(See Alexmoon's Launch Window Planner for the calculations.)

Getting to the point in my 0.90 KSP game where I am ready to start thinking about putting orbital bases around Kerbin, the Mun and Minimus.  And the next step after that would be sending Kerbals to the inner plants (Moho, Eve, Duna) and hopefully bringing them back alive.

When planning a mission like this and if you need to be fuel-efficient, you have to pay attention to launch windows.  Going from Kerbin's orbit to Eve's orbit can consume as little as 2711 m/s of delta-V or as much as 24,000 DV if you start the transfer at the wrong time.  And if you want to bring the kerbals home again, you need to know the return windows.

Note: There are 426.08 Kerbin days to the Kerbin year.

Kerbin -> Eve (ballistic)

Y01D001 - 3700 m/s 170 days transit
--
Y02D125 - 2975 m/s 135 days
Y02D151 - 2711 m/s 199 days
Y02D205 - 3125 m/s 177 days
--
Y03D237 - 3036 m/s 244 days
Y03D391 - 2627 m/s 188 days
Y04D047 - 3354 m/s 184 days

Eve -> Kerbin

Y02D53 - 3250 m/s 178 days
Y02D194 - 2745 m/s 248 days
Y02D240 - 3500 m/s 211 days
--
Y03D280 - 3457 m/s 188 days
Y04D009 - 2578 m/s 223 days
Y04D065 - 3612 m/s 169 days

So a mission that leaves Kerbin on Y02D151 (2.35 years into the calendar) needs 2711 m/s to leave Kerbin's orbit and arrive in Eve's orbit after 199 days in transit.  The first return window is towards the end of year 3 and requires about 3000 m/s and a return trip of about 215 days.  Arriving back at around 4.50 years into the game.  So a two-way trip requires 2.15 years worth of food for the Kerbals (915 days).  Plus about 10-15% for margin of error.

I suggest using "mid-course plane change" option on the launch window planner.

The larger the blue (and dark blue) area the easier it will be to hit your departure window.

For the moment, I'm mostly interested in lobbing unmanned probes at Moho, Eve and Duna in order to get communications networks setup around those planets.  For some of them, there will be signal delays measured in tens of seconds (Eve can be as bad as 78 seconds).  So use of MechJeb or the Remote Tech flight computer will be required.

Early departure windows for unmanned probes to inner planets (mid-course plane change):

Moho - 5500 m/s Y01D020 112 days transit (fairly wide window if you can get 6000 m/s of DV into orbit)

Eve - 5000 m/s Y01D063 157 days transit, optimal window is not until Y02D086 (2800 m/s)

Duna - 2800 m/s Y01D049 321 days transit or 2500 m/s on Y01D262 with a 154 day transit

--------------------------------------

Updated list (ballistic transfers, 426.08 days/year):

Goal of this list is to give rough ideas of when transfer windows occur during the first few years of game play.

Departure Key: earliest - optimal (transit) - latest

Kerbin-Moho

  • Y1 D84 - Y1 D108 - Y1 D133
  • Y1 D253 - Y1 D268 - Y1 D282
  • Y2 D79 - Y1 D92 - Y2 D104
  • Y2 D228 - Y2 D244 - Y2 D260
  • Y3 D79 - Y3 D84 - Y3 D89
  • Y3 D204 - Y3 D221 - Y3 D238

Kerbin-Eve

  • Y2 D117 - Y2 D151 (199d) - Y2 D180
  • Y3 D378 - Y3 D401 (185d) -  Y3 D422
  • Y5 D181 - Y5 D211 (181d) - Y5 D239

Kerbin-Duna

  • Y1 D217 - Y1D236 - Y1 D255
  • Y3 D291 - Y3 D310 - Y3 D328
  • Y5 D339 - Y5 D364 - Y5 D390

Kerbin-Dres

  • Y1 D341 - Y1 D351 (1y157d) - Y1 D365
  • Y3 D105 - Y3 D120 - Y3 D134

Kerbin-Jool
  • Y1 D181 - Y1 D229 (4y128d) - Y1 D266
  • Y2 D228 - Y2 D248 (3y222d) - Y2 D268 
  • Y3 D259 - Y3 D274 (2y368d) - Y3 D294

Kerbin-Eeloo
  • Y2 D245 - Y2 D258 (4y201d) - Y2 D270