New Horizons and the Pioneer Effect

[robnissen]

Someone posted that New Horizons can not look for the Pioneer effect because it is (or is not, I don't remember) spin stablized. If the Pioneer effect is real, there is a major flaw in our understanding of gravity and/or dark matter and/or dark energy. Since most missions are not fly-bys, it seems to me that New Horizons should have been programmed to look for the Pioneer effect after it was done with its primary mission. If it was a case of New Horizons needing to be spin stabilized (or not spin stablized as the case may be), would it have been possible to turn off (on?) spin stability after its primary mission was over. After New Horizons fly-bys are done, it could have done a tremendous service by proving whether the Pioneer effect is real or now. Am I missing something?

 

[vogon13]

Modeling the heat emissions from the RTG and how it could perturb the trajectory is quite complicated. Reflections from the close by, irregularly shaped body of the craft is the big problem.<br /><br />NH is planned to encounter (hopefully) 2 more KBOs after Pluto/ Charon flyby, suspect course deflections for the subsequent encounters that far out would mess up the data set too. Pioneer 10 had no encounters after Jupiter, P11, none after Saturn.<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>

 

[bonzelite]

<i>in my opinion,</i> the Pioneer Effect will eventually be encountered as the solar system, continually accelerating as it expands, will meet <i>all of the craft sent outward</i> as long as all craft remain coasting and non-accelerating. spin-stabilization will be irrelevant as the P-effect has nothing to do with craft spin, and everything to do with expansion of the solar system going out to meet the craft. eventually, all craft may return to the vicinity of the orbit of the planets, perhaps, eventually, going into orbit around one. or the sun. <br /><br />unless a craft can perpetually overcome the relative expansion of the solar system, it will be overtaken by the solar system and "return" to the local neighborhood. since the Voyager craft are traveling quite faster than the Pioneers, their P-effects will be longer in coming, yet will be eventually detected.

 

[vogon13]

Will the crafts themselves be larger or smaller when we catch up with them?<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]

Well, you can't just program the probe to look for the effect. It has to be designed a certain way. Basically, it needs to be spin-stabilized. The upshot of spin stabilization is that you don't have to use thrusters to correct your antenna's aim at Earth. Since every single thruster firing adds uncertainty to your spacecraft's true speed and position, this normally negligible effect becomes significant over a long period of time.<br /><br />So spin-stabilization shoudl also buy you reduced propellant consumption. This is why many commsats have been spin-stabilized as well. It's cheaper.<br /><br />But it has some significant disadvantages too. The biggest disadvantage by far is that you cannot slew the spacecraft. Pioneers 10 & 11 were limited in the kinds of pictures they could take because they were spin-stabilized. The Voyagers greatly outclassed the Pioneers because they could not only slew themselves, they also had science instruments (including the cameras) on a moveable arm -- the scan platform. The drawback to a scan platform is that it's got moving parts; Voyager 2 almost lost the use of its scan platform before the Neptune flyby, but engineers were luckily able to coax it back most of the way. (The lubricant was freezing.) Neither Voyager can use its scan platform today.<br /><br />Newer probes don't generally use scan platforms or spin stabilization. Instead, they use gyroscopes both for stabilization and for attitude control. Cassini can use its reaction wheel assemblies to slew itself around with remarkable delicacy, far beyond that acheivable with thrusters, but it has thrusters also as a backup. I don't believe they are sufficient to fully stabilize it; Cassini is an enormous probe, easily the most massive ever sent into the outer solar system. Galileo had an intriguing (but complicated) strategy: most of the probe was spin-stabilized, but the bottommost part was not. Many science instruments were placed onto the despun section. This <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>

 

[bonzelite]

<font color="yellow"><br />Will the crafts themselves be larger or smaller when we catch up with them? </font><br /><br />larger, as everything else will be as well. relative to the earth, the planets, et al, everything will remain appearing the same size.

 

[vogon13]

Then maybe everything is really shrinking?<br /><br />{think about it, subtle, but profound}<br /><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>

 

[bonzelite]

i see what you mean, but my premise is that everything is expanding, accelerating (thus creating "gravity" which is nothing but a geometric effect of acceleration due to relative size expansion, ie, the earth's relative expansion is larger than a space probe, which is small by comparison, yet all expanding at the same rate). <br /><br />as long as the solar sytem, as one thing, continues to expand, it will meet the pioneer craft (which is also expanding), as the craft is overataken by the acceleration and expansion rate of the solar system itself. it will, then, "return" to our solar system.

 

[vogon13]

Space is contracting all down about you . . . .<br /><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>

 

[bonzelite]

that is another take on it, an opposite one. but another take on it, yes. <br /><br />