GoSlash27

Okay, So in FAR, how much is that G limit increased? What acceleration is required in FAR to get you to/keep you at terminal velocity early in the launch? My lightbulb just went on... -Slashy

This software will allow you to produce comparison charts for multiple engines as well. He just posted the single engine charts as a quick reference while he finishes up. Best, -Slashy

Congrats! Not that you've got the first one under your belt, the rest should come easy. If you "go advanced" to edit your OP, it's hiding in there in a dropbox.

Arkie, Was this made with the assumption of a vertical launch throughout? 'Cuz the closer you get to horizontal, the less rapidly you're rising, and thus the less rapidly the terminal velocity is increasing. Upshot is (at least in my experience) the thrust requirement actually goes down with altitude, not up. Best, -Slashy

Well... (sheepish grin) I like helping folks and most folks who need help are running stock. So I focus on gaining as much knowledge and experience as I can in the unmodified engine. Plus, altering my setup from stock just seems wrong somehow. Weird, I know -Slashy

Just experience and a fuzzy theory. In stock KSP, the gravity turn doesn't begin until 7K or so. And from the gravity turn on, the ideal curve seems to favor much lower t/w than the conventional wisdom suggests. I think it's because "terminal velocity" isn't what matters, but rather the "delta terminal velocity". It's not a matter of matching the terminal velocity itself, but rather accelerating at the same rate at which your terminal velocity is increasing. If your rate of climb is about 100M/sec, you don't have to accelerate at 2G to match your terminal velocity. So since the Vt wall doesn't take much acceleration to match, the thrust requirement is greatly reduced over most of the flight. Ditching the excess thrust seems to save more DV over the course of the launch than more rapid acceleration in the vertical phase and then throttling back. tl;dr... The DV savings from carrying powerful engines in the early going winds up getting wiped out in the later going by carrying more engine mass than I need. So I start very close to 1 and let the fuel burnoff increase my acceleration. I don't know if my explanation is sound or not, but I *do* know it seems to work. I just launched a payload into orbit that weighed more than the ship that put it there. I don't know if that's ever been done before or not, but I do know that that sort of thing doesn't happen with inefficient launch profiles. Scratchin' mah head, -Slashy

Honestly... The more I experiment in stock, the more I'm convinced that the optimal t/w at engine start is 1. Crazy, but there it is... But disclaimer, all of my launches the last couple months have been hyper- efficient SSTOs, so that's probably skewing my results. Best, -Slashy

http://s52.photobucket.com/user/GoSlash27/slideshow/KSP/Lifter-Ception/Flight Bwaaahahah!! Info Time: 40:57 Cost: √54,849 Weight: 21.75 tonnes Kerbals: 0 Returned to KSC: No Notes: Delivered a payload to LKO that weighed more than the vehicle itself (22.7t) and returned safely. LifterCeption!! -Slashy

http://i52.photobucket.com/albums/g13/GoSlash27/KSP/Lifter-Ception/LifterCeption2_zps86143252.jpg http://i52.photobucket.com/albums/g13/GoSlash27/KSP/Lifter-Ception/LifterCeption3_zpsd46cf3d4.jpg As you can see here, the lifter weighs 21.75 tonnes fully fueled at launch. http://i52.photobucket.com/albums/g13/GoSlash27/KSP/Lifter-Ception/LifterCeption4_zpsfe4283e2.jpg And here it is at 44.45 tonnes with the payload. The payload weighs more than the lifter! Can it do it??

How's this for an odd one: Single stage to LifterCeption: an SSTO so powerful that it could lift a copy of *itself* into LKO as payload! I seem to be taking my challenge cues from movie titles... -Slashy

I'm definitely all for this. I posted a wall of math this morning, and it looked like roadkill Best, -Slashy

I'm thinking that they "hid" it for a reason. They have some surprises they don't want to spoil. I'm guessing that they're integrating biome scanning sensors into the game. If not in this release, then forthcoming. Best, -Slashy

I'm racking my brains trying to figure out a way to explain this in a way that won't get muddled... If you add a low- drag part to an assembly in KSP, you have still added drag. It does not matter that it's less drag than what would've been added with a normal part, it is still more drag than you had without it. And that's really all that matters. You cannot add drag and then expect lower losses from it. It simply doesn't work that way, at least not in stock soupodynamics. If you add drag, you increase losses from drag. Really bad analogy: Imagine you have a truck dragging a boulder down the street. That sucks, so you say "Let's strap another, smaller boulder onto the truck. It's more boulder overall, but the overall drag per pound of boulder is less." Does the workload of the truck increase, or decrease? It increases. And the fuel economy of the truck decreases. So the drag and the losses from the drag get worse. It does not matter that the little boulder was less- draggy than the big boulder. All that matters is that it's another boulder. I'm probably gonna have to let someone more eloquent have a go... Sorry, -Slashy

So that means you made it?? -Slashy

Oh, absolutely that's possible. We had a member make a successful 2 stage rocket from Eve a couple months ago. If you can do it with a rocket, you can do it with a plane. Now... having said that, I should point out that the 2 stage rocket was grossly mass- inefficient and there were far smaller and more efficient options out there. The 2 stager was merely built to see if it was possible to do it. I've never tried to build a multistage Eve spaceplane, but I suspect it'd look like this: Stage 1: Aerospike Stage 2: LV-N Stage 3: Ions Dropping empty tanks and engines along the way...

Spatzimaus, In this case, I'm talking about KSP failure modes, not real- world. A KSP launch is most likely to fail because either a) control is lost or the vehicle ran out of fuel before establishing orbit. At least, that's how it works at my house. KSP launch failures generally don't happen where large chunks of the vehicle have decided to take a separate vacation. So option A: vertical lifter with payload Hanging enough parachutes on it to save the payload severely reduces the efficiency, which is why I'm using an SSTO lifter in the first place. If I'm clearly not going to orbit, I have no choice but to jettison the payload and pop the chutes. The payload is dead. Option B: spaceplane with payload I don't need chutes because I can fly. If I'm clearly not going to orbit, I can simply fly to the nearest dry land, set 'er down, and hail a cab. Option B is clearly the better option when Kerbin lives are in the balance. And since wings weigh less than engines, my cost efficiency for my spaceplanes is actually *better* than with my vertical lifter. So from a safety standpoint, my Kerbals are forbidden to hitch a lift on a vertical lifter. Strictly cargo only. From a cost- effectiveness standpoint, the spaceplane is still more economical than the vertical lifter. So "if it fits, it ships", as the old commercial goes. For everything else, it's the chunker. Now... that's not to say that a chunker *couldn't* be made safe. Just a matter of adding an escape tower at the very least. Sorry for the rambling! -Slashy

It seems you've actually got it pretty-well indexed. Were you to check your velocity at fixed times through the burn, you would find that your velocity is much higher during the prograde burn than the vertical at any point after you've gotten into the gravity turn. In fact, even going *retrograde* will be more efficient than escaping vertical! So you get a boost from having gone prograde and picking up the free velocity from the rotation, but that's not where the profit comes from. The profit comes from expending your fuel while going as fast as possible (the Oberth effect) because changes in periapsis are ultimately dependent on your kinetic energy, not your change in velocity. And kinetic energy is proportional to the *square* of velocity. So changing your velocity (i.e. accelerating) when you're going fast has a bigger effect than when you're going slow. And since you were going prograde instead of up, your acceleration was much more rapid because you weren't having 10 m/sec^2 stolen from you by the gravity fairy during the whole burn. Happy Saturday! -Slashy

I find it disturbing that when I quote RIC, it's almost always to say "^ What he said"... and here I'm doing it again. ^What he said. Placing parts with low drag coefficients in the front of a vehicle and parts with high drag coefficients is a good way to make them fly pointy- end first at very high speeds. Failure to compensate for this leads to a lot of spaceplanes that prefer to fly tail- first on reentry. I only figured this out myself within the last couple months, and I've been doing spaceplanes for a while. Best, -Slashy

No, Sir. I can assure you that this is not the case. The negative acceleration produced by the drag force is still higher than it otherwise would have been. Applying a drag force of .3Kn to a 2 Kg mass as opposed to applying a .2Kn force to a 1Kg mass may *seem* like less, but the mass itself is misleading. You were pushing the the mass with a (comparatively high) thrust, and you have negated more of that thrust than you otherwise would have. You took away .1Kn more thrust than what you had previously. You also added a Kg of mass, but that's a whole other issue. As an experiment to confirm this for yourself, you could try dropping a pair of assemblies, one with a nosecone attached and one without from a sounder rocket. The object without the nose cone will actually have a higher terminal velocity. It's soupodynamics. Best, -Slashy

No, Sir. You were correct the second time. (*counts toes*) Yeah. The second time Your drag losses are still increased by adding the nose cone in stock. While the drag for that part is reduced, it's drag is still a positive finite number. Since the drag is cumulative for all parts, your total drag is still increased, just by a smaller amount than it otherwise would've been. *edit for clarification* Drag in KSP is calculated as .004ÃÂv^2dM and is accumulated for every part used. As an apples-to-apples comparison, we're just interested in the dM part If we have a part with (say) a mass of 1kg and a Cd of .2, then our drag from that is .2. If we add to that another 1kg part with a Cd of .1, then our drag from that becomes .3. The drag coefficient of the entire vehicle collectively becomes lower, but the total drag produced is still increased. */edit* The only way to actually reduce the drag of an assembly in stock soupodynamics is to add a part that exhibits negative drag, such as a control surface. Under the advice of my counsel, I respectfully invoke my fifth amendment rights... Best, -Slashy

LD, Not taken as such. Neat resource and thanks. Best, -Slashy

I've been following what you're doing with that julia code, and I'm very thankful you're bringing it back for us. It's an awesome resource! Best, -Slashy

Okay. So the problem is that 1) your flight profile is not optimal. and 2) you're kicking in the rockets too early. Here's my tutorial on how to efficiently fly a spaceplane: http://forum.kerbalspaceprogram.com/threads/102182-So-you-want-to-build-a-space-plane?p=1582529&viewfull=1#post1582529 Take a look at it and see if you can spot somewhere in your launch that's not in agreement with this procedure. -Slashy

Very interesting problem! I would think your burn would be the same either way because your velocity would be the same. Interesting concept to look at: It may be cheaper to raise your periapsis first, then correct your inclination and finish your transfer. You might want to check that with some maneuver nodes. You could also see what it costs to do a radial in burn at the ascending node until your apoapsis is at the descending node, and then correct your inclination at the new apoapsis. I could be totally wrong, so I'm interested to hear what the others have to say about it. Best, -Slashy

Okay. Let's see if we can sort it out. So what seems to be the problem? Are you running out of fuel? Having trouble controlling it? -Slashy