How does this all really work? Can anyone help?

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brooklynspacecadet

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i always wanted to know this.<br />the mars rovers took 7 months to arrive on mars. ok first question how did they guide them to get there? isnt mars 36 million miles away? what propulsion could get them to get that far? <br />secondly now that they are there how do they remote control these rovers to tell them to do what they want them to do with such specific commands at 36 million miles away? we can't even get good cell phone reception from distances of only miles away.<br />how is it possible? what technology do they use to do it?<br />if anyone knows please let me know.<br />thanks.
 
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jimfromnsf

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1. The spacecraft have star trackers and guidance systems on board<br />2. The rocket that launched them, sent them on their way. The rovers basically coasted all the way. In space, constant thrusting isn't required.<br /><br />3. They don't give it specific commands, they tell it to go to a specific point and the rovers do it themselves.<br /><br />4. Cell phones are vary different, they have interference to deal with (buildings etc). There isn't any in space. The issue that the rovers deal with is time delay. It takes 20 minutes for a signal from earth to arrive at Mars.
 
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PistolPete

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<blockquote><font class="small">In reply to:</font><hr /><p>secondly now that they are there how do they remote control these rovers to tell them to do what they want them to do with such specific commands at 36 million miles away? we can't even get good cell phone reception from distances of only miles away. <br />how is it possible? what technology do they use to do it? <p><hr /></p></p></blockquote><br />Welcome to SDC, brooklynspacecadet.<br /><br />The picture below is how NASA communicates with planetary and deep space probes. The antennas they use are just a bit bigger than a cell phone antenna. <img src="/images/icons/wink.gif" /> The one in the picture is 230 feet across.<br /><br />Deep Space Network homepage<br /><br />As mentioned by Jimfromnsf and Newsartist, because there is no wind resistance to slow a spacecraft down once it leaves Earth's atmosphere it can essentially coast forever. It is not like a car or an airplane which constantly needs to push against the friction of air moving around it. That being said, the speed that an interplanetary spacecraft needs to reach before it can coast is so great that the rocket that pushes into outer space is little more than a giant gas can with a rocket engine on the bottom. Almost all of the fuel is burnt within the first nine minutes of flight. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>
 
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no_way

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<blockquote><font class="small">In reply to:</font><hr /><p>...how do they remote control these rovers to tell them to do what they want them to do with such specific commands at 36 million miles away?<p><hr /></p></p></blockquote><br />In the words of a True Master: very carefully.
 
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usn_skwerl

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i too wondered what they use to communicate with interplanetary probes...good stuff!<br /><br />*sees the pic and suddenly has a flashback to a clip from "Howard the Duck"* <div class="Discussion_UserSignature"> </div>
 
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3488

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I just wanted to welcome you to SDC brooklynspacecadet.<br /><br />A great question & a great first post.<br /><br />Please look at the Deep Space Network links that have been provided for you on this thread, by<br />ThereIWas & PistolPete.<br /><br />Also during the Voyager 2 encounters with Uranus & Neptune, the Very Large Array in <br />New Mexico was pressed into action, to help with the reception from Voyager 2 at that distance.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>
 
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usn_skwerl

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looks like one of the dishes on the right is talking to (playing for) the other team.... <div class="Discussion_UserSignature"> </div>
 
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holmec

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There are documetaries to show how. They actually program a drive and investigation. That is many steps at a time. They make the drive by driving a virtual simulator of the rover on the current ground. So its a combination of virtual reatlity, batch commands, automation, and rocks that don't move. <br /><br />If they were studying animals on another planet, this system would not work. More automation on part of the rovers would be needed. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>
 
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holmec

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<blockquote><font class="small">In reply to:</font><hr /><p>3. They don't give it specific commands, they tell it to go to a specific point and the rovers do it themselves. <p><hr /></p></p></blockquote><br /><br />Actually they do. That's how computers work. The specific commands are created in a VR simulation of where the rovers are at and of the rovers themselves. So the programming is like driving the vehicle and the computer records the commands to do that and that set of commands gets sent to the rovers which executes the commands and passes on data and pics. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>
 
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brooklynspacecadet

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thanks for all the welcomes guys. glad to be apart of the space community.<br />wow. that is amazing. that is a beautiful satellite. so grand and large. this answers alot of my questions but creates a few more. i mentioned 36 million miles. this is the average distance from mars to earth. with any communication device whether is be a gargantuan satellite or an abysmal fm transmitter, the more distance you are dealing with, the weaker the signal and communication gets. now we are talking about 36 million miles here. i mean that is an uncanny amount of distance away. <br />the other poster later who had a great explanation of how we communicate and control spacecrafts of even further distances from mars like the craft that was sent to saturns moon titan and exploratory probes to neptune which is staggering 2.6 billion miles from earth.<br />i mean i am a pretty enlightened person but it just seems impossible how something so unbeleivable far away can be controlled and communicated with.<br />another poster also mentioned that there is no interference like we have on earth with buildings and many antennas around. but isnt it true in space there are solar winds from the sun, asteroids and comets that can cause interference? so not only is there this great distance there is also the interference to deal with.<br />i guess like most things in my life i would actually have to see this in action to beleive it. i am a hard man to convince;)<br />
 
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MeteorWayne

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Huh?<br /><br />That's in response to?<br /><br />"In the words of a True Master: very carefully."<br /><br />I thought it was a pretty witty comment, which I wish I had thought of first!<br /><img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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holmec

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Agreed. I was just elaborating. Did I kill the mood? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>
 
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Huntster

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>>with any communication device whether is be a gargantuan satellite or an abysmal fm transmitter, the more distance you are dealing with, the weaker the signal and communication gets.<br /><br />That's absolutely true. However, consider that we are still communicating with and receiving data from Voyager 1, which is over 9.5 <i>billion</i> miles away from the Sun, and is beginning to exit the solar system.<br /><br />To grasp this, remember that when you are receiving transmissions from an FM radio station, that station is broadcasting in all directions at once, which costs power and range. The Deep Space Network and similar systems are highly directional, meaning that they point their transmitters/receivers at a particular point in the sky. This lets them put a significant amount of power into one direction, as opposed to the FM station which broadcasts in every direction. Many of the space probes use this same kind of system to send information back to Earth.<br /><br />As for other objects in space interfering with the radio signal, you have to remember that asteroids and comets and such are very widely spaced, so its more a matter of the radio signal trying to hit it, rather than it accidentally interfering.<br /><br />I'm certainly no expert, but I hope that made some sense (and I'm sure the others will correct me if I've messed any of this up). <div class="Discussion_UserSignature"> </div>
 
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PistolPete

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36 million miles in not an inconsequential distance, especially when you take into consideration the fact that radio wave signal strength decreases with something known as an inverse square law. Put in layman's terms it means that if you double the distance, the signal strength decreases by a factor of four. The transmitters on the Mars rovers are not that powerful so the signals recieved by the Deep Space Network is very weak indeed. You wouldn't be able to pick them up with an FM radio.<br /><br />This, however, can be counteracted by a larger antenna. It works even better if you use something called a parabolic dish. Jackrabbits and other animals have ears that work similarly to a parabolic dish. If you want to try an experiment, cup your hands behind your ears and you will find that you can hear the faintest of sounds. This works because your hand increases the area of your ear and focuses the sound into your ear canal. A parabolic dish works the same way: it takes the faint radio waves that are spread out over a large area and focuses them onto a small point, making a weak signal stronger.<br /><br />Remember that the dish in the picture I showed you was 230 feet in diameter. If you divide 230 to get the radius then square that number and multiply it by Pi you get 41,548 square feet as the area of the dish. That's almost an acre! Now let's say that the dish focuses all of that area onto a smaller antenna that is one square foot in area. Now you have a ratio of 41,548 to 1, so you could say that a dish that big would make it seem as though a signal coming from 41,548 miles away were coming from just one mile away. If you then divide 35 million miles by 41,548 you get 842 miles. That's not very far away when you are talking about line of sight radio communication. Sat Phones in use on Earth today can fit in your hand and easily be picked up by a satellite well over 842 miles away.<br /><br />I hope that I was able to mathematically break it down for you <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>
 
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holmec

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Don't forget about the receiver's amplifiers. To compensate for a weak signal, you have to also increase the power to your receiver's amplifiers. This is akin to turning up the volume on your regular radio.<br /><br />I don't know how much power goes into the ground base receivers on the deep space network, but I bet its a lot. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>
 
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thereiwas

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The big dish antennas, in addition to focusing all the transmit power in one direction, also help on receive. The bigger your 'ear', the more of the spreading signal you intercept. The transmitters on the deep space probes and Mars rovers are not powerful at all.
 
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earth_bound_misfit

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Here's what happens when the beam arcs over to the closest bush <img src="/images/icons/wink.gif" /><br /><br />Link to more pictures of the serious Canberra bush fire that killed four people and destroyed numerous home. It also destroyed the Mt Stromlo Observatory that is run by the ANU <img src="/images/icons/frown.gif" /> <div class="Discussion_UserSignature"> <p> </p><p> </p><p>----------------------------------------------------------------- </p><p>Wanna see this site looking like the old SDC uplink?</p><p>Go here to see how: <strong>SDC Eye saver </strong>  </p> </div>
 
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Huntster

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Ohh, that's so wrong. Funny, but so wrong <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>
 
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darkenfast

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Brooklyn, the usual distance between Mars and Earth is actually a lot more than 36 million miles. Both planets orbit the Sun, with Mars being further out, and taking about twice as long to go around. This creates a constantly changing relationship between the two planets. To get from one to the other within the limits of our present propulsion systems, your interplanetary navigator must plot a very complex trajectory. Picture the two planetary orbits. Your spacecraft is currently in Earth's orbit around the Sun. You fire your engine and increase your speed until you are in another, more elliptical orbit, which gradually rises further away from the Sun until at the top it reaches the orbit of Mars (and hopefully at the same time that Mars happens to be there). You actually travel a LOT further than the distance between the orbits of Earth and of Mars. To return, you have to wait until the planets are in an appropriate position, and then decelerate (relative to the speed of Mars going around the Sun), thus entering a descending orbit that will bring you back to Earth's orbit. Doing all this with the minimum amount of fuel, combined with the problem of the planet's positions in their orbits, means that the time for a round-trip to Mars and back runs about two and a half years. The amazing thing is that all of this (and the way to calculate it) was figured out a long time ago by some very smart men with no computers! Hope this helps.
 
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holmec

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Right. So most of your transmission power and reception power is on Earth, while the probes' are limited. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>
 
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brooklynspacecadet

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that was a great post.<br />i read and just absorbed everything you wrote.<br />so what you're saying is in way the propulsion of the spacecraft is something like a fighter pilot trying to time his fire at a target moving in diffrent directions but in this case in a much slower firing situation which would take 7 months to reach its target and all dependent on the movements of both panets in their perspective orbits!<br /> wow. so it's possible that after 7 months of traveling 10's of millions of miles it could have missed mars if their timing was off on the 6780 km diameter target?<br />this deep space network nasa uses to issue commands to the rovers and receive data back from them. can't this network also steer the spacecrafts in case they are off on their targets? are these crafts only powered by a one directional propulsion or to they have some kinds of rudders and wings that can steer them?<br /><br /><br />
 
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spacester

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There is no steering in spaceflight. You start off on a trajectory and you better get it right because it takes a lot of energy to make large changes. Typically, you had a hard enough time getting enough propellant stored for the normal mission that you don't have huge reserves.<br /><br />What you DO have are trajectory correction maneuvers - TCMs. That's where they command the spacecraft to a particular orientation (often simply along the line of flight) and have it fire the rocket engines for a few seconds. This adds to or redirects the energy of your orbit and tweaks your trajectory just a bit. <br /><br />Here is a depiction of a round-trip mission to Mars starting in 2014 and taking 160 days on the voyage out and 215 days on the way back in. <div class="Discussion_UserSignature"> </div>
 
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