Empiro

Wait until the velocity prograde marker meets up with the where you're pointing (which should be about 10 degrees if you're turn at 70 m/s), and then release SAS. The golden rule in FAR is that if your rocket is properly balanced and stabilized, it will "want" to go wherever the green marker is. If you point too far away from it, your rocket will break apart. A perfect gravity turn requires no further input from you until your cut your engine when your AP is above the atmosphere. And ideally, your time to AP should never be more than 40 seconds away from you. This minimizes the delta-V you need to circularize.

Also just as a quick addendum: I went into the game and tested this out via hyperedit, and it looks like LethalDose's new numbers are pretty accurate. You can squeeze and save a bit more by burning a bit more retrograde on your initial maneuver so that your PE is within the atmosphere and aerobrake until your AP matches your target.

Thanks for showing the video. I think it's allowed us to see what's going on and give analysis and suggestions. The thing about your craft is that it has a really high TWR, and as such you're not really performing a gravity turn since the TWR is so high. If you look at some FAR ascent videos with TWR of about 1.4-1.5, you'll see what happens is that at 50 m/s, you pitch over about 5 degrees (depending on your TWR and other factors), and then turn off SAS and basically let the rocket fly itself. This works well for small and large rockets, and makes the likelihood of breaking apart due to aerodynamic stress very low. Gravity turns actually require very little control input, because you need to pitch over so little. 4 of the controllable winglets is sufficient (and as far as I can tell, in FAR with large crafts, drag is extremely high if you don't have fins of some sort, so you need them no matter what). I recommend that you try to build the same rocket except with just a skipper engine instead of a mainsail (it will have a TWR of 1.47). Do a gravity turn like I described above. if you do it right, you shouldn't have to give any input after the initial turn, and your trajectory will be about 45 degrees at 10km, and flatten out fairly close to horizontal when your AP reaches 80km or so. Circularize at 80km, and transfer to the Mun. I bet you'll wind up with more delta-V than either of your two existing tests, even though this rocket is cheaper, and has less thrust. You might have to try a few times to get things just right, but like any skill it takes practice, and once you get it, you'll be able to reliably do it in the future.

I think I've definitely run into a similar bug before. I could get my RAPIER engines to operate in Air Breathing mode well after the intake air had run out at 40+ km. I couldn't reproduce the issue though, and it went away after a reload.

I always think that the game should just have a rotation series of quick / auto saves. Many games do this, and it really prevents this kind of aggravation if the last 5 saves / auto saves were always kept around along with the timestamp and in-game time. That way, if you accidentally quick save over something, you can just load up the one before that. If you accidentally load a quick save that goes too far back (and the game auto-saves), you can just load up an earlier auto save. It lets you recover from mistakes while not slowing you down by having extra confirmations to click through or extra stuff to have to pay attention to. The only cost is a little bit of extra disk space.

I've done the Jool-5 with a pretty big craft (it had extra living quarters, a science lab, and enough life support to last the mission). The design phase took a very long time, but the execution isn't too bad if you allow yourself to reload if you splatter into Tylo. If you use a multi-stage lander for Tylo, then it's likely that the ascent stage can handle all of Vall, Bop, and Pol. The design of a light-weight spaceplane for Laythe also takes a while (for example, I used a B9 VTOL engine to make the landing easier). But once you have all that, it's really just a matter of strapping on enough fuel to visit all of Jool and having enough patience to perform the long burns. Eve is much more challenging if you're trying to do it "legit" -- for example, no external command chairs. The craft needs to be built with tons of delta-V, lots of thrust, and a way to actually land without breaking the gears or toppling over.

As others have said, inclination changes are cheaper if you're moving more slowly (usually means at a higher altitude). However, if you're able to combine maneuvers, then that usually leads to even greater savings (think of a triangle). For example, if your AN/DN was instead right at the PE, which touches the orbit you're trying to match, then doing a normal burn combined with a retrograde burn at the same time at PE might lead to greater savings even though it's more expensive to do the inclination change there. In your particular example, I think the cheapest would be to do the following: -At either the AN or DN (try both to see which is cheapest), add a maneuver node with enough of a normal component to match inclination. Because your inclination change is pretty large, you'll want to add a radial / retrograde component to make it so that your PE is within the atmosphere. Play around with adding more / less of each and see what would be the cheapest. You don't care what your AP is, just that your PE is in the atmosphere. -Then allow yourself to aerobrake until your AP matches the target orbit -Raise your PE to match the target orbit.

Yeah I made a mistake in my calculations (by assuming that you burn out of Laythe and then burn out of Jool, which is extremely inefficient), but my numbers still come out to around 1300 m/s. I'll probably just run a test tonight though. I guess how much you can get on jets depends on which mods you're using -- I always play with FAR, so you can't get as fast on Turbojets / Rapiers as you can in stock aerodynamics. Still, it does mean that 4500 m/s is plenty to get back, and I think that you'd gain very little from using any sort of gravity assists (versus the amount of work you have to put in). Panzer, the reason why it takes less delta-V to get back is because of the Oberth effect. Laythe is moving very fast around Jool (3220 m/s), in addition you're moving very fast around Laythe (1800 m/s, though you had to pay that cost using your jet and rocket engines to get into orbit around Laythe). Combined, it means that even though you have to pay to first escape Laythe, the cost is much lower overall due to the savings from the Oberth effect. Edit: mumerobis' explanation is more complete than mine since he's correct that the two halves of the transfer orbit are asymmetric.

What is your PE at Jool? If you put a maneuver node down as soon as you enter Jool, it shouldn't be too costly to get the Laythe encounter. If you're finding it too expensive, you can even try to get the encounter before you enter Jool's SOI (just make sure not to warp right when you switch SOIs). Another option is as you said, to try to Aerobrake and put your AP just past Laythe's orbit. You're guaranteed to eventually get an encounter with Laythe. Once you do, if you make the adjustments as early as possible before entering Laythe's SOI, it shouldn't take much delta-V to put yourself in Laythe's atmosphere. I'm not sure what the best approach is to get back to Kerbin from Laythe. I would suspect that a Tylo gravity assist at just the right time would be ideal, but I think it would be hard to get everything set up just right. I think a straight burn from low Laythe orbit on a trajectory that puts you out of Jool's SOI and straight back to Kerbin would be both straightforward and fairly efficient because of Laythe's relatively high orbital velocity and gravity. However, my math still works out to about 2000 m/s to get back from Laythe. This means that I'd actually recommend 5000 m/s after taking off Kerbin to allow for getting to Laythe (~2000 m/s), taking off from Laythe (~700 m/s), getting back from Laythe (~2000 m/s), and also giving you some extra breathing room (~300 m/s) to make small mistakes and adjustments.

How much delta-V are you using to get to Jool? It shouldn't take more than 2000 m/s, and if you're using more than that it means that you're probably not launching at the right transfer window. I'd recommend getting the Kerbal Alarm Clock mod which tells you the proper times to launch. If you're still having trouble, come back and we can give more specific advice. The key to getting a good close encounter is to start early. Before you even enter the body's SOI, you can make small adjustments. Double click on the body to see your path within that SOI, and make small adjustments. Normal/Anti-Normal burns have a huge effect on the inclination, while pro/retrograde burns have a huge effect on the PE. The earlier the better, though if the adjustments are too sensitive, you can always wait until a bit later. I usually make a mid-course correction to get a good close encounter with Jool (at close to 0 inclination, and PE just outside the atmosphere), and then make a second correction as soon as I enter Jool's SOI to get a good close encounter with Laythe. I like the precise node mod because it lets me tweak maneuver nodes really carefully.

I'm not too surprised to see this. One way to look at gravity turn -> injection is that at some point during your burn, your PE goes from under ground to above the surface, and at that point you're "in orbit", even though you're in the atmosphere at ~30-40km. You're maximizing the Oberth effect as you continue to burn into a transfer to the Mun. The atmosphere is so thin at that point that the drag losses are pretty minimal.

I've considered a similar approach as well. I think that it's more of a cost-savings issue than a time-savings issue since as you said, you need to bring things back (and re-fuel it, and dock it, etc.). I think the thing I'd do differently is that I'd use this engine just for raising the AP but still within Kerbin's SOI. This way I don't have to turn around and burn -- I can just wait for AP and put myself in the atmosphere for aerobraking using very little delta-V. Otherwise, you'd have to slow down quite a bit (~1000 m/s) if you're going somewhere like Jool. I think that long burns will get a bit better in the next version, since we'll have the piloting assists that do things like point your craft toward the maneuver node, so you can just do a 4x warp and not have to keep doing corrections.

Yeah I think that one thing to keep in mind is that delta-V is not the only measure of efficiency out there. Total mass, total fuel burned, and total cost are all things that can be taken into account as well. Where the the standard LKO -> Mun transfer approach shines is that your upper stage can be a single light, efficient engine. This means that everything below it can be made much lighter and smaller.

In that case, it sounds like you've already got enough lift. More lift is only needed if you're having trouble getting off the runway or if you can't maintain level flight at ~25km while building your speed up to 1500 m/s or so. The general advice is that as long as your speed is still increasing, try keep the engines in air-breathing mode longer by throttling down. Did you try to reduce the mass further by not carrying excess oxidizer? The perfect fuel mix would be if you're left with 0 LF and 0 Oxidizer if you burn until your engine shut off. FAR is a mod: http://forum.kerbalspaceprogram.com/threads/20451-0-25-Ferram-Aerospace-Research-v0-14-4-11-24-14 which adds more realistic aerodynamics. I generally only make spaceplanes in FAR, so I can't really give the best advice for stock aerodynamics. It does weaken air-breathing engines quite a bit though (stock jet engines are way too powerful), so a lifting body probably won't work and you'll probably need wings on your craft.

Lift doesn't really reduce the amount of delta-V you need to get into orbit. What it lets you do is get away with lower TWR because you can accelerate horizontally while using the lift to keep a relatively slow climb. Landing gears and ladders are massless (and the small batteries are as well). Small accessories add very little extra weight, so I'm thinking that your ascent profile needs to be tweaked. How fast are you going before you switch the RAPIERs to closed-cycle? In stock, I've heard of people going 2000 m/s on the air-breathing mode, which means that you almost need no LFO to make it into orbit after that. If you're really interested in making space planes, I'd recommend FAR, though I believe RAPIERs max out around 1600 m/s there before having to switch to closed-cycle mode.

When you burn diagonally, your gravity losses are lower. For example, to experience 1g acceleration straight up, you'd need a TWR of 2. To get 1g when burning at a 45 degree angle, you'd only need a TWR of 1.41 (square-root of 2). This is because gravity has no effect on the horizontal component of your burn. Using your numbers, to do a horizontal burn with a TWR of 4, you'd need to pitch up only about 14.5 degrees (sin(14.5 degrees) = 0.25 * 4g) to cancel out gravity. Your horizontal acceleration would be cos(14.5 degrees) = .968 * 4g = 38 m/s/s. You'd need to burn 88 seconds, or about 3462 m/s delta-V. The gravity losses are only 3462 - 3352 = 110. This doesn't even take into account that once you're at ~2200 m/s you don't need to cancel out gravity at all, since you're at orbital velocity.

You can definitely get more delta-V if you're willing to deal with very long burns and very low TWR. The specific impulse of nuclear engines is 800s, you'd need a wet-to-dry ratio of about 4.5 to 1 to get 12000 m/s dV.

I think that your numbers are reasonable. When going into a very high orbit, burning straight up and then circularizing is not that different than burning sideways and then circularizing, because your final orbital velocity is relatively low, so you don't benefit too much from the Oberth effect in either case for your second burn. However, the key is that you're assuming an impulsive burn. In the practical case, your TWR is not infinite, and every single second you're burning against gravity is 9.8 m/s delta-V lost due to gravity drag. For example, even with a very high TWR of 4, your net acceleration is 3g or ~30 m/s, and you would need to burn for over 100 seconds to accelerate to ~3300 m/s. This means that you've actually burned over 4400 m/s delta-V and you're spending an extra 1100 m/s fighting gravity. When you take into account the fact that having such a high TWR necessitates lots of extra mass in the form of engines, the balance tips even more in favor of a standard gravity turn. Even if you wind up spending a few more m/s, you've probably gained more than that delta-V from just leaving a few of your engines at home. On the other hand, burning straight up gives you less air drag losses (because you exit the atmosphere faster). This brings things a bit more in favor of vertical burns in stock KSP, where air drag losses are relatively high, but not in FAR, where air drag accounts for a small amount of the loss in delta-V (I think it's about 200 m/s or so).

I like this idea. My suggestion would be to use curved lines to denote descent / ascents (since your trajectory when taking off and landing are curves), and always show separate arrows for landings then takeoffs. I thought that was the only thing that wasn't intuitively clear when looking at your original example. I actually like the suggestion that it mostly be linear -- it would be a nice way to summarize a mission in a compact form. Having a massive flowchart would only make it harder to quickly read. I can see the benefit of having small branches to denote crafts splitting off each to do their own mission, but I would argue that usage case would be the exception rather than the common case.

Adding more control surfaces helps. I play with FAR, and I've found that having a all-moving tailplane at the back can often provide the extra leverage to take off.

The thing is, while you can relate energy to dV, this relationship is extremely non-linear, so it's rarely ever helpful in expressing things in terms of energy. For example, doubling the amount of fuel doubles the amount of chemical energy in the fuel, but in general, it doesn't double the amount of dV. Likewise, two maneuvers that necessitate the same change in kinetic energy might require vastly differing amounts of dV because of the Oberth effect. This is the reason why we use dV maps instead of delta-Joule(per kg) maps -- in the former case, you don't need to break out the calculators to see exactly how much fuel you'll actually wind up burning.

I want to first say thanks for the great mod. I've been using it for a while now and it's a staple for all my long term games. I have a few suggestions for features. The first would be automatically adding kill-warp alarms for soi changes. As we all know the game behaves badly if you warp though soi changes too quickly, so I always set these alarms. I don't know how hard it would be to automatically detect soi changes (and keep the alarm updated in case I make further maneuvers). I wouldn't mind automatic alarms for when I create a maneuver node either. It could stop burn time / 2 before the node (if the burn time can be estimated). Finally I would love to have an "enter atmosphere" trigger. Again, this helps prevent issues where you warp through the atmosphere, and also helps me know when aerobraking will occur. Again, thanks for your effort on this supremely useful mod.

Yes, I do this all the time. If you do it carefully, it can definitely help keep an even TWR and squeeze out a few m/s Delta-V. In career mode, it's by far the cheapest to use SRBs to get your orbit above the atmosphere, and then circularize with a small engine.

I'm still not too sure what you're attempting to accomplish -- if you're trying to get upper atmosphere data, then you'll want to be as high as possible while within the atmosphere (138km). Keep in mind that you need to be on a sub-orbital trajectory to count as flying, you'll basically want to aerobrake at high altitude (making multiple passes as required) until you're sub-orbital, take your readings, then get out as quickly as possible. The craft as given is probably not going to be able to get "flying low" and still make it out. I'm not sure what altitude that is, but you'll probably need well over 15k m/s Delta-V to make it out from those altitudes.

Hmm interesting, though in the case of hovering, it's due to your craft not pointed directly "up". If the launchpad isn't 0 degrees with respect to Kerbin (because the VAB and launchpad is one giant slab that doesn't follow the curvature of Kerbin), then it means that your rocket is actually pointed ever so slightly to the west, which will give your craft a bit of drift as you hover for long periods.