OhioBob

EDIT: THIS POST HAS BEEN MODIFIED TO REMOVE THE AV-R8 FINS FROM THE TEST VEHICLE. THEY ARE SHOWN IN THE IMAGE BUT NOT INCLUDED IN THE TEST RESULTS. As suggested earlier in this thread, I tested a launch vehicle with solid rocket motors. I only tested one design, which is shown below: I wanted a design that made extensive use of solids so we could really see how much of a difference it made in comparison to an all-liquid design. As you can see, I went with six SRBs. Two of the six are set to 100% thrust and burn out after about 42 seconds. The other four SRBs are set to 50.5% thrust and burn out after about 84 seconds. The center sustainer engine is a "Skipper". All engines and motors ignite at liftoff. The top propellant tank is just ballast to simulate a payload (the propellant is not used). Although I've test flown this vehicle in the game, the data that I report here is from the same computer simulation used when recording my opening findings. The results should be comparable. In the game, the test vehicle flew well and was easy to control. This time I didn't bother optimizing for Δv because I see no practical reason why anyone would want to do so. There was very little difference between the payload fraction optimized and the cost optimized versions - the cost optimized version had just one small additional propellant tank. (The picture shows the payload optimized version.) It is no surprise that with the lower performing solid propellant, the payload fraction of the SRB launcher is significantly less than that of the all-liquid design. I am surprised, however, to discover that the SRB launcher is more expensive per tonne of payload. One of the main reasons for this appears to be because of the large amount of "extras" needed, such as decouplers, nose cones, struts, etc. If we add up the cost of just the propellant, tanks, engines and SRBs, then the SRB launcher is less expensive - 917/t vs. 1035/t. The fleet of launchers that I used prior to version 1.0 typically delivered payloads to orbit less expensively when solids were used. I assume the results that I'm now seeing are due to the rebalancing that has taken place since v0.90. Of course, it's also likely that a more cost effective SRB design can be found than the sample tested here. Here are the test results: Optimized for Maximum Payload Fraction Strap-on SRBs: Number of SRBs = 6 Inert mass = 1,675 kg each, 10,050 kg total Propellant mass = 6,150 kg each, 36,900 kg total Rated thrust = 250 kN sl, 300 kN vac per each Thrust limiter = 2 each at 100%, 4 each at 50.5% Burn time = 2 each at 42.2 s, 4 each at 83.6 s Burnout, 1st group: z = 4.85 km, v = 271 m/s, φ = 68o Burnout, 2nd group: z = 17.25 km, v = 618 m/s, φ = 35o Core stage: Dry mass = 8,600 kg Propellant mass = 40,000 kg Thrust = 568.75 kN sl, 650 kN vac Burn 1 cutoff: z = 40.9 km, v = 2342 m/s, φ = 3.1o Burn 2 Δv = 64 m/s Total launch mass = 114,957 Total liftoff thrust, sea level = 1,573.75 kN Liftoff TWR = 1.40 Payload mass = 19,407 kg Payload mass fraction = 0.1688 Total Δv, vacuum = 3,440 m/s Δv losses = 854 m/s gravity, 180 m/s drag Total cost = 26,722 Cost per payload tonne = 1,377 Optimized for Minimum Payload Unit Cost Strap-on SRBs: Number of SRBs = 6 Inert mass = 1,675 kg each, 10,050 kg total Propellant mass = 6,150 kg each, 36,900 kg total Rated thrust = 250 kN sl, 300 kN vac per each Thrust limiter = 2 each at 100%, 4 each at 50.5% Burn time = 2 each at 42.2 s, 4 each at 83.6 s Burnout, 1st group: z = 4.30 km, v = 236 m/s, φ = 75o Burnout, 2nd group: z = 16.3 km, v = 509 m/s, φ = 45o Core stage: Dry mass = 9,100 kg Propellant mass = 44,000 kg Thrust = 568.75 kN sl, 650 kN vac Burn 1 cutoff: z = 42.6 km, v = 2363 m/s, φ = 1.6o Burn 2 Δv = 40 m/s Total launch mass = 120,216 Total liftoff thrust, sea level = 1,573.75 kN Liftoff TWR = 1.335 Payload mass = 20,166 kg Payload mass fraction = 0.1677 Total Δv, vacuum = 3,514 m/s Δv losses = 963 m/s gravity, 146 m/s drag Total cost = 27,522 Cost per payload tonne = 1,365

I'm planning to test a few different options, however I don't want to go overboard with it because it takes a lot of time to run through all the optimization iterations. I'll probably pick two or three viable candidate configurations and leave it at that. I've considered doing something like that. I've never had a problem controlling small solids using reaction wheels, but I've had trouble steering big launchers unless I've had at least one gimbaled liquid engine. I'm not sure I really need to worry about it for the tests that I'll be performing. My tests are strictly a theoretical exercise focused on trying to find the optimum TWR etc. Control/steering is an in game problem that requires a practical solution. There is no guarantee that the optimum configuration revealed by the computer simulations will be a practical design that can be reliably controlled. - - - Updated - - - I have frequently used SRBs in this manner. I think drop tanks may be a very practical solution for a low TWR launcher. One thing that I didn't discuss in my opening post is that as we stack more and more propellant tanks, the launch vehicle becomes more and more slender. The "optimized for minimum payload unit cost" design has an extremely high slenderness ratio. I suspect that it would be very wobbly in flight. Using drop tanks would significantly reduce the slenderness and make the vehicle more stable and structurally sound.

Champ was replying to this: According to that definition, the payload fraction is 50 t / 50 t = 1 = 100% But that is incorrect. We divide by the total mass including payload, 50 t / 100 t = .5 = 50%

It's just an Excel spreadsheet. I've tried some different things over the years but, in the end, I've found that Excel is the easiest to work with.

I'll have to work on that. I can think of several configurations: (1) Two-stage liquid core, thrust augmented with SRBs. SRBs and liquid stage both ignite at liftoff. (Atlas V) (2) Single stage liquid core with SRBs. SRBs and liquid stage/sustainer both ignite at liftoff. (Space Shuttle) (3) Single stage liquid core with SRBs. SRBs ignite at liftoff, liquid stage is air-lit after SRB burnout. (Titan III) I'm not sure which option is most effective. Option #1 is quite popular on Earth, but the Δv requirement to get to orbit in KSP is low enough that I doubt a second liquid stage is necessary. And I'm concerned that option #3 may not provide enough steering. That makes me lean toward option #2.

Asparagus staging has its place, but I favor solids as well. I haven't come up with a good set of guidelines for using solids (at least nothing that I can back up with data). What I've done in the past is to go with a two-stage liquid fueled launcher as my first option. However, when I'm caught between two engines options - for example, a Skipper is too small and a Mainsail is too big - I go with the smaller option and supplement it with solid strap-on boosters to get my liftoff TWR where I want it.

I know there have been numerous threads on this topic already, but I have some new test results that I'd like to share. The test was of a simple two-stage liquid fueled launch vehicle. The first stage was powered by a LFB KR 1x2 "Twin-Boar" Liquid Fuel Engine. The second stage was powered by a RE-I5 "Skipper" Liquid Engine. These engines were selected because my previous v0.90 tests found them to be an ideal pairing for a two-stage rocket. The first stage included four AV-R8 Winglets and the second stage included an Advanced Reaction Wheel Module, Large. Both stages included a Rockomax Brand Decoupler. The payload was just a dummy mass with a RC-L01 Remote Guidance Unit and Protective Rocket Nose Mk7. The test payload provided good drag characteristics, but not optimum. Actual performance will vary depending on the drag characteristics of your specific payload. To the first and second stages I added propellant tanks in various sizes and quantities until I found the ideal combination that maximized performance according to three different modes of measurement. First, I found the configuration that resulted in the lowest total Δv. Second, I found the configuration that resulted in the highest payload fraction. And third, I found the configuration that resulted in the lowest cost per unit mass of payload. The tests were performed using a computer simulation rather than performing test flights within the game. This eliminated unwanted human error and variation in performance. The tests launches were performed under carefully controlled and ideal conditions. In all cases, the payload mass was found experimentally as the mass that resulted in 100% of the propellant being used to achieve a 75 km circular orbit. The payload includes everything not described above as being as part of the first and second stages. Thus, a fairing, if used, is counted as payload. The ascent profile consisted of a slow gradual turn beginning after 100 meters of climb. The launch vehicle maintained a constant negative angle of attack throughout the turn. The angle of attack was found experimentally as the angle required to produce the most efficient ascent and to deliver the maximum payload mass to orbit. My tests show that high thrust-to-weight ratio is best for minimizing the Δv required to attain orbit, while low thrust-to-weight ratio is best for minimizing the cost per tonne of payload. This is because lower TWR is obtained by simply adding more propellant tanks on top of a given engine. The engine is already paid for, so our marginal cost is only that of the relatively cheap propellant and tankage. With more propellant we can launch a heavier payload. It is found that the cost per tonne of payload goes down as more and more propellant is added. Although unit cost goes down, the vehicle becomes less efficient in terms of Δv. We can only add so much propellant before the vehicle becomes so inefficient that unit cost begins to rise. Below are the results of my simulations. Although there is an almost unlimited number of launch vehicle configurations that you can come up with, the data below might help in establishing some general design guidelines. Note that this is theoretically ideal conditions; actual in game performance is likely to be lower. Cost is for the launch vehicle only, payload is extra. Optimized for Minimum Δv First stage: Dry mass = 11,300 kg Propellant mass = 36,000 kg Thrust, sea level = 1866.67 kN TWR, ignition = 1.90 Stage Δv, vacuum = 1,308 m/s Turn angle-of-attack = -2.70o Cutoff conditions: z = 12.3 km, v = 660 m/s, φ = 40o (z = altitude, v = velocity, φ = flight path angle) Second stage: Dry mass = 6,600 kg Propellant mass = 24,000 kg Thrust, vacuum = 650 kN TWR, ignition = 1.25 Stage Δv, vacuum = 1,893 m/s Burn 1 cutoff: z = 42.7 km, v = 2319 m/s, φ = 3.7o Burn 2 Δv = 78 m/s Payload mass = 22,376 kg Payload mass fraction = 0.2231 Total Δv, vacuum = 3,202 m/s Δv losses = 669 m/s gravity, 210 m/s drag Total cost = 33,410 Cost per payload tonne = 1,493 Optimized for Maximum Payload Fraction First stage: Dry mass = 13,800 kg Propellant mass = 56,000 kg Thrust, sea level = 1866.67 kN TWR, ignition = 1.46 Stage Δv, vacuum = 1,658 m/s Turn angle-of-attack = -0.86o Cutoff conditions: z = 17.9 km, v = 842 m/s, φ = 28o Second stage: Dry mass = 6,600 kg Propellant mass = 24,000 kg Thrust, vacuum = 650 kN TWR, ignition = 1.10 Stage Δv, vacuum = 1,597 m/s Burn 1 cutoff: z = 42.3 km, v = 2348 m/s, φ = 2.5o Burn 2 Δv = 51 m/s Payload mass = 29,576 kg Payload mass fraction = 0.2275 Total Δv, vacuum = 3,255 m/s Δv losses = 765 m/s gravity, 152 m/s drag Total cost = 37,160 Cost per payload tonne = 1,256 Optimized for Minimum Payload Unit Cost First stage: Dry mass = 16,300 kg Propellant mass = 76,000 kg Thrust, sea level = 1866.67 kN TWR, ignition = 1.21 Stage Δv, vacuum = 1,953 m/s Turn angle-of-attack = -0.25o Cutoff conditions: z = 21.9 km, v = 927 m/s, φ = 23o Second stage: Dry mass = 6,600 kg Propellant mass = 24,000 kg Thrust, vacuum = 650 kN TWR, ignition = 1.03 Stage Δv, vacuum = 1,464 m/s Burn 1 cutoff: z = 42.4 km, v = 2362 m/s, φ = 1.6o Burn 2 Δv = 39 m/s Payload mass = 33,784 kg Payload mass fraction = 0.2156 Total Δv, vacuum = 3,416 m/s Δv losses = 968 m/s gravity, 118 m/s drag Total cost = 40,710 Cost per payload tonne = 1,205

My general rule is to accelerate vertically until my velocity is 1/8th orbital velocity, pitch over to 45o and continue accelerating until my velocity is 1/4th orbital velocity, pitch over to horizontal and continue accelerating until the planned apoapsis is reached, cut the engine and coast to apoapsis, then perform a circularization burn at apoapsis.

I assume you mean Y+ is up, X+ is towards you, and Z+ is to your left (you didn't specific + or -). That doesn't agree with the above. If X+ goes from "towards you" to "to the right", then Z+ goes from "to the left" to "towards you". Your first description are right-handed coordinates and your second description are left-handed coordinates. My diagram above is a the right-handed system. I knew Y+ was up, but I was guessing at the other axes.

Each set of three numbers are for a different face of the drag cube, ordered X +/-, Y +/-, Z +/-. Within each set of three numbers, the values are area, drag coefficient, and depth of the part. The drag cube looks something like this: Using the Mk1 Command Pod as an example, we have: PART { url = Squad/Parts/Command/mk1pod/mk1Pod/mk1pod DRAG_CUBE { cube = Default, 1.015811,0.6656196,0.7373285, 1.015811,0.6769236,0.7315681, 1.250829,0.4787524,1.097382, 1.250829,0.9474788,0.3448916, 1.013055,0.6620117,0.7325699, 1.013055,0.6601633,0.7441065, 0,0.104412,-0.001005709, 1.268897,1.132536,1.270908 } } Therefore, tabulating the data into a more easy to read format, we have: [TABLE=class: outer_border, width: 500] [TR] [TD=align: center]Surface[/TD] [TD=align: center]Area[/TD] [TD=align: center]Cd[/TD] [TD=align: center]Depth[/TD] [/TR] [TR] [TD=align: center]X+[/TD] [TD=align: center]1.015811[/TD] [TD=align: center]0.6656196[/TD] [TD=align: center]0.7373285[/TD] [/TR] [TR] [TD=align: center]X–[/TD] [TD=align: center]1.015811[/TD] [TD=align: center]0.6769236[/TD] [TD=align: center]0.7315681[/TD] [/TR] [TR] [TD=align: center]Y+[/TD] [TD=align: center]1.250829[/TD] [TD=align: center]0.4787524[/TD] [TD=align: center]1.097382[/TD] [/TR] [TR] [TD=align: center]Y–[/TD] [TD=align: center]1.250829[/TD] [TD=align: center]0.9474788[/TD] [TD=align: center]0.3448916[/TD] [/TR] [TR] [TD=align: center]Z+[/TD] [TD=align: center]1.013055[/TD] [TD=align: center]0.6620117[/TD] [TD=align: center]0.7325699[/TD] [/TR] [TR] [TD=align: center]Z–[/TD] [TD=align: center]1.013055[/TD] [TD=align: center]0.6601633[/TD] [TD=align: center]0.7441065[/TD] [/TR] [/TABLE]

Congratulations, carneyvich. The fun is just beginning. I think my biggest thrill was the first time I successfully landed a probe on Mun. Although it was unmanned, it was a big step that gave me the confidence to know that I could start getting much more ambitious.

The rough rule of thumb is that similar stages should produce the same ÃŽâ€v. So if your total ÃŽâ€v is 3500 m/s, you should aim for about 1750 m/s in the first stage and 1750 m/s in the second stage. When you have dissimilar stages, such as a kerosene fueled first stage and a liquid hydrogen fueled second stage, then you should give more ÃŽâ€v to the one with the higher ISP. However, that's not an issue in KSP because everything is similarly fueled (except for the "Nerv", but that's not an engine you'd use on a launcher). - - - Updated - - - I had developed a group of rules that I used for rocket design pre-1.0 that worked very well. I optimize the design using computer simulations. I've been meaning to do the same thing for post-1.0 but haven't gotten around to it yet. My pre-1.0 rules were: Payload fraction = 0.16 First stage TWR = 1.65 Second stage TWR = 1.30 Stage-2 thrust / Stage-1 thrust = 0.35

Since the release of 1.0.x, I've done some updating to the Wiki. I agree that much more needs to be done. However, part of the problem is that the Wiki is experiencing migration problems. This prevents such things as uploading images, or using math text. These limitations can cause some frustration when trying to make updates. We can make plain text updates, but that's about it. I think Squad needs to fix the problem before we make a really serious effort to get it updated.

I try to make my missions small enough that one launch will do it. When that doesn't work, then Kerbin orbit rendezvous.

That is my concern as well. No harm in trying, though. DalisClock, if you do try spin stabilization, please report back and let us know how it worked. It might be a good experiment that we can all learn from.

I've never tried this before in KSP, but you could attempt to gyroscopically stabilize your craft during the burn. Get the vehicle carefully aligned in the right direction for the burn, and then put it into a roll around its long axis. Once spun up, turn off the SAS so that it continues to spin on its own. The spin should counteract the asymmetry. Once you've made it through the burn, turn SAS back on an de-spin. Be sure to do a save beforehand in case it doesn't work.

From Kerbin, Mun has a smaller apparent angular diameter than the Sun. Therefore, solar eclipses are the annular type. There shouldn't be a dark umbra shadow. - - - Updated - - - Mun should experience total lunar eclipses. Minmus is too far away from Kerbin for total eclipses, but it should have partial ones. As you say, other moons should also experience eclipses.

There's no easy solution to that problem. I've estimated it be using a computer simulation. Unfortunately the technique is way too involved to try to explain here in the forum. 1) Download and install the AeroGUI mod. 2) Perform a test flight with the AeroGUI display open on your screen 3) During the flight, periodically note the dynamic pressure, drag force, and Mach number. 4) For each Mach number, compute the drag coefficient, Cd = Fd * 1000 / (q * A), where Cd is drag coefficient, Fd is drag force (kN), q is dynamic pressure (Pa), and A is the area of the vehicle normal to the flow (m2) Note that drag coefficient is a function of Mach number, so that's why you have to perform multiple measurements over a wide range of Mach numbers. You need to generate enough data to plot a graph of drag coefficient versus Mach number.

The following web page discusses the mathematics: http://www.braeunig.us/space/orbmech.htm#maneuver Equation 4.73 is used for simple plane changes, while equation 4.74 is used for combination burns, such as when a plane change is incorporated into an orbit insertion burn.

I don't think the approach speed is any higher than it use to be. Mathematically it just isn't possible to approach Jool any slower. You can consider approaching a planet as just the reverse of escaping it. To escape a planet you must increase your velocity to at least escape velocity. Therefore, when a spacecraft approaches a planet from deep beyond its sphere of influence, the spacecraft must be traveling at no less than the planet's escape velocity. As the spacecraft is pulled in by the planet's gravity, its velocity increases. At all points along its trajectory, the spacecraft's velocity will be greater than the escape velocity at that altitude. At the top of Jool's atmosphere, escape velocity is 9,547 m/s. Therefore, any spacecraft entering Jool's atmosphere from a hyperbolic escape trajectory must hit the atmosphere going at least 9,547 m/s.

It is still possible with the right spacecraft design, but it’s really tricky. Below is a re-post from another thread in which I describe my experiments on this problem: While that is effectively true, atmospheres in KSP do tapper off to zero pressure and zero density at the upper boundary level. However, the atmospheres of Jool and Eve do so in a rather artificial way in which they drop off quite rapidly as the boundary nears. This means that the atmospheres thicken very quickly, and in an unrealistic manner, once dipping below the boundary.

That's a good question. I completed my previous to-do list under v0.90 just before v1.0 was released. That list included landing on and returning from every planet and moon in the solar system (at least robotically, but in many cases manned). Since then I've mostly taken a break from the game. Since v1.0's release, I've only tinkered around in sandbox mode to check out the new aerodynamic and heating models. I've yet to get into it really seriously, mainly because I haven't decided what I want to do next.

ditto

Aerospike engines are better than bell nozzles over a broad range of atmospheric pressure, but they are typically less efficient than a bell nozzle when operating in the environment for which the bell nozzle has been optimized. Therefore, if the engine is to operate in only one environment, e.g. a vacuum, it is better to use a bell nozzle. Aerospikes should be considered only when they are to operate through a region of significantly changing ambient pressure.

Congratulations. One-way unmanned probes to Duna and Eve where my first interplanetary missions as well. After Mun and Minmus, Duna was also the target of my first manned landing and return. I took things cautiously and performed an unmanned landing/return mission first. Looking back on it, that was probably unnecessary as I'm sure I could have gone straight to the manned landing. As other have said, a manned return from the surface of Eve is likely the most difficult thing you'll do. I haven't tried it since v1.0, so I don't know how much it has changed. There's less drag now but engines as less effective, so maybe its a wash. It is definitely not a mission for the faint-hearted.