# Nicias

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162

1. ## UnHohmann transfers

Ok, so I mathed the heck out of this. I used Mathematica for all of my calculations. I did everything as if you are going from Eeloo to Kerbin. I could re-run it to go the other way if I just change the AoP of Eeloo to negative its current value. I first ignored inclination. I determined both the dV for transfer with minimum eccentricity at a given departure angle. I also determined the minimum dV for a departure at the given departure angle with periapsis at Kerbin's orbit. The results range from 3141 m/s to 3740 m/s for both methods, departing at apoapsis for worst case and periapsis for best. Note that periapsis is at 0 or 360 degrees and apoapsis is at 180 degrees. https://imgur.com/rzZXYtZ https://imgur.com/usf927a As other have mentioned, the dV is dominated by the Eeloo burn. Now adding in inclination I first did it by correcting the inclination at the AN or DN that is on the way down to Kerbin. Again I used minimum eccentricity and optimized for dV transfers. For the least eccentric I got a range of 3782 to 5013 m/s. Departing at 226 degrees and 291 degrees. The range in inclination change is the largest of the factors. Breaking down the dv budget as Eeloo departure, inclination change, Kerbin capture gives: 3782 = 1221 + 410 + 2151 and 5013 = 1732 + 1289 + 1993. As you see the inclination burn is the biggest factor. (410 versus 1289) https://imgur.com/4LYot79 The same calculations minimizing dv gives: 3584 @ 100 degrees to 4882 @ 309 degrees. With breakdowns: https://imgur.com/SXO9sB4 3584 = 1289 + 203 + 2092 and 4882 = 1664 + 1255 + 1964 The minimum transfer one saves dv on the inclination by going a little farther out. than the mimimum eccentricity one. If you look at the graphs for these two you'll notice a sawtooth pattern to the inclination changes and hence the total. As the departure location of the transfer orbit approaches the line of nodes, the transfer gets cheaper as you are departing closer and closer to the node. As the departure location passes the node (100 and 280 degrees) then you have to correct at the lower node. So that 1255 in the above example is correcting right outside Kerbins SOI. This explains the jumps in the graphs. In practice you could roll that correction into the Kerbin capture and then have Pythagorean and Oberth savings. Finally I allowed for correcting the inclination at either node. That gave: 3619 @ 146 and 4512 @ 10 for least eccentric with breakdowns: 3619 = 1101 + 345 + 2172 and 4158 = 1834 + 417 + 1906 https://imgur.com/iT3COSl dv optimized were: 3531 @ 125 and 4495 @ 8 degrees, with breakdowns of: https://imgur.com/FjXfSgk 3531= 1122 + 265 + 2144 and 4495 = 1835 + 755 + 1906.
2. ## UnHohmann transfers

Slashy, Thanks for giving it a look :). That change is correct, the difficulty is in finding theta. Theta is the angle between the vectors. It is only the angle between the orbits if the velocity is purely tangential (so at apoapsis or periapsis). Take the limit of two orbits that 90degrees inclined to each other, but highly elliptical. If they have 1000 m/s radial and 1m/s tangential, then the angle between the two velocities is only about 0.08 degrees, rather than the 90 degrees. So you need to find that angle, it isn't just the relative inclination. Or you have to find the tangential velocity, which is easier, because it is just given by h/r (where h is the angular momentum of the orbit) but then you need to find the radius when you do the burn. Which means you need to find out where on the transfer ellipse the AN/DN is, which means you need to find the AoP of the transfer ellipse, which leads to my question about AoP. Basically, I am asking how you calculated velocity at the inclination change? -N
3. ## UnHohmann transfers

I am trying to run the numbers on this, and I think I almost have it. I just need to add in the inclination change. I have a couple of questions. 1) I'm trying to use the formula for an inclination change given at: https://en.wikipedia.org/wiki/Orbital_inclination_change My question is in that expression, if the inclination change is happening at one of the nodes, then f is 180 - w or -w right? w measures the angle between the semi major axis and the line of nodes, and f measures the angle between the current position and the sma. So if we are at one of the nodes, then f is the measure to the next node from the sma, so since the nodes are 180 degrees apart, its either -w (if we are changing at the ascending node,) or 180 - w (if we are changing at the desending node), That would make w+f 180 or 0 right? 2) I am parametrizing the transfer orbits by true anomaly (f) and eccentricity of the transfer orbit. To use the formula for inclination change I need the argument of periapsis for the transfer orbit. I know my radius from the sun at departure (r), I can work out the new aop (w) using: r = a * (1-e^2)/(1-e Cos[f-w]) Solving this for w gives: w= f +/- ArcCos[ (a (1-e^2)-r)/ e r ] With +/- depending on if I my current radial velocity is outward or inward at this time. Does that seem correct? With that done, added in, I think I could definitely work out the problem for any planet to/form kerbin. If one end is not circular, I don't think I could get it to work.
4. ## Do I need to toggle RCS for Vernors?

You could also turn off the RCS monoprop *tanks*.
5. ## UnHohmann transfers

The way to deal with inclination changes is to roll the into one of your burns. Then you get an Oberth boost, but more importantly a Pythagorean savings. For instance, doing a 700 m/s inclination change on top of a 2000 m/s ejection burn only costs: Sqrt(2000^2+700^2)=2119 m/s. @GoSlash27 I was looking at doing the math for a Hohmann transfer ellipse to ellipse, and found it to be rough. Even just doing ellipse to circle was rough. I couldn't figure out how to find the optimal burn to go from a given point on a given elliptical orbit to an new elliptical orbit with a given periapsis. Is there an easy way? Is it a safe assumption that the burn should be entirely retrograde?
6. ## UnHohmann transfers

I think @Tig is suggesting that the "every year" is "every synodic period." (Which is about a year for targets with very long orbits) Ignoring inclination, the question is then: Given two orbits, with given SMA and eccentricities (and AoP). If you departed your original planet at any random transfer window, what would be the maximum DV you would have to spend on the transfer (just counting hyperbolic excess, which is what I think he means by "from the edge of the SOI"). Equivalently. If you left the original planet's orbit (around the sun) at any point in the orbit using a Hohmann transfer to the target planet's orbit (but not necessarily hitting the target planet) what is the most DV you would need? In other words, there are good transfer windows and bad transfer windows, how bad are the bad ones?
7. ## [1.7.x] Stockalike Station Parts Redux (May 21st)

This is just incredible! Great work!
8. ## [1.6-1.7] Modular Fuel Tanks v5.12.3

Is there a reason you don't have fuel in the 2.5-3.75 adapter? Also, looking the source, if I want to add a tank to a part, I just do this: @PART[Size3TinyTank] { MODULE { name = ModuleFuelTanks volume = 1800 type = Default } } To make this tank use MFT? https://github.com/linuxgurugamer/RecycledParts/blob/master/Release/GameData/SpaceTuxIndustries/RecycledParts/RSCapsuledyne/Parts/FuelTank/Size3TinyTank.cfg
9. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

I've had trouble with where Advanced Transfer. I want to use it to plot an intercept from, for instance, Laythe to a station in orbit around Jool and I consistently get the error. "Ejection Optimization failed, try manual selection."
10. ## CKAN (The Comprehensive Kerbal Archive Network); v1.26.4 - Orion

Modular Fuel Tanks has been updated to 1.3.1
11. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

Thanks for the release! The fuel-sim fixes seem to work for me. Haven't built anything crazy, but it works on my test craft.
12. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

Here you go: https://pastebin.com/EYNBjtLM Also, the Kerbal X shows the error if you slap a mechjeb pod on the capsule.
13. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

I'm still having this trouble with the dV calculator not using drop-tanks properly. With #771. Am I the only one having this trouble.
14. ## [1.7.3] Community Delta-V Map 2.7

I recently did a trip to Dres with life support, using this mod, and found that I had a trip home only about ~90 days after I arrived based on the map I was prepared for a stay of over a year. I looked into the maths some more and I realized the following: 1) I think the "average time between windows" you calculate is just the synodic period. 2) I think you can work out the time to return window as follows. Let say we have two planets P1 and P2 with orbital periods T1 and T2. We start at P1. Hohmann transfer to P2, dwell there for time D and Hohman transfer back to P1. We can calculate the time required for the (round trip) transfer orbit from the periods P1 and P2 of the planets. Call that time Th. I am going to measure angular position out of 1, rather than 360 degrees of 2pi radians for simplicity. The total time the mission takes is D + Th. In that time P2 makes (D+Th)/T1 laps. The vessel does half a lap on the way out, half a lap on the way back and does D/T2 of a lap at P2. If we set these two numbers to be equal we get: (D+Th) / T1 = 1+ D/T2 Solving that equation for D gives: However, we don't actually have to solve that equation. The two sides don't have to be equal, they can differ by an integer (which is 360 degrees) so we actually solve the equation: (D+Th) / T1 = 1+ D/T2 + k to get: D= (1 + k - Th / T1) / ( 1/T1 - 1/T2). And use the smallest positive D we can get by trying different k's. That gives dwell times of: Moho: 79 days Eve: 554 days Duna: 529 days Dres: 89 days Jool: 340 days Eeloo: 250 days I haven't checked these times out in the game, but the math works. Might you want to include that information on the map? Also, could we please get an update for the OPM map that includes Karen?
15. ## [1.7.x] Snacks! - Friendly, Simplified Life Support

So, If I had 4 kernels and one hitchhiker, will soil build up?
16. ## Docking

Caps-lock for balanced translation and Navball Docking Alignment Indicator FTW.
17. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

Double checked with a clean 1.3.1 install same problem.
18. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

Still not working. I seem to be on #768. Screenshot attached: https://imgur.com/a/Jljjp
19. ## [1.7.x] Anatid Robotics / MuMech - MechJeb - Autopilot - [2.8.4] [14 June 2019]

I was noticed last night that mechjeb wasn't calculating deltaV for a droptank, connected with a small hardpoint. It was assigning all of the fuel to the first stage. Has anyone else had a similar problems? When I get a chance I'll post a minimal craft file with screenshot.
20. ## Frustrating Launch

I like to do both of these. Going up from the cupola, 1.25m decoupler backwards, then 2.5m fairing (upside down) then big nosecone. This big fairing goes down to cover all of the draggy bits.
21. ## Suggestion: one-way crossfeed setting for decouplers

If possible, I vote for "ALL", What if you have a mix of LF only and LF/OX engines on the craft, you might want to keep using the LF even though the OX is empty. I can't quite think of an exact use case now.
22. ## Trouble Targeting Station & Orbits

I used to be able to click on the orbit of a craft or body and have it bring up the "focus/target/switch" dialog. Now I can't. I think the change happened when I upgraded from 1.2 to 1.3 Is it possible to bring the old behavior back?
23. ## Space station?

I put rcs pods on decouplers so I can chuck them after I've docked the module.
24. ## [1.3.1, 1.4.5, 1.5.1, 1.6.1, 1.7.2] SpaceTux Industries Recycled Parts

Thanks, I think I'll do that as part of my 1.3 upgrade this weekend.
25. ## [1.3.1, 1.4.5, 1.5.1, 1.6.1, 1.7.2] SpaceTux Industries Recycled Parts

Would switching to this from Atomic Age break vessels currently in flight?