Author Topic: Wonderful Photographs from Mars  (Read 82850 times)

Offline Count Zero

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Re: Wonderful Photographs from Mars
« Reply #30 on: August 20, 2012, 08:48:38 PM »
...the supposed telecasts from the Moon which were in fact shot in lot 171 in the Nevada Desert.

"What makes one step a giant leap is all the steps before."

Offline ka9q

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Re: Wonderful Photographs from Mars
« Reply #31 on: August 20, 2012, 09:51:48 PM »
sts60, thanks for your answers. I remember hearing "thermal batteries" in the EDL commentary and thinking they were a natural choice for that application -- a long storage period, then a very short service life at very high power.

Does the rover use any supercaps? I know it has two lithium-ion batteries serving a similar role as the CM entry batteries on Apollo - to cover short demand peaks beyond the capability of the primary electricity source (RTG for Curiosity, fuel cells for Apollo). If these batteries are essential then they will probably set the rover's lifetime. Supercaps still have a much lower energy density but they have the enormous advantage of a cycle life measured in the hundreds of thousands. They could cover demand peaks (very brief motor actuations) that exceed the RTG's steady state output after the li-ion batteries die.

l've been thinking about supercaps a lot for LEO amateur satellites. They're usually eclipsed on every orbit, and that's very hard on chemical batteries. Of our satellites not in short-lived orbits (e.g., ARISSat-1) battery failure usually kills us. A supercap that can at least keep the computer alive during eclipse would be a big win.


Offline gillianren

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Re: Wonderful Photographs from Mars
« Reply #32 on: August 20, 2012, 10:41:58 PM »
Your Excellency, that's a wonderful image that is from the wrong part of the movie and subtly misquoting.  (It's "I do not think it means what you think it means.")  But it is nonetheless completely appropriate here.  "Fact" means something different to these people!
"This sounds like a job for Bipolar Bear . . . but I just can't seem to get out of bed!"

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Offline cjameshuff

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Re: Wonderful Photographs from Mars
« Reply #33 on: August 20, 2012, 10:55:21 PM »
There's probably supercaps in there somewhere, but just incidentally as something that came along with some RTC. I think the very poor energy density would make them undesirable for anything that requires storing significant amounts of energy. They are comparable to lead acid batteries. Lithium batteries will deteriorate, yes, but they start off storing much more energy for a given mass.

A Maxwell BCAP0150 puts 150 F in a 32 g package. Rated operating voltage is 2.7 V at 65 C, 2.3 V at 85 C. Assuming 2.3 V full charge with useful discharge down to 1 V, that's 320 J of useful stored energy, just over 10 kJ/kg. Lithium ion batteries are generally in the range 360-900 kJ/kg. A 500 kJ/kg Li-ion battery would need to degrade to 1/50th its normal capacity to become worse than an equivalent mass supercapacitor. If cycle count is enough of a concern, you might look into other battery chemistries before supercapacitors, such as nickel-hydrogen or even nickel-iron batteries.

Offline Count Zero

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Re: Wonderful Photographs from Mars
« Reply #34 on: August 21, 2012, 12:27:35 AM »
Your Excellency, that's a wonderful image that is from the wrong part of the movie and subtly misquoting.  (It's "I do not think it means what you think it means.")  But it is nonetheless completely appropriate here.  "Fact" means something different to these people!

Mea culpa.  I was shooting from the hip.  My original idea was (after the bolded quote) to just post a picture of Inigo and let Those-Of-Us-Who-Know work-out the context.  When I did a GIS, the above image came-up so I ran with it.  I haven't been online for several weeks and am still catching-up.  Please forgive the rush-job.
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Offline Andromeda

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"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny...'" - Isaac Asimov.

Offline slang

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Re: Wonderful Photographs from Mars
« Reply #36 on: August 21, 2012, 06:53:44 AM »
Armalcolite?  It should be Armcolalite.  CMP's name goes before LMP.

That was the first idea, yeah. But, you know, trademark issues 'n such.

Offline Tedward

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Re: Wonderful Photographs from Mars
« Reply #37 on: August 21, 2012, 07:18:16 AM »
With regards speed. You call it ramming speed sans crunch?

Offline Andromeda

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Re: Wonderful Photographs from Mars
« Reply #38 on: August 21, 2012, 07:18:58 AM »
Prepare for ludicrous speed!
"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny...'" - Isaac Asimov.

Offline sts60

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Re: Wonderful Photographs from Mars
« Reply #39 on: August 21, 2012, 12:07:09 PM »
In space, the only thing that could legitimately be called full speed is C.

I don't think the MSL managed to quite reach that speed.
Insted of "Seven Minutes of Terror", it would have been "Seven Milliseconds of Plasma".

Offline Glom

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Re: Wonderful Photographs from Mars
« Reply #40 on: August 21, 2012, 03:26:12 PM »
In space, the only thing that could legitimately be called full speed is C.

I don't think the MSL managed to quite reach that speed.
Insted of "Seven Minutes of Terror", it would have been "Seven Milliseconds of Plasma".

That long?

Offline Count Zero

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Re: Wonderful Photographs from Mars
« Reply #41 on: August 21, 2012, 09:26:40 PM »
Reminds me of this recent article on relativistic baseball.



The rest of the what-if articles are just as fun.
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Offline ka9q

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Re: Wonderful Photographs from Mars
« Reply #42 on: August 22, 2012, 12:41:30 AM »
I didn't know about that "what-if" series on xkcd. What fun!

Naturally I had to spot-check at least one of his calculations. A regulation US baseball has an average mass of about 146 grams, so if it were moving at 0.9c - and ignoring relativistic effects - it would have a kinetic energy of about 5e15 J or about 1.2 megatons of TNT. So yeah, there'd be a large fireball and the stadium would be replaced with a large crater.

Relativistic effects would only increase this.

Offline cjameshuff

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Re: Wonderful Photographs from Mars
« Reply #43 on: August 22, 2012, 01:12:30 AM »
The one thing where I think his analysis goes wrong is that the ball stays too intact and behaves too much like a solid object speeding through a fluid medium. From the ball's perspective, it's being blasted with 17 GeV N and 19 GeV O nuclei (lots more than the binding energy of those nuclei), plus 7 660 keV beta particles for each of the former and 8 for each of the latter.

I think it's going to look less like a fusion zone in front with a vacuum behind, and more like atoms splattering and fusing all through the ball with a trail of nuclear debris and reaction products behind, the ball itself more or less instantly ceasing to resemble a solid object and instead smearing out along its trajectory.

Offline Chew

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Re: Wonderful Photographs from Mars
« Reply #44 on: August 22, 2012, 02:42:52 AM »
I didn't know about that "what-if" series on xkcd. What fun!

Naturally I had to spot-check at least one of his calculations. A regulation US baseball has an average mass of about 146 grams, so if it were moving at 0.9c - and ignoring relativistic effects - it would have a kinetic energy of about 5e15 J or about 1.2 megatons of TNT. So yeah, there'd be a large fireball and the stadium would be replaced with a large crater.

Relativistic effects would only increase this.


Heh. The relativistic mass increase would be by a factor of 2.29. So 2.9 megatons of TNT. That would make a crater about 1 km in diameter and one fourth of that deep. The 5 PSI blast radius (most buildings inside the 5 PSI blast radius are destroyed) would be 7.3 km. Exposed people would receive third degree burns out to 17 km.
« Last Edit: August 22, 2012, 02:47:24 AM by Chew »