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(Space.com)   New Horizons Pluto explorer spacecraft is now 50 AU from the sun. If you don't know what an AU is, you can remember it with "A, U, come back with my spacecraft"   (space.com) divider line
    More: Followup, Pluto, New Horizons, Kuiper belt, Jupiter, Dwarf planet, Voyager 1, New Horizons' epic mission, NASA  
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401 clicks; posted to STEM » on 19 Apr 2021 at 7:42 AM (3 weeks ago)   |   Favorite    |   share:  Share on Twitter share via Email Share on Facebook



19 Comments     (+0 »)
View Voting Results: Smartest and Funniest
 
2021-04-19 3:12:55 AM  
The flyby of Pluto was July 2015? Almost six years ago? Fuuuuu.....
 
2021-04-19 3:43:47 AM  
50 golds?
 
2021-04-19 3:52:02 AM  
HOTY is over

shut 'er down
 
2021-04-19 5:06:14 AM  

MaudlinMutantMollusk: 50 golds?


Yes! They just invented the technology to have 2 atom thin gold, so with some back-of-eyelid calculations, I'd wholly expect 50 golds pressed out with this tech to be an accurate measurement of somesort. In my professional opinion, of course.
 
2021-04-19 7:57:31 AM  
But what about the OLD Horizon?

Horizon
Youtube QlXhHQQFCfk
 
2021-04-19 8:07:33 AM  
Haha good headline, got me subby.
 
2021-04-19 8:10:34 AM  

bingethinker: The flyby of Pluto was July 2015? Almost six years ago? Fuuuuu.....


Those 4 years of the 45th president are like a memory hole! All I can remember are something about tweets.
 
2021-04-19 8:18:17 AM  
We should start powering spacecraft designed to leave the Solar System with RTG's based on Americium-241 instead of Plutonium-238.   Americium only has about a quarter of the power density of Pu-238, *BUT* it's got a half-life that is 4 times greater.   So instead of limiting your spacecraft to maybe 40 to 50 years of operational life, you can have them last for at *LEAST* twice that, and maybe a lot more.

Some of that would depend on how the RTG's thermocouples degrade, of course, but there is no denying that it would result in much longer-lived spacecraft.   If weight was a concern, you could use both:  For the high-power requirements of flybys early in the mission you've got RTG's powered by Plutonium, with a couple of Americium ones that provide lower power, but for much longer.

Instead of returning data from out to 170 AU and then having your spacecraft "die"*, you could be looking at getting data from 240 AU, or 300 AU, maybe even out past 400 AU.

*Technically, they don't die when they can no longer talk to us because not enough power to run the radio transmitter, which is a power hog.  There is enough to run the other functions, at least for a while.  For all we know the Pioneer spacecraft were functional for years after they stopped having the capability to run their transmitters.  They could hear us, most likely, but couldn't respond.
 
2021-04-19 8:30:47 AM  
AU! Get your filthy hands off my desert!
 
2021-04-19 9:10:09 AM  
Ah, yes, the golden unit of measurement!
 
2021-04-19 9:13:09 AM  
I'll always think about the 82 AU goof:

Fark user imageView Full Size
 
2021-04-19 9:16:37 AM  

MaudlinMutantMollusk: 50 golds?


No, because it's not capitalized right. It's obviously a state postal abbreviation. Must be Aurkansas.
 
2021-04-19 10:06:27 AM  

dittybopper: We should start powering spacecraft designed to leave the Solar System with RTG's based on Americium-241 instead of Plutonium-238.   Americium only has about a quarter of the power density of Pu-238, *BUT* it's got a half-life that is 4 times greater.   So instead of limiting your spacecraft to maybe 40 to 50 years of operational life, you can have them last for at *LEAST* twice that, and maybe a lot more.

Some of that would depend on how the RTG's thermocouples degrade, of course, but there is no denying that it would result in much longer-lived spacecraft.   If weight was a concern, you could use both:  For the high-power requirements of flybys early in the mission you've got RTG's powered by Plutonium, with a couple of Americium ones that provide lower power, but for much longer.

Instead of returning data from out to 170 AU and then having your spacecraft "die"*, you could be looking at getting data from 240 AU, or 300 AU, maybe even out past 400 AU.

*Technically, they don't die when they can no longer talk to us because not enough power to run the radio transmitter, which is a power hog.  There is enough to run the other functions, at least for a while.  For all we know the Pioneer spacecraft were functional for years after they stopped having the capability to run their transmitters.  They could hear us, most likely, but couldn't respond.


Man I am glad there are people on Fark smarter than all the NASA engineers....

Oh wait useable electricity was first generated from Americum in 2019.... thanks for playing.  Also learn how to use GOOGLE.
 
2021-04-19 10:57:26 AM  
On Saturday night (April 17), New Horizons will reach 50 astronomical units (AU) from the sun, a distance achieved by just four other operational probes in the history of spaceflight. (One AU is the average Earth-sun distance - about 93 million miles, or 150 million kilometers.)


I'm confused, didn't it start out at 1 AU?
 
2021-04-19 11:29:27 AM  

Obama's Left Nut: Man I am glad there are people on Fark smarter than all the NASA engineers....

Oh wait useable electricity was first generated from Americum in 2019.... thanks for playing.  Also learn how to use GOOGLE.


Explain to me, in actual detail as opposed to "I just Googled it, hurr durr!", why it's such a bad idea.

The reason why it hasn't been used in the past mostly boils down to mass.

Early spacecraft like Pioneer, Voyager, the Viking landers, etc., needed a relatively dense power source, and Pu-238 provided a relatively decent balance between power output and longevity, especially given the power-hungry circuitry needed to run those spacecraft.

Back then, we didn't know how long they would last.  It was hoped that the Pioneers and Voyagers would last through their Jupiter and Saturn encounters, and anything past that was pure gravy.

New Horizons was a bit of an exception, as it had to be extremely light to be able to encounter the Pluto/Charon system in a reasonable amount of time.   So it was actually very bare bones, which is why it took so long to send back images:  For example, New Horizons has a 2.1 meter dish, and a 12 watt transmitter, compared to the 3.7 meter dish antennas and 22.4 watt transmitters on the two Voyager spacecraft.

Today, though, we know we can build machines that last for many decades in space.   So why not leverage that by making them last even longer?   Put the basic research into building Americium powered RTGs and Stirling engines.  Then we can start putting them on spacecraft.

Why not plan to use those longer-lived spacecraft for things like ultra-long interferometric radio wave observations?   Why not use their cameras to get better and more accurate distances to the local stars via parallax measurements?

This is the kind of stuff that the engineers and scientists back in the 1960's and 1970's couldn't really count on doing, because there were just too many unknowns.   But a lot of them are knowns now.   We can start planning on very long duration space probes.

We can do more with less, electrically speaking.  The power requirements today for spacecraft, both housekeeping and to run instruments, is *MUCH* less than it was when the Voyagers were built.

For example, on the Voyagers, the Wide Angle and Narrow Angle cameras each used around 33 to 34 watts (including the associated heaters).   LORRI and ALICE, the cameras on New Horizons, use about 5.8 watts and 4.4 watts respectively.  Well, if you do the math the Voyager cameras used 33.5 / ((5.8 + 4.4)/2) = 6.5 times more power than the ones on New Horizons*.   And the same mass of Americium puts out about 1/5th the amount of power as Plutonium, so in theory you could use the same amount in terms of mass of Am-241 to power modern cameras as you needed to power the old vidicon tubes on Voyagers using Pu-238.

And yeah, Americium has been thought about for a while now for RTGs.   It was even considered back in 1960 as a "short listed" candidate:

https://thewire.in/science/plutonium-​r​tg-isro-americium

According to a report published by the US Department of Energy in October 1960, this is how Mound went about shortlisting their candidates:

Initial elimination of isotopes as heat sources was made on the basis of half-life. Any isotope which had a half-life of less than 100 days or greater than 100 years was discarded. A few exceptions were made to insure not overlooking a likely isotope.
...
Unlike NASA - and ISRO, both of which are in countries that have access to domestic plutonium-238 - the European Space Agency (ESA) has to consider alternatives. One of them is americium-241, one of the shortlisted candidates in the 1960 report.


In essence, Pu-238 is in very short supply because it has to be made.  But Pu-241 is a natural waste product of nuclear reactors, and it relatively quickly decays into Am-241.  So there's plenty of Americium available, and the only commercial use for it is smoke detectors, which use very tiny amounts.

Pu-238 was relatively cheap back in the 1960's because you could make it in the reactors you used to make weapons-grade Plutonium-239.   Today, it's no where near as cheap, and even with the US starting up Pu-238 production after a 30 year hiatus, it's only going to yield about 1 kg of Pu-238 a year.


I get the impression that you don't actually have the capability for independent thought on these kinds of matters.   Because you took what I said as a criticism of NASA and it's engineers, when in fact, it's *NOT*.  It's a suggestion, one that I'm not alone in thinking about.   And oddly enough, it's a suggestion I won't live to see come to fruition:  I'm old enough that even Pu-238 powered spacecraft launched today will almost certainly outlive me.


*I did that calculation on my Pickett N200T Pocket Trig slide rule.
 
2021-04-19 1:39:59 PM  
Yes but where is that Tesla Roadster?
 
2021-04-19 7:03:35 PM  

Skyfrog: Yes but where is that Tesla Roadster?


https://www.whereisroadster.com/ just about 28m (highway) miles away.
 
2021-04-19 7:13:32 PM  

dittybopper: Obama's Left Nut:

snip


here's the issue though. once you are out of the solar system there's really not all that much. Having lots of power for cameras and thrusters really doesn't make a lot of sense.

What we really need is a high power source for the first 30 years then a med to low power source for the next couple hundred. I don't know if RTGs are gona get you there. maybe a big scoop that can hoover up the interstellar hydrogen and convert it into a fuel cell or something.
 
2021-04-20 4:28:51 PM  

khitsicker: dittybopper: Obama's Left Nut:

snip

here's the issue though. once you are out of the solar system there's really not all that much. Having lots of power for cameras and thrusters really doesn't make a lot of sense.

What we really need is a high power source for the first 30 years then a med to low power source for the next couple hundred. I don't know if RTGs are gona get you there. maybe a big scoop that can hoover up the interstellar hydrogen and convert it into a fuel cell or something.


There isn't enough hydrogen out there to do that.

And using Am-241 in the RTGs means they are likely going to be usable for a couple hundred years.   Less power density, but far longer half-life.

Technically, you could even do something like having rechargeable batteries for the close encounters.  The RTGs could keep them topped up until they are needed during an encounter, where you need to power cameras and higher power on the radio for decent bandwidth, but during the "cruise" portion you don't need as much bandwidth, so lower power on the transmitter, and you don't need to run as much of the equipment.

There was actually a proposal for a Pluto flyby years ago that didn't use RTGs, but used thermal batteries for the high power requirements for the close encounter, and what were essentially scaled up versions of pacemaker batteries for the long term "cruise" portion.  This was looked at because of both the cost and the baggage that goes with launching radioactive materials.

The proposal was to put the satellite into orbit around Pluto, take as many pictures as they could and transmit them back to Earth, then crash the craft on to the surface.

I have a book published in 1988 called "Interplanetary Spacecraft" edited by Bill Yenne that explores the concept.

I can't find an online link for the project itself, but here is a link to the book:
https://www.amazon.com/Interplanetary​-​Spacecraft-Bill-Yenne/dp/0671096052
 
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