sevenperforce

Oh, I agree absolutely. Not worth it at all. People make too much of Elon saying that the first stage can SSTO by itself. Sure, it can, but with negligible payload. I wanted to run the numbers to see. It wouldn't make sense for SpaceX to do this, anyway. If they have an end of life booster they will either cannibalize it for parts or they will launch it on an expendable ordinary mission.

It could burn up to orbital velocity, MECO, release payload, burn retrograde back down to a safe re-entry speed, and then re-enter for a high-speed landing a la JCSAT-14. Of course payload might be negative. The empty first stage masses 22.2 tonnes and needs at least 20 tonnes of reserve fuel for re-entry burn and landing burn from a MECO of 2,321 m/s. That's from the JCSAT-14 hot landing. By the rocket equation, a burn from 2,321 m/s to 7,800 m/s and back down again (i.e., zero payload) requires almost 11 km/s of dV. With a terminal mass of 42.2 tonnes, the Falcon 9 first stage would need 1,516 tonnes of propellant left...more than the entire propellant capacity of Falcon Heavy. Even with an aerospike engine to push the vacuum ISP to 348 seconds, it would still require 1,019 tonnes of propellant to come back. Of course, if you are talking about expending an end-of-life Falcon 9 first stage, then with altitude compensation you could get a good solid 3 tonnes of payload to orbit.

If you think about it, the space programs of the USA and Russia didn't start with science as the primary objective; they were a colossal measuring contest between military superpowers. So it is all rather muddled.

Mars had a good deal of water. And you only need water 500 m deep to make a 500 meter high tsunami. Most of the water on Mars escaped into space because its gravity is a touch low.

Like, like, like, quadruple-like.

While, again, I TOTALLY want major human presence in space, I just don't see it. Surely it is cheaper to allow for a command lag than to ship humans a light-hour from Earth.

Any in-practice examples of this?

You cannot even assume that the English language will still exist if you change the future. Although you can preclude this by traveling back to a more recent time. There is a nice little pop theory about this. If you were going to time travel without leaving obvious traces, there are some practical considerations. First of all, you definitely need to go to a time prior to widespread photography and videography and photo ids, or you are just running asking for trouble. The last decade of the 19th century is about the latest you could possibly go. At the same time, you don't want to go too far into the past, or you will stick out like a sore thumb due to your accent and language issues, and you will be SOL if you need emergency medical care. You don't much want them to chop off your leg if you stub your toe. So you want to go post-American-Revolution, preferably post-American Civil War just for the medical improvements. This means the prime time for time travel is 1830-1890, with a particular advantage from 1870-1890. This also means that if we were looking for evidence of clandestine time travel, we should look between 1830 and 1890. What evidence might a time traveler unwittingly leave behind? Artifacts are unlikely, and knowledge about the future is impossible to find in the glut of fakers out there. He could leave behind ideas, however. Ideas in philosophy, in literature, in science. Particularly in fiction. What ideas in fiction would we look for? Well, virtually all tropes in fiction are essentially timeless, going back to Greek myth and earlier. Human flight? Daedalus and Icarus. Teleportation or superluminal speeds? Mercury. Aliens match up with visitors from the stars in Greek and Roman myth. Prophecy, communication over long distances, magical healing...it's all right there in Greek myth. Except one thing: reverse time travel. Time travel never exists in Greek myth, or in any fiction of antiquity. In fact, time travel into the past never exists in any literature...until the 19th century. Predki Kalimerosa: Aleksandr Filippovich Makedonskii, 1836. A Russian science fiction story which is the first mention of time travel into the past. Missing One's Coach, 1838. The first English-language story about time travel. Paris avant les hommes, 1861. Magical travel to prehistoric times. Hands Off, 1881. Time traveler changes history, creating an alternate universe. The Clock that Went Backward, 1881. A machine to transport people short periods into the past. El Anacronópete, 1887. A vessel which travels through time. The Time Machine, 1895. Wells's time travel masterpiece. A Connecticut Yankee in King Arthur's Court, 1889. Twain's time travel masterpiece. So time travel abruptly enters the world of fiction PRECISELY at the point in history we would expect time travelers to choose as a destination.

The biggest problem with scramjets to orbit is the airbreather's burden. When acceleration drops (which it MUST do with high Mach numbers for an airbreather, simply because the increasing speed of the airstream DIRECTLY sucks away net thrust), you end up having a longer acceleration stage, which rapidly destroys the advantage of specific impulse. Specific impulse is proportional to thrust, not to acceleration. For a pure rocket, your thrust-specific acceleration increases with increasing speed, because your vehicle is getting lighter and lighter. For an airbreather, your thrust-specific acceleration decreases with increasing speed. And that's what kills you. At lower Mach numbers, you gain an advantage by using the increasing airstream speed for ram compression to improve the efficiency of your reheat, but this goes away rapidly at higher Mach numbers and you are desperately trying to squeeze impulse out of a losing battle. Rules of thumb: When vvehicle <<< vexhaust, airbreathing is great. When vvehicle < vexhaust, airbreathing is not so great. When vvehicle = vexhaust, airbreathing is not worth it. When vvehicle > vexhaust, airbreathing produces negative thrust. The ideal SSTO/PSTO* solution, I think, is to use airbreathing up to 50-60% of your exhaust velocity, then go to pure rocket mode. IF you can repurpose your airbreathing hardware for re-entry landing (lift fans, movable vanes for re-entry control or heat shielding, etc.), then do so; otherwise drop them. Note that a tripropellant arrangement becomes a little more lucrative here, as a higher exhaust velocity from methalox or hydrolox gives you a longer airbreathing boost phase. *PSTO stands for Parallel Stage To Orbit, which basically means you use the same engine from liftoff to orbit, but you drop a parallel assistance stage on the way.

Hmm, those figures might be attainable but you'd be measuring something that's pretty hard to figure out just from looking at it...

Yeah.

I've thought about this before...I think it is possible to come up with sufficiently extraordinary evidence that we would be safe to accept that SOMETHING out of the ordinary happened. In some cases, time travel might be the best explanation What would that evidence look like? Well, if you were traveling back in time and wanted to leave irrefutable proof of your presence, what would you write down? You might not be able to leave behind predictions of future events, because you don't necessarily know whether your presence will alter the course of history. Same with language; writing a message in modern English won't do you any good if the English language never develops. You could, however, leave information that isn't subject to change, but that the ancients would have no way of knowing. For example, you could carve out maps of the surface of the moon and of Mars, along with a large scaled chart of the solar system showing the orbits of the planets, the major moons of each planet, and a variety of comets (particularly ones that could not have been discovered until modern times). You could carve out a large globe showing the exact shape of the continents. You could put skulls next to Vesuvius, Krakatoa, Huaynaputina, Santa Maria, Novarupta, and Mt. St. Helens (since altered history won't keep volcanoes from exploding). You could also record stuff from science and physics, like the ratios of the masses of all the subatomic particles (that's my avatar, by the way) and/or various physical constants which couldn't be determined until modern times. You could carve out an image of the Milky Way. Of course, in all those cases, it doesn't PROVE that you time traveled. The same information might conceivably come from an alien visitor. But it's extraordinary enough that time travel would be a reasonable conclusion. One can casually construct non-causality-violating time travel systems.

It also depends on whether we are talking about the old rule (first to invent) or the new rule (first to file). For example: Carl writes an email to his chef dated January 1 mentioning an idea for bacon-wrapped seaweed, but they don't make any. On May 1, Alice comes up with the idea for bacon-wrapped seaweed and applies for a patent. Under the old rule, Carl could apply for a patent after Alice, citing his January 1 email, and he would get the patent. Under the new rule, Alice would get the patent because she applied first. Carl has an interview with a newspaper on January 1 and mentions that they will be adding bacon-wrapped seaweed to their menu, but they never do. On May 1, Alice applies for a patent on bacon-wrapped seaweed. Carl points out that he already published the idea in a newspaper four months earlier, and so the patent is thrown out and both Alice and Carl are free to sell bacon-wrapped seaweed. On January 1, Carl begins selling bacon-wrapped seaweed to a small number of his customers, but doesn't put it on the menu. On May 1, Alice applies for a patent on bacon-wrapped seaweed and puts it on her menu. Carl sues, alleging that he came up with the idea first. He loses the lawsuit, because he can't stop Alice from making it since he never applied for a patent, but Alice won't get her patent because Carl was already making the stuff. On January 1, Carl files a patent for bacon-wrapped seaweed. On May 1, Alice begins selling bacon-wrapped seaweed. Carl sues for patent infringement. Alice's lawyer finds a trade magazine from 1981 which discusses the possibility of bacon-wrapped seaweed, proving the idea is "prior art", and Carl's patent is thrown out, leaving both parties free to sell it. One critically important point is the difference between #1 and #3. In case 1, Carl merely came up with the idea. Under the new rules, this won't keep Alice from getting a patent on it if she comes up with the idea independently. In case 3, Carl not only came up with the idea, but developed it and began producing it. In this case, Alice can't get a patent on it. This difference demonstrates the value of actually developing and producing an idea. Anyone can come up with an idea, but you have to actually do the work (either by producing it or by going through the patent process) or it's really not worth much. It should also be noted that after any of the above cases, Peter from Peter's Pleasure Palace can come up with a method for producing bacon-wrapped seaweed, and that is a new idea which can be patented "on top of" the old idea, regardless of whether the old idea is patented or prior art or anything else.

Now we just have to make it bigger and put engines on it! Oh, hello there, SERV.

A patent is a lot like a contract between an inventor and a government. The inventor agrees discloses how his new idea works, and the government agrees to enforce a 20-year exclusive use arrangement for the inventor. This benefits the inventor, because he is now (theoretically) guaranteed two decades of potential profit, and it benefits the government, because after those 20 years have elapsed, the invention becomes available for public use. Everybody wins. Another option is to keep your invention a trade secret. If you simply never explain exactly how your invention works, then no one else can reproduce it. Coca-cola did this with their recipe for their eponymous product. Trade secrets, unlike patents, give you the ability to profit from your invention for far longer, as long as no one figures it out. You can't patent something that someone else invented and produced, even if you came up with the idea independently, and even if they never patented it. If something is already being produced, it is considered "prior art" and so the government will not consider it to be patentable; they are only interested in patenting ideas that otherwise would remain trade secrets. In the past, ownership of a patent was based on who invented it first. So if Carl's Crab Cafe and Alice's Awesome Eatery both file a patent for bacon-wrapped seaweed at the same time, but Carl has emails proving he invented bacon-wrapped seaweed first, then Carl would get the patent and Alice would not. But just a few years ago, the USPTO changed the rules. Now, the patent is awarded to whoever files first, regardless of whether they actually invented it first. This encourages people to file sooner rather than later, sharing their invention earlier and resulting in more progress. If you create an idea and decide not to patent it, but just begin production, your competitor may actually still be able to apply for a patent. However, if they attempt to enforce their patent, you can show that you were already PRODUCING the invention, making their claim prior art and getting their patent thrown out. You can also get their patent thrown out if you can show that the idea was already published long before either of you came along. That's what happened with Blue Origin and SpaceX; BO took out a patent for barge landings of first stage rockets, then sued SpaceX for trying to land their rockets on barges. SpaceX pointed out that the Russians had published plans to land rockets on barges long before, and BO's patent was tossed. Finally, if you don't mind other people using your invention but want to keep someone else from patenting it, you can file a patent directly into the public domain for free. Disclaimer: not a patent attorney, but I did stay at a Holiday Inn Express last night.

Not in absolute terms, no. Except for the trunk; the trunk probably weighs about the same. But more in relative/breakdown terms. For example, if we knew the mass of the Dragon 1 pressure vessel, we could use the square-cube law to estimate the mass of the DV2 pressure vessel.

I have been digging around online for a while and haven't really come up with much of anything, so I figured I would croudsource this. The Dragon V2 is listed with a dry mass of 6,400 kg. Does that include crew amenities, like seats, displays, life support, that sort of thing? What's the best estimate of how much of that mass is the trunk, how much is the heat shield, how much the SuperDracos weigh, how much the onboard fuel tanks weigh, the mass of the aeroshell and pressure vessel, and so forth? Can we use figures from Dragon 1 to estimate?

I mean, I don't WANT to believe that the future of space travel is robotic. I just can't think of any near-term reason why squishy, fragile humans would be more economical than disposable robots. And if robot operation is standard when asteroid mining becomes lucrative, it will likely be cheaper to make it happen with robots.

I think the trick is to use a biaxial or even triaxial configuration. One axis minimizes drag for vertical takeoff (perhaps with some body lift to counteract gravity drag in an airbreather) and one axis provides high drag and/or lift for re-entry and gliding flight.

I'm inclined to argue that what Blue Origin is doing cannot really be classified as a space program. They are testing a launch system for commercial flights. Now, if one of their New Shepard test launches is used to launch a suborbital probe for NASA to test inflatable re-entry shields, that would be more like a space program. But it is ultimately semantic.

Not. Not in comparison to anthropogenic climate change. Unlike the scientific community, there is no peer review here to separate the informed from the uninformed, the facts from the emotion, the thoughtful from the clueless. That's why the scientific community HAS formed a consensus. And, like it or not, there is a consensus here too. It is a plurality, not a majority, and it is buried under a lot of noise from misinformation, but it is here. You just have to know what to look for. Obviously I was referring to all the fallacious claims in your post, not to the existence of sunspot cycles. The notion that there is some equal balance between scientists and Nobel laureates who accept anthropogenic climate change and those who reject it is a laughable fantasy. More generally... A few years ago, Enbridge Oil was operating a crude oil pipeline which suffered a catastrophic rupture. Due to a ridiculous amount of corporate stupidity, proper safeguards were not in place and so they continued pumping crude straight out the end of the ruptured pipe and into the Kalamazoo River for over 24 hours before they finally realized what had happened. After a year-long investigation, federal government issued just three sanctions. The first was a 3.5 million dollar fine, the largest ever levied against an onshore oil pipeline operator. The second was a massive, company-wide recertification of all their operating procedures, at a cost nearly equal to the fine. The third was perhaps the simplest: Enbridge was required to shut down their entire system for about three days, long enough to perform pressure testing to ensure there was no chance of a similar rupture in the future. Enbridge paid the fine. Enbridge did the company-wide recertification. No problem. And that third sanction? Enbridge sued the United States to avoid having to shut down their system for three days. Because the fine and the cost of recertification and the cost of a 40-month federal lawsuit was NOTHING compared to the amount of money they would have lost by shutting down their system long enough to test it. And they didn't even own the oil. They were merely being paid to transport it. THAT is how much money is involved in fossil fuels. And that's why I laugh and laugh every time I hear someone claim that there is some secret environmentalist lobby paying scientists to agree with global warming. It is pretty much the most ridiculous thing ever.

As much as I wish that were true, it really isn't. There is very little space stuff that a robot can't do for cheaper. Most of human usefulness in space has been figuring out human presence in space...which is great, and which I totally support, but it doesn't pay for itself. A small-as-possible SSTO crew ferry would be fantastic, don't get me wrong, but I can't figure out a way to make it economically viable. All you need is an engine with a really great TWR and a really low thrust specific fuel consumption. I'll wait.

...said no peer-reviewed scientific study ever.

Too bad. It performed the actual orbital insertion to circularize, so I thought it might have more kick.

Did the OMS have enough thrust to push the Shuttle clear of the launch stack if the tank and SRBs were jettisoned?