RCgothic

It's impossible to take a 2028 crewed mission date seriously and no tears will be shed when it's missed. They might possibly still launch an uncrewed flyby that year. It's possible Zubrin is being disingenuous by conflating those.

Would definitely love to hear the story of the astronauts on the other side of the short vacuum gap during Starliner's docking approach. Was anyone on the ISS even in the loop as events progressed? If Starliner had totally lost control, would one of the Dragons been sent on a rescue excursion? Or would Butch and Suni have just been left to drift off to their fate? What could they have actually done?

So about 1010 MeV is actually recoverable from the initial 1880MeV, (about 54%) and then in the form of heat we can turn that into electricity at about 40% efficiency with a steam cycle, for just over 20% of the initial input. Antimatter is a really inefficient storage medium, but it's so powerful and energy dense that you probably don't care about inefficient conversion factors. (Although be sure to vent byproduct heat somewhere or you'll need to start caring quick!) I think I've already hinted at the huge inefficiency in getting to antimatter in the first place, so yeah, lose a lot of energy both ways.

Mind a little bit blown by the idea of Protonium, Positronium, and Muonium, but on looking them up they're all super-unstable and decay by annihilation within a hundredth of a second of production.

Anti-hydrogen would love to escape containment in much the same way that hydrogen does, and neutral materials couldn't be compelled to remain separate from matter, so whatever it was would need to have a charge of some sort. I went down a bit of a rabbit hole of suggesting using a plasma of anti-Beryllium or anti-Flourine. They both only have one stable isotope and are significantly more massive than hydrogen, which simplifies the plasma dynamics. But plasma containments remain horrendously leaky in the grand scale of things, and Anti-Be and Anti-F are both very hard to fabricate from anti-H: I believe Be is primarily made from spalling a larger element with cosmic rays, and Flourine needs a rare branch of supernova fusion. So back to the drawing board! No Plasma. We use solid anti-carbon in diamond form for it's vacuum stability, and we then give it a charge and suspend it electrically in a vacuum. Safe, vacuum-stable antimatter storage! Power would be extracted by bombarding the solid antimatter with a matter beam. This would probably top up the charge as well, as the matter beam would need to be charged. Carbon can be formed from 3 helium atoms fused in short succession before the intermediate Beryllium 8 has time to realise it's unstable and decay. It's a very not easy process and we are nowhere near being able to do that ourselves, but it's necessary if we want anything solid with decent vacuum stability. A civilisation capable of fusing to anti-carbon would need to have significant energy abundancy, and would probably only use this process for extremely demanding applications, such as interstellar travel.

Burning Earth doesn't necessarily end the solar system's habitability. Parts could remain habitable as the sun expanded, so the deadline for getting out might be on the order of 4.5 billion years. The Andromeda collision is also in about 4.5 billion years. The nearest supernova candidate is IK Pegasi at 150 light years. Apparently type 1A supernovas are particularly violent, and I is likely to be one of those. Could occur in the next billion, they're unpredictable as depends on the rate of matter consumption from the companion star. The closest major stellar nursery is the Orion Nebula at about 1350 light years away. The absolute closest is the Rho Ophiuchi Cloud Complex at approx 450 light years, about 100 times further away than Alpha Centauri.

If talking "before the sun burns out" timescales, it's also worth considering "before the stars around us burn out" as well. Where's the nearest stellar nursery? Might also be worth considering "before Andromeda hits us" as well

Whilst the F-35 may or may not have a physical kill switch in it, the lack of operational independence in testing, spares and updates, combined with perceived reduced reliability of the US has an ally, has US foreign partners concerned. There's a good chance that concern rubs off on foreign orders of the F-47. As a result it's likely to face stiff competition in foreign air forces from the British/Italian/Japanese GCAS and Spanish/German/French FCAS, even if those systems can't match the effectiveness of the F-47 in a straight-up comparison, operational independence from the US could be a major selling point. Also, the F-47 is from Boeing. Concerns over whether it will achieve its objectives are probably not unfounded.

No we wouldn't have single launch crewed missions to Moon/Mars now because the crew spacecraft doesn't exist, and still wouldn't exist even if there'd been prior intent.

Hip size need not be a limit. It is in humans, but we're taking about aliens where the birth canal needs not pass through the pelvis, or the pelvis could have evolved more sensibly. For a hard shell, passage through a human-like birth canal would restrict the max size of brain at hatching compared to at birth. Baby heads squish, hard shells do not. Even if the brain is not developed at the time of laying, it'd develop under the constraints of a shell that needs to pass the birth canal. Soft shell eggs could potentially change shape/relax shape after laying though to accommodate a larger brain than could be passed through a birth canal. The brain wouldn't have developed at that point, and a shell would potentially be able to accommodate a greater degree of squish. Births might even be comparable easy, laying a long thin egg that adopts a more spherical profile once passed. However, everything the baby needs for development would need to be in the egg, whereas in utero they can be continuously supplied with what they need by the mother. So an egg may need to be comparatively large to fuel that growth compared to a baby. From what I can look up, chicken eggs convert egg mass into baby mass at an efficiency of somewhere between 60-80%. So an equivalently heavy egg could be expected to produce a comparatively small baby. However, a lot of the mass loss is through evaporation, so potentially eggs laid in water might better retain water mass in the baby. So there are potentially a few interesting differences there. In terms of gender ratios at birth, egg-laying species can exhibit much greater disparities than mammals*. The effects of temperature on egg-laying species can be hugely influential, with clutches ranging from 100% male to 100% female depending. The body condition of the mother can also have a strong influence - between 25% to 87% daughters in peafowl. (*Pygmy hippos in captivity are mammals with a distorted female:male birth ratio of up to approx 3:2. Apparently the male can control the ratio of X:Y in their gametes to a degree.)

Radiation poisoning effectively scrambles the biological programming of living cells, together with other assorted micro-damages. The level of medical technology required to repair acute radiation poisoning after the fact is very, very high indeed. Today's treatments effectively involve palliative care (which is problematic because morphine side effects exacerbate a lot of the symptoms of ARS) and hoping there's enough cellular machinery intact that the patient can pull through. A fatal dose is a fatal dose. To avert that would require the ability to detect and repair a significant majority of every molecular defect present within the patient. That's so far beyond our current understanding it's not even funny.

With Gamma you might decide you don't need to defeat the armour. Just kill the crew. The amount of shielding required for protection from penetrating radiation would be prohibitive on all but the largest capital ships (good ol' square cube law). Unfortunately such a capital ship would then be vulnerable to hypervelocity mass drivers. Too big and heavy to dodge. Unfortunately gamma kills crew slowly over a period of weeks. A brief encounter could leave both ships intact but with both crews fated to an unpleasant death.

I think we still can't rule out that they collided the engine bell with the mating cone. I think there's also a mechanism where formally extremely competent people can become incompetent. Catching superheavy, the cadence and price point wins of F9, and the Starlink constellation deployment are all staggering engineering achievements. But it's also true that something may have come a bit loose at the top of the chain recently.

Those powers are not equal because equal power will not produce equal cutting of steel at different wavelengths. Gamma would probably pass through the 0.5in steel without significant heating. Radio would probably reflect harmlessly.

My puzzle is that an engine would need to run LOX rich for quite a while to fall catastrophically. Surely they could just... turn the engine off? Which begs the question why didn't they? Also whilst it's probably worth trying, low lox levels in the tank for a static fire probably wouldn't be sufficient to replicate the long duration and high G environment that may be causing harmonic vibration issues in flight in the ground.

It hadn't occurred to me that too much power could be an issue!

Did Peter Beck ever say anything about eating his hat if RL ever used Marine Assets?

I went and looked it up. NRHO isn't *that* long a period, at about 6.5 days. So your nominal stay is at least that long, generally multiples thereof. Then the worst case abort is 4 days depending on orbiting element phasing. So the lander needs at least a week's endurance, or more likely 2 weeks. That's a lot more than the Apollo LM. Ref: https://engineering.purdue.edu/people/kathleen.howell.1/Publications/Conferences/2018_AAS_WhiDavBurMcCPowMcGHow.pdf

Inclination is only one part of the equation. With long-period orbits like NRHO correcting the phase angle to achieve a rendezvous without an unreasonable starting DV can then take weeks.

No, because if the distance is fixed at the same for each, then the plane is no longer making up for being more dangerous per trip by going further. As Tomf mentioned earlier, the risks of flying are concentrated around landing and take off. It's not much less risky to cut down the cruise phase, which is statistically the safest bit of the flight. And actually, short-haul aircraft are smaller, more vulnerable to sudden cross-winds and vortex interference, undergo more frequent landing, take-off, temperature and pressure cycling, and are less well maintained on average. Trains easily come out on top over short distances. Edit: Although now that I'm following that logic in the opposite direction, I suppose there might be a distance over which trains become less safe. Every section of track and every set of points crossed is a potential accident. So extending the trip linearly increases the risk of a train journey, whereas a plane is safely in cruise mode.

Trains are safer in terms of fatalities per trip. Planes are safer in fatalities per mile. The difference is that planes traverse vastly larger distances on each trip than the typical train journey. If you could make the same trip by either mode of transport, trains would be the safer option.

Pretty sure there *are* blast shields between each engine. That's what the black cylinders around each engine are.

Booster engine missed ignitions: Flight 7: Engine to the left of bottom dead centre engine in the ring of 10 on the diagram. Flight 8: 2 engines to the right of bottom dead centre engine in the ring of 10 on the diagram. Engine that didn't restart was the one immediately to the right of the bottom engine. I believe the diagrams are arranged "belly" side down. So engines at the bottom of the diagram would be earth-facing for a pitch up manoeuvre, if that's the direction it goes.

No way did an external fire burn a concentrated hole in an engine nozzle. I could see a leak from a damaged nozzle leading to entrained flames that appear like an engine bay fire as it gets worse. Two engine bell failures is surely an external cause

If Blue Origin ends up lapping SpaceX, cool. That'd be showing a bit less graditem and a bit more ferociter, and progress is progress no matter who makes it. I don't think think that's imminent though. They didn't land, let alone catch, their (smaller) booster, and the second stage they left in orbit caused a high orbit debris event shortly thereafter. At least SpaceX is working out their issues before contributing to Kessler. That said, V2's record is now 0/2 and Booster again didn't light engines for Boostback, one of which stayed off this time, so there clearly are problems that need to be worked out. I remain sceptical the problems are localised to the engines, I think it's more likely to be overall system integration and flight dynamics being uncooperative. That RVac could be solely at fault this time, definitely. It just strikes me as a little weird it looks like a bell extension failure. Bell extensions aren't exactly novel and SpaceX have heaps of experience with them. There must have been some sort of impact event. I think the booster engine-outs were on the same side as last time, so those might have been rotation related maybe? Impressive it made it back to a successful catch with multiple missed engine ignitions.