Star 48b Third-stage Motor, Leaving the solar system Options

[Bob Shaw]

Even where actual trips from Earth to Mars itself are concerned, Mariner 9 isn't the record holder -- the Atlas-Centaur had so much excess capacity for the much lighter 1969 Mariner Mars flyby craft that they were able to pound them to Mars in only 5 and 4 months, with a leisurely 1-month gap between launches.  I imagine this record will stand for a while.

Bruce:

Any idea of Mariner 6 and 7's furthest point from the Sun? As in, how far into the Great Galactic Ghoul did they get?

Bob Shaw

[punkboi]

The third stage is 15,000 km away from NH according to Alan Stern's new PI Perspective on the NH APL site

[Comga]

Obviously retro reflectors work out to 400k km, but how far out would they work beyond that?  Perhaps one could do radar reflection using Arecbo / DSN instead?

Doug

Sorry, but this won't work. The Pioneer anomoly is a grand distance effect. 400M km is barely at Jupiter distance, but that would diminish the return from a Lunar Retroreflector Array by a factor of one trillion (1E12) as it goes as R^4. At Neptune's distance of 4G km the signal would be down by a factor of 1E16. And in order to keep the mass down, the array would have to be more than a factor of ten smaller, which could cut into both legs reducing the signal by ANOTHER factor of 100 at best. No conceovable amount of technological progress would make this signal detectable. Plus one would have to put the retro on the rocket nozzle end to face back at Earth. A radio retroreflector would have to be quite large to have any effect, and could not be carried.

A spent stage is just innert mass on an uncontrolled trajectory. It would be very hard to find a use for this mass that would not have imposed additional requirements on the mission. New Horizons survived by avoiding distractions and extraneous burdens.

Other missions have used their boosters as photographic targets, and NH knows its velocity relative to the spent third stage with high precision, and would be looking at the sunlit side. Don't know if imaging it would serve any purpose.

[Bob Shaw]

Other missions have used their boosters as photographic targets, and NH knows its velocity relative to the spent third stage with high precision, and would be looking at the sunlit side.  Don't know if imaging it would serve any purpose.

Oh? Which ones photographed their boosters?

Bob Shaw

[AndyG]

...400M km is barely at Jupiter distance, but that would diminish the return from a Lunar Retroreflector Array by a factor of one trillion (1E12) as it goes as R^4.

Is that right? I can see that a normal return (radar, for example) from an astronomical body would obey R^4 laws, but the whole point of a retroreflector is to minimise divergence of any reflected signals. So, surely a well made retroreflector should be nearer R^2 than R^4 - a big difference at large ranges, and a more practical option than you seem to suggest?

Andy

[ugordan]

So, surely a well made retroreflector should be nearer R^2 than R^4 - a big difference at large ranges, and a more practical option than you seem to suggest?

Nope, a flat retroreflector would still follow the R^4 law. Consider that a flat reflector receives 1/4 of the power at twice the distance and it also presents only 1/4 of the angular surface area seen from Earth so that combines to 1/16 of the power received back than at the original "unit" distance.
I can imagine that if you had a spherical reflector whose curvature would follow the curvature of the sphere centered on the light source on the Earth, you could get a R^2 return power function as it would focus all received light/radio signal back at the source.
Then again, that's purely theoretical reasoning and you'd have to change the curvature of the reflector with increasing distance and keep it really precisely pointed back that it's probably undoable.

[Bob Shaw]

When the LRRR hare was first set running I simply assumed that there'd be some sort of spatially distributed array of cubical LRRR modules all over the exhausted stage, so that it's orientation was not particularly important (but which could be obtained by applying some sort of statistical process to the light curve of the stage). Such cubical LRRRs would reflect internally and would *not* need to be pointed in any more than a general direction.

The logarithmic issues still apply, of course, but imagine the possibilities inherent in the US military experiments in high power lasers, then add an array of optical telescopes (seeking to resolve only a point source, remember, where optical arrays *are* good).

Plainly, though, as Alan Stern pointed out, every bit of mass left on the booster is something left off the spacecraft. Still, let's assume that NH2 flies, and there's (for whatever reason) some spare mass budget - the experiment could be quite interesting... ...and cheap!

Bob Shaw

[Comga]

I can imagine that if you had a spherical reflector whose curvature would follow the curvature of the sphere centered on the light source on the Earth, you could get a R^2 return power function as it would focus all received light/radio signal back at the source.
Then again, that's purely theoretical reasoning and you'd have to change the curvature of the reflector with increasing distance and keep it really precisely pointed back that it's probably undoable.

We are agreed on the R^4 scaling, but even adaptable curved surfaces wouldn't help. The diffraction limit is the diffraction limit. That is assuming you could do it for zero mass and zero power with passive controls..... At these distances, anything acts like a point source algeit with limited divergence.

This is a wild hare, isn't it?

[Comga]

Oh? Which ones photographed their boosters?

Bob Shaw

A Surrey microsat imaged its booster, and another satelite after rendezvouing using butane cold gas thrusters. It was a test of navigation and pointing. Here's a reference. http://www.spacedaily.com/news/microsat-00x.html

[Bob Shaw]

A Surrey microsat imaged its booster, and another satelite after rendezvouing using butane cold gas thrusters.  It was a test of navigation and pointing.  Here's a reference.  http://www.spacedaily.com/news/microsat-00x.html

Interesting... ...so when do we build one?

Bob Shaw

[ljk4-1]

Earlier thread on this:

http://www.unmannedspaceflight.com/index.p...indpost&p=20609

[Katie B]

With the third stage's passing of Pluto's orbit coming up in two months, I was wondering (and have been asked) whether there is any way of tracking its location. From this thread, I gather there is not. Correct?

[djellison]

Correct.