Terwin

Wikipedia says the burn-time of f-9 first-stage using FT engines is 162 seconds. Even just a quick visual inspection of the engines of a Falcon 9 would mean maintenance time > run time. So if each first stage took less than 1 hour of inspections/repairs per launch, it would still be getting maintenance > 2x the total burn time of the engines, something that would likely put most airlines out of business. (9*162 / 60 = 24.3 minutes of total burn time per launch. May not include <1m for landing burn)) If SH takes 2 hours from landing to launch, it could still average > 10x maintenance time per flight-hour. (F9 takes just less than 10 minutes from launch to landing for RTLS) I do not see much value in taking SH maintenance down to even a 1:1 ratio of flight time to maintenance time, as the falcon 9 needs >30 minutes to load fuel, and I would not expect SH to be faster than that. (As refueling is often counted as maintenance, taking SH down below 10:1 maintenance time:flight time might well be impossible even if the only maintenance is refueling)

Mechanical power from water is easy and is more than 5000 years old, so that will clearly be a thing very quickly. Mechanical wind power is almost 3000 years old, both less concentrated and less reliable, but still pretty useful and should be back fairly quickly. Turning either of those into electric power mostly requires magnets and wire, so intermittent local power(like a flour-mill that doubles as a battery charger) should be reasonably common, but if it gets set up by someone with limited understanding of electric theory(such as myself) such a charger is likely to damage the batteries with every charge. Fortunately, batteries are more than 200 years old, so if you have copper and zinc, you can turn those into electrical power as well. Unfortunately, oil is of limited use without refineries, and refineries would be a primary target(tanks run poorly without fuel after all), so only chemists would be able to run vehicles until new refineries were produces(I think fractional distillation can provide something functional, but I would expect it to be hard on any engine that uses it) Straight crude could be burned as fuel, but would generally be inferior to coal, as liquids are harder to store and handle than solids. Wood would likely be superior to both where it is available, as it is much less likely to produce hazardous fumes when burned. So long as fuel reserves held out, food production would be in good shape, but would go down dramatically once farmers run out of diesel. Food processing would likely have issue before that however. Fortunately, it looks like almost all of the population is is major cities(86% in cities of 50k+ in 2020 for the US), so a drop in food production is probably not as critical as it would otherwise be. There would probably be at least a decade of 'everyone is a farmer' with the related loss of population to starvation before we stabilized and started growing again. Assuming no one was in a position where they could take advantage of our weakened state to invade.

Mars can be as little as 34 million miles or as much as 250 million miles. When on the other side of the sun, mars is more than 7x the distance from Earth as when it is close, and when it is close, there is no need to detour around the sun, making it even further. No matter what sort of transfer you make, multiplying the distance by more than 7 has a major impact on if the transfer is even possible, not to mention the time increase.(There are many parts of the orbit where waiting to launch will make you arrive earlier)

If you can ignore gravity and have a vacuum -only drive, why not just throw on a propeller? Either the prop is enough to accelerate you or you can use your vacuum drive. It can even be an electric prop so you only need fuel for the vacc drive.(You could throw it inside a shell for protection, but just making it retractable would likely be better)

I was thinking that mars and the moon would primarily start as retirement communities, with support personnel, etc. The lower gravity should reduce strain on the body and allow for more autonomy for people too weak to get out of bed on earth. Might even allow for better longevity as it would reduce the minimal functional strength of bones joints and muscles(including the heart). Sure such individuals would need to be in a liquid bath for launch and possibly landing, but they would have the funds and low concern about long-term viability needed for such an endeavor. The colony would be the laborers and heath workers supporting the retirees.

Looks like the plan is for Starship V3 to have a capacity of 200t to orbit. Why would NASA be worried about an early prototype not being as capable as the expected delivered rocket? Especially when the delivery plan provides greater performance than was initially expected? Did you also expect NASA to complain when grasshopper never made orbit?

You need incredibly good precision to manage replaceable parts. One person would likely spend their entire life just working through the steps to get to a precision where things like interchangeable parts could actually work, and that assumes access to materials that the romans never made use of(and thus may not have had access to). There are many things that took one or more life-times of refinement to get things to a point where other things could be done. Measuring precision(length, weight and volume, each taking a great deal of effort), materials purity(each material needing lots of effort, and often other highly pure materials needed as reagents) I would expect that an immortal with unlimited modern knowledge and authority that went to the 1st century Roman empire could manage to double or triple the rate of advancement, even cutting out a few hundred years of non-progress during the dark ages if they had unlimited food/no need to eat as well. I'm not sure if preventing or encouraging wars would be more beneficial to that advancement, but the wrong choice would obviously cause set-backs. Unlimited authority and immortality would both be needed or else someone would kill or imprison you in the first few months because you were trying to do something that would annoy someone ruthless/powerful.

I believe you need to use an engineer to 'perform maintenance' to transfer fuel from a nuclear fuel container into a reactor and transfer depleted fuel from a reactor to a nuclear waste container. Automatic maintenance can also perform this function(but I think the engineer is still needed)

Considering the speed of bureaucracy, this might well be a prompt response to IFT-1

Anywhere you transition from flesh to bone/chitin is a possible vector of infection. Much like our gums need regular maintenance to avoid infections that lead to tooth loss, even though they are in an environment that is hostile to most microbes. Why make the hands out of chitin? Also, a small tube on the back of the arm should be less prone to clogging/obstruction(sort of like a urethra and just as prone to infection if not kept clean). 70' seems unlikely, even 20' seemed pretty optimistic and you still need to hit the same spot with both squirts, so anything more than 5-10' is probably useless unless a majority of an individuals caloric intake is dedicated to producing the liquids along with a large internal reservoir to build up enough to have a decent chance to hit farther away. (How far away can you spit and hit a quarter laying on the ground, consistently enough to be useful when you only get 1 try per day? Now try the same trick with your urethra, but you only get 0.5-1ml per day and you need to hit the same quarter-sized patch with both arms. A palm-vent would be even worse as even finger-placenent would affect the stream direction.) Also, humans are expert throwers, so don't pretend your theoretical species is just really better at rage, as humans are already fairly optimized at that. Tldr; a bi-reactant biological ranged weapon, even if feasible to make, would be terrible to use and probably not have a greater useful range than an extendable club/baton or a baseball bat.

If the compression wave hit the entire surface at the same time, that seems like it would make the impact have a shorter, sharper duration. Considering that you are already needing a shock-absorber, that does not seem like a good change. If the explosion is off center, having curved surfaces could also introduce lateral jiggle, potentially causing severe wear or even destruction of the shock-absorbing mechanic. A flat surface where all forces striking and rebounding from it should only push you froward seems like a safer bet. On the other hand, if you are close enough that you could cover a larger proportion of the shock-wave with less material by curving it, then it may be worth the extra engineering.

That is called burning and it turns the diamond into CO2. Once the diamond is lit, it can keep burning even at very low temps, even submerged in liquid O2. Methane is great because it is 40% 25% hydrogen by weight. (Water is only 20% 11% hydrogen by weight)(Forgot neutrons) Pure hydrogen is much better for the isp but ts very low density and hard to handle . Adding anything to it just before burning can only hurt isp.

The storage requirements for metallic hydrogen make it a non-starter for rockets. 90% of your launch mas would be fuel tank, limiting you to short, low-velocity hops. There was a theory that metallic hydrogen had a metastable island that could make it almost shelf-storable and remove that constraint, but it did not work when tested. Methane is used because it is a much more dense and easier to handle holder of hydrogen. It would be silly to turn hydrogen into methane for rocket fuel unless you planned to store it for a while. Diamond melts around 4500c and hydrogen evaporates at -253c, so you are not combining those in any direct way. Metallic hydrogen converting to hydrogen gas(H2) releases much more energy than burning it does, and leaves you with pure hydrogen reaction mass, giving a theoretical isp of 1700. Adding anything to it will only reduce that number.

Well, depending on you definition, might have been Ikaros in May of 2010(first solar sail)

Unless you are shipping tons of rare resources off-world, you cannot 'run out of' resources, you can run out of conveniently available or cost-effective to harvest resources, but you cannot run out of the resources themselves. (Volatiles like oil may need to be reconstituted, but that is still an option) Worst case scenario is resources are more or less evenly distributed and we need to harvest them similar to how we harvest 'rate earth minerals' now(they are not rare, they just do not occur in usefully concentrated forms)

In capitalism Entrepreneurs create jobs. More entrepreneurs = more jobs. So long as there is enough capital made available to entrepreneurs, there is no limit to the number of potential jobs. Also, productive labor produces capital, allowing for the exponential growth of wealth we have seen in the last few hundred years. From 1ad to 1000 ad, india' gdp per capita stayed arout $450(1990's dollars), while china grew from $450 to $466. Roman Italy was ~$800 in 1ad By 1500ad India grew to $550, and china to $600, with Italy still at the top with $1100(this was the Renaissance with Michelangelo and da Vinci) In 1750, 1st world gnp per cap was $804(still 1990 $), but by 1990 that ballooned to 15,413. A 10x increase over ~250 years when the prior wealth levels had been stable for ~1700 years. I attribute this growth to the growth of industry, ie capitol. Population was also only growing very slowly. 190M in 200ad, 275M in 1000ad, 610M in 1700ad, 1B in 1804, 2B in 1927, 3B in 1960, etc More people means more jobs and more wealth per person(on average) because people performing productive work creates wealth. Not to mention that someone living in public housing today has luxuries that were simply unavailable, even to kings, a few hundred years ago.

While it may make sense to supplement the heating with microwaves if your nozzle can handle higher temps than your reactor, converting from heat to electricity to microwaves to heat cannot be as efficient as just conducting the heat directly. So heating up your reaction mass to the reactor temp while simultaneously using it to cool the reactor is much more efficient.

It makes sense that being much closer to success would mean fewer things to address, and as there was no real additional hazard area for this flight, the faa is probably not terribly concerned about the mishap, so long as there is a plan to do better.

Straight lines are used because they are easier to draw and visualize. Actually the lense will bend all light that hits it. This is part of why you generally have camera lenses in an opaque black tube: to minimize extraneous light that could interfere or obscure part or all of the image . Much like friction-less inclines, those lines are a simplification to provide a clearer explanation, not a fully accurate reflection of reality.

I had hoped that following the flight path all the way to the end might not count as a mishap, but at least the additional hazard should be close to zero. I expect that most of the mitigation is to improve control, which SpaceX wants to do anyway.

Not at all, a rocket is a controlled conflagration(just like a lighter, gas stove, gas water heater, fire place, coal power plant, etc.). There is research into continuous detonation engines, but it is very difficult to maintain the continuous detonation(but would greatly increase ISP) The reaction mass carries away the heat, and generating the heat to heat up the reaction mass is the entire reason you have the antimatter on board, this is a benefit, not a cost. Orion has much more of a heat problem than a rocket because the pusher plate absorbs some of the heat and you have no productive way to get rid of that heat, more over, the further you get form the explosion(and the heat) the worse you thrust and isp get. The best option to manage for the heat for Orion that I have seen is to coat your pusher pate with some sort of liquid, cutting down on how much of your pusher plate gets vaporized with each bomb, but this is only a partial option as running the Orion continuously will still heat up the plate until it finally gets soft enough to get splattered by the next bomb. Nope, Unless you are using some sub-optimal configuration to avoid destroying your launch mount, you always use the same bomb, the largest you can safely use for propulsion. This maximum safe size may go down as your pusher plate gets eroded, but it will never go up. (moving the bomb further away has the same effect as using a smaller bomb, so using a larger bomb further away just wastes materials) Sort of, as you will have the non-charged particles wearing away at your nozzle hardware, giving you the life-span limitations of Orion, combined with the massive energy requirements of an ion engine because you need to generate the magnetic fields to push away the charged particles(but much less efficient than an ion engine because the particles are much further way from the field), giving you the combined draw-backs of Orion and ion engines.

I would appreciate you explaining the physics of this to me, because everything I know about rocketry says that antimatter pulse is stupidly wasteful and inefficient compared to thermal antimatter rocketry, for both ISP and TWR. Are you assuming that pulse propulsion does not need reaction mass? Nuclear pulse requires a tungsten plug to work as the reaction mass that hits the pusher-plate, and antimatter pulse would also require a large amount of reaction mass to throw against the pusher-plate, much of which would miss and be wasted, along with > 90% of the energy in the antimatter explosion, much like nuclear pulse. The only difference is that a nuculear pulse is ~ 1,000,000 times as energy dense as chemical reactions, letting you get 100 times the push with only 0.1% of the efficiency. (antimatter pulse does *not* have this advantage over antimatter thermal, because they both have the same energy density)

Um, no. Consider a regeneratively cooled rocket nozzle. It is able to withstand great temperatures and a lot of well-controlled pressure coming in an easy to predict way. Now design something that can withstand highly variable temperatures and pressures with the ability to change rapidly, both in intensity and direction, with much tighter weight restrictions because it can only harness a fraction of the energy it is being battered with, as most of it is pushing the wrong way. Note: temperatures and pressures can get much higher than the nozzle interacts with. You are suggesting that it is easier to design and build a mobile structure to resist tornadoes than it is to build a stationary, reinforced wind-break that only needs to survive 1% of the wind-speed of a tornado, from one direction. For the same energy release, a rocket is always better than external combustion. Always. Thermal antimatter will always be more efficient in both TWR and ISP than any sort of external combustion antimatter. * If your materials can withstand a temperature of X, then running your thermal antimatter at (x-safety margin) will always equal or beat being far enough away form an explosion so that it cools down to (x-safety margin) as you will, at best, get the same result, but only by benefitting from a small fraction of your fuel and reaction mass. * Anything you can do to get a better result from your am-pusher plate, can also be done to get the same benefits(or more) in a thermal rocket. * A rocket gets to benefit from roughly 100% of the pressure from the heated reaction mass, while any sort of pusher-plate will, at best, get less than half of the pressure from an external combustion event(because to get any more, it would need to be inside your reaction chamber, even 50% would require half of the event be inside of a chamber of some sort, but much of that would be laterally focused and thus lost), usually only a small fraction of 1% because being any closer means your vessel gets vaporized by the explosion if you make it large enough to be a useful external reaction.

It seems reasonable that SpaceX may include starlinks as payload on attempts 4+ They may wait until 5, but loading 4 seems plausible

External combustion is the *least* efficient option. Not even modern trains use external combustion any more. External combustion is only viable if there is no other option. Thermal antimatter is entirely doable as a rocket, so external antimatter reactions can never be within an order of magnitude of the most efficient option. Not unless we learn something that would re-write every physics textbook from jr high on up