So far, the Republicans in Congress have been following along with Trump's lead. It seems unlikely that they will pick this as the issue to break ranks with him.
My comments were on the technical part-- this site is news for nerds, you know. Whether you should be "afraid" is a completely different question.
I do point out that this is, so far, 480 posts (on slashdot alone) discussing details of a 140-character tweet. That's 3.4 posts for each character of the tweet, including the blank spaces at the end.
Escaping the moon's gravity is the easy part. The moon is in a really high orbit. To get something from the moon to the Earth, you need to either lose enough of your angular momentum to fall
It turns out, however, the higher an orbit is, the easier it is to kill your angular momentum and drop. So the fact that the moon is in a "really high" orbit helps here. You need about 1 km/sec to kill the moon's orbital velocity, actually less than the 2.38 km/sec escape velocity to throw the rock off the surface.
But delta-Vs don't add; energies add. Once your mass driver has gotten your rock to 2.38 km/sec, it only takes another 0.2 km/sec to kill the orbital velocity and make it drop. (Less, if you want to take an indirect trajectory via the "fuzzy boundary", but those take a lot more time).
...and, yes, actually I am a rocket scientist.
...
TL;DR: If it were easy for things from the moon to fall to Earth, the moon would have fallen down already.
Original submission: Brianna Wu Is a Harsh Mistress.
Exactly. And the Heinlein reference answers the point made in the last line of the summary, that it "would still require escaping the satellite's gravitational field, a task that requires the power and thrust contained in a huge rocket.": You wouldn't use a rocket. You would use a mass driver.
With that said, it would take some pretty big rocks to project the "power of 100s of nuclear bombs." But, assuming by "rocks" you mean quite large boulders-- a hundred thousand tons or so-- the statement is accurate.
That's an old graphic, but yes, we have an excellent artist aboard. Of course, they mostly want to go for what looks the most aesthetically pleasing, while I'm always niggling on the technical details;) The conversations usually go like,
"But.... you can't have people living there, the ballonets are going to expand into that when they launch the ascent stage... either the ballonets are going to dramatically expand or the habitat is going to dramatically collapse, take your pick. And if you store the ascent stage that close, it's going to destroy the whole habitat if there's a mishap while it's fueled. And how can I possibly fit all of that floor area into the fairing? Plus I don't see any scrubber for ISRU... it's going to need to be big, I'm struggling to get the absorption figures to work for sufficient resource collection with a 4.2 meter prop.....";) But really, so long as their final graphics don't end up with a giant pirate flag or anything like that, I'm sure we can deal with a bit of "artistic license":)...
Oh wait a minute, I just noticed your username. Geoffrey.landis? As in, the Geoffrey Landis? Oh wow, hey, we should chat some time.;) (bare minimum, I at least need to ask for permission to reproduce some figures from a few of your papers). If you get a chance, definitely drop me a line at mQeme@eaQku.neQt (remove Qs to despammify). I actually just dropped by Slashdot as a break in the middle of working on some graphics illustrating non-Hohmann transfer times vs. delta-V between Earth, Mars and Venus, demonstrating the advantage Venus has due to the Oberth effect;)
I'm part of a group called Venus Labs that's actually developing the concept further, doing more detailed studies on each component of the concept that Landis presented.:)
Lunar distant retrograde orbit (DRO) turns out to be pretty stable. It's the close orbits that are unstable. http://ccar.colorado.edu/asen5... http://www.sciencedirect.com/s... Another virtue of lunar DRO is that when they do decay, they tend to drop into the moon or to escape, not down to the Earth
Part of the problem with the moon is that it's just not a great place for ISRU. Volatiles are rare.
That was the old, Apollo-era thinking. The newer thinking is that once you get away from the equatorial regions, volatiles aren't so rare. In the high latitudes, you have hydrated minerals (seen by Chadrayaan), and in the actual polar craters, ice (as seen by Lunar Prospector, LCROSS, etc.).
We've never even sampled any moon that aren't depleted in volatiles, although there's some data to suggest that various volatiles might be scattered in permanently shaded areas
Exactly. The problem with Apollo era sampling was that they never got more than about 20 degrees from the equator.
...
Of course, I prefer Venus to Mars, but that's neither here nor there;) I'd like to see a parallel program for both, as the same sort of booster and transfer stage can be used for both, so it's only habitat / ascent stage development costs that are doubled. And once you get past the differences in feedstock sources, production industrial processes converge (Venus advantaged by the higher power availability and easier ability to get rid of heat - excepting in the case of cryogenics, where Mars holds the advantage)
Their research is more serious than your unsupported opinion.
Most of the space elevator research assumes that the problems of making long, perfect carbon nanotubes can be solved, that they be made in volume at very low cost, and that they will have an ultimate tensile strength equal to that calculated from theory of perfect carbon, and not one that is the actual measured tensile strength of nanotubes in the real world.
Unfortunately, carbon nanotubes not only have never been made with this theoretical strength, newer work makes it look like they cannot reach this theoretical strength. The pentagons of perfect nanotubes spontaneously convert into pentagons and heptagons under strain, which reduces the breaking stress. https://www.newscientist.com/a...
Right now, the materials needed to make a low cost space elevator are still in the future. Later materials science may make us revise that estimate, but right now: it's still hard.
As noted, Clarke did not invent the concept of the space elevator, although he was one of the first two writers to highlight it in science fiction (with Charles Sheffield the other). The concept of the space elevator was invented independently several times, the first time Artsutanov (who only published in Russian), then by Isaacs et al, and then by Pearson.
Clarke didn't invent the concept of a geosynchronous satellite, either, although he was the first to point out that geosynchronous orbit was an excellent orbit for communications.
Name one study offering a credible alternative explanation for observed phenomena.
What observed phenomena?
This, for a start: http://berkeleyearth.org/wp-co... . On the subject of replication, note that this image graphs results from four different research groups.
A question I have is whether you are actually interested, or if you merely pretending interest, Indeed, if you're actually interested, there is a lot of work being done in analyzing data and comparing data from different times, which is (as you imply) indeed not always trivial. And there is a "damned if you do, damned if you don't" problem for the people doing the actual work, of course, because if they don't correct the data errors, they're criticized for not correcting them, and if they do, they're criticize for "adjusting" the data. They deal with this by being very transparent in how they analyze the data, which is extensively documented.
The first thing to know is not the sensitivity of the thermometer, though; it is the statistics of measurement. I do assume you're aware that a large number of measurements is more precise than a single measurement, right? So the first question you should be asking is, how many measurements are being incorporated into each statistical data point. Ten thousand measurements with a precision of 1 degree, for example, give an average with a precision of 0.01 degrees. Good introductions to statistics of data analysis are available many places, including on the web, for example:
https://www.princeton.edu/~cap/AEESP_Statchap_Peters.pdf or somewhat more detailed,
Moving in to measurements: there are four main institutions that are doing the reconstruction of long-term temperature measurements; most of your questions about thermometry are answered by citations in the references of the papers they publish on their technique. It does take some work to dig down through the references, though. If you want to start, most of the recent papers are online. I would start with the Goddard Institute of Space Studies papers. The full list is here:
https://pubs.giss.nasa.gov
The two papers you should probably start with are Hansen and Lebedeff 1987,
https://pubs.giss.nasa.gov/abs/ha00700d.html and Hansen et al 2010:
https://pubs.giss.nasa.gov/abs/ha00510u.html
If you don't want to dive that deep, there are some review papers that cover most of the material you're interested in. The Berkeley Earth Surface Temperature project has a couple of good top-level papers, with an overview:
http://static.berkeleyearth.org/papers/Methods-GIGS-1-103.pdf and a paper on data quality:
I wouldn't brush off someone threatening to beat my head in with a baseball bat. I'd be calling the cops.
Good idea, but if you don't have it on tape, it's your word against his, and the result is he gets a mild warning "say, Jim, you should be more careful in how you phrase things, ha, ha, some people are taking it wrong," while you get tagged as "too sensitive" and "not a team worker" and are the one let go at the next downsizing.
Name one study offering a credible alternative explanation for observed phenomena.
What observed phenomena?
This, for a start: http://berkeleyearth.org/wp-co... . On the subject of replication, note that this image graphs results from four different research groups.
It's not heresy if the science is sound. Simply questioning isn't valid, though.
Questioning, of course, is always valid. But "questioning" is useless when the questioner has no interest in listening to anybody answering the question.
Far too much of the "questioning" about climate science is from people who have no interest in any of the science, the measurements, or the data, and won't bother to learn anything about it.
Many studies have been done on anthropic climate change, but almost no experiments.
The infrared absorption of carbon dioxide is experimentally measured in the laboratory. And there is a vast amount of measured data on the earth's atmosphere and climate, from surface, atmospheric, and orbital probes, not to mention probes of other planets; and we acquire terabytes of additional data every year. The basics of Earth's energy balance are well understood, and they are understood, in part, because of this vast amount of experimental and observational data.
Slashdot Mirror
So far, the Republicans in Congress have been following along with Trump's lead. It seems unlikely that they will pick this as the issue to break ranks with him.
My comments were on the technical part-- this site is news for nerds, you know. Whether you should be "afraid" is a completely different question.
I do point out that this is, so far, 480 posts (on slashdot alone) discussing details of a 140-character tweet. That's 3.4 posts for each character of the tweet, including the blank spaces at the end.
It's possible that you're overthinking it.
I'd put it at least an order of magnitude smaller than 1km...
Since "small" is subjective, you can certainly define it like that if you like.
By your definition, a "small" rock from the asteroid belt will still "indeed do nuclear-weapons-scale damage if hitting the Earth at orbital speeds."
Escaping the moon's gravity is the easy part. The moon is in a really high orbit. To get something from the moon to the Earth, you need to either lose enough of your angular momentum to fall
It turns out, however, the higher an orbit is, the easier it is to kill your angular momentum and drop. So the fact that the moon is in a "really high" orbit helps here. You need about 1 km/sec to kill the moon's orbital velocity, actually less than the 2.38 km/sec escape velocity to throw the rock off the surface.
But delta-Vs don't add; energies add. Once your mass driver has gotten your rock to 2.38 km/sec, it only takes another 0.2 km/sec to kill the orbital velocity and make it drop. (Less, if you want to take an indirect trajectory via the "fuzzy boundary", but those take a lot more time).
...and, yes, actually I am a rocket scientist.
...
TL;DR: If it were easy for things from the moon to fall to Earth, the moon would have fallen down already.
In fact, rocks splashed off of the moon actually do hit the earth, of course: http://meteorites.wustl.edu/lu...
I'd actually love to hear some context for her comments.
The context is: it's a tweet, not an essay on technologies for space warfare.
Bonus points for having read Heinlein, but, really, you can't read much into a tweet. It's 140 characters.
Who would vote in an egg head into congress?
Actually, I think it would be cool to have some more science-fiction readers in Congress.
Depends on what you mean by "small".
On a scale of asteroids, I'd say "small" means less than a kilometer or so in diameter.
By comparison the LEM weights 2 tons dry and 15 tons total, with 8 tons fuel.
Uh, but that's to land and then take off again. The LM Ascent Stage is what you need to compare to:
Dry mass: 2,150 kg
Propellant mass: 2,353 kg
--but, as noted above many times, nobody's suggesting a rocket to do this. Heinlein proposed this decades ago. You'd use a mass driver.
Original submission: Brianna Wu Is a Harsh Mistress.
Exactly. And the Heinlein reference answers the point made in the last line of the summary, that it "would still require escaping the satellite's gravitational field, a task that requires the power and thrust contained in a huge rocket.":
You wouldn't use a rocket. You would use a mass driver.
With that said, it would take some pretty big rocks to project the "power of 100s of nuclear bombs." But, assuming by "rocks" you mean quite large boulders-- a hundred thousand tons or so-- the statement is accurate.
That's an old graphic, but yes, we have an excellent artist aboard. Of course, they mostly want to go for what looks the most aesthetically pleasing, while I'm always niggling on the technical details ;) The conversations usually go like,
"But.... you can't have people living there, the ballonets are going to expand into that when they launch the ascent stage... either the ballonets are going to dramatically expand or the habitat is going to dramatically collapse, take your pick. And if you store the ascent stage that close, it's going to destroy the whole habitat if there's a mishap while it's fueled. And how can I possibly fit all of that floor area into the fairing? Plus I don't see any scrubber for ISRU... it's going to need to be big, I'm struggling to get the absorption figures to work for sufficient resource collection with a 4.2 meter prop....." ;) But really, so long as their final graphics don't end up with a giant pirate flag or anything like that, I'm sure we can deal with a bit of "artistic license" :)...
Oh wait a minute, I just noticed your username. Geoffrey.landis? As in, the Geoffrey Landis? Oh wow, hey, we should chat some time. ;) (bare minimum, I at least need to ask for permission to reproduce some figures from a few of your papers). If you get a chance, definitely drop me a line at mQeme@eaQku.neQt (remove Qs to despammify). I actually just dropped by Slashdot as a break in the middle of working on some graphics illustrating non-Hohmann transfer times vs. delta-V between Earth, Mars and Venus, demonstrating the advantage Venus has due to the Oberth effect ;)
Sure, I should do that; see what you're doing.
I'm part of a group called Venus Labs that's actually developing the concept further, doing more detailed studies on each component of the concept that Landis presented. :)
http://venuslabs.org/a?
Wow, nice graphic! I'll be fascinated to see what you come up with!
Lunar distant retrograde orbit (DRO) turns out to be pretty stable. It's the close orbits that are unstable.
http://ccar.colorado.edu/asen5...
http://www.sciencedirect.com/s...
Another virtue of lunar DRO is that when they do decay, they tend to drop into the moon or to escape, not down to the Earth
Part of the problem with the moon is that it's just not a great place for ISRU. Volatiles are rare.
That was the old, Apollo-era thinking. The newer thinking is that once you get away from the equatorial regions, volatiles aren't so rare. In the high latitudes, you have hydrated minerals (seen by Chadrayaan), and in the actual polar craters, ice (as seen by Lunar Prospector, LCROSS, etc.).
We've never even sampled any moon that aren't depleted in volatiles, although there's some data to suggest that various volatiles might be scattered in permanently shaded areas
Exactly. The problem with Apollo era sampling was that they never got more than about 20 degrees from the equator.
...
Of course, I prefer Venus to Mars, but that's neither here nor there ;) I'd like to see a parallel program for both, as the same sort of booster and transfer stage can be used for both, so it's only habitat / ascent stage development costs that are doubled. And once you get past the differences in feedstock sources, production industrial processes converge (Venus advantaged by the higher power availability and easier ability to get rid of heat - excepting in the case of cryogenics, where Mars holds the advantage)
Hey, we're thinking along parallel lines!!
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022668.pdf
The numbers come from this book: https://www.amazon.com/Space-E...
Their research is more serious than your unsupported opinion.
Most of the space elevator research assumes that the problems of making long, perfect carbon nanotubes can be solved, that they be made in volume at very low cost, and that they will have an ultimate tensile strength equal to that calculated from theory of perfect carbon, and not one that is the actual measured tensile strength of nanotubes in the real world.
Unfortunately, carbon nanotubes not only have never been made with this theoretical strength, newer work makes it look like they cannot reach this theoretical strength. The pentagons of perfect nanotubes spontaneously convert into pentagons and heptagons under strain, which reduces the breaking stress.
https://www.newscientist.com/a...
Right now, the materials needed to make a low cost space elevator are still in the future. Later materials science may make us revise that estimate, but right now: it's still hard.
As noted, Clarke did not invent the concept of the space elevator, although he was one of the first two writers to highlight it in science fiction (with Charles Sheffield the other). The concept of the space elevator was invented independently several times, the first time Artsutanov (who only published in Russian), then by Isaacs et al, and then by Pearson.
http://www.isec.org/index.php/10-resources/18-the-history-of-the-space-elevator
Clarke didn't invent the concept of a geosynchronous satellite, either, although he was the first to point out that geosynchronous orbit was an excellent orbit for communications.
Name one study offering a credible alternative explanation for observed phenomena.
What observed phenomena?
This, for a start: http://berkeleyearth.org/wp-co... . On the subject of replication, note that this image graphs results from four different research groups.
Here is the fit of theory to experiment:
http://berkeleyearth.org/wp-co...
on behalf of all skeptics, i'll just say "the fit of that graph is not good enough to convince me!"
The challenge was to put forth a credible alternate explanation.
I think all polls should have a Cowboy Neal option. .. of course if they did, he's probably be president now...
Nobody else noticed that this story almost exactly echoes the slashdot poll from a couple of weeks ago?
https://slashdot.org/poll/3025...
In this poll "more than 40 percent of respondents never worry about [losing their job to a robot]."
in the slashdot poll, "I think my current job will be replaced by a robot/software: Never (why not?) 5963 votes / 43%"
And I'd thought slashdot polls were unscientific!
A question I have is whether you are actually interested, or if you merely pretending interest, Indeed, if you're actually interested, there is a lot of work being done in analyzing data and comparing data from different times, which is (as you imply) indeed not always trivial. And there is a "damned if you do, damned if you don't" problem for the people doing the actual work, of course, because if they don't correct the data errors, they're criticized for not correcting them, and if they do, they're criticize for "adjusting" the data. They deal with this by being very transparent in how they analyze the data, which is extensively documented.
The first thing to know is not the sensitivity of the thermometer, though; it is the statistics of measurement. I do assume you're aware that a large number of measurements is more precise than a single measurement, right? So the first question you should be asking is, how many measurements are being incorporated into each statistical data point. Ten thousand measurements with a precision of 1 degree, for example, give an average with a precision of 0.01 degrees. Good introductions to statistics of data analysis are available many places, including on the web, for example:
https://www.princeton.edu/~cap/AEESP_Statchap_Peters.pdf or somewhat more detailed,
http://www-library.desy.de/preparch/books/vstatmp_engl.pdf
Moving in to measurements: there are four main institutions that are doing the reconstruction of long-term temperature measurements; most of your questions about thermometry are answered by citations in the references of the papers they publish on their technique. It does take some work to dig down through the references, though. If you want to start, most of the recent papers are online. I would start with the Goddard Institute of Space Studies papers. The full list is here:
https://pubs.giss.nasa.gov
The two papers you should probably start with are Hansen and Lebedeff 1987,
https://pubs.giss.nasa.gov/abs/ha00700d.html
and Hansen et al 2010:
https://pubs.giss.nasa.gov/abs/ha00510u.html
If you don't want to dive that deep, there are some review papers that cover most of the material you're interested in. The Berkeley Earth Surface Temperature project has a couple of good top-level papers, with an overview:
http://static.berkeleyearth.org/papers/Methods-GIGS-1-103.pdf
and a paper on data quality:
http://static.berkeleyearth.org/papers/Station-Quality.pdf
It's when we're 'there,' when we're in the future, that we can look back ...
But we're no more "in the future" now than we were yesterday, or the year before.
We've always lived in yesterday's tomorrow.
I wouldn't brush off someone threatening to beat my head in with a baseball bat. I'd be calling the cops.
Good idea, but if you don't have it on tape, it's your word against his, and the result is he gets a mild warning "say, Jim, you should be more careful in how you phrase things, ha, ha, some people are taking it wrong," while you get tagged as "too sensitive" and "not a team worker" and are the one let go at the next downsizing.
Name one study offering a credible alternative explanation for observed phenomena.
What observed phenomena?
This, for a start: http://berkeleyearth.org/wp-co... . On the subject of replication, note that this image graphs results from four different research groups.
Here is the fit of theory to experiment:
http://berkeleyearth.org/wp-co...
It's not heresy if the science is sound. Simply questioning isn't valid, though.
Questioning, of course, is always valid. But "questioning" is useless when the questioner has no interest in listening to anybody answering the question.
Far too much of the "questioning" about climate science is from people who have no interest in any of the science, the measurements, or the data, and won't bother to learn anything about it.
Many studies have been done on anthropic climate change, but almost no experiments.
The infrared absorption of carbon dioxide is experimentally measured in the laboratory. And there is a vast amount of measured data on the earth's atmosphere and climate, from surface, atmospheric, and orbital probes, not to mention probes of other planets; and we acquire terabytes of additional data every year.
The basics of Earth's energy balance are well understood, and they are understood, in part, because of this vast amount of experimental and observational data.
For a different view:
Science Isn't Broken (It’s just a hell of a lot harder than we give it credit for.)