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Post by twinstead on Aug 4, 2005 13:28:10 GMT -4
Confute? A clearly clever way to suggest it is impossible to refute the chronically confused...it's impossible to confute.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 4, 2005 13:30:46 GMT -4
ARE YOU THE LAND OF THE FREE? This forum is not the land of the free. It is privately owned and the owner can do whatever he wants.
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Post by papageno on Aug 4, 2005 13:37:23 GMT -4
Confute? Maybe English is not his first language. For example, "to refute" can be translated as " confutare" in Italian.
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Post by LunarOrbit on Aug 4, 2005 13:40:54 GMT -4
I didn't think it was a word either, but it is listed on Dictionary.com and it apparently means the samething as refute.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 4, 2005 13:46:29 GMT -4
Wrong. Cassini has a smallest mass. The Sun can't slow down it. Study more carefully orbital mechanics. I'm about to do something I normally try very hard not to do... Wildbill, YOU'RE AN IDIOT! You should be banned for shear stupidity if nothing else. You're willfully ignorant, you're rude, you listen to no one, you contribute nothing of value, and you've defied at least three bans already. So, for example, if I were to say "I strongly suspect that WildBill is a sockpuppet of unknown and I'm probably going to ban him", what would the concensus be? I think you know my answer to this question.
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Post by twinstead on Aug 4, 2005 13:49:59 GMT -4
You mean it's considered bad form for laymen to admonish people who study orbital mechanics to "study more carefully orbital mechanics"? I'm shocked!
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Post by sts60 on Aug 4, 2005 13:55:46 GMT -4
If Cassini follows this path the sun will affect it with its gravity: www.space.com/php/multimedia/imagedisplay/img_display.php?pic=h_cassini_trajectory_02.gif&cap=The
But the problem is not here. No. The gravitational influence of the Sun affects every body in this solar system. In fact, that is a good definition (though not the only one) of the solar system: The system of bodies gravitationally bound to the Sun. Planets, spacecraft, asteroids, comets, dust particles: the whole shebang is gravitationally bound to the Sun. In other words, that's why they orbit the Sun. Your specific trajectory inside the system doesn't change that. (Extrasolar objects on parabolic or hyperbolic trajectories, such as galactic cosmic rays or the ship from Clarke's Rendezvous with Rama are on a one-way trip through and are not properly part of this solar system. Of course, they, too, are influenced to some extent by the gravitational field of the Sun. Yes, even massless photons are affected by this field; this was predicted in General Relativity and confirmed a century ago.) The problem is that NASA engineers don't consider the earth's velocity in their calculations, so they will never be able to go to Mars or Saturn.Of course they consider the Earth's velocity. That's one of the first steps in the computation of any deep-space trajectory. You really need to understand that neither the mass nor the specific trajectory of a spacecraft somehow exempt it from the Sun's gravitational pull, any more than it exempts it from the Earth's gravitational pull as it departs. That's simply not the way things work. This is centuries-old knowledge. (edit: expanded parenthetical part)
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Post by frenat on Aug 4, 2005 14:02:24 GMT -4
So, for example, if I were to say "I strongly suspect that WildBill is a sockpuppet of unknown and I'm probably going to ban him", what would the concensus be? I would support it as well.
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Post by wildbill on Aug 4, 2005 14:13:27 GMT -4
> The problem is that NASA engineers don't consider the earth's velocity in their calculations, so they will never be able to go to Mars or Saturn.
>>> Of course they consider the Earth's velocity. That's one of the first steps in the computation of any deep-space trajectory.
>>>>>> Show some calculations that demonstrate NASA engineers consider the earth's velocity, please
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 4, 2005 14:24:32 GMT -4
>>>>>> Show some calculations that demonstrate NASA engineers consider the earth's velocity, please You wouldn't understand it.
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Post by ottawan on Aug 4, 2005 14:28:39 GMT -4
Pardon me for being a bit slow on the uptake but has not "wildbill" already been banned twice or is this the re-incarnation of someone else?
I'm confute!
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Post by echnaton on Aug 4, 2005 14:36:25 GMT -4
> The problem is that NASA engineers don't consider the earth's velocity in their calculations, so they will never be able to go to Mars or Saturn. >>> Of course they consider the Earth's velocity. That's one of the first steps in the computation of any deep-space trajectory. >>>>>> Show some calculations that demonstrate NASA engineers consider the earth's velocity, please You still have a chance to avoid a ban. Since this is your assertion, why don’t you present a relevant calculation where NASA doesn’t consider the Earth’s velocity.
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Post by sts60 on Aug 4, 2005 14:48:14 GMT -4
> The problem is that NASA engineers don't consider the earth's velocity in their calculations, so they will never be able to go to Mars or Saturn. >>> Of course they consider the Earth's velocity. That's one of the first steps in the computation of any deep-space trajectory. >>>>>> Show some calculations that demonstrate NASA engineers consider the earth's velocity, please Sure. Here, for example, is described how you add or take away energy from the spacecraft's orbit around the Sun - which initially is the same as the Earth's; that is, it shares the Earth's orbital velocity to start. Of course, to get into an initial orbit around the Earth, you need consider the Earth's rotational speed when you take off. I am looking at the databook reference for Cassini, which shows the inertial velocity of the spacecraft - that is, it's orbital speed with respect to the center of the Earth. It's 1,341.2 fps at liftoff; the vehicle, the booster, the launch pad are all moving that speed about the center of the Earth. They launch with the Earth's rotation to take advantage of that; then the spacecraft went against the Earth's motion to head towards Venus for its first gravity assist.
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Post by sts60 on Aug 4, 2005 15:30:19 GMT -4
Show some calculations that demonstrate NASA engineers consider the earth's velocity, please
From the Cassini Alternate Mission and Power Study (JPL 1994), section A.1, Trajectory and Propulsion Background Information:
The spacecraft's velocity with respect to the Sun, if found by vector addtion: the Earth's velocity with respect to the Sun is added to the spacecraft's asymptotic, hyperbolic departure velocity with respect to the Earth. For transfers to the outer solar system, the net effect of the Earth departure hyperbola is to increase the spacecraft's velocity with respect to the Sun above the value corresponding to the Earth's velocity. This requires that [the hyperbolic excess velocity] be pointed in the same general direction as the Earth's velocity vector. For transfers to the inner solar system, however, the spacecraft's velocity must be decreased, requiring [the hyperbolic excess velocity] to be opposed to the Earth's velocity.
From the Casini EIS supporting study, vol 3 (Earth Swingby Plan):
For a collision to occur, the Earth and spacecraft must be present within the intersection ellipse at the same time. The average probability of collision, P', is proportional to the arc distance measured along the Earth's orbit for which any part of the Earth lies within the intersection ellipse. This arc distance normalized by the heliocentric distance of the Earth is eta = tau * abs(U) / sqrt(Ux^2 + Uz^2) where tau is the impact radius, divided by the heliocentric distance of the Earth, abs (U) is the magnitude of the velocity of the spacecraft relative to the Earth divided by the heliocentric velocity of the Earth, Ux is the radial (Sun to Earth) component of U, and Uz is the component of U normal to the Earth orbit plane direction.
Now, can we dispense with the factually incorrect claim that interplanetary mission planners - whether they be from the U.S., Russia, or anywhere else - don't take the Earth's velocity into account? That's like saying airline flight planners don't take winds aloft into account. It's just fundamentally wrong.
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Post by JayUtah on Aug 4, 2005 15:36:13 GMT -4
Basically because we're talking about orbits here, the Earth's velocity is added, but it's just not relevant.
If a spacecraft stays very close to Earth -- say, in orbit around it -- then it is essentially drawn along with Earth in its path around the sun. Move that spacecraft far enough away from Earth so that Earth's gravity isn't a very strong force, then that spacecraft begins to pursue its own orbit around the sun. In order to do that, it has to basically move around the sun at the same speed as the Earth does. So just to stay at the same distance from the sun as the Earth, a spacecraft has to go at the same speed as the Earth.
In order to advance outward to a higher orbit, such as Saturn's, the spacecraft must add energy to its trajectory. Because of the way orbital mechanics works, this actually results in a lower velocity (eventually), but in a higher altitude. This is how transfers between orbits are accomplished.
Traveling between planets in the solar system is not like driving to Vegas. It's not a matter of pointing the vehicle in the direction of some stationary target and stepping on the gas, and the harder you step the faster you get there. There are gravitational forces at work in interplanetary trajectories that laymen almost always fail intuitively to understand.
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