Get to Minmus as fast as possible without crashing

[physius]

KSP Twitter challenged us to do this.

So I said challenge accepted.

I'd like to see some other people try this and beat my time 2d 3h 22m 15s.

Honestly mine is probably a mediocre speed because I bet there's someone out there that's made it in way less and probably just never recorded it, but either way it's a quick and easy challenge and I thought making my first video was pretty fun.

I see already where I can improve in video making and narration if I ever make another. Let me know what you think of the video and I'd like to see other submissions!

edit: also, if you want to see the raw video without my annoying commentary and edits, it's here - https://youtu.be/TgsOaL11ass

 

 

Edited November 17, 2022 by physius

[farmerben]

That's pretty good.  My first attempt took 6 days 2:30 .  I flew direct without orbiting either body.  But I didn't want to accelerate halfway because I got my apoapsis lined up with minimus.

 

second attempt: 3days 1:30

 

third attempt:  fatal crash 3 hours 21 minutes, collision with Minimus at over 3000m/s

 

fourth attempt: 5 hours 44 minutes success

Edited November 17, 2022 by farmerben

[physius]

  On 11/17/2022 at 11:22 AM, farmerben said:

That's pretty good.  My first attempt took 6 days 2:30 .  I flew direct without orbiting either body.  But I didn't want to accelerate halfway because I got my apoapsis lined up with minimus.

 

second attempt: 3days 1:30

 

third attempt:  fatal crash 3 hours 21 minutes, collision with Minimus at over 3000m/s

 

fourth attempt: 5 hours 44 minutes success

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How did you manage 5 hours 44 minutes, that's nuts!

[18Watt]

I just did a run in 3 hours 8 minutes.  Pretty sure I can shave at least 8 minutes off that, I didn't aim very well and spent a lot of my dv adjusting course.

I'm playing stock KSP.  No cheats, just a really big rocket.  I flew a single Kerbal in a capsule (Jeb).  Flight path was basically straight up from KSC.

[18Watt]

Update- new time 2 hours 51 minutes 19 seconds.  [ 02:51:19 ]  Launch to landed on Minmus.

Imgur is down right now, I'll post some pics when I'm able to get Imgur working.  But this run used the same rocket as my first run, with Jeb riding in a capsule.  I aimed a little better this time, and was able to use more dv accelerating to Minmus (and then decelerating...), so I was able to shave about 17 minutes off my previous time.

Here's some screenshots-

First run:

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I didn't take very many screenshots of the first run, because I didn't think I'd actually get to Minmus in one piece on the first try.  In this shot, I've managed to get a Minmus intercept (collision), and have accelerated to about 5000 m/s.  I'll need to lose all that velocity before I hit Minmus.

Landed on Minmus, about 3 hours 8 minutes after launch.

Second run:

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Here's the rocket on the pad.  It's the exact rocket I used for my first run.

Launch.

Climbout is straight up.  No gravity turn.

After the bottom stage is used up, I switch to the intermediate stage, which is powered by a Wolfhound engine.  The dv readout on the upper (landing) stage is incorrect, the upper stage actually has over 4000 dv, with a single Terrier engine.

I've accelerated to well over 5000 m/s, and am now coasting towards Minmus.

Still coasting.  I've decided that I don't need to start decelerating until I'm inside Minmus's SOI.  

Inside Minmus SOI.  I chickened out, and started braking before I really needed to.

Descending.  I estimate I wasted at least 2 minutes due to decelerating too early and too aggressively.  Would have been much faster if I could accurately do suicide burns to the surface.

Landed on Minmus, 2 hours 51 minutes 19 seconds after liftoff.

Here's a few more screenshots of the rocket I used:

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The upper landing stage is just a capsule, battery, RTG, fuel tank adapter, and Terrier engine.

The center stage is a couple of fuel tanks and a Wolfhound engine.  There's a SAS unit on there too.

The lower stage is a few of the really big fuel tanks, with 5 Vector engines.  The SRBs are the biggest ones in the stock game.  I have two of them set to full-blast, and 2 of them set to about 75% power- so I don't drop them all at the same time.

Here's a screenshot showing some of the stats.  Costs about $300K to launch it.  32 parts, 1,135 tons, 42 m tall.  Just taking a wild guess, I'd say it has well over 12,000 m/s dv in it.  I was able to launch straight up and hit about 5500 m/s.  Reaching Minmus I then had to get rid of all that velocity, and land.  And I probably used another 500 m/s adjusting my course to get an intercept.

 

[farmerben]

  On 11/20/2022 at 9:08 PM, physius said:

How did you manage 5 hours 44 minutes, that's nuts!

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I launched vertically when Minimus was directly overhead.  Once I was above the Karman line I corrected course a little bit East.  I lined up my trajectory with the center of Minimus, then I would burn prograde, then course correct.

Eventually I figured out the angle on the Navball where I could burn continously and stay lined up with Minimus.

[18Watt]

  On 11/20/2022 at 9:08 PM, physius said:

How did you manage 5 hours 44 minutes, that's nuts!

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Expanding on what @farmerben said, I also waited to launch until Minmus was positioned close to the equator.  In other words, since Minmus’ orbit is inclined you might need to aim slightly north or south of vertical to head for it.  If you time your launch to occur when Minmus is passing one of the equatorial nodes, you can simply fly straight up, making the ascent a little less complicated.

For my first run, I didn’t bother to do that, and launched when Minmus was about 10 degrees behind vertical.  I then had to use a lot of DV adjusting my course.

For my second run, timed the launch to coincide with Minmus crossing the equatorial plane, and then launched when Minmus was about 5 degrees behind vertical.

However, I think @farmerben has it right- next time I would launch when Minmus is nearly directly overhead.  My intention on my first two launches was to ‘lead the target’, assuming Minmus would move before I reached it.  Turns out that in two hours Minmus does not move very much!  So launching when Minmus is directly overhead is probably a better strategy than my plan of ‘leading the target’.

[MythicalHeFF]

Just managed to get to Minmus in 1 hour, 55 minutes, and 56 seconds (01:55:56). Jeb is certainly quite a bit more comfortable this time than he was during my last run, in which I crashed into Minmus at over 3,000 m/s and somehow he survived.

Vehicle & Run:

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The rocket I used to do this run was designed specifically with having a high thrust-to-weight ratio in mind, since I will be launching directly upwards once Minmus is directly overhead, leading to high delta-V losses due to gravity. In order to maximize delta-V, it also has a tiered setup, with four sets of asparagus stages that get progressively smaller as the craft burns fuel (from 3.75m all the way down to 0.625m)

Once out of the atmosphere, the fairing is shed and the second stage is activated. The second stage is the only stage to not have any sort of asparagus setup.

Third stage

Ended up having to do a correction burn in order to reach Minmus, as I was going to end up slightly to the left of it.

Maximum velocity reached. From here on out, it's all braking.

First attempt at the suicide burn, in which I crashed at over 3,000 m/s as mentioned earlier.

Starting the burn earlier this time

Final approach

Landed at 01:55:56

Jeb surviving a crash at 3.7 km/s:

 

 

[farmerben]

I just pulled it off in 2hrs 40 minutes with a safe landing, no part breakages.

 

Next attempt, success in 2 hrs 16 minutes.  Getting to Minimus in fewer than 2 hours is very impressive.   I can't beat Jack's current record.  It requires going over 6000m/s toward Minimus and being able to slow down.  

 

 

Edited November 26, 2022 by farmerben

[18Watt]

  On 11/25/2022 at 3:22 AM, Jack Joseph Kerman said:

Just managed to get to Minmus in 1 hour, 55 minutes, and 56 seconds (01:55:56).

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I am getting my times down to the 2:30 range, but to get under 2 hours I need a lot more dv and a higher TWR in the early stages.  I'm using a single tier of asparagus stages, but I'm going to have to go a lot deeper with the asparagus staging.

I'm also using a capsule for the Kerbal.  (the challenge rules don't actually say you need a Kerbal...).  At first I figured that the 1 ton capsule would not make much difference, considering the ultimate size of the launch vehicle.  However, I'm now rethinking that assessment.  These massive multi-stage rockets resemble a pyramid, and a flattened-out pyramid at that.  So every kilogram at the top of the rocket ends up adding tons at the bottom of the rocket.

So I'm thinking my next attempt will use a lot of asparagus staging, and I'll either put a Kerbal in a lawn chair, or just send a probe.  The good news is my aim is getting better!  I do still need to do some corrections in flight to hit Minmus.  But I've been able to do those corrections without using maneuver nodes.  I just keep burning full thrust, and tweak my course by 'eyeballing' my path.  Probably a little wasteful, but getting a Kerbal to Minmus in under 2 hours is never going to be an economical endeavor.

[18Watt]

After several more attempts, I managed to get a time under 2 hours.  My best time is now 1 hour 54 minutes 05 seconds.  [01:54:05].

Here's one attempt:

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They're getting really big and heavy.

Liftoff.  I honestly don't know how many engines are on these things, I lose track.  It's a lot.

Got up to roughly 7500 m/s.  But had trouble maneuvering the thing.

Approaching Minmus.

Landed, just a little over 2 hours.  Getting close.

Here's a better run:

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Tried using all LFO engines on this version.  I don't think I gained much doing this, except I managed to make the core stage a little less wobbly, which helped greatly.  That had nothing to do with the LFO outer boosters though, I think I could do just as well with SRBs on the outside.  Anyhoo..

Liftoff.  Staging is a busy process, there's about 7 stages dropped before leaving the atmosphere.

I can get up to about 7500 m/s, about the same as the previous version which had SRBs on the outside.

Braking towards Minmus.

Landed, under 2 hours!  Yay!  I think I can shave off a few minutes though.  I want another shot at this.

And one last attempt, using the same rocket as the last attempt:

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1 hour 54 minutes 05 seconds.  [01:54:05]

 

 

[physius]

Just now seeing these submissions, holy kraken you guys are quick! Challenged accepted again 

[18Watt]

  On 11/25/2022 at 3:22 AM, Jack Joseph Kerman said:

Jeb surviving a crash at 3.7 km/s:

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I thought it was hilarious!  I loved how, after surviving that impact, Jeb calmly gets right to flag-planting duties.  During one of my attempts I mis-judged the braking, and it was clear I was going to impact at a little over 2,000 m/s.  Instead of reverting, I let Jeb give it a try.  Hey, if it worked for @Jack Joseph Kerman, maybe it'll work for me!  Sadly, Jeb didn't survive..

Also, when I said I mis-judged one of my attempts, that was a lie.  I actually mis-judged quite a few times.  

 

[farmerben]

The two hour mark is a difficult challenge.  The Kraken tends to destroy my rockets if I have too much asparagus.  I tried with Nukes and was unable to slow down fast enough

[physius]

  On 12/5/2022 at 1:23 PM, farmerben said:

The two hour mark is a difficult challenge.  The Kraken tends to destroy my rockets if I have too much asparagus.  I tried with Nukes and was unable to slow down fast enough

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So far I've gotten it down to 4 hours, using the same craft I used in the video. I think if I tweaked it a little for just getting to Minmus, I could definitely hit that 2 hour mark. Slowing down safely is the only real challenge

[farmerben]

New best time is 2hrs 13 minutes, jeez that two hour mark is tough.

[vyznev]

I might try this later. In the mean time, some random thoughts:

• It looks like most (all?) attempts so far have spent some time coasting under time warp. That's wasted time that could've been spent accelerating (and later decelerating), if one just had more delta-v. Over two hours seems long enough that nukes or even ions might be worth using for their high Isp (and consequently high achievable delta-v), even with their low TWR.
• At the kinds of velocities and accelerations involved, both Minmus and Kerbin gravity should be basically negligible. So is the orbital motion of Minmus, too. That means it should possible to approximate the ideal flight profile with some basic high school physics.

In particular, I believe an ideal flight profile (using stock KSP with no fancy autopilot / landing assist mods) should look roughly like this:

1. Time warp until Minmus is near its ascending / descending node.
2. Time warp further until Minmus is overhead from KSC.
3. Set Minmus as target and burn towards it until your remaining delta-v approximately equals your velocity relative to Minmus (with a bit of safety margin).
4. Turn around and coast (hopefully not too long) until your time to target is somewhere around half(!) your total remaining burn time.
5. Burn retrograde to slow down. Make sure not to miss the target.

(The "half your remaining burn time" estimate is assuming constant thrust and neglecting gravity. A proper suicide burn calculator should be able to give a more accurate estimate, or you could just quicksave and use trial and error to find the optimal start time for the deceleration burn.)

[farmerben]

  On 12/7/2022 at 2:16 AM, vyznev said:

I might try this later. In the mean time, some random thoughts:

• It looks like most (all?) attempts so far have spent some time coasting under time warp. That's wasted time that could've been spent accelerating (and later decelerating), if one just had more delta-v. Over two hours seems long enough that nukes or even ions might be worth using for their high Isp (and consequently high achievable delta-v), even with their low TWR.
• At the kinds of velocities and accelerations involved, both Minmus and Kerbin gravity should be basically negligible. So is the orbital motion of Minmus, too. That means it should possible to approximate the ideal flight profile with some basic high school physics.

In particular, I believe an ideal flight profile (using stock KSP with no fancy autopilot / landing assist mods) should look roughly like this:

1. Time warp until Minmus is near its ascending / descending node.
2. Time warp further until Minmus is overhead from KSC.
3. Set Minmus as target and burn towards it until your remaining delta-v approximately equals your velocity relative to Minmus (with a bit of safety margin).
4. Turn around and coast (hopefully not too long) until your time to target is somewhere around half(!) your total remaining burn time.
5. Burn retrograde to slow down. Make sure not to miss the target.

(The "half your remaining burn time" estimate is assuming constant thrust and neglecting gravity. A proper suicide burn calculator should be able to give a more accurate estimate, or you could just quicksave and use trial and error to find the optimal start time for the deceleration burn.)

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That's pretty accurate.  Nukes are not adequate to slow down 6000 within Minimus' sphere of influence.  I've switched to the aerospike for the final stage, in fact I want higher TWR to slow down than initially.

 

I haven't been worrying about the AN/DN etc.  Launching when nearly overhead works well, I can just hold straight up to escape Kerbin then eyeball it onto target pretty easy.  Holding toward target on the navball works for most of the burn.  

New personal best 2 hrs 3 minutes (still struggling).  Also I'm relying on 5 layer onion staging, as asparagus is too Kraken prone for me.

[farmerben]

 

Finally 1:47:55 !!!  After about a dozen different attempts.  This one started with a Rhino surrounded by 8 Skippers.  I still used aerospike for most of the slowdown, but finished off with a terrier because its light.  Capsule is less Kraken prone than command seat designs.  No payload fairing.

 

[farmerben]

And then I went to the Mun in 39:12

 

[physius]

  On 12/7/2022 at 12:23 PM, farmerben said:

And then I went to the Mun in 39:12

 

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LOL you can't just go from under 2 hours straight to 39:12 and not tell us how!! 

[farmerben]

Well the Mun is closer than Minimus

 

 

 

My slowdown is bamboo staged with a terrier ~3000dV, aerospike ~3000dV, Rhino >2000dV remaining

The magic number was about 8000m/s before timewarping.  That number gives me time to slowdown in Minimus SOI.

 

Speeding up to that point was all onion stages 8 skippers because fuel for the high efficiency Rhino and max ISP in vacuum was important, changing to skippers from mainsails was an improvement.  Then Mammoths 8 x 3 onioned on.

 

 

 

 

Edited December 10, 2022 by farmerben

[vyznev]

Here's 1:37:10:

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Here's the craft in the VAB:

And here it at Minmus, just starting the deceleration burn:

Also, for some reason I can't help but giggle at this image:

(Context: My landing burn wasn't ideal and I had to dodge a mountain ridge, leaving Val floating a few kilometers above Minmus once I got her horizontal velocity killed. And with Minmus's gravity it would've taken way too long to just float down, so…)

More screenshots and flight details on the imgur album: https://imgur.com/a/xul1flc

I actually kind of messed up this flight by dropping one of my booster stages while it was still half full, which probably cost me nearly 1000 m/s of total delta-v. With that mistake fixed and better flying in general, I think this rocket could probably do sub 1 hour 30.

Craft file here: https://kerbalx.com/vyznev/Minmus-Express

Edited December 11, 2022 by vyznev

[farmerben]

1:36:11

 

 

 

 

[vyznev]

Same rocket as before, new flight, this time without premature staging. No mid-flight reloads this time, either. Time at landing 1:31:24. So close to 1:30…

(Don't ask me where the heck the F3 display pulls the "highest speed achieved" value out of. My actual peak velocity at the start of the coast phase was just a hair over 9,500 m/s.)

Edit: Here's the whole flight, sped up 4x:

 

Edited December 13, 2022 by vyznev
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