herbal space program

I'm actually pretty convinced that they're worse and not better. While the performance of both RAPIERs and TJs at the high end of the air-breathing envelope is indeed significantly improved, the lowered ISPs and weak thrust at the low end have more than canceled that out in my experience. I was getting on orbit in 1.0.2 with 30% payload fraction in just fuel, giving me a whopping 4km/s deltaV on orbit, and now the best I can do seems to be closer to 3km/s and a 24% PF. I am continuing to redesign my planes to try to get back to where I was, but right now it's not looking so good. - - - Updated - - - Seriously! I am getting pretty fed up with spending hours and hours designing space planes and then just having to throw them away! I was actually going to start a thread in the Suggestions sub-forum just to complain about this.

RIC: "Not well. I tried the 1km/s route to Jool a few times, but could never get the second gravity assist right. So I went back to refining my design, which got me to 4km/s of dV in orbit, which I thought might squeak out a return if I could catch an assist from Tylo on the way out from Jool, but now I think it won't get to orbit with that much dV. I may have to give up on the return. :/" Yes, I feel about the same. I was able to thread the pork chops reasonably well after a couple of very time-consuming false starts, and although I never actually went past the second Kerbin encounter, it looked like my best launch was going to get to a Jool encounter for around 1400 dV all told. Starting with around 4Km/s at LKO, which was the best I could do in 1.0.3 after countless ascents and re-tweaks, it seemed like I could just maybe pull it off. Unfortunately, 1.0.3 has now broken that space plane completely, and with a redesigned plane I can't seem to hit orbit with more than 3-3.5 km/s using just RAPIERs. They're just too weak (and thirsty too!) at low speeds for me to do the sort of rapid ascent profile that I've found key to conserving fuel. Last night I spent a fair bit of time trying with 2 RAPIERs plus 2 TJs, and that plane's initial ascent to transonic territory looked great, but it just poops out too soon at the high end. I'm losing a good 100 m/s of speed and 50 m/s of ascent rate at a 29km switchover altitude vs. all RAPIERs in 1.0.2. The ideal ratio of engines for this rig seems to me to be 3 RAPIERs, 1 TJ, and 1 nuke, but building that is not so easy. My patience for this endless exercise is statting to wear thin, but I think maybe tonight I'll try putting 1 TJ, 1 nuke, and 1 RAPIER canted outwards on a tri-coupler in the middle, with 2 more RAPIERs on the outside. The resulting plane is sure to look ugly and fly even worse, but I think it might be able to find the deltaV sweet spot that way. Maybe I'll try a honking Mk3 design with 2+2+6 as well. At least that one won't require placing engines crookedly...' ...So after spending another evening learning how to fly my plane again, it looks like I can actually get the same deltaV on LKO I could before or maybe even better. It took lots of changes to both the design and the ascent profile, but now it seems to work pretty well again This plane has >4km/s dV on orbit, so I guess I can try again with this Laythe thing now...

I guess I should clarify that when I say harder I mean less efficient. I am trying to make the longest-range SSTO I can, and while I have to admit I have only spent a couple of hours working on it so far, the best I have been able to until now is 24% fuel payload fraction on orbit. My previous model in 1.0.2, which could get 30% on a good climb, barely flies at all in 1.0.3. Adding wings and removing intakes, I've found that the RAPIER engine does seem to be able to go a bit higher than it could before on air, but its nerfy thrust at lower elevations and the lower ISP has my air-breathing climb sucking up substantially more fuel than it did before. Maybe I still just need to re-find the optimal lift-drag balance for 1.0.3, or else revisit shipping a TJ engine instead of just RAPIERs, but my experience so far has been somewhat discouraging.

.....D'OHHHHH!! The new aero regime in 1.0.3 completely broke my Leythe-and-back space plane. It's basically a brick now. They were half way there, rounding Kerbin for the first time, and now I have to start over. I suppose I could revert my version to finish the job, but what's the point if that's not reality anymore? And since the change I haven't been able to get to orbit with nearly as much PF in fuel as I could before. Maybe 24% vs. a whopping 30in the previous version. It seems like the lift and engines got nerfed out of proportion to the lessened drag and air requirements. How is everybody else doing?

Well rockets might be easier now, but AFAICT space planes just got a fair bit harder. My edge-of-the-envelope SSTO designs are all totally broken now.

1.0.3 is giving me a huge sad because my Laythe-and-back spaceplane, of which I had a fleet of four half way to Jool via a crazy Eve-Kerbin-Kerbn multi-assist trajectory, is now totally broken in the new aero model. It flies like a brick, and other than invoking System Restore there's nothing I can do to get all that mind-boggling amount of productively wasted time back. WAAAHHHH! ....Also too I can't seem to make orbit now with anywhere near the same amount of fuel, even if I change the design to adapt to the new regime. In 1.0.2 I was getting a 30% payload fraction in just propellant on a really good ascent, and the best I've done so far in 1.0.3 is maybe 24%. Back to the #$%&! drawing Board....

I hadn't considered how hot I'd be coming in on my final return from Kerbin, but if I actually get that far before being thwarted I'll consider it a great victory As to leaving Jool, It's true I won't have the slow orbital velocity of Pol coming from Laythe, but I will have the awesome slingshotting power of Tylo pretty close by. I seem to recall in the past having gotten all the way to a Jool escape trajectory by swinging around Tylo from Laythe, but I guess we'll see. Again, if I even get that far I'll consider it a victory.

That's useful information about the 2:1 resonance to get 2 assists from the same body. At the link RIC posted above, the OP did a Munar assist to get to a trajectory that encounters Eve from the inside at around 9:30 o'clock from the original position of Kerbin. This Eve encounter results in an orbit that reaches nearly out to Duna's on the major axis but has a periapsis still around Eve. The trajectory results in a Kerbin encounter that OP then used to set up a 2:1 resonance orbit with Kerbin, with apoapsis well past Duna. After the second Kerbin encounter, the apoapsis was right at Jool. OP claims it was all done with only 1000dV. In practice, I have needed around 1200dV just to get to the first Eve encounter, with or without the Munar assist, but I am doing it all manually by trial and error, not with McJeb or any online calculation tools, so there's probably considerable room for improvement. Nonetheless, I think you were right about the Munar assist not getting you much. I was mistaken about the size of the of my burn at Munar periapsis in my previous post. Anyway, I have verified that if you line up this Eve encounter correctly, you do end up with the subsequent Kerbin encounter, however I have not taken it past there yet. OP's times to each encounter appeared to be off by a factor of 2 to me for reasons I don't understand. OP said that the second Kerbin encounter was only 362 days after leaving LKO, but just one Kerbin orbit is over 400 days, so that seems plain impossible. Did they change all the orbital periods between versions somewhere? Regardless of that, my plan is to launch a fleet of 4-5 ships separated by a couple of days, in the hope that at least one of them can hit everything just right. If I can get to Jool with under 1500dV, I'm pretty sure I can get my current SSTO to Laythe and all the way back as well. My best LKO so far leaves me with just over 3900 dV on orbit if I burn it all with the nuke engine, quite more obviously if I can use the jets, and a bit less if I burn the 250 units of Ox I have left. From the right Jool encounter trajectory, I should be able to aerobrake directly into Laythe, and in theory be able to land the ship without burning much of anything, although this brick-with-winglets won't really land acceptably deadstick. IIRC flying back to orbit on Laythe is significantly easier than on Kerbin, and I should have over a third of my takeoff fuel still on board at this point. If I can make Laythe orbit again with something like 1200dV left, I should be able to boost to a very high deltaV Tylo assist with a couple hundred to spare. Again if I do everything right, I believe I can get to some sort of Kerbin encounter from there. I seem to remember that if you eject from a Laythe-Tylo transfer retrograde and outward, you can raise your apoapsis past Jool and drop your periapsis nearly all the way down to Kerbin. From the slow top of that orbit, it also doesn't take very much dV to tweak things to the point of getting some kind of encounter. We'll see. I think it will be close, but I'm still a long way from really knowing. It's a fun challenge though!

I actually already got the Munar assist to Eve part worked out for my ship. IIRC, I had to make only a minor boost at my Munar periapsis to get an Eve encounter, saving me maybe 100 dV overall vs. what ejecting straight from Kerbin would have. It's lining up all the rest of it that seems truly daunting to me, although RIC's link should be very helpful for that. Another way in which I thought perhaps a Munar assist might be helpful is in terms of giving you another place to make use of the Oberth effect. If you have a really low TWR, that might allow you to split your boost between Kerbin and Munar periapses and thus enhance efficiency. However I have no idea how much the Oberth effect helps you boosting from 6000m above the Mun vs. 70km above Kerbin. Maybe some of the extra smart people around here could enlighten us on that point.

That is most definitely illuminating! Thanks! If only he'd had a slightly wider shot at the beginning that showed where Jool is. I think I can still figure it out from that though. I spent hours last night trying to puzzle this out by trial and error but gave up. If I can actually make the Jool system with only 1000+/- dV, then I think maybe I can pull it off!

As RIC pointed out to me in another thread, that 2000 m/s dV is only if you do the whole burn at Kerbin periapsis. How much will you actually lose smearing it out that much, especially on the last burn? This has been an issue for me even with a nuke at TWR around 0.2-0.25, where my last burn would take only around 6 minutes.

It's a slight variant of this: So far my best deltaV on LKO is around 3600 burning the nuke, which would be 27000 on the RAPIERs burning air. I could get to Laythe easily with that doing a regular Hohman transfer to Jool, but if I want to get back off of Laythe I need to find a cheaper way to do it.

Thanks! That looks like a good start.

Hello all, I've got an SSTO that I fantasize I can get all the way to Laythe landing and back without refueling, but I will need to use every gravity assist trick in the book to get there with enough fuel. I tried for several hours last night to work out a Kerbin-Eve-Jool or Kerbin-Eve-Kerbin-Jool slingshot maneuver, but was unsuccessful. Has anybody out there posted a calculator for this or even some kind of primer on gravity assists in KSP? Even a list of how much deltaV you can milk out of various bodies would be very helpful. For example, what is the best boost that you can get off of a prograde Munar slingshot? Does it even help you? Does dividing your ejection boost between Kerbin periapsis and your Munar periapsis gain you anything? Etc. Etc. TIA for any help!

I managed to get my ship on LKO with around 3600 dV in fuel left burning the nuke engine, 27000 burning the RAPIERs on air. I think that if I squeeze every bit of dV out of gravity assists to get there, I might just be able to make it back, but it isn't going to be easy. Does anybody have a link to a primer of some kind on multiple gravity assists? I got nowhere trying to work it out on my own last night. The best I could seem to do off of Eve was halfway to Duna orbit, which doesn't seem to get me anything.

I spent my whole evening trying to figure out how to get my SSTO to Laythe and maybe even back. I managed to get it to a 75km LKO with around 3600 dV (based on burning my nuke engine), carrying a whopping 26.7% payload fraction in fuel. Using my RAPIER engines on air at Kerbin, that would be 27000 dV, not sure how the ISP translates to the thin air on Laythe. I also have a couple hundred units of oxidizer, which I think (well, hope) is just enough to push me back into Laythe orbit when I top out in atmospheric flight on the return trip. If all I wanted to do was touch down on Laythe empty, I could easily make it to the Jool system by a direct Hohman transfer, with plenty of maneuvering fuel left to manage my Laythe approach, but if I want to get there with enough fuel to seriously think about getting back, I'll need to get fancy with the gravity assists. I spent several hours trying to figure out how to do the Kerbin-Eve-Kerbin-Jool slingshot to no avail. I'm not quite ready to just go look it up, but I am wondering if trying to go Mun-Duna-Jool would help me any. I think if I can shave something like 600dV off of my Jool transfer, getting back would not be out of the question. Once I'm in Laythe orbit, I could probably manage a Tylo transfer for another 900-100dV, which I believe can get you ejected from the Jool system entirely if you set up the gravity assist right. I imagine that boosting prograde at an 8km Tylo periapsis will also get me some serious Oberth, maybe enough for me to eject from Jool straight to a Kerbin encounter with my remaining fuel. With all the possibilities for gravity assists and aerobraking, it's tough to say just how far I could get. It would be great to have some kind of tool for calculating how much dV you can get out of various assist maneuvers, but I have not seen one around. Anyway, I guess I'll keep trying tonight....

On my most recent space plane, I did multiple aerobraking passes pitched up like this and ended up not even having any flames on re-entry. The trick is to hit the top of the atmosphere with maybe a 40km periapsis at a low angle (e.g. descending from a 150km apopapsis) and pitched up like 40 degrees above prograde. My periapsis kept increasing as I approached it from the lift I was generating. I was thus able to skim along the top of the atmosphere around 50 km until my speed was below 1400m/s, at which point I started to stall and had to pitch down more, but I never even reached the point where my ship was engulfed in flames, unlike it was going to orbit!

Yes I guess you're losing speed pretty quickly in that first hour after Kerbin periapsis, even if you're on an escape trajectory. I guess I'll find out if it's a problem anyway, As I'm going to see if my SSTMAB can make it to Leythe!

You can't take yourself to the top Kerbin orbit in stages, do say a 600m/s escape burn, until you're fairly to close to the desired ejection angle, then wait an hour or two on that trajectory before finishing? It doesn't seem like you'd lose too much in efficiency doing it that way, but then I haven't tried...

Yes I got that after reading up the thread. Sorry to jump in without enough information. Anyway, even at TWR<0.25 there are only a few situations where you'd really to burn more than 3 minutes at a time, like braking into Moho. For high deltaV Munar and interplanetary transfer burns, they can easily be done in multiple stages.

I think I stepped into something here without looking upthread enough. I'm not arguing that the nukes' heating should be nerfed, just that for some applications, like moving whole asteroids or seeing how far you can get in the Kerbolar system with a single-fueled SSTO, you're going to have to deal with some pretty low TWRs. I suppose you could always choose not to do such missions.

Sometimes you've got no choice.

Generic replies are fine with me! I used my nuke as an afterburner in the design I posted, but I think you'd need to go pretty big to support 2 or more nukes. As using just turbos + nukes, I don't think the turbos can sustain enough speed at the high end to allow for the most efficient flight to orbit. I also use the RAPIERS during my Mun landing to bleed off velocity quickly. It requires less accuracy that way, plus the rapid deceleration makes up or the lower ISP to a significant extent. Landing without them would have been very hard! Anyway, I'd love to see you prove me wrong about the turbos!

After spending a truly life-damaging amount of time working on it, I finally managed to get a stock 1.0 space plane to land a Kerbal on the Mun and bring him back safely to Kerbin without refueling: You can look through the album to see the details of how I did it. This seemed right on the edge of what is possible to me, and 4 RAPIER engines plus one nuke seems like the magic formula. I believe this design could just make it to the surface of Laythe as well, and I will test it for that challenge later. It mey requires some fancy gravity assists! However landing on the Mun and returning has its own unique challenges. Can you do better than this? Can you: Do it with lower takeoff weight? Do it with more than one Kerbal? Do it with more fuel in the tank when you land? Visit any other body as well? Do it without using a nuke engine? Land back on the KSC runway? Ground rules include all stock, 1.0.2, and no abuse of part clipping or any other physics exploit!

After endless hours of trying, I finally got a 1.0.2 SSTO to the Mun and back with a Kerbal and without refueling (yeehah!). I used a ship that weighed 47 tons at takeoff and had 4 RAPIER engines and one nuke. I will post an album (and maybe a challenge) tomorrow. I used the nuke as an afterburner both while breaking the SB and at the top of my air-breathing envelope, then milked about another 3000 deltaV out of it as an OMS and lander engine. I don't think there is any combination of engines that could do this that does not involve the nuke. It is indispensable when you need both long-range OM capability and a TWR that can land you on all the smaller bodies. That nuke burned almost 10 tons of fuel on the way there and back. The next most efficient engine, the LV-909, would have required 23.5 tons of fuel to generate the same total impulse, and more still to generate the same deltaV. You just can't do it without the nuke.