Starman4308

Quick question before I try it out; would a kOS script whose sole purpose is to stage when resources are depleted be acceptable? I mean, the rest of the mods I use would rule it out of any coherent scoring (6.4x scale, FAR, Real Fuels, etc), but there may be other players with stock physics who are more familiar with kOS than Smart Parts.

If it helps, I looked into reentry heat loads a bit. The Wikipedia page on ablative heatshields gives a range of figures, and I went with a conservative 150 W/cm^2 thermal load. Even for a 1.25m heatshield, you're talking about wicking away 920 kW of heat generation (920 kJ/sec), and a rough estimate would put efficiency at 60% tops (given a perfect Carnot engine, shockwave temperature 2000K, part temperature 800K). Realistically, you're looking at > 2000 kW of cooling necessary for a 1.25m heatshield. For perspective: Wall outlets in the US are capped at around 1.6 kW The official spec on the S9G reactor powering the Virginia-class submarines is 30,000 kW of peak power Lithium-ion batteries store about 850 kJ/kg Water's heat of vaporization is 2,257 kJ/kg Given how most people peg 1 kW to be around 1 EC/sec, I have two main conclusions: KSP batteries are hilariously underpowered by a factor of around 40. Even assuming a generous 40 kW = 1 EC/sec, if you're aiming for realism, you'd want active cooling to draw 50 EC/sec to cool a 1.25m circle at peak load. That's... kinda brutal.

Excellent mod; I'll be sure to download that once the other mods I use (Real Fuels, FAR, DRE, etc) are updated. And, for a bit of scale: the largest stock antenna will occasionally reach Mars from Earth, and your 10x antenna will usually reach Saturn (unless Saturn is at opposition from Earth). I suspect RSS configs antennas to reach much further out, but still: wonderful little antenna you two made. EDIT: Excuse me, wonderful huge antenna you two made.

It's alright. As you can probably tell from me having that equation (in a quick-and-dirty Java program I use for off-the-cuff stuff to boot), I tend to be very precise about things. I'm the sort to immediately hit timewarp after a maneuver node completes so there is the least possible error caused by the non-rails physics engine.

On high vs. low-thrust engines: that's a big part of why people are looking into VASIMR engines, as you can trade specific impulse for thrust for the same electrical consumption. I'm not 100% sure what you're saying about propellant density is correct. Tankage dry mass is wholly independent of specific impulse; it comes out inside the logarithmic instead of the multiplicative part of the rocket equation. It does lead to some interesting math, though: dV = Isp * g0 * ln(payload + fuel + tankage / payload + tankage). The equations I'll use when explicitly including dry tank masses: dV = g0 * Isp * ln(payload + fuel + tankage / payload + tankage) fuel# = fuel + tankage (as I'm usually looking to add a total tank mass to some fixed payload + engine) tank ratio = full tank / dry tank I'll use alternating ({({ })}), because multiply nested parentheses get confusing. dV = g0 * Isp * ln (payload + fuel# / payload + (fuel# / tank ratio)) fuel# = payload * ({e^(dV/{g0 * Isp})} - 1) / (1 - {e^(dV/{g0 * isp}) / tank ratio) Because it makes the math a lot cleaner: expDV = e^(dV / {g0 * Isp}) fuel# = payload * (expDV - 1) / (1 - {expDV / tank ratio})

Assuming you are posting in good faith: calm down, step away from the computer, and take a break. It's easy to get too wound up. Come back with a more open mind, and look into aerodynamics more. I am now tempted, however, to suspect Panzer is right, and that you are not, as point of fact, posting in good faith, in which case I'll simply point out that I have thousands of hours played.

Ergion, I will ask a question. Who here has sent rocket after rocket after rocket after rocket into space successfully without a hitch? Who here seems to be having difficulty getting one into space without first effectively leaving atmosphere? I would postulate here that the people who have sent rocket after rocket after rocket after rocket might have a slightly better grasp on aerodynamics. Also, the point of having engines a long way away from CoM: if everything is radially symmetric, all the torques cancel out, and if you're gimbaling the engine, you want it to be temporarily unstable, you want a net torque.

"Geometric center", whatever you mean by that, has nothing whatsoever to do with aerodynamic stability. All that matters is if CoL is behind CoM and your vehicle isn't too far off straight flight. You must also account for changes in CoM as the flight progresses; if you are draining from a tank above CoM, that's naturally going to drag the CoM downwards. Usually it's not a huge deal for rockets, but it's important for aircraft. CoM being up at the top just makes it even more stable (assuming CoL is towards the bottom); that causes the lever arm of aerodynamic stability to be that much longer, producing an even larger torque towards the flight vector. That would even improve control authority provided by gimballed engines, assuming they're radially symmetric. Of course, too much control authority creates a twitchy craft that tends to overcorrect.

Yes. And they do. When your rocket flips out and becomes debris, you will notice they still have a great deal of upwards momentum; that hasn't changed. What your rocket doesn't have is angular/rotational momentum; as a rocket is flying straight and true, it literally has zero angular momentum (relative to CoM) to resist torques. When your rocket flips out, it is because aerodynamic forces are exerting a torque on your rocket that exceeds its control authority. There are two primary mechanisms to address this: aerodynamic stability and spin-stabilization. For aerodynamic stability: by having more cross-sectional area to the rear of your craft, aerodynamics tends to exert a torque which resists any deviation from your current velocity vector. You can think of drag as pulling at your aircraft, at the center of drag, in the direction opposite your current velocity. With CoL (approximately the center of drag) behind CoM, this balances things, with CoL in front of CoM, it makes it aerodynamically unstable and flip-happy. One way to visualize that; imagine center of lift and center of mass as being the two ends of a rod. With CoL behind CoM, aerodynamics are pulling CoL behind CoM, keeping the rod sraight. With CoL in front, aerodynamic forces are pushing at the rod, and it's now a balancing act, where any slight deviation from straight will amplify itself. The other method is spin-stabilization. You know how I said a rocket flying straight and true has no angular momentum? A rocket flying straight, true, and spinning has lots of angular momentum, which will naturally resist torques (up to a limit, of course).

Redesigned the Moho relays, this time with more delta-V, both from a stronger (TWR and Isp-wise) pulsed inductive thruster carrying a silly overkill of argon (27 km/sec full, insertion burn is ~ 10 km/sec of delta-V thanks to less-terrible TWR), and from a hypergolic kick stage used on the transfer burn. They're all in orbit now, still getting the inclination to 0 and into a stable circular orbit, however. A large Moho orbiter, despite its kick stage, had to complete the transfer burn on its ion engine. Those of you acquainted with that Murphy fellow might know what happened next. There may have been unintended consequences of how the sigint radar dish deployed itself. Fortunately, you get a lot of solar power at Moho; a single blanket array was delivering 800-1100 EC/sec (started over 1000, seemed to drop over time for some reason). The first module of the planned Duna station has been designed, about 70 tonnes, requiring the use of the 100-tonne booster to send it to Duna. The first mission to the Duna station will be "deliver 32 Kerbal-years of life support supplies to fill up the completely empty tanks on the station because that's the only way we could fit it onto the largest booster in inventory". Said supply will take the second largest booster in the inventory. Part of this is pure paranoia, basically "if everything but the station dies, I want the 6-Kerbal team to survive until resupply can come", but it's still illustrative of the absurd amounts of life support Kerbals will need for interplanetary missions. What was your descent slope like? If you come in too steep, that can be a problem; you want to come in with a periapsis of several kilometers above the surface such that you can bleed off a lot of horizontal velocity before landing.

For most engines, it's probably much less wear-and-tear on the engine, it's probably just difficulties in starting the turbopumps and igniting the propellants. Not all mixes are hypergolic; the cryogenics (hydrolox, kerolox, etc) require some external ignition source, and that is what is usually limited. For first-stage engines, there's also the mechanism used to spin up the turbopump to start delivering the propellant, which may be single-use. Granted, with certain propellants (particularly kerosene), there may be buildup of residue, and very-high-performance engines might simply wear out too quickly, but it's not too hard to imagine designing something like a hydrolox engine which just needs to be topped off with hypergolic starter fluid every so often.

A decent mod, like Navyfish's docking port alignment mod, makes docking significantly easier. I'l be honest: I'd probably be pretty hopeless at docking without it, or at least something similar to it (there's also a mod to add an indicator to the navball).

So, added the ascent to the simulations in two ways. First, I just assumed a single stage for both descent and ascent, and second, I just assumed the ascent stage would be completely independent of the landing stage and not share any parts or other shenanigans. Updated code: https://www.dropbox.com/s/c0mw713bvmn74zq/Calcathing-v2.java?dl=0 Results for single-stage: https://www.dropbox.com/s/e7wh0fsdvzcend8/singleStageFracts-all.xlsx?dl=0 Results for ascent-only: https://www.dropbox.com/s/gnuv094wlfj383p/ascentMassFracts-all.xlsx?dl=0 As an aside: the wonder-negative-masses from last night were mostly because, when updating the mass fraction (relative to the start) at the end of each ascent simulation timestep, I forgot to add in the delta-V consumed by the landing. Overall, for ascent-only stages, you'll want a little bit more TWR than descent-only stages, in part because you've got the most gravity losses when your craft is the heaviest, unlike landing where gravity is strongest after shedding the most fuel. Stock Mun: optimum is 2.1 (again, assuming engine with 200 kN/ton and 340 s Isp) Stock Minmus: optimum is 1.8. Stock Tylo: optimum is 1.7. 64k Mun: 3.75 64k Minmus: 4.2 64k Tylo: 2.0 For single-stage land/ascend vehicles, this trend is amplified for the smaller moons, but reversed for the big moons (Tylo, 64k Mun, see note on 64k Tylo). Stock Mun: 2.2 Stock Minmus: 2.05 Stock Tylo: 1.15 64k Mun: 3.35 64k Minmus: 4.55 64k Tylo: heeheehaahaa, they're coming to take me away, hee-hee, ho-ho, haha, to the funny farm! Not even hydrolox cuts it here; the only solution is maybe a LOX-boosted nuclear thermal rocket. 64k Tylo with stock engines and tanks: there's a little corner in the lower-left which corresponds to "LV-N hacked to have way more thrust than it should".

Let it not be said that I do not put mine money wherein be mine mouth. My overall conclusion is that for small bodies, I should be using a higher TWR than I am, but I'm in an excellent range for the colossal bodies like Tylo, where surface gravity is high and delta-V requirements are through the roof. Note: I will probably revisit this shortly, because I completely forgot to simulate the ascent. Assumptions: THE PROGRAM: https://www.dropbox.com/s/ot471gupq469e0c/Calcathing.java?dl=0 THE RESULTS: https://www.dropbox.com/s/uovrt0ctafn08pt/landerMassFracts-All.xlsx?dl=0 THE POM.XML: https://www.dropbox.com/s/963o55bs4plsnmo/pom.xml?dl=0 THE SHORT DIGEST (at isp 340): Stock Mun: optimum is 1.95 Stock Minmus: optimum is 1.75 Stock Tylo: optimum is 1.35 64k Mun: optimum is 3.4 64k Minmus: optimum is 4.05 64k Tylo: optimum is 1.2 My conclusion from the stock-64k difference is that the much better thrust-to-mass ratios of RealFuels engines make it trivial to just slap on a giant engine and call it a day, because it doesn't mass much, except for Tylo which just hates you forever. EDIT: Ladies and Gentlemen: when attempting to SSTO off 64k Tylo, the optimal TWR for 340 isp is 1.2, providing an amazing landing weight of negative 21.7139 tons. I'm sure this is a real result and not because the math returns a bogus result for situations like "not physically possible to SSTO at that Isp and wet/dry tank ratio even with infinitely light/powerful engine". I think I'm going to finish implementing land-and-ascend tomorrow, and actually play some dang KSP today.

Thing there is that exponential growth is only significant when your final TWR is very, very close to 1.0. Trigonometry is your friend for landing. In the final moments of an ideal suicide burn, the vertical component of your velocity must be 1.0, thus TWR * sin(angle) = 1. The fraction of your thrust lost to gravity is not (1.0 / TWR), but rather 1 - cos(angle) = 1 - cos(sin-1(1/TWR)). The effects during the rest of the burn are a bit more complicated to calculate; while you'll have less TWR (having not burned through all your fuel), effective gravity will be less than 1, because of orbital effects. Anywhere save very near 1.0, increasing TWR doesn't help gravity losses much, and does require significant increases in engine mass. Now, the full story is more complicated than that; you have to integrate these losses over the entire descent profile, and you can be more aggressive with high TWR, as low TWR burns often entail planning to go over not only the hills you see, but also the hills hidden behind the curvature of the Mun. I'll try to get some simulations going, but I do rather specifically remember that somebody already did a lot of these calculations, and came up with the conclusion that for many moons, particularly the heavier ones, optimal starting TWR is pretty close to 1, and sometimes less than 1.

No, but there are real practical limits, and hilarious practical limits, such as "mass until space vehicle exceeds the Chandrasekhar limit and collapses", "number of parts until Unity engine gives up", "filled the VAB entirely with xenon drop tanks", "mass at which exhaust cannot reach escape velocity from vessel's gravitational field", "used every atom in the universe", etc. For real-ish advice, Near Future Propulsion has some excellent ion engines, such as one with 12000 isp that I recently used to make a Moho transfer vehicle (for 6.4x) with.. ah... 20 km/sec of delta-V. Funny how that works.

Thing is, high TWR is more delta-V efficient, but not always more mass efficient. You pay for that higher TWR with a heavier engine, meaning more propellant to get the same delta-V. Thus, at constant mass, higher TWR uses less dV but has less dV to start with, and the optimal point is often pretty close to 1.0, assuming an efficient descent profile. It doesn't help matters that fuel tends to be cheaper than engines. I mean, you may already know that, and just sanely choose "hey, I could save 10 kg on the lander, or I could save my sanity. Which do I choose?".

I think I'm just going to continue laughing at this point. And maybe a little bit second-guessing my decision to play at 6.4x scale with my compulsive "must land/ascend efficiently with bare minimum of TWR" habits.

I can't say much for MJ landings (I basically never use it), but people can and will use lower TWRs; I've landed on the Mun (6.4x resize, 3.2x rescale) multiple times with starting TWR of 0.95-ish. I think somebody once ran a bunch of plots showing that most moons, the optimal TWR is close to or less than 1, it just requires a lot of patience and judgement on how fast to descend without making a too-strong first impression on the Mun. I laughed. Hard.

First, that's 200,000 tons, not 200 million. Second, even if it were 200 million tons, Kerbin would still outmass it by a factor of 265 billion. Gilly out-masses 200 million tons by a factor of 620,000. I know it's probably hyperbole on your part, but I get a smidge annoyed when people underestimate just how gigantic celestial bodies are. On my own end: finally landed on Gilly. Very difficult at 6.4x scale; you need to remember to hit the thrusters before landing, because 45 m/sec is just a smidge too fast for most landing legs. Labor of Hercules, I tell you. Finally got that E-class asteroid into Munar orbit for a contract (WHY), after five lunar slingshots because of course I came in retrograde. Moho is going to be the death of me. A robotic lander (not even a very heavy one) is costing me nearly a million roots, a large fraction of which is going to the xenon propellant for a 12-engine ion cluster. That engine is amazing in many ways; it needs 2,000 EC/sec (would be utterly impractical to run on solar anywhere but Moho/Eve), consumes ludicrously expensive xenon, has a pittance of thrust relative to its mass (43.45 kN for a 2-ton engine which needs over 2 tons of solar panels... at Moho), and has a wonderful, wonderful 12,000 s-1 of specific impulse, giving me > 20 km/sec of delta-V. Maybe were it not so close to the Sun, I'd go for a nuclear thermal rocket instead, but at Moho, cryogenic NTR fuels are going to boil like mad. Also: sprach Zarathustra:

Best advice: put CoL way in front of CoM. Then fly backwards. For actually-serious advice: A, put CoL a bit behind CoM (further back means more stability and more margin for fuel depletion; closer to CoM gives more maneuverability), and B, check to make sure that your aerodynamically stable aircraft stays aerodynamically stable when the fuel is gone. Way back in 0.25, I lost an SSTO that way; very stable at the start of the flight, but after delivering a full load of fuel to orbit, the CoM had shifted significantly backwards, and it span out of control after reentry.

Also: "robust", and "capable of exceeding necessary mission parameters". Though: playing at 6.4x scale, 2 km/sec is not terribly egregious for a lunar lander if you plan to return it to low Mun orbit for rendezvous. It's probably not quite enough to return to Kerbin directly, but 2 km/sec leaves a comfortable 500-600 m/sec margin for returning to Mun orbit. Granted, my landers are often quite... robust, often still having a few hundred m/sec of dV left in the transfer stage when I begin my landing... with the lander itself being overbudgeted for capture into lunar orbit and landing and returning to orbit.

There is a name for something that modifies configuration files. It's called a "mod". It ain't stock anymore when you do that. Sure, most current mods exist as sets of DLLs, configuration files, and models, but in the early days before Module Manager (endless thanks to Sarbian and ialdabaoth for that), you would have had to over-write stock .cfg files; Module Manager just lets you modify them at load-time instead of altering the original files. Back to Sharpy: there were some inflatable balloon/blimp mods at some point (no idea if they're still up-to-date), and maybe you could use a balloon to ascend to upper Eve atmosphere, deflate the balloon, and then go for orbit.

Maybe Real Fuels with the stockalike configs (at least once they're updated to 1.2)? I regularly pack 6 km/sec into cryogenic upper stages, and I've come close to Kerbin SSTOs in 6.4x scale. Given that I'm hardly the world SSTO expert, I suspect it may be possible to get off 6.4x Kerbin, and by extension, stock Eve.

The ion-powered relay had over 10 km/sec in the tanks, enough to burn for almost two hours, and solar panels to give it 70% thrust even when the batteries were wholly depleted. Where did it go so wrong? Why is the relay flying back off into solar orbit? How can that little rock be so insanely difficult to capture into?