sevenperforce
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Posts posted by sevenperforce
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15 minutes ago, wumpus said:
If I was part of reaction systems, I would certainly want to go this route. It might be a long shot, but I'm sure it is a long shot that has a better chance than straight to SSTO.
I'm sure that SABRE can use kerosene. I'm less sure that such a plane makes sense for flights where the mass of kerosene might not be higher than the the dry mass of the plane. LH2 might make more sense. Obviously you need LH2 if you want SSTO.
The SABRE engine cannot use kerosene, by definition, because it is an airbreather that requires you to dump LH2 through a precooler.
But you wouldn't actually need LH2 to get Skylon to orbit. Strengthen the frame, replace the SABRE engines with a pair of steel-ducted Merlin 1D clusters, and fill it up with kerolox. It would carry triple the payload to orbit. Mass fraction wouldn't be as good, but that doesn't really matter because kerosene is cheap as heck and simple to tank.
The proposed Skylon vehicle is REALLY big.
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It is a battery, not a capacitor. That was my first question as well.
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1 hour ago, HebaruSan said:
Each hospital typically receives about a briefcase-sized shipment per week, I believe. So it may only work for dense population centers where a large number of those shipments for different hospitals could be bundled together on the same flights.
Perhaps a regular hypersonic transport between two nodes carrying a series of time-sensitive cargo packages + passengers?
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4 minutes ago, KerikBalm said:
The only market would be military... and that's not a large enough market.
The US military in particular likes the concept of a prompt global strike (PGS or soemthing like that). I even saw a concept for a one way method to deliver a squad of special forces using some suborbital lifting body re-entry vehicle (somewhat like the X-33. Also I think it landed with a parasail and didn't need a large landing space).
They've considered ICBMs with "conventional" (chemical explosives) rather than nuclear warheads... but that's far too provacative given that most ICBMs are nuclear equiped (indeed, for an ICBM, nuclear is conventional) and every launch risks starting a nuclear war.
A hypersonic aircraft/missile would appear to be the solution (though well positioned railgun equipped ships could take care of a lot of stuff).
The military often likes to spend a lot of money to have a capability that it rarely if ever actually uses. A hypersonic special forces delivery vehicle may interest them... but extraction would be problematic...
The problem is that it actually has to be used in order to generate revenue.
32 minutes ago, HebaruSan said:Molybdenum-99 has a half life of 66 hours, has inelastic demand from hospitals for nuclear medicine procedures, and is shortage-prone (two reactors in the world make it, and the one providing 80% of the supply has been shut down twice in the last decade, and both are nearing end of life).
While current transport methods are probably adequate for 99Mo, maybe you could transport other industrially useful isotopes with shorter half lives.
Intriguing. I wonder how large an average shipment is. Partial passenger/partial cargo is a possibility if there is some regular need...
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16 minutes ago, Nibb31 said:
It's a clever idea, but I don't think such a market exists.
For freight, air transport is already only really viable for perishable goods or parcels. Parcels spend more time in triage centers and trucks than they do on the plane. In most cases, logistics companies seek regularity and cost rather than speed. I don't think there are many cases where it makes a difference if cargo takes 6 hours to arrive rather than 24 hours on a regular plane route.
For passengers, the time required to get to the airport, go through customs and check-in also means that the difference between a hypersonic and a supersonic flight is negligeable.
You really would want to go cargo, simply because the LV requirements are thus rendered substantially less onerous and you have a lot more flexibility. Unfortunately, I can't think of any suitable cargo either. There's really nothing in the world that needs to be shipped in bulk to the other side of the world in a matter of hours...at least, not so desperately that people would pay for a suborbital spaceflight to accomplish it. I suppose there are certain particularly expensive consumables with short lifetimes that could be harvested and shipped to high-end restaurants, etc., but the demand would not be high enough to be a major driver.
That leaves you with human cargo, with all its nasty "keep the cargo alive and air-conditioned" requirements. There's a glimmer of hope here, because while the difference between hypersonic and supersonic flight may be fairly low, supersonic options don't currently exist, and there is a big difference between hypersonic and subsonic flight. Subsonic flight means a trip to the other side of the world can take a day or longer; supersonic cuts this to several hours...suborbital hypersonic means no two points on the globe are more than an hour apart. There's a fair probability that the ability to commute around the world would prove attractive to enough people/businesses to service at least one or two routes from the start. I don't know what the maximum viable ticket price would be.
Ideally, you could use existing airports by adding a dedicated spaceport terminal at lower cost than building an entirely new launchpad.
The suborbital/orbital transition would probably be accomplished by having some portion of the passenger cabin be replaceable with an extended fuel tank. E.g., you can take 30 people to the other side of the world in an hour for $90,000 each, or you can take 10 people to orbit for $350,000 each.
41 minutes ago, sgt_flyer said:now such a design would face the same problem as supersonic jetliners - you can't go supersonic above the ground - clearly limiting the avaible destinations. one of their idea was to propose to go from europe to australia by flying over north pole then above the pacific.
Well, this is a suborbital spaceflight, not a high-altitude sustained hypersonic flight. With a steep ascent and re-entry trajectory, only two sonic booms reach the ground.
41 minutes ago, sgt_flyer said:in addition, the airports that would receive such a plane would have to build and maintain the infrastructure for storing and fueling the LH2 (+ ongoing costs to maintain the cryogenic temperatures). that'll cost a lot for 1 plane ! especially given the low density of LH2 and cryogenics, you won't be able to use a fueling truck - you'd need to bring the plane to the LH2 tank instead.
LH2 is a non-starter, I think. You need to be able to run on RP-1. Or LP/LNG at the very least.
That's not a bad thing. A high propellant mass fraction is okay...you WANT to be able to carry a lot of fuel...and high density means better T/W ratios and a smaller overall vehicle, which drives down vehicle reuse costs.
7 minutes ago, tater said:This is another cart before the horse thing. Businesses exist to serve the needs and demands of consumers. There is certainly a demand for faster air travel, but that demand requires that the price point is roughly the same as the current price scheme. I doubt there is sufficient demand in the billionaire class for hypersonic aircraft past the corporate/charter level (it it's even justified for that).
Yeah, but the horse is a lot closer to the cart than the rapid-reuse-orbital-flight version.
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33 minutes ago, HebaruSan said:
Hmm, interesting. Not all data is compressible (e.g., zipping a JPEG or PNG will generally make it bigger, not smaller), and I'm not sure how well this would work for the quanta in the universe. If we have 10 quadrillion atoms with the same velocity, then that data could compress really well, but if they're distributed evenly across a spectrum, it's less helpful (or potentially makes the problem worse).
I just realized something.
Chemistry is a compression algorithm for a subset of physics. There are certain physical particle interactions which happen the same way every time and thus can be represented in abbreviated form.
Biology is a compression algorithm for a subset of chemistry. Psychology is a compression algorithm for a subset of biology. Sociology is a compression algorithm for a subset of psychology.
A neat way of thinking about it, anyway. The supercomputer could "compress" by simulating chemistry rather than physics when particles were in the correct energy ranges, and so forth.
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13 minutes ago, FreeThinker said:
The problem with lithium as a propellant in a NUclear Engine is that it poisons the neutronisicy of the reactor
Only Lithium 7 has a change of working in a NTR as any high energy neutron obsorbed , will generate another neutron
Lithium-7 has a vanishingly low probability of absorbing the high-energy neutrons in a nuclear reactor. It needs ultra-high-energy fusion neutrons for the absorption to have any reasonable probability.
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SSTO RLV proponents often argue that once a vehicle with rapid reuse potential exists, it would create the market which would enable it to be cost-effective. Unfortunately, it's doubtful than anyone will bother to build or design such a craft unless the market for rapid small-payload LEO launch already exists. This creates a chicken and egg problem, where the market won't exist until the launch vehicle does, and the launch vehicle won't exist until the market does.
It's possible, however, that a launch vehicle could be designed for a broader market, thus becoming available without requiring the rapid small-payload LEO launch market to exist first. From an economic/investment standpoint, it is much more attractive to build a vehicle which can use an existing market than it is to build a vehicle on the speculation that it will create a nonexistent market.
Such a market could potentially be realized in a similar way to how we first got into space: using the same vehicles for suborbital and orbital flights. The US and the USSR both figured out that the gigantic missiles they were planning to use to lob nukes on suborbital trajectories could, when properly staged, be used to boost payloads into orbit.
Many orbit-capable vehicles would make excellent hypersonic suborbital transports, suitable for transporting a large payload between any two points on Earth in an extremely short time. With a decent-sized fleet of such vehicles* servicing regular hypersonic transportation around the globe, you would have the support infrastructure necessary to service those same vehicles on orbital flights, either with reduced payloads or with a launch assist stage.
The question, then: does such a market exist? Is there a need for large cargo (or, on the other hand, passenger transport) to be whipped around the world in a matter of hours, regularly? Who would pay, and what is the probable market saturation?
*Skylon could potentially serve such a role, as it likely has excellent suborbital hypersonic flight capacities. It's not ideal, though, because it requires a great deal of LH2.
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8 minutes ago, HebaruSan said:
That rules out options #2 and #3, since it wouldn't be the whole universe, and/or it wouldn't be tracking the motion of each single atom. My argument above addresses whether #1 is possible (my contention being that a universe capable of hosting a galaxy-sized computer requires no less power to simulate atom-by-atom than one that already has one).
Atom-by-atom is easy.
But the universe is splitting atoms all the time. So it really needs to go quanta-by-quanta, which is not so easy.
XKCD #505 is apt...
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On 4/18/2016 at 7:18 PM, fredinno said:On 4/18/2016 at 10:50 AM, sevenperforce said:
[Planet 9 is] forcing orbital periapse arguments for the other bodies, which is exactly what orbit-clearing gravitational dynamical dominance is supposed to do.
But wouldn't objects move back in during its million-year orbit?
Nah. Planet 9's subtle adjustment to the sun's gravity well extends all the way across the solar system; it's not like its gravitational influence just drops to zero when you get far enough away. Otherwise the L3 Lagrange point wouldn't be a thing.
On 4/18/2016 at 7:18 PM, fredinno said:But the Earth will eventually tidally lock with the moon (the Sun will probably not consume Earth). Is the Moon no longer a moon then?
Under my definition? No, it wouldn't be. Right now, the moon is tidally locked to Earth but Earth is rotating independently of the moon. When the dynamics of the system shift so that both Earth and the moon are tidally locked to each other, it will become a double-planet system.
I mean, we would still probably call it "the moon" for the sake of history, but there's nothing wrong with recognizing such a change. After all, the Earth and the moon are already very close to being a double-planet system; the moon doesn't actually go around the Earth at all. They're just in very close solar orbits and the Earth's gravity perturbs the moon's solar orbit enough to tidally lock it and make it appear to orbit Earth.
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4 hours ago, PB666 said:
Carbonated Ice will be the heaviest in hot spots (volcanic, but nine may be so old, it does not need to be the same age as our system, it could have been a neutron star or a planet from a system that went supernova during the previous generations of stars so volanism may not be major).
Could have been a neutron star? I don't think so.
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For anyone paying attention, they have rotated the F9 first stage and are lowering it onto the transport rings right now. http://www.portcanaveralwebcam.com/
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58 minutes ago, FreeThinker said:
Also in a high neutron environment, the Lithium would actualy turn into Tritium
Lithium-7 has a really low fast neutron cross-section and needs ultra-fast D-T fusion neutrons to actually fission into tritium and helium. Not enough neutrons to do it, even in an NTR.
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'Twas pointed out to me elsewhere that Pluto is large enough to retain Rhea as a "real" moon -- that is, with the barycentre inside of Pluto.
However, Pluto would still become tidally locked to Rhea in astronomically brief time.
Thus, I propose an adjusted definition for "natural satellite". A natural satellite is a self-gravitationally-bound object orbiting a barycentre inside a larger body, too small to force mutual tidal locking with the larger body. This makes intuitive sense; if two objects are tidally locked then they are orbiting each other, even if the barycentre is within one body.
A moon is a gravitationally-rounded natural satellite of a substellar object. A planet is a body large enough to have a moon. This cutoff is about 6.3e22 kg, comfortably greater than the mass of Eris but comfortably lower than the mass of Mercury. A dwarf planet is a gravitationally-rounded body too small to have a moon.
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12 hours ago, PB666 said:16 hours ago, fredinno said:
Phobos and Deimos won't like you
Honestly though, people would get liquided about Phobos losing its "moon" status if you redifined moon like that, just like what happened with Pluto. It's creating one problem by solving another.
We can call them moonitoids
Better yet, dwarf moons.
16 hours ago, fredinno said:But Planet 9 orbits so slow, it hasn't really cleared its orbit despite being so massive.
It's forcing orbital periapse arguments for the other bodies, which is exactly what orbit-clearing gravitational dynamical dominance is supposed to do.
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I may give this a shot in Demo. Won't come anywhere close to y'all's results, of course, but it will be an interesting design challenge.
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1 hour ago, Motokid600 said:
And it dwarfed the crane that was holding it... ha. Anyway supposedly they were talking in EJ's stream about smoke having been seen a half hour ago. Something like they burned off some excess fuel or TEA/TEB. Hopefully nothing bad...
Yeah. I was expecting them to drain the ignition fuel (pyrophoric TEA-TEB) but instead it appears they simply burned it off by triggering the reignition sequence. Presumably it was something they needed to do while they had the rocket firmly strapped down, before attempting to transport it.
Speculation that this should have been done automatically on OCISLY but some part of the automated process failed.
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Recovery updates....
I have been keeping up pretty closely with the live stream video to the stage 1 recovery. They have removed an access panel covering one of the engines and are going through what is apparently a pretty involved process. The workers are wearing fire protection suits, so they are probably setting up to remove the engine igniters.
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22 hours ago, Jetski said:
Is this more what you had in mind? Demo parts and capsule survived from LKO. Technically had landing legs, but they didn't survive. If I had infinite patience I could tweak the last Flea for a few more dV and probably survive after a million quickloads
Looks like a win, though it's a shame the landing legs didn't survive. Hint: try parallel-staging the landing boosters with radial decouplers, so you can ditch them at touchdown. I'll try now with a suborbital flight....
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10 minutes ago, KSK said:
Just thinking aloud but would you need actuators on the landing legs? Make them spring loaded (with decently stiff springs so you don't end up with wet noodle legs), have the upper pivot point above the booster's centre of gravity and presto - a self compensating system?
Edit - and is it just me, or are the cold-gas thrusters at the top of the booster firing? They could help keep it stable, at least for a little while after touchdown.
Yes, the cold-gas thrusters at the top were the first thing I noticed.
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6 minutes ago, PB666 said:
Yes, because, like, telephone poles are much better at landing on barges out in the Atlantic,
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The rocket is emptied of most of its contents, the engines are the most dense part of the craft, it has landing stuts to move the tipover point further away from the center. Its a little bit better than a telephone pole at staying upright.
Talking about size, not aerodynamics or COM.
If I didn't know better, I would think the landing video was a telephone-pole-sized rocket landing on a basketball-court-sized barge...not a 737-sized rocket landing on a football-field-sized carrier.
I've asked people how large the booster looks and they say "a couple stories high" and I tell them it is twice as long as a semi-truck, landing on a football field, and their jaws drop.
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2 minutes ago, Ten Key said:
That rocket is roughly the same height as the Statue of Liberty. That's mind blowing.
It is. Pictures just don't do it justice.
This is not a telephone pole, folks.
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Yeah, a boneless creature has some serious advantages. Especially if they can survive in open air by respirating through their skin.
It's even theoretically possible that a boneless creature could survive unprotected EVAs without difficulty. If they can handle the transition from high pressure to atmospheric pressure then that last atmosphere shouldn't be much of a problem if they can mitigate moisture loss.
Ability to handle very high gees could lead to ground-based launches like launch cannons, especially because it is far easier to build a large underwater structure.
Generation Ship
in Science & Spaceflight
Posted
Four of each animal is also not nearly enough to create any sort of sustainable population, either. If you want a small temporary breeding population of tasty or useful animals, a few hundred embryos per desired species might be enough. But if you want a permanent sustainable population you will need 100,000 individuals minimum in order to have enough genetic diversity for the population to survive in the wild, and that is if you have already achieved 95%+ terraforming on the target world.
If the trip only takes 45 years, why would most of the passengers have never seen Earth?
Is artificial gravity based on linear acceleration, centrifugal acceleration, or handwaved? Handwaved selectable artificial gravity is technology on a level with Alcubierre FTL drive.