longhornchris

Question for BAC9 and company - any plans to update this to play nice with Career mode?

If you want to try your hand at spaceplanes then FAR is a must have. It makes spaceplanes behave much more realistically... although it does make it harder initially until you learn how to build a stable aircraft. If you have FAR then in order for your rockets to work you need fairings... and Procedural Fairings are your best bet, although the KW Rocketry Fairings work well too.

Assuming the system calculated your burn time correctly, I start my burns ~1/3 the burn duration ahead of the burn. So for a 15 sec burn I start at T-5. Using KES or MechJeb this results in long burns delta-V consumption match the originally predicted burn. As to what engines to use, this is a loaded question. Technically the delta-V calculated assumes an instantaneous burn - or infinite thrust to weight ratio. The lower your TWR, the longer the burn and potentially less efficient burn - especially when in a highly elliptic orbit. The tradeoff is that the low thrust engines tend to have the best ISP which more than offsets the losses due to long duration burns. One way to minimize losses due to long-duration burns is to break your maneuvers up. As an example, when attempting to get to Mun rather than performing a single burn to get away from Kerbin, perform multiple burns over a few orbits at periapsis to raise your apoapsis.

You should probably get Kerbin engineering system (KES) and the subassembly loader. KES can give you thrust-to-weight ratios for all the different bodies so you can size your lander for your target planet. Subassembly loader will allow you to save your lander and attach it to another spacecraft rather than re-build it.

The OP's question has been mostly answered, but I'd like to add a few more details that I think are germane to the discussion. Delta-V can be thought of as a normalized, or linearized, measurement of a rocket's available fuel. Unlike cars, airplanes, etc, a spacecraft has 'unlimited' range but changing vector velocity either in speed or direction requires fuel OR an outside force (gravity & drag being the two most common). Delta-V is the measurement of how much change in vector velocity is available. As capi3101 noted, the Tsiolkovsky Rocket equation is logarithmic. The equation also accounts for the engine efficiency, or ISP (Ve / g) and provides a measurement that can be treated as linear. What Delta-V allows you to do is compare rockets and probes in a normalized manner. As an example, after some practice (or mechjeb) you can find out how much Delta-V is needed to reach a specific orbit. As an example, lets say you place your orbit at an altitude that requires 3000m/s (if I remember that's between 80km and 120km but its been a while since I flew stock, I've got FAR installed). Your other rockets intended to reach that orbit should have that much delta-V (not counting propellant for use on orbit). There will be some variability for drag and gravity losses, but this gives you a baseline. Also, the amount of delta-v needed to change orbits will (with few exceptions) be the same regardless of spacecraft. As a simple example, it will take the same amount of Delta-V to go from 80km circular to 100km circular. Larger rockets will require more fuel by mass (assuming same engines), a craft with more efficient (higher ISP) engines will require less fuel, and one with a higher thrust-to-weight ratio will take less time for each burn, but the delta-V should be the same or very close.

Well, I can't give you everything, but here's a few general tips. 1: Center of lift behind but not too far behind your center of mass. This is important as if the COL is in front of the COM the aircraft will be unstable. If your COL is too far back from your COM then you won't have enough pitch authority to take off. 2: Its probably worth grabbing at least the landing gear out of Taverios' Pizza and Aerospace part package. The larger gear makes it easier to get off the ground without tail strikes. 3: Place your main (rear) gear far enough forward that you can actually pitch the aircraft up. If your landing gear is too far back you can't takeoff... if its too far forward then you risk tail strikes. Also, I've found that removing the nose gear from the braking action group will prevent the aircraft from pitching over the nose when landing or throttling up while braking. 4: The bulk of your mass will be fuel tanks, engines, and the cockpit. Build your fuselage & engines w/o wings first. If at all possible have an equal amount of fuel ahead and behind your COM so it doesn't move to much during flight. For spaceplanes I've found that 3-1 ratio of rocket tanks (fuel + ox) to jet fuel tanks (just fuel) gets me to space w/ enough jet fuel in reserve to have a powered landing. This does require having enough total fuel to get to space and move around. 5: TAC fuel balancer is almost necessary for space planes. Default fuel drain goes front to back, so w/o the fuel balancer you risk going unstable 6: Avoid having mixed control surfaces - have elevators for pitch on canards or a horizontal tailplane, a rudder on the vertical tailplane for yaw, and ailerons at the edge of your wings for roll. Adjust the max deflections to keep from stalling. 7: Read the help file for the graphs and stability derivatives - this explains what the terms and plots mean and how they should trend. Play around with the flight conditions. Also, remember when adjusting stability derivatives it is possible to create 'nonsensical' flight conditions like high mach #, low actual velocity conditions where the derivatives won't make sense. 8: FAR makes KSP more realistic - so start with designs that look like real airplanes. You should have success with something that looks like an F-16.

While Soyuz was born during the Russian lunar program, its design was ultimately setup to go to the various Russian space stations. The idea was that the Cosmonauts wouldn't spend much time in the capsule - so not much need for working or living space. The real time in space would be spent onboard the station, which was designed to be 'disposable' once it had reached its end of life. As to the US approach so far, vehicles like Dragon seem to have a similar concept - limited space in the capsule and get to a station quick. As for SLS I'm not sure what the approach will be but if I had to guess it will be a hybrid - where the re-entry capsule is only a portion of the total living space.

Those are part of the Autostaging. I know the 'pre' delay suspends the auto-staging from occurring immediately... I'm not sure what the 'post' does except maybe delay the next sequence from automatically triggering. I've used the 'pre' delay to prevent strap-on boosters from being jetisioned until the core has gone back to full thrust to minimize the chance of a collision.

Well, in real life a compressor stall is a very, very bad thing. At the most basic level, jets work by having the air exiting move faster than it entered. When a compressor stall happens out air stops flowing through the engine - essentially you go from providing thrust to providing drag near instantly. If the engine is centerlined then you just slow down... if its off center you have a serious yaw moment applied which is BAD. For more detail, if the intake (for supersonic aircraft) or compressor stalls then the pressure in the combustion chamber drops rapidly. This cuts the air available for combustion, which in turn causes the air-fuel ratio to go rich and thus the engine flames out. Additionally, the pressure and temperature drop reduces the energy the turbine can extract which cuts the input power to the compressor. Finally, the temperature/pressure at the nozzle drops and thus the thrust falls off. Dealing with compressor stall and intake instability were major design problems for high speed aircraft. Today the subsonic intake is pretty well mastered but supersonic intakes are still complicated.

If I could make a request of Bac9 - any chance you can add battery modules that complement your reaction wheel selection? Now that the SAS system uses electricity it would be nice to not have unsightly batteries bolted on or stuck inside a cargo bay. With that request made, this is a great set of parts for building spaceplanes, can't fly without it!

There are a few things I've found that can help when dealing with the stability problem. My easiest to fly designs are canard designs, with the main wing aft of the COM with flaps on the main wing. I try to place the subsonic no-flaps COL right behind the COM but very close. Next I adjust the max flaps to ensure that max deflection moves the COL aft - if the deflection is too large it will push the COL forward and/or stall which is bad. Because the COL moves aft as you transition to supersonic flight, the I use the flaps to start with my COL aft when fully deployed. Don't forget to set the flaps to action groups so you can adjust them. While you are in the action groups it I've found it helps to remove your nose gear from the brake command. Now, for the basic flight profile. The first thing is to set your flaps to max deployment. Takeoff however you prefer and gain some altitude, but keep an eye on your mach number. As your speed approaches mach .8 cut your rate of climb to increase your acceleration through the transonic range. Next, start raising the flaps. This takes some timing, but the idea is to shift the COL forward by raising the flaps while the transition to supersonic speeds so your COL stays in approximately the same location. Once you've reached Mach 1.2 or better resume your climb. If you are going to use the analytical methods, remember that you have to adjust mach number, speed, and air density. Because all 3 are inputs you can create some non-nonsensical situations (ex. high mach number & low airspeed) where the stability derivatives don't make sense. It took me a few flights to figure out what speed/altitude I could hit the critical mach .8-1.2 range.

Quantum struts is a good mod if you like performing orbital construction. I found its great for reinforcing docking ports because even the 2m docking ports are so strong. The new SAS system makes this less necessary because it doesn't wobble as bad but its still nice to add rigidity. Also, if you like spaceplanes the B9 is the package to get. The S2 fuselage system is well setup for making SSTO spaceplanes.

It shouldn't. The orbit is determined by velocity, independent of mass, provided you get periapsis above 70km where the drag kicks in (for Kerbin, see the wiki for other planets). Now it does take a lot more propellant to get more mass to orbit, hence normalizing fuel using delta-V rather than propellant mass (it also accounts for the logarithmic nature of the rocket equation). For 2 different rockets the delta-V to achieve the same orbit should be close - with the flight path and drag being the key additional variables. Two spacecraft in the same orbit should have the exact same velocity at the same point in their orbit (angle relative periapsis).

Well, while the new SAS is much better behaved, I still think they are running a PID based control with a few extras thrown in. My guess is that C7 added filtering either on the feedback input or the PID output, and adjusted the scaling to account for both control authority / inertia ratios. The filtering would prevent/limit the oscillations as the controller won't drive high frequency, while the scaling would ensure control doesn't go bang-bang unless you have little control to start with. That said, FAR adds in a few significant complications. First, control authority in FAR is heavily dependent on flight conditions and varies with altitude and airspeed (dynamic pressure really). My guess is that while the SAS gains 'adjust' in real time with the vehicle inertias, I doubt the scaling accounts for any FAR adjusting items. Second, and perhaps more troubling, is that aircraft have significantly more complicated and variable cross-axis coupling - with roll-yaw coupling being the simplest. The cross axis coupling is both design and flight condition dependent, and real aircraft designers have to take this into account when setting up control aids and/or autopilots. With the extra variables, its likely that the 'properly damped' SAS for rockets is under damped for many FAR planes, at least under certain flight conditions. The only solution I've found so far is to have a stable and properly trimmed plane until I get high/fast enough for SAS to be stable... and that varies with each airplane.

Well, first I'd suggest getting FAR because the modeling is more realistic which for me made the design more intuitive. It does, however, punish you for mistakes, etc. Next, having Mechjeb is a huge benefit, if only for information. The surface and orbital information tabs help planning maneuvers, timing burns, and flying a 'clean' ascent. The TWR info in the hangar will keep you from over-designing the bird. The 'Utilities' tab is nice as the 'Prevent Flame-out' will automatically manage the throttle to keep you from having a flame out. TAC Fuel balancer is also crucial - as your CG will move as fuel burns. Because the forward tanks burn first your CG will move aft if not balanced... this can be a very bad thing. Finally, having some parts mods will help just to build bigger planes. Taverio’s Pizza and Aerospace v1.4.1 has bigger landing gear, which make takeoff much easier (tailstrikes suck). Its also got some extra wing parts making it easier to get more lift w/o having huge wobbly wings made of lots of parts. B9 Aerospace has a ton of great spaceplane parts too. Having the different part sizes (mostly fuel tanks) helps get the right fuel/oxidizer ratio - as a good spaceplane needs extra jet fuel compared to oxidizer. Now, for the design. As others said for stock parts Ram intakes are best. If you get Taverio's or B9 then their 'spike style' intakes work equally well. I generally go for a jet-only TWR around 1.5, any more and you've got too much thrust (and thus 'dead weight'), less and you will be have trouble at altitude/speed when the thrust starts to fall off. I've found the rockets being at 1.5 at 'launch' works well for me to reach orbit from max jet altitude. For fuel/ox ratio, remember the rocket fuel tanks are 'balanced' while the fuel tanks are just fuel. I've found 4 parts rocket fuel tanks to 1 part jet fuel tanks works about right, but usually I fly at 3-1 because of tank selection. This also provides me extra jet fuel for landing. Other things to remember in the design - center of lift (COL) needs to be near, but behind the center of mass (COM). Remember that as fuel burns off the COM will move, even with the fuel balancer. I try to make sure I have equal fuel fore and aft of the COM so that, when balanced, the COM doesn't move much. If the COL is ahead of the COM the plane will be unstable. If the COL is too far back, however, you won't have sufficient pitch authority - so its all about finding a good balance. Also, if possible have an odd number of jet engines and place the center one last. The last engine placed is the first to flame out... and a center engine flameout won't put you in a flat spin. Finally, don't forget RCS, you may need it to maneuver once in space. Before you leave the design, make sure you assign action groups. I typically put Rocket toggle on '0,' Jet and Intake toggle on '9.' Closing the intakes cuts your drag, so its worth doing once you switch to rockets. Now, from a flight perspective, the key is patience above about 15Km. MechJeb's surface tab provides rate of climb info (so does the GUI, but its on a log scale and small). The key is to climb slow enough that you gain speed and altitude together as air intake rate is speed and altitude dependent. I've found 50m/s or less vertical works fairly well. Gain altitude too quickly and you won't have sufficient airspeed to drive the air intakes, flameout, and have to try again (if you don't get thrown into a spin). You can squeeze more from the engines IF you throttle down (or use mechjeb auto-throttle) to keep gaining speed at altitude. One you've squeezed the jets for everything, its time to engage the rockets and climb again. MechJeb's orbital information tab is useful here - when both your apoapsis and periapsis stop growing you've maxed out... this doesn't necessarily happen when you stop accelerating. There's a small window where the added speed gained by the rockets will provide extra air for the jets - but be prepared to shut them down quickly. Once on rockets there is no need be in the atmosphere so pitch up some to get out of the air and drag. I typically go to about 30 deg nose-high. Downrange speed raises your orbit (apoapsis and periapsis), while vertical speed only really gets you out of the atmosphere. Climb to steep and you will need a longer burn to circularize. Burn until your apoapsis is high enough - 75Km to 80Km works nicely. Then kill the throttle. For drag minimization, pitch back down so you are nose-on your velocity vector. You may need to tap the throttle to maintain apoapsis as drag will slow you down. Once you clear the atmosphere, setup a maneuver node at apoapsis and raise periapsis accordingly. I like 75Km to 80km because it give me time between clearing the atmosphere and hitting apoapsis to get everything lined up. If you gained enough speed down low, it shouldn't take a huge amount of delta-V to circularize.

It looks like something has been tweaked in the drag model. I know that for FAR the drag model is much more forgiving in .21 than in .20. I rebuilt my basic designs and I'm not getting to orbit with ~40% ox/fuel where in the past I was making orbit with ~20% ox/fuel. Additionally, I've got extra fuel from the atmospheric portion of the flight. I'm still hitting roughly the same speed/altitude when I switch to rockets so I think that is being driven by the engine/air intake model.

@Ferram: I'm trying to work out how to use the control surfaces as air brakes. Here's the behavior I'm getting: When I set a surface to brake it activates when I hit the 'B' key to the max deflection. Nothing happens when I bind the 'raise/lower' to action groups, nor do I see 'raise/lower' in the action box when in flight. What I'd like (if possible) is to both break the hard link to the 'B' key so I can have air brakes operate separate from landing gear. Additionally, I'd like to be able to use them like the BAC9 surface air brakes where they can be incrementally adjusted using action groups. Overall, this is the best mod for KSP.

I've found that it works fairly well at mid-to-high altitudes, but causes issues in areas where my stability is low and my control authority is high. Specifically, I can't use it to hold a climb rate below 10km at any speed, but it works well once I'm above 15km and leveling off for my acceleration phase. I use it to keep the trim adjusted so I can get to Mach 5 and make the most of my jets before climb out. It also works well on the rocket-powered escape - I can set my climb angle and let it go. What SAS definitely sucks at is understanding if there is a stall - so if you are stalling out SAS is only going to make it worse my trying to put on more control after your control authority is gone.

For what its worth, I don't think a 'momentum saturation' should be added to the game (unless as an optional mod). Sizing momentum exchange systems correctly is a difficult problem, one of the key aspects in spacecraft design. Additionally, large vehicles like many manned spacecraft (ex. all US systems except for the ISS) use RCS alone because the size, weight, and power required for reaction wheels or CMGs is more than the required propellant for the 'short' durations of the mission and the vehicle is large enough that the minimum thrust is small enough to prevent limit cycling and other non-linear effects that hamper precision pointing. What I would like for squad to implement is the ability to add more non-RCS torque capability to the vehicle that consumes electricity and has a significant weight penalty. Thus for short missions RCS is a better choice, but for long missions a CMG / RW package may be better.

Reaction wheels or control moment gyroscopes are used for routine control. That said, both only function as momentum exchange devices so RCS, torque rods, or some other methods are needed to allow the vehicle to dump excess momentum if the vehicle accumulates it due to some sort of imbalance. The key advantage to CMGs or Reaction Wheels is that they are very precise while RCS thrusters tend to have a minimum thrust and thus a minimum torque which makes precision pointing difficult. In order to make KSP behave like real life, there would have to be an angular momentum accumulation that keeps track of how much is being stored in the reaction wheels or CMG array and have the vehicle saturate when the maximum momentum is reached.

Mechjeb doesn't do to well with FAR while in the atmosphere. Mechjeb is useful, however. The 'Prevent Flameout' works fairly well if you set the margin high enough; I use 10% with most designs. Additionally, the information tabs are quite useful for determining when you have a good apoapsis for the climb out. Just don't use Mechjeb to fly the ship when in the atmosphere for planes. For rockets, ascent guidance works but you need to have a cleanly designed rocket. Additionally, I've found that any active fins should be set to 'roll' only or you risk having your rocket shake itself to pieces. Additionally, you need lots of gimbal authority to stay under control until you get up to speed where the vehicle becomes aerodynamically stable. That, and EVERYTHING needs to be in a fairing or the drag is going to be really high.

Load up the maneuver planner, there is a box on the lower right that indicates the tolerance. Default is 0.1m/s so double that and it should help. Note that this means mechjeb will terminate the maneuver you are that many m/s away from the deltaV required to match that maneuver node so you are allowing mechjeb to 'quit' early.

I've had this happen before. I found there are two options: 1: Add more control authority to the vehicle, usually RCS, to hold the vehicle stable a bit longer to complete the burn 2: Increase the allowable tolerance for the maneuver. Default is sometimes too tight for craft with poor rotational control.

Wait for FAR to be updated to 0.21 Clean install followed by: - FAR, because its tough to go back to the stock Aero model - B9, KW Rocketry, and Taverio's Pizza and Aerospace parts packs - more good stuff to build rockets and planes with - MechJeb 2.0.x - because the info is nice to have and sometimes I'm lazy - TacFuelBalancer - keeps planes from going 'Aft-CG' and spazing out - SubAssembly loader - makes building standard equipment easier - KerbComAvionics - this is the RCS balancer - almost a must on SSTO spaceplance as it is very hard to properly position RCS units because the CG moves around - Lazor Docking Camera - this should really be stock (since Romfarer is now on the dev team) as it provides the right camera angles for docking - i.e. right out the docking port. If you've ever seen how the shuttle docked to the ISS, they were basically flying off a camera (or window) right next to the docking port. Then its time to rebuild my space station and space planes - try out that new ASAS.

ZRM - this is a great mod. I do have a question/suggestion. Is it possible for you to add in the ability to remove or ignore engines in the engine control mode? It would be nice to have a VTOL lander that also has a separate set of OMS type engines to move around the orbit but that screws up the solver since they are included - thus the thrust vector isn't vertical.