I regard this as basically a red herring, not to mention mixing up two different things.
The epicyclic frequency and disk stability has to do with the fluid dynamics of an accretion disk - that kind of stability does not require a black hole (look at Saturn's rings, which also have sharp edges).
The key word in Innermost Stable Circular Orbit is "stable" - the meaning is not that this orbit is not decaying (it is), but that it is stable to small perturbations. Inside the ISCO, a small perturbation will cause big changes, and the orbit will rapidly decay. So, outside the ISCO, the orbit is slowly decaying - "inspiraling" - while inside the ISCO, the orbit will decay very rapidly (i.e., "plunge" into the black hole). But, still, if you had a super-duper rocket, you could escape to infinity from inside the ISCO, as long as you hadn't crossed the event horizon.
All of this ignores tidal deformations, which convert orbital energy into heat and can also rapidly decay orbits.
A lot. If you had a super-duper rocket, and were orbiting at the innermost stable orbit, you could escape the black hole. If you went through the event horizon, you could not.
In Newtonian gravity, 2-body orbits are stable, unless there is drag or some other non-gravitational force.
In General Relativity, orbiting bodies emit gravitational radiation, which carries away orbital energy, and so no orbit is truly stable. However, this only really becomes important near a neutron star or (even more so) near a black hole, where the gravitational radiation energy loss can be significant, and objects can spiral into each other fairly rapidly.
Of course, in either theory, the question of the stability of 3 or more body orbits is very complicated, and still an open area of research, but suffice it to say that N >2 body orbits need not be stable, although ejection of orbiting material is more likely than capture by the central body.
Yes, I know that, but the US (or anyone else) does not get to claim extraterrestrial bodies, so they are not (US) public land.
Now, I would not be surprised if some future law or Executive Order came about where we would treat asteroids as if they were public lands, but it isn't in place yet. And, I would look for a new treaty move along that time, to clear these matters up.
Also, note that Article 8 talks about "on a celestial body," but is silent about what happens _inside_ a celestial body. If you want to make an asteroidal version of Sealand, better put it underground.
Why is a federal reg which allows for meteorite collection on public land bad for asteroid mining? This favors, in a small way, the exploitation of extraterrestrial resources, and so I would view it as a positive (if very weak) precedent.
Note, BTW, that asteroid are not public land under the Outer Space Treaty.
Translation : They couldn't guarantee that it wouldn't hit the ISS (or, more exactly, avoid a safety buffer around it), so they couldn't do the burn.
An upper stage may have a short time window where they can re-ignite (batteries run out, cryogenics will eventually boil off, etc.), so they may be out of luck.
– Both Saturn V and the shuttle launch system were designed to handle failure of at least one engine
Yes, and at least one Apollo launch had an engine failure (Apollo 13). At the time it didn't seem like too big a deal, but they could have lost the mission and the crew.
You really don't want to be having engine burn-throughs, which is what it looks like happened to me. Having one engine of 9 shut down is no big deal, but having one blow is a big deal, even if it didn't take the rest of the system with it.
I wonder if this was an attempt to reverse engineer what the supposed aliens were doing, which didn't produce much usable technology. That is an interesting (if expensive) way to prove or disprove the existence of UFO's.
The general rule of thumb is that human factors restrict you to an rpm of 2 or so (although I cannot find a good primary source for this). This paper suggests that people can get used to 23 rpm (!), which would mean you could do a Mars gravity in a single, decent sized, spacecraft. I must admit that I have some doubts about this. A 2 rpm Mars gravity would require a 85 meter tether. A 8 meter tether (or spacecraft) would suffice at 6 rpms, and I suspect that that would be more along the lines of what would be chosen. Astronauts would just have to get used to it in their training (or not go).
You don't need to exit the rotating state to do course corrections. You don't even need rockets on both ends, but that would be best.
As far as thermal control and communications, etc., are concerned, remember that there is over 54 years of experience with spin-stabilized spacecraft. The things you are worried about have solutions dating from decades ago. (Note, by the way, that Apollo voyaged in "rotisserie mode," where it spun about its long axis, to spread the thermal load around. If you decide to do this sort of thing, it will offer engineering advantages as well as challenges.)
The tethered spacecraft plans I have seen for Mars have as a design goal 1 Mars gravity, not 1 Earth gravity. As that is 0.379 of an Earth gravity, and as a = Omega**2 R, and as Omega is bounded by human factors, that makes the tether 85 meters, which is a lot better. The basic tether should mass a kilogram or less, so there could be lots of redundancy there.
It is a reasonable bet that, if you had 2 spaceships tethered together like this, the crews wouldn't be visiting each other very often in flight. But, the relative velocity would be only 35 meters/sec, so, if they had to, they could. And, they could do high bandwidth video (trivial over 85 meters) whenever they felt like it.
Or, you could, as you suggest, lose some redundancy and put the crew on one side, and "not needed on voyage" stuff on the other.
Does anyone know of plans for the Mars mission (what kind of vehicle will be used)?
You need to look at the Design Reference Mission - see also this presentation on the Design Reference Architecture 5.0. These aren't exactly plans, but they are a fairly fleshed out mission design, to get people something specific to refer to and a benchmark to research against. If you look at DRM 7.1.2, it talks about artificial gravity, but basically puts this as "to be determined."
Why rotate. Nuclear powered spacecraft could simply keep accelerating at 1G until it was time to turn around and decelerate at 1G. Problem solves, and they would get there a lot quicker too.
Because we don't have anything like the energy density required to do that (at least for times longer than microseconds, i.e., nuclear bombs).
Energy density drives the engineering here. If we had enough energy density, we could soup up ion rockets or use nuclear thermal and get to places very fast.
Make or find a ton of antimatter or so, and let's talk.
The ability of humans to perform well on the surface of any planet after months of zero-g seems doubtful. Build the spacecraft big enough, and rotate it. Better yet, send two spacecraft, tether them together, and rotate both of them about their center of mass. It will solve a lot more problems than the relatively minor one of dealing with in-space surgery.
Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience.
Better yet, always add a bit to every can of coffee you brew. Of course it'll take extensive tests to determine the ideal mix. Very extensive i bet; any volunteers?
This excellent corporate video suggests that Starbucks is working on it.
Once we have space elevators, the disc and the Echostar satellite it is attached to will be a dangerous nuisance and will be junked and removed in some fashion.
The best this disc can probably hope for is to be put in a landfill on the Moon (energetically easier to get to). More likely, it will be in the Air and Space Museum (or its equivalent) by 2112 or so.
This will be attached to an Echostar satellite in a valuable orbit. Now, at "end-of-life" its orbit should be raised, but still, it will be be up there, at that point available for either junk or salvage. I would regard the prospects of this lasting 500 years as very dim, much less 5 billion years.
I always regard these sorts of things (like the Voyager gold discs) as being much more likely to be picked up by future humans (or post-humans) than aliens anyway. From that standpoint, copies of mundane texts (like, say, the US Census, or some popular novels, or a history of the world) seem much more likely to be valuable than some photos of cave art or kids standing on a beach. (If civilization between now and then has not collapsed, they will know what's on the disc. If it has, then send details, not art, as the details are what tends to get lost.)
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I regard this as basically a red herring, not to mention mixing up two different things.
The epicyclic frequency and disk stability has to do with the fluid dynamics of an accretion disk - that kind of stability does not require a black hole (look at Saturn's rings, which also have sharp edges).
The key word in Innermost Stable Circular Orbit is "stable" - the meaning is not that this orbit is not decaying (it is), but that it is stable to small perturbations. Inside the ISCO, a small perturbation will cause big changes, and the orbit will rapidly decay. So, outside the ISCO, the orbit is slowly decaying - "inspiraling" - while inside the ISCO, the orbit will decay very rapidly (i.e., "plunge" into the black hole). But, still, if you had a super-duper rocket, you could escape to infinity from inside the ISCO, as long as you hadn't crossed the event horizon.
All of this ignores tidal deformations, which convert orbital energy into heat and can also rapidly decay orbits.
A lot. If you had a super-duper rocket, and were orbiting at the innermost stable orbit, you could escape the black hole. If you went through the event horizon, you could not.
In Newtonian gravity, 2-body orbits are stable, unless there is drag or some other non-gravitational force.
In General Relativity, orbiting bodies emit gravitational radiation, which carries away orbital energy, and so no orbit is truly stable. However, this only really becomes important near a neutron star or (even more so) near a black hole, where the gravitational radiation energy loss can be significant, and objects can spiral into each other fairly rapidly.
Of course, in either theory, the question of the stability of 3 or more body orbits is very complicated, and still an open area of research, but suffice it to say that N >2 body orbits need not be stable, although ejection of orbiting material is more likely than capture by the central body.
Yes, I know that, but the US (or anyone else) does not get to claim extraterrestrial bodies, so they are not (US) public land.
Now, I would not be surprised if some future law or Executive Order came about where we would treat asteroids as if they were public lands, but it isn't in place yet. And, I would look for a new treaty move along that time, to clear these matters up.
Also, note that Article 8 talks about "on a celestial body," but is silent about what happens _inside_ a celestial body. If you want to make an asteroidal version of Sealand, better put it underground.
Why is a federal reg which allows for meteorite collection on public land bad for asteroid mining? This favors, in a small way, the exploitation of extraterrestrial resources, and so I would view it as a positive (if very weak) precedent.
Note, BTW, that asteroid are not public land under the Outer Space Treaty.
"Benign" is an interesting word choice. It's probably not good if Curiosity is shedding parts, but I wouldn't expect them to be dangerous.
Since it was found directly beneath the rover, I bet they can figure out what assembly it came from.
Translation : They couldn't guarantee that it wouldn't hit the ISS (or, more exactly, avoid a safety buffer around it), so they couldn't do the burn.
An upper stage may have a short time window where they can re-ignite (batteries run out, cryogenics will eventually boil off, etc.), so they may be out of luck.
– Both Saturn V and the shuttle launch system were designed to handle failure of at least one engine
Yes, and at least one Apollo launch had an engine failure (Apollo 13). At the time it didn't seem like too big a deal, but they could have lost the mission and the crew.
You really don't want to be having engine burn-throughs, which is what it looks like happened to me. Having one engine of 9 shut down is no big deal, but having one blow is a big deal, even if it didn't take the rest of the system with it.
I wonder if this was an attempt to reverse engineer what the supposed aliens were doing, which didn't produce much usable technology. That is an interesting (if expensive) way to prove or disprove the existence of UFO's.
Why do you need negligible Coriolis effects?
The general rule of thumb is that human factors restrict you to an rpm of 2 or so (although I cannot find a good primary source for this). This paper suggests that people can get used to 23 rpm (!), which would mean you could do a Mars gravity in a single, decent sized, spacecraft. I must admit that I have some doubts about this. A 2 rpm Mars gravity would require a 85 meter tether. A 8 meter tether (or spacecraft) would suffice at 6 rpms, and I suspect that that would be more along the lines of what would be chosen. Astronauts would just have to get used to it in their training (or not go).
You don't need to exit the rotating state to do course corrections. You don't even need rockets on both ends, but that would be best.
As far as thermal control and communications, etc., are concerned, remember that there is over 54 years of experience with spin-stabilized spacecraft. The things you are worried about have solutions dating from decades ago. (Note, by the way, that Apollo voyaged in "rotisserie mode," where it spun about its long axis, to spread the thermal load around. If you decide to do this sort of thing, it will offer engineering advantages as well as challenges.)
The tethered spacecraft plans I have seen for Mars have as a design goal 1 Mars gravity, not 1 Earth gravity. As that is 0.379 of an Earth gravity, and as a = Omega**2 R, and as Omega is bounded by human factors, that makes the tether 85 meters, which is a lot better. The basic tether should mass a kilogram or less, so there could be lots of redundancy there.
It is a reasonable bet that, if you had 2 spaceships tethered together like this, the crews wouldn't be visiting each other very often in flight. But, the relative velocity would be only 35 meters/sec, so, if they had to, they could. And, they could do high bandwidth video (trivial over 85 meters) whenever they felt like it.
Or, you could, as you suggest, lose some redundancy and put the crew on one side, and "not needed on voyage" stuff on the other.
Does anyone know of plans for the Mars mission (what kind of vehicle will be used)?
You need to look at the Design Reference Mission - see also this presentation on the Design Reference Architecture 5.0. These aren't exactly plans, but they are a fairly fleshed out mission design, to get people something specific to refer to and a benchmark to research against. If you look at DRM 7.1.2, it talks about artificial gravity, but basically puts this as "to be determined."
Why rotate. Nuclear powered spacecraft could simply keep accelerating at 1G until it was time to turn around and decelerate at 1G. Problem solves, and they would get there a lot quicker too.
Because we don't have anything like the energy density required to do that (at least for times longer than microseconds, i.e., nuclear bombs).
Energy density drives the engineering here. If we had enough energy density, we could soup up ion rockets or use nuclear thermal and get to places very fast.
Make or find a ton of antimatter or so, and let's talk.
The ability of humans to perform well on the surface of any planet after months of zero-g seems doubtful. Build the spacecraft big enough, and rotate it. Better yet, send two spacecraft, tether them together, and rotate both of them about their center of mass. It will solve a lot more problems than the relatively minor one of dealing with in-space surgery.
Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience.
C. S. Lewis
Definitely lay off the cop. There are way too many police in this country.
This is what decent people get for putting up with drug tests.
How hard is it to understand that fascists will never stop taking more?
Better yet, always add a bit to every can of coffee you brew. Of course it'll take extensive tests to determine the ideal mix. Very extensive i bet; any volunteers?
This excellent corporate video suggests that Starbucks is working on it.
It's going to rather hard to hide the Earth from something aliens find in Earth orbit. They won't need a map or trajectory to figure that one out.
Once we have space elevators, the disc and the Echostar satellite it is attached to will be a dangerous nuisance and will be junked and removed in some fashion.
The best this disc can probably hope for is to be put in a landfill on the Moon (energetically easier to get to). More likely, it will be in the Air and Space Museum (or its equivalent) by 2112 or so.
This will be attached to an Echostar satellite in a valuable orbit. Now, at "end-of-life" its orbit should be raised, but still, it will be be up there, at that point available for either junk or salvage. I would regard the prospects of this lasting 500 years as very dim, much less 5 billion years.
I always regard these sorts of things (like the Voyager gold discs) as being much more likely to be picked up by future humans (or post-humans) than aliens anyway. From that standpoint, copies of mundane texts (like, say, the US Census, or some popular novels, or a history of the world) seem much more likely to be valuable than some photos of cave art or kids standing on a beach. (If civilization between now and then has not collapsed, they will know what's on the disc. If it has, then send details, not art, as the details are what tends to get lost.)
First, it's a double transit.
Second, check out this double transit here in our solar system.
I am also old enough to remember the speculation about Kohoutek.
It is notoriously hard to predict the brightness of "new" comets, as you know nothing about their history.