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Post by pierre1985 on Jul 25, 2005 13:17:58 GMT -4
I wrote: "Close to Saturn Nasa engineers have slowed down their probe at 1,400 miles per hour" Mr. Professor wrote: False. You have been told several times to consult the field of orbital mechanics. That is the study of the behavior of bodies whose motion is dominated by momentum and gravity. It is the science behind the navigation of spacecraft. Go here please: saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=94"...The engine burn will slow the spacecraft by 626 meters per second (1,400 miles per hour)...". and here: "http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=98 "...During Wednesday's maneuver, Cassini's main engine burned for 38 seconds to slow the spacecraft by about 3.6 meters per second (about 8 miles per hour)...". False is what you say, dear Mr. Professor.
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Post by sts60 on Jul 25, 2005 13:21:45 GMT -4
Those answers are not brush-offs. You're simply so far from reality with your understanding that it's impossible to explain it to you until you make the effort to understand a few basic facts about how the planets go around the Sun. I recomment you look at JPL's Basics of Space Flight. Right now, it's like talking to you about great circle aircraft routes when you think the world is flat. That's how far off you are in your understanding. I'm not trying to be rude - I'm trying to indicate to you that you need to do a little work before making claims like the one above.
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Post by pierre1985 on Jul 25, 2005 13:52:51 GMT -4
"I recomment you look at JPL's Basics of Space Flight" Nasa actors have not considered earth velocity in their calculations. Why should you slow down velocity of your probe from 140,000 kph at 60,000 kph? You can brake when you are close to Saturn, or not? How can they brake their probes? Do they turn them 180 degrees and turn on rocket engines?
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Post by gdwarf on Jul 25, 2005 14:15:02 GMT -4
Did you even read that first article? It's being slowed down so that it can be captured in Saturn's orbit, which actually disproves your theory, rather then make the probe go too slow they made it go faster so that they would get there sooner and would have to slow it down. Once again, did you read the articles? NASA is slowing down the probe as it reaches Saturn, so that they can make it go where they want with minimal risk. Don't you slow down your car when entering a parking lot? Or do you simply drive around one at 60 mph until you find a place to park, at which point you stop on a dime? Once again, although I know very little about physics in space I know that that is wrong, the Earth would have to be heading directly toward Saturn and it's Rotation would have to be the right way for your idea to work. I'm positive that there are other limiting factors, but even a basic knowledge of grade 10 physics could tell you what I just did. I answered that above, but it's quite simple, 1. NASA did not do all of the slowing, physics did some. 2. It would probably not be going 140 000 km/h, as high school physics would tell you. 3. So that it could orbit Saturn and not simply fly past, limiting the Data that NASA could get. 4. So that it could be manouverd with more ease, see above. This line confuses me, because the answer seems obvious, yes, what's so different about Saturn that would stop you from braking there? Edit: Ah, it seems I was wrong. As Jay Utah said below the Rocket is turned around, not always 180 degrees, now that I think about it that does seem like a perfectly logical and useful idea.
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Post by JayUtah on Jul 25, 2005 14:23:21 GMT -4
"...The engine burn will slow the spacecraft by 626 meters per second (1,400 miles per hour)..."
False is what you say, dear Mr. Professor.
The spacecraft will slow naturally via orbital mechanics as it reaches aphelion. This is common for all orbits: Kepler's third law tells us this. However, spacecraft can, and sometimes do, use their engines to slow down as they approach their destinations. This is to facilitate the insertion manuever.
To "insert" into orbit around the destination object, the spacecraft's speed must be reduced so as to be consistent with the desired altitude. Small spacecraft often cannot do this in one manuever because they lack the impulse. The Apollo spacecraft, for example, could insert into lunar orbit because the SPS engine is powerful. To go from a transfer orbit to parking orbit with a small engine may require several burns. Once the spacecraft has entered the destination sphere of influence, it can bleed off some of the energy from the transfer.
But this does not change the basic property of all orbits -- including transfer orbits -- that the orbiter slows toward apoapsis.
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Post by JayUtah on Jul 25, 2005 14:27:20 GMT -4
I recomment you look at JPL's Basics of Space FlightMost of us have considerably more advanced knowledge than that. Nasa actors have not considered earth velocity in their calculations.Irrelevant. Please give your qualifications to discuss orbital mechanics and space navigation. Why should you slow down velocity of your probe from 140,000 kph at 60,000 kph?It has been explained numerous times. You simply don't understand enough about space travel to know how the answer fits. You can brake when you are close to Saturn, or not?I don't understand what you're asking. How can they brake their probes? Do they turn them 180 degrees and turn on rocket engines?You mean you're an "expert" in space navigation and you don't even know how to steer a spacecraft? LOL! Yes, they turn the spacecraft so that the engine axis is aligned with the desired direction in which velocity is to be added. That's not necessarily 180 degrees away from any particular direction, since spacecraft do not travel in straight lines in space. They travel in orbits, either parking orbits or transfer orbits. And how do they tell when they're pointing in the right direction? They use the stars.
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Post by sts60 on Jul 25, 2005 15:36:35 GMT -4
To be charitable, Pierre hasn't said he's an expert in space navigation. He's only claimed to be an expert in wide-angle photography (although he didn't even know that "fisheye" and wide-angle referred to the same thing). And I was the one recommending (to Pierre) that he looked at the JPL site.
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Post by pierre1985 on Jul 25, 2005 15:39:15 GMT -4
Well, you use stars only to point in the right direction.
But if you are "above" or "bilow" Saturn of 1,000,000 kilometers and continue to go forward, you will never be able to meet Saturn.
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Post by LunarOrbit on Jul 25, 2005 15:44:54 GMT -4
First of all, I'm pretty sure most (if not all) of the planets are on the same plane, so the probe wouldn't start out 1 million miles above or below Saturn. I could be wrong about that though.
But even if the probe was above or below the plane that Saturn is on, why couldn't it travel up or down to meet Saturn? The is nothing preventing the probe from navigating in three dimensions.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jul 25, 2005 15:51:26 GMT -4
But if you are "above" or "bilow" Saturn of 1,000,000 kilometers and continue to go forward, you will never be able to meet Saturn. Earth and the destination planet are in slightly different orbital planes but usually not more than a few degrees. The spacecraft is launched into a transfer orbit that intersects Earth's orbit at the launch point and the destination planet's orbit at the rendezvous point. There is nothing magical about it, but it does involve very complex mathematics to figure out.
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Post by pierre1985 on Jul 25, 2005 15:51:58 GMT -4
"But even if the probe was above or below the plane that Saturn is on, why couldn't it travel up or down to meet Saturn? The is nothing preventing the probe from navigating in three dimensions".
But you have not technology to see in which relationship is your probe as regards Saturn.
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Post by twinstead on Jul 25, 2005 15:59:39 GMT -4
"But even if the probe was above or below the plane that Saturn is on, why couldn't it travel up or down to meet Saturn? The is nothing preventing the probe from navigating in three dimensions". But you have not technology to see in which relationship is your probe as regards Saturn. Says who?
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Post by LunarOrbit on Jul 25, 2005 16:02:06 GMT -4
What technology do we need other than a telescope and a calculator?
I'm a webpage designer not a rocket scientist, so I'm not the best person to explain how it's done, but I do know that the planets move in predictable orbits. I'm sure we can even predict where Saturn will be 1000 years from now (or 1000 years in the past) with pretty good accuracy. To send a probe to Saturn we only need to know how where it will be at a certain point in the future, and then launch a powerful enough rocket into an orbit that intersects Saturns orbit at the right time.
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Jul 25, 2005 16:02:44 GMT -4
But you have not technology to see in which relationship is your probe as regards Saturn. What makes you say that? Of course we have the technology. The spacecraft's position is usually determined by homing in on its radio transmissions. Altitude and azimuth is read directly from the position of the receiving antenna. Distance is determined by measuring the travel time of the radio signals. The signal's Doppler shift is used to determine the spacecraft's line-of-sight velocity. By obtaining several such measurements the spacecraft's position can be determined with a high degree of accuracy.
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Post by pierre1985 on Jul 25, 2005 16:07:55 GMT -4
"To send a probe to Saturn we only need to know how where it will be at a certain point in the future, and then launch a powerful enough rocket into an orbit that intersects Saturns orbit at the right time".
You are in 3D space not on a level surface. On a plane you have many and many possibilities to mistake, but in 3D space you have infinite possibilities to mistake.
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