wumpus

I remember John Carmack (back when he was working on Armadillo) complaining that HTP was essentially impossible for him to obtain. I suppose if you can get red fuming nitric acid (inhibited or not), you can probably get HTP, but such things provoke a bit of attention. After reading Ignition, I'd also expect that most of these older methods are obsolete. If you can handle LOX, that is probably the ideal oxidizer for high power rockets. Obviously RP1 is the favorite fuel, but the alcohol (mixed with water to drinkable levels) used in V-2s had almost the same ISP with wildly lower temperatures (something like 1000C less). The conclusion of Ignition appears that in the end, they couldn't find a mixture that could beat these (although hydrolox obviously wins the ISP race). Nitrous oxide is also a favorite oxidizer for hobbyists. It is typically used in hybrid rockets (rubber solids plus liquid oxidizer), but might make a good oxidizer with alcohol (although I'd spend a great deal of time in the library before venturing into the lab for any such mixture). That the stuff is sufficiently tame to be used in commercial kits for car modification implies it is a whole lot safer than liquid oxygen.

A high-information signal would likely be one of uniform power and frequency distribution (although this might only be true over longer periods of time than you are looking at, you really don't know with other life forms*). A noisy [natural] signal would likely have a power distribution more often associated with natural causes. When we say "indistinguishable from noise" we typically mean "indistinguishable from uniformly selected values", not that such uniform values typically exist (they often follow power or 1/f laws). * it might have other weird properties as well, but it should still look "unnatural".

You would get roughly an increase of a factor of five over the the delta-v it took to get it off the Moon and toward Earth. If you really want to hammer the Earth, you need to grab some asteroids and maneuver them from there. Yes, this always bugged me as a RAH fan in my youth. It would work, but it would only give you a factor of 25 times over the energy used in the launcher. I'd expect that it will always be more than 25 times easier to get energy out of a bomb than to lift spacecraft (unless we build Orion).

Not only that, a sufficiently compressed signal should be indistinguishable from pure noise. And even worse, it will likely contain FEC (forward error correction, absolutely needed since retransmission will be so slow) such that the signal+FEC data will only be indistinguishable from pure noise if the signal/noise ratio is *just* high enough (because they are talking to/focused on *you*). And even then you will likely have a compressed signal that is meaningless without the decompression method. My understanding is that hard drives are well into this point (if you lose significant data, the whole thing is gone). It really doesn't matter if the thing is encrypted or not, if you don't have the s/n *and* the decoding scheme (and then the compression method), you aren't recovering the signal. You aren't going to be decoding any signal from a high tech source unless such bandwidth is essentially free. If they are using a specific frequency, that bandwidth is certainly *not*. On the other hand, AM radio (amplitude modulation with dual sidelobes, carrier present: the most obsolete modulation possible) still exists. It is an absolute efficiency disaster from a broadcasting standpoint, but an absolute trivial means of recovery. I'd suspect that any such message would be *meant* to be decoded, and likely exist as messages (for whatever reason) for wildly more primitive civilizations (as the receiving tech would be less than the broadcasting tech). It would most certainly not be used for primary communication.

And don't even consider building anything without the precision available from later days. The Wright brothers could fly thanks to a ~25hp engine. The V-2 had a 4000hp fuel pump. You aren't getting the delta-v you need in the 19th century. The Victorians might have had the possibility to get off of Kerbin, but not Earth.

It also doesn't help if somebody is using a word with a very specific meaning to mean something else (like an effect associated with the "old" technology). Holography is the production of images through use of interference patterns. If you are familiar with the effect of sending light through slits to get sets of bands, the effect is similar but uses at least as many "slits" as pixels to produce a full image. While I imagine the technique is now becoming possible (not sure how it is computed, but presumably similar to a FFT) I'm less sure about the actual production. Such a display has to know the exact position of each eye looking at it, and adjust for each eye (this automatically happens with lasers, due to their single wavelength and coherence). It is also mostly pointless for direct eye vision (because you will automatically get a 3d effect by having two such displays), and I'm sure the Microsoft system uses LCDs or oLEDs like everybody else. To be honest, for sufficiently small displays, you really *could* make a real holographic display this way. Transistors are smaller than visible light, so pack them close enough and play games with the individual light arrays. Difficulty: even in volume a square inch* display will cost over $1000. So you *could* make a VR headset this way, but the latency would be huge and causing the user to throw up (getting the latency down is a huge problem in VR, with one of these you then have to compute the interference pattern. Don't count on lunch staying down. Of course, the final advantage is that things out of focus will remain out of focus (presumably fixable with software and careful measurement of the eye for current systems) in exactly the right way. So maybe this will be the 22nd century display scheme, but it doesn't make sense now. * 645 mm**2, probably about twice as large as can be built on a standard process. I'll try to keep avoiding SAE units as well.

Personally, I've written on less technical fora exactly why the replicator is ridiculous (although 3d printing from roughly atomic stock might be possible). But think about the human side. These people have a starship capable of exceeding the speed of light, beaming people hundreds or thousands of km, and basically indifferent to any reasonable energy use. Try imagining describing your phone to anyone (preferably an engineer or other type who could understand it) from the twentieth century (preferably before car phones brought cell tech to the masses) after describing that vast amount of tech you admit that you mostly use it to "play flappy bird". Twentyfifth century people want "tea: earl grey, hot". They have an infinite supply of energy and the magic needed to transform it. So they use it all in a blindingly inefficient way to make "tea: earl grey, hot". Think how many deep technology stacks that are horrifyingly inefficient (hopefully mostly in software, but I think we burn energy badly in places as well) we have simply because the tech base and infrastructure are too deep to really fix (and of course there's no budget for it). So yes, both the technology and the use are completely ridiculous. I think it would be better science fiction to insist that such a device uses atomic stocks and "magics" them into the right position and correct bond (and this obviously takes some extreme magic). But most of this is because this tech would likely be discovered first and not be replaced by something stupidly inefficient (but just might if the magic was wonky and the tea never tasted right). It mostly fails the Occam's razor for where it would be on the tech tree. But it certainly doesn't fail the test of how humans use tech (typically create/buy for something important, then repurpose it for whatever is wanted).

I suspect that a high altitude parachute wouldn't be that hard to design for aerocapture. Basically, the whole thing would have a much higher surface area that the vehicle and withstand a reasonable temperature (made out of aluminum foil, possibly a reasonably high temperature alloy). Of course such a thing would only be good for aerocapture (and possibly de-orbiting), but descent and landing would require an additional system. I suspect nobody wants to carry the weight (however small, since the total surface area wouldn't be all that high a multiple of the surface area of the vessel) of an extra system, nor have an extra system whose failure could doom the mission.

Are there any good electricity conductors that don't conduct heat? I know diamond is about the least exotic material that conducts heat but not electricity. Static electricity should be a temporary problem, one that should dissipate reasonably quickly once the positively and negatively charged bits are strapped together (there might not be a ground in space, but you certainly have no net charge (nothing entered or left the vehicle). Getting rid of the static electricity simply involves "wiring" the positive and negative buildups together. The difficulty with cryogenics is that there are some parts that you don't want to tie conventional conductors to (because the whole point is temperature differential that nearly all conductors will work to eliminate). Note that you rarely need "good" electricity conductors to fight static (like the diamond example going the other way). Static electricity is typically handled with materials that are barely conductive at all. Measure the resistance of those shiny (or reddish) anti-static bags that CMOS components come in and you will barely register anything (although it *will* move, unlike paper). You might need a little more as the cryogenics might keep pumping in static buildup, but don't expect to need to match a copper ground strap. PS: Do NOT wear a wrist or other ground strap with less than a megaohm or so to ground. Even when working with the single digit voltage levels of digital electronics, it makes sense to make a habit of not being fully grounded (hey, it might save the equipment as well). You will be thankful the next time you open up a power supply or otherwise play with hundreds or more volts.

To try to get midway between a stratolaunch and a falcon 9, consider a rocket with a jet engine as a first stage. It would probably require a runway like Edwards air force base and still have wing issues (your first stage would likely be elongated for aero reasons). You would have all the landing issues of Blue Origin (throttling shouldn't be an issue) and still not even have their delta-v. I can't imagine how many launches you would need to justify such a stage over the cheaper and vastly more capable (if thirstier) rocket engine. No reason to design the rest of the airplane if all you want is a rocket stage. I'm less convinced that ground based power (such as Escape Dynamics) is completely dead. Mostly due to US Naval projects trying to use lasers as weapons, they seem to have immense budgets (that Escape Dynamics could only dream about) to try to get power from ships to elsewhere via EM waves. Has anybody really considered mountain launch (well, since the 1950s)? Russia launches over land all the time, but my best two guesses had nasty range issues downstream (Leadville, CO and Cayambe, Equador).

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090012109.pdf As of 2009, that's NASA's plan for Mars (they've canned the nuclear option, but haven't updated the whole thing yet). It isn't an issue about "going to Mars", it is an issue of getting more than one president to stick to a plan (if we wait for NASA, there is the real chance we have to wait for the tech to exist to build the thing in 8 years or less) and convincing Congress to go into space (this is a harder nut to crack, but perhaps giving SLS a real mission will convince them). I'll agree that a capsule isn't going to happen (with today's tech). Even with hibernation (how far away would that be?), it just seems too small for a several month's journey. Every suggestion I've taken seriously expects an ISS-sized transport vessel (and similar for a Mars base).

Considering how much the Air Force/Navy pays to train each pilot (let alone the cost in blood) I'd assume that Boeing/AAI (the global hawk company)/Lockheed Martin would be churning out the next generation drone well before we churned through half of our force. A drone vs. drone war would also force yet another questioning of warfare technology similar to the reaction of the horrors of the Great War and also of nuclear weapons (and nothing of note happened...).

I guess with Harvester gone, they aren't asking for Portuguese speakers. Not sure how I missed the whole kurfluffle.

There still is absolutely no reason to *ever* launch a pegasus from stratolaunch. Initial or not, it will almost certainly exist only as a paper capability (since nobody will buy it). A pegasus2/3 might make sense, but without a real rocket (that can't be launched cheaper on L-1011) Stratolaunch and $5 gets you coffee.

The Apollo capsule was designed to do this. I *thought* it was used, but I'm not sure. In practice, I'm not sure which parts the capsule should be above/below where the orbit would take it returning from the Moon.

Except this only makes sense if you are launching one at a time. There's no way to finish Startolaunch and turn around and use it cheaper than the L1011 (for single launches). For three launches, it is unbelievable that all three launches wanted that same window, nor that they couldn't be grouped on a bigger rocket cheaper. They are looking for a sucker to invest in this thing, but probably need a better patter than this.

The rings are amazingly thin, essentially having zero width on any meaningful astronautical distance (which I think means meters, but it might be a bit wider). You could sit just above/below the rings and pick the ones you wanted without really being in danger (of course, any colony would eventually perturb things a bit...). I can't imagine this being a place to inhabit, but you wouldn't be in danger from the rings themselves.

In order of silliness/hype... EM drive: impossible. Not only impossible, but you could presumably do the same thing by using a cyclotron-based system as a rocket for arbitrarily high Isp. So you are presumably working on a system that relies on breaking the laws of physics instead of something that will possibly work (I'm not pretending that the energy efficiency of either makes sense, just the ISP). Space Cannon: don't even think about it in a single stage, might make sense as a first stage. Downside: presumably exists entirely to send fuel and other raw materials into space, and requires a massive number of launches to justify itself. Likely obsoleted before construction is finished by Martian/asteroid colonies. SSTO: A favorite of those who have no understanding of the rocket equation. Anything an SSTO can do, a "TwoSTO" can do better (especially since spacex has demonstrated landing a first stage). Really should go down lower on the list do remotely possible systems like the X-43 project, escape dynamics, and SABRE (all of which rely on huge ISPs), but it comes up enough and needs to be heavily squashed. Space Fountain: Only down this far due to lack of perceived hype. Wildly more silly than a space cannon, but this is sufficiently obvious to keep it from coming up too often. Space Loop: Same issues as the space fountain. All the issues of a space cannon only with more complexity (although crewed flight is remotely possible). Space Elevator: Basically requires unobtanium. Fortunately, small batches of unobtanium are available in labs (for sizes not even close to workable). If you really want to get into space (and have the unobtanium), you will build this. Orion: Considering the thing has been possible to build since the 1960s, this can only go at the end. Yes, there are huge issues (and it has to be launched from Antarctica), but things like that nifty laser the Navy is using might make things more interesting (that laser would come in handy for a few other interesting crafts, but since the whole point would be causing fusion explosions the classification of the laser would be insignificant to the overall classification of the Orion).

I was under the impression that the [recoverable] first stage was expected to provide a ton more delta-v than the [recoverable] falcon 9. I'm pretty sure I've seen numbers like 6km/s floating around (and I've always been wary of such issues for falcon heavy), but this could have easily been mistaking mach 6 for 6km/s. Breaking your stages into 2km/s and 7km/s seems unlikely to be optimal, especially with the same fuel (the falcon 9 is much closer to even when launched with no recovery attempt). I suspect they may want the first stage to go faster, although having that monster come in hot would certainly be scary.

While I wasn't old enough to know the technical coverage of the Apollo days, I can certainly say that none of the science fiction of the day assumed *any* knowledge past the high school physics class (Have Spacesuit Will Travel may have included the most surprising information. Which was probably obsolete after serious satellite design was possible). Reentry was probably not all that well known even by NASA (no wind tunnels capable of such speeds, simulations were pretty limited). I've *always* heard the "skip off the atmosphere" danger, typically followed by "into space forever" and not "for another orbit out as far as the Moon, which life support can't handle" (which I've *only* heard in KSP-based tutorials). The general (and even space-enthusiast) population simply wasn't expected to understand orbits. I think even Scott Manley mentioned hitting "infinite distance" with escape velocity (something KSP players quickly learns means a distance varying between 0-2AU) in an *extremely* early video (possibly technically correct, since KSP didn't have a solar system for that version). People *might* have understood rocket engines, but I'm only aware of detailed explanations of turbine engines in thermodynamics classes (and physics classes teaching thermo). The whole concept of the turbopump isn't something you can dumb down to "average" levels. Consider the modern example: how many people can explain the working of transitors/gates/CPU instructions/compilers/programming languages/OSs/TCP-IP stacks/Cell phone workings/RF coding tricks (especially past [DSBCP*]-AM). The magic happens and the internet works. Pretty much how things go from the corn on the field (don't ask what's involved in generating the seeds and fertilizer) to the dinner table. Something I am as ignorant (and less justifiably as my life depends on it) as most people are about orbits and the TCP-IP stack. * AM as we know it really means "[Dual Sideband Carrier Present] Amplitude Modulation. Old school TVs used an AM system without both sidebands (well one was highly attenuated) nor the carrier. One of the reasons [classic] AM took off/still exists is that it is so extremely simple to decode, you really only need a cat's whisker [wire], a crystal, and some headphones. The downsides are amazing inefficiencies to broadcast (both in power and in spectrum).

You can run them together with kerolox (the densities are close enough together), but I'm guessing that you need separate turbopumps to drive the different densities of methane and oxygen (you do with hydrogen and oxygen). Presumably it makes more sense to go fuel-lean on the oxygen side and avoid sealing issues. Remember, a BFR can tolerate a shut down engine or two. It is unlikely to tolerate an exploding engine. Leaky seals could easily lead to an exploding engine.

This assumes that the "cargo only" ships are chemical (probably methane&oxygen) and use hohmann transfers with similar delta-v requirements. From your numbers above ["6.4 and 8 km/s",vs. "3-4 km/s on a slower trajectory"], cutting the delta-v in half should cut the fuel needed by an order of magnitude (not so much if the McargoT is coming back without being refueled at Mars). While the cost of the fuel (on Earth) might be trivial, getting it to LEO is over $1000/lb (so far). Going the "slow way" via gravity tricks should work with Mars (although it and Venus have the least benefit of such tricks). Also using ion propulsion would reduce the fuel mass by at least 80%. The only reason that costs should be anywhere near 90% of a crewed MCT is impatience and cost of designing a completely different McargoT. Beyond that, consider the benefits of using such a McargoT to transport fuel to an eccentric orbit (heading toward Mars) around Earth with ~2000m/s delta-v difference between it and LEO. The crew docks with the fuel tanker (likely a fueled up stage, until "we" are that confident in in-space refueling) and then proceeds to burn at Perigee. This bypasses the tyranny of the rocket equation by breaking the burns into two 2km/s burns instead of one 4km/s. And while you can't really break natural laws, you *can* pay for the extra 2km/s in cheap ion propulsion delta-v instead of expensive methane/oxygen delta-v. Less sure about cycler ships: typically the delta-v needed to dock/capture/etc plus the cost to get it started should end up a wash. Presumably any justification would be due to life support benefits and/or the benefits of maneuvering an asteroid to serve as the base of a cycler (even then the delta-v to dock/undock isn't free). These are so far in the future to not worry about (and hopefully propulsion systems will have changed by then).

NASA's X-43A managed mach 9.6 (~3000m/s). http://www.nasa.gov/missions/research/x43-main.html Gotcha's: It just barely made positive acceleration vs. drag, it had zero payload and was not reusable. https://hapb-www.larc.nasa.gov/Public/Documents/AIAA-2006-1-317.pdf Why you would want it? Basically the thing has a (fuel) Isp of over 2000 (around mach 6) and still over 1000 at mach 9 (I've linked to one that had it, unfortunately this forum lacks a real search function). https://info.aiaa.org/Regions/Western/Orange_County/ASAT Conference 2013 Presentations/The Specific Impulse Potential of Hydrogen Scramjet.pdf Basically, a technology that is only slightly less "blue sky" (in that prototypes have at least fired) than most of the blue sky work that is discussed here. It has a long way to go, and considering that NASA basically handed the research over to the USAF (which seems to be ignoring it), it looks like one of those "the technology of tomorrow, and always will be". As far as pulsejets go, they sound like more of an expert model rocket maker's chance to move to more exotic launch techniques. On the other hand, I suspect that the only advantage would be altitude as the things just can't produce delta-v. Using a weather balloon as a "first stage" would make a lot more sense to get through the atmosphere.

I'm pretty sure that "big hydrogen tank" is redundant. That stuff basically doesn't have a density. Is the tank for the oxydizer 1/6th the size or even less?

Reminds me of the "black foe" of NASA, William Proxmire. A Senator [Wisconsin] that thought that the US government existed entirely to produce cheese subsidies. I'm fairly sure the US government still buys, stores, and typically throws away cheese (you know times are bad when they dig into the cheese hoard). While I'm sure Proxmire wasn't around when they started, I'm sure he kept it running well after the Depression. I'm sure readers of old Robert Heinlein novels are fairly familiar with the name Proxmire.