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The Pioneer Anomaly
edstrick
post Aug 30 2005, 08:52 AM
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Climate orbiter was not radar tracked, it was transponder tracked. You get precise distance, but have to model angular position on the sky from indirect data. One way to get precise relative position in the sky is differential interferometry, where one vehicle, say a mars orbiter, is a reference source, and the approaching vehicle's position relative to the reference can be measured.

The problem with Climate orbiter was not with the tracking data, it was modelling the trajectory based on that data when bogus information <incorrect spacecraft peturbation values from the momentum wheel offloading with thruster firing) was included in the solution. The nav team had recognized and been bothered the entire flight by considerably (several times?) larger trajectory calculation variations than normal, but not been able to find a cause of the error with available time and resource.

Polar Lander wiped out due to either 1.) a programming error in the descent software that was almost guaranteed to eat their lunch. or 2.) any of considerable number of design defects that added risk to the landing but weren't "smoking gun" errors.

The Pioneer anomaly is just that.. it's a departure of observations from very precise, but known imperfect calculations. We don't know if there's a physical something based on "deep" important physics, or if our engineering models of non-gravitational forces on the spacecraft are subtly wrong.

It will cost at least a few hundred million dollars to fly a mission that will convincingly and unambiguously prove an "important" physics cause is either present or not, and *PRECISELY* measure that effect if it exists as a function of distance from the sun. *** NOT TRIVIAL ***.

There are a lot of other research proposals and proposed space missions with equal or greater chances of testing and getting an important answer to "deep" physics questions that would cost the same or less than a Pioneer Anomaly mission. The best strategy is to pick the strongest tests with the greatest likelyhood of surprise, for the least amount of money and do or fly those..... and to pick tests that test fundamentally different possible suprises in deep physics. Things like dark matter detection experiments, gravity wave observatories, Dark energy investigations have far more chance per doller of real surprises than a pioneer anomaly mission. We need to keep it as an open question with the possibility of a mission, but right now, it seems a high risk, probably low yield mission for the money.
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Mongo
post Aug 30 2005, 07:12 PM
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QUOTE (edstrick @ Aug 30 2005, 08:52 AM)
There are a lot of other research proposals and proposed space missions with equal or greater chances of testing and getting an important answer to "deep" physics questions that would cost the same or less than a Pioneer Anomaly mission.  The best strategy is to pick the strongest tests with the greatest likelyhood of surprise, for the least amount of money and do or fly those..... and to pick tests that test fundamentally different possible suprises in deep physics.  Things like dark matter detection experiments, gravity wave observatories, Dark energy investigations have far more chance per doller of real surprises than a pioneer anomaly mission.  We need to keep it as an open question with the possibility of a mission, but right now, it seems a high risk, probably low yield mission for the money.

The problem with a 'dark matter' mission is that the putative dark matter is entirely hypothetical, and may not (I would say probably doesn't) exist. Stanley Milgrom's MOND theory or Jakob Bekenstein's TeVeS theory seems to me to explain the observations in question much more easily than any dark matter theory does. There are also indications that the effects ascribed to 'dark energy' may also be a natural result of a full MOND or TeVeS theory.

http://xxx.lanl.gov/abs/astro-ph/0504130

On the other hand, the so-called 'Pioneer Anomaly' appears to be genuine. The alternative explanations (solar wind, asymmetrical thermal radiation, etc.) appear to be several orders of magnitude too small to adequately explain the observed acceleration. I personally would say that a proper investigation of the 'Pioneer Anomaly' would be at least as important as Gravity Probe B, and could be mounted at a reasonable cost too. The spacecraft itself would be relatively inexpensive; the biggest cost would be the launch vehicle.

Here are links to papers discussing possible approaches to a mission:

http://xxx.lanl.gov/abs/astro-ph/0504634
http://xxx.lanl.gov/abs/astro-ph/0409373
http://xxx.lanl.gov/abs/gr-qc/0409117

Bill
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Bob Shaw
post Aug 31 2005, 11:28 AM
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Bill:

Your links, er, don't!

Bob Shaw


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Mongo
post Aug 31 2005, 02:45 PM
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That's strange; I just clicked on them and they sent me to the reports that I had referenced...

If they still don't work, I suppose that you can just go to

http://xxx.lanl.gov/find/astro-ph

and do a search for 'Pioneer Anomaly'. Or else just type out the links on your address bar.

Bill
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Bob Shaw
post Aug 31 2005, 03:42 PM
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QUOTE (Mongo @ Aug 31 2005, 03:45 PM)
That's strange; I just clicked on them and they sent me to the reports that I had referenced...

If they still don't work, I suppose that you can just go to

http://xxx.lanl.gov/find/astro-ph

and do a search for 'Pioneer Anomaly'.  Or else just type out the links on your address bar.

Bill
*



Bill:

I promise, linky no worky.

________________________________________________________

Access Denied
Sadly, you do not currently appear to have permission to access http://xxx.lanl.gov/find/astro-ph

If you believe this determination to be in error, see http://xxx.lanl.gov/denied.html for additional information.

_________________________________________________________

Bob Shaw


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Remember: Time Flies like the wind - but Fruit Flies like bananas!
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Mongo
post Aug 31 2005, 03:57 PM
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QUOTE (Bob Shaw @ Aug 31 2005, 03:42 PM)
I promise, linky no worky.


Okay, I'll try posting the files directly to the board. Hope this works.

The first file is the 'dark energy' in TeVaS paper. The other three are the 'Pioneer Anomaly' papers.

Bill
Attached File(s)
Attached File  0504130.pdf ( 111K ) Number of downloads: 231
Attached File  0504634.pdf ( 485.63K ) Number of downloads: 282
Attached File  0409373.pdf ( 152.4K ) Number of downloads: 255
Attached File  0409117.pdf ( 124.76K ) Number of downloads: 212
 
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The Messenger
post Aug 31 2005, 06:56 PM
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I am at least as interested in the flight path eccentricities of Odysseus, Galileo and Pioneer 6 as the Pioneer 10 and 11. While the Pioneer probes indicate an acceleration towards the sun, an unsolicited acceleration away from the sun had to be used to model the paths of Odysseus and Galileo, and one of a greater magnitude: ~1x10^-8m/s^2.

Likewise, I mentioned the navigational problems associated with the Polar Lander and Climate orbiter, not because of the failure modes, but because of the difficulty navigators had both predicting and tracking the probes – with or without a unit conversion error.

After the Climate Orbiter failed to achieve a non-intersecting orbit, two teams of navigators worked on the flight path of the Polar Lander. Each time they tried to model and predict solar wind effects, they were frustrated – they could not correlate the small force corrections due to the solar wind with the path of the probe.

On both missions, NASA tried to use triangulation as well as the Doppler ranging data, and triangulation yielded surprisingly unsatisfactory results.

Please allow me enough latitude to use a hypothetical to demonstrate why I think we must track down the exact causes of these small force and/or navigational errors. Assume the forces are real, and assume they are caused by a gravitational equivalent to a change in the permeability-of-free-space that is a function of mass. This would mean that a probe moving towards the sun would be slowed as more energy is stored in a stronger ‘mass field’ nearer the sun.

The Newtonian equation for velocity then becomes a function of total proximal mass, not just the mass of the object in motion (Ek=Mv^2/2f(x) where f(x) @ 1 AU = 1, and becomes larger as the object approaches the sun, leaving more energy in the potential energy pool (Remember, this is ALL HYPOTHETICAL and the force changes are very small and tightly constrained.)

Look what would happen: As a probe approaches the sun, less potential energy is 'released' as kinetic. The velocity increases at a slightly slower rate than Newtonian predictions. Leaving close proximity to the Sun, the probe would require slightly less energy to achieve a greater acceleration, returning the probe to the predicted path. This is EXACTLY what the residuals look like in the Pioneer 6 pass near the limb of the sun, peaking (slowing) at closest proximity to the sun. Likewise, the 1/r ‘spring constant’ Anderson used to model the Solar wind effects upon Odysseus and Galileo follow this model.

There is more: If more potential energy is stored in a more massive environment, probes to Venus are proportionally slowed, while probes to Mars would experience a slight acceleration, achieve a slightly different orbit. This would cause us to overestimate the mass of Venue, and underestimate the mass of Mars. When we interpret the orbital gravimetric data, the smaller accelerations near the mountain peaks on Venus would then appear as negative gravity anomalies, and likewise, valley floors would appear as positive anomalies. This is what we observe.

On Mars, the situation is exactly opposite: The increase in the transfer to kinetic energy would cause us to underestimate the mass of Mars from orbiters, so the mountain peaks would be interpreted as positive gravity anomalies while valley floors would appear negative. This is also precisely what we observe.

There is more.

We now have gravity maps of Mars from distances varying from 300 to 800 km, but the 800 km data cannot be reconciled with the 300 km maps. The 300km data showing greater anomalies. The moment of inertia for Mars appears to be different if ranging data to the surface probes (Pathfinder and Viking) is used than the inertial moment necessary to explain the orbital gravity anomalies.

All of the Martian probes have landed at higher velocities than expected and, entered at higher attitudes. All descent trajectory models have required a thinner-than-expected upper atmosphere, and high surface winds.

I can go on and on, but I think that you get my point: It would not take a major change in solar dynamics to produce surprising errors. I have been arguing with Jason and Bruce that the rocks, the craters, the strata, and the Doppler descent data from Huygens could be better modeled with less shear wind and more mass.

Fortunately, missions are already in progress that can disprove this hypothesis: Messenger will pass close enough to the sun that the ‘limb effect’ observed by Pioneer 6 could be repeated. MRO will provide gravity maps at 150 km – if this hypothesis is true, MRO will map greater gravity anomalies than prior orbiters that cannot be fit with harmonic extrapolations. MCO will also provide us with a good average atmospheric gradient, one that will be steeper than expected if the planet is more massive.

Finally, careful mapping of the effects of Saturn’s moons on Cassini should reveal ‘unmodelable drag’ forces and even greater gravity anomalies than Galileo found on Ganymede.

I don’t expect any degree of agreement with this assessment, but I hope I have peaked your interest in the manifold scientific data returning from the robotic planetary missions; and there just might be more to learn than mission planners dreamed, a truly revolutionary prospective of the cosmos, one just as foreign to scientific thinking today as the Ptolemic model.
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dvandorn
post Aug 31 2005, 07:24 PM
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Hmmm... well, the effect must be very, very minor (at least in the local solar-system neighborhood), or else the planets wouldn't orbit in such a way as to generally validate the inverse-square law of gravitation.

It *does* occur to me that the inverse-square law relates to the "classic" three physical dimensions, and cosmologists are always saying that as many as 19 physical dimensions *must* exist. As far as we can tell (since we cannot directly measure anything outside of the three dimensions that are apparent to us), gravitation doesn't propogate along any of these other physical dimensions. Perhaps this is an indication that it *does* and the effect we are seeing is actually a relation between some other physical dimension(s) and the three we can perceive? This would mean that the inverse-square law could be maintained; we're just applying that law to a dimension that is not obviously connected to the three we can see.

I think it's time to start contemplating how these extra dimensions that cosmologists believe must exist inter-relate with the Universe as we observe it. Rather than assuming that these dimensions simply collapsed and vanished as energy levels decreased shortly after the Big Bang, maybe they still exist and interact with such things as gravitation... However, I think it's too early to say that this effect happens near massive bodies, and it's definitely too early to start making mass itself a variable factor, relative to its distance from other masses.

-the other Doug


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antoniseb
post Aug 31 2005, 09:58 PM
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QUOTE (The Messenger @ Aug 31 2005, 01:56 PM)
I am at least as interested in the flight path eccentricities of Odysseus, Galileo and Pioneer 6 as the Pioneer 10 and 11. While the Pioneer probes indicate an acceleration towards the sun, an unsolicited acceleration away from the sun had to be used to model the paths of Odysseus and Galileo, and one of a greater magnitude: ~1x10^-8m/s^2.
*


Hi The Messenger,

We've interacted a few times on another forum. This is the clearest statement of what you've been trying to get to that I've seen. Thanks. I will now be trying to keep an eye on this.
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Guest_Richard Trigaux_*
post Sep 3 2005, 09:07 AM
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Guests






Thanks to recent posters this thread took an interesting turn, that we could summarize that a mission specifically dedicated to the Pionneer anomaly would be potentially very interesting, but that it is not likely to fly one day.

It could become more likely if it is send with other equipments, for instance for the study of solar wind effect, interplanetary magnetic fields, etc. The overal design of such a probe could allow to measure the "Pioneer effect" with much more accuracy, or at least to prove/disprove its existence.

How could such a probe work?
Basically a test mass, a raw piece of metal, should freely navigate into the solar system, on a trajectory fleeing the sun, while being protected of any spurious accelerations: solar wind, electric/magnetic effecs, outgassing, position control, etc.

To achieve this, it would be completelly enclosed into a metal casing, while having no physical contact/interaction with it. The casing would use thrusters to lock itself on a fixed position relative to the test mass.

So the overall thing navigates as if it was in really complete vacuum, without solar wind, outgassing, etc. and it can provide accurate informations of pure gravitationnal nature, eventually different of the 1/r2 law, or accounting for unknown bodies. The info on the trajectory corrections achieved by the casing would on its side provide very accurate data on solar wind. This makes this probe more interesting and more likely to fly than just a Pioneer anomaly test probe.

The only spurious gravitationnal effect on the test mass would be... the gravitationnal field of the probe itself. Thus the test mass should be placed right at the center of mass of the probe. An error on this would produce a permanent offset that we could not distinguish from true effects. If preleminary calculations show this is a problem, we can use a better overal design: the probe is formed of three parts, linked with cables: at the centre the protective casing, and at the extremities the radio transmitters, thrusters, and any other payload useful for science (and also useful to make this mission more likely). The whole thing rotates on an axis which is perpendicular to the sun direction, right around the test mass.
This design will allow to know preciselly the centre of mass and to adjust it. But above all, any permanent offset will be cancelled, as it will pull at times toward the Sun, at times opposite to the Sun. So we can really maintain the test mass free of spurious gravitationnal effects from the probe itself.

Such a probe would be relatively light wheight, so that it could be launched on an interstellar trajectory directly from the surface of the Earth, without using gravitationnal assistance. So it could bring results after only a few years. Otherwise we can use Jupiter' assistance.


Will this design lead one day to a real experiment?
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Guest_Richard Trigaux_*
post Sep 3 2005, 10:07 AM
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Guests






A rather interesting prospective explanation of the Pioneer anomaly could come from a completelly different field, from the exploration of the cosmic background radiation at 3°K by COBE and WMAP.

These two probes found results which strinkingly match the predictions of the standard cosmologic inflation theory in the very early stages of the universe, excep for some points. Here is a paper on this:
Cosmic Symphony (I did not read it, I read the french publication in the science review "Pour la Science", french edition of the Scientific American).

Among the possible explanations on these discrepancies was evoked the possibility of a cloud of matter (dust or neutral gas) near the solar system or in orbit around it. Such a cloud would be essentially of a very low density, and thus very transparent at any wavelengh. It would emit/absorb only radiations matching its black body temperature, which is, for a free body in far space, at equilibrium with the cosmic background! This would explain that such a cloud was never detected before: only a precise measurement of the cosmic background could allow for its discovery.

If such a cloud exists, its very low density multiplied by its huge dimentions would lead to a sizeable mass, more than a planet, and even in the order of a star mass.

This would perfectly explain the Pioneer anomaly, and even the variations found on this effect (at times toward the Sun, at times opposite) according if the probe goes toward the cloud or in another direction.

Eventually a Pioneer effect probe becomes more interesting.
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remcook
post Sep 3 2005, 10:18 AM
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some people seem to agree and applied for funding from ESA's cosmic vision 2015-2025:

http://sci.esa.int/science-e/www/object/in...fobjectid=35202

QUOTE
Title:  A Mission to Test the Pioneer Anomaly and to Probe the Mass Distribution in the Nearby Outer Solar System
Proposed by: Orfeu Bertolami et al.
Contact Email: orfeucosmos.ist.utl.pt

[...]

Title:  Testing the Pioneer Anomaly
Proposed by: Hansjörg Dittus et al.
Contact Email: dittuszarm.uni-bremen.de

[...]

Title:  Experimental investigation of the Pioneer anomaly
Proposed by: C. Kiefer et al.
Contact Email: kieferthp.uni-koeln.de

[...]

Title:  Significance of the Pioneer Anomaly
Proposed by: Claus Lämmerzahl et al.
Contact Email: laemmerzahlzarm.uni-bremen.de

[...]

Title:  LISA Mission and the Pioneer anomaly
Proposed by: José Luis Rosales
Contact Email: JoseLuis.Rosalesesp.xerox.com
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The Messenger
post Sep 3 2005, 05:00 PM
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Richard's proposed test of the Pioneer Anomaly is clever, and controls several variables. Unfortunately it also has the potential of introducing another new one: Shielding the test mass from the 'unknown force', especially if it is electromagnetic in nature: In this case if the results were nil, the Pioneer Anomaly could be constrained to a possible emf - but what emf?

The cloud solution is also interesting, but the two Pioneer probes were heading for opposite sides of the solar system and produced the same relative error. (Two identical clouds?) Also, Nieto and other researchers have been able to all but eliminate the Oort cloud and Kuiper belt objects as likely candidates for the PA, and this evaluation seems to apply to rouge clouds as well. (They also constrain the potential for local Dark Matter & Energy.

http://lanl.arxiv.org/abs/astro-ph/0506281

Antoniseb has started a thread to discuss second WMAP release, specifically in the context of the 'local' anomalies, and I will post a response there. As you know from my postings on this thread, I am of the opinion many quirky observations are interelated.

http://www.unmannedspaceflight.com/index.php?showforum=44

There is much to learn.
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Guest_Richard Trigaux_*
post Sep 4 2005, 07:03 AM
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Guests






Messenger,

my idea was intended to detect a gravitationnal effect (or gravitationnal-like). We could modify the shielding, for instance using a transparent shield to allow for electromagnetic effects. But in this case, we shall not know if the effect is gravitationnal or electromagnetic...
Or we can make several experiments, several test mass... but the probe has only one mass center. I do not come with more "clever" designs, unless to use several concentric shields around the test mass: one metallic, shielding the test mass from EM effects, and locked on the test mass without physical contact. And around, a second shielding, avoiding solar wind but transparent to electromagnetic effects, and locked on the first shield. This may allow for a separate measurement of both three effects, gravitationnal, EM and wind effect. But this fairly complicates the design, and does not make sure that the result would be better. Especially the intermediary shield will need some thrust, and thus it will "pollute" the results of the outer shield.

So I think it will be better to keep with my first simple design, perhaps adding it sensitive electromagnetic instruments. If gravitationnal effects are ruled out, we can still check for electromagnetic effects, but they offer much less potential for interesting discoveries. (but they cost much less to search)

Thank you also Messenger for your contribution on the Oort clouds and similar. We know litle things about the Kuyper belt and Oort cloud. We usually assume they have a syymmetrical structure (a disk for the Kuyper belt, a sphere for the Oort cloud). At least they would have gained such a symmetry after rotating around the Sun for 4 billion years. If they have such symmetrical structures, they cannot have gravitationnal effects in the inner solar sytem (a hollow spherical structure has no gravitationnal effect inside).

But many things may cause such clouds to have transcient or permanent "lumps" in it:
-part of the mass is in the form of massive bodies, such as the one recently detected which is larger than Pluto. (Many trajectory calculations should be remade accounting with it). It could even exist very dark and cold massive gaseous planets very far from the Sun.
-the solar wind shockwave with the interstellar wind concentrates mass
-a spherical cloud is in orbit around the Sun
-an interstellar cloud is currently at close vicinnity with the solar system (such clouds can have mass ranging from a giant star mass to Earth mass)
-a large wandering planet is currently at close vicinnity with the solar system


A last there is one difficulty with my probe: it will only tell us what there is in one direction. If we obtain enough precision, we could try to model the effect with an 1/R2 gravitationnal field, and find the culprit. But this will take ten years, and if the probe flight path is not in a proper direction, it will not work. So ideally we should send three probes in three perpendicular directions to definitively find (or rule out) any gravitationnal effects. In practice we could send one, wait two or three years to see the results, and take the decision to send another one in a proper direction.
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jamescanvin
post Sep 5 2005, 12:13 AM
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QUOTE (Richard Trigaux @ Sep 3 2005, 07:07 PM)
How could such a probe work?
Basically a test mass, a raw piece of metal, should freely navigate into the solar system, on a trajectory fleeing the sun, while being protected of any spurious accelerations: solar wind, electric/magnetic effecs, outgassing, position control, etc.

To achieve this, it would be completelly enclosed into a metal casing, while having no physical contact/interaction with it. The casing would use thrusters to lock itself on a fixed position relative to the test mass.

So the overall thing navigates as if it was in really complete vacuum, without solar wind, outgassing, etc. and it can provide accurate informations of pure gravitationnal nature, eventually different of the 1/r2 law, or accounting for unknown bodies. The info on the trajectory corrections achieved by the casing would on its side provide very accurate data on solar wind. This makes this probe more interesting and more likely to fly than just a Pioneer anomaly test probe.

The only spurious gravitationnal effect on the test mass would be... the gravitationnal field of the probe itself. Thus the test mass should be placed right at the center of mass of the probe. An error on this would produce a permanent offset that we could not distinguish from true effects. If preleminary calculations show this is a problem, we can use a better overal design: the probe is formed of three parts, linked with cables: at the centre the protective casing, and at the extremities the radio transmitters, thrusters, and any other payload useful for science (and also useful to make this mission more likely). The whole thing rotates on an axis which is perpendicular to the sun direction, right around the test mass.
This design will allow to know preciselly the centre of mass and to adjust it. But above all, any permanent offset will be cancelled, as it will pull at times toward the Sun, at times opposite to the Sun. So we can really maintain the test mass free of spurious gravitationnal effects from the probe itself.

Such a probe would be relatively light wheight, so that it could be launched on an interstellar trajectory directly from the surface of the Earth, without using gravitationnal assistance. So it could bring results after only a few years. Otherwise we can use Jupiter' assistance.
Will this design lead one day to a real experiment?
*


Interesting idea, and pretty much identical to the concept for the LISA gravitational wave mission, which would reduce the costs of such a mission considerably if the systems could be reused.

Of cource that would rely on LISA ever geiing off the ground, I wrote a undergraduate report about LISA and that was a long time ago! (~9 years) I can't remember what the planned launch date was back then but I don't think it was more than ten years, today, still ten years (2015)!

James


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