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KBO encounters
Alan Stern
post Nov 10 2018, 04:55 PM
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QUOTE (jasedm @ Nov 10 2018, 01:56 PM) *
Wow, I had no idea this was even on the cards!

Would a search for possible candidates wait until all the Ultima Thule data is safely back on Earth, and the health of the spacecraft and available fuel is assessed? or are efforts already in progress as regards booking time on Earth-based telescopes and Hubble?

I imagine there would be an extremely narrow 'cone of possibility' as regards reaching another KBO with the remaining fuel.

51 days to go to the main event - can't wait!



Owing to our remaining expected fuel supply we will have to search for small targets, which are more numerous. Calcs show this is most likely to be a flyby of a pristine comet nucleus. Such objects are about V=35 from Earth: hence undetectable, even with HST.

So we would have to detect it with LORRI on New Horizons itself, which can see 3-10 km targets up to about 6 months ahead of us. Feasibility calcs will be done in 2019 (preliminary calcs are pessimistic but we really haven't scoured this to a solid conclusion). We'll see if this can work-- I hope so. It would be very cool to detect and target all from New Horizons with a "target of opportunity" flyby sometime n the 2020s!
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jasedm
post Nov 11 2018, 03:46 PM
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Fantastic possibilities!

Good luck with the feasibility exercise, I really hope it bears fruit for you.



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rogelio
post Nov 11 2018, 06:09 PM
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Some back-of-the-envelope calculations on how easy it will be to find another target after Ultima Thule, based on Alan’s post:

He mentioned being able to spot a target 6 months prior to a fly-by. NH will cover about 1.45 AUs during that time. That’s about 30 times its current distance from the sun (approximately 43 AUs). So, being 30 times nearer to a target, it will be 30 squared = 900 or about 7.5 magnitudes more “powerful” than an earth-based scope.

If the limiting magnitude of an earth-based scope is about 35 (per Alan) and one subtracts 7.5 magnitudes, LORRI will need to spot a target at magnitude 27.5.

From the link below it seems that LORRI’s limiting magnitude is 17 using a 10 second exposure. To reach 10 magnitudes dimmer (27), it would need an exposure time 10,000 times as long = 100,000 seconds = about 30 hours. Presumably these are the “pessimistic” calcs that Alan alludes to?

Unless some tricks/work-arounds are in the offing?

Go New Horizons!

LONG-RANGE RECONNAISSANCE IMAGER ON NEW HORIZONS

http://www.boulder.swri.edu/pkb/ssr/ssr-lorri.pdf

“LORRI has a 4×4 pixel binning mode, for which its limiting magnitude requirement is V>17 in a single exposure of 9.9 s. This 4×4 pixel-binning mode will be used to search for the target KBO and to perform optical navigation on approach. A special spacecraft guidance mode is available for the KBO search in which the spacecraft will hold the target within the 4×4 pixel pointing tolerance for 10 second exposures. At 40 AU from the Sun, LORRI is predicted to be able to detect a 50 km diameter object, of albedo 0.04 and at phase angle 25°, from a distance of 0.35 AU, more than 40 days before the object would be encountered”
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HSchirmer
post Nov 11 2018, 06:32 PM
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To quote Yogi Berra,

"Deja vu, all over again..."


QUOTE (rogelio @ Nov 11 2018, 06:09 PM) *
Some back-of-the-envelope calculations on how easy it will be to find another target after Ultima Thule, based on Alan’s post:


QUOTE (HSchirmer Sep 8 2015)
http://www.unmannedspaceflight.com/index.p...st&p=225998
We expect 11 KBOs at random to be in a .5 degree radius "flight cone" 20 AU long,
That flight cone is .5 degrees half angle, stretches from 30 to 50 AU
That's a cone 20 AU long, 1 degrees wide eh, ~.64 cubic AU in volume.
If there are 11 KBOs in .64 cubic AU, that's ~17 KBOs per cubic AU.

What area of space can NH search?
NH has about 15 AU left to travel through the main Kuiper belt.
Figure the faintest KBOs at 28th magnitude are visible at 2/3 AU.
That's ¶ x Radius^2 x length=3.14 x .67 AU x 15 AU ~ 21 cubic AU.
At 17 KBOs per cubit AU, that's ~357 KBOs.


http://www.unmannedspaceflight.com/index.p...st&id=37680
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fredk
post Nov 11 2018, 06:37 PM
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QUOTE (rogelio @ Nov 11 2018, 07:09 PM) *
NH will cover about 1.45 AUs during that time.

That's a pretty conservative estimate. In reality if they spotted an object at 0.35 AU as per your quote, that gives about 10 magnitudes over Earth. I guess it's a question of the brightness/size distribution of the objects, which is probably not known very well at these smaller sizes.

And why do you compare to a limiting magnitude of 35? Might such objects not appear considerably brighter from Earth?
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HSchirmer
post Nov 11 2018, 07:51 PM
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QUOTE (fredk @ Nov 11 2018, 06:37 PM) *
That's a pretty conservative estimate. In reality if they spotted an object at 0.35 AU as per your quote, that gives about 10 magnitudes over Earth. I guess it's a question of the brightness/size distribution of the objects, which is probably not known very well at these smaller sizes.

And why do you compare to a limiting magnitude of 35? Might such objects not appear considerably brighter from Earth?


Well, those were back of the envelope calculations from 3 years ago.
There was an, er, "animated", discussion about whether NH could detect objects during spin stabilized flight.
- The discussion 3 years ago was rehashing a discussion about 6 years ago, IIRC-
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rogelio
post Nov 11 2018, 10:17 PM
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fredk wrote: "And why do you compare to a limiting magnitude of 35? Might such objects not appear considerably brighter from Earth?"

That's a quote from Alan Stern a few posts upthread: "Such objects are about V=35 from Earth: hence undetectable, even with HST."

Switching from glass half-empty to half-full: LORRI's 8.2" aperture is equivalent to a 250" earth-based scope when peering ahead 1.5 AU's, or a 1000" scope at 0.35 AU's. And it's a dedicated scope, unlike HST.

Go New Horizons!
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Steve5304
post Nov 14 2018, 03:57 AM
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Would be great if we spotted another large object with the LORRI

How much longer can the cameras function with the RTG I wonder. Right about now the voyagers had to shut down
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HSchirmer
post Nov 14 2018, 12:36 PM
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QUOTE (rogelio @ Nov 11 2018, 10:17 PM) *
fredk wrote: "And why do you compare to a limiting magnitude of 35? Might such objects not appear considerably brighter from Earth?"

That's a quote from Alan Stern a few posts upthread: "Such objects are about V=35 from Earth: hence undetectable, even with HST."

Switching from glass half-empty to half-full: LORRI's 8.2" aperture is equivalent to a 250" earth-based scope when peering ahead 1.5 AU's, or a 1000" scope at 0.35 AU's. And it's a dedicated scope, unlike HST.

Go New Horizons!


IIRC, prior discussions considered the "spin problem" (can't effectively search in spin stabilized mode), the "steady problem" (it burns fuel to stay in steady mode)
and the"bandwidth problem" (you have to download the images to look for things).

Without some sort of AI event detection software, NH isn't going to identify promising candidates on it's own...
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Alan Stern
post Nov 14 2018, 01:57 PM
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QUOTE (Steve5304 @ Nov 14 2018, 03:57 AM) *
Would be great if we spotted another large object with the LORRI

How much longer can the cameras function with the RTG I wonder. Right about now the voyagers had to shut down



We think its pretty easy to get to the mid-2030s. With ingenuity, years longer.
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stevesliva
post Nov 14 2018, 05:51 PM
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QUOTE (HSchirmer @ Nov 14 2018, 08:36 AM) *
Without some sort of AI event detection software, NH isn't going to identify promising candidates on it's own...


It might be semantics, but blink comparison like Tombaugh did isn't either AI or event-driven.
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HSchirmer
post Nov 14 2018, 07:46 PM
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QUOTE (Hal)
Without some sort of AI event detection software, NH isn't going to identify promising candidates on it's own...


QUOTE (stevesliva @ Nov 14 2018, 06:51 PM) *
It might be semantics, but blink comparison like Tombaugh did isn't either AI or event-driven.


But how do you know when to check?

As I understand it, NH has to pivot to send images to Earth, then pivot back to get back to looking.
And data downloads from 40+ AU aren't exactly cheap, nor are they fast.

Concern is, burning propellant to look for a new target, might expend fuel and prevent you from getting to the new target.

Point is, Would be better for manouvering fuel if NH had some AI software that allowed it to just stare ahead and only turn around when if finds something interesting...

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jasedm
post Nov 14 2018, 10:32 PM
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I'm sure that some very talented people are looking at every possible option to try to realise the aim of a third(fourth?) encounter within the inevitable financial constraints.

Guess it's a trade-off between feasibility/budget/time/competing priorities/risk/CPU capacity/fuel/DSN availability/science return etc etc

Based on the ingenuity and determination displayed for the mission thus far, I'm not betting against them.......






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