billkerbinsky

It's still under construction. Follow the IRC chat linked above if you need real-time updates and play-by-play, or wait for someone to post here saying that the site is ready...

Not Safe When Running is, I think, a good way to describe a Nuclear Salt Water Rocket.

Yes, the engine bell extension does that in flight (I guess the extra weight of the mechanism is less than the weight of a longer interstage). For an example of this in KSP, see @Nertea's Cryogenic engines pack - the Ct10 'Chelyabinsk' is inspired by the RL10. There are also deployable vacuum nozzles on a couple of the engines in his Kerbal Atomics pack. A DeployableEngine plugin handles the animation.

The effect is observable (but not significant) even below 1000x timewarp. It also doesn't affect solar power even at 100000x.

I like the new NTR's and the new LH2 boiloff mechanism, but it looks like it's exposed an anomaly the NFE reactors.. When building an LH2-NTR-powered craft to head out an outer planet I noticed an anomaly with the NFE reactors producing power at warp. As best as I can tell, you need battery capacity proportional to the power draw times the warp factor to buffer the power output of the reactor at warp. The upper stage was powered by the gas-core NTR (LV-N-GE 'Liberator') with fuel stored in a Mondo-60 and an HI-530. Total power draw for cooling was about 130 Ec/s, well within the 400Ec/s capacity of an MX-4, so I added an MX-4 and a few radiators. Had about 15km/s delta-V with good TWR. Worked great until right after the burn for the interplanetary transfer, when I went to 100000x warp. Stored Ec immediately dropped to zero, and boiloff started. Aborted back to VAB, added about 400 Ec/s worth of solar panels (which wouldn't do in the outer system), and started experimenting in a 3000km circular orbit at varying warps. With solar panels as the power source, batteries stayed topped up at warp (except when in eclipse). With the MX-4 as the power source, it looks like stored power stabilizes at a deficit to full that was proportional to both the warp factor, and the power draw. With only a few thousand Ec storage, going to higher warp (10000x and 100000x) blew through that in no time and sent the tanks into boiloff mode. Looks like stored power stabilized with a deficit that was approximately (0.023 * warp-factor * consumption) below full. So (for instance) with cooling enabled for both the Mondo-60 and the HI-530 it stabilized at about 298000 Ec below full. So I tacked on a bit over 300000 Ec of batteries (!) and I finally had a ship that wouldn't boil off when the tanks were powered by the MX-4 at 100000x warp.

Large zero-boiloff LH2 tanks take significant power for cooling - at the extreme end, the HI-530 takes 115.20 Ec/s. Stock launch clamps provide 1 Ec/s each. (The SpaceY large launch clamps provide 2 Ec/s each). Seems like there's an unfilled niche for a higher-power bit of ground-support equipment to keep cryo tanks powered and topped off. (Just for fun, It should probably emit a vent plume like you see for most liquid-fueled launches..)

No, the propellant never comes in direct contact with the solid nuclear fuel. See also https://en.wikipedia.org/wiki/Gas_core_reactor_rocket#Open_cycle_versus_closed_cycle

Also should include StageRecovery-like hook that penalizes you if anything nuclear-powered crashes and/or burns on the surface of Kerbin. Besides reputation, I'd expect it to immediately cost cash (for cleanup & decontamination), as well as increased part cost.. And if you drop it in or around KSC, you might have to wait for any short-lived isotopes to decay before you can use the pad again..

If we wanted to model it like how things work in real life, you wouldn't worry about boiloff on the pad -- launch clamps would keep tanks topped off until just before launch.

If we're getting boiloff and heavier ZBO tanks, can we get electric engines that use LH2 back? BTW, in the real world, ULA is working on this cryogenic storage and in-space refueling - see https://en.wikipedia.org/wiki/Advanced_Cryogenic_Evolved_Stage and http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/DepotBasedTransportationArchitecture2010.pdf . They're planning to profit from boiloff in part by burning the boiled-off gases in an internal combustion engine to generate electric power; they're also planning to use cryogenic fuels for RCS, eliminating the need for additional tanks for hydrazine.

The space shuttle used a ratio of 2.7l of H2 per liter of lox; that would be a volumetric ratio of 0.27 liters of OX and 0.73 liters of H2 per liter of tank volume. (On the mass side, because of hydrogen's fluffiness, that inverts to 6kg of oxidizer per kg of hydrogen. 8:1 is the stoichiometric mass ratio, but it looks like the SSME runs fuel-rich). Hydrolox rockets should have a definite volume penalty - you just need much bigger tanks to contain the needed mass of propellant.

I think it makes more sense to assume there's a smart reactor controller involved, and have the exposed interface be a targeted maximum throttle; while nuclear fuel consumption should depend on the actual amount of heat generated and discarded. If you don't have enough radiator capacity, the controller will just slow down the reaction (and extend the core life) to avoid meltdowns. I'm sure that will disappoint the explody segment of the user community though...

Getting the sign or slope or relative difference wrong breaks immersion for me in a way that getting the absolute magnitudes wrong doesn't. All else being equal, I'd rather see the relative Isp of heavier molecular weight propellents in the same engine be lower, with Xe winning out for other reasons when it makes sense.

That's certainly the case for thermal engines -- for a given temperature, lighter-molecular-weight propellants move faster. (Isp is directly proportional to exhaust velocity). If Xe has an advantage I'd think it would be tank volume per mass of propellant.

Likewise. I built a fueling station out of a bunch of those ridiculous 10m spherical LH2 tanks...

Got a link for the paper? (There is a plan to include a widget to produce O2 from the Martian atmosphere on the next NASA rover in 2020 as an ISRU test; IIRC the generated oxygen wouldn't actually be used for anything. Other ISRU proposals involve hauling H2 to Mars and combining it with atmospheric CO2 via the sabatier reaction to produce methane, but modelling that starts to creep into RealFuels-level detail..

How about a fuel-switching variant that allows you to choose (for the solid-core NTR's) between stock liquid fuel at an ISP of around 400-500s and H2 at an ISP of 900s; this (roughly) reflects what you'd get if you attempt to put heavier atomic-weight reaction mass through a solid-core NTR...

Tankage volume (LH2); extreme power; low-ish TWR once you add reactors or acres of solar; otherwise, reward for slogging deep into the tech tree

You also have to have additional server capacity available to do the encryption, which may be small but isn't free.

Just to be clear: the patched dll allows reactors to be started and stopped. Reactors generate power and heat, but there's something off about heat generation during timewarp (reactor equilibrium temp during higher warps is significantly higher than at 1x speed; radiator configs that avoid overheat during long NEP burns are not sufficient to prevent the reactors from getting explody at 100x warp..). They're also not yet using the new "core temp" mechanism that was added to 1.0.5.

Seconded.

Nope. Research into what became the Internet started in the 1960's. The UNIX operating system and the C programming language (which began life in the early 70's) use a format for timestamps that is a count of seconds since 1 January 1970 00:00 UTC. Which year a zero timestamp shows up as depends on your time zone. If you're in a timezone west of the prime meridian (in other words, North & South America, more or less) a zero timestamp shows as some time during 31 December 1969; timezones to the east (Europe, Africa, Asia, Australia) show it on 1 January 1970.

Still haven't seen an answer to this: Any way to retrieve my old subscription list? I was assured before the transition that subscriptions would be kept across the transition so I didn't do anything to back up my list of the 100+ threads I was following. (I'm kicking myself for not doing this and thinking of a particular scene from Animal House....)

What's more, it has one entry for each new post, rather than one entry for each thread sorted by recent activity. The old way was much more efficient for catching up on things a mod at a time.

Yep. As I said in a post that mysteriously disappeared, there would be much honor and no shame in declaring this migration a failure and rolling back to the old forum system until such time as a lossless migration becomes possible.