h a l f b a k e r yI didn't say you were on to something, I said you were on something.
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A set of satellites orbiting the sun instead of the Earth could (using well established GPS technology) aid space probes in navigating around the solar system.
Chronology of Sun Exploration
http://www.eoascien...ce/10/sun/sun7.html
Boatloads of probes in solar orbit. [phoenix, Oct 17 2004, last modified Oct 21 2004]
Satellite Navigation Using GPS
http://esapub.esrin...bullet90/b90mur.htm
Example of GPS use that is what I had in mind that could be expanded to "SPS" [talldave, Oct 17 2004, last modified Oct 21 2004]
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// could ... aid space probes in navigating around the solar system // |
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What would this provide that is not currently being accomplished? |
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Keeping an eye on those pesky Martians, for one thing. They could be anywhere. |
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myorp gewurztraminer leader, earth-snarfy. |
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Why not? It's not like it's traveling *through* anything. Aren't we hearing big bang-era echoes from jillions of light years away on radio frequency? |
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I was just watching a show on the Science channel and they used a sophisticated imagining system that used the stars for tracking. It was promoted as one of the first probes to guide itself. I think they are normally guided by Earth based signals, Newton's Laws and tracking from Earth based stations. |
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It's true that there would a huge difference in the fraction of signal intensity (intesnity goes like 1 over the distance squared) received since the distance is so much bigger, and this may be the deal breaker. |
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Would there not be lots of interference? |
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//I was just watching a show on the Science channel and they used a sophisticated imagining system that used the stars for tracking. It was promoted as one of the first probes to guide itself. I think they are normally guided by Earth based signals, Newton's Laws and tracking from Earth based stations.// |
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NASA scientist: "Whatdda mean you used degrees? The table's in radians!" |
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<probe takes a left turn at Saturn and is dragged into Jupiter> |
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A feature of CJ Cherryh's space-based sci fi stories, and I am sure many others. |
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Once we get to doing some serious motoring around the Solar System, this will be essential. Until then, we don't send enough stuff up to worry about general placement. |
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I don't believe the author intends this for general use, though that would be fun. You could watch your coordinates change as the earth rotates and revolves around the sun. |
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The name needs to be changed to SSPS or SPS (for solar [system] positioning system). |
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Have we ever yet put anything in orbit round the sun? |
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Sure, everything "we" have is in orbit around the sun save for a couple of probes that have left the solar system. |
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You know what I mean [Bris].
Have we ever sent a powered vehicle to the sun and placed it into e.g a geostationary orbit reference the Sun itself?. I'm asking here! |
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I don't know if anything has been put in a "heleosynchronous" orbit, though that seems like it would be useful for observering solar cycles in order to study the sun in general. (If that's what you were asking...?) |
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I have a few of question: |
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First, will somebody that knows something about it please post something on the subject of the size (mass), speed, and radius of orbit required of satellites to stay on track; and not escape the gravity, or fall into the body around which they are orbiting? |
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Second, would it be possible to put broadcasting stations on some of the sun’s natural satellites? E.g. The planets, or their satellites. |
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And one last question. How is it possible to stay in one relative position over the sun? I understood the sun to be made up mostly of Helium and Hydrogen, two non-solids. I suppose it would be possible to stay in the same position relative to the line segment between the center of the universe and the sun, is that what you meant? |
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sorry for not knowing the definition of one question… |
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To answer Swamilad's question: (And no offense, but I'm going to try to use as much non-technical language as I can.) |
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Mass, as long as that mass is tiny compared to the thing it orbits is unimportant. (More mass means more gravity which means it's being pulled harder, but more mass also means more inertia which means it is harder to pull. The two things cancel each other out.) |
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Size (in this case) is also pretty unimportant. |
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Depending on the distance there is a particular speed that will give the object a circular orbit if the path is at right angles to the line joining the satellite and the thing it orbits (the radius). |
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If the speed is a bit faster, the orbit will be eccentric, it'll be elliptical, with the starting point being the closest to the orbitee. (Okay, orbitee, that's a made up word, oh well...) |
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If the speed is a bit slower, the orbit will also be eccentric, this time with the initial position being the farthest from the orbitee. |
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They might seem that way, but orbits aren't that mysterious... If you throw your keys (for instance) through the air, the arc it follows (forgetting about air resistance) is a part of an orbit. |
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True, a very elliptical orbit and one that intersects the surface of the Earth, but an orbit nonetheless. |
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As to the second question, yes the sun doesn't have a solid surface, but it does have rotational motion. Think of the atmosphere of Jupiter. There are some persistent features that revolve around the globe. Different latitudes rotate at difference rates, so it would be pretty arbitrary which rate you chose. |
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I hope I didn't kill anyone with the physics lesson.... |
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Swamilad! Swamilad! Wake up! (smack smack) |
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Oh my God, I don't think he's breathing! Someone call 911! |
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talldave, thanks for the little lesson, and thanks for the word “orbitee.” I was searching for that before my first post. |
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Not to argue, but I would swear I was taught that an object’s path through the air in part of a parabola. I don’t know whether or not a segment of a parabola is the same as an ellipse for that portion, but it doesn’t seem like it could be, given their definitions. That said, I do think your explanation certainly is reasonable. Could you crush this doubt in my mind? |
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Even if you could create a "heliostationary" orbit with reference to some solar surface feature, I'm not sure what the point of that would be. GPS satellites are geostationary because you don't want a thing's coordinates to keep changing if it stays at the same spot on the Earth's surface, and you want to be able to find places in a predictable way. But nothing in the solar system is ever "standing still" with respect to the sun, and even if there's some predictably moving feature on the sun's surface, it would be of no particular use in navigation. |
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[gnomethang] - I understand that a couple of satellites that are used to monitor the sun are effectively in a heliostationary orbit by being placed in a position where the gravitational pull from the earth and from the sun cancel each other out, a couple of million miles away. Needless to say, the satellites are on the sunward side of the earth! |
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"So, where are we at now?"
"Who knows? I can't read the damn thing, the numbers keep cycling too fast." |
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//GPS satellites are geostationary// |
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They are not. If they were it would be very difficult to get latitude information from them. |
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Too low to be geostationary. They circle about two times a day and at about 19,000 miles altitude instead of the 22,500 or so needed to be stationary. |
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There are quite a few objects up there in heliocentric orbit, both intentionally and otherwise. |
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Several early shots at the moon missed, and went into independent orbits around the sun. |
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One of the first intentional US launches to heliocentric orbit was Pioneer 6, on which NASA expended far too much of their supply of good luck. (Intended lifetime 6 months; recently celebrated 35 years and it still won't shut up) |
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What happens at night when the earth is blocking the signals from the sun's orbit? |
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It gets dark? Okay. I give up. What happens? |
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Whew! Lots of people saying lots of things..... |
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In the approximation of constant gravity (which is a really good approximation to hundreds of feet) the path of a projectile is a parabola. |
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If you take the variation of gravity with distance into account the path is elliptical. |
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So is the path an ellipse? Yes. Is it a parabola? Practically, yes. Mathmatically they only match at one point. Practically, they are in very close agreement in a small section. |
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Okay, now to clarify, a Solar Positioning Satellite system would not involve Heliosynchronous orbits (if such a thing really exits). In fact, like GPS, in would involve satellites in polar orbits. |
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The crux of the idea is that if space probes could have simpler, more reliable electronics for guidance they could be cheaper, more dependable in general and maybe smaller and lighter, further decreasing the cost. |
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Does this savings justify the considerable cost of the network? Probably not now, but eventually maybe. |
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There could be some side benefits: |
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I've heard that general relativisitc effects are taken into account in the GPS network. I'm not clear on the details, but timing is crucial for the system and there are some time dilation effects both from the motion of the satellites (special relativistic) and from gravitational concerns (gravitational time dilation). I don't know if similar concerns for a solar positioning system would be interesting to physicists looking at general relativity. |
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I suspect that measurements of planetary orbits could be done with a greater degree of precision, maybe also improvements could be made in the measurements of the mass of the sun and the gravitational constant (G) of the universe. |
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Re: cheaper, more reliable space probes - yes. Absolutely. |
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Plus, consider that current probes are getting autonomous navigation capability because we don't have sufficient radio dish equipment or time to provide navigational support, and you get a reduction in extended mission cost as well. |
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You could place them in stationary
orbits around other planets and
combine the effects to measure
the whole solar system. |
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With extremely precise measurements of the orbits of planets, I wonder if it would easier to plan complicated slingshot orbital manuvers. |
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A gps is useful because it provides information about your location on a rigid surface, the surface of earth. |
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A ssps would tell you your position in an arbitrary framework around the solar system, but that framework wouldn't correspond for long to anything in the real universe. For example, the ssps coordinates of the earth and the moon would be in constant flux, making this not that helpful in navigating between points of interest which are in motion(all of them). |
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What FloridaManatee & phoenix wrote. |
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Damn, someone's already done this one. |
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I was thinking that a SSPS would allow to you meet someone at a certain time by specifying a position. If you gave a certain very precise location along the earth's orbit, the person would have to meet you there at the exact time that a certain building passed through that space. Hard to calculate though. |
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