fommil

oooh, that is true! The Pe is indeed lower and the reintercept would not be on the Pe, I'd be at an angle (non-ideal as you say). But when I GA from the right, the Ap gets a lot bigger and I don't know how to explain that, I'd need to go and look at the quicksave to see what happened to the Pe. Or maybe I was actually observing the effect from the Mun GA and confusing it with the impact from the Kerbin one. I should investigate again in isolation. Because I did a correction burn (like you say, at Ap to raise Pe), I can't confirm this first point, but of course it would make logical sense because (assuming I were to reintercept exactly in phase) it would be with exactly the same relative speed as before. Thank you for the explanation, it's really good to hear that what I did wasn't in my imagination! And totally ironic that I discover this on my final manned return mission (to Tylo) and can now consider the game somewhat complete :-D ... if only I'd known earlier. But to be honest I think GAs (or, rather, their consequences to spacetravel, since the principal itself is simple) are the most complicated part of the game so it makes sense to only learn this latterly. this is great insight, thank you! Elon Musk owns SpaceX and the Boring Company. The sink just got in.

This is very interesting. I'd like to understand this a bit more. In my return back to Kerbin I noticed that the assist off Kerbin itself (before I came back for the second pass) definitely reduced my Ap and made my next pass be at a much lower relative speed, but maybe there was something else at play there. It's probably, like you say, because I got a different relative speed to the Sun that it gave me a lower energy orbit around the sun but at that particular moment in time I didn't get any advantage relative to Kerbin which is why I only reaped the rewards on the second pass. Something else I'd like to understand would be how much of a gravity assist I can reasonably expect off any given body, in dv. Presumably the limit is whatever that body's speed is relative to their parent, but it'd be good to know what some typical values are. e.g. how much can the Mun give depending on how close you get, if it's pointing in the right direction.

I have always been scared of gravity assists, but when exploring the Jool system I was amazed to discover that I could get a free capture by flying close to Tylo or Laythe. Up until that point I had thought aerobraking was the only way to achieve this kind of thing. So on my return journey, which was a 1k dv burn from Laythe back to Kerbin (incredible! especially when compared to the dv chart) I decided to do some playing around with the Kerbin insertion. I noticed that when I approach a body from the left (i.e. as if I were to insert into an inverted, or clockwise, orbit) my craft becomes more aligned with the body I'm flying past, as if I had burnt retrograde. It doesn't seem to matter if I'm jumping up (Kerbin to Jool via Tylo or Laythe) or down (the opposite) an orbit. And conversely, if I approach from the right (i.e. as if I were to insert into a normal, or counterclockwise, orbit) then the body is actually adding to my velocity and the gravity assist looks like I burnt to prograde. Is what I found generalisable or is it just working out this way by accident? I managed to time a flyby of both the Mun and Kerbin on my return from Laythe, both pretty close and from the left, which brought me into an orbit with an Ap somewhere between Duna and Dres, which is a pretty big dv saving given that I was coming from Jool! I was impatient and wanted my next Kerbin approach within a year, so I spent about 300dv at that point to get a quick rendezvous but I could imagine waiting some more years and it would have come along naturally. My approach speed after doing this was very very safe for an aerobrake into Kerbin at that point, whereas it would have been touching cloth to have gone straight for the aerobrake first time. However, it occurred to me that when doing an aerobrake it always has to be from the right (counterclockwise) to go with the surface movement. But that's actually counter-productive compared to the non-aerobrake scenario. Are there any situations where it's worth going into the atmosphere from the left, and staying quite high, to get the benefit of both kinds of decelerations at once? The GA effect from the left is definitely my preference when I can do it, because it is just so much safer than risking the craft on a high speed aerobrake. Anyways, that's what I've figured out with experimenting. I'd be really interested in knowing if there are any in-depth tutorials that go into more detail than this. I watched Advanced Orbital Mechanics by Bradley Whistance (undoubtedly the king of gravity assists) but I found it lacking in detail... e.g. the approaching from the left vs right and tricks. On my return to Kerbin I ended up spending a bunch of dv to get an intercept on the followup orbit , but is there maybe a trick to get that for free? e.g. maybe trading off some of the saving to get exactly the right orbital period to come back round again for the next pass (within 2 years), I wasn't able to get it to work. My only remaining challenge in the game is the Grand Challenge, so I'm thinking of using some techniques to avoid having to mine for fuel along the way.

no, that's not it. The numbers are just in a completely different basis. e.g. I have a Kerbin to Jool transfer and Alex Moon's ejection angle is supposed to be "114 to Prograde". Trial and error in the actual maneuver node gives me an Ejection for the Maneuvre node at "-160.5". It's just completely off and I can't find any stable point to use as the reference for how to convert between the two bases.

If I use Alex Moon's calculator, e.g. http://alexmoon.github.io/ksp/#/Kerbin/100/Duna/100/false/optimal/false/1/1 it will give me an Ejection Angle for my initial burn, e.g. 153° to prograde. What I would like to do is to be able to add a maneuver with that exact ejection. Unfortunately, the Advanced Orbit tab gives me an Ejection in a seemingly different basis. It will tell me "angle between the craft, the orbited body and the parent" as an angle from [-180, 180] and I can't work out how to convert between Alex Moon's number and this number. It's not a simple case of the zero has moved, it just doesn't seem to make any sense to me at all. I end up eyeballing it and sliding the maneuver around until my full burn's Ap is maximised. It would be really nice if there was a way to do that with a level of precision instead of having to slide the actual maneuver backwards and forwards. Maybe I'm missing some button or key combo? As a bonus question: is there any way to see what the actual phase number is between 2 bodies (without mods)? It's not really important because I just trust the Alex Moon numbers, but it'd be nice to get the confirmation and it's useful for sub-system transfers like in Jool when it feels overkill to use a calculator. Somewhat related thread: https://forum.kerbalspaceprogram.com/index.php?/topic/184668-17-advanced-orbital-info-tab/

just reporting back, my SSTO return to Laythe (with stops at all the other moons, except Tylo) was a success! Laythe, Val, Bop then Pol, then back home from there, my deltav return from Pol was probabyl incredibly inefficient because I tried to use Tylo for one last GA but totally messed it up, then realised it didn't matter because I had enough to burn from Pe anyway to get back to Kerbin. That was the most fun I've had since an Eve return!

this was plan A, but I've heard so many people talk about gravity assist from Tylo that I kinda want to do it. It feels like one of Those milestones in the game. Promoting Tylo GA to Plan A!

ok, I guess if 1km altitude on Duna isn't gonna capture you, then nothing will oooh, this is a really nice hack, thank you. I've been noting my Pe velocity, then decreasing at Ap and noting what it is afterward, which is obviously inaccurate since I didn't measure at my true Pe (on either end of the maneuvre). Basically my current mission is an SSTO to Laythe. I can carry 3k dv in that thing, without a tug. The Alex Moon orbital transfer cost is 2k from Kerbin (and I still haven't got the hang of gravity assists from the Mun/Minmus on a full tank), which I can do comfortably. The insertion burn to enter Jool (not Laythe!) on an elliptical orbit is quoted at just over 1k in the dv map. Converting to the relative speed to Laythe is tricky but in the worst case, I aerobrake around Jool until I get a pass across Laythe which should be another ~1k aerobrake. OK, so I really never need to aerobrake more than 1k at a time here, so I'm overthinking it. I can do that in pretty high orbital passes. And probably can just do it in one go with Laythe, given that I know I can aerocapture 1.5k dv on Kerbin already. Refs: http://alexmoon.github.io/ksp/#/Kerbin/100/Jool/210/false/optimal/false/33/1 https://wiki.kerbalspaceprogram.com/wiki/List_of_orbital_velocities_for_low_orbit The confirmation I'm hearing from you is that I can aerobrake as much dv as I like if I go deep enough into the atmo, it's just that I need to be super careful about the exact Pe that I pick, so there's no alternative to trial and error once you get there. So no need to do endless Debug runs, like an Eve takeoff needs Just gotta pick a landing site now. I'm assuming that Laythe has lots of natural runways. At least, Bradley Whistance always seems to be able to land anywhere on any body, so I'm probably overthinking that too.

they are, thank you! Apologies, I think I was using the wrong terminology. When I was talking about approach speeds, I meant the orbital speed plus the dv needed for a circularisation burn. This is super easy to get from Alex Moon's calculator without even needing to experiment (and I think even some of the more crazy multi-gravity assist tools also give this info). but that's maybe a bit too much margin. Kerbin's atmo is much denser than Duna so the thermal increase happens over a much shorter period of time. What I'm also not sure about is what the maximum is at Duna before I run out of air. It's a pretty thin atmo so how much could I feasibly expect to shave off? Oh, wow, that is interesting. Is there a simple calculation to convert Kerbin max speed into Duna / Laythe / whatever max speeds? I would intuitively (but probably incorrectly) assume that I could go faster through lighter atmos like Duna, but would have to be more careful at Eve. Maybe it's a case of noting "I burn up at 1.5k/sec at 40km on Kerbin, which is equivalent to X on Laythe" by consulting the atmosphere pressure charts. Thanks for the heads up, I was lazy and didn't read the charts! I will study it in detail now. Thanks for your insights here, it's definitely helping me understand how the drag / atmosphere approximations are working! There is a lot of material out there but it is hard to know which version of the game it corresponds to so I find that even things from 2 or 3 years ago regarding SSTOs are out of data already. BTW I found https://alterbaron.github.io/ksp_aerocalc/ in https://wiki.kerbalspaceprogram.com/wiki/Calculation_tools which is a bit out of date, but I'll investigate to see how far off it is since any physics models got updated.

yeah it's pretty cool, especially to speed up the Human Space Program simulator (aka debug position/orbit) but it has a couple of flaws that make it unreliable for me. It doesn't support airbrakes (which was a critical part of my Eve missions), doesn't support upper stage projections (although I can always design accordingly so that I can adjust final approach with side mounted engines or RCS), and seems to get the inflatable heat shield projections completely wrong. But for spaceplanes, it might be just the ticket (airbrakes not feasible at this speed anyway). It also doesn't do the "your ship will start to break up here" projection, which is something I'm interested in.

What I'm interested in is understanding the limits, so that I can design for it without leaning too much on the debugging cheats like set position/orbit (aka Human Space Program simulator). e.g. if I know my craft's drag at 10km at 1k / sec at kerbin (should be enough to extract the coefficients for the underlying cube based model), how does that translate into other planets. If I know that my craft starts to burn up at 15km at 1.5k / sec (i.e. the safe thermal zone of my cube based model) then I could use that to work out what my lowest altitude should be at Duna if I'm coming in at X k/sec, kinda thing. But I can appreciate that it would be too complex to simulate that. If the KSP model was more documented, I'd be tempted to code this up myself! (Disclaimer: I've worked on atmospheric reentry projects with ESA and I find this sort of thing to be more fun than I really should.) I'm really only interested in the initial capture, not the subsequent aerobrakes because they are pretty much a given.

Yup, I'm using that. The total drag at some fixed speed and altitude doesn't seem to differ too much between the version with the engine plate and the version with the radial attachments. That's what's so weird about this! It's possible I'm measuring wrong so maybe I should do this properly and actually write stuff down on some paper. I was especially confused to see that the radial mounts contributed any drag at all, because the wiki docs claim that they do not have any physics, I guess that's just out of date. OK, that makes a lot of sense. Engine plate it is! And even better if I use one that matches the size exactly. That means using the Mk3 Mount or a Mk3 convertor to 3.5m and then the 3.5m engine plate. The extra parts contribute more drag but the total must still be less than what it was.

I've been trying to find if anybody has made a chart or simulation for rules of thumb for how much deltav one can reasonably expect to shave off from a full insertion burn from an aerocapture around Laythe, Jool, Duna, Eve and Kerbin. I can imagine there being too many degrees of freedom to make it realistic, especially since the vessel's drag and thermal characteristics are the limiting factor and hard to quantify (besides mass and Pe approach speed which are pretty easy to obtain).

I have an SSTO with a Mk3 profile and I have an EP-37 engine plate at the back (which is just slightly larger than the Mk3 to be annoying) with 5 RAPIER engines (4 radial + 1 center). It is a decent SSTO, but I wanted to improve it, so I swapped the engine plate for 4 radial attachment points (BZ-52) to get the same 4+1 profile. According to the wiki, these points have no drag but using the debugging menu tells a different story. The drag from the radial attachments and the fuselage is quite significant, but still comparable to what it was before. However, my SSTO is not an SSTO anymore. It fails to ever generate enough thrust to get past mach 1. What's going on? This is very confusing. This doesn't seem to be purely drag related. Is it possible that one of my engines is getting clipped and not contributing the thrust that it says it is? Wouldn't it be heating up the surrounding engines in that case? I ended up using a smaller engine plate and displacing the engines, which is lighter than before and less drag, I think (I'm eyeballing it, so I'm not able to tell the difference when it's marginal). But this is still weird, and I'd like to know why I can't use the radial attachments instead of an engine plate (I have no need for the decoupler or the extra mass!) Before anybody flags it up: the Mk3 engine mount is useless here because it doesn't let me change the number of engines. I can put it between the fuselage and engine plate, to get less drag, but the extra mass cost is crazy. Would be better spending that mass budget on another engine!

I sent my Robotug to Dres and forgot to put extra solar panels on it, having only specced it out for Kerbin and Duna distances. Now it eats way more electric than the solar panels can produce. Is there a way to throttle how much mining and converting is done, so that I don't have to stop/start manually? I'm happy turning it down to 1% or 10% if it means I can go do other things and come back in a year. (there's no option in advanced tweakables, so I'm guessing this is going to need savegame modification or a mod)