Chaos, Pioneer & V-ger

[brellis]

I have another layman's question about orbit calculations:<br /><br />When they devised the gravity-assist plan to send spacecraft to the outer planets and beyond, they loaded the craft with fuel for course corrections. My question is, were the planets in the precise place predicted when the craft arrived, or were any course corrections simply due to unknowns in gravity assitance?<br /><br />Oh, and are they still studying the ramifications of chaos theory in data sent from these distant craft? <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[CalliArcale]

The fuel isn't just for course corrections; it's also for attitude control. The Pioneers were spin-stabilized (technically, they still are even though they aren't responding to Earth anymore) but the Voyagers weren't. To orient their instruments at scientific targets and to point their high gain antennas towards Earth, they must burn propellant. This is why the Voyagers continue to consume propellant even though they are no longer trying to maintain any particular course.<br /><br />But in answer to your question, yes, they did burn propellant for what are technically called trajectory correction maneuvers. These were not because the locations of the planets were unknown or unpredictable, however. It was to set up exactly the right approach to each planet so that the spacecraft would encounter the planet just right. The angle needed to propel the spacecraft on to its next target is very precise, and odds are the previous encounter won't set it up that perfectly. Additionally, there were specific targets of interest for each planetary flyby -- especially moons and rings. Sometimes these were decided after the spacecraft were launched. The only way to set these up after the fact is to burn propellant.<br /><br />Really, the remarkable precision of the missions is a magnificent demonstration of how accurate traditional Newtonian celestial mechanics is at most scales.<br /><br />Mission scientists have continued to observe the spacecraft in hopes of seeing a gravitational deflection from a previously unknown object. Additionally, an unexplained deceleration may have been observed in Pioneer 10. (The significance of the data is debated.) Unfortunately, Pioneer 11 gave out too early to confirm the finding, and the Voyagers, as they are not spin-stabilized, do not provide accurate enough data to reproduce the result. If this effect is real, it's not likely to be due to chaos theory in and of itself; something has to be causing it. Theories have ranged from denser- <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[brellis]

Well, at least the TimeLady will tell us <img src="/images/icons/smile.gif" /><br /><br />The mention of moons and rings brings another Q:<br /><br />Cassini arrived at a Saturn with 18 known moons, and has since discovered another<br /> http://www.nasa.gov/centers/jpl/news/cassini-051005.html<br /><br />so does it look straight ahead to make sure it doesn't run into an undiscovered moon?<br /> <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[vogon13]

<br />Between Titan encounters, Cassini travels an ellipse around Saturn. Looking straight ahead wouldn't help. And since Cassini typically takes a group of photos, and then turns toward earth and unloads the data recorder all at once, even if it did, we wouldn't find out in time to do anything about it.<br /><br />Pioneer 11 came within a couple thousand km of a previously uncharted object and managed to not get snuffed, but remember, even with all the 'stuff' around Saturn, space is still pretty big.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[CalliArcale]

The moons Cassini has been discovering are all embedded in the ring system, and it is safe from those. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>