PB #52: Prayer

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Re: PB #52: Prayer

Postby Skydancer » Tue Oct 24, 2017 7:20 am

The evidence is not there -yet-, but it looks likely. We know where to look. The Drake Equation is valid, we just need to find out what the actual values are. We're getting down to cases on # of planetary systems, # of habitable planets, and perhaps % chance of life starting on a likely world.

The next question is, how likely is it that bacteria will result in advanced life?

And of course, this is life as we know it. We have absolutely zero data on even the possibility of crystalline life forms, energy-field life forms, or degenerate-matter life (Dragon's Egg style).
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Re: PB #52: Prayer

Postby Scott » Tue Oct 24, 2017 8:38 am

Skydancer wrote:The evidence is not there -yet-, but it looks likely. We know where to look. The Drake Equation is valid, we just need to find out what the actual values are. We're getting down to cases on # of planetary systems, # of habitable planets, and perhaps % chance of life starting on a likely world.

The next question is, how likely is it that bacteria will result in advanced life?

And of course, this is life as we know it. We have absolutely zero data on even the possibility of crystalline life forms, energy-field life forms, or degenerate-matter life (Dragon's Egg style).

We just haven't gone out to get the evidence, because it's a really freaking expensive trip (either to Mars or heaven forbid Europa).

And quite honestly, I'm pretty sure that there's not a good argument for making a trip out there just to fill in the actual values of the Drake Equation. Sure, if we were making a trip out there for some other reason(say, finding fuels/resources) and we also fill in the numbers for the Drake Equation, that's one thing. But to drop literally billions of dollars just to fill in some numbers? Ask Elon Musk to do that.
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Re: PB #52: Prayer

Postby Skydancer » Tue Oct 24, 2017 8:45 am

Scott wrote:
Skydancer wrote:The evidence is not there -yet-, but it looks likely. We know where to look. The Drake Equation is valid, we just need to find out what the actual values are. We're getting down to cases on # of planetary systems, # of habitable planets, and perhaps % chance of life starting on a likely world.

The next question is, how likely is it that bacteria will result in advanced life?

And of course, this is life as we know it. We have absolutely zero data on even the possibility of crystalline life forms, energy-field life forms, or degenerate-matter life (Dragon's Egg style).

We just haven't gone out to get the evidence, because it's a really freaking expensive trip (either to Mars or heaven forbid Europa).

And quite honestly, I'm pretty sure that there's not a good argument for making a trip out there just to fill in the actual values of the Drake Equation. Sure, if we were making a trip out there for some other reason(say, finding fuels/resources) and we also fill in the numbers for the Drake Equation, that's one thing. But to drop literally billions of dollars just to fill in some numbers? Ask Elon Musk to do that.


For machinery, it's actually a more expensive trip to Mars than to Europa... longer to Europa, of course, but less of a gravity well to land in at the end of the trip. Time in transfer orbit is cheap, though.
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Re: PB #52: Prayer

Postby Spambot » Tue Oct 24, 2017 6:18 pm

Skydancer wrote:
Scott wrote:
Skydancer wrote:The evidence is not there -yet-, but it looks likely. We know where to look. The Drake Equation is valid, we just need to find out what the actual values are. We're getting down to cases on # of planetary systems, # of habitable planets, and perhaps % chance of life starting on a likely world.

The next question is, how likely is it that bacteria will result in advanced life?

And of course, this is life as we know it. We have absolutely zero data on even the possibility of crystalline life forms, energy-field life forms, or degenerate-matter life (Dragon's Egg style).

We just haven't gone out to get the evidence, because it's a really freaking expensive trip (either to Mars or heaven forbid Europa).

And quite honestly, I'm pretty sure that there's not a good argument for making a trip out there just to fill in the actual values of the Drake Equation. Sure, if we were making a trip out there for some other reason(say, finding fuels/resources) and we also fill in the numbers for the Drake Equation, that's one thing. But to drop literally billions of dollars just to fill in some numbers? Ask Elon Musk to do that.


For machinery, it's actually a more expensive trip to Mars than to Europa... longer to Europa, of course, but less of a gravity well to land in at the end of the trip. Time in transfer orbit is cheap, though.


Europa seems almost designed to be a colony site, what with the liquid water and abundant nearby rocky bodies. I'd probably just take the discovery of life there as a sign that it was specially prepared as a new world to be opened up. I don't know why Musk is so interested in Mars, when you've got a more hospitable destination in a rather scenic location.
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Re: PB #52: Prayer

Postby Scott » Tue Oct 24, 2017 10:58 pm

Mars has the advantage of a much shorter travel time (with a drive capable of 0.1m/s/s, it's 40 days to get there), and more importantly the advantage of not having Jupiter's radiation belts.

Putting people onto Europa requires a beastly drive (to limit solar wind-induced radiation exposure and zero gee time, IIRC 40 days or so is the practical limit without gravity), and avoiding the Jovian radbelts.
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Re: PB #52: Prayer

Postby Zarpaulus » Wed Oct 25, 2017 12:42 am

Scott wrote:Mars has the advantage of a much shorter travel time (with a drive capable of 0.1m/s/s, it's 40 days to get there), and more importantly the advantage of not having Jupiter's radiation belts.

Putting people onto Europa requires a beastly drive (to limit solar wind-induced radiation exposure and zero gee time, IIRC 40 days or so is the practical limit without gravity), and avoiding the Jovian radbelts.

At the right time of the year at least.

Mars might only be 1.5 times as far from the Sun as Earth, but whether that means Earth and Mars are .5 AU or 2.5 AU apart depends on their relative orbits.

Jupiter though, around 5 AUs from the Sun, Saturn's twice that.
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Re: PB #52: Prayer

Postby Spambot » Wed Oct 25, 2017 1:13 am

Zarpaulus wrote:
Scott wrote:Mars has the advantage of a much shorter travel time (with a drive capable of 0.1m/s/s, it's 40 days to get there), and more importantly the advantage of not having Jupiter's radiation belts.

Putting people onto Europa requires a beastly drive (to limit solar wind-induced radiation exposure and zero gee time, IIRC 40 days or so is the practical limit without gravity), and avoiding the Jovian radbelts.

At the right time of the year at least.

Mars might only be 1.5 times as far from the Sun as Earth, but whether that means Earth and Mars are .5 AU or 2.5 AU apart depends on their relative orbits.

Jupiter though, around 5 AUs from the Sun, Saturn's twice that.


According to Scott's information, a Hohmann transfer orbit would be unsuitable for a manned mission to Jupiter. I doubt it would require a brachiosochrone trajectory, but we might be getting to that territory.

Hmm, I see the wisdom in an outpost at Mars, even if it is terribly inhospitable. Being 40 days in transit, it's at the limits of launches from Earth, but an outpost there, or more importantly industrial capacity, would allow missions to the outer solar system be staged from Mars instead of Terra.
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Re: PB #52: Prayer

Postby Scott » Wed Oct 25, 2017 11:33 pm

Zarpaulus wrote:
Scott wrote:Mars has the advantage of a much shorter travel time (with a drive capable of 0.1m/s/s, it's 40 days to get there), and more importantly the advantage of not having Jupiter's radiation belts.

Putting people onto Europa requires a beastly drive (to limit solar wind-induced radiation exposure and zero gee time, IIRC 40 days or so is the practical limit without gravity), and avoiding the Jovian radbelts.

At the right time of the year at least.

Mars might only be 1.5 times as far from the Sun as Earth, but whether that means Earth and Mars are .5 AU or 2.5 AU apart depends on their relative orbits.

Jupiter though, around 5 AUs from the Sun, Saturn's twice that.

If you have a drive capable of 0.1m/s/s continuous burn, even the 2.5AU max distance between Earth and Mars is 47 days (0.5AU is ~18 days). I will admit that a drive that powerful is currently fictional, but it's within the current limits of materials science. So no, it doesn't really depend much on relative orbital positions. All hail the brachistochrone badassery!

That same drive would get you out to Jupiter in about 65 days (average distance of 787million KM), and to Saturn in about 90 days (average distance of 1,430million KM). It's a non-linear relationship between distance and travel time because you're continuously accelerating. You'd have a relatively linear travel time with burn-and-coast.
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Re: PB #52: Prayer

Postby Wanderer » Wed Oct 25, 2017 11:41 pm

Glossary: Brachistochrone: Characterized by the Brachistocrone Curve, or "curve of fastest descent", i.e. the shortest distance between the two points.

I could almost feel people wondering. :werewolf:
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Re: PB #52: Prayer

Postby Spambot » Wed Oct 25, 2017 11:55 pm

Scott wrote:
Zarpaulus wrote:
Scott wrote:Mars has the advantage of a much shorter travel time (with a drive capable of 0.1m/s/s, it's 40 days to get there), and more importantly the advantage of not having Jupiter's radiation belts.

Putting people onto Europa requires a beastly drive (to limit solar wind-induced radiation exposure and zero gee time, IIRC 40 days or so is the practical limit without gravity), and avoiding the Jovian radbelts.

At the right time of the year at least.

Mars might only be 1.5 times as far from the Sun as Earth, but whether that means Earth and Mars are .5 AU or 2.5 AU apart depends on their relative orbits.

Jupiter though, around 5 AUs from the Sun, Saturn's twice that.

If you have a drive capable of 0.1m/s/s continuous burn, even the 2.5AU max distance between Earth and Mars is 47 days (0.5AU is ~18 days). I will admit that a drive that powerful is currently fictional, but it's within the current limits of materials science. So no, it doesn't really depend much on relative orbital positions. All hail the brachistochrone badassery!

That same drive would get you out to Jupiter in about 65 days (average distance of 787million KM), and to Saturn in about 90 days (average distance of 1,430million KM). It's a non-linear relationship between distance and travel time because you're continuously accelerating. You'd have a relatively linear travel time with burn-and-coast.


I had thought that the main problem with a brachiostochrone mission wasn't so much that that level of acceleration was impossible, but that it would require an absurd amount of reaction mass with current technology. Though I may be thinking of a lower-efficiency drive meant to burn at 1G continuously.
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Re: PB #52: Prayer

Postby Zarpaulus » Thu Oct 26, 2017 1:11 am

Spambot wrote:
Scott wrote:
Zarpaulus wrote:
Scott wrote:Mars has the advantage of a much shorter travel time (with a drive capable of 0.1m/s/s, it's 40 days to get there), and more importantly the advantage of not having Jupiter's radiation belts.

Putting people onto Europa requires a beastly drive (to limit solar wind-induced radiation exposure and zero gee time, IIRC 40 days or so is the practical limit without gravity), and avoiding the Jovian radbelts.

At the right time of the year at least.

Mars might only be 1.5 times as far from the Sun as Earth, but whether that means Earth and Mars are .5 AU or 2.5 AU apart depends on their relative orbits.

Jupiter though, around 5 AUs from the Sun, Saturn's twice that.

If you have a drive capable of 0.1m/s/s continuous burn, even the 2.5AU max distance between Earth and Mars is 47 days (0.5AU is ~18 days). I will admit that a drive that powerful is currently fictional, but it's within the current limits of materials science. So no, it doesn't really depend much on relative orbital positions. All hail the brachistochrone badassery!

That same drive would get you out to Jupiter in about 65 days (average distance of 787million KM), and to Saturn in about 90 days (average distance of 1,430million KM). It's a non-linear relationship between distance and travel time because you're continuously accelerating. You'd have a relatively linear travel time with burn-and-coast.


I had thought that the main problem with a brachiostochrone mission wasn't so much that that level of acceleration was impossible, but that it would require an absurd amount of reaction mass with current technology. Though I may be thinking of a lower-efficiency drive meant to burn at 1G continuously.


Hence why "The Expanse-verse" needed the Epstein Drive to reach the Outer system about a century after colonizing Mars.
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Re: PB #52: Prayer

Postby Scott » Thu Oct 26, 2017 4:48 am

Yeah, the big drives capable of multiple gees for days/weeks so beloved by Clarke et al back in the Golden Age of Scifi require an utterly impractical amount of reaction mass for real life (heck, some of them are so overpowered that they require matter/antimatter fuel/remass or some other total conversion of mass to energy).

But a 0.1m/s/s drive is actually pretty reasonable for an in-system drive. Still requires an immense amount of remass, but it's achievable. You could actually do it with a nuclear-thermal rocket, but you'd need to get a nuclear reactor of some flavor into orbit. Let's see here... That Mars example I used earlier has a delta-V requirement of a little under 3.2million m/s/s. That's huge, but it's do-able. You'd need one heck of a big ship, though.
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Re: PB #52: Prayer

Postby Mike Van Pelt » Thu Oct 26, 2017 5:12 am

That's why some writers, like G. David Nordley, put the reaction mass and energy source in a fixed location close to the star, and fire reaction mass "brilliant pebbles" at the vehicle to accelerate it.
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Re: PB #52: Prayer

Postby Spambot » Thu Oct 26, 2017 6:02 am

Mike Van Pelt wrote:That's why some writers, like G. David Nordley, put the reaction mass and energy source in a fixed location close to the star, and fire reaction mass "brilliant pebbles" at the vehicle to accelerate it.


Is there such a thing as a fixed location in space?
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Re: PB #52: Prayer

Postby Skydancer » Thu Oct 26, 2017 7:39 am

Spambot wrote:
Mike Van Pelt wrote:That's why some writers, like G. David Nordley, put the reaction mass and energy source in a fixed location close to the star, and fire reaction mass "brilliant pebbles" at the vehicle to accelerate it.


Is there such a thing as a fixed location in space?


Only relative to a point of interest. And even then it depends on how fast you're going.

There was a young lady named Bright
Who could travel much faster than light
She set out one day
In a relative way
And returned on the previous night.
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Re: PB #52: Prayer

Postby Scott » Thu Oct 26, 2017 10:58 am

Spambot wrote:
Mike Van Pelt wrote:That's why some writers, like G. David Nordley, put the reaction mass and energy source in a fixed location close to the star, and fire reaction mass "brilliant pebbles" at the vehicle to accelerate it.

Is there such a thing as a fixed location in space?

Relatively. (Pun totally intended)

They're places like the Lagrange Points, where the various gravitational forces balance out.
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