Kerbal Engineer - Some Specific Questions

[KBoy420]

Hi Everyone,

So after logging around 60 hours in KSP without use a single mod (and having successfully orbited Kerbin, the Mun, and completing one successful Mun landing, 1-way lol - Tedrim will be up there a while), I decided to get Kerbal Engineer. I decided against MechJeb simply because KE would do what I wanted it to (mainly dV calculations while building). So I have a few specific questions regarding the use of KE:

1) The dV calculations are pretty straight forward. I also found a "map" showing the dV needed to get to various locations through the solar system, which was hugely helpful. At least I now know how much dV I should be building into my designs. What I am finding, however, is that even though I have 6,400 m/s of dV, I am still running out of fuel before landing on the Mun. According to the map, I should only need around 6,200 ms of dV for a complete Munar landing and return to Kerbin. So I am piloting my ship inefficiently, I assume. How can I use the data in KE to adjust my flying, staging, etc. so that I am able to get the dV out of my design?

2) In the surface display (either surface or orbit, can't remember), there is an atmospheric efficiency display, 0% to 100%. I am assuming that I want this as close to 100% as possible at all time, in order to maximize fuel/dV efficiency. What I am finding is that getting up to 10k-15k m, that percentage drops significantly. Does that mean I am moving too slow?

3) Is it more efficient to gain stable orbit around Kerbin before moving to the Mun? I had typically tried to wait until a good alignment and lift off Kerbin and then move right into a lunar/munar trajectory before establishing a Kerbin orbit.

4) TWR. I understand (in theory) what a thrust-to-weight ratio is comparing. But I do not understand how it pertains to my design and how to utilize the information correctly.

5) Any other useful tips for how to get more out of KE? Other tips on how I can better use it to adjust my designs and better evaluate how far I can go?

6) Any other add-ons that would help me get better at designing more efficient rockets? I don't want to use a bunch of add-ons. I tend to like to keep games stock and incorporate add-ons at a minimum. But KSP is no ordinary game so maybe there are others that would help.

Thanks!

[Red Iron Crown]

1) Delta-V maps are for an ideal transfer with instantaneous burns, you have to add some cushion for inefficiency. I used to add about 20%, now I add 10% and generally don't run out of fuel.

2) Once you get out of the thick part of the atmosphere you will not be able to keep up with terminal velocity (atmospheric efficiency measures how close you are to terminal). It just rises too fast for any reasonable rocket to keep up with. Don't worry about it, as long as you're not exceeding 100% you should be fine.

3) That is the subject of some debate. It is certainly easier, timing wise, to circularize around Kerbin before transferring to the Mun.

4) On or near a planet, a TWR of <1 will not be able to get off the ground or slow for landing. Once in space higher TWRs make burns more efficient but cost dV in the form of additional dry mass.

5) Try making your own customized displays, there is a lot of info in there.

6) MechJeb can help with efficiency testing as it removes pilot skill from the equation.

Also, moving this add-on related question to General Add-on Affairs.

[Tank Buddy]

Mr. Red Iron Crown answered your questions pretty well, but I have some things to add.

3. It is much simpler and it will give you better practice for interplanetary missions if you enter an orbit first, then use a Hohmann transfer orbit (http://en.wikipedia.org/wiki/Hohmann_transfer_orbit) to get to the moon.

4. TWR is the ratio of your ships trust (In KiloNewtons) to weight (in KiloNewtons [mass in tons (1000 kg) * gravitational acceleration (9.8 m/s^2). Kerbal Engineer displays the TWR for the current body i.e. it changes if you are on Kerbin or on the Mun. (I also noticed Kerbal Engineer takes into account that as you get further away g decreases, so the TWR increases as you are further from a planet) TWR allows you to do several things:

A. Determine if your ship can lift off from a planet. If TWR > 1, you will lift off, but a TWR of 1.5 or greater is best for lifting rockets on any planet/moon. A TWR of 1.0 will hover, or not take off at all, depending on perspective.

B. Determine the acceleration of the ship once in orbit. To find this, you multiply the TWR by 9.8. You can also use newtons 2nd law, F = ma, rearrange it to: a = F/m, so thrust in KN/mass in tons = acceleration in m/s^2

C. Determine the acceleration when fighting gravity. Same as the previous, but subtract 1.0 from the TWR.

5. Just use the Delta V readout to design your ships based on Delta V charts (It is very good that you know how to use them, I'm impressed ) As I mentioned, use the TWR to make sure your ship can lift off/slow down fast enough. You can change the reference body in the VAB to show you the TWR on different moons/planets. Lastly, you can design sub-assembly lifting stages by putting a dud payload on top and designing it to have 4500 m/s of Delta V.

6. I would HIGHLY recommend RCS build aid. http://forum.kerbalspaceprogram.com/threads/35996-0-90-RCS-Build-Aid-v0-5-5; it shows you the Center of mass when the ship is emptied of fuel (dry center of mass), which is very helpful for plane building. Not to mention it helps with RCS placement. I could recommend you mods that I like to play with (I initially didn't want to play with mods, but I changed my mind), so I'll respect your decision. For general game-play, I would recommend Kerbal Alarm Clock and the Trajectories Mod, but RCS Build Aid probably is best for you.

Good Luck!

Edited January 27, 2015 by Tank Buddy

[Alshain]

I'm going to adds some additional info to what Red Iron Crown said.

1. If you are using FAR or NEAR, be aware that atmospheric planet values will be wrong (I've never seen a map specifically for FAR/NEAR) but Kerbin ascent is closer to 3600 dV. This does assume a good ascent, I can come under 3600 but that is due to a whole lot of practice. The dV maps should be considered guidelines (regardless of aerodynamics). For transfers, you can play with the maneuver nodes to find more optimal burns, this also takes a little practice.

2. Nothing really to add here.

3. The Oberth effect would suggest that the closer you are to a gravitational body, the more efficient the engine will be. However, the debate is mostly over practicality. It's harder to set up a perfect launch to mun. It's significantly easier to get there when you can pick any spot in your orbit to start from. While it may be more fuel efficient to do a direct transfer, would it be worth it?

4. If you are using engineer make sure you have the correct celestial body selected. Obviously TWR on Minmus is not the same as Kerbin. Also, what Red Iron Crown said assumes rockets. Planes use wings to lift and do not require TWR of 1 or higher.

5. Yep, make your own displays. Also you can make your own custom HUDs, you can add more than the default ones as well. I never even open the KER window anymore, the HUDs are an amazing and fairly recent addition, I'm not sure how I ever got along without them.

6. FAR, but that's not just getting efficiency, that's an aerodynamic overhaul. RCS Build Aid helps building craft that move evenly when translating, that makes more efficient RCS usage.

[KBoy420]

Thanks for the reply guys. Going to work on getting KER customized and utilizing a customized HUD. Didn't know those could be changed but that will be hugely helpful and free up some screen space. I'm definitely not opposed to using add-ons - I just firmly believe you learn to play games better by not using them first. You could play this entire game without thinking by using add-ons (from my understanding) and I just don't see the point of that. But using an add-on to simply display existing information in more use-able ways, would be silly not to if it is helpful. So I will definitely check out some of the others you all recommended.

One final question, more along the lines of staging and how it relates to total vessel delta v. You design a 4 stage rocket, and the total delta v for the vessel is shown. Does this take into account the staging, or does that not matter? What I mean is say first stage is SRBs to get you going. I am matching terminal velocity well up until about 8k m when I activate second stage and my m/s drops significantly, dropping me well below terminal velocity but still accelerating. Did I just lose all my delta-v or did the vessel total delta v account for this inefficiency when calculating in the VAB? Hope that makes sense lol. Does in my mind.

[Crzyrndm]

Total dV is the sum of stage dV (and each stage is calculated with all prior stages removed where applicable), so no, staging hasn't just "thrown away" a bunch of dV unless that stage hadn't exhausted all it's propellant.