ajburges

I said the Poodle was a better performer, but it still requires that 2.5m node. How does the drag of the Poodle + adapter compare to the Swivel? I would assume the 1-2 Swivel does better on drag. You need a touch over 3 Terriers to match the thrust of one Swivel. Again, fewer parallel stacks should translate to less drag (assuming you need more thrust than the Terrier gives to begin with). IMHO there are two main classes of space plane: Lifters and interplanetary craft. Lifters just need to reach LKO with payload (and return). Extra trust allows for lower part count, more payload flexibility, and fewer parallel stacks. Interplanetary craft need the Isp efficiency, but those craft are less practical than a transportation network. For reference, what kind of anaerobic TWR are we talking about here? I tend to aim for an anaerobic takeoff weight TWR of .7 if there are no RAPIERs. I could likely reduce thrust some more, but that then eats into my flight margin.

As long as you don't change SoI it is always more efficient to do multiple burns. The efficiency loss you are alluding to is your choice of sub-optimal prograde burns away from Pe or cosine losses with an averaged burn. Peak efficiency is prograde exactly when velocity is highest. It is all about compromise. I've heard 1/6 an orbital period quoted and that seems a fairly reasonable compromise between cosine losses and burn time.

The LV-T45 offers a nice compromise of thrust, Isp, node size, drag, and tech availability. Terriers tend to be light on the thrust for simple ascent burns. You either need a tuned ascent or more engines. Flying efficiently with low thrust is not trivial. The LV-T30 has less Isp and that is a poor trade for the greater thrust. The LV-T40 has plenty of thrust. The Poodle is a much nicer engine, but the node size adds drag (or does it?) The aerospike is better for practical use, but that is late tech tree.

Unless your craft has non-orthogonal lift vector's, 30° AoA is about the critical AoA. You have enough speed that stalling is less a concern than losing said speed. Try to keep constant speed during the pitch up. Remember: airspeed, altitude, or brains; you always need at least two. - - - Updated - - - That's not efficiency that's just sand bagging dV. I caution against LV-N without RAPIERs. They are too heavy and/or too weak for efficient ascent on their own. Once you have RAPIERs, you can use the LOX in the adapter parts for a quick burst of thrust via rocket mode. That thrust will will push Ap out and give the nukes plenty of time to circularize.

I have experienced this problem as well. The work around I've found is to ensure that the root part of the vessel being merged is the initial root. You can't just change the root via the tool. You need to also detach the rest of the vessel, trash then replace the root part, and reattach the rest of the parts.

The basic space plane ascent is an aerodynamic flight to the edge of the aerobic flight envelope followed by a transition to a ballistic profile (gravity turn) on anaerobic engines. The details of your engines and aerodynamics determines your profile. The edge of the aerobic flight profile is 1-1.4 km/s depending on engines and aerodynamics. You need to double that for orbital velocity. You need to thrust with prograde to gain that speed. If you thrust above prograde, you are using thrust to fight gravity more than gaining speed (a small AoA is okay because of the nonlinear cosine decay). On the other hand, if you pass Ap before you circularize, prograde now points downwards! The key to efficient anaerobic ascent is to pull your velocity vector up so that you enter a gravity turn that will give you the time to build that orbital velocity by the time you reach Ap (and prograde matches horizon). The lower your anaerobic TWR the more burn time needed to accumulate orbital speed and the steeper your initial ballistic velocity needs to be (time to Ap is a function that is dominated by vertical velocity while suborbital). I propose a slight adjustment to your flight profile. Accelerate to max jet speed between 16-17 km. Light rockets at 1 km/s (keep jets on to) and pitch up (20-30 degree AoA) to pull your prograde up. As your jets starve, GRADUALLY reduce AoA to 0. Once you do, engage hold prograde and see where you wind up. If you went suborbital, you need a harder pitch-up. If you overshoot, you can relax it a little. You want to keep Whiplash engines to 16-17 km while accelerating. That's about their optimal power range. 1200 m/s is also fast for them. You want to start pitch-up before they lose their thrust (you need that thrust to aid the trajectory change)

Please produce a picture of this behavior. Asymmetrical body lift display can either be a graphical bug or actual lack of lift. If your plane is pulling port or starboard it could be a few things: 1) incorrect manuvering: yaw is to control slipstream not turn. 2) excessive yaw authority: see above 3) CoP too far ahead: you need a larger/additional verical stabilizer (or more yaw authority and a fly-by-wire system we don't have)

Low anaerobic thrust will be (comparatively) very costly to get to orbit. The anaerobic thrust stage can be conceptualized as the question of how do you reach orbital velocity by Ap? The speed building stage of aerobic flight leaves you with a horizonal prograde (near Ap). You want to use your wings and cheap thrust at the end of aerobic mode to alter trajectory to ballistic and push time to Ap out far enough that your gravity turn will reach orbital speed. Low TWR designs need a lot of time to accelerate that needed 1.2 km/s. If you have RAPIERs, the oxidizer you can store on just the adapter parts can really push that Ap to the future and give the OMS time to finish circularizing (RAPIERs can also give you more aerobic speed in jet mode, but LOX is cheap). An alternative thrust solution is an incorporated (or staged) SRB. SRBs have a ton of thrust for their weight and cost. The final solution is more anaerobic engines, but there is little comparative advantage in disabling orbital insertion engines once in orbit. Once you pass 24 km wings generate too little lift. Almost all of what keeps you up at that range is momentum. - - - Updated - - - TLDR: For efficient orbital insertion: aerobic mode should terminate into the start of a gravity turn. You want enough anaerobic thrust so that you reach orbital speed before Ap while thrusting near prograde.

Ya, learned of the Aldrin cycler concept today. Fairly close to my idea. Such cyclers only become practical once there is a good use for heavy, reuseable station parts (like self sustained life support). Still, plotting and executing a resonant flyby 3 patches ahead (with fp error and no correction) sounds like quite the navigational achievement.

Prograde is cheaper, but a sidereal rotational velocity of 9.0416 m/s means you only save 32 m/s round trip. Retrograde allows for free-return trajectory which is an interesting abort mode and cheaper for fly-by returns. Unfortunately free-return offers no net benefit if you capture. Hmm... I think I may have just had an idea for a challenge. Lunar rendezvous Mun landing. Mother ship can not thrust more than 5-30 m/s between lunar injection burn and lander return (so it can't capture and needs a trajectory that would establish a Mun resonant, elliptical orbit for a second flyby). To the sandbox! ... not sure what the judging criteria would be though

I think that one thing people overlook is that the STS shuttle was overdesigned. One of its mission profiles was a once around polar flight. Such profiles are trivial for SSTO space planes, but SSTO rockets don't have the cross range for a return to KSC without extra fuel for a normal burn. Still, the kid size planet makes space access too easy to skip straight to 100% recovery solutions. Any STS shuttle is a few jet engines and some fuel away from being an SSTO solution. The closest I've come to practical STS shuttles are Duna space planes.

I follow a different line of thought. This gives way more launch windows with minimal dV cost. Establish and execute transfer orbit that will intercept target orbit > Plot intercept trajectory > Correct encounter for prograde, retrograde, or polar flyby > align the Pe with an intercept of target orbit (you want Pe to touch target orbit) During capture burn, you can easily get 10+ degrees of inclination change for (essentially) free due to trigonometric ratios. Doing this at intercept allows you match orbit quickly. If you need a lot of inclination change, do an elliptical capture (with 10+ degrees of inclination change) and finish all but 5 degrees of inclination change at Ap. Remember, small orthogonal thrust is nearly free during a large burn. This approach also allows for a 1 orbit rendezvous every time! This approach works due to the non-linear ratio of trigonometric functions sin(x)+cos(x) (the sum of the component trust vectors) is greater than 1 for angles (0,90) (degrees). At 10 degrees AoA, you still realise 98.5% prograde efficiency, but also get 17.3% orthogonal thrust. For about an extra 1.54% burn time, you get a 11x return. That's better than the Oberth effect! However, remember that the returns are based on AoA: smaller AoA yields higher returns for the increased burn time.

I've come to the line of thinking that inclination tuning is the last concern for incoming trajectory. In order: 1) intercept 2) pro/retrograde equatorial/polar orbit (avoid orbit reversals) 3) establish planar intercept with target orbit at Pe (I want to do as much plane change work as possible for "free" with the capture burn) 4) if possible use minor radial adjustment and follow up to decrease arrival time and/or inclination difference. The added advantage of this approach is I can get a 1 orbit, 1 (rarely 2) burn intercept with any target in the SoI upon arrival. Most my satilite contracts also complete with the capture burn.

Yes but no. The normal dV component is indeed smaller with the low V burn vs the high V burn. The savings comes from the non-linear behavior of trigometric functions and the large dV cost of a capture burn. For an off prograde burn of angle a the prograde component uses the coefficient cos(a) and the orthogonal component has a coefficient of sin(a). The sun of those coefficients is greater than 1 for the range (0°, 90°). That means that the sun of the burn components is greater than the burn. As a result, while the normal component of a high V burn may be greater, adding it to a large burn is paradoxically cheaper than the small burn at a low dV. Note the primary savings is due to the trigometric sum. The trigometric sun is greatest at 45°. Past that, the sum decreases. A 45° off retrograde capture burn will not even produce 45° of inclination change. The math may indicate a lower thrust angle being the break even point. Someone would need to derive the equations to evaluate the optimal solution. Even then, there will be no easy answer since it depends on SoI, initial V, and initial Pe. The cherry on top of this is this manuver is the one of the few times that the optimal manuver is also the fast one. - - - Updated - - - My phone does not like it when I speak math. Please excuse the excessive auto complete errors.

Speaking of ham sandwiches and Gilly: Wouldn't be better to "land" the lander on Gilly and use the claw to directly attach a miner? The gravity is low enough that you could use RCS to position as needed.

If you suck at SSTO design then I'm a rank amatuer! I'm copying that bi-coupler use. Should be less drag than Mk1 radial stacks. From the picture, this is a slow ascent plane. 50 t on 2 RAPIERs is a large load, but others have done more. I don't have the patience for such slow ascents so I'll leave it to others to help you with that. The way the atmo currently works, the most practical place to get transonic speed on RAPIER engines is ASL. The power vs altitude curve is too harsh unless you are already at Mach 1. Get to about 330 m/s ASL and then climb as fast as possible while slowly accelerating slowly. Level off at angels 7-10 to push past 500 m/s and hit the power band. You get negative lift with negative AoA. That Mk2 fuselage is also a wing. When you point below prograde that body will produce negative lift. If it has a different CoL than your inclined wings, you can also get complex lift vector behavior.

"Gravity Losses" is a deceptively broad term. Orbital mechanics can approximate any suborbital trajectory as an orbital trajectory that goes below the surface of the orbited body. Orbital insertion then becomes a problem of how to grow am elliptic orbit efficiently starting at Pe with limited TWR (and atmosphere). There is no "gravity losses" from suborbital trajectories alone. What gravity losses actually are is radial thrust to keep you from the section of the trajectory that is subterranean; most craft don't do well underground much less several hundred km below the surface. Once you complete a gravity turn, you can eliminate that radial thrust completely. From an impulse perspective, applying thrust at any point other than Ap and Pe is a suboptimal way to alter the orbital energy. Thrusting of prograde is a different form of inefficiency. Which approach to orbital insertion is better is evaluating which inefficiency is greater. Thrusting off Ap/Pe or raising Pe from the lower Ap (and thus raising Ap with less velocity). Typically, the low difference in phase from PE means that insertion to high orbit is more efficient than raising a low orbit with the velocity loss. High Ap insertion spends less time in atmo. Note: a naive reader could take this as support for the notorious up and turn right approach. This is not so. Remember, we are trying to grow an extremely small, elliptic orbit without going subterranean. Going "up" is radial thrust starting with 0 component velocity. Better to use some of the velocity we get from planetary rotation. Going "up" is just to prevent us from passing Ap and needing even less efficient thrust application. Inclination changes are another interesting aspect. The role velocity plays in plane adjustment would imply that plane correction for arrival should occur at the Ap of a minimal capture (since the highly elliptical orbit is a prerequisite to circular capture). In practice, for small plane changes, I often find that a normal component in my capture burn is cheaper because of trigometric ratios of an already large capture burn make normal components incredibly cheap. The sum of sine and cosine is greater than 1 between 0 and 90 degrees! That means you can get net component thrust greater than their combined vector!

A challenge! Your description of torque behavior would work if the lift vector was constant in scale. However, KSP lift vector scale is proportional to AoA. Abstracting the CoL to be the CoP, lift will always work with a strength proportional to the AoA. If the CoL is behind CoG, that force will generate torque which will work to reduce the angle (and increase if positions are reversed). When AoA is negative, so is there scalar component. The aspects of CoP != CoL is true. For the scales we use CoM == CoG. Rounding errors mean we can't construct scenarios where CoG and CoM are appreciably different.

I disagree. For any given design, optimal ascent in absence of atmosphere is to burn prograde and circularize before you pass Ap. Up and to the side has more cosine losses than launch at angle theta hold prograde and control throttle to both avoid mountains and circularize at Ap. You essentially want to turn an elliptic orbit with you at the Ap traveling a surface speed (with 1g constant radial thrust) to a higher circular orbit. We all know that the most efficient way to raise an orbit at Ap is to thrust prograde (horizontal). The radial (vertical) component is to push Ap ahead so we don't pass it and lose altitude (or hit a mountain). You want to minimize it as much as possible. Better to pay the cost as a trigometric fraction of that requisite prograde thrust. SAS function to hold heading relative to horizon would be godsend though.

OP did not specify what they were optimizing for. Horizontal burn is only optimal from a dV standpoint. It also assumes a high TWR. For any given craft though, the quicker your gravity turn trajectory is tangent to the ground (without loosing altitude or colliding) the more efficient. Mass optimal ascent is more complicated and involves lander design. You are optimizing for engine size, fuel, and ascent path. Time optimal ascent is fun. Mostly 'cause you use Moar Boosters!

A few observations I've had with rovers: Any part on the outside (or on a bay wall) with an impact resistance of less than your driving speed is fodder. Keep fragile parts enclosed. For this reason, Mk2 and Mk3 fuselages make great rovers. A wheel that takes a collision on its own will pop, either accept that or work to minimize the scenarios where one wheel takes all the abuse. Landing gear in front can help if you don't mind the aesthetics. Time warp is king. A 10 m/s rover that can travel under 4x physics warp covers terrian just as fast as one that goes 20 m/s at 2x. 20 m/s is fast by terrestrial standards, but is dead slow by orbital standards.

As a bonus, a locked tank in front means you enhance aerodynamic stability as you ascend. Almost all my designs have the forward tank locked if the is a high moment of inertia with the fuel.

I'm more a proponent of learning on turbojets and rockets first. While less efficient, the turbojet ascent profile has wider margins. I just can't get past the poor aesthetics of wing incidence on Mk2 and Mk1 designs though. Makes it too easy to rationalize zero incidence designs. Maybe I'll toy with some non conventional wing designs. I tried experimenting with wing incidence on a previously working Mk3 design and found it made the craft more squirrelly. Fighting the pitch up tendency (not terribly hard, just annoying) caused me to spend too long too low and miss orbit. The wing has two pairs of engine pods and offset RCS, so fine rotation wouldn't be very easy to tune. Maybe my issue was simply that adding incidence sifted my CoL past CoM. Has anyone had problems with changing CoL with Mk2 designs? The difference in lift vector angles should make for potentially scary CoL shifts at the stall angle. Or do you just keep you designs stable enough to be stall resistant?

One thing to note: with the different angles of incidence for the wings, your CoL will shift with AoA. Until the critical angle, the CoL will shift towards the greater magnitude aligned lift vector sum as AoA increases. That critical angle has crazy behavior though. Given that your zero incidence surfaces are ahead of the CoM, your craft should have a stronger stabilizing response with AoA as long as you stay within the critical angle. However, once you pass that angle, the CoL will suddenly shift way forward. Once it does that, it will likely exceed your aerodynamic control authority. It would be very hard to return to controlled flight then.

KER can also display other aspects, Check the settings! I personally prefer the the time to node displays. But there is also phase read outs. KAC (Kerbal Alarm Clock) can also give you alarms on node. Burning away from node is wasteful (cosine losses) for plane transitions anyway. Only change plane away from node as part of a larger burn.