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A New Horizons Clone To 2003 Ub313?
SFJCody
post Dec 22 2005, 01:07 PM
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Pluto's current distance from the Sun: ~31AU
2003 UB313's current distance from the Sun ~97AU

Is an all chemical (no electric propulsion, solar sails, etc) mission to 2003 UB313 possible? I'm thinking of a travel time and spacecraft mass similar to New Horizons. Perhaps NASA's new Shuttle derived launch vehicle (payload capacity 125 metric tonnes to LEO) will be up to the task and could do this on a test flight.
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ugordan
post Dec 22 2005, 01:45 PM
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A quick and dirty calculation shows that even with a heliocentric average speed of 20 km/s you'd need over 20 years to reach that distance.
That's comparable to the Voyager 1 spacecraft, currently at 97 AU from the sun and it took 2 gravity assists and over 25 years to reach that distance. And it's the fastest escaping probe out there.

I doubt anyone would ever launch a mission that would have to wait more than 20 years before any scientific return would be made. IMHO, chemical propulsion is totally out of the picture, nuclear powered ion propulsion or perhaps efficient solar sails would be possible alternatives.

EDIT: A very large cryogenic upper stage might do the job, but really, lifting a hundred tons of propellant into low earth orbit just to kick-start a few hundred kilograms on a very fast trajectory seems like a huge waste of resources. Not to mention that the faster you launch the probe, the faster you whizz by the target (in a matter of few minutes). Ideally, you'd want to slow down (possibly even braking into orbit) to have more time to get the highest resolution measurements available, again fission powered ion engines seem like the only alternative.


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JRehling
post Dec 22 2005, 02:51 PM
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QUOTE (ugordan @ Dec 22 2005, 05:45 AM)
A quick and dirty calculation shows that even with a heliocentric average speed of 20 km/s you'd need over 20 years to reach that distance.
That's comparable to the Voyager 1 spacecraft, currently at 97 AU from the sun and it took 2 gravity assists and over 25 years to reach that distance. And it's the fastest escaping probe out there.
*


Are all gravity assists made equal? I'm sure they're not. The Voyager path was chosen to hit the needed planets, not for superspeed. It's another matter how fast a spacecraft would go if it were intended to get maximum heliocentric speed and Jupiter-Saturn gravity assists were timed accordingly. I doubt that the Voyagers hit those marks, and the difference could be considerable. Someone capable of simulating that?
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djellison
post Dec 22 2005, 03:00 PM
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But, Maximum possible speed from a flyby, and the course required for your intended target are almost certain to not be the same thing as well smile.gif

I'd have thought, if you were intent on doing a misssion out to near 100AU then you're going to have to go with Ion or even more interesting propulsion ( A solar powered Ion 'stage' to the spacecraft, ejected once prop is exhausted after perhaps 12 months of thrusting adding a few km/s to the velocity of the RTG powered spacecraft )

Doug
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ugordan
post Dec 22 2005, 03:05 PM
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QUOTE (JRehling @ Dec 22 2005, 03:51 PM)
The Voyager path was chosen to hit the needed planets, not for superspeed.
*

Wasn't Voyager 1's flight path targetted for passage through the Io flux tube? If so, it would mean it passed quite close to Jupiter already. I suppose even closer flybys are feasible, but it brings the question on additional radiation hardening of the electronics. In any case, I wouldn't go closer than 200 000 km from Jupiter, about half of Voyager 1 C/A distance (OTOH).
Also, there's only so much a gravity assist can boost, it's a function of the planet's tangential velocity. In any case, I don't believe reasonable (10 years) flight paths are feasible with a Jupiter slingshot. Arranging the geometry for a Saturn flyby as well would be even more difficult.


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ugordan
post Dec 22 2005, 03:20 PM
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QUOTE (djellison @ Dec 22 2005, 04:00 PM)
I'd have thought, if you were intent on doing a misssion out to near 100AU then you're going to have to go with Ion or even more interesting propulsion ( A solar powered Ion 'stage' to the spacecraft, ejected once prop is exhausted after perhaps 12 months of thrusting adding a few km/s to the velocity of the RTG powered spacecraft )

I was wondering about the feasibility of a weak ion engine that would be powered off the surplus energy from an RTG during most of the cruise. How feasible would it have been for NH to have included a 100 watt ion engine that would slowly accelerate during 8 years or so of (otherwise dormant) interplanetary cruise? What cumulative delta-Vee could we expect from that on a 500 kilogram probe? A fast kick-start would still be needed during Jupiter injection, but if the long thrusting period shaved a year off the trip time, it might just have been worthwhile. Have any studies been done on that?

Of course, a very reliable ion engine would be needed, possibly similar in design to Hayabusa's microwave driven one? As I gather there is no weardown of the electrodes in that case which would make it very convenient. Then there's the problem of the drive failing and the achieved final trajectory would probably not reach Pluto but fell short.
I wonder if a thrust angle profile could be set up so that at any point if the engine was cut-off the Pluto fly-by geometry would be set up, yet only the arrival date varied by continuing thrusting onward? In other words, the engine would continually move the aimpoint to earlier arrival times, keeping the C/A distance pretty much constant. Orbital dynamics probably don't allow for that, though.


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tasp
post Dec 22 2005, 03:30 PM
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Pioneer 11 passed Jupiter at less than 30,000 KM.

High angle across Jovian equator drastically cut radiation exposure.

Sending craft out of the ecliptic with maximum gravitational assistance form Jupiter seems entirely within our capablitites.

High speed at the target object remains a problem, though.
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djellison
post Dec 22 2005, 03:32 PM
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I doubt you could run any sort of Ion engine off normal RTGs - certainly not one worth investing the time, money and particularly mass and volume in.

You need something like a kw or 2 to make it worth while

Doug
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um3k
post Dec 22 2005, 03:49 PM
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One thing I would like to point out is that a mission to 2003 UB313 would need an extremely sensitive camera. The brightness of sunlight at 97 AU is .01 percent of the brightness at 1 AU! That means either a very large light-collecting mirror, an extremely sensitive CCD, or a combination of both! Another option, of course, is to skip imaging altogether, but... *cringes*
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ugordan
post Dec 22 2005, 04:14 PM
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QUOTE (tasp @ Dec 22 2005, 04:30 PM)
Sending craft out of the ecliptic with maximum gravitational assistance form Jupiter seems entirely within our capablitites.
*

Yeah, but sending the probe sharply above or below the ecliptic plane inherently diminishes the Jovian gravity assist, does it not? I'd think the biggest speed gain is when your outbound velocity is directed along Jupiter's orbital velocity, not upwards or below. That means the greates speeds achievable using gravity assists will be more or less in the ecliptic plane.
I guess... unsure.gif

um3k: That problem could be partly alleviated simply by using longer integration/exposure times. This again prefers slower flyby speeds as motion blur would be smaller. Motion blur would probably be a big problem with the highest resolution imagery around C/A even when using target motion compensation as the target area viewing vantage point is changing in addition to doing a simple translation (which motion compensation takes care of) when viewed from the spacecraft point.

All points show ordinary chemical propulsion would pretty much suck at the task.


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SFJCody
post Dec 22 2005, 06:04 PM
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QUOTE (um3k @ Dec 22 2005, 03:49 PM)
One thing I would like to point out is that a mission to 2003 UB313 would need an extremely sensitive camera. The brightness of sunlight at 97 AU is .01 percent of the brightness at 1 AU!
*



Ah, but the sunlight at Neptune (30 AU) was about 0.11 percent of the brightness at 1 AU. And Voyager 2 successfully imaged Proteus (with a 6% albedo) at that distance. With vidicon tube technology! If 2003 UB313 has an albedo of ~70% (which seems to be the case given the difficulty in seeing it with Spitzer), it will have a surface slightly *brighter* than Proteus, even at 100AU. In that case, all we're left with is the increase in velocity. If New Horizons to UB313 carries a CCD with just 5 times the efficiency of Voyager's mid 70s vidicon tube technology (not asking much), it will be able to image 2003 UB313 as successfully as Voyager 2 was able to image Proteus even if it moves 5 times faster.
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ugordan
post Dec 22 2005, 06:17 PM
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QUOTE (SFJCody @ Dec 22 2005, 07:04 PM)
If New Horizons to UB313 carries a CCD with just 5 times the efficiency of Voyager's mid 70s vidicon tube technology (not asking much), it will be able to image 2003 UB313 as successfully as Voyager 2 was able to image Proteus even if it moves 5 times faster.
*

But if we were to send a probe across such an immense distance, we wouldn't be settling for a C/A distance of 150 000 km or so. We'd like at least a 10 times closer approach distance which will make any motion blur problems 10 times worse. So, if you wanted highest resolution observations during closest approach, you'd need 10 times more sensitivity in the cameras apart from your 5x. That's 50 times more sensitive than a vidicon.


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SFJCody
post Dec 22 2005, 06:25 PM
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QUOTE (ugordan @ Dec 22 2005, 06:17 PM)
...you'd need 10 times more sensitivity in the cameras apart from your 5x. That's 50 times more sensitive than a vidicon.
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50x might not be out of the question, esp. given that the launch vehicle under discussion wont become available for a decade or so. That's about 40 years after the Voyagers were built. Does anyone have the photosensitivity specs on the Voyager vidicons and the latest in cutting edge CCDs?
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ugordan
post Dec 22 2005, 06:35 PM
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Then again, newer propulsion methods will probably be available by that time also so all bets are off.

I'm no expert on CCD technology, but it's based on semiconductors. The lower the temperature of the detector, the better the signal/noise ratio is. However, at very low temperatures the semiconducting properties of the detector start to degrade.
IIRC, sillicon based elements have a low threshold around 80 deg Celsius, I might be wrong, my electronics are a bit rusty. All this would imply there's a lower limit to how sensitive a CCD can get.


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SFJCody
post Dec 22 2005, 06:40 PM
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QUOTE (ugordan @ Dec 22 2005, 01:45 PM)
EDIT: A very large cryogenic upper stage might do the job, but really, lifting a hundred tons of propellant into low earth orbit just to kick-start a few hundred kilograms on a very fast trajectory seems like a huge waste of resources.
*


Normally, yes, but it might make an interesting 'dummy' payload for a test launch of the SDLV. IIRC large cryogenic upper stages for the new heavy lifter are needed for the Earth to Mars transfer if they go with in orbit assembly of a Mars 'stack'.
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