To the Mun and back, for 5060 m/s

[camacju]

I'm probably being too petty here but I had someone argue that a rocket with 5200 delta-v cannot go to the Mun and back. It was your standard fare of "It takes 3400 m/s to get to orbit" and "you need 800 m/s to land on Mun" etc, etc. But this is what made me want to actually do this mission:

So, tac, here you go!

Craft in VAB. 5114 vacuum delta-v and 4510 surface delta-v. There's some part clipping and aero trickery going on here, but no sources of free energy.

Journey to Mun:

Spoiler

On runway. Low drag means I can fly a very shallow ascent and lose very little delta-v to either gravity or drag.

"Ascent" is really more just accelerating horizontally.

I throttle down because of heat and also because apoapsis increases very rapidly here

Coasting to space

Circularization. Note that Mechjeb says 2372 m/s of delta-v expended. I'm not quite sure how it calculates this.

In orbit with 2546 m/s of delta-v. I know that 2500 m/s should be enough to complete a Mun mission from LKO, but the margins might be tight.

Using a test craft, I note down certain orbital elements. This will be useful later.

Mun transfer. This series of Mun assists puts me into an orbit similar to the one from the test craft.

Fine tuning final periapsis

Deep space maneuver at apoapsis to encounter Mun with lower relative velocity

And here we see the purpose of that initial test craft. I can capture around Mun for 203 m/s capture burn plus 17 m/s deep space maneuver, for 220 m/s total, as opposed to 280 from a direct transfer.

Descent over Mun. High TWR means a very effective suicide burn.

Burning

At this point, KSP ate a bunch of memory on my laptop so I used Mechjeb for terminal descent. Normally I can hand-fly a descent more efficiently, but lag made it impossible here.

Landed on Mun with almost 900 m/s of delta-v remaining. More than enough to get home

Return trip:

Spoiler

Ascent

Coast to Ap

In orbit

KSP crashed a couple times and some funny stuff happened corrupting my save. I took this opportunity to fly a slightly more efficient ascent.

Since I have ample margin at this point, I plot a direct return instead of using more gravity assists. However, had I really wanted to, I could have saved around 50 m/s over this.

Aerobraking

Chute reefed

Chute deployed

Landed back on Kerbin! Margin looks tight, but as explained above, it's probably more permissive than it seems.

Total vacuum delta-v spent is 5114 - 54 = 5060 m/s. (Thanks to @Poppa Wheelie for the correction - 46 m/s as shown in the last screenshot is from sea level).

My best estimate for delta-v actually spent (based on Mechjeb's readings) is 2372 + 70 (ascent and circularization) + 2546 - 54 (vacuum dv spent) = 4934 m/s.

 

 

 

Edited July 23, 2022 by camacju

[Lt_Duckweed]

SMH no Minmus assist.

[camacju]

Not sure what I want to do next in KSP, but it'll probably involve some Minmus gravity love.

[IntellectualTortoise]

Very impressive! I wish I knew about those efficient flying techniques when I did my last Mun mission. They might have saved me the trouble of having Bob push the capsule onto a suborbital trajectory.

[Poppa Wheelie]

Your aerobraking screen shot shows 54ms of dV at 38km ASL.  You had at least this much (probably a little bit more) before reentry began.  The 46ms you had upon landing is not vacuum dV.  I think your "total vacuum delta-v spent" should be no more than 5114 - 54 = 5060.

[camacju]

8 hours ago, Poppa Wheelie said:

I think your "total vacuum delta-v spent" should be no more than 5114 - 54 = 5060.

Good catch, I forgot that the Spark took that much of an Isp hit at sea level