camacju

The challenge was to make an entirely rocket based SSTO that launches vertically. I added another element of challenge which is that I only used 1.25m parts. This means that I can't get the same performance as if I used a Mammoth and a cluster of nuclear rockets, but this approach keeps part count and mass down. The rocket consists of a Vector engine for Kerbin takeoff and landing, and two Nerv engines for everything else. Inside the fairing are a command seat, reaction wheel, battery, and a bunch of Mk 0 fuel tanks. This rocket is very aerodynamic so I take a shallow ascent profile. At 1500 m/s I shut off the Vector engine and let the Nervs continue. I'm not using all the oxidizer here because I need it for the landing back on Kerbin. In Kerbin orbit I use the same sequence of Mun assists that I always use for an Eve transfer. Mun assist brings me into an orbital resonance that gives me a better assist three orbits later, which brings me into an orbit that gives me a final assist 3/4 of an orbit later. This flings me onto a 6:5 resonance with Kerbin, where I intersect Kerbin for another Mun assist, which drops my orbit down and gives me a plane change, where I get an intersection with Eve's orbit. I don't have enough Eve relative velocity to do a Kerbin-Eve-Kerbin-Kerbin-Jool route. So I do a Kerbin assist, followed by another Eve assist, to get greater Kerbin relative velocity. This gives me a Kerbin assist that puts me onto an orbit intersecting Jool's orbit. I need to intersect with Jool's orbit at the ascending node of Eeloo with Jool, but Jool is in the wrong place. So I swing by Kerbin one more time to adjust my orbital period. My problem now is not too little energy, but too much energy. I have to eject from Jool in a nearly prograde direction in order to reduce my Eeloo relative velocity, but that would put me on an escape trajectory. Instead, I use a Laythe assist to bleed off velocity relative to Jool and also do a plane change to line up my descending node with Eeloo's apoapsis. Doing this reduces the capture burn significantly. Laythe assist Only 35 m/s to capture around Eeloo. That's quite good In low Eeloo orbit, and I've got plenty of fuel to land and take off again. This rocket is tall so landing was a bit of a challenge. I had to quickload a bunch of times. Eventually, I found a flat enough place to touch down. The question is, is 1403 m/s enough to get home? Eeloo ascent In Eeloo orbit with 820 m/s remaining. This should be enough, as long as I remember to save enough liquid fuel for the powered landing on Kerbin. Jool transfer. As you can see, I can't get a Kerbin transfer orbit directly from a Jool transfer. Instead, I use a Tylo assist to build up relative velocity to Jool. The problem with this is that I can't eject from Jool at the right angle. Closeup of Tylo assist. 570 m/s left. I definitely have enough to make it home at this point so I accept a less than optimal correction burn. I solve the problem of ejection angle by setting up a second Jool assist at a better angle. Kerbin encounter plotted. I use Kerbin and Eve to slow down, and thanks to the double Jool assist I have more than enough energy to do so. Using the body lift of the near empty fuel tanks to slow down Terminal descent using the last of the oxidizer. Landed back on Kerbin.

If you're gonna make it an advanced signal processing unit then another purpose could be an antenna extender so you can save antenna mass or cost or something.

Thank you!

In VAB. I purposely over-engineered this because this is the first time I've actually tried doing a solid fuel only mission. Launch with the Clydesdale booster Circularizing orbit with the Thumper booster. First major sign of overengineering here - the Hammer booster was supposed to be the orbital insertion stage but instead I just left it in orbit because I can't really use it for the Eve transfer. Six Shrimp boosters provide the Eve transfer Fine tuning Eve encounter with a few stages of Sepratrons Aerobraking Shrimp booster raises orbit at the right altitude to get a good Gilly intersect. From here it's all Sepratrons Fine tuning Gilly encounter I can't get the landing burn exact so I get close then lithobrake the rest of the way. Landing burn Second major sign of overengineering - only the top ring of Sepratrons was intended to land on Gilly, hence the absurdly low TWR of some of the upper stages. At least I know I have way more delta-v than needed to get home. I wait until Gilly's facing in about the right direction and then burn straight upward. I can't get enough fine control to get into an orbit first. Shrimp booster detaches Eve escape burn - very inefficient because I do have the margin required Fine tuning Kerbin encounter Fine tune burn Burning off the rest of the solid fuel to make aerobraking easier Aerobraking Parachute deployed Successfully landed back home

I would just use sepratrons to get within 50m/s of the correct value and then lithobrake. I'm actually gonna try doing this challenge and see how I end up doing.

@HenryLV you might have posted the wrong file there (:

Bradley Whistance did a 564 kg rocket. Not sure that it's possible to go lower than that

I'll paste my parts idea from another thread: My suggestion for new/revamped parts is to do something jet engine related. There are certainly good jet engines in KSP but there may be some gaps that could use filling. -Scimitar engine: The RAPIER without the rocket mode. Many SSTO designs use only the jet engine mode of the RAPIER, trading its high top speed for its lower efficiency and using a dedicated rocket instead of the RAPIER's rocket mode. Maybe as a trade-off between the Scimitar and the RAPIER, the Scimitar could be lighter or more efficient, or cheaper. This engine would be used a lot for SSTO craft. -Pulse jet engine: A very cheap and light jet engine for the beginning of career modes. Maybe have it replace the Juno in the tech tree and bump the Juno up a level, or maybe have the pulse jet down a level. The pulse jet engine would be a lot less efficient than other more advanced jets (1000-1500 Isp?) but it would be useful for puttering around the KSC area and getting some early game science, or for building micro jet engine craft, or for doing cheap contracts. The part number could be J-31, inspired by the Ford PJ31 pulsejet. -Rolls-Royce Olympus: A very efficient jet engine that tops out at just over Mach 2. The Goliath engine would fill this role except it doesn't really look like it's a dedicated supersonic jet engine. If the Goliath does fill this role, then an actual GE90 that tops out at about Mach 1 would be nice. -Ramjet engine: An intermediate between the RAPIER and the Whiplash. The J58 wasn't a true ramjet and couldn't get as high of a speed as one. The ramjet would have intermediate efficiency and top speed. Maybe the Whiplash could be nerfed to accommodate this. -Whiplash afterburner: The J58 had an efficient afterburner, so I feel like the Whiplash engine should have a more efficient dry mode and a slightly less efficient wet mode, just like the Panther engine. -Liquid air cycle engine or air turborocket: An engine that has high specific impulse at sea level and its specific impulse gets gradually lower as the atmosphere thins. Good for very high speed atmospheric flight but less optimal in space. This would be useful for large and streamlined craft. The RAPIER would fill this role except its rocket mode doesn't quite work this way. -A more realistic precooler: The real purpose of a precooler is to slow down the incoming air that comes into a jet engine, as well as cooling it down to increase the engine's efficiency. The precooler could maybe increase the Mach limit of any engine attached to it, and/or increase its specific impulse. For balance, its internal fuel tanks could be removed, while keeping dry mass the same. -Motorjet engine: Has a much flatter thrust curve than other jet engines and thus gives higher low-Mach thrust and TWR. Would be good for STOL / carrier landings. Other random ideas: Have the Nerv generate electricity when idle - after all, there's a pretty big nuclear reactor in there. Have RTGs decay with a half life of 80 years or so. Time will become a pretty big factor in missions to Eeloo or something. Have the gas generator outlets on gas generator engines produce thrust.

My suggestion for new/revamped parts is to do something jet engine related. There are certainly good jet engines in KSP but there may be some gaps that could use filling. -Scimitar engine: The RAPIER without the rocket mode. Many SSTO designs use only the jet engine mode of the RAPIER, trading its high top speed for its lower efficiency and using a dedicated rocket instead of the RAPIER's rocket mode. Maybe as a trade-off between the Scimitar and the RAPIER, the Scimitar could be lighter or more efficient, or cheaper. This engine would be used a lot for SSTO craft. -Pulse jet engine: A very cheap and light jet engine for the beginning of career modes. Maybe have it replace the Juno in the tech tree and bump the Juno up a level, or maybe have the pulse jet down a level. The pulse jet engine would be a lot less efficient than other more advanced jets (1000-1500 Isp?) but it would be useful for puttering around the KSC area and getting some early game science, or for building micro jet engine craft, or for doing cheap contracts. The part number could be J-31, inspired by the Ford PJ31 pulsejet. -Rolls-Royce Olympus: A very efficient jet engine that tops out at just over Mach 2. The Goliath engine would fill this role except it doesn't really look like it's a dedicated supersonic jet engine. If the Goliath does fill this role, then an actual GE90 that tops out at about Mach 1 would be nice. -Ramjet engine: An intermediate between the RAPIER and the Whiplash. The J58 wasn't a true ramjet and couldn't get as high of a speed as one. The ramjet would have intermediate efficiency and top speed. Maybe the Whiplash could be nerfed to accommodate this. -Whiplash afterburner: The J58 had an efficient afterburner, so I feel like the Whiplash engine should have a more efficient dry mode and a slightly less efficient wet mode, just like the Panther engine. -Liquid air cycle engine or air turborocket: An engine that has high specific impulse at sea level and its specific impulse gets gradually lower as the atmosphere thins. Good for very high speed atmospheric flight but less optimal in space. This would be useful for large and streamlined craft. The RAPIER would fill this role except its rocket mode doesn't quite work this way. -A more realistic precooler: The real purpose of a precooler is to slow down the incoming air that comes into a jet engine, as well as cooling it down to increase the engine's efficiency. The precooler could maybe increase the Mach limit of any engine attached to it, and/or increase its specific impulse. For balance, its internal fuel tanks could be removed, while keeping dry mass the same. -Motorjet engine: Has a much flatter thrust curve than other jet engines and thus gives higher low-Mach thrust and TWR. Would be good for STOL / carrier landings. Other random ideas: Have the Nerv generate electricity when idle - after all, there's a pretty big nuclear reactor in there. Have RTGs decay with a half life of 80 years or so. Time will become a pretty big factor in missions to Eeloo or something. Have the gas generator outlets on gas generator engines produce thrust.

I like trying to fly missions with as low of a launch cost as possible. It's another dimension of optimization that is often overlooked, and the rules are different from mass optimization in some areas and the same in others. Some of the main rules of thumb: -No jet engines or ion engines. They're efficient but way too expensive -Use the Baguette fuel tank -Use liquid fueled rockets for your transfer stages and landers; use solid rockets for the launch -Don't use RCS -Try not to use electrical systems where possible (but I tend to keep electrical systems for ease of use) Some low cost missions I've already done: 9995 fund rocket to Moho, Eeloo, and back: 24070 fund Jool 5 mission: (For Jool 5 challenge) 1738 fund Mun mission: (For the Mun and back Cheapskate Challenge) Next I'll probably try a low cost mission to just Tylo and back. Or maybe Duna. Note: If anyone can get a cheaper mission than what I've done, please let me know! I usually leave some pretty low hanging fruit for further optimization on the missions that I fly.

Ok this'll probably be my last reply here. If what I've explained already hasn't been clear enough, nothing will ever be. The measure of energy that I use is to get apoapsis as high as possible. When I do a gravity assist, that corresponds to leaving the assisting body in a direction that is exactly prograde. There's no need to say why this is the case; it should be enough that it is the case. This is why I say that a prograde ejection maximizes your energy. The best way to realize this is, again, to try it yourself. Without doing that, it's a bit like explaining primary colors to someone who's been blind since birth. Eject prograde from Kerbin. Without using any subsequent maneuvers, try to reach a significantly higher altitude over the Sun than you originally had. You won't. Edit: I'm racking my brain trying to figure out what's being missed here. It's probably something that I think is obvious enough not to need explanation, but is actually quite unintuitive at first and only becomes obvious through practice. If that's the case, then this communications mishap is probably my fault. (For the record, the members of the more technical KSP Discord servers are all of the same opinion as I am).

@iamn00b I used some aerodynamic tricks along with part clipping. The parts you see aren't what they seem like. No mods, just some creative part placement.

I've done missions that quite easily prove the point I'm making. And you're not understanding the reason for the Eve assist. First, I hope you can agree that the most efficient use of a gravity assist is to eject perfectly prograde relative to the assisting body's orbital velocity. I also hope you agree that no matter what you do, if you only use one assisting body, you cannot get more energy than a perfectly prograde ejection. If you're still confused, the Wikipedia article on gravity assists should clear some things up. Let's do some example orbits to demonstrate. First, I do a 1200 m/s prograde burn from low Kerbin orbit, such that I eject perfectly prograde. My speed relative to Kerbin upon SOI exit is 1350 m/s. My apoapsis is 25708 Mm. This is the highest altitude that I could possibly achieve with a 1350 m/s exit velocity from Kerbin, for what should hopefully be obvious reasons. (Kerbin's orbital velocity plus my relative velocity are both directly prograde). Then, I do the same burn, but adjusted so I eject radially and I encounter Kerbin one year later. Then, to get the maximal effect from the gravity assist, I make sure that my exit vector is perfectly prograde. Note that my Kerbin exit velocity is 1350 m/s and my Kerbin entry velocity is the same. In other words, it's exactly the same as the previous relative velocity. Note also that my final apoapsis is the same as if I did the initial exit burn properly in the first place! No matter how many Kerbin flybys you attempt, you cannot get any extra energy from them! You need a second body. This is the true reason for the Eve assist, which I will show later. Next, I do the same magnitude of burn, but adjusted so I eject retrograde and get an Eve gravity assist. I purposely don't use the full effect of the Eve gravity assist, to simulate the effect of a less massive body. Hopefully this will satisfactorily disprove your assertion that Eve's greater mass plays any essential role in this. Because of my normal and radial component to the burn, my Kerbin exit velocity is lower - 1005 m/s. However, this is still instructive. Now, after my Eve gravity assist, I encounter Kerbin again. Note that my Kerbin entry velocity is higher than 1005 m/s! This is the real reason for the Eve gravity assist - to increase your relative velocity to Kerbin. An encounter with a body of any size is sufficient for this, which I've hopefully proven with my low powered gravity assist. Eve's mass just makes this require fewer assists. Mass doesn't really matter with gravity assists as much as the relative energy differences between orbits.

You're close enough. At some point you don't get significant extra benefit from repeating gravity assists, so you need to swing off a different body. That's why in a K-E-K-K-J route some people stick an extra Eve and Kerbin assist between the two Kerbin assists, to "reset" the gravity assists and get more Kerbin-relative velocity.

Yes, that's it. Your velocity relative to the assisting body will not change, which means that at some point you'll saturate the gravity assists and not be able to get any more energy relative to the parent body. See the comment just above yours for more detail.

I haven't actually put that much thought into this. Thanks for explaining it quite well! I tend to sidestep this issue by putting enough thrust into my transfer stages that I don't need any periapsis kicks in the first place. So I haven't had much experience with it. I'm better with chaining gravity assists together (:

Not necessarily same speed and direction - only same speed relative to the body. Fly it yourself and see. How do you propose to do this without a deep space maneuver? Sure, ellipses can intersect multiple times, but you don't get any benefit you wouldn't get from a simple resonant orbit. Changes relative speed to Kerbin, yes. Changes relative speed to Mun, no. Again, fly it yourself and see what your relative velocity to Mun is at each encounter.

Increasing thrust is a lot less important than reducing drag. Parts inside fairings or cargo bays don't produce drag, so try to keep as many parts hidden as possible. Minimize wing area to further reduce drag, use nose cones on any open nodes on the craft, etc. You'll find that you'll be able to break the sound barrier much more easily.

You can see the Rapiers in air breathing mode to prove I'm not using them in closed cycle. Here's a picture in VAB showing zero oxidizer and only liquid fuel. Jet engine world record is 2113 m/s so I'm still a ways off.

Yes - I should have clarified that I was talking about a body in a mostly circular orbit. You again miss my point. You have two Mun assists, but your relative velocity to Mun will not change at all. Again, I've been talking about relative velocity this whole time, which is the most important factor in gravity assists. If you actually fly this path then you'll realize that while the direction of your exit velocity will change, because that's the entire point of a gravity assist, your Mun relative velocity won't. Not to be pedantic but you say this and then immediately come up with a case where you do benefit from periapsis kicks. You want to do as much of the burn as close to periapsis as possible for this exact reason. Cosine losses aren't actually a problem because gravity is redirecting your velocity. If cosine losses were a problem, then doing two prograde burns on opposite sides of the planet would cancel each other out. Instead, they raise you into a higher orbit (Hohmann transfer). You're right. I meant to say relative velocity.

I've got a craft that can do 2100+ m/s. I'll probably record a video of it tomorrow

I think there may be some misunderstanding here. Note the deep space maneuver in your screenshot. This means you expend extra delta-v where that's not necessary if you're smarter with gravity assists. Edit: It seems you haven't actually read my post. This means that you can use two gravity assists in a row off the same body. However, neither gravity assist will change your relative velocity. It simply redirects your pre-existing relative velocity into a different direction. You seem to be putting words in my mouth here. My point is that it isn't different. Each gravity assist will have a similar effect. No single gravity assist will change your relative velocity to the assisting body. I'm not sure where the block is here.

You may be thinking of something else. Normally, when you do multiple assists from one body, it's because you have a deep space maneuver half an orbit away, in order to increase your relative velocity. While this is more efficient than a naive direct burn, it's still less efficient than a completely ballistic trajectory. This was used in the MESSENGER mission, Parker Solar Probe, and the Stardust mission (although I'm not 100% sure on the last one). The one exception to this is when your relative velocity is high enough that you can't bend your trajectory all the way around with just one assist. However, if you look at the numbers, your relative velocity before and after the flyby will be exactly the same. There's a pretty simple argument involving potential and kinetic energy as to why this is the case. To actually gain energy, you need to do gravity assists off 2 or more bodies, hence the Mun and Kerbin flybys before getting to Eve. You can see this in the Kerbin-Eve-Kerbin-Kerbin-Jool route that many people use to get to Jool for a reasonably low delta-v cost. The Kerbin->Kerbin assist does not change your Kerbin relative velocity at all. Instead, it redirects that velocity closer to prograde, raising the orbit. Meanwhile, Kerbin->Eve->Kerbin does arrive back at Kerbin with greater relative velocity than you left, since you passed by a second body during that time - and that's the important part.

As other people have wonderfully explained in this thread, a lower orbit is better. Ideally you'd want to be as close to the atmosphere as possible - and if your craft is properly drag optimized, you'd even want to be inside the atmosphere. I've seen missions that circularized at a 10 km orbit to maximize the Oberth effect as much as possible, since the crafts had so little drag. I prefer a 72-75 km orbit, except for when I'm feeling particularly lazy, in which case I go into a higher orbit. Low TWR actually isn't an issue for low orbits, as long as you plan properly. Even if you don't have the requisite thrust to weight ratio, you can split the burn into multiple smaller burns so you don't accidentally do an atmospheric dive. This also does more of the burn at periapsis when you're moving faster, taking extra advantage of the Oberth effect. This also has been addressed in previous comments. The main problem with periapsis kicks is that if your destination is outside Kerbin's sphere of influence, you need to perform an ejection burn, which might take a long time. If your TWR is low enough, then something like a 10 minute ejection burn just isn't going to work. However, if you've needed to optimize cost and/or mass enough to require that low of a TWR, then you are probably going to benefit from gravity assists. Using gravity assists, you can actually get anywhere in the Kerbol system for only the cost of the initial Mun transfer. This means that all you need to do is wind up your orbit to the Mun's orbit, which doesn't suffer from any TWR limitation. This is actually the cheapest possible way to get anywhere in the system, so it's a very useful trick even when you don't strictly need it. I've done a bunch of missions using this flight path. The first step is to get an orbit that is just below the Mun's orbit, and get a gravity assist that passes behind the Mun, throwing you into a higher orbit of Kerbin. Then, do it a couple more times to eject from Kerbin with as much energy as possible. There's a problem with this, however: the energy from Mun assists isn't actually enough to get anywhere by itself. It's just short of an Eve or Duna transfer. This means that instead of ejecting with maximum energy, you need to eject into an orbital resonance with Kerbin. What this means is that the period of your orbit, divided by the period of Kerbin's orbit, forms a nice fraction, like 6/5 or 5/6 or 4/5. Then, after a few orbits, you'll encounter Kerbin again, letting you do another gravity assist. The gravity assist won't be off of Kerbin, however, Since you left Kerbin with a certain velocity, you'll encounter Kerbin with that same velocity. You won't gain any extra energy from swinging around Kerbin. Instead, you use the Mun another time, passing behind the Mun while you're on a hyperbolic trajectory. (To encounter the Mun in the right place in its orbit, do a burn one or two orbits before, in order to adjust your orbital period). This gravity assist gives you less energy than the initial Mun assists, but it'll probably be enough to get you to Eve. If not, just eject into another orbital resonance, and do the same thing one more time. Once you've gotten an Eve assist, you're practically home free. Pass in front of Eve to get an orbit crossing Moho's orbit; pass behind Eve to reach Kerbin with more speed than you left it and continue to Duna, Dres, or Jool.

For lighter payloads I use a SSTO unless I'm feeling really lazy in which case I use a conventional rocket. For heavier payloads I always use a conventional rocket. My conventional rocket designs aren't very mass efficient but they're usually pretty cheap. A stage of solid rockets, then a liquid rocket stage, is usually sufficient to get into orbit for pretty low cost.