Rosetta Fly-By To Probe "Pioneer Anomaly"

DynaSoar writes "On Friday November 13th, ESA'a Rosetta probe will get its third and final gravity assist slingshot from Earth on its way to its primary targets, the asteroid Lutetia and Comet 67P/Churyumov-Gerasimenko. But the slingshot itself will allow ESA scientists to examine the trajectory for unusual changes seen in several other probes' velocities. An unaccountable variation was first noticed as excess speed in Pioneers 11 and 12, and has since been called the Pioneer Anomaly. More troubling than mere speed increase is the inconsistency of the effect. While Galileo and NEAR had appreciable speed increases, Cassini and Messenger did not. Rosetta itself gained more speed than expected from its 2005 fly-by, but only the expected amount from its 2007 fly-by. Several theories have been advanced, from mundane atmospheric drag to exotic variations on special relativity, but none are so far adequate to explain both the unexpected velocity increases and the lack of them in different instances. Armed with tracking hardware and software capable of measuring Rosetta's velocity within a few millimeters per second while it flies past at 45,000 km/hr, ESA will be gathering data which it hopes will help unravel the mystery."

Comments

Just so nobody fucks up the units from the start

[Anonymous Coward]

45000km/hr 45 000 km = 45 000 000 meters = 45 000 000 000 millimeters. 1 hour = 60 minutes = 3600 seconds. Rosetta's velocity is thus 12 500 000 millimeters per second.

Not the Pioneer Anomaly

[CheshireCatCO]

This isn't the Pioneer anomaly. The latter was seen not in flybys but during extended cruise phases with no maneuvers. As far as I know, it has only been seen in Pioneers, although that may be due to the particular nature of those spacecraft that make them excellent tests for this effect. (Assuming it's not entirely intrinsic to the spacecraft in the first place.)

This effect is a flyby effect and is different from the Pioneer Anomaly, as the article itself pretty clearly notes.

Re:Not the Pioneer Anomaly

[BadEvilYoda]

The Planetary Society has an interesting FAQ on this subject: http://www.planetary.org/programs/projects/innovative_technologies/pioneer_anomaly/update_20050720.html

Also explains why it is seen with Pioneer 10 and 11 and not Voyager 1 or 2 or other more "modern" spacecraft.

From the FAQ: The Pioneers are spin-stabilized spacecraft. The Voyagers are three-axis stabilized craft that fire thrusters to maintain their orientation in space or to slew around and point their instruments. Those thruster firings would introduce uncertainties in the tracking data that would overwhelm any effect as small as that occurring with Pioneer. This difference in the way the spacecraft are stabilized actually is one of the reasons the Pioneer data are so important and unique. Most current spacecraft are three-axis stabilized, not spin stabilized.

Re:Not the Pioneer Anomaly

[DynaSoar]

This effect is a flyby effect and is different from the Pioneer Anomaly, as the article itself pretty clearly notes.

The situations in which they are measured differ. This is what TFA states. But it is by no means certain that the cause differs, and TFA makes no claims one way or the other. John Anderson of JPL and colleagues published in 1998 and 2002 examinations of the Pioneers, Ulysses and Galileo trajectories and hypothesized a single phenomenon, a time dilation effect due to gravity. The fly by effects may be more pronounced due to greater frame dragging than trajectories more or less straight to the heliopause, but the velocity changes when noted are of the same magnitude. Mbelek's recent paper looks at fly by data to determine whether special relativity may account for the anomalies in fly bys, but does not exclude applying the same to non-fly by situations. If the math proves valid, and sufficient data is obtained, then it may be able to be determined whether the two discrepencies have a single cause. The data collection on Rosetta is being done in part to try to determine whether or not they are the same. If there weren't at least hypothesized 'same or different' consideration, there'd be no mention of Pioneers.

Re:Not the Pioneer Anomaly

[DynaSoar]

As far as I know, it has only been seen in Pioneers, although that may be due to the particular nature of those spacecraft that make them excellent tests for this effect.

According to Wikipedia the problem is that other spacecrafts have too much built-in disturbance (e.g. from thrusters) to measure such a small effect.

However I wonder why no one has built a spacecraft that explicitly avoids all such disturbances so the effect can be checked with the best accuracy possible. Also, put all sorts of additional measurement devices on it (of course only of the sort that doesn't disturb the path measurement, e.g. nothing producing large amounts of heat), e.g. to look at the matter density around (maybe there's simply more gas out there than expected, which is slowing down the space craft by friction). And of course, also measure as much of the internal state as possible, in order to find out about unexpected effects like gas leaks.

The problem with Voyager data is that they course correct using thrusters and so their exact location is more uncertain. Pioneers and most system bound probes are spin stabilized and so can be measured and predicted more reliably.

Several probes have been testing some of the relevant effects in Earth orbit for years. LAGEOS I and II detected an effect of relativity called frame dragging. This is an effect which is hypothisized to be greater near a planet, but also noticeable across great solar system distances. Gravity Probe B has measured it to a greater degree, is still collecting data, and is observing some unusual effects within the data. One of the LAGEOS teams is planning another probe, LARES, to be launched within a year or so, looking at this effect (also called the Lense-Thirring effect) with greater accuracy. Getting good numbers on this effect will allow others to determine if the effect is involved in any of the cases noted. It may also help to explain why it is not seen in different instances on the same probe (Rosetta 2005 vs. 2007) if the frame dragging is due to rotation, is asymmetrical, and the probes are found to have passed through the planetary field with vs, opposite the direction of rotation.

Re:Not the Pioneer Anomaly

[CheshireCatCO]

If there weren't at least hypothesized 'same or different' consideration, there'd be no mention of Pioneers.

Unless they're often confused, which they are. Two anomalies involve spacecraft trajectories are obviously easy to mix up, whether or not there is any reason to suspect a relationship.

Re:Not the Pioneer Anomaly

[arminw]

...This effect is a flyby effect and is different from the Pioneer Anomaly...

How does anyone know? Everybody assumes (believes) that the spacecraft as a whole are scrupulously electrically neutral. If that is not the case, which is very likely, then the electrical and magnetic fields in space would certainly affect its motion. An electric field, even a very weak one, affects a charged object 36 orders of magnitude more than gravity. Depending on the polarity of the charge, which can sometimes be negative and sometimes positive, there can be a change of either slowing down or speeding up.

The particles of the solar wind (electrons) ACCELERATE by the action of an electric field, where as they should slow down slightly if gravity were the only force affecting them. The Pioneer probes may have a slight positive charge, which means they would slow down a little more than we would expect by gravity alone.

Re:Not the Pioneer Anomaly

[CheshireCatCO]

The problem with Voyager data is that they course correct using thrusters and so their exact location is more uncertain.

No, not really. The location is what's being measured. The problem with Voyagers is that since they use thrusters, you don't know precisely enough what impulses were applied to them. If you don't know that, you can't remove it from the tracking data to reveal the small anomaly.

Also, if it is frame dragging, it doesn't explain Pioneer very well I can't imagine (being really damn far from any rotating mass and all). Additionally, I don't believe it makes sense to ascribe different instances on the same probe being due to passing Earth with rather than against the rotation: unless the probe is going out in the solar system and then, later back in again, the flyby will have the same orientation, albeit at different distances and latitudes. (On the other hand, you'd expect different effects, but not *zero* effect in one case, no matter what the relationship between the flybys is.)

Re:Just so nobody fucks up the units from the star

[snspdaarf]

Yeah, Mars is one thing, but if this hits Earth, it could wipe out the dinosaurs all over again!

That's Pioneer 10 and 11

[Cliff Stoll]

Pioneer 10 and 11, of course (not 11 and 12)

The Pioneer 10 & 11 spacecraft both flew by Jupiter, and Pioneer 11 went on to Saturn encounter.

I remember it well - while a grad student at the Lunar & Plantetary Labs, I helped with the Imaging Photopolarimeter during Saturn Encounter.

The spacecraft, designed in the early 1970's, had essentially no onboard memory, so instructions had to be uploaded in real time. The several hour-long communications delay made for real excitement at encounter (Did the spacecraft survive the ring crossing? Did the instruction arrive? Did the sensor point in the correct direction? Is it returning images?)

We'd spent months in advance, preparing alternative sequences for the encounter. Each sequence was on punched papertape. Then, at encounter in September 1979, we'd pick the tape, mount it on a teletype, and send the data out over the NASA deep space network, then anxiously wait to see if the instructions worked on Pioneer 11.

Re:That's Pioneer 10 and 11

[Neil Hodges]

Wikipedia has an article pertaining to this.

Re:That's Pioneer 10 and 11

[Anonymous Coward]

My father worked on some long distance space probes in the 1970s, as well. The excitement you're talking about is very real.

One day during the summer, when I was maybe 12 or 13, he came home from work early. It turns out the probe he was working with at the time was crossing the asteroid field or positioning itself to take some pictures or something, and well, he got very excited. So excited that he shit his pants while in mission control.

So he came home, had to change, and went back to work.

Metric only

[jbeaupre]

Could you please tell me what that is in metric time? These crazy 60 second minutes and 60 minute hours are too confusing. It might have been ok for the Summarians, but it's time to use a modern unit divisible by 10.

Re:Metric only

[Zerak-Tul]

Wait, 60 isn't divisible with 10 now?

Re:Metric only

[DynaSoar]

Could you please tell me what that is in metric time? These crazy 60 second minutes and 60 minute hours are too confusing. It might have been ok for the Summarians, but it's time to use a modern unit divisible by 10.

Metric and English seconds are exactly the same, if you start at minus 40. You can also use the metric version called Absolute Seconds, which start at minus 273 seconds (minus 4 minutes, 33 seconds). I'm pretty sure this is what NASA is using since they have an automatic hold scheduled into all their count downs at around T minus 4 minutes. It probably takes them that 33 seconds to change the clock faces from 60/60/24 markings to 10/10/10 markings. Actually, the time researcher Vernor Vinge presented a time standard in one of his studies "A Fire Upon The Deep" based on a 100/100/100 (100, 10,000, 1,000,000 seconds; about a minute and a half, 2 3/4 hours and 11.5 days) scale. The proposed system suffers from association with a communications system proposed to allow open discussion between individuals in distant locations, with intermediaries assisting in the transmission either in order simply to participate, or if providing large amounts of bandwidth, for a fee. This ridiculous concept is obviously untenable, and having it intermixed with this time standard causes one to disbelieve both.

Re:Metric only

[theIsovist]

Apparently so is math

Re:First post !

[maxwell demon]

I'm sorry but your post encountered a fly-by anomaly when passing one of the big Internet routers, and therefore was delayed, thus allowing other posts to come before it.

Re:Is it Dust?

[maxwell demon]

That might explain the Pioneer slowdown, but I don't think it could explain the energy gain on fly-by.

Mond 4 life, bitches!

[SlappyBastard]

This sounds like a case for . . . Modified Newtonian Dynamics!

Re:Just so nobody fucks up the units from the star

[MozeeToby]

I think you mean 3.74698572 × 10^12 Planck Lengths per Planck Time. It's high time we abandonded this archaic 'metric' system for one that more accurately expresses the universe.

Re:Center of earth...

[MozeeToby]

I would think that such an effect would have been discovered in the various 'gravity maps' that have been made of the Earth. If so, I can't imagine that they forgot to take that into account when trying to solve (or resolve) one of the mysteries of modern physics.

Cliff Stoll?

[Anonymous Coward]

Are you the same Cliff Stoll that wrote that Cuckoo's Egg book back in the '80s?

Re:Cliff Stoll?

[Cliff Stoll]

Yep, same guy.

Before Cuckoo's Egg, I was better known as a planetary scientist. My PhD dissertation relied on polarization data taken by Pioneer 10 & 11 to understand the scattering characteristics of Jupiter's upper atmosphere.

Cheers,
-Cliff