Pegasi. Over the course of a year, the anticipated spin axis drift for the geodetic effect is a minuscule angle of 6,614.4 milliarcseconds, and the anticipated spin axis drift for the frame-dragging effect is even smaller, only 40.9 milliarcseconds. This angle is so small that if someone were to climb a slope of 40.9 milliarcseconds for 100 miles, he would rise only one inch in altitude, measured to an accuracy of better than 1/100th of an inch. The GP-B mission has already achieved many extraordinary accomplishments: * GP-B is the first satellite ever to achieve both 3-axis attitude control (pitch, yaw, and roll), and 3-axis drag-free control (while orbiting the Earth, the whole spacecraft flies around one of the science gyros). * The GP-B gyros, which are performing perfectly in orbit, will be listed in the forthcoming edition of the Guinness Book of World Records as being the roundest objects ever manufactured. * The spin-down rates of all four gyros are considerably better than expected. GP-B's conservative requirement was a characteristic spin-down period (time required to slow down to ~37% of its initial speed) of 2,300 years. Recent measurements show that the actual characteristic spin-down period of the GP-B gyros exceeds 10,000 years-well beyond the requirement. * The magnetic field surrounding the gyros and SQUIDs (Super-conducting QUantum Interference Device) has been reduced to 10-7 gauss, less than one millionth of the Earth's magnetic field-the lowest ever achieved in space. * The gyro readout measurements from the SQUID magnetometers have unprecedented precision, detecting fields to 10-13 gauss, less than one trillionth of the strength of Earth's magnetic field. * The science telescope on board the spacecraft is tracking the guide star, IM Pegasi (HR 8703), to superb accuracy, and it is also collecting long-term brightness data on that star. The GP-B program will not release the scientific results obtained during the mission until after the science phase has concluded. It is critically important to thoroughly analyze the data to ensure its accuracy and integrity prior to releasing the results. NASA's Marshall Space Flight Center manages the GP-B program. NASA's prime contractor for the mission, Stanford University, conceived the experiment and is responsible for the design and integration of the science instrument, as well as for mission operations and data analysis. Lockheed Martin, a major subcontractor, designed, integrated and tested the space vehicle and built some of its major payload components. If time passes differently under changed gravity, then time passes differently at the earth's center, than at the surface, (or a point above the surface). Hands up all those who think the earth's center takes a different amount of time to complete an orbit of the sun, than the surface??????????????? Jim G c'=c+v |
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In message , Jim
Greenfield writes If time passes differently under changed gravity, then time passes differently at the earth's center, than at the surface, (or a point above the surface). Hands up all those who think the earth's center takes a different amount of time to complete an orbit of the sun, than the surface? I think you'll find that time does _not_ pass differently for an outside observer (and every particle of an object is effectively an outside observer). So, no problem. And just why can't you follow netiquette and trim text? -- What have they got to hide? Release the ESA Beagle 2 report. Remove spam and invalid from address to reply. |
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In message , Jonathan Silverlight
writes In message , Jim Greenfield writes If time passes differently under changed gravity, then time passes differently at the earth's center, than at the surface, (or a point above the surface). Hands up all those who think the earth's center takes a different amount of time to complete an orbit of the sun, than the surface? I think you'll find that time does _not_ pass differently for an outside observer (and every particle of an object is effectively an outside observer). I'm fairly sure I got that exactly backwards :-) Is the difference in time a necessary result of the gravitational attraction between an object at the centre and the surface? Or even the cause, in some sense? An object on the sunward side does take a different time to complete an orbit than one at the centre. That's because of the sun's gravity, which causes tides which will eventually slow the earth so it always faces the sun. It's an interesting question. Help! |
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Jonathan Silverlight wrote in message ...
In message , Jonathan Silverlight writes In message , Jim Greenfield writes If time passes differently under changed gravity, then time passes differently at the earth's center, than at the surface, (or a point above the surface). Hands up all those who think the earth's center takes a different amount of time to complete an orbit of the sun, than the surface? I think you'll find that time does _not_ pass differently for an outside observer (and every particle of an object is effectively an outside observer). I'm fairly sure I got that exactly backwards :-) Is the difference in time a necessary result of the gravitational attraction between an object at the centre and the surface? Or even the cause, in some sense? An object on the sunward side does take a different time to complete an orbit than one at the centre. That's because of the sun's gravity, which causes tides which will eventually slow the earth so it always faces the sun. It's an interesting question. Help! Is that one hand up, and one down? The earth is one body, and orbits the sun as one entity, calculated by us as being 1 year. But it has differing gravitational "zones", which, if they DID alter time, logically mandate that each zone would have a different length "year" (according to GR). ie, each zone takes a different interval to complete a circuit...... lol Your first answer was more on the usual Relativity support system; that observers can BOTH be correct. In this case, one observer can only view one "shell" of the earth, and make his assesment of its position in the orbit-- highly unlikely, Jonathon. Help is NOT at hand for GR. Jim G c'=c+v |
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In message , Jim
Greenfield writes The earth is one body, and orbits the sun as one entity, calculated by us as being 1 year. But it has differing gravitational "zones", which, if they DID alter time, logically mandate that each zone would have a different length "year" (according to GR). ie, each zone takes a different interval to complete a circuit...... lol But that was my point. A tidally locked body is only one entity if it has the strength to resist tidal forces. But I can see that there are problems looking at the poles (assuming no inclination) OTOH, gravitational red shift and time dilation has been experimentally demonstrated (see http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/gratim.html#c2 for instance). If you say that's not due to relativity it's up to you to show how. -- What have they got to hide? Release the ESA Beagle 2 report. Remove spam and invalid from address to reply. |
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Jonathan Silverlight wrote in message ...
In message , Jim Greenfield writes The earth is one body, and orbits the sun as one entity, calculated by us as being 1 year. But it has differing gravitational "zones", which, if they DID alter time, logically mandate that each zone would have a different length "year" (according to GR). ie, each zone takes a different interval to complete a circuit...... lol But that was my point. A tidally locked body is only one entity if it has the strength to resist tidal forces. But I can see that there are problems looking at the poles (assuming no inclination) OTOH, gravitational red shift and time dilation has been experimentally demonstrated (see http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/gratim.html#c2 for instance). If you say that's not due to relativity it's up to you to show how. "A meter is the distance light travels in (?) secs"- by Relativity definition. From that first point on, which erroneously ASSUMES that light travels independent of source, all data is false, as true distances are compromised. Similarly with the clocks; they malfunction with reference to 'universal time". Do you not think it quite ridiculous, that traveller A sees B's clock going faster (or slower), and vice versa? The observers are mistaken into misbelief due to the finite duration of light to travel a course. The simultaneity or otherwise of two or more actions is not ALTERED by the observers positions- they are just lead to make wrong conclusions. Would you expect an hour glass to operate at the same "rate of transfer" under differing gravity? Well why shouldn't the same apply to atomic clocks? (actions at a subatomic level). Physicists have decreed that their super duper clocks are infallible, and NEVER alter- and yet they still have to be changed every now and then in order to agree. These "mistakes/malfunctions seem to be conveniently overlooked when doing experiments such as taking one around the world! Jim G c'=c+v |
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If time passes differently under changed gravity, then time passes
differently at the earth's center, than at the surface, (or a point above the surface). Hands up all those who think the earth's center takes a different amount of time to complete an orbit of the sun, than the surface? In article , Jonathan Silverlight writes: It's an interesting question. Help! As usual in these sorts of questions, the key is to keep in mind what reference frame each "observer" is using. From the context, I assume we want to ignore secular perturbations, the fact that a year is not an integer number of days, and the Sun's acceleration in its orbit around the Galaxy. For an observer in a reference frame fixed with respect to the Sun, the Earth's center and a point on Earth's surface take the same time to complete a year. However, observers at different gravitational potentials will have clocks that run at different rates. This is just gravitational redshift. In article , (Jim Greenfield) writes: Similarly with the clocks; they malfunction with reference to 'universal time". How, exactly, is one supposed to measure "universal time?" Do you not think it quite ridiculous, that traveller A sees B's clock going faster (or slower), and vice versa? Doppler shift is pretty easy to demonstrate. An observer on the ground hears a train whistle at a different pitch than a rider on the train. Likewise, a train rider would hear a stationary whistle at a different pitch than the observer on the ground. Each whistle is, in effect, a clock (just add a microphone and a counter). What is so ridiculous about these clocks running at different rates, depending on who is measuring them? -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
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"JG" == Jim Greenfield writes:
JG If time passes differently under changed gravity, then time passes JG differently at the earth's center, than at the surface, (or a JG point above the surface). Hands up all those who think the JG earth's center takes a different amount of time to complete an JG orbit of the sun, than the surface??????????????? My hand is up. As Steve Willner has pointed out already, gravitational fields do affect the rate at which time passes. A hypothetical observer fixed out in space over one of the Sun's poles will measure a different number of seconds for the Earth to complete one orbit than would an observer on the surface of the Earth. The reason is because the observer on the Earth is in a larger gravitational potential than the one out in space. This is a well-known effect and has to be taken into account in order that the GPS system works. -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
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