The key thing is mass budget. If it helps Blue Origin land more reliably to add a ton of structural bracing or whatever, it's no big deal. For SpaceX its a huge deal.
Each satellite only lasts a few years and successive ones are not identical, so they are not as good as you think. Also measuring the temperature of the lower atmosphere from satellites is inherently quite hard, so these measurements start with a lot of uncertainty.
Your patten also catches scientists who were being cautious and conservative to start with, so where there is uncertainty they adopt the option that gives the least radical results, the smallest anomaly, etc.
Then as the data and the methodologies improve and the uncertainties are resolved the results naturally become MORE surprising.
II'm still waiting for someone to tell me what the temperature is supposed to be.
That's fairly easy, but there are two answers:
1. If large scale exploitation of fossil fuels had not occurred in the 19th -21st centuries the global mean temperature calculated according to the Hadcrut4 methodology and averaged over a decade or so would probably have been between about 0.7 and 1.1 kelvins below the average for the last decade (ie about 287 rather than 288 Kelvins).
2. More tentative -- if agriculture had not been widespread over the last 10000 or so years, global temperature might be significantly colder as we headed down towards another ice age.
As the subject says -- "fuel cell" -- that means no IC engine hydrogen and oxygen (from air) produce water and electricity directly. No Carnot cycle, no moving parts. After that the drive train is electric, just like a battery car.
You can make hydrogen by electrolysis, which is not so efficient, but you can do it whereever and whenever you have cheap electricity. Alternatively if you have methane that you are allowed to burn (whether it's natural gas or from rotting sewage) you can make hydrogen pretty cheaply from it.
See also the remarks above about Audi stress-testing their tank -- the only thing that touched it was an armour-piercing round, which made a hole and no fire. A hydrogen leak is generally much LESS dangerous than a gasoline leak because it doesn't hang around at ground level and soak into things. Given half a chance it'll just diffuse away.
Fair enough. You're effectively increasing the stage count by 1 (although the extra stage has no engines) so you'll need to pay the mass for the connectors between the engine stage and the fuel tank stage, and the structural elements needed to make the two stages independently handleable.
I guess the next few years will tell us which approach best suits todays materials, engines, fuels and building techniques. Should be interesting.
The key element is cost/speed of turnround. The fuel tanks in a first stage may not be very expensive, but hooking up and testing new tanks will take time, and then checking the integration takes more time. SpaceX are aiming for a model where there is not much more to do that pump in fuel, a cursory visual inspection and ask the avionics to self-check. Engines would need a full inspection every so many firings. If they can pull this off it almost has to be cheaper than any model involving more reintegration.
The South pole of the Moon is quite a good site. There are mountains permanently lit (for power) and crater bottoms in permanent shadow a few hundred meters away (for the telescopes). Having a large mass (like the moon) to anchor you against vibration from your own systems, light pressure, etc. and serve as a heat sink has considerable advantages.
Since you ask I think the UK has it about right. No guns at all except for law enforcement when authorised by a senior officer, single shot target weapons kept at gun clubs, shotguns (licensed) for pest control and a few licensed rifles for specific kinds of hunting. And before you mention knives and illegal guns, our total homicide rate by all meand (per 100K people) is less than the US's gun homicide rate.
Whether they can keep it upright long enough to refuel to fly back to land... well that's a whole different kettle of fish.
Do you actually know that that is the plan? I assumed they'd return the first stages by sea. They need the drone ship because in some configurations and for some missions they can't spare the fuel to fly back to the launch site.
Why? Surelty better to explore multiple bodies at a lower cadence. That way each mission can learn from more earlier ones and scientists with a larger range of interests get more data.
For me, a Uranus or Neptune orbiter is the big obvious hole in the plans, followed by a Mars sample return.
The speaker I saw (a professional astronomer) said that they ran huge families of simulations and in many of them gas giants fomed far from the star (not much option there, close in the radiation from the star pushes the gas away) and head inwards as they interact with the remainder of the proto-planetary disk, Then the simulations split into two families -- hot Jupiter scenarios where the gas giants stay very close in and others where they move back out -- something to do with how fast the small bodies and dust get cleaned out, I think.
I thoiught current thinking was that Jupiter and Saturn formed pretty far out then were drawn in, swapping places with each other and collectively with Uranus and Nepture (and possibly ejecting a fifth large planet) going closer to the Sun than their present locations before finally settling down.
There are other theories. TFA is rooted in inflation theory in which there is also no singularity -- the "modern:" universe condensed from an inflating universe with quite different properties as a very hot very dense expanding space. A ball of that a few cm or m across has eventually become our entire observable universe.
The theory you reference is in the very early stages of theoretical physicists playing with mathematical theories. Which is fine, but quite a bit of progress would be needed before it got as much attention as inflation, on which quite a bit of progress has already been made.
One answer to this is that the rest of space was equally packed with mass, so the gravitational pull on each parfticle was more or less balanced.
Another is that nothing has escaped. We're still there, it's just strectched. To use a very weak analogy, if you are trapped inside a balloon as it is being inflated you have more room to move around, but are still trapped.
Still another answer is that space itself was expanding.
Recycling the waste to reuse the fissionables it contains is not the same thing as running a breeder, which makes U238 into something usable.
That said, both of these things have been tried pretty extensively in Europe and both were deemed failures.
The problems are not fundamental, but the minor and medium scale engineering problems were just too hard. I know more about recycling, and there the problem was essentially that to get the fuel to remain stable inside the reactor you want to make it into something heat resistant and chemically inert. Now you get the same thing, except that a proportion of it has changed into a whole soup of other elements, most of them as radioactive isotopes, and you want to dissolve it, separate them purify the recyled fuel and concentrate the remaining junk into something you can store. All of this in equipment you have to build, start up, and then never go near again. When the hot radioactive concentrated nitric acid corrodes its way through a weld or a valve jams because of neutron embrittlement or... you can't just go in and hit it with a hammer. In many cases the solutions begins with "flood it with water" so now you have LOTS of slightly radioactive water to store, or concentrate or.....
The end result was plants that were shut down more than they ran, and still leaked to the environment.
Some genius engineer might be able to design a better plant, but don't make the mistake of thinking it's easy.
We don't have the "continual rise" in temperature so often modeled and predicted as we have, it appears, flat (or actual declining) temperatures with occasional big events that cause a shift in the baseline..
That's what you get if you superimpose a cycle on top a continuous rise
You might as well ask "why is the weak nuclear force weaker than the strong nuclear force?"
And people do, extensively. Physics is the quest to explain as much as possible of the universe from as few assumptions as possible. Then if you have a few assumptions that explain a lot, you can predict outcomes of experiments/observations and see what happens. History suggests that this works rather well. James Clerk Maxwell found that you could explain electricity and magnetism as one thing instead of two and out of that came radio and electronics.
The simulation is probably accurate, the summary article not so much. The simulation answers a rather more nuanced question -- something like "where in the galaxy could Earth;s history possibly have been replayed?" Some places there aren't enough heavy elements, others there are too many supernovae, or near-misses with other stars. Yes, life could evolve in other places, maybe -- on a neutron star, or in the complex magnetic structures in gas clouds near the central black hole or..... but, although the article suggests it, that is not really the question being answered by the simulation here. Also note that elements much heavier than iron are pretty rare everywhere. Even if you could identify a feasible biochemistry based on iridium or something, there is very unlikely to be enough iridium anywhere for it to evolve.
rather than landing the plane, just drop the passenger module(s) into a magnetic decelerator (like a railgun, but backwards) at the airport, meanwhile use another cannon to launch the next passenger module (and perhaps a full fuel tank) to dock with the plane. Now the plane never has to decelerate or land, it can be built just to cruise round and round the world at Mach 0.9. No heavy landing gear, much smaller engines,.... Of course the aim and timing on the magnetic cannons does need to be rather precise.....
But that's true of everything. The only reason we know the sun exists is that if it isn't there our model for predicting what we should see when we look up doesn't work.
Slashdot Mirror
The key thing is mass budget. If it helps Blue Origin land more reliably to add a ton of structural bracing or whatever, it's no big deal. For SpaceX its a huge deal.
Each satellite only lasts a few years and successive ones are not identical, so they are not as good as you think. Also measuring the temperature of the lower atmosphere from satellites is inherently quite hard, so these measurements start with a lot of uncertainty.
Your patten also catches scientists who were being cautious and conservative to start with, so where there is uncertainty they adopt the option that gives the least radical results, the smallest anomaly, etc.
Then as the data and the methodologies improve and the uncertainties are resolved the results naturally become MORE surprising.
II'm still waiting for someone to tell me what the temperature is supposed to be.
That's fairly easy, but there are two answers:
1. If large scale exploitation of fossil fuels had not occurred in the 19th -21st centuries the global mean temperature calculated according to the Hadcrut4 methodology and averaged over a decade or so would probably have been between about 0.7 and 1.1 kelvins below the average for the last decade (ie about 287 rather than 288 Kelvins).
2. More tentative -- if agriculture had not been widespread over the last 10000 or so years, global temperature might be significantly colder as we headed down towards another ice age.
As the subject says -- "fuel cell" -- that means no IC engine hydrogen and oxygen (from air) produce water and electricity directly. No Carnot cycle, no moving parts. After that the drive train is electric, just like a battery car.
You can make hydrogen by electrolysis, which is not so efficient, but you can do it whereever and whenever you have cheap electricity. Alternatively if you have methane that you are allowed to burn (whether it's natural gas or from rotting sewage) you can make hydrogen pretty cheaply from it.
See also the remarks above about Audi stress-testing their tank -- the only thing that touched it was an armour-piercing round, which made a hole and no fire. A hydrogen leak is generally much LESS dangerous than a gasoline leak because it doesn't hang around at ground level and soak into things. Given half a chance it'll just diffuse away.
Fair enough. You're effectively increasing the stage count by 1 (although the extra stage has no engines) so you'll need to pay the mass for the connectors between the engine stage and the fuel tank stage, and the structural elements needed to make the two stages independently handleable.
I guess the next few years will tell us which approach best suits todays materials, engines, fuels and building techniques. Should be interesting.
The key element is cost/speed of turnround. The fuel tanks in a first stage may not be very expensive, but hooking up and testing new tanks will take time, and then checking the integration takes more time. SpaceX are aiming for a model where there is not much more to do that pump in fuel, a cursory visual inspection and ask the avionics to self-check. Engines would need a full inspection every so many firings. If they can pull this off it almost has to be cheaper than any model involving more reintegration.
The South pole of the Moon is quite a good site. There are mountains permanently lit (for power) and crater bottoms in permanent shadow a few hundred meters away (for the telescopes). Having a large mass (like the moon) to anchor you against vibration from your own systems, light pressure, etc. and serve as a heat sink has considerable advantages.
See http://citeseerx.ist.psu.edu/v...
Since you ask I think the UK has it about right. No guns at all except for law enforcement when authorised by a senior officer, single shot target weapons kept at gun clubs, shotguns (licensed) for pest control and a few licensed rifles for specific kinds of hunting. And before you mention knives and illegal guns, our total homicide rate by all meand (per 100K people) is less than the US's gun homicide rate.
Whether they can keep it upright long enough to refuel to fly back to land... well that's a whole different kettle of fish.
Do you actually know that that is the plan? I assumed they'd return the first stages by sea. They need the drone ship because in some configurations and for some missions they can't spare the fuel to fly back to the launch site.
Why? Surelty better to explore multiple bodies at a lower cadence. That way each mission can learn from more earlier ones and scientists with a larger range of interests get more data.
For me, a Uranus or Neptune orbiter is the big obvious hole in the plans, followed by a Mars sample return.
The speaker I saw (a professional astronomer) said that they ran huge families of simulations and in many of them gas giants fomed far from the star (not much option there, close in the radiation from the star pushes the gas away) and head inwards as they interact with the remainder of the proto-planetary disk, Then the simulations split into two families -- hot Jupiter scenarios where the gas giants stay very close in and others where they move back out -- something to do with how fast the small bodies and dust get cleaned out, I think.
I thoiught current thinking was that Jupiter and Saturn formed pretty far out then were drawn in, swapping places with each other and collectively with Uranus and Nepture (and possibly ejecting a fifth large planet) going closer to the Sun than their present locations before finally settling down.
Don't think so. I think they gave up on that some time ago, but they can't get the concrete deep enough or keep it there long enough to set.
There are other theories. TFA is rooted in inflation theory in which there is also no singularity -- the "modern:" universe condensed from an inflating universe with quite different properties as a very hot very dense expanding space. A ball of that a few cm or m across has eventually become our entire observable universe.
The theory you reference is in the very early stages of theoretical physicists playing with mathematical theories. Which is fine, but quite a bit of progress would be needed before it got as much attention as inflation, on which quite a bit of progress has already been made.
One answer to this is that the rest of space was equally packed with mass, so the gravitational pull on each parfticle was more or less balanced.
Another is that nothing has escaped. We're still there, it's just strectched. To use a very weak analogy, if you are trapped inside a balloon as it is being inflated you have more room to move around, but are still trapped.
Still another answer is that space itself was expanding.
Recycling the waste to reuse the fissionables it contains is not the same thing as running a breeder, which makes U238 into something usable.
That said, both of these things have been tried pretty extensively in Europe and both were deemed failures.
The problems are not fundamental, but the minor and medium scale engineering problems were just too hard. I know more about recycling, and there the problem was essentially that to get the fuel to remain stable inside the reactor you want to make it into something heat resistant and chemically inert. Now you get the same thing, except that a proportion of it has changed into a whole soup of other elements, most of them as radioactive isotopes, and you want to dissolve it, separate them purify the recyled fuel and concentrate the remaining junk into something you can store. All of this in equipment you have to build, start up, and then never go near again. When the hot radioactive concentrated nitric acid corrodes its way through a weld or a valve jams because of neutron embrittlement or ... you can't just go in and hit it with a hammer. In many cases the solutions begins with "flood it with water" so now you have LOTS of slightly radioactive water to store, or concentrate or.....
The end result was plants that were shut down more than they ran, and still leaked to the environment.
Some genius engineer might be able to design a better plant, but don't make the mistake of thinking it's easy.
A surprising amount of the work can be done by aerodynamics. If you tilt the falling booster at high speed, the air resistance pushes it sideways
We don't have the "continual rise" in temperature so often modeled and predicted as we have, it appears, flat (or actual declining) temperatures with occasional big events that cause a shift in the baseline. .
That's what you get if you superimpose a cycle on top a continuous rise
It seems so. The common kind have large planets (or companion brown dwarves possibly) very close in to the star, often in quite elliptical orbits.
You might as well ask "why is the weak nuclear force weaker than the strong nuclear force?"
And people do, extensively. Physics is the quest to explain as much as possible of the universe from as few assumptions as possible. Then if you have a few assumptions that explain a lot, you can predict outcomes of experiments/observations and see what happens. History suggests that this works rather well. James Clerk Maxwell found that you could explain electricity and magnetism as one thing instead of two and out of that came radio and electronics.
The simulation is probably accurate, the summary article not so much. The simulation answers a rather more nuanced question -- something like "where in the galaxy could Earth;s history possibly have been replayed?" Some places there aren't enough heavy elements, others there are too many supernovae, or near-misses with other stars. Yes, life could evolve in other places, maybe -- on a neutron star, or in the complex magnetic structures in gas clouds near the central black hole or ..... but, although the article suggests it, that is not really the question being answered by the simulation here. Also note that elements much heavier than iron are pretty rare everywhere. Even if you could identify a feasible biochemistry based on iridium or something, there is very unlikely to be enough iridium anywhere for it to evolve.
The idea could be taken so much further....
rather than landing the plane, just drop the passenger module(s) into a magnetic decelerator (like a railgun, but backwards) at the airport, meanwhile use another cannon to launch the next passenger module (and perhaps a full fuel tank) to dock with the plane. Now the plane never has to decelerate or land, it can be built just to cruise round and round the world at Mach 0.9. No heavy landing gear, much smaller engines,.... Of course the aim and timing on the magnetic cannons does need to be rather precise.....
Coating the inside of high end telescopes and related equipment to reduce stray reflections.
But that's true of everything. The only reason we know the sun exists is that if it isn't there our model for predicting what we should see
when we look up doesn't work.