OhioBob

The general rules of thumb for optimizing staging are, 1. Stages with higher Isp should be above stages with lower Isp. 2. More Δv should be provided by the stages with the higher Isp. 3. Each succeeding stage should be smaller than its predecessor. 4. Similar stages should provide the same Δv.

Ariel

Poughkeepsie

Sigma Sagittarii

Alamogordo

It depends on what you mean by "most fuel efficient possible" and "most opportune". For example, fuel efficient launch windows to Jool occur at intervals of just over one year, but some of these require more Δv than others. The really good launch windows occur at intervals of about 11 years. I always perform my transfers at the opening of one of the launch windows (and at the most optimum time within that launch window), but I don't sit around for years waiting for the best of the best to occur. For Jool, the difference between the best and the worst launch windows might be only 200 m/s or so. However, for some planets the difference can be >1000 m/s. In the latter case I'm likely to pass on a particularly poor launch window and wait for a more opportune one to arrive. It depends a lot on the size of my payload and how big of a rocket I need. If I can realize dramatic savings by waiting, then I'll wait.

Yeah, my numbers have a little bit of margin in them as well. The way I build and fly my missions, a total of 4800 m/s is a reasonable expectation (that's landing only). I am surprised, however, by your return trip numbers. For takeoff and return you have only 300 m/s. I usually require about 400 m/s. What are you doing that allows you to return to Kerbin using only 300 m/s?

If you decide to perform these calculations for yourself, just remember that the game gives you the planet's altitude, while the Vis Viva equation takes radius. Be sure to add to the altitude the radius of the sun, which is 261,600 km. I too find it a little aggravating that these numbers can't be easily found in the game. It seem like something that should be readily available. After all, pre-space age Kerbals would know a lot more about the orbital characteristics of these bodies than they would about their physical and atmospheric characteristics. Yet the information they would know best is the information we're not given. I hoping that maybe some of this data is included in the upcoming KSPedia, but I have my doubts about it.

You're correct, the info panel gives the physical characteristics of the body but no orbital information. However, it does give the gravitational parameter (GM) of each body. Although there are some mods that will give semimajor axis from inside the game, I don't know if there is a way to do this in the stock game. However, I'm sure the numbers in the Wiki are correct because I've checked them. (edit) One mod that gives the orbital elements is Hyperedit. If you want a mathematical way to compute semimajor axis from information given in the game, just click on a planet and note its velocity and altitude. You can then use the Vis Viva equation to compute the value of a, though the precision of this method is limited by the precision of the input variables.

Well, I did say a "one way" trip to Minmus, so I wasn't counting the return. The numbers I used were: 3500 Kerbin orbit + 100 plane change + 930 transfer + 160 capture + 300 landing = 4990 m/s. I usually try to launch as close as possible into the correct orbital plane, so my 100 m/s plane change is just a contingency to fine tune it. For the return trip, I generally budget: 230 launch + 170 transfer = 400 m/s.

Landing on Minmus requires the least Δv of any destination in the game. I one way trip to the surface of Minmus shouldn't take more than 5,000 m/s. That should be well within the reach of chemical rockets.

I see now why you prefer a liftoff TWR of 1.5. When I'm using all solids to launch off the pad, I too prefer a TWR up around 1.5. However, my tendency is to use a liquid-fuelled first stage (yes, I know it is more expensive but I just like it better). In that case I like to load up on propellant to bring the TWR down to about 1.3-1.4.

It looks like you have a heat shield on the lander can but I don't see a decoupler. If you make no other changes, at least add a decoupler between the Rockmax adapter and the 1.25m heat shield. Also, the Mk16-XL parachute should be enough, I don't think you need those radial parachutes.

Adding the TWR together isn't a hard and fast rule, it's just that when I can I tend to go toward the lower end of my preferred TWR range on the second stage if the first stage's TWR is toward the higher end of my preferred TWR range, and vice verse. This produces a more consistent total burn time and average acceleration during ascent. I feel this gives me greater consistency in my ascent profile so that all my rockets fly about the same. When both stages have low TWR, or when both stages have high TWR, I find I have to fly the rockets differently and I don't get the same consistent ascent trajectory that I like. When a rocket doesn't behave as I'm accustomed to, I have a tendency to get outside of my preferred ascent corridor and I sustain greater steering losses. In a perfect world, both my first and second stages are right in the middle of the preferred TWR range.

I fairness to Victor3, he got quite a few suggestions, so it's not entirely surprising that he might have gotten a bit confused. I'm actually the one that suggested adding (to the sample rocket shown in the third post) a FL-T100 to the second stage, but that was after suggesting adding a third FL-T400 to the first stage. I've since reconsidered that configuration and now prefer the configuration listed in my last post. The more recent configuration provides almost as much Δv but with 0.5 t less propellant, and I think it also has better TWR numbers. I probably underuse the Reliant. I've always preferred the Swivel because of the thrust vectoring, but there are likely applications where the Reliant might be a better choice. I should probably really think about using it more often.

This is absolutely correct in principle, and in KSP. However, in real life there can be very small changes in Isp resulting from high acceleration or shifts in the mixture ratio. Mixture ratio (MR) is the ratio of oxidizer to fuel. Changing the MR effects the combustion characteristics, such as the flame temperature and the molecular weight of the exhaust gases. Therefore, a change in MR changes an engine's specific impulse. Although an engine is typically designed to operate at a specified mixture ratio, the mixture ratio can shift slightly during flight if the respective flow rates of oxidizer and fuel change. High acceleration can also alter the flow rate of oxidizer and fuel. Under high g-loads, the liquid pressure upstream of the turbopumps is increased, which can increase the propellant flow rate to the engine. Clearly a higher propellant flow rate increases thrust, but it can also change Isp because of a higher combustion chamber pressure. Both of these effects are usually pretty small, and in KSP they are non-existent. I just thought I'd mention as a side note in case anyone is interested. In some cases, mixture ratio is changed intentionally, which can produce fairly significant changes in Isp. One example is the Saturn V, in which both the F-1 and J-2 engines had a "propellant utilization subsystem" that monitored the remaining oxidizer and fuel and shifted the MR near the end of the burn to assure simultaneous depletion of oxidizer and fuel. In the case of the J-2 engine, the shift was achieved by changing the position of a valve controlling the flow of oxidizer to the engine. The PU shift decreased the oxidizer flow rate, resulting in a pretty dramatic decrease in thrust. Although the thrust decreased, the Isp actually went up by several seconds.

@KocLobster, I agree with everything @Snark just wrote. The only difference is that I prefer a slightly lower liftoff TWR, anything in the 1.3-1.5 range is acceptable. For the second stage I typically like something in the 1.1-1.3 range. Ideally, I want my stage 1 + stage 2 TWR to be equal to 2.6. From my personal experience, I like the way that performs. For me, I rarely even look at my velocity during a launch. Since I try to build all my rockets to a set standard, I get similar performance no matter what I'm flying. Therefore, I just watch my pitch, altitude, and apoapsis. Like Snark, I want my pitch to be 45 degrees at 10-12 km. I like to be horizontal by 35-40 km. And I like to kill the engine at about 50-55 km, when my apoapsis has reached 75-80 km. If I do that, then I get a good launch. Other than at engine cutoff, I can't tell you what my speed is at any given altitude because I honestly don't know.

Congratulations! That's a nice milestone to get out on the way. Now that you've done it once, you can do it again, practice, and get better. Having a design that is known to work is a good starting place. You can now tweak it to see if you can make it better. Once you have something that you're really happy with, you can use it as a template for future rockets. At some point you should try experimenting with side-mounted boosters. (edit) Did you really have two FL-T400 + one FL-T100 fuel tanks on the second stage? If so, that might be a bit too much. That would give your upper stage a thrust-to-weight ratio at ignition of only 0.93. You can make that work with the right trajectory, but it's lower than I typically like for my second stage. Why don't you try one FL-T400 + one FL-T200 on the second stage (TWR=1.26)? I think the higher stage 2 acceleration will allow you to fly a trajectory that is a bit more forgiving. Additionally, the higher TWR will allow for a modestly heavier payload. With the lighter second stage you can probably also try switching back to the Swivel engine. I think the following would work really well. Plenty of Δv and good TWR. MK16 parachute MK-1 command pod Decoupler FL-T200 fuel FL-T400 fuel LV-909 "Terrier" Decoupler FL-T200 fuel FL-T400 fuel FL-T400 fuel LV-T45 "Swivel" There is enough rocket there that you could add a heat shield (60 kg ablator) and perform a Mun flyby. Of course that's assuming you fly an efficient enough ascent that you're not wasting Δv. That's the next thing you should practice, getting to orbit efficiently. Flying the above rocket on a really good trajectory should allow you to get your command pod (no heat shield) to low Kerbin orbit with about 1500 m/s Δv remaining. If you are way worse than that, then you have some work to do on your piloting skills. (I just did a test launch and got into a 78 km orbit with 1507 m/s Δv to spare.)

Altoona Wait a minute, Olympia doesn't follow from Alderney. So I'll go with Ypsilanti

When the rescue vehicle reaches the stranded vehicle's periapsis, what you can do is perform a burn to adjust the rescue vehicle's orbital period so that the two vehicles will meet at a controlled time. For instance, let's say that when the rescue vehicle arrives at the stranded vehicle's periapsis, the stranded vehicle is exactly 120 hours from periapsis. Change the rescue vehicle's orbital period so that it will complete some whole number of orbits in that 120 hour period. For example, if the rescue vehicle's has an orbital period of 28 hours, then perform a burn to raise its periapsis until it has an orbital period of exactly 30 hours. Now the two vehicles will meet at the same location and time after 4 complete orbits of the rescue vehicle.

@Victor3 I just noticed also that you have a heat shield on your command pod. If you are just going to low Kerbin orbit, then the reentry heat won't be great enough to require a heat shield. Delete the heat shield and you won't need as much rocket to get your pod to orbit. Heat shields are only needed for high speed reentries from either a high orbit or from interplanetary space. And even in that case it may not be necessary to carry the full amount of ablator. If you right-click on the heat shield there is a slider that allows you to decrease the ablator mass. A 1.25m heat shield has a maximum ablator mass of 200 kg. For a return from Mun or Minmus, you can safely dial that back to 60 kg, maybe less. For a return from high orbit, the rule of thumb I use is that I set the ablator mass to 5% of the reentry vehicle mass. For interplanetary transfers, the entry velocities can be much greater. In that case you may need 100% ablator.

Yeah, I think you're over complicating things. If you are just trying to get to Kerbin orbit, there is no reason why you would ever need more than two stages. In the image that I posted, the bottom engine is a LV-T45 "Swivel" and the upper engine is a LV-909 "Terrier". Those engines have plenty of thrust to spare. You can easily add another FL-T400 fuel tank to the first stage*, which would give you another 500 m/s to play around with. (You can even add a FL-T100 to the second stage for another 200 m/s.) You don't need that extra fuel just to reach orbit, but once there you'll have plenty of fuel to fly around and perform orbital maneuvers. Once you've made it to orbit and have a design that you know works, you can then start playing around with different variations. You'll figure out what works and what doesn't, and in the process you'll make better and better rockets. (* By "first stage" I mean the bottom stage, i.e. the first to burn. I am not referring to the staging sequence numbers as seen in the VAB.)

Below is a rocket that can easily get to orbit using early career game technology. Only 13 parts and 9.8 tons.

You should be able to easily get into orbit under those restrictions. Below is a good tutorial on how to design a rocket. http://forum.kerbalspaceprogram.com/index.php?/topic/128838-how-to-build-a-rocket-ship-for-a-mission/ If you can you post an image of your rocket design, we might be able to tell what you're doing wrong. Increasing the part/mass/size restriction requires upgrades to the Launch Pad and Vehicle Assembly Building. Just right click on the building and select upgrade, however funds are required to do this. If you can't get to orbit, then you're not likely to be able to complete the contracts needed to raise the funds. The Level 2 upgrade to the Launch pad costs 75,000 funds and allows 36-m high and 140-ton vessels. The Level 2 to upgrade to the Vehicle Assembly Building costs 225,000 funds and allows 255-part vessels.

The rules of the challenge are simple, so I used a simple and low cost solution...