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Lowest mass challenge - Solids to the Mun


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Time for another "Oh that's simple" challenge.

Land a kerbal on the Mun and return him safely to the surface of Kerbin, without using liquid fuel, xenon, or monopropellant. RCS for rendezvous and docking is fine as long as you're not dramatically changing your orbit. No mods. No stock props.

Lowest liftoff mass wins.

Leaderboard:

Spoiler
  1. @Muetdhiver: 43.4 tonnes
  2. @Human Person: 49.9 tonnes
  3. @vyznev: 56.9 tonnes
  4. @MarvinKitFox: 134.7 tonnes

 

Edited by sevenperforce
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Launch: trivial

Orbit: no problem

Get to Mun: easy-peasy

Land: omfgwegonnadiehelphelphelpaaargh!

launch, Mun orbit: easy

return: easy

land: easy, with parachutes

 

So, I can do 6/7 of the challenge.

update: 2 ulcers later.

Note: due to the nature of SRB's, this involved many,many F5-F9 cycles. And even then... owch.

Basic brute force lifter, at 134.7 tons.

fancy-schmancy lander, with multiple seperatrons set to very low throttle, providing about 1.2 mun-g of deceleration.

   and with throttle-control by having each pair of seperatrons on ejectors, for when I don't want their thrust any more.(final landing)

imgur album here:

https://imgur.com/a/n5sItx1

Edited by MarvinKitFox
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I'm going to brute force this so hard. No orbital insertions at all: straight up until Mun impact, land and then straight up again to return.

The first try missed the Mun but I got to test reentry.

screenshot119.png?width=1440&height=603

screenshot115.png?width=1440&height=603

screenshot128.png?width=1440&height=603

Yup, works fine. now I need to actually hit the Mun

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2 hours ago, Human Person said:

screenshot119.png?width=1440&height=603

We seem to be converging to a rather similar design:

aCYfKOI.png

f8Z13i2.png

Your upper stages do look a lot lighter than mine. I'm not sure if your flight plan is more efficient, or if you're just being excessively optimistic. Oh well, we'll see. :cool:

(FWIW, I'm sure this vessel can do it, since I've already flown each part of the mission separately in practice runs using Alt+F12. The Mun landing stage even turns out to have way more delta-v than it really needs, since I designed it for landing from a 15 km orbit rather than the 8 km orbit that I managed to reach when I actually tried flying the whole mission without cheats. It turns out, however, that the lower altitude and the excess delta-v also completely mess up my carefully planned landing burn sequence, so I'll probably have to give it a few more tries. :/)

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15 hours ago, vyznev said:

(FWIW, I'm sure this vessel can do it, since I've already flown each part of the mission separately in practice runs using Alt+F12. The Mun landing stage even turns out to have way more delta-v than it really needs, since I designed it for landing from a 15 km orbit rather than the 8 km orbit that I managed to reach when I actually tried flying the whole mission without cheats. It turns out, however, that the lower altitude and the excess delta-v also completely mess up my carefully planned landing burn sequence, so I'll probably have to give it a few more tries. :/)

Well, I finished it. Without further ado, here's my reliable and elegant spacecraft:

q91x0SN.png

It's powered by 44,759 kg of solid rocket fuel, contained in one Kickback booster, three Thumpers, two Hammers and 36 Sepratrons (including four that I ended up discarding unused!). The total mass at liftoff is 56,857 kg (plus one Kerbal = approx. 94 kg). Here's the craft file, if you'd like to give it a try.

But let's start by examining it from the top down, the way I designed it:

Spoiler

Here's the Mun ascent and Kerbin return stage:

RNUxaTy.png

It consist of one small reaction wheel, one battery to power it, one command chair, one 1.25 m heat shield (with no ablator, reducing its weight to just 100 kg) and three pairs of sepratrons: one for Mun takeoff, one for Mun orbit insertion and one for the Mun-to-Kerbin transfer burn.

Here's the same stage with an extra RCS tank added as a dummy passenger, showing the approximate delta-v values of the three stages. (They're only approximate, since the RCS tank weighs 6 kg more than a real Kerbal.) Note that two of the sepratron pairs have their fuel load reduced to save a bit of weight; the return burn to Kerbin, for example, takes about 275 to 300 m/s of delta-v, so we only need to bring just enough fuel to achieve that.

eQHXSvR.png

On top of the ascent stage is a decoupler with two more sepratrons attached. These have had their thrust limiter set so that their TWR is very close to 1. The idea is that, after braking down to a velocity of about 5 m/s downwards,  I can fire this pair of sepratrons and gently float down the last few hundred meters to the surface at a safe landing speed. Once on the surface, I can then decouple the sepratrons and have them fly away (and hopefully land safely some distance away).

UsqeZem.png

On top of that is another decoupler carrying the actual landing stage. This stage works on the same principle: I can fire the sepratrons in pairs to bring my velocity down to zero, and then decouple the stage to effectively stop the final burn short if needed:

JnwR0Tw.png

Again, I've added an RCS tank as a dummy Kerbal to make KER show more or less accurate delta-v figures. I tested this stage quite a few times by using Alt+F12 to teleport it to Mun orbit, and it worked perfectly. What I didn't account for in my testing, however, is that the Set Orbit cheat doesn't let you set a Mun orbit below 15 km, even though on a real flight it's quite safe to go as low as 8 km or even lower. So I designed my landing stage with enough delta-v for landing from a 15 km orbit, which was way overkill. I could've easily left out at least four of the sepratrons on this stage, and probably reduced the fuel load on some of the remaining ones. :/ 

Oh well. At least we know that there's still room for improvement left in this challenge. :D

Full mission report with screenshots here on imgur.

Edited by vyznev
Forgot to include total mass at liftoff.
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11 hours ago, vyznev said:

Well, I finished it.

Me too. 

my mission went similar though the margins were a little bit tighter I think

screenshot189.png?width=1318&height=552

 

more images are in this spoiler:

Spoiler

I launched at night to enable a daytime landing on the Mun. Figuring out the exact time to launch took some trial and error 

screenshot152.png?width=1318&height=552

crossing into sunlight further up 

screenshot145.png?width=1318&height=552

screenshot149.png?width=1318&height=552

screenshot154.png?width=1318&height=552

bracing for impact

screenshot158.png?width=1318&height=552

the final landing burn took a few  quickloads

screenshot168.png?width=1318&height=552

screenshot189.png?width=1318&height=552

screenshot190.png?width=1318&height=552

At this point I realized there was a flaw in my plan. The Mun is tidally locked to kerbin so there is no way for me to directly return. The Mun is in the way so to speak.

I rearanged the sepratrons to stage in pairs and went for a ballistic arc westward.

screenshot202.png?width=1318&height=552

screenshot205.png?width=1318&height=552

still suborbital, I was able to plot a node to return with the last pair of sepratrons

screenshot207.png?width=1318&height=552

screenshot210.png?width=1318&height=552

screenshot211.png?width=1318&height=552

reentry was only 14g. Not the Maximum g-force in this mission

screenshot219.png?width=1318&height=552

the landing location presented an epic scenery, enjoy

screenshot223.png?width=1318&height=552

screenshot229.png?width=1318&height=552

screenshot234.png?width=1318&height=552

 

7

Motors used: 1 Kickback, 3 Thumpers, 1 Flea and 8 Sepratrons

Score: 49.903 t 

Craft file: https://kerbalx.com/Physics_Student/Solid-Impact

Edited by Human Person
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14 minutes ago, Human Person said:

@vyznev actually our missions aren't that similar at all. you flew the mission like a standard Mun mission (first LKO then Mun orbit then landing) while I just went sraight up for a direct lunar impact.

Even so, our spacecraft look remarkably similar. I admit to seeing your screenshots before I'd finished building my Kerbin ascent stage, so I may have been influenced by your design a bit there. But the return stages (which appear to differ mostly in part placement, and the inclusion of a docking port on yours) seem to be a genuine example of independent convergence. :) 

(It does look like my return stage is probably slightly lighter than yours, which suggests that a hybrid craft using your direct flight plan could do better that either of our current entries so far.)

Edited by vyznev
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6 hours ago, vyznev said:
6 hours ago, Human Person said:

@vyznev actually our missions aren't that similar at all. you flew the mission like a standard Mun mission (first LKO then Mun orbit then landing) while I just went sraight up for a direct lunar impact.

Even so, our spacecraft look remarkably similar. I admit to seeing your screenshots before I'd finished building my Kerbin ascent stage, so I may have been influenced by your design a bit there. But the return stages (which appear to differ mostly in part placement, and the inclusion of a docking port on yours) seem to be a genuine example of independent convergence. :) 

(It does look like my return stage is probably slightly lighter than yours, which suggests that a hybrid craft using your direct flight plan could do better that either of our current entries so far.)

I believe the standard mission is cheaper, dV-wise.

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  • 3 weeks later...

Here is my Entry for the solids to Mun.

The vessel total mass is 43419 kg, with 1 Kickback, 2 thumpers and 44 separatrons. Here is the weight saving tricks I used :

  1. Hammer and Flea SRB's have terrible dry masses, leading to ballooning weight if used in the upper stages. Also, Flea has close to the ISP of the separatrons, but way worse dry mass. So I used only separatrons once in LKO. My first attempt with those was above 100T. Not good.
  2. The kickback and 2 thumpers + a pair of separatrons allow for 75x90 LKO. For further weight saving I have the bare minimum for Mun transfer, with 830 m/s. I just waited fir Mun to be at the right place for the ejection burn.
  3. No chutes, and I decided to use the 1.25 service bay instead of a thermal shield. Same weight, but I'm used to do things that way :)
  4. Direct eject from Mun. That means landing on the "back" side of Mun w.r.t its orbit, so that a direct normal burn does the trick. 1052 m/s for the return.
  5. Only mod is KER and Decoupler shrouds to "prettify" rockets a little bit.

Dv margins are super tight, I don't think I can trim things down any further.

Pics in the spoiler.

 

Spoiler
iTlpWHo.png
oKVSWMC.png
Smart Powder B on the pad
P76wmSG.png
Ejection Burn
W9Ip5Y3.png
On Mun afer a trash landing. Impact at 15 m/s wrecked to descent stage, leaving only the decoupler :)
FEQjnir.png
15G return ejection burn. That is with separtrons at 50% thrust XD
8EolEfl.png
Agressive Reentry
lu3GBAr.png
Soviet Style paradrop landing. Incredibly close to KSC by luck
 

It was a lot of fun, thanks for the challenge :)

Edited by Muetdhiver
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