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Originally Posted by djellison
It doesn't. When a spacecraft can be targetted to within less than a km from a range of tens of millions of km - the model does not fail.
Please present the observational data that demonstrates that the current value of the mass of Mars is wrong by 2-14%. Given the exceptionally successful Mars flyby by Rosetta - and the planned flyby by Dawn. Those flybys would deviate- a very VERY significant amount - from predictions. The vehicles in orbit around Mars would be lost, years ago - and the vehicles that have landed on Mars, would not have done so. John Anderson, discussing the flyby anomaly on PR last week, said the effect is so small, it's not worth modeling for interplanetary navigation.
You're continuing to insist that a dramatic, drastic, massively critical value required for interplanetary navigation s wrong by an ENORMOUS amount - and there is not one IOTA of evidence to prove that it is. There is massive massive amounts of evidence to prove that our knowledge of the mass of Mars is DAMN accurate, time and time and time again.
Prove it Jerry - show me evidence that our value for the mass of Mars is wrong. Prove it - just a shred of evidence.
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Quick question: How did we determine the mass of Mars? We studied the orbits of the moons of Mars, then used Newton's central mass formula to determine the mass of the planet. Simple and straightward, this was verified first using flybys, landings and orbiting probes. But all of these determinations are
completely dependent upon Newton's big assumption:
The Newtonian Equivalance Principle. None of these orbital determinations test this principle because if it is incorrect, the only number that changes in these first-order equations is the mass of the planet.
If the equivalance principle is wrong; and I am arguing that it is, it takes less kinetic energy to sustain an orbit about Mars than it would if Mars were the same distance from the Sun as the Earth. Thus using Newton's equivalance assumption and the 'universal' G constant, the mass of Mars would appear to be less than it really is. When we put probes in orbit about Mars, we do not test the Equivalance Principle; but what we do works because
we base the calculation for the mass of Mars upon observed orbital mechanics, not the other way around.
The orbits of thes probes and moons to not provide rigorous tests the equivalence principle, but the landing probes do, as do the gravitational mapping probes, especially while they are in highly elliptical orbits. When I went looking, I really did not expect to find data that is consistent with a failure of the Newtonian Equivalence Principle. But I did, in every Mars mission:
1) Degeneracies in the gravity mapping from different altitudes. In general, the further the probe is from Mars, the higher the surface gravity appears to be...No, it is the other way around.
2) Degeneracies in the Love numbers, the mass distribution of Mars, depending upon whether the surface probe or orbiting probe data is used.
3) Higher-than-expected acceleration during the Viking landings; consistant with a greater drag coefficient in the performace of the Viking parachutes.
4) Higher-than-expected velocity during Pathfinders descent and entry, and an under performance of the Pathfinder's parachute - designed almost identical to the Viking parachutes that over-performed.
How can higher and lower performance of parachutes both by symptoms of the same bad physics? The Pathfinder's descent was tracked using Doppler - no accelerometers. The Viking missions contained accelerometers, but no long-range Doppler. Greater acceleration and greater velocity are both predicted if the mass of the planet is greater than Newtonian estimates; but if a lower mass is used in reducing the data; whether this result in a lesser or greater drag coefficient depends upon whether you constrain acceleration or velocity.
The drag coeffiencents were determined on earth, and they shouldn't have change - one of many, many unresolved landing anomalies. Notice that you cannot use acceleration to derive velocity and visa versa unless the wind gradients are also constrained, which they were not. Phoenix will have both Doppler and radar telemetry data throughout the descent; and without a drag coefficient to blame it on, mission scientists will not understand why the probe fell so fast in the upper atmosphere. (They used a major league downdraft to model the rapid descent of the Jupiter probe, I guess that is always an option.)
Pathfinder Parachute:
http://techreports.larc.nasa.gov/ltr...-2003-2126.pdf
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Flight reconstruction of the entry using MPF flight accelerometer data revealed that Pathfinder decelerated faster than predicted based on the estimated value of the MPF parachute CD of 0.50; a value which was determined from low altitude Earth flight tests and wind tunnel data during the development of the MPF parachute (see Ref. 3). An explanation of this underperformance of the MPF parachute system from that which was predicted is still not known.
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From the Viking descent reports:
http://techreports.larc.nasa.gov/ltr...6-cr159388.pdf
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the Acceleration Vector inclination was expected to be ~ -1.0m but it was measured at –1.12 and –1.13
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- that's 12-13%
Errors in Viking Lander Atmospheric Profiles Discovered Using MOLA Topography
Withers, Paul; Lorenz, R. D.; Neumann, G. A.
NASA Center for AeroSpace Information (CASI)
Lunar and Planetary Science XXXIII, LPI-Contrib-1109 , 20020401; April 2002
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Originally Posted by Withers
Each Viking lander measured a topographic profile during entry. Comparing to MOLA (Mars Orbiter Laser Altimeter), we find a vertical error of 1-2 km in the Viking trajectory. This introduces a systematic error of 10-20% in the Viking densities and pressures at a given altitude. Additional information is contained in the original extended abstract.
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The surface gravity measured by the Viking probes is 12.20099-12.24428 ft/sec^2;
which puts a hell of a lot of mass near the surface. However, the Bouguer gravity anomalies find serious under-dense regions in every major rift and low feature. How can the subsurface enviroment be both extremely dense and and underdense at the same time? A poor estimate of the mass of the planet resolves this conundrum: The surface density does not have to be high to explain the acceleration if the entire mass is greater than the mass assumed in making the calculations.
See this thread for more:
Mars: Hard to hit, or are Probes hitting too hard?
I think this is strong enough evidence
pointing in the same direction to be considered a trend, and a trend that only makes sense if the Strong Equivalance Principle is not so strong after all.