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sts60
Skeptic Friend
141 Posts |
 Posted - 08/10/2005 : 09:52:33 [Permalink]
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Thanks, everyone, for the welcome. I used to lurk here a while back. ktseibos, nice to see you here.
1) How fast was Cassini actually going when the launch vehicle quit pushing it? (In other words, I can't find verification of the 36,000 mph figure.)
2) How high (from the Earth) was Cassini when the launch vehicle quit pushing it? (Close to Earth, the primary gravitational "drag" will be from the Earth itself.)
The Titan IV/Centaur databook prepared for the Cassini safety analysis (and made available for public review before the launch) gave a figure of 33500 fps (10200 m/s) and altitude of 10,883,000 ft (3,317,000 m) at separation of the Centaur upper stage.
At the Target Interface Point, reached 50 minutes later, the inertial speed is 22900 fps (6980 m/s) and altitude is 75,753,000 ft (23,394,000 m). The TIP can be considered the "starting point" of the interplanetary trajectory.
The altitude, of course, is basically the height of the spacecraft above the Earth's surface. The speed is relative to the center of the Earth, so before liftoff the speed was 1341 fps (409 m/s).
You can also look up elements for Cassini (or lots of other things at [url=http://ssd.jpl.nasa.gov/horizons.html]JPL's Horizon system[/url]. |
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tw101356
Skeptic Friend
USA
333 Posts |
Posted - 08/10/2005 : 09:57:08 [Permalink]
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quote:
Originally posted by bigbrain
>>> Cassini would have been able to fly along a straight line travelling for less than 1 000 000 000 miles.
>>> 65,000 miles per hour (earth velocity) + 36,000 miles per hour (spacecraft's velocity) = 101,000 miles per hour
>>> 1 000 000 000 miles : 365 days : 24 hours : 101,000 miles per hour = 1.13 years
>>> >>> If NASA engineers considered the earth's velocity, Cassini could meet Saturn in one year!
If the above were true, then an immobile object sitting on the surface of the Earth, such as my house, would result in the following:
1. 65,000 miles per hour (earth velocity) + 0 miles per hour (My house's velocity) = 65,000 miles per hour .
2. 1 000 000 000 miles : 365 days : 24 hours : 65,000 miles per hour = 1.76 years
3. Therefore my house should be in orbit around Saturn right now.
4. I don't think so.
You're applying 1 dimensional (aka straight line) calculations to a three dimensional situation. The math is invalid.
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- TW
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sts60
Skeptic Friend
141 Posts |
Posted - 08/10/2005 : 10:04:44 [Permalink]
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quote:
Nasa engineers don't consider Earth's velocity in their calculations
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 addition: 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.
From Basics of Space Flight at http://www2.jpl.nasa.gov/basics/bsf14-1.html]:
If a spacecraft is launched from a site near Earth's equator, it can take optimum advantage of the Earth's substantial rotational speed. Sitting on the launch pad near the equator, it is already moving at a speed of over 1650 km per hour relative to Earth's center. This can be applied to the speed required to orbit the Earth (approximately 28,000 km per hour). Compared to a launch far from the equator, the equator-launched vehicle would need less propellant, or a given vehicle can launch a more massive spacecraft....
For interplanetary launches, the vehicle will have to take advantage of Earth's orbital motion as well, to accommodate the limited energy available from today's launch vehicles. In the diagram below, the launch vehicle is accelerating generally in the direction of the Earth's orbital motion (in addition to using Earth's rotational speed), which has an average velocity of approximately 100,000 km per hour along its orbital path.
The same thing is also available at http://www.au.af.mil/au/awc/awcgate/jplbasic/bsf14-1.htm, which includes a diagram labeled "Launch Using Earth's Rotation and Orbital Velocities". |
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sts60
Skeptic Friend
141 Posts |
Posted - 08/10/2005 : 10:13:21 [Permalink]
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You're applying 1 dimensional (aka straight line) calculations to a three dimensional situation. The math is invalid.
It's worse than that. He thinks that gravity doesn't affect space probes because their "mass is smallest" (from a post on apollohoax). Of course, when it was pointed out that this would make it impossible to have things such as communications satellites, he made no reply.
Remember, this individual thinks a can will fall off the tip of your finger when it rotates to "360 degrees".
I've seen mental patients with a better grasp of reality, 3-year-olds with better conversational skills, and U.S. Congressmen with less ignorance of simple physics. I am not exaggerating. |
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bigbrain
BANNED
409 Posts |
Posted - 08/10/2005 : 11:40:37 [Permalink]
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"I've seen mental patients with a better grasp of reality, 3-year-olds with better conversational skills, and U.S. Congressmen with less ignorance of simple physics. I am not exaggerating".
Since yoy can't refute my statement, you then offend me: "I've seen mental patients with a better grasp of reality"
Since I'm European you offend me again: " 3-year-olds with better conversational skills"
Since you speak like a professor, you think to be superior "and U.S. Congressmen with less ignorance of simple physics. I am not exaggerating"
Dear professor (who knows, does; who doesn't know, teaches)
you wrote:
"... For transfers to the inner solar system, however, the spacecraft's velocity must be decreased ..."
This is a biggest stupidity because to go to Saturn you must travel to the OUTER solar system.
Only an idiot could decrease velocity of the probe.
sts60, you can only do involved reasonings to confuse people.
Your probe runs at 101,000 miles per hour and you decrease its velocity and then you pass near Venus for 2 times to increase velocity.
You reason like NASA engineers. Do you work for NASA?
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"Obsequium amicos, veritas odium parit" (Flattery gets friends, truth hatred)
Publius Terentius Afer, "Terence", Roman dramatist
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Valiant Dancer
Forum Goalie
USA
4826 Posts |
Posted - 08/10/2005 : 11:49:33 [Permalink]
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quote:
Originally posted by bigbrain
"I've seen mental patients with a better grasp of reality, 3-year-olds with better conversational skills, and U.S. Congressmen with less ignorance of simple physics. I am not exaggerating".
Since yoy can't refute my statement, you then offend me: "I've seen mental patients with a better grasp of reality"
Since I'm European you offend me again: " 3-year-olds with better conversational skills"
Since you speak like a professor, you think to be superior "and U.S. Congressmen with less ignorance of simple physics. I am not exaggerating"
Dear professor (who knows, does; who doesn't know, teaches)
you wrote:
"... For transfers to the inner solar system, however, the spacecraft's velocity must be decreased ..."
This is a biggest stupidity because to go to Saturn you must travel to the OUTER solar system.
Only an idiot could decrease velocity of the probe.
sts60, you can only do involved reasonings to confuse people.
Your probe runs at 101,000 miles per hour and you decrease its velocity and then you pass near Venus for 2 times to increase velocity.
You reason like NASA engineers. Do you work for NASA?
The whole gravitational pull of the earth thing really escapes you, doesn't it.
Might I suggest some rudimentary physics courses?
From STS60's link the spacecraft is never going 101,000 mph ever. It has to overcome that pesky rotational movement which will decrease it's top speed and have to continually thrust to get to a point where the earth's gravity will not appreciably slow it down. That is one hell of a lot of fuel for a single mission. It is more cost effective to use the Venus Sun Venus Earth path to send missions to Saturn where you don't have to carry such copious amounts of fuel into space and lift it plus the probe.
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Cthulhu/Asmodeus when you're tired of voting for the lesser of two evils
Brother Cutlass of Reasoned Discussion |
| Edited by - Valiant Dancer on 08/10/2005 11:56:26 |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 08/10/2005 : 11:52:04 [Permalink]
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| You must decrese velocity to avoid the moon in sagittarious, DUH. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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filthy
SFN Die Hard
USA
14408 Posts |
Posted - 08/10/2005 : 12:05:53 [Permalink]
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It is what I love about these folks; they bring forth some really excellent info. And some rather silly shit, as well..... A little earlier, I successfully balanced a full can of beer (Coke is not allowed in my house) on the tip of my finger just to see if it could be done. Whaddya know; it can.
I took a large, cheap, plastic funnel, that's been kicking around here for years, and cut off it's spout. I glued a bit of 1 inch dia. dowel in the hole in such a way that it barely extruded into the cone and extended perhaps 1/2 inch out -- about 3/4 inches over all. To this, I attached a piece of 1/4 inch plywood about 3 inches in dia. I balanced the funnel, plywood up, on my finger tip and placed the can on it. After a couple of tries (it ain't as easy as it sounds -- gotta get the can centered exactly) it worked, and I rewarded myself by having the beer for lunch.
If it had not worked, I'd have simply attached some weights to the rim of the funnel -- yes, I do have too much time on my hands.
It's rather like the Space Program and life in general, is it not. You solve a problem by building the solution, not by wishing at it. I think I'll keep my ruined funnel and name it 'The Lunar Lander'. 
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"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
"The default position of human nature is to punch the other guy in the face and take his stuff." ~~ Dude
Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist! 
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Cuneiformist
The Imperfectionist
USA
4955 Posts |
Posted - 08/10/2005 : 12:17:18 [Permalink]
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quote:
Originally posted by bigbrain
Since you can't refute my statement . . .
Just because you say you haven't been refuted doesn't mean that you haven't been refuted.
Here's what I suggest, since this, uh, debate seems to be going nowhere. Bigbrain, why don't you begin anew by making a specific assertion. You should back this up with facts, ideally directly related to yout assertions and not simply a link to a lengthy webpage with myriad data to go through. And again, this should be a very specific assertion.
Once you've made your assertion, others who disagree with you can attempt to refute it. They should do this by addressing the data your present, showing the flaws in your logic, etc. You can attempt to defend your statements, data, etc., but both sides must stick to the original assertion; tangents should be avoided and introduced only when related to the data at hand.
My hope is that with these parameters in mind, we'll be able to get to the bottom of the question of if humans really have sent spacecraft to Saturn and Mars! |
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pleco
SFN Addict
USA
2998 Posts |
Posted - 08/10/2005 : 12:24:03 [Permalink]
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The fact is that there is no way a coverup that big can be kept secret by thousands of people for such a long time - same as the moon landings and any other wacko conspiracy theory out there.
Mel Gibson you are not. |
by Filthy
The neo-con methane machine will soon be running at full fart. |
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| Edited by - pleco on 08/10/2005 12:24:44 |
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bigbrain
BANNED
409 Posts |
Posted - 08/10/2005 : 12:52:28 [Permalink]
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This is a forum for sceptic people or not?
Is there anyone who thinks like me  |
"Obsequium amicos, veritas odium parit" (Flattery gets friends, truth hatred)
Publius Terentius Afer, "Terence", Roman dramatist
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Dave W.
Info Junkie
USA
26021 Posts |
Posted - 08/10/2005 : 12:59:06 [Permalink]
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quote:
Originally posted by sts60
Thanks, everyone, for the welcome. I used to lurk here a while back.
A hearty "welcome back," then! And a big "thank you" for the data.quote:
The Titan IV/Centaur databook prepared for the Cassini safety analysis (and made available for public review before the launch) gave a figure of 33500 fps (10200 m/s) and altitude of 10,883,000 ft (3,317,000 m) at separation of the Centaur upper stage.
So it's safe to say that the 36,000 mph figure bigbrain is tossing around is baloney. In reality, it was no more than 22,841 mph (about 6.34 miles per second).quote:
At the Target Interface Point, reached 50 minutes later, the inertial speed is 22900 fps (6980 m/s) and altitude is 75,753,000 ft (23,394,000 m). The TIP can be considered the "starting point" of the interplanetary trajectory.
And in just 50 minutes, the craft has slowed by over 3,000 m/s. Damn, the Earth really sucks!quote:
The altitude, of course, is basically the height of the spacecraft above the Earth's surface. The speed is relative to the center of the Earth, so before liftoff the speed was 1341 fps (409 m/s).
So, since the velocity of Earth itself is closer to 66,000 mph (on average), the craft, if flung off at a tangent to Earth's orbit, could (at TIP) be going no faster than 66,000 + 15,614 mph, or 81,614 mph. About 80% of the figure bigbrain would have us use.
Thanks again! |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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filthy
SFN Die Hard
USA
14408 Posts |
Posted - 08/10/2005 : 13:01:49 [Permalink]
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quote:
Originally posted by bigbrain
This is a forum for sceptic people or not?
Is there anyone who thinks like me
Do you mean septicly? Well, Dr. Mabuse is our local Septic Fiend, if that will help.
Beyond that, I rather doubt it. Here, we base our thoughts upon verifiable evidence, as can be read in this and many other threads. In short, we think critically, and if NASA should come up with trash, we would be quick to comment on it.
Skeptisism is not doubting so much as witholding judgement until all of the evidence in gathered. Then, the matter can be supported or debunked as the situation calls for. Critical thinking, examination of the evidence, that's being a skeptic...
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"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
"The default position of human nature is to punch the other guy in the face and take his stuff." ~~ Dude
Brother Boot Knife of Warm Humanitarianism,
and Crypto-Communist!
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pleco
SFN Addict
USA
2998 Posts |
Posted - 08/10/2005 : 13:02:30 [Permalink]
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quote:
Originally posted by bigbrain
This is a forum for sceptic people or not?
Is there anyone who thinks like me
You are not a skeptic. |
by Filthy
The neo-con methane machine will soon be running at full fart. |
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furshur
SFN Regular
USA
1536 Posts |
Posted - 08/10/2005 : 13:04:54 [Permalink]
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bigbrain don't forget that Jupiter and the Earth are orbiting in the same direction so the space craft is trying to "catch up" to Jupiter therefore if I use your logic the relative speed of the space craft would be:
65,000 miles per hour (earth velocity) + 36,000 miles per hour (spacecraft's velocity) = 101,000 miles per hour - 30,000 miles per hour (Jupiters average velocity) = 71,000 miles per hour
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If I knew then what I know now then I would know more now than I know. |
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