I support breeder reactors, but it should be pointed out that (as long as high-tech society does not collapse in the mean time) there are other ways of jump-starting production of isotopes like Plutonium-239 and Uranium-233.
All that is really required is a large neutron source; a deuterium fusion reactor (even one that can't produce net electrical power) or a very efficient particle accelerator could do the job easily enough. Once enough feedstock is acquired for a single fission reactor run, cheaply breeding more becomes possible again.
It would be a shame to waste all the Uranium-235, but it's not like it would be impossible to recover from that mistake.
An ICE might be around 20%, half as efficient as a power plant.
A modern automotive ICE can be way better than 20% efficient - the cylinder engine in the Honda Prius is 38.5% efficient.
The whole chain of transmission, charging, battery and electric engine is still around 90% if not more efficiency.
Each of those stages individually is about 90% efficient, meaning that the chain in aggregate is much worse than that.
Grid distribution of power is something like 90% efficient (actually worse than that in India, due to their lousy infrastructure). Charge/discharge efficiency for large Lithium-Ion battery packs is about 85%. A high-powered electric motor + controller is about 90% efficient.
90% of 85% of 90% of 42% = 29%, versus 38.5% for a good ICE
Any economic/environmental benefits to the electric car are entirely due to other factors, such as regenerative braking and the greater range of power sources available to the grid (nuclear, hydro, solar, etc.).
From the point of view of the sun, it is exactly as I explained above. You fly quicker out of the "gravity well" then you needed time to enter it.
Sorry, but no. Such a thing would be possible under Relativity, but in Newtonian mechanics all observers must agree about the timing of events (provided that they are truly being asked the same question).
In the train example, an observer on the platform and one on the train will both give the same answer to the following questions:
1) How much time passed from the point at which the ball was 10 meters from the front of the train, until it hit the train?
2) How much time passed from the point at which the ball hit the train, until it was again 10 meters from the front of the train?
In the same way, the time for a spacecraft receiving a gravity assist to "enter" and to "fly... out" are both defined based on the craft's altitude above the assisting body, which is moving from the Sun's perspective. The motion of the body synchronizes with that of the craft in such a way as to make the time-line consistent, regardless of whether you observe it from the Sun's perspective, or the assisting body's.
This seems to be borne out somewhat in the real world, in that in the USA all new electrical generation capacity is overwhelmingly in "direct" conversion.
The fact that direct generation is "winning" economically in the United States right now is basically a coincidence - it is driven by a combination of environmental regulations (ever stricter emissions controls for coal, and NIMBism for nuclear), mandates and huge subsidies for renewables, and (as you pointed out) the present glut of natural gas from fracking.
By this argument, both nuclear fusion and nuclear fission aren't going to be economical, ever.
While few near-term plans take advantage of it, there is great potential for "direct" energy capture from both fission and fusion.
For fission, look up Dusty Plasma Reactors. For fusion, several promising reactions release most of their energy through charged particles, making non-thermal energy capture straightforward: Deuterium + Helium-3, Helium-3 + Helium-3, and Hydrogen + Boron-11
Outside of exotic applications like space flight, I doubt that Dusty Plasma fission reactors will ever be more economical than a simple Lead-Cooled Fast Reactor. For fusion though, it is likely that if it is technically and economically viable at all, one of the aneutronic reactions that I listed above will be the preferred option in the long term due to the vastly reduced radioactive waste, as compared to the standard Deuterium + Tritium or Deuterium + Deuterium reactions.
Internet advocates always seem to be pushing the Liquid Fluoride Thorium Reactor (LFTR), but the Lead-Cooled Fast Reactor look like the best Generation IV reactor design to me, by far.
The chemistry problems associated with Molten Salt Reactors - especially the need to continuously reprocess the salt-fuel mixture on site - sound pretty hairy from an engineering perspective (speaking here of costs, not safety).
In contrast, a Lead-Cooled Fast Reactor is much more straightforward to design and maintain. It is also (as far as I can tell) the safest fission reactor design yet conceived; only Molten Salt Reactors are in the same league, safety-wise, but I think Lead-Cooled is still better for various reasons.
The Lead-Cooled design has the distinct advantage that it has already been deployed operationally, whereas LFTR is still just a research project.
Ha ha. Very funny. I'm not that dumb. Pluto has been politically marginalized - not "liberated" by the military.
My fellow Americans, it is with sadness and righteous anger that I make this address to you tonight, for new intelligence indicates that Pluto is not a democracy. This great crime against humanity and the American people must not go unavenged!
Furthermore, Pluto has maintained a cold, indifferent silence in the face of all demands to publicly denounce Al Quaeda and the Islamic State. No response has been received to our request to join our Coalition of the Willing.
Taking into consideration its massive stocks of carbon monoxide - a potential chemical warfare agent - it becomes clear that Pluto represents an imminent, existential threat to the security of the American People and the American Way of Life, justifying a pre-emptive military intervention. (But I will direct any legal challenges to this doctrine to the United Nations Security Council, whose formal resolutions we respect.)
Therefore, effective immediately, I am launching Operation Democracy Export So That Rights are Observed, Yeah. The first wave of autonomous B83 military advisors are en route as we speak.
(In particular, the bit about a large moon in a low orbit being useful, even if the planet itself is not, is something I don't recall every seeing pointed out in any of the "serious" discussion I've read on this topic - but should be rather obvious to anyone who's experimented much with gravity assists in the Jool system.)
Note: For simplicity, I shall assume a Newtonian two-body system (meaning the only significant force, is the gravitational pull of a single massive planet upon a passing spaceship).
That is wrong.
Indeed it is; I forgot a factor of two: the actual limit is twice the assisting body's speed. That's just the theoretical maximum, though; getting close to this in practice requires:
1) A massive assisting body (many moons are too small to be useful)
2) A very close approach (the need not to collide with the body limits this parameter)
3) Precise timing (as I mentioned in my previous post)
4) Proper alignment of the trajectories of the spaceship, the assisting body, and the destination
The gravity assist comes from the difference of duration "falling" to the body "from behind" versus escaping the gravity field when "in front" of the body.
This is incorrect; Newtonian two-body non-intersecting free fall trajectories are always symmetrical in both time and space across an axis drawn through the periapsis (point of closest approach) and the other body. This is the basis for Kepler's laws, which state that all such trajectories are conic sections with the massive body at the focus.
(You can benefit from escaping faster than you fell in - if you do an engine burn at periapsis to accelerate your escape. But then you're using the Oberth Effect, not just a gravity assist.)
A spaceship receiving a gravity assist follows a hyperbolic trajectory. From the planet's frame of reference, the spaceship doesn't actually acquire any additional energy or momentum from the encounter at all; what happens instead is that the direction of the spacecraft's motion is changed, but its speed upon leaving the planet's sphere of influence is the same as it was upon entry (the speed up while falling is exactly cancelled out by the slow down while escaping).
Nevertheless, from an outside frame of reference - such as that of the Sun - the spaceship may gain substantial speed/energy/momentum from the encounter. How? I'll just let the Wiki explain this part:
"A close terrestrial analogy is provided by a tennis ball bouncing off the front of a moving train. Imagine standing on a train platform, and throwing a ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees the ball approaching at 80 km/h and then departing at 80 km/h after the ball bounces elastically off the front of the train. Because of the train's motion, however, that departure is at 130 km/h relative to the train platform; the ball has added twice the train's velocity to its own."
If that's confusing and unintuitive - consider giving Kerbal Space Program a try (or just watching some tutorials on YouTube). That's what made this stuff finally "click" for me...
That could be; I don't know all the details. The Exclusion Zone is huge though, so I don't see why they would deliberately construct something like this in one of the really bad areas.
Regardless, it would not be unwise for the crew to bring a Geiger counter and some dosimeter badges...
The Exclusion Zone isn't actually that dangerous now; they've been allowing some tourism and scientific research for a long time now. There's a big difference between "safe place to live and raise a family" versus "safe place to visit for a few hours/days/weeks".
The reactor building itself is another story, of course...
A far out planet could be useful for gravitational assists to the outer solar system.
Pedantically speaking... An actual gravity assist from the planet itself would be worth little - certainly not enough to justify the 1,000+ year diversion (not exaggerating) required to actually take advantage of it.
Getting a gravity assist is analogous to bouncing off of the assisting body. If the body is moving quickly and in an appropriate direction, the spacecraft can pick up a lot of speed (relative to the rest of the solar system) in the process. These conditions would certainly not apply to the hypothetical planet discussed above though:
1) A planet orbiting at that altitude would have an orbital velocity no more than ~7% that of Earth - maybe much less. A gravity assist cannot boost the velocity of the spacecraft by more than the velocity of the assisting body.
2) Achieving a worthwhile gravity assist requires waiting for the orbital phase of the assisting planet and the actual destination to line up right. This could be a loooonnnnggggg wait given that the planet in question would have an orbital period between about 3,000 and 40,000 years...
Having said that, if the planet just so happened to be in roughly the right place already, it might still be worth swinging by it for two reasons:
A) If it had a large moon in a relatively low orbit that was roughly aligned with the plane of the ecliptic, that moon might provide the gravity assist which the planet itself could not.
B) The point of closest approach to the planet may be a good place for an engine burn, to take advantage of the Oberth Effect (which is distinct from a true gravity assist).
Of course - all this "orbital ballet" gravity assist stuff is only necessary because our current propulsion technology is inadequate; any realistic plan for humans to explore the outer solar system would require an upgrade.
I have two problems with the way you're portraying things:
1) You very wrongly dismiss everyone who didn't vote for either Obama, Romney, or McCain in those two elections as "not caring". This is ridiculous; I didn't vote because none of those three candidates came anywhere close to representing me, not because I didn't care. Refusing to choose the "lesser of two evils" does not equate to "not caring".
2) You simply assume that Congress' job is to obey the will of the majority of Americans who voted, whereas the United States is actually constituted as a Republic.
America's system of elections and offices at the Federal level was intentionally designed not to equate to direct democracy, but rather to balance the interests of various groups: the People (via the House of Representatives), each State individually (via the Senate and the Electoral College), minorities (via various constitutional rights, enforceable by the courts which are not directly subject to the majority), etc.
You are essentially demanding that the Senators ignore the groups who elected them, which they are intended to represent, in favour of following the Presidential vote - despite the Presidential vote having been deliberately designed to favour a different constituency.
The only 'voter intent' that matters is *how the votes tallied up.*
Why do only the votes for President count, and not the votes for Congress?
I could just as easily argue that Obama should submit to the manifest will of the voters, revealed by who they voted into Congress - especially since the congressional vote is more up-to-date.
As the majority of travel would be intercontinental even the sonic booms could occur over the ocean prior to turning inland to make the Mach-2 flight to the other coast.
The sonic boom is generated continuously the entire time the plane is flying at supersonic speed, not just at the moment the plane "breaks the sound barrier". The only ways to not affect people on the ground, is to either stay below Mach 1 over populated areas (what Concorde did), or to optimize the plane's aerodynamics to weaken and spread out the pressure spike from the part of the shockwave that is directed toward the ground (what Boom Aerospace is trying to do).
And while a 30% turnout doesn't equate to an electoral mandate for 100% of the citizenry, an electoral victory does equate to a mandate for the percentage of the citizenry that actually gives a shit enough to spend 10 minutes* filling in bubbles.
Now your bias is showing. While it is not 100%, there is definitely a sizeable percentage of people who abstain from voting because they don't want to endorse any of the available candidates, not because they don't care. Particularly in the general election for President, it is absurd and manipulative to suggest that anyone who refuses to accept one of the two choices (in some states, the law prevents others from even getting on the ballot) just "doesn't give a shit".
As to how we can increase electoral turnout, etc. - that is quite far off topic. My original point was simply this: Congress is not obligated to do give Obama what he wants, just because 30% of the country voted for him to be President (not one-man Senate).
There may be many other reasons that Congress should cooperate, but the bare fact that Obama won the last Presidential election is not good enough by itself. The Constitution itself recognizes this; that's why Obama is required to seek Congressional approval in the first place...
I'm simply asking: why should the ballots cast for President be interpreted as instructions to Congress, if we're forbidden to even "have a discussion about voter intent"?
Concorde was capable of supercruise, that is, sustained supersonic flight without afterburners.
Makes sense. The Concorde's range was very impressive, for a supersonic aircraft.
Also, burning fuel at twice the rate isn't a big problem when you're going three times as fast.
Halving the specific impulse does not mean twice the fuel burn - it means twice the fuel burn per unit thrust. Even at high altitude, supersonic flight requires sustaining higher thrust compared to subsonic, so the Concorde really was a lot less fuel efficient per unit distance covered.
I don't have precise numbers, but a quick look suggests that the Concorde burned fuel about 10x faster than the 737 NG (a subsonic aircraft of comparable range and passenger capacity). It also flew 2.6x faster, so that would make it 3-4x more fuel hungry per passenger-kilometer.
And lastly, oil prices have taken a dive recently. I know the situation isn't permanent, but it won't change overnight.
This could help a lot with ticket prices, but it doesn't help at all with range. Aircraft range is basically limited by how much fuel can be crammed on board, without making the plane too heavy to fly safely.
The only way the Concorde could achieve comparable range and passenger capacity to the subsonic 737 NG, was by being a much larger aircraft (180 tons versus 80 tons) with a higher fuel fraction (50% versus 30%?). This technique is expensive, and can only be taken so far. Even with no payload at all, the airframe, engines, etc. will still cap the fuel fraction at perhaps 70%; no plane based on the Concorde's (quite advanced) engines and airframe could ever fly all that much further than the Concorde did, unless it refueled on the way somehow.
I'm leaning toward drag scales with the square of velocity, so mach 2.2 is going to take about 9x the power of commercial airlines mach 0.7.
Lift is roughly proportional to the square of velocity, as well. This allows faster planes to fly higher, where the air is thinner and drag is lower.
Supersonic flight is less fuel efficient, but not really for the reason you think. It's actually because:
1. The type of jet engines (low bypass turbofans or turbojets, usually with afterburners) required to sustain supersonic speeds are 1/2 to 1/4 as efficient as the high-bypass turbofans that work so well for subsonic flight.
2. The maximum achievable lift-to-drag ratio drops significantly as the sound barrier is broken. (This is a totally separate effect from drag's v^2 scaling.)
The end result is that supersonic transports are inefficient, but not nearly as bad as you might expect - as long as they operate at extremely high altitude: 18 km for the Mach 2 Concorde, or 25 km for the Mach 3+ SR-71. Both of these aircraft achieved ranges about 1/2 half that of some high-endurance subsonic competitors (the 747 and the U-2, respectively), at the cost of somewhat inferior payload capacity. This is far, far better than naive v^2 scaling would predict (especially for the SR-71!), without accounting for the higher cruising altitude.
That would make it quieter inside the plane, but probably have no meaningful effect on how loud it sounded from the outside.
The sonic boom is simply air that had to be shoved out of the way to make room for the passage of the plane; whether the plane's surface is soft or hard, the same amount of air still needs to be displaced.
Maybe make the wing edges serrated so that the shockwaves cancel out? Or a giant metal ring that reflects the sound waves back?
This is more along the lines of how they actually make supersonic planes quieter: adjust the planes shape so that the shockwaves (partially) cancel out, or maybe so that they are directed upward, away from people on the ground. There have been a number of research projects along these lines in the past 25 years or so, such as the NASA Shaped Sonic Boom Demonstration.
I believe that the excessive takeoff and landing noise of the Concorde was actually caused by the high-power turbojet engines, though; that plane wasn't generally allowed to fly fast enough to generate a sonic boom over land. A lot of research and development has been done since then on making jet engines quieter, as well. I'm not sure how much progress has been made specifically for the low/no bypass engines required for supersonic flight, though.
Sure, but then you're also making the assumption that people who have chosen not to vote have chosen to speak in other ways. And you have no way of knowing that.
No, when the entire system is defined as 'vote for the candidate you want,' the only possible way to determine the candidate somebody wants is to tally the votes. If you *ever* have to have a discussion about 'voter intent,' you've already given up completely.
So why shouldn't Congress apply that same reasoning?
Why should Congress interpret 30% of the country voting in Obama as President, as indicative of a "voter intent" on the part of "the American people" as a whole, that Congress cooperate with Obama's efforts to fill the Supreme Court vacancy?
If we're not allowed to guess at "voter intent", then how can we dismiss the possibility that "the American people" got exactly what they wanted at the polls: a deadlocked system?
There are many reasons not to vote, you pointed to one of them and said that the 60% of the population that didn't vote decided not to for that reason.
A fair point. I guess my bias is showing.
I do think that the fact that both the President and Congress have generally maintained minority job approval ratings in recent years suggests that "I am fine with either candidate" is probably not the main reason people don't vote, though. Moreover, several of the more successful recent Presidential candidates - Obama, Trump, Carson, and maybe Sanders and Cruz - have recognized that emphasizing their (alleged) status as "outsiders" to the corrupt/dysfunctional Washington political system is necessary to attract voters.
Regardless, the fact remains that getting ~30% of the population to vote for a person as president, doesn't equate to an electoral mandate from "the American people" for Congress to cooperate with that President's efforts to appoint someone to the Supreme Court.
You can attempt to muddy the water, but the US scale of left/right is mostly focused on how much regulation is applied to capitalism, with some ancillary points as they apply to taxation and social services.
If that's how you want to define it, then sure you can have a coherent discussion on that basis. Your definition is far from universal, though.
If what you really mean is, "There has been a strong shift [towards deregulation of business] in America for the past 40 years[, which is a bad thing]" - then why not just say that? You'd probably provoke more thoughtful responses, and less tribalistic name-calling that way.
What has the embargo of Cuba actually accomplished (in recent decades), other than impoverishing its people? How has it improved the political situation there, or American security?
Those are serious questions - I'd really don't understand why the embargo wasn't lifted 2+ decades ago.
Politics has more than one defining axis. The left/right dichotomy is very much a false one.
Obama is quite far "left" on some social issues (i.e., homosexuality and abortion). But, I wouldn't classify him as left or right on some other important issues, such as:
- State Surveillance - the Nazis are often held up as an example of an out-of-control "right", while Stalin's Communists are an example of an out-of-control "left". And yet, neither of them had surveillance systems as extensive as that established by Bush ("right"), Obama ("left"), and their recent predecessors.
- The role of Wall Street in the American economy today is not consistent with either Capitalism or Communism - more like Corruption... (Again, this didn't change much under Obama versus Bush.)
- Militarism - The drive to conquer (or merely destroy, as with Iraq, Libya, and Syria) other nations is not exclusive to either the right or the left. The way that Hitler and Stalin at first agreed to divide the conquest of Eastern Europe between the two of them at the opening of World War II is a fine example of this.
- Religious Freedom - This has been both suppressed and supported by both the "left" and the "right" at various times and places in history.
The whole "left versus right" thing should be ditched in favour of multi-dimensional classifications.
Slashdot Mirror
I support breeder reactors, but it should be pointed out that (as long as high-tech society does not collapse in the mean time) there are other ways of jump-starting production of isotopes like Plutonium-239 and Uranium-233.
All that is really required is a large neutron source; a deuterium fusion reactor (even one that can't produce net electrical power) or a very efficient particle accelerator could do the job easily enough. Once enough feedstock is acquired for a single fission reactor run, cheaply breeding more becomes possible again.
It would be a shame to waste all the Uranium-235, but it's not like it would be impossible to recover from that mistake.
An ICE might be around 20%, half as efficient as a power plant.
A modern automotive ICE can be way better than 20% efficient - the cylinder engine in the Honda Prius is 38.5% efficient.
The whole chain of transmission, charging, battery and electric engine is still around 90% if not more efficiency.
Each of those stages individually is about 90% efficient, meaning that the chain in aggregate is much worse than that.
Grid distribution of power is something like 90% efficient (actually worse than that in India, due to their lousy infrastructure). Charge/discharge efficiency for large Lithium-Ion battery packs is about 85%. A high-powered electric motor + controller is about 90% efficient.
90% of 85% of 90% of 42% = 29%, versus 38.5% for a good ICE
Any economic/environmental benefits to the electric car are entirely due to other factors, such as regenerative braking and the greater range of power sources available to the grid (nuclear, hydro, solar, etc.).
From the point of view of the sun, it is exactly as I explained above. You fly quicker out of the "gravity well" then you needed time to enter it.
Sorry, but no. Such a thing would be possible under Relativity, but in Newtonian mechanics all observers must agree about the timing of events (provided that they are truly being asked the same question).
In the train example, an observer on the platform and one on the train will both give the same answer to the following questions:
1) How much time passed from the point at which the ball was 10 meters from the front of the train, until it hit the train?
2) How much time passed from the point at which the ball hit the train, until it was again 10 meters from the front of the train?
In the same way, the time for a spacecraft receiving a gravity assist to "enter" and to "fly ... out" are both defined based on the craft's altitude above the assisting body, which is moving from the Sun's perspective. The motion of the body synchronizes with that of the craft in such a way as to make the time-line consistent, regardless of whether you observe it from the Sun's perspective, or the assisting body's.
This seems to be borne out somewhat in the real world, in that in the USA all new electrical generation capacity is overwhelmingly in "direct" conversion.
The fact that direct generation is "winning" economically in the United States right now is basically a coincidence - it is driven by a combination of environmental regulations (ever stricter emissions controls for coal, and NIMBism for nuclear), mandates and huge subsidies for renewables, and (as you pointed out) the present glut of natural gas from fracking.
By this argument, both nuclear fusion and nuclear fission aren't going to be economical, ever.
While few near-term plans take advantage of it, there is great potential for "direct" energy capture from both fission and fusion.
For fission, look up Dusty Plasma Reactors. For fusion, several promising reactions release most of their energy through charged particles, making non-thermal energy capture straightforward: Deuterium + Helium-3, Helium-3 + Helium-3, and Hydrogen + Boron-11
Outside of exotic applications like space flight, I doubt that Dusty Plasma fission reactors will ever be more economical than a simple Lead-Cooled Fast Reactor. For fusion though, it is likely that if it is technically and economically viable at all, one of the aneutronic reactions that I listed above will be the preferred option in the long term due to the vastly reduced radioactive waste, as compared to the standard Deuterium + Tritium or Deuterium + Deuterium reactions.
Internet advocates always seem to be pushing the Liquid Fluoride Thorium Reactor (LFTR), but the Lead-Cooled Fast Reactor look like the best Generation IV reactor design to me, by far.
The chemistry problems associated with Molten Salt Reactors - especially the need to continuously reprocess the salt-fuel mixture on site - sound pretty hairy from an engineering perspective (speaking here of costs, not safety).
In contrast, a Lead-Cooled Fast Reactor is much more straightforward to design and maintain. It is also (as far as I can tell) the safest fission reactor design yet conceived; only Molten Salt Reactors are in the same league, safety-wise, but I think Lead-Cooled is still better for various reasons.
The Lead-Cooled design has the distinct advantage that it has already been deployed operationally, whereas LFTR is still just a research project.
Ha ha. Very funny. I'm not that dumb. Pluto has been politically marginalized - not "liberated" by the military.
My fellow Americans, it is with sadness and righteous anger that I make this address to you tonight, for new intelligence indicates that Pluto is not a democracy. This great crime against humanity and the American people must not go unavenged!
Furthermore, Pluto has maintained a cold, indifferent silence in the face of all demands to publicly denounce Al Quaeda and the Islamic State. No response has been received to our request to join our Coalition of the Willing.
Taking into consideration its massive stocks of carbon monoxide - a potential chemical warfare agent - it becomes clear that Pluto represents an imminent, existential threat to the security of the American People and the American Way of Life, justifying a pre-emptive military intervention. (But I will direct any legal challenges to this doctrine to the United Nations Security Council, whose formal resolutions we respect.)
Therefore, effective immediately, I am launching Operation Democracy Export So That Rights are Observed, Yeah. The first wave of autonomous B83 military advisors are en route as we speak.
in order to "get" a planet for political reasons!
Out of curiosity - what were these "political reasons"? Was Pluto threatening to run as a third party candidate or something?
You caught me. ;-)
(In particular, the bit about a large moon in a low orbit being useful, even if the planet itself is not, is something I don't recall every seeing pointed out in any of the "serious" discussion I've read on this topic - but should be rather obvious to anyone who's experimented much with gravity assists in the Jool system.)
Note: For simplicity, I shall assume a Newtonian two-body system (meaning the only significant force, is the gravitational pull of a single massive planet upon a passing spaceship).
That is wrong.
Indeed it is; I forgot a factor of two: the actual limit is twice the assisting body's speed. That's just the theoretical maximum, though; getting close to this in practice requires:
1) A massive assisting body (many moons are too small to be useful)
2) A very close approach (the need not to collide with the body limits this parameter)
3) Precise timing (as I mentioned in my previous post)
4) Proper alignment of the trajectories of the spaceship, the assisting body, and the destination
The gravity assist comes from the difference of duration "falling" to the body "from behind" versus escaping the gravity field when "in front" of the body.
This is incorrect; Newtonian two-body non-intersecting free fall trajectories are always symmetrical in both time and space across an axis drawn through the periapsis (point of closest approach) and the other body. This is the basis for Kepler's laws, which state that all such trajectories are conic sections with the massive body at the focus.
(You can benefit from escaping faster than you fell in - if you do an engine burn at periapsis to accelerate your escape. But then you're using the Oberth Effect, not just a gravity assist.)
A spaceship receiving a gravity assist follows a hyperbolic trajectory. From the planet's frame of reference, the spaceship doesn't actually acquire any additional energy or momentum from the encounter at all; what happens instead is that the direction of the spacecraft's motion is changed, but its speed upon leaving the planet's sphere of influence is the same as it was upon entry (the speed up while falling is exactly cancelled out by the slow down while escaping).
Nevertheless, from an outside frame of reference - such as that of the Sun - the spaceship may gain substantial speed/energy/momentum from the encounter. How? I'll just let the Wiki explain this part:
"A close terrestrial analogy is provided by a tennis ball bouncing off the front of a moving train. Imagine standing on a train platform, and throwing a ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees the ball approaching at 80 km/h and then departing at 80 km/h after the ball bounces elastically off the front of the train. Because of the train's motion, however, that departure is at 130 km/h relative to the train platform; the ball has added twice the train's velocity to its own."
If that's confusing and unintuitive - consider giving Kerbal Space Program a try (or just watching some tutorials on YouTube). That's what made this stuff finally "click" for me...
That could be; I don't know all the details. The Exclusion Zone is huge though, so I don't see why they would deliberately construct something like this in one of the really bad areas.
Regardless, it would not be unwise for the crew to bring a Geiger counter and some dosimeter badges...
The Exclusion Zone isn't actually that dangerous now; they've been allowing some tourism and scientific research for a long time now. There's a big difference between "safe place to live and raise a family" versus "safe place to visit for a few hours/days/weeks".
The reactor building itself is another story, of course...
A far out planet could be useful for gravitational assists to the outer solar system.
Pedantically speaking... An actual gravity assist from the planet itself would be worth little - certainly not enough to justify the 1,000+ year diversion (not exaggerating) required to actually take advantage of it.
Getting a gravity assist is analogous to bouncing off of the assisting body. If the body is moving quickly and in an appropriate direction, the spacecraft can pick up a lot of speed (relative to the rest of the solar system) in the process. These conditions would certainly not apply to the hypothetical planet discussed above though:
1) A planet orbiting at that altitude would have an orbital velocity no more than ~7% that of Earth - maybe much less. A gravity assist cannot boost the velocity of the spacecraft by more than the velocity of the assisting body.
2) Achieving a worthwhile gravity assist requires waiting for the orbital phase of the assisting planet and the actual destination to line up right. This could be a loooonnnnggggg wait given that the planet in question would have an orbital period between about 3,000 and 40,000 years...
Having said that, if the planet just so happened to be in roughly the right place already, it might still be worth swinging by it for two reasons:
A) If it had a large moon in a relatively low orbit that was roughly aligned with the plane of the ecliptic, that moon might provide the gravity assist which the planet itself could not.
B) The point of closest approach to the planet may be a good place for an engine burn, to take advantage of the Oberth Effect (which is distinct from a true gravity assist).
Of course - all this "orbital ballet" gravity assist stuff is only necessary because our current propulsion technology is inadequate; any realistic plan for humans to explore the outer solar system would require an upgrade.
I have two problems with the way you're portraying things:
1) You very wrongly dismiss everyone who didn't vote for either Obama, Romney, or McCain in those two elections as "not caring". This is ridiculous; I didn't vote because none of those three candidates came anywhere close to representing me, not because I didn't care. Refusing to choose the "lesser of two evils" does not equate to "not caring".
2) You simply assume that Congress' job is to obey the will of the majority of Americans who voted, whereas the United States is actually constituted as a Republic.
America's system of elections and offices at the Federal level was intentionally designed not to equate to direct democracy, but rather to balance the interests of various groups: the People (via the House of Representatives), each State individually (via the Senate and the Electoral College), minorities (via various constitutional rights, enforceable by the courts which are not directly subject to the majority), etc.
You are essentially demanding that the Senators ignore the groups who elected them, which they are intended to represent, in favour of following the Presidential vote - despite the Presidential vote having been deliberately designed to favour a different constituency.
The only 'voter intent' that matters is *how the votes tallied up.*
Why do only the votes for President count, and not the votes for Congress?
I could just as easily argue that Obama should submit to the manifest will of the voters, revealed by who they voted into Congress - especially since the congressional vote is more up-to-date.
Oh I agree with what you're saying there.
Whoever said that Congress is obligated to do anything other than meet up in the Capitol building every once in while?
I think Sowelu did above, which is why I first entered this thread.
As the majority of travel would be intercontinental even the sonic booms could occur over the ocean prior to turning inland to make the Mach-2 flight to the other coast.
The sonic boom is generated continuously the entire time the plane is flying at supersonic speed, not just at the moment the plane "breaks the sound barrier". The only ways to not affect people on the ground, is to either stay below Mach 1 over populated areas (what Concorde did), or to optimize the plane's aerodynamics to weaken and spread out the pressure spike from the part of the shockwave that is directed toward the ground (what Boom Aerospace is trying to do).
And while a 30% turnout doesn't equate to an electoral mandate for 100% of the citizenry, an electoral victory does equate to a mandate for the percentage of the citizenry that actually gives a shit enough to spend 10 minutes* filling in bubbles.
Now your bias is showing. While it is not 100%, there is definitely a sizeable percentage of people who abstain from voting because they don't want to endorse any of the available candidates, not because they don't care. Particularly in the general election for President, it is absurd and manipulative to suggest that anyone who refuses to accept one of the two choices (in some states, the law prevents others from even getting on the ballot) just "doesn't give a shit".
As to how we can increase electoral turnout, etc. - that is quite far off topic. My original point was simply this: Congress is not obligated to do give Obama what he wants, just because 30% of the country voted for him to be President (not one-man Senate).
There may be many other reasons that Congress should cooperate, but the bare fact that Obama won the last Presidential election is not good enough by itself. The Constitution itself recognizes this; that's why Obama is required to seek Congressional approval in the first place...
What relevance does that question have?
I'm simply asking: why should the ballots cast for President be interpreted as instructions to Congress, if we're forbidden to even "have a discussion about voter intent"?
Concorde was capable of supercruise, that is, sustained supersonic flight without afterburners.
Makes sense. The Concorde's range was very impressive, for a supersonic aircraft.
Also, burning fuel at twice the rate isn't a big problem when you're going three times as fast.
Halving the specific impulse does not mean twice the fuel burn - it means twice the fuel burn per unit thrust. Even at high altitude, supersonic flight requires sustaining higher thrust compared to subsonic, so the Concorde really was a lot less fuel efficient per unit distance covered.
I don't have precise numbers, but a quick look suggests that the Concorde burned fuel about 10x faster than the 737 NG (a subsonic aircraft of comparable range and passenger capacity). It also flew 2.6x faster, so that would make it 3-4x more fuel hungry per passenger-kilometer.
And lastly, oil prices have taken a dive recently. I know the situation isn't permanent, but it won't change overnight.
This could help a lot with ticket prices, but it doesn't help at all with range. Aircraft range is basically limited by how much fuel can be crammed on board, without making the plane too heavy to fly safely.
The only way the Concorde could achieve comparable range and passenger capacity to the subsonic 737 NG, was by being a much larger aircraft (180 tons versus 80 tons) with a higher fuel fraction (50% versus 30%?). This technique is expensive, and can only be taken so far. Even with no payload at all, the airframe, engines, etc. will still cap the fuel fraction at perhaps 70%; no plane based on the Concorde's (quite advanced) engines and airframe could ever fly all that much further than the Concorde did, unless it refueled on the way somehow.
I'm leaning toward drag scales with the square of velocity, so mach 2.2 is going to take about 9x the power of commercial airlines mach 0.7.
Lift is roughly proportional to the square of velocity, as well. This allows faster planes to fly higher, where the air is thinner and drag is lower.
Supersonic flight is less fuel efficient, but not really for the reason you think. It's actually because:
1. The type of jet engines (low bypass turbofans or turbojets, usually with afterburners) required to sustain supersonic speeds are 1/2 to 1/4 as efficient as the high-bypass turbofans that work so well for subsonic flight.
2. The maximum achievable lift-to-drag ratio drops significantly as the sound barrier is broken. (This is a totally separate effect from drag's v^2 scaling.)
The end result is that supersonic transports are inefficient, but not nearly as bad as you might expect - as long as they operate at extremely high altitude: 18 km for the Mach 2 Concorde, or 25 km for the Mach 3+ SR-71. Both of these aircraft achieved ranges about 1/2 half that of some high-endurance subsonic competitors (the 747 and the U-2, respectively), at the cost of somewhat inferior payload capacity. This is far, far better than naive v^2 scaling would predict (especially for the SR-71!), without accounting for the higher cruising altitude.
Put sound insulation around the airframe?
That would make it quieter inside the plane, but probably have no meaningful effect on how loud it sounded from the outside.
The sonic boom is simply air that had to be shoved out of the way to make room for the passage of the plane; whether the plane's surface is soft or hard, the same amount of air still needs to be displaced.
Maybe make the wing edges serrated so that the shockwaves cancel out? Or a giant metal ring that reflects the sound waves back?
This is more along the lines of how they actually make supersonic planes quieter: adjust the planes shape so that the shockwaves (partially) cancel out, or maybe so that they are directed upward, away from people on the ground. There have been a number of research projects along these lines in the past 25 years or so, such as the NASA Shaped Sonic Boom Demonstration.
I believe that the excessive takeoff and landing noise of the Concorde was actually caused by the high-power turbojet engines, though; that plane wasn't generally allowed to fly fast enough to generate a sonic boom over land. A lot of research and development has been done since then on making jet engines quieter, as well. I'm not sure how much progress has been made specifically for the low/no bypass engines required for supersonic flight, though.
Sure, but then you're also making the assumption that people who have chosen not to vote have chosen to speak in other ways. And you have no way of knowing that.
No, when the entire system is defined as 'vote for the candidate you want,' the only possible way to determine the candidate somebody wants is to tally the votes. If you *ever* have to have a discussion about 'voter intent,' you've already given up completely.
So why shouldn't Congress apply that same reasoning?
Why should Congress interpret 30% of the country voting in Obama as President, as indicative of a "voter intent" on the part of "the American people" as a whole, that Congress cooperate with Obama's efforts to fill the Supreme Court vacancy?
If we're not allowed to guess at "voter intent", then how can we dismiss the possibility that "the American people" got exactly what they wanted at the polls: a deadlocked system?
There are many reasons not to vote, you pointed to one of them and said that the 60% of the population that didn't vote decided not to for that reason.
A fair point. I guess my bias is showing.
I do think that the fact that both the President and Congress have generally maintained minority job approval ratings in recent years suggests that "I am fine with either candidate" is probably not the main reason people don't vote, though. Moreover, several of the more successful recent Presidential candidates - Obama, Trump, Carson, and maybe Sanders and Cruz - have recognized that emphasizing their (alleged) status as "outsiders" to the corrupt/dysfunctional Washington political system is necessary to attract voters.
Regardless, the fact remains that getting ~30% of the population to vote for a person as president, doesn't equate to an electoral mandate from "the American people" for Congress to cooperate with that President's efforts to appoint someone to the Supreme Court.
You can attempt to muddy the water, but the US scale of left/right is mostly focused on how much regulation is applied to capitalism, with some ancillary points as they apply to taxation and social services.
If that's how you want to define it, then sure you can have a coherent discussion on that basis. Your definition is far from universal, though.
If what you really mean is, "There has been a strong shift [towards deregulation of business] in America for the past 40 years[, which is a bad thing]" - then why not just say that? You'd probably provoke more thoughtful responses, and less tribalistic name-calling that way.
What has the embargo of Cuba actually accomplished (in recent decades), other than impoverishing its people? How has it improved the political situation there, or American security?
Those are serious questions - I'd really don't understand why the embargo wasn't lifted 2+ decades ago.
Politics has more than one defining axis. The left/right dichotomy is very much a false one.
Obama is quite far "left" on some social issues (i.e., homosexuality and abortion). But, I wouldn't classify him as left or right on some other important issues, such as:
- State Surveillance - the Nazis are often held up as an example of an out-of-control "right", while Stalin's Communists are an example of an out-of-control "left". And yet, neither of them had surveillance systems as extensive as that established by Bush ("right"), Obama ("left"), and their recent predecessors.
- The role of Wall Street in the American economy today is not consistent with either Capitalism or Communism - more like Corruption... (Again, this didn't change much under Obama versus Bush.)
- Militarism - The drive to conquer (or merely destroy, as with Iraq, Libya, and Syria) other nations is not exclusive to either the right or the left. The way that Hitler and Stalin at first agreed to divide the conquest of Eastern Europe between the two of them at the opening of World War II is a fine example of this.
- Religious Freedom - This has been both suppressed and supported by both the "left" and the "right" at various times and places in history.
The whole "left versus right" thing should be ditched in favour of multi-dimensional classifications.