A1Ch1

Neither: (I'm in the same boat, wish I had made a 1.0.2 backup before Steam updated it)

Which heavy launcher? Falcon Heavy or BFR? Because Falcon Heavy has great LEO performance but terrible high-energy performance, and SLS is designed for high-energy missions. And BFR doesn't have a name, or a finalized design, or a finalized engine, so it's hard to imagine it being ready before SLS, which is completing CDR now.

This is like asking what's better, an A320 or a 777? They're designed to do different things. You don't fly a 777 from LA to SF and you don't fly an A320 from LA to Frankfurt. The question needs to specify what the vehicle will be tasked with to judge which is better.

It's going to be named via an essay contest for schoolchildren, as were Spirit, Opportunity, Endeavour, Sojourner, Curiosity, etc. Those all ended up with nice names

Saturn gets about 1% the sunlight Earth does, which is equivalent to a typical overcast midday. The darkest clouds reduce illumination to about 0.1%

Which is why rocket-grade LNG would have to be standardized.

There's no such thing as standard LNG, contracts are for a certain energy/mass (or energy/volume). Suppliers add bulk if their LNG is too high energy. So not all LNG can be burned as-is, and rocket-grade LNG would have to be standardized. Regardless, LNG containing nearly pure CH4 is readily available using existing refining.

Debris traveling retrograde would intersect every 45 minutes. An elliptical debris field in a polar orbit of maybe 250 km x 800 km and an argument of perigee near ISS orbital plane would intersect every 90 minutes, as unlikely as that is.

The optimum O/F ratio for kerosene/LOX is around 2.5. LNG/LOX O/F is 3.5. This somewhat offsets the lower density of LNG so the total volume is about 15% larger, not a dealbreaker. 4-5% Isp represents a similar increase from from going from gas generator to staged combustion.

The increased pressure isn't from using four vs five engines. The reason is the core is taller than the ext tank and stack will accelerate at a max of 3.3 g vs the shuttle's 3 g. This results in a LOX head pressure of ~1.8 MPa vs the shuttle's typical 1.2 MPa. Part of the engine testing program is to certify for the increased pressure.

The throttle drops slowly enough that it will not reach zero if shift is being held down when auto ascent is disengaged. Not that I don't wish MJ didn't cut engines, but holding shift reliably prevents cutoff.

Mechjeb shuts down engines for three reasons: the throttle limit is exceeded, the apoapsis hits the target altitude, or autopilot is turned off. For the first, just leave throttle control off and use Engine Groups to throttle if needed, for the second, set the orbit altitude to way above your target orbit and use "Turn end altitude" to define the target orbit, then perform the final direct (that is, one-burn) injection manually (MJ performs dual-burn injections, to do these automatically set Turn end to just below the target orbit altitude and then change Orbit altitude to the target once you're near orbital velocity). To keep MJ from shutting off engines when autopilot is disengaged, hold down left shift while clicking disengage, then hit Z to return throttle to full if needed.

While making configs for the LionHead Ariane 6 and Vega, I got sick of doing thrust curves manually. So I created a spreadsheet to help out. Just input the vacuum thrust, Isp, tank volume, and starting throttle, then manipulate the "Delta throttle" column, which is essentially the slope of the curve at that point. It will then compute elapsed time, thrust at that time, and the rate of change of the thrust. Any changes made will update all the other values so tweaking the curves is less of a pain, and the elapsed time output keeps things on track. The delta thrust allows smooth curves to prevent Unity-spiking. It also generates a thrust law chart in real time to compare: If start or burnout mass are added, it creates an acceleration chart to compare: It's here to copy. The Ariane 6 and Vega configs are just about finished; hopefully this saves someone else some time

I actually think we need a generic vernier, 2-4 kN or so, that switches between common fuels (LH2/LOX, KER/LOX, LNG/LOX, various hypergolics). Lots of engines use gas generator exhaust for roll control, seems like the closest way to simulate that. I've been using a cloned LR-101 for that purpose on my rockets. Of course a vernier to control a fixed nozzle J-2T rocket would require a higher thrust, more like the verniers on Soyuz 2.1v. Regardless, it seems reasonable to imagine that had J-2T development continued a small vector range (maybe 1.5 or 2 degrees?) could have been developed. Now that gimbal range can be set in individual configs we can always leave the default fixed and have a gimbaling version for the sake of playability.

Oh, if the SRM T/W is still over 1 then that's not the bug, the bug is that radial decouplers impart a slightly asymmetrical thrust that can cause SRMs ejected in an airstream to come right back at the core. I'd still recommend the bug fix module though. But real GEM60s burn out relatively quickly, going from ~70% max thrust to 0 within 10 seconds or so. It's the RO GEM60 goes from 70% to 0.06% in about 10 seconds but then stays that way for a long time.

That collision is actually a bug, you can fix it with the Stock Bug Fix Modules mod. The GEM60 as currently implemented don't burn out completely but fall to a very small %thrust and stay that way for a loooooong time. The reason the dv jumps up at the end is because dv is calculated using current thrust, and includes the thrust from the Delta 4 core stage. When the SRM thrust tails off, Mechjeb or KE calculates a new time to burnout and therefore the dv remaining increases because they'll be attached to the core longer. The updated thrust curves tail-off but stay high enough to deplete the propellant and actually burn out like the actual GEM60 (thrust and burn rate are related to pressure inside the SRM, once pressure falls below a certain level the burn rate declines even further and thrust terminates, it doesn't decline to a fraction of a % and stay that way).

Depends - the shuttle SRBs were jettisoned while still producing something like 250 kN so the orbiter's main engines didn't have to drag along their inert mass any longer than necessary. Additionally, large boosters like those on Shuttle or Ariane 5 call for a long, gentle trail-off that is less sensitive to variation in burn rate between the boosters than a faster tail-off would be. Smaller boosters can tail-off more quickly and have a low burnout mass compared to the vehicle so they aren't jettisoned until they've stopped producing thrust (and exhaust). The boosters on the Delta 4, for example, are little more than empty casings at separation: https://youtu.be/JOfuKw7XEy4?t=124

This actually will change with the next RO update - since the plume effects can't be made to fade out as thrust tails off (at least not to my knowledge) the GEM60 and GEM46 will now trail off to zero thrust by the end of their burn time. It just looks too weird to have the engines producing virtually no thrust but still look like they're at full throttle, especially when it's time to jettison and they go tumbling away with the huge plumes still firing in every direction. Edit: This is the current burnout situation and this is how it will look Edit 2: I've been informed that linking plume effects to thrust should be possible in the future, allowing more realistic-looking SRM burnouts

The sound on the RS-68 was actually fixed in a recent RO update. Leave a note if you find any other engines with the same problem

Engine Group Controller allows you to select groups of engines to throttle at the same time. Just assign engines arbitrary group names, then the EGC button on the toolbar lets you throttle all engines with the same group name at the same time. An example is the Delta 4 Heavy (https://youtu.be/yYUfKutMjNg) where EGC is located at the upper left side of the screen. Here it is used to reduce core throttle at around 35 s and could be used to reduce booster throttle to control G forces, though it wasn't needed in this case. This lets you easily throttle groups of engines separately from the global throttle.

Thank you NK

Late response, but: those videos are pretty old; I made them when RO still had overpowered reaction wheels and used those for first stage roll control. The newer videos use vernier engines and RCS instead. I don't remember exactly what those things at the bottom of the stage were, but they were probably just struts for the boosters since Kerbal Joint Reinforcement didn't work as well back then.