Alistone

I always contemplated moving fuel from tanks on one side or the other of the CoM in order to balance it. But balancing thrust AND making strong connections to withstand the thrust requires a fair bit of planning. Sort of has to be planned as a mothership instead of just a space station.

The mun orbits kerbin at 540 m/s. If you were traveling faster than that when you left the mun SOI then you may have turned yourself around at that time. To fix your orbit the lowest dV method is often to sling yourself out to the closest moon and intercept it at the perfect time and angle so that it's gravity will change your orbit for you. More commonly and much easier to pull off, you switch to a VERY VERY elliptical orbit. With a highly elliptical orbit you will be moving relatively slowly at your furthest point form Kerbin. This makes the dV to turn around also much lower.

That seems sooo much easier than the pair of upside down small solid rocket boostera I used to try to squeeze onto my rockets. Definitely going to test those out.

http://en.wikipedia.org/wiki/Tonnes maybe they switched their defination with the alternate usage where a tonne is only 10kg Short ton, Long ton, Metric Ton, historical tonnes of materials... ton is varied enough that I try to ask for its definition rather than assume the one being used at the time.

I did it with a single launch vessel, but a common theme is that your entire ship cannot land and take off from Duna. Instead, you'll need to leave a large part of your mass in Duna orbit while you ride down in a lander. It is relatively easy to escape Duna's surface... on the other hand, it was pretty close and I only had about 15% of my fuel left when I redocked with the tank in orbit. Interestingly, I just had a docking port on my main fuel tanks instead of a stack seperator. Even with no command pod of any sort I was able to redock with it for the trip home.

Currently it doesn't have enough thrust. Try replacing the 4 tiny radial engines below the orange tanks with Mainsail engines (really big). And add another 4 large orange fuel tanks above the current tank 4 radial orange tanks. That will probably get you to orbit just fine. From there you can probably figure out how to do additional tweaks. Alternately you could just add more of a different engine.... but from what I see you need more thrust. EDIT: You see I'm asking you to add essentially 10x as much thrust with thos big engines; and then I'm asking you to double the fuel load. I'm just "eyeballing" the simplest way to add get to a better T/W ratio. You could do all sorts of redesigns that will be even more efficient. You could find a way to stack sets of 3 engines beneath each orange tank and then you wouldn't have to add more fuel. I'm just trying to keep it simple & direct. EDIT EDIT: Also, by using fuel lines with no symetry you can route your fuel to empty just 2 radial tanks first; decouple them, then run the other 2 radial tanks empty, then decouple them with still a full center tank. This makes your ascent more efficient because you aren't hauling the weight of empty fuel tanks all the way up with you.

Alternately, if you have a very low T/W ratio sometimes adding an engine can help. Specifically, if you can't reach 200m/s before you reach 12,000 feet then you are losing a lot of energy due to gravity losses during launch. Getting a better balance of thrust to weight will make reduce your gravity losses and can greatly improve your delta V Usually though people start by adding another fuel tank. Unless you have other "opportunities" where you can improve your efficiency of maneuvering or launching then it becomes simple math. 1. Reduce non-fuel weight (fewer engines; fewer everything; possibly jettison empty parts); 2. Add more fuel weight; 3. Use engines with a higher ISP. 4. (Possibly practice "sling-shot" maneuvers to steal dV from other objects?)

Yeah, my first duna landing and return was when I had an "accident" that damaged one of the the docking ports when lifting up 2 large orange tanks and a tug for a station. My 3 man tug/lander was just sitting on top of nearly 2 full orange tanks of fuel... No parachutes, but managed a powered soft landing on Duna and had enough fuel to make it back to orbit to redock with the orange fuel tanks which still had plenty of fuel for the trip home to kerbin. This was stock... So redocking for fuel really doesn't seem to be essential for kerbin departure... but still seems essential if you're planning a return trip from an atmospheric surface. Besides, space stations are cool and why have them if not for some functional purpose.

The point at which the forces are equal is near terminal velocity. A chart can be found on the wiki http://wiki.kerbalspaceprogram.com/wiki/Basic_Maneuvers Altitude (m) Aprox. Terminal Velocity (m/s) 500 105 1,000 110 2,000 120 3,000 130 5,000 160 8,000 215 10,000 260 (remember to start your gravity turn!) 13,000 350 15,000 425 16,000 470 32,000 2250

So... I know everybody loves talking about how great the Oberth effect is for preparing for interplanetary burns. But this wonderful tool seems to be confirming something I suspected. http://ksp.olex.biz/ That the delta V of your ejection burn is less if you leave from a higher parking orbit. For example, from Kerbin to Duna: 100km parking orbit: delta V of ejection burn 1043.06 m/s 500km parking orbit: delta V of ejection burn 882.08 m/s 2,000km parking orbit: delta V of ejection burn 690.65 m/s Admittedly my stations tend to be in orbit of muns or low kerbin orbit; I expect the longer period of the more distant orbits makes rendevous a bit more time consuming. But it may also have the benefit of slowing down the constant turning caused as the target progresses through its orbit. This would make the docking easier. Yes, it takes more fuel to get your station way up there, but if you are docking to refuel anyways you seem to be better off from a higher orbit. Additionally, since ejection burns take quite a while, by not being perfectly horizontal at the start/end often requires a correction burn. By having a much longer orbital period (and a smaller ejection burn) this variance and correction burn should be reduced. Last night was busy putting all the HOME modules on minmus. Tonight I'll make a 8,000,000 m orbit station and see how easy/difficult it is to make it work docking work. The real future use of a "tug" may be to have efficient engines to pull fuel tanks from LKO out to a 8,000,000 orbit station. I'll try it out later tonight. Thoughts?

Just eyeballing it, the center of mass seems to be near the command capsule. The "Quick Fix" is to disable the top set of RCS thrusters. If you still get excessive torque turning your ship when using RCS then disable the very bottom set as well. With just the 1 remaining set that is closest to the center of mass you should experience less rotation during translation. The imbalance that is present should be small enough (with just the thrusters nearest the center of mass running) that ASAS can balance it out using torque from the command capsule.

Remember downward facing lights for nightside landings (and a power supply for them). Remember parachutes for the trip home Remember to verify your landing legs and ladder with a test landing on Kerbin before you try your munshot.

A full orange tank into a 100km orbit with a "tug" is generally a heavy payload. It takes a lot of work, and it may be a mostly empty tank while you're learning the optimal launch curve. But practicing with a fuel payload gives you a lot of wiggle room while you're learning since you probably won't run out of fuel. Since your tug should have some efficient atomic engines, it is very little fuel needed to move from a 100km to a 200km orbit. If you can launch a full orange tank; then you learn docking and make a space station. After than you can refuel in orbit if you need more fuel for a longer mission. It takes some balance of your terminal velocity. If you have to throttle back to avoid excessive drag losses then you could be carrying more fuel or less engines. If you can't reach terminal velocity during launch you could be carrying more enginges (or less fuel). It is common to burn half of your launch fuel before you reach 12,000 meters in elevation.

If you choose to use a bi-eliptic to go from a 80km circular orbit to a 200km orbit and you just happen to chose your middle burn as 100km Then your first burn at 80km periapsis raises your apoapsis to 100km. Your 2nd burn at 100km apoapsis raises the periapsis up to 200km. During that burn, as the periapsis crosses 100km it becomes the apoapsis AND you have just circularized your orbit as you continue to burn. Finally at your 200km apoapsis you burn to circularize in a 200km orbit. I fully understand that to be more efficient it will usually go the other direction; you burn from 80km to lower your periapsis to 70km, then you burn at periapsis lower in the gravity well to push your apoapsis out from 80km to 200km. In this latter example the orbit is never circularized in the middle. So it's not exactly 2 hohmann transfers. But it's really not that different since you can choose to do a bi-eliptic transfer at whatever orbit you like (but efficiency varies.) I know the middle step can vary, but I'm not saying they are identical. A bi-eliptic transfer versus 2 hohmann transfers aren't really that different either.

... not sure if trolling... So two hohmann transfers would have 4 burns...Burn from orbit A to orbit B, Burn at orbit B, Burn at orbit B to orbit C, Burn at orbit C. And if you realize that the "burn at orbit B" and the "Burn at orbit B to orbit C" could occur back to back as essentially the same burn you would notice 3 burns. The point is to be thrusting horizontally and preferably as much as possible as low as possible in the gravity well. Those primary attributes are shared whether you do it as a single hohmann transfer or a bi-eliptic transfer.

And the bi-eliptical transfer essentially just using two hohmann transfers to get a greater oberth effect... so yes?

I use a 3 man command pod on my tug and often also on my orange station fuel tank. It seems to turn pretty well without using RCS. If you're going to redock the tank, just in a different orientation, then you transfer all the fuel out of it before undocking and fill it back up after you re-dock. Alternately, you could try to balance it a little bit by moving fuel in/out of your tug fuel tank

You are correct... But I will defend my mistake by pointing out the efficiency of a Hohmann transfer comes from its use of the Oberth effect. In a Hohmann transfer the majority of the energy is exerted at the higher speed lower orbit... so I hope it's a forgiveable mistake. ... at least I didn't call if hoffman...

My short guide with some tips: 1) launch your target and get it into as perfect a circular orbit as possible. Preferably at a round number. if you can get it at exactly 120km up at both periapsis and apoapsis then it makes your intercept easier. You know exacly what orbit you are trying to match. 2) design your docking vessel. It should include: RCS thrusters that can turn/move the ship in all 3 axis. Plenty of RCS fuel. ASAS. Plenty of fuel for a rocket engine to achieve a close approach/intercept. Also it should have lights and a power source to illuminate the docking port. 3) launch your docking vessel; and set your target as your target using a right click in the map view. 4) At either the ascending or descending node burn south or north to "align" your orbit with the target. Just click on them to set a maneuver nod and adjust the pink triangle orbit accordingly. You'll know you're aligned when you see the AN/DN quickly flip sides. 5) Generally I start in a lower orbit and "catch up" to your target. As you get closer, speed up at apoapsis (or sooner if necessary) into a slightly higher orbit getting closer and closer to the targets orbit. The closer you are to your targets orbit the slower your relative speed will change. If I overshoot then speed up to a higher orbit (higher than the target orbit). Burns are often imperfect; you may need to repeat step 4 to ensure the orbits are aligned. 6) When you get to within 5km of the target click on the velocity display and toggle it from "orbit" to "target". Then point your nose at the target Purple circle using the nav-ball and accelerate toward it at 10-50 m/s. As you close turn and prepare to burn opposite your relative velocity (they yellow circle with an x in it) 7) When you notice that you are no longer getting closer to your target burn toward the yellow circle with an x in it until you reach zero relative velocity (with the target). 8) Repeat 6 & 7, but as you get closer you will need to reduce your speed to just a few m/s. If you find yourself within 100 meters of your target you should burn to zero relative velocity and move to RCS power and "docking mode" 9) Disable your rocket engines. When you are trying to maneuver for docking you will probably accidentally throttle up your engines. Just disable them to avoid a problem. 10) Point yourself at your target and use RCS thrusters to move closer. I usually leave SAS on, but wait until in "docking" mode to turn on the RCS. Just be prepared to turn off RCS as you are "coasting" in so that SAS doesn't use all your RCS gas just keeping it stable. 11) When you get really close (less than 30 meters) don't move toward the target but instead move toward the empty space along the side/end where you intend to dock. Once you reach that space near the docking port, then zero your relative speed, go back to the "normal" maneuver mode to turn your craft to directly align your docking port with the target docking port. Then switch back to docking mode and close the last 30 meters with very careful RCS maneuvers. 12) If you bump the target and it begins spinning then time accelerate briefly to stabilize it and then repeat step 11 to try again.

It's a tradeoff. By burning straight up into your ejection from Kerbin you can benefit from the hohmann effect of doing your accelerations low in the gravity well; BUT you will be burning straight up which means your effective thrust will be reduced by the force of gravity. The higher your T/W ratio the less the effective of "gravity drag" will be. Thus it can be better. But if you have a lower T/W ratio then you are better off establishing a low kerbin orbit and burning out from there. Ejection burns from orbit tend to be horizontal and do not suffer "gravity drag". Also, the path tends to keep you in low kerbin orbit for longer (curved arc of a circle) which gives low T/W ratio rockets a greater hohmann effect than a direct vertical burn (short straight line). Considering the relatively low power (and corresponding low T/W ratio) for the fuel efficient rockets generally used for interplanetary travel; and considering the better control you have of using a maneuver node to plan your burn from low kerbin orbit, the vast majority of people find it easier and "better" to establish orbit first.

With hexagonal geometry I place them at aproximatly the vertical center of mass for the empty tanks. Your urge is to have them point outward, but this will often catch one of your still running and very hot rocket engines with hot seperatron exhaust that can cause a sudden increase in overheating and explode your remaining rocket engine(s). To avoid this, I usually use a pair of them with a 120 degree angle so they are pointed mostly toward eachther. Just use snap to angle and make sure its exhaust is turned enough to not be pointing at the adjacent tanks.

1. Rocket engine blows up: some possible causes from my experience: a. Initial launch too jerky. Before starting the stage the engine weight hangs down a bit. The sudden jerk of starting can cause it to impact whatever is above it instead of just pushing upward. I have sometimes overcome this by activating and then throttling up the engines before releasing the launch clamps b. Too much force/power. When using a large orange tank with a mainsail engine near my final stage I find that it tends to break apart due to sheer engine power. Other than using as many struts as possible I finally found that burning fuel from higher tanks and leaving the fuel tank directly above the engine full would keep my vehicle in one piece. (f=ma, so less mass on top requires less force to accelerate thus reducing the force passing through the middle section to the top. When it burned the fuel directly above it then it worked in reverse; raising the center of mass for the rocket and eventually causing catastrophic failure in the connecting segments.) I also avoid using RCS fuel tanks anywhere that will experience "mainsail" thrust. The RCS fuel tanks are just too flimsy. c. Overheating? Not sure if this is your problem, but the solution tends to be less throttle and a close eye. Sometimes seperatron rockets placed in a bad spot will cause an engine to explode as they pass it when staging. 2. I avoid wings on my rockets... too many kerbals lost to changing force vectors of lift as a result of the velocity and atmospheric density. 3. I don't pay much attention to center of mass for rockets, but top-heavy is prone to tipping over and hard to steer. Having engines thrust as far down as possibly makes it easier to steer with thrust vectoring but you have to leave ASAS running if you have a topheavy craft because if it turns too far sideways it is like balancing a broomstick on the palm of your hand and it will just fall over. 4. There are mods that allow you to do "orbital construction" and "launch from orbit". I haven't tried them though.

You can do "slingshot" maneuvers in KSP even without n-body phsics. What he meant was that if you can get up from kerbin enough to enter the mun SOI that you can use the mun's gravity to pull you further toward it which is upward and further in an equatorial direction. Usually just "skipping across the SOI once won't do it, but it's only a matter of time before you enter again and eventually it pulls you into a close encounter where you can either do a course correction burn / land / or be flung out much further into space. You can use this energy to pull you in from a slightly lower shallow kerbin orbit. Other techniques about how you enter the mun's SOI can have it help slow you down as well. If you are falling toward the mun as it is moving away from you then you will be falling for a longer period of time because of the distance it is moving while you are falling. This gives you extra dV. If you are falling toward the mun as it is moving towards you then you are falling (being sped up) for a shorter period of time, if you then use its gravity to turn your craft 180 degrees then you will be moving in the same direction as the mun and you will be slowed down for a longer period of time as the mun is still moving toward you as you are coasting away from it.

Oberth effect means it is more efficient to wait as long as possible before you do your decelerating landing burn so you're going as fast as possible. After deciding I didn't like the trial and error of I'll slow down at 30km...splat....F9....I'll slow down at 50km... too high... F9... My preferred method now is to get my mun periapsis at about 5km above the surface. This ensures I'll be going nearly maximum velocity for my slow down burn. (If I want to change from an equatorial to a longitudinal orbit I slow down just enough to remain in very oblong Mun orbit and change my orientation at the apoapsis) I burn at periapsis to make my orbit circular and it allows me to be tightly orbiting at still relatively high velocity (high velocity = good fuel economy for landing burns). For landing I just continue decelerating at full power along the horizon, only pointing my nose up enough to keep my vertical velocity near zero. Once I have no velocity at all I do a controlled slow descent the last 5000 feet. This is especially useful since I often use a pair of low power high ISP atomic engines to land. For a vertical descent they would have to start slowing down very very early due to low T/W ratio. But by using a tight periapsis they can easily do most of their decelerating maneuver at low altitude and high speed without splatting my lander into the mun. Saves me the trouble of having to bring an extra rocket engine along just for the lander. Don't forget some downward facing lights if you want to land on any dark areas.

I created a mainsail asparagus vessel designed to get a full orange tank plus an additional 3 man "tug" into to kerbin orbit. Launchpad weight of about 600 tons. It took a lot of trial and error before I could successfully get it into orbit; but I can now routinely lift 70 tons to 100km LKO. It's starting weight of 600 tons is launched with 7 Mainsail Engines; giving a thrust to weight ratio of just about 1.75. This was necessary becuase the massive vessel would succumb to "physicks" forces and break apart if it were experiencing more than about 2.5 times the force of gravity. My experience has been to turn slightly at about 12km (maybe 10 degrees) then above 30km turning to about halfway between the orbital yellow circle and the horizon. Burning in a direction other than the horizon wastes thrust due to gravity losses. Burning in a direction other than the yellow circle wastes thrust due to steering losses. The minimum loss (in neglibible atmospheric resistance) is half way in between. Optimally you could wait until apoapsis (where your yellow direction is on the horizon) and suffer "no" loss. But due to my low T/W ratio I would not be able to reach orbital velocity before I crashed back into Kerbin if I waited until apoapsis. Also; little "pro-tip" I discovered on my final linear stage. The Mainsail kept thrusting up through the rest of the ship blowing everything up. But if I turn off the fuel tank directly above the mainsail then that tank remains very heavy and absorbs more of the force from the engine. By burning fuel from higher in the column it reduces the stresses on the joints as the top becomes lighter. You just have to make sure you remember to transfer the fuel back to the top before you jettison the mainsail & tank from the bottom.