n00b needs help!!!

[SgtFlash]

as said in the title, i need some help with some basic stuff.

i dont know how to dock in space to make space stations, i used to be able to get to the moon but with the new update i cant get there with my old design so what do i need to do to make a basic to the moon rocket (plus how should i set up the nodes for this), and how do i get to duna? (again, how to set up the nodes).

any help is appreciated and picture will help alot aswell.

cheers

[soulsource]

Scott Manley, one of the more famous KSP youtubers, made a nice

. Beware, it's really, really long, and to be honest I haven't watched it, but from what I've seen of his works, they should be very extensive and include some actual science.

[CaptainApollo]

SgtFlash, I can give you more extensive details if you message me, your choice.

But for Duna, you first achieve a stable orbit around Kerbin, it does not have to be a high one. Then you make a node to get your orbit to escape velocity; where you orbit the sun. Complete the burn, time warp, you should now be orbiting the sun. After this, click Duna and set it as your target, then you will see the AN and DN appear. Burn normal or anti-normal with a node to get this to 0.0, but I found that 0.1 works. After this, make another node and pull prograde, then move it around until the two arrows that have appeared connect, and the 'Encounter' icon appears on the map. Time warp, and when you get to the encounter, burn retro to get an orbit. I hope I helped, more if you message me!

[selfish_meme]

You know you don't need to burn first to get out of soi before setting a transfer node. Not saying it's better but as long as the phase angle is right you can do it from orbit.

[soulsource]

What you're suggesting, CaptainApollo, is ignoring Oberth effect and therefore wasting quite a bit of fuel.

Here's what I'd do for a one-way Duna mission, step by step:

1. When building the probe/lander, plan ahead if you want to do a powered landing, or if you want to rely on parachutes. I'd do the latter, as they'll help you keep your craft oriented, but you'll either need about five times the number of chutes you'd use for the same mass on Kerbin, or the RealChute mod. It's of course also possible to do a combination of parachute and powered landing, relying on chutes to eat away most of the velocity and to keep your craft stable, but to kill the last bit of speed by doing a short burn right before touchdown. I don't know about 1.0.4, but in 1.0.2 heatshields were optional on Duna when landing from a low orbit, as atmospheric entry happens at relatively low velocity.
   
2. Calculate (of course with taking Oberth effect into account - see below) or look up the required change in velocity (Delta-v, or dV), and build your craft to have enough fuel for this using the rocket equation or a mod that displays available dV (I recommend VOID). Beware that most dV charts already take into account Oberth effect, so if you first go to escape velocity, and do a second burn in kerbolar orbit, you'll probably run out of fuel. Also, for transfers to planets with inclined orbits (luckily Duna has negligible inclination) you should also take into account the dV needed for the inclination change.
   
3. Calculate or look up the phase angle for a transfer between Kerbin and Duna, or just install either Transfer Window Planner or Kerbal Alarm Clock.
   For a transfer to Duna usually circular approximation is good enough. Calculation is rather easy, as the phase angle is just the angle traveled by Duna during the time the transfer takes (minus half a circle).
   First, we'll need the time our transfer orbit takes. The orbital period is given by T=2*pi*sqrt(a^3/GM), where GM is the standard gravitational parameter (in this case of Kerbol, so it's 1.1723328e18 m^3/s^2), and a is the semi-major axis of the orbit. This formula can be derived by setting centripetal force (m*omega^2) equal to gravity (GM/r^2). As for the transfer the periapsis is at the orbit of Kerbin, and the apoapsis at the orbit of Duna, a is given by the average between the semi-major axis of Kerbin and the semi-major axis of Duna, yielding 1.7163e10 m. With these numbers, our orbital period for the transfer orbit is 1.3048e7 s, or 151 earth days, or 604 Kerbin days. This is the orbital period, the transfer from periapsis (Kerbin) to apoapsis (Duna) takes half the time.
   Now we'll need the angular frequency of Duna. Here the same argument regarding forces can be used, the formula is then omega=sqrt(GM/a^3). Here we input the semi-major axis of Duna's orbit and of course again GM of Kerbol, yielding omega=3.6285143e-7 rad/s, or omega=2.078986e-5 degree/s.
   Multiplying the angular frequency of Duna with the time the transfer takes yields an angle of 135.6°. Subtracting a half-circle (180°) gives the phase angle of -44.4°.
   This tells you that the ideal moment for the transfer is reached, when Duna is 44.4° ahead of Kerbin. So, in order to hit the right spot, either get one of the mods I mentioned above, or look at the Kerbol system from above/below, center your view at Kerbol, and time-warp until the angle between imaginary lines Kerbol->Kerbin and Kerbol->Duna is about 44.4°.
   
4. At the correct phase angle it's time to launch your ship. After bringing it to low Kerbin orbit, place a maneuver node and plan a prograde burn with the dV of the first burn needed for the transfer, maybe slightly more. If you're using a dV map, that's the sum of the numbers between Low Kerbin Orbit and Duna Intercept. Now move the maneuver node around your orbit, until the planned trajectory gets tangential to the orbit of Kerbin around Kerbol. Of course you could also calculate this ejection angle, but I've found that it's a waste of time, as dragging the node around works just as well. After having the node placed in such a way, look if you're already lucky and have an intercept. If not, the two markers "target position at intersect" and "closest approach" will be your best friends, as an intercept happens when these two markers are close enough. Check if there's are node-lines visible, and how big the inclination of your plotted course is with respect to Duna's orbit. If the inclination is large (I'd say above 0.2°) try placing a maneuver node at the nodeline and to correct the inclination. If that gives you an intercept: bingo. If not, I'd play slightly with the first maneuver node (the one placed on LKO), by slightly increasing or decreasing the dV number. If you cannot get an intercept, check the phase angle again. If it's too early, wait a few in-game days and try again. If it's too late, you'll probably need more dV for the initial burn.
   
5. Once your ship is on the way, check its trajectory regularly. I'd have a look after about half the transfer, and if necessary do slight corrections. Apart from maybe inclination changes, these correction burns should usually just take a few m/s. You should also consider to fine-tune the target-orbit around Duna already quite some time before entering Duna SOI. Early course corrections are more difficult, but if carried out correctly usually take less dV.
   
6. After entering Duna's SOI, make last course corrections if needed. I wouldn't aerobrake in 1.0, but rather first enter an orbit around Duna. I'd aim for a rather low orbit, maybe 10 km above the edge of Duna's atmosphere.
   
7. For landing with parachutes, I'd do a deceleration burn to bring periapsis to about 30 km or so, maybe even lower (I haven't been to Duna with stock atmosphere in 1.0, only with FAR, so this is an educated guess based on the pressure data given on the Wiki) and try to keep the heatshield (if present) pointing front.
   
8. I wouldn't fire the parachutes until the probe/lander has slowed down to about 300 m/s, except if the ground comes dangerously close. Below 10 km you should get serious deceleration due to atmospheric drag, so there should be plenty of time to open the chutes.
   
9. If you don't use chutes, I'd first test the lander on Kerbin. Of course unmanned, as Kerbin has a higher gravity and you'd need a higher TWR for a successful landing. The reason is, that you'll need to make sure that your lander either is aerodynamically stable during descent and has the engines pointing forward, or that you'll have at least enough torque to orient the lander this way when needed. If you can control your lander at 10 km above sea level on Kerbin, it'll probably also stay under control everywhere on Duna.
   

Edit: On the Oberth Effect.

I just found that the Wikipedia article on Oberth effect is not very descriptive, and I think that adding an example will help to illustrate.

For this, let's start from a circular low orbit around Kerbin. Our orbit has a certain radius r, and our ship has a certain velocity v0. We already used the formulas on the Wikipedia article on Hohmann transfers to calculate the dV needed to enter the Hohmann orbit to Duna (let's call it dVh), but that number applies only if we are already free of Kerbin's gravity. Naively one might now think, that one could simply add the dV needed to escape Kerbin to the dVh needed to go into the Hohmann transfer, but the situation isn't that easy. Thing is, there's the principle of conservation of energy, and energy is the quantity we can add here. Let's assume we burn and add to our current velocity v0 an additional velocity dV0. The kinetic energy of our ship after the burn will then be m*(v0+dV0)^2/2. In addition, we sit in Kerbin's gravity well, adding a (negative) energy of -GM*m/r, where GM is the standard gravitational parameter of Kerbin. After we leave Kerbin's gravity well, we would still like to have enough kinetic energy to enter the Hohmann transfer, so we'll need a kinetic energy of m*dVh^2/2. This gives us the energy balance:

m*(v0+dV0)^2/2-GM*m/r=m*dVh^2/2

The required dV for a burn using Oberth effect can now be found by solving this equation for dV0.

(I'm not sure if this is really correct. Please notify me if there's a mistake, I'll fix it asap.)

Edited June 24, 2015 by soulsource
Paragraph on Oberth effect added.

[xnorb]

Only 2 words: Scott Manley.

Watch his videos and all your questions will be answered.

[mrclucks]

Watch Scott Manley's videos, especially his tutorial for begginers. You can also install mech jeb and learn how by seeing how and where mechjeb places maneuvers.

[CaptainApollo]

Soul, you've got a point. I'm still a new player, and don't know that much about KSP. You know far more than me, evidently!

[Vanamonde]

These questions about how to play the game have been moved to Gameplay Questions.

[maceemiller]

Try the Docking Port Alignment mod. Its great. I can dock manually without mods however the DPA mod makes it far quicker