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All you do is point a particle accelerator at it, and it's fed. This is simple enough. The problems are in keeping black hole confined and in working with radiation. Though, simply putting a shield at the back of the rocket would already give you 1/4 of total available thrust, which really isn't bad for a photon drive. The biggest questions, like the authors said, are in quantum gravity. Strictly speaking, BH drive does not conserve many quantum numbers. There are models that predict non-conservation under certain conditions, but whether BH actually qualifies is a question.

A lot. For the most famous example, SR-71 Blackbird used a hybrid ram/turbojet. Basically, it had a ram air bypass leading straight to the afterburner, allowing it to operate as a ram jet at Mach 3.2 cruise. These days, people are more interested in scramjets for hypersonic flights. Off the top of my head, the Boeing X-51 WaveRider is a great example of a currently operational test platform.

If that surprises you, wait 'till you see how low it can go. In principle, there isn't really an absolute cutoff for minimum speed, but it gets more and more challenging as you drop the lower speed. And you get less and less thrust out of it, so it becomes incapable of sustaining speed before it actually becomes inoperable. But at 300m/s you can actually get enough thrust out of one to accelerate. I doubt I'd be able to find good references right now, but some experimental flights Soviets have done were dropped from another airplane at under 900km/h. That's less than 250m/s, and these ram jets were able to go supersonic afterwards. Absolutely. While scram jet is a type of a ram jet, it's designed for much higher intake speeds. I don't think there is a specific cutoff for these either, but in practice, you need to be well into supersonic before you can start using a scramjet. In principle, the only part that has to be different is the combustion chamber. Scramjet and ramjet can share an intake. So you might be able to build a scram/ram jet at expense of just a few moving parts to switch from one mode to the other. I don't know if you could get both maximally efficient, but since ram jet only needs you to get to scram speeds, if you can make operation at the hypersonic speeds as efficient, it's probably good enough. So I still think this idea has promise for a small, reusable shuttle. So? It's a technicality. Reason we want an SSTO is to cut launch costs by reusing the craft as much as possible. Yes, R/JATO boosters would technically be a stage. But in terms of practical use, they are just consumables. We aren't talking about Shuttle SRBs, here. We are talking about small boosters attached to pylons which just get the ship off the ground. With what you are going to save on weight with (sc)ram jets, you are still going to end up way ahead even if your R/JATO are single use. In fact, you might even still be ahead compared to using a true SSTO with SABRE-like engines. P.S. While I still think maglev to 300m/s would be too expensive to be worth it, I'd definitely look into pneumatic catapults, similar to these used on aircraft carriers. Nothing new to invent, hardware exists, and it can get you to a pretty good fraction of that starting speed.

The moons are brightest when Jupiter is. In fact, their luminocity is always proportional. Magnitudes aren't, because of logarithmic scale, but if you convert these to luminosity, you'll see that they have the same range. So you are still going to have the best chance of seeing them when Jupiter is brightest. My objection wasn't based on "I can't see them." I haven't had 20/20 since I was six. It was based on a rough estimate of dispersion of Jupiter's light, which has turned out to be too rough. I have seen ran the simulation, output of which you can find in this thread, which has demonstrated that only the inner two moons are impossible to see because of Jupiter's light. The outer two Galilean moons at maximum elongation might be visible with perfect eyesight. By the way, right now seems to be a good time for it, based on PakledHostage's photograph and what I've been able to catch through the telescope. If your eye is sensitive and focused enough to see the moons of Jupiter, you should be able to see them now.

While you can use that for suspension, you can't use that design for propulsion. Inductrack relies on train to generate its own propulsion. That's fine for a train, because it can be heavy without serious consequences. If you are launching an SSTO, it needs to be as light as possible. So all of your propulsion system has to be in the track. That means that you can't have an unpowered track. You have to have an active linac pushing your SSTO, and that's going to be way more complicated.

Sounds like a plan. The basic setup is to have your objective lens set up a virtual image for the ocular lens to look at. So you'd be using the inspection lens as if you are actually looking at a small object right next to it. The virtual image from an object that's "infinitely" far away is going to be right at the focal distance. So you'd set up the inspection lens just past the focal point of your 6" objective lens. The virtual image needs to end up just a bit under focal distance from inspection lens. That should give you a sharp image and maximum magnification.

You can do precisely that. I used to demo that to students during optics labs at uni. Obviously, an expensive, high quality telescope is going to be more complicated, but your basic Galilean telescope is just two lenses with the right spacing. It works best if your objective is low power lens and your ocular is a high power lens. Large diameter of the objective also helps.

You only need the speed of sound at the narrowest part of the intake. As the intake narrows, incoming air speeds up, so you can get Mach 1 at the narrowest part even at subsonic speeds. You still need to be going fast, but 300m/s is quite reasonable for ramjet operation. Maintaining magrail operation isn't just about energy. It's still going to cost you a lot of money to operate, even if energy is free. Besides, electricity is cheap. Taking a 100T ship to 300m/s would take 1.1MWh. Magrail can be over 80% efficient. Even if you have to pay 15 cents per kWh, that's less than $200/launch. That's nothing. The entire cost is going to come from crews that will have to operate, maintain, and inspect it. All of the replacement parts, etc. Take a look at how much money goes into running a facility like JLab. There are a lot of similarities between running large magrail and particle accelerator.

That got me to drag my telescope outside. I really should invest into something with a better stand at some point. So much shaking, I could barely see the moons. And then the Earth turns, and I have to re-train the scope again, which is horrible with this stand. And all of that in the snow.

I don't think building a maglev is going to be economical here. You are probably better off using solid rocket JATOs to get yourself up to ramjet speeds. That way, you can take off from conventional runways. Cost of JATOs is going to be lower than cost of building and operating a maglev, even in the long run. Other than that, yeah, the idea of using ramjet for early portions of ascent is pretty appealing. I was thinking of something similar for a hybrid rocket. Basically, you have your solid fuel chamber, you can feed liquid oxidizer into it to run as a conventional hybrid, but you also have a ram intake sitting at the top which can let you run the whole thing with external air. Now, a solid fuel ramjet might sound pretty crazy, but honestly, it's not that different from operation of a hybrid. And you get some limited throttling with this.

I don't know if you missed the part about dynamic range, or if the implications didn't sink in. This is what the signal on your retina is going to look like. The difference is that your eye has a great dynamic range and is sensitive to local contrasts. The image is limited to 8 bits of depth. The part that's completely white in the center is saturated at that range. The actual light from Jupiter is 1,000 times brighter than that of the moons. So the central point of that circle is way brighter. Your brain will interpret it as a bright dot with a bit of a halo. But this rendering can only pick up the halo's diameter, and that's the white disk you see here. If I set the contrast to the level where you can see Jupiter as a bright dot with just a bit of halo, the moons wouldn't be visible at all. I could play with gamma correction to try and fit the actual range of that image into the available depth to try and make it more believable-looking. But that wasn't the point. The point was to compare the light of the halo to the light from the moons to see if light from Jupiter prevents you from seeing the later. And this image is quite sufficient for that.

If you spotted it at 150m? No, it's gone before the round can reach it. But you don't. Typical acquisition distance to a low flying plane is about 10km. These systems are usually placed pretty strategically. That gives you over 20 seconds at Mach 3. If you've ever seen AAA guns in action, you know that it's more than they need. The actual reaction time is measured in seconds. So a couple of kilometers lead is sufficient. Even in tricky terrain, you aren't going to fly by even a mid-cold war AAA system, like Shilka. Modern systems? Forget about it. Not only are they equipped with passive radar, meaning holes in your fuselage are your first warning, but they have much better reaction time. Some of the systems, such as these that are set up on US carriers, are designed with maneuvering ICBM warheads in mind. If it has a chance to shoot down a re-entering warhead, do you really think it would have any trouble with Mach 3? The only possibility of sneaking by one is if it's not armed. There, you rely on human reaction time, and that you can beat with a low flying plane easy enough. Might be good for a sneak attack, but experience shows that major wars rarely start completely out of the blue.

If you couldn't make organic compounds without life, where would life come from? You just need hydrocarbons, heat, and pressure. I would be surprised if some amount of natural oil wasn't present on, say, Titan. (There's a though, maybe we can use that to convince US to send an exploration mission.) That said, Mars isn't a particularly good environment for it, so yeah, it'd have to be extinct life. Which, still, isn't all that unlikely.

Depends. What kind of a plane?

In the 50's, such a system might have been an ultimate weapon, but now a modern AAA takes something like that out with no trouble.

Last I checked, the only qualification for a U.S.M.C pilot I didn't make was age by about a year. Eye sight is just barely passing, but passing still. I don't think there is any specific reason to disqualify me from a space mission. On the other hand, there are people way better qualified and more fit, so I doubt I'd have a snow ball's chance of actually making into a program.

Because of limited coherence length of the laser beam. If we had lasers with arbitrary precision in holding frequency, we'd have clocks with arbitrary precision in keeping time. And we don't have these. We do have lasers that would be able to measure distances precisely enough over a few km. They are the size of a small building. This is a very, very hard problem. And limitations we are running into are no longer just a matter of engineering. We have no physical principles to extend coherence length with.

My point about transponder was that every other aircraft in the zone of operation is already going to carry one. So we can get good information about everything in the air from a radar. Obviously, only at certain altitude, but civilian traffic bellow that altitude should be restricted to takeoffs and landings, anyways. So we do have a way to manage drone traffic. Rest of avoidance can be done with vis-rec and a low power radar. It's not trivial, but still way simpler than Google car. And I'm not talking about the kind of octocopter Amazon used for their PR stunt. These things just don't have the range. The only civilian use of copter drones I've seen is camera drones for news agencies. A local news agency was using one to make establishing shots at my campus. These things are great for that. I'm sure this will be a common thing before we know it. But they aren't for carrying stuff. We are talking about a far more expensive machine. Yes, it will have to have a transponder, decent avionics, an entire boatload of sensors, much larger motors and batteries, lifting body that will allow it to go from hover to a cruising flight, and lots of other navigation and safety aids. We are talking about tens of thousands of dollars here. But that's your typical cost of a delivery van. Naturally, a van will deliver more stuff per day, but not by a huge enough margin to make this commercially nonviable. Especially if we can reduce human workload. You'd have to be in position to charge a nice premium, so there has to be a great convenience factor. Not just a novelty one. For mail order, it's unlikely that you'll have a warehouse in a hop's range with stuff you need right now. And anything that has to be transported from a remote location would make drone on final leg pointless. General idea is right with pizza delivery. But the cheap-o drones will break someone's window or worse, and people who order pizza generally aren't the people who will waste money on a delivery by something sophisticated enough not to be a liability. If we are talking realistically about a business making use of a drone for deliveries with a goal of making money on deliveries, and not just for advertisement, I'm going to go with an expensive restaurant. Large city, big wealth distribution gap, lots of value on showing off in higher circles, and not much in ways of regulations that can't be fixed with bribes. My top three picks for the first place with real operating drone delivery service would be Dubai, Moscow, and Shanghai. I'm actually a little surprised that it hasn't happened yet. In US it will take just a bit longer. As you've said, there are some regulation hick-ups to still sort. They are being discussed, but so has been switching to metric altitudes for the past couple of decades. They'll probably make it work once there is economic pressure, but it really needs to pick up in the rest of the world first. Then we can shame FAA into fastballing it with the whole, "birthplace of aviation," thing. And US population tends to be way more thrifty with their spending. So the cost of operating drone delivery needs to come down a bit. But the technology's there, infrastructure is there, and the interest is there. It's going to happen sooner than you expect.

And that's different from the timing issue how, exactly? We are talking about a small fraction of coherence length here to achieve sufficient precision. We just can't achieve a stable enough signal to get position precisely enough.

What's your point? We aren't even discussing sensitivity or density of the rods. They are both sufficient and aren't the problem.

Eh, Moon's surface is overrated. I'd be fine with flying the CM. Of course, being LM pilot is fun too. Either one works. Now, Mars I'd want to step on. But I don't think there is any mission plan that leaves a crew member stuck in orbit, so it's not something I have to think about.

There are a few problems with that which go a bit beyond engineering. First, I agree with the ~20km estimate, but that's just to resolve it as a point. Basically, you'd be able to confirm that it's not a point object, which we already know. If you want to image anything of its features, you'll need a significantly larger effective aperture. Just to say, "Hey, look, clouds" you'll need something like 10x larger size. Of course, if we are doing this with a swarm, it's not really a huge problem. We can build an interferometer thousands of km across. In fact, anything smaller than Earth orbit is kind of pointless. But the larger you go, the more challenging it gets with precision. So lets talk about that. Starting with there not being a terribly good way to build an optical interferometer telescope. It's easy enough in radio astronomy. We just build an array, record the actual time-dependent signal, and use computers to sort out the rest. We can't do that with a signal in optical frequencies. So we have to build an actual interferometer. And again, on ground, it's not impossible. You just have to tune everything, like you said, to nanometer precision. The fact that this is something that's been understood for many decades, and we still only have a couple of arrays that are actually capable of doing something useful, with a few more planned or under construction, should tell you how difficult a task it is. On the ground, where things don't shift around, and we can measure distances with incredible precision. Distance is still a limiting factor. Across a few hundred meters, we can use lasers to measure distances very, very precisely. As distances grow, you start having problems. Not only is it hard to measure distances, but they constantly change. And then we go to the big problem. Space. First of all, holding station with required precision is impossible. Just forget about that. Things are going to move and drift, and you'll have to find a way to deal with that. No mechanical system is going to move with sufficient precision and with little enough vibration to allow this to work. You'll have to measure precise positions of the objects and find non-mechanical ways to adjust distances that beams have to travel. Fortunately, there are electro-optical systems that can work for you, but nearly all of them require polarized light, so you'll have losses there requiring larger mirrors on telescopes. But that's ok, we can deal with that. Measurement, though... Lets start with the fact that GPS can pinpoint your position on the ground to within a few meters. You'll have to do better. Even if we forget about doing this full scale, and try to build a swarm just 200km across somewhere, you'll end up doing 200x better than GPS on timing along. So we went from error in meters, to that in centimeters. Perhaps, millimeters. We are still 4-5 orders of magnitude short. You can do improvements with the right geometry, doing some adjustments, improve timing techniques used for positioning, and you might be able to shave a couple of orders of magnitude off that. But you are still way short. Using interferometry to image exoplanets is a great idea, but we are not going to do this with modern technology. We can't. The only way we'll have chance is if we can do the same thing we do with radio interferometry and do computer processing. And to do that, we need optical computers. When that becomes a standard for computation, we can start talking about ways to build a large space array for imaging exoplanets.

Alright, so I did the simulation, and while Io is completely washed out, and Europa is barely there, Ganymede and Callisto stand out surprisingly well. This simulation only accounts for the diffraction (6mm aperture, 17mm focal length) of an ideal thin lens, everything I found about human vision says that for perfect eye sight, that accounts for about 90% of aberration strength. This does not account for diffraction and scattering in atmosphere or sensitivity of human retina. So it's not proof that you can see these moons, but it does show that they are within limitations of optics. So a camera with perfectly manufactured lens, having same aperture and focal length as human eye, would definitely be able to image the outer two moons from orbit. So I withdraw my objection that it's impossible from perspective of optics, substituting it with mild skepticism. It is definitely impossible to see Io or Europa, though. That I have no doubt of. Here is the output of the simulation. Each pixel corresponds to 2.5μm, giving roughly the equivalent pixel density to density of rods or cones. (Turns out, their maximum densities are about the same, 150k/mm², but achieved in different parts of the eye.) Contrast is set to make the outer moons clearly visible. Actual sizes of all objects on this picture would be less than one pixel across. So disk in the center isn't Jupiter itself, but area of the sensor saturated by its light. Actual human eye has greater dynamic range, so you'd see a significantly smaller disk, but the only thing that matters here is contrast of the moons, and light from Jupiter significantly overpowers that of Io and mostly that of Europa. Oh, one more detail. I've put all four at maximum elongation, alternating direction from Jupiter. That can actually happen for the inner 3 moons, but I'm not sure it's ever the case with Callisto. But since only the outer two moons end up visible anyhow, it's a moot point.

Yeah, I'm trying to get simulation going that shows exactly what an image of Jupiter and moons looks like on human retina. Just need to get the right numbers for the aberration coefficients, but I think I found what I need in the articles.

It's optically impossible. You can say as much as you want that you have seen it, but even at maximum elongation, light from Jupiter proper is too strong to make it possible to see something that's 2x10-3 away without some sort of an aid. Like lajoswinkler pointed out, you can use something to obstruct light from Jupiter and then just be able to see these, but there is absolutely no way to see them without doing something. Human eye can't do it. Period.