RCgothic

Soft docking becomes more reasonable in orbits with longer periods or in deep space. Around Earth, Mars or Lunar low orbits it's probably not advisable.

The issue with a flexible connection is that unless the two are hard-docked, station keeping becomes extremely challenging, particularly whilst exchanging large quantities of fuel. Unless the centres of masses of the two vehicles are exactly along and remain exactly along prograde/retrograde, the two vehicles will effectively want to exchange altitudes over the course of an orbit. Plus one vehicle passing fuel aft will want to accelerate and gain altitude, and the one receiving will want to decelerate and lose altitude. Hard docking seems necessary IMO.

Those people were mostly National Team wilfully misrepresenting the process. There just one docking between the mission ship and the depot when it's ready, and every other HLS system required at least some on orbit assembly too.

XKCD WhatIf also covers gas-giant submarines: https://what-if.xkcd.com/138/ Although it doesn't specifically combine the two, I'm not sure what adding a submarine hull gets you. The craft can stand a higher density/pressure so needs less wing, but it's much heavier, so it needs much more wing, and it's flying at a much hotter level, which requires exotic cooling, which requires more wing and more power. My gut feel is that this isn't a net gain. Do not exceed depth for a modern submarine (~300m >30bar) isn't even 200km below the 1bar level (at 71.5k km radius). I'm not sure a submarine hull changes the basic conclusions.

The cargo Starship would be able to carry a substantial solid or hypergolic 3rd stage without too much issue. This 3rd stage plus payload could weigh up to 150t or so whilst fully reusing Starship Alternatively, an expendable-variant Starship could arrive in LEO with about 265t of payload/fuel. The expendable Starship would then manage about 6km/s for a 12t payload. If Superheavy was expended as well, that'd be about 525t of payload and fuel. That's about 6km/s to a 52t payload. Of course both of these beg the question - why not just do a couple of refilling flights and save the cost of expending anything at all? With a top up in LEO starship can shoot a JWST-sized object through 4.2km/s and still propulsively return. There are use cases where the Starship itself can be counted as part of the payload. Depot starship for instance. It's effectively an expendable starship mission (although reused in orbit). Counting both hull and fuel, that's ~300t of payload to a useful parking orbit. Ditto Lunar Starship. All of that can be counted as useful payload to LEO.

If that depot starship (propellant aggregator, lol. They still can't say depot) is scaled correctly that launch stack would be over 130m tall!

The airlock picture has been identified as the interior of the NT lander, oops lol.

The universe is likely to be infinite in the same way the surface of a balloon is infinite, except with additional dimensions.

Imagine if Elon was your boss. "What's taking so long?" "Well it takes a fortnight just to retract the platforms." "ಠ_ಠ"

It's not possible to fly on a gas giant for very long. It takes roughly 3x the power to maintain level flight. There's no way to turn bouyancy to your advantage without enormous heating power expenditure. There's no way to refuel. It takes way too much DV to escape to even a low orbit. When out of fuel the vessel will sink and be crushed. At any level that flight is possible gravity will be uncomfortable to intolerable to crew. Only nuclear powered craft would have any endurance in a gas giant's atmosphere and even they would eventually succumb.

Also, in an infinite universe, technically every single point of the sky is occupied by a star. It's just that some points of the universe are further away than the age of the universe in light-years, so the light hasn't reached us. And since most of the universe is expanding away from us faster than the speed of light it never will. If the cosmic speed limit is eliminated, now the sky will be completely full of star. Being completely surrounded by star is thermodynamically equivalent to being within a star. The entire universe will be at the temperature of stars. Which as has already been mentioned, will all be going supernova with infinite energy. So infinitely hot stars. And because c is infinite, the mass of matter will not increase with speed. Which means that it can also be accelerated to infinite speed. Which means all the matter in the universe will gain infinite energy, be accelerated to infinite speed, and then blasted through every point in the universe simultaneously. So yeah, this is a very very big bang scenario.

Direct from Astra: Interesting read.

Graphite cores are very very not cheap. They're comparatively huge, requiring vastly more massive shielding and much deeper foundations. The AGR fuel handling arrangements are also vastly more complicated and expensive. For graphite cores it takes hundreds of tonnes of mobile shielded connectable pressure vessels. And multiple specialised grabs for handling standpipe shield plugs. Plus because the fuel assemblies are so physically huge they have to be disassembled on site whilst screamingly radioactive so as to be storeable. PWRs just flood the reactor head, unbolt the whole thing, and transfer the spent fuel whole to their storage cannisters using a comparatively simple bridge crane. There's a reason nobody builds graphite cores like this anymore, and the #1 reason is cost. PWRs are much cheaper. Yes, they allow access to unspent fuel for plutonium. Yes, they use comparatively low-enriched uranium which is also better for generating plutonium. These designs were developed out of military reactors which were designed to do just that. But the AGRs, and the Magnoxes apart from early Chapelcross and Calder Hall didn't. Can't speak for the RMBKs. These graphite reactors were theoretically cheaper than PWRs in operation, but weren't. I suspect you may be conflating the apocryphal "RMBK control rods were tipped with graphite tips because it was cheaper" with the cores themselves being cheaper. RMBK control rods weren't tipped with graphite because it was cheap. They were tipped with moderator because you *want* the reaction to increase when you withdraw the control rods. Otherwise the voids would have been filled with water, which is like replacing control rod with more control rod. The mistake (which may have been for cost reasons) was to not have the graphite tips extend to the bottom of the reactor core. Therefore *locally* the cores experienced an increase in reaction at the bottom of the core when the rods were inserted. But they're were graphite tipped for a sensible reason.

It's the combination of graphite moderator with water that's the problem (although that's extremely power dense, which may be desirable in a space reactor) - graphite moderated gas-cooled cores like AGR and Magnox don't have positive void coefficients. The reasons we don't build gas-cooled graphite moderated reactors anymore are: 1) They're physically big and therefore comparatively expensive to build 2) Although graphite absorbs fewer neutrons allowing lower enriched uranium to be used, the cost of enriched uranium fell. 3) Although being physically bigger permits refuelling options without opening the reactor and therefore in theory zero downtime (making up for point 1), in practice this couldn't be made to work.

I don't think it's true that the mere fact of boiling water is a problem in microgravity. With *forced* flow the loop will keep moving as usual. Pressure gradients still function. What doesn't work is bouyancy-dependent steam separators (which can be redesigned - centrifugal), and using convection (a bouyancy effect) to assist the flow - 100% of the effort needs to be pumped.

Not sure why you want to use an RMBK specifically, but the main problem with reactors in space is the cooling issue as has been mentioned. Vast, fragile radiators to carry away waste heat. An ideal black body would carry away something on the order of 2000W/m2 at the reactor exhaust temperatures. An RMBK 1500 has about 4.8MW thermal power and produces 1.5MW electrical power, so must reject 3.3MW. Double sided that would take ~850m2 of radiators (33mx25m). Probably twice that once accounting for grey bodies. Of course you can use a heat pump to concentrate the heat to improve the radiator power density at the cost of extra energy consumption. Anything that uses steam separators in the reactor would need a redesign, and additional pumping effort will be required to overcome the lack of convection assistance. The UK's AGR primary circuit would probably still function with extra pumping effort because the coolant is already a gas and so there are no phase changes to get messed up by lack of bouyancy. The normal metres thick biological shield (concrete) on earth based reactors would be an extremely effective debris shield, but I'm not sure concrete is a great material for space. I think it outgasses and decays under UV, plus launching the thousands of tonnes would be a challenge. A directional shield to any crew compartments would be fast more effective, with a thinner shielding and physical clearance being counted on for protection in other directions. You'd also want some sort of whipple shield for protection of the reactor itself.

No.

43/93 block 5 flights have been completed by just 4 boosters. All 4 now on 10 or 11 flights each.

I don't think that looks salvageable TBH.

UK minister confirms there will be no negotiation on this point: Roscosmos aren't launching any more OneWeb sats.

The main thing the Russian section provides is propulsion. This is needed for 1)Reboosts and 2) Desaturating the attitude control gyros. 1) Can now be done by Cygnus and potentially soon Starliner (and I wouldn't put it past SpaceX to be able to rig a re-boost module for the trunk pretty quick). 2) Could in theory be done by careful coordination of docked craft, or by one craft docked in the right place, but the development required for this hasn't yet been done AFAIK.

We've been discussing this in this thread: Where I think there are clearer images, but I hadn't seen this satellite view before.

It's not possible to transport Starship or Superheavy to the cape from Boca by road. F9 is basically the biggest road-transportable rocket in the US. It's also not clear SS/SH can be horizontally transported. Transporting SS/SH by barge would also likely be prohibitive in this case. The remaining options are fly there, with overflight of Florida (not happening any time soon), or build locally, which it looks like they're planning.

SLS *may* still be the way to get crew back to the moon at the earliest, but this certainly isn't sustainable. There are existing heavy lift rockets capable of assembling an EOR mission for a fraction of the price. There are no long poles for a crewed expendable Superheavy mission, and it's looking somewhere in the region of 3x as capable as SaturnV for a marginal cost in the region of Falcon Heavy. With a little bit of waiting, Starship plus full reuse plus refilling blows all of these options away. There really is no need to keep spending vast sums on SLS. With HLS for the marginal price of a single SLS launch we're getting *two* lunar landings, one of which crewed, development price included. Just add LEO taxi.

Roscosmos will refuse to launch OneWeb unless assured OneWeb will not also be used for military purposes. I doubt this assurance can be given, so the OneWeb contract with Roscosmos is effectively dead.