KSK

There Aint No Such Thing as a Free Launch?

Okay, that's cool - thanks for the explanation! At the risk of being a terrible old pedant though, it may be worth starting to think of 'mileage' as a series of velocity changes (if you're not doing so already). For example, an Apollo style trip to the Moon required one burn (velocity change) to break out of low Earth orbit, another to enter Lunar orbit, and a third to depart from Lunar orbit and head home. The landings of course required additional velocity changes. In principle, one could make a fourth burn to re-enter Earth orbit and complete the round trip, but Apollo didn't have that capability. A couple of advantages to the above in my opinion. Firstly - it's how everyone else thinks about spacecraft trajectories (or at least, it's better aligned to how everyone else thinks about spacecraft trajectories) so if you're looking stuff up about spaceflight or discussing spaceflight with other people, it's easier to be thinking in terms of 'series of velocity changes' rather than 'mileage' and having to mentally translate between the two all the time. Secondly, if you're writing space science fiction (unless you're going full on fictional physics as per @sevenperforce's post) then talking about velocity changes will sound more authentic than talking about mileage. Personal anecdote. Back in school when I started learning about equations of motion in Physics, it made zero sense to me that distance, or displacement, was denoted by 's' rather than 'd' and all my early notes used 'd' instead. Eventually though, it just got to be too much of a pain to use 'd' when my textbooks and teacher were using 's', so I gave up and went with the standard 's' instead.

Okay then. Busting out my trusty copy of George Dyson's Project Orion (George is the son of Freeman Dyson who worked on Orion), the original design was intended to be capable of a total delta V of 20km/s (round trip to Moon levels of delta-V) with a mass ratio of 1.5:1. Interplanetary versions were designed with total delta-Vs of between 50 and 80 km/s with mass ratios of between 3 and 5. The mass ratio is the mass of the fully fueled (for want of a better word) Orion divided by the mass of the empty Orion. So, a mass ratio of 1.5 implies a vehicle that's about 30% propellant, whereas a mass ratio of 5 implies a vehicle that's about 80% propellant. Compare that to Mini-mag Orion with its 100 km/s delta v and a mass ratio of about 3.3 (66% propellant). That's considerably more efficient than Orion. So yeah, you've got it about right. Assuming that you just point the ship at the nearest star and run the engine till you're out of propellant, you'll end up going faster in a Mini-Mag but it'll take you longer to get to that top speed. Mileage doesn't really mean much in space travel - not as a means of comparing vehicle performance anyway. Simplistically, once you start moving at a given speed, you're not expending propellant to keep moving (like you are in a car), so you can travel as far as you like provided you're not worried about journey time. [Yes, yes, orbital mechanics and all that - I said 'simplistically' .] The main reason you'd build an Orion over a Mini-Mag Orion is if you needed an actual launch vehicle. Orion will get you off the ground, Mini-Mag won't. Also, as you said, you can build Orion on the ground, whereas Mini-Mag would probably need to be assembled on-orbit. Also, you don't need to imagine a scaled up Mini-Mag to compare with Orion - at least not from a performance perspective. The rocket equation deals with ratios, so it doesn't matter whether you're talking about a 100 ton vehicle or a 100,000 ton vehicle - the amount of propellant needed as a fraction of total vehicle mass will just depend on the ISP of the engine. I suppose the payload fraction might be higher with the 100,000 ton vehicle but figuring that out would require knowing a whole lot more about the vehicle design, i.e. does a 100,000 ton Orion require a pusher plate / shock absorber assembly that's 1000 times heavier than that of a 100 ton Orion. My gut says 'probably not' which is why bigger Orion was almost always better, but then my gut knows both jack and squat about aerospace engineering.

Yup. Although the thrust to weight ratio for mini-mag isn't bad. Mass at launch (including full propellant load) is 732 tons, thrust is 642 kN. Pretty good for an engine with an ISP of 9,500 but 0.88 ms-2 acceleration ain't enough to lift off from Earth. [Edit, 0.88 ms-2 not 0.88g as originally posted. Silly KSK - drink coffee first, then try basic arithmetic.] @SpacescifiThe total mission delta-V for that particular version of mini-mag was 100km/s, with a payload of 100 tons. Even with such a high efficiency engine (and 9,500 is getting close to that 10,000 ISP required for an SSTO having 10% fuel that you mentioned earlier), the mini-mag vehicle was still about 2/3 propellant by mass. The rocket equation is unforgiving. Addendum. If my coffee free maths is correct, that's an acceleration of 0.09g which can be sustained for a little over 31 hours. Just to put the idea of a 3g constant acceleration drive into a bit of context.

MiniMag Orion study report. Wayback Machine (archive.org) Uses magnetic compression of tiny fission pellets (see Figure 10) to initiate a fission reaction in those pellets. Magnetic field is created by extremely high current pulses (as in 70 mega amp pulses). Plasma created by the exploding pellets is directed by a magnetic nozzle to generate thrust. Pulsed power unit (essentially a large capacitor bank) is charged between pulses either by tapping the energy released by the pulses or by a steady state power unit (nuclear reactor?) which is used for engine start and to recharge the capacitor bank in the event of pellet misfires or non-fires. The proposed thermal management system was non-trivial, weighing in at about 15.5 tons (see Tables I and II) but is a relatively low percentage of vehicle mass compared to the mass of the pulsed power unit (7 tons), steady state power unit (9 tons) and magnetic nozzle (103 tons) it. So, waste heat is not the limiting factor on acceleration here.

Doping propellant with metal beads sounds like one of those ideas that might be useful in some circumstances but any benefit obtained is probably going to be outweighed by the difficulty of getting the engine to work. My understanding is that the metal will increase thrust at the expense of ISP. For chemical propulsion that’s not a great trade-off - chemical rockets usually have pretty good thrust already but relatively low ISP. This might be useful for ‘changing gear’ on a high ISP / low thrust engine (such as a fusion rocket) where a temporary boost to thrust might be situationally useful and the reduction in ISP is acceptable. However, I can think of a number of drawbacks to metal doped propellant. In no particular order: Keeping the propellant homogenous and avoiding having the beads settle out on the bottom of the propellant tank or any internal tank structures (slosh baffles for example) Wear and tear on the turbopumps. Those things are spinning at ungodly speeds and shot blasting them with metal beads sounds like a quick way to a broken engine. Beads clogging the injector plate and being a general pain to move through the engine plumbing at any sort of speed. Unwanted reactions between propellant and beads although that will be highly dependant on which propellant and which metal you choose. Crudding up the engine with metal deposits. There are probably more issues that I haven’t thought of, not being an actual rocket engineer (or indeed any sort of engineer!)

This an odd thread in that the title is a question but the first post assumes an answer (10%) and then goes on to discuss some of the reasons why that answer is impractical or undesirable. So why the insistence on 10%? This is actually the kind of question that the (and stop me if you've heard this one before) rocket equation can answer very easily. You know the approximate delta-V required and antimatter solid core engines have a specific impulse of around 1000s. Or, more properly, a couple of paper designs for antimatter engines that work in this scenario (sort of reasonable thrust to weight ratio with sufficient shielding to absorb the gamma rays and charged nasties created by antimatter annihilation), have an ISP of about 1000s. Assume a delta-V of 10 km/s, an ISP of 1000s and a wet vehicle mass of 100 metric tons (because round numbers are easy). Plug that lot into the rocket equation and you get a dry vehicle mass of 36 tons. So, from that, I conclude that a likely (for optimistic values of likely) propellant to ship ratio for an SSTO powered by an antimatter-thermal rocket is about 2:1, or 66% propellant. Waste heat should not be a problem since the engine is a solid core engine and has been designed with the melting points of its various components in mind - hence the relatively modest ISP. Lifting figures straight from Atomic Rockets, 11 tons of that dry vehicle mass is engine, and the engine has a thrust-to-weight ratio of 40:1. Thrust to-weight ratio of the fully fueled vehicle is therefore a bit under 4:1, which should be more than enough oomph for requirements. In practice, if I was writing about such a beast, I would probably assume a wet vehicle mass of 200 tons, giving me 72 tons (or roughly 60 tons after the engine has been accounted for), of vehicle and payload to play around with. That would have a thrust-to-weight ratio of about 2:1 off the pad which is still fairly sporty. How much of those 60 tons would need to be set aside for antimatter storage, I have no idea. Incidentally, if you do want an SSTO with 10% fuel, you need an engine with an ISP of about 10,000s. And an engine that can operate at that kind of efficiency with a high enough thrust-to-weight ratio to get off the ground -- is not going to happen outside of fiction. For pretty much the reasons you've already mentioned - waste heat. Atomic Rockets has some hilarious figures for a gas-core antimatter engine. Ignoring the fact that sitting on top of a rocket powered by a ball of tungsten vapor which is being used as an antiproton target is probably a good working definition of insanity, the ISP for the beast is a mere 5000s (so nowhere near what we need for 10% fuel), and it weighs in at 182 tons, about half of which is radiators. Accordingly, it has a miserable thrust to weight ratio of 2.5 x10-2, making it somewhat unsuitable for an SSTO.

This seems like an opportune moment to recommend ‘Ignition’ by John Clark. For those that don’t already know, it’s an informal history of rocket propellants written (mostly) for a lay audience, and covers a pretty good range (I don’t know enough to say ‘all’) of the weird, wonderful and outright what propellant combinations that have been tried. See, for example, his sage words on chlorine trifluoride as quoted in this article. https://www.science.org/content/blog-post/sand-won-t-save-you-time

You would think that giving customers cancer would be bad for business too. Didn't stop the tobacco companies. With sufficient lobbying and FUD spreading, the status quo (and profits) can be maintained in the face of all evidence to the contrary. I expect the same to happen here. Yes, I am a climate change pessimist. Especially after seeing the utter farce that was humanity's attempt at a coordinated global response to the Covid pandemic.

That would be nice but instead I fully expect BP and their ilk to carry on making a fat profit by selling the dwindling amounts of readily available oil at ever increasing prices and then demand subsidies (or just smile and pocket the offered subsidies when they're deemed politically necessary) to start extracting the harder to reach stuff. Sources: current economic circumstances in my country followed by an OPEC decision to reduce extraction to maintain profits, plus the general response to the recent pandemic, which was to make a fast buck from it if at all possible. I have zero faith that anything as abstract as the fall of civilization is going to get a look in over the next quarterly results.

Or have a look online for rocket equation calculators. Apologies for the advert spam but this one looks good. Tsiolkovsky Rocket Equation Calculator • Model Rockets • Online Unit Converters (translatorscafe.com) Dry mass of rocket, wet mass of rocket, specific impulse or exhaust velocity, required velocity change. Input any three and it'll calculate the fourth for you.

Going to LEO first also gives you time to make doubly sure that the spacecraft is in good working order after the climb to orbit before heading out to the moon. Maybe not the issue it was during the Apollo days but still helpful I think, at least for crewed flights.

NASA probably have what you’re looking for somewhere - for the US missions at any rate. It’s not precisely what you asked for but the Apollo flight journals get pretty technical. They’re based on actual communications between the crews and Mission Control, so they include burn details and suchlike. https://history.nasa.gov/afj/ And yeah - I don’t play KSP these days but one of the best things about having played it, is that I can read something like the Apollo flight journals and have a good visual feel for what’s going on, even if the maths behind it all is rather out of reach!

I don't have a dog in this fight since I was already firmly in the 'buy it once the reviews are out' camp and I'm not especially interested in a sandbox only version of KSP2 since I had plenty of 'building cool rockets' already in KSP1. Hence, I'm not particularly likely to pick this up in early access. With all that said - are the developers trying to get review bombed to Eeloo and back on Steam? Because a $50 early access game without any of the major features that've already been trailed is going to get review bombed to Eeloo and back on Steam. And sadly, although most Steam 'reviews' aren't worth the paper they're written on (in my opinion), Steam review scores do seem to have a disproportionate impact on a game launch.

We've thought about getting an instant pot many a time but so far, our three crockpots have refused to break and getting a fourth, similar pot, seems excessive. OK, more excessive. Anyway - we made this a couple of weeks back and it's gone on The List. 1.5 lbs of chicken breasts 16 oz jar of salsa (we've started experimenting with two smaller jars, one smoky or hot, one regular) 15 oz can of black beans 1/2 lb frozen or canned corn 1 tablespoon chilli powder 1/2 tablespoon ground cumin 1/2 teaspoon oregano 1/4 tsp cayenne pepper if you want a bit more kick. We haven't bothered so far. 2 cloves minced garlic black pepper to taste To make. Arrange raw chicken breasts in bottom of crock pot. Drain canned ingredients and pour over top. Throw in everything else. Stir. Cook on low for 8 hours. Turn off crockpot, shred chicken with a fork. Not as fancy (or likely as tasty!) as Biff Stew but it also takes about five minutes to prepare, including rooting around in the cupboards for all the stuff. Serve with - well whatever you like. Rice and green vegetables, tortilla wraps and sour cream, stuff it in a baked potato. It's all good.

Also - and I think this is probably less likely here - it’s relatively easy to slide a magnet along a surface than it is to pull it off that surface. Having the heat shield buckle because the tiles start sliding and riding up over each other at max Q is probably a suboptimal outcome.

Green button. One species (well two if you count the pond scum aftermath of pressing the red button) vs countless millions? That’s an easy choice even if the one species is mine. Get rid of the planet trashing murder hobos and hope something more intelligent evolves next time around. I find it telling that the green goo tastes of chicken.

Why not stick with tradition and go with tulip bulbs?

…expialiadocious. Even though its exotherm is something quite atrocious. Do try not to sneeze near it, or you’ll wind up on Venus… hexanitrohexaazaisowurtzitane… …expialiadocious.

Bill & Ted I and II with my best friend's kids. Luckily, they enjoyed them rather than just rolling their eyes. Then we watched Bill & Ted III as well and... yeah. Two old dudes. Life didn't go the quite the way they figured it would but they're still hanging in there, still friends, still listening to the same music and enjoying the same stuff, even if the long hair is turning a mite grey. Only now with kids in tow. Talk about art mirroring life.

That looks very interesting - cheers! Will give it a go and see if I get along with it. Finished Chapter 7 of Quenta last night. Suspect I'll need to find a map of First Age Middle-earth (and probably re-read whilst making notes) to make more sense of which group of Elves went where and what they've decided to call themselves. Also, Feanor needs a slap. Pity there aren't many around who would dare. Skilled and mighty he may be but he's also one arrogant SOB. Edit: Moving back on topic, I'm thinking that Meteor Man is a new character, probably some other Maiar, and will play a similar role in the Second Age to the one that the Istari did in the Third. He might be Gandalf but if that turns out to be the case, please remind me to take an internet break for a week or two because the commentary will be heading (further) south in a hurry.

Nope - and thank Jeb that I've finally found somebody else who likes it too! I know Lord of the Rings reasonably well but the times I've tried to read the Silmarillion I bounced off it. Rings of Power has inspired me to give it another go. So no, I don't know all the First Age lore, but I do know, for example, how Celebrimbor is likely to fit into all of this. And incidentally, whoever is playing him in RoP has got the character down cold in my opinion. The Celebrimbor we see on screen seems like exactly the kind of person that would... well do the stuff he does in the source material. For that matter, I can totally see RoP's Elendil going on to do what he does in the source material. I thought the sets and CGI for Numenor were great. Very much their own thing but tying in nicely (aesthetically speaking) to Minas Tirith from the Peter Jackson films. Which makes sense of course but it didn't have to be that way and it's nice that it was. I liked the way the Harfoot storyline progressed in Part III. And yes, I thought it was entirely consistent with the 'everyone stays on the track, nobody gets left behind' mantra from the previous parts. I liked the reason why Durin was so salty in Part II and watching Elrond come to terms with that reason and apologise. I'm quite comfortable with RoP being an adaptation given the length of time that's passed since the source material was written and the amount that society has changed since then. Besides: "Yet some things there are that they cannot see, neither alone nor taking counsel together; for to none but himself has Iluvatar revealed all that he has in store, and in every age there come forth things that are new and have no foretelling, for they do not proceed from the past." If it's good enough for the Ainur, it's good enough for me. Thanks for the opportunity to enthuse about the show, folks. The wider internet has been distinctly depressing in that regard so far.

Apologies for the messed up formatting - this site isn’t the easiest on mobile devices. Serious question though - assuming that a market for point-to-point human transport by rocket does open up - why bother going orbital? I’d have thought that a series of sub-orbital hops be easier? At first sight it would be a lot less operationally challenging in terms of vehicle design, be a lot more forgiving in terms of vehicle dry mass, and probably be safer because your vehicle (and passengers) don’t have to re-enter from orbital speeds on every journey. The decline (and failure to rebuild) of supersonic air travel is a pretty good indicator that there’s not a big enough market for ‘need to be there right this hour’ passengers to justify the costs. By analogy, I’m not convinced that there would be enough demand for true ‘anywhere to anywhere in one hop’ travel to justify an orbital point-to-point service.

Carefully.

Yeah, it was the Civil War subs that I was thinking of, which seemed like deathtraps on a good day. I read a very interesting book (by Rachel Lance - it's referenced in the Wikipedia article) about the Hunley which succeeded in its mission but the crew died under mysterious circumstances, still at their posts with no obvious sign of panic or distress. Lance made the case in her book that they were killed by blast trauma from the torpedo detonation. I think the book referred to a couple of times where torpedo ramming did work but I'd have to re-read it to be sure. In any case, it's a pretty good warts-and-all popular science version of her investigation - can recommend if you're interested in such things.