A New Thread to Discuss 5thHorseman's Challenge

[arkie87]

I have started a new thread to discuss this challenge, since it has derailed other threads, and confused many-a-person.

The challenge is as follows:

Build the cheapest craft (in terms of Kerbucks) capable of taking the lander described below from Surface of Kerbin to an Orbit around the Mun (Ap and Pe must both be below 30 km). Lander must arrive at mun without any fuel having been drained from it. You do not (and should not) land it or return to Kerbin.

As a side note, once you enter Mun's SoI, you cannot leave it (i.e. no fancy-shmancy gravity assists are allowed).

The lander consists of the following parts (in order):

Mk16 Parachute

Mk1 Command Pod

TR-18A Stack Decoupler

FL-T400 Fuel tank

LV-T30 Liquid fuel engine

Disallowed Parts: extra torque-providing parts and control surfaces

Mods required: FAR (you may disable aerodynamic disassembly)

Modded Parts allowed: none

Videos are encouraged.

5thHorseman said:

Here's my craft file:

[defunct site link removed by moderator]

Here's what it looks like:

[defunct site link removed by moderator]

And here's the video:

[Superfluous J]

This is correct, with the addition that the final orbit must be less than 30x30km (aka the apoapsis must be under 30km) and you cannot use the lander itself during the lifting/transfer/orbit.

I've done this with a ship that (in 0.25) costs just under $10k. It uses lots of SRBs and a little bit of regular fuel/oxy for more fine tuned maneuvers, and frankly I'm surprised it flies as well as it does.

[arkie87]

This is correct, with the addition that the final orbit must be less than 30x30km (aka the apoapsis must be under 30km) and you cannot use the lander itself during the lifting/transfer/orbit.

I've done this with a ship that (in 0.25) costs just under $10k. It uses lots of SRBs and a little bit of regular fuel/oxy for more fine tuned maneuvers, and frankly I'm surprised it flies as well as it does.

Ok, i wasnt sure if we were allowed to use the lander fuel. I need to redesign then I will revise OP to incorporate this fact.

[Superfluous J]

I don't think we stated it, but I also didn't use the lander's engine. Felt cheaty to me.

[Vanamonde]

This challenge has been moved to Challenges.

[Captain Sierra]

Any particular reason you're not using a 200 and a 909? That works on the Mun and is dramatically more efficient in terms of being payload mass.

[The_Rocketeer]

This isn't a "challenge" per se, and it doesn't meet the challenge forum submission guidelines. It's just to test a theory propounded in another general discussion thread.

[Superfluous J]

Any particular reason you're not using a 200 and a 909? That works on the Mun and is dramatically more efficient in terms of being payload mass.

Because the actual lander doesn't matter except to be the payload we take to Mun. Tweaking it's efficiency isn't the challenge. Getting it to Mun orbit with the cheapest lifter is.

[arkie87]

So I was able to do it with $11,352 with some fuel remaining (~70 m/s, but i was also significantly below 30km x 30km mark). Screenshot of rocket design and results:

Javascript is disabled. View full album

What does yours look like?

[arkie87]

I don't think we stated it, but I also didn't use the lander's engine. Felt cheaty to me.

Yeah, it makes sense that it would be cheating. The lander is a payload. Payload cannot be used.

[arkie87]

This is correct, with the addition that the final orbit must be less than 30x30km (aka the apoapsis must be under 30km) and you cannot use the lander itself during the lifting/transfer/orbit.

I've done this with a ship that (in 0.25) costs just under $10k. It uses lots of SRBs and a little bit of regular fuel/oxy for more fine tuned maneuvers, and frankly I'm surprised it flies as well as it does.

Can you post a pic? I would like to see what you did, and try to fly it vertical and horizontal and see what happens.

As it is, my craft was wobbling around like crazy during ascent-- i had to spin it around in circles really fast to stabilize it so i'm wondering how you managed to get it to turn without flipping out

[Superfluous J]

So I was able to do it with $11,352 with some fuel remaining (~70 m/s, but i was also significantly below 30km x 30km mark). Screenshot of rocket design and results:

http://imgur.com/a/A1FE4

What does yours look like?

Impressive. I did not think you could get it that low in cost, though admittedly I never tried this in FAR and as you said, this would never work in stock.

I can't try it right now but hopefully in a few hours I should be able to. Mine is not as elegant looking as yours and has multiple stages. Though looking at yours makes me wonder if I can make something similar, but even cheaper.

I'll put the $10k ship up as soon as I've flown it in .90 with FAR, and then try a remake.

Can you post a pic? I would like to see what you did, and try to fly it vertical and horizontal and see what happens.

As it is, my craft was wobbling around like crazy during ascent-- i had to spin it around in circles really fast to stabilize it so i'm wondering how you managed to get it to turn without flipping out

I don't have a pic, and can't play for a few hours.

The trick is to never turn more than about 10 degrees off of prograde. If you turn at the exact right time, you barely ever need to wander from prograde, and because you're never going crazy fast the ship doesn't spin like crazy.

Edited December 17, 2014 by 5thHorseman

[arkie87]

Impressive. I did not think you could get it that low in cost, though admittedly I never tried this in FAR and as you said, this would never work in stock.

I can't try it right now but hopefully in a few hours I should be able to. Mine is not as elegant looking as yours and has multiple stages. Though looking at yours makes me wonder if I can make something similar, but even cheaper.

I'll put the $10k ship up as soon as I've flown it in .90 with FAR, and then try a remake.

I don't have a pic, and can't play for a few hours.

The trick is to never turn more than about 10 degrees off of prograde. If you turn at the exact right time, you barely ever need to wander from prograde, and because you're never going crazy fast the ship doesn't spin like crazy.

I actually tried flying my rocket in horizontal mode configuration--- i was trying to lower nose down towards east the whole time (my finger was smooshed down on the keyboard) but the rocket wouldnt turn!!!

I tried raising the large boosters higher up, but that was a big mistake --- rocket flipped the $%^#$ out...

[Superfluous J]

Okay I reworked my rocket when I realized that the biggest SRBs were 3x the size of the mid sized ones, and not 2x as I mistakenly thought.

The entire rocket. It took quite a bit of finagling to get it under $10k.

[defunct site link removed by moderator]

Most of the finagling involved using the translate tool and cubic octagonal struts, something impossible in 0.25 and before.

[defunct site link removed by moderator]

Note the lack of struts here. I'm as surprised as you that this thing flew, and flew quite well. It got the payload into a sub-30k mun orbit with over 200m/s to spare. In other words, it could have done about half of the landing burn.

[defunct site link removed by moderator]

But the much nicer, redesigned rocket is so much cooler.

I call it "The Pencil" and it's as simple as it gets. The hardest part is actually falling East but it's pretty forgiving in the first 200m/s or so, so you can wrestle it into place so long as you don't let it wander too far. And you can't argue with the $9322 price tag (Including payload!)

[defunct site link removed by moderator]

I've filmed the 2nd ship but won't be able to post it today. Rest assured, it got into a 28x25km orbit with (again) over 200m/s to spare, even though I screwed up the ejection bur and had to turn around and slow down a bit. Then I overshot THAT and had to speed up a little again. Probably 10-15 m/s total though so no bigs. I may have had 300m/s in the tank when all was said and done, which is actually better than the above monstrosity.

[arkie87]

5thHorseman said:

Okay I reworked my rocket when I realized that the biggest SRBs were 3x the size of the mid sized ones, and not 2x as I mistakenly thought.

The entire rocket. It took quite a bit of finagling to get it under $10k.

[defunct site link removed by moderator]

Most of the finagling involved using the translate tool and cubic octagonal struts, something impossible in 0.25 and before.

[defunct site link removed by moderator]

Note the lack of struts here. I'm as surprised as you that this thing flew, and flew quite well. It got the payload into a sub-30k mun orbit with over 200m/s to spare. In other words, it could have done about half of the landing burn.

[defunct site link removed by moderator]

But the much nicer, redesigned rocket is so much cooler.

I call it "The Pencil" and it's as simple as it gets. The hardest part is actually falling East but it's pretty forgiving in the first 200m/s or so, so you can wrestle it into place so long as you don't let it wander too far. And you can't argue with the $9322 price tag (Including payload!)

[defunct site link removed by moderator]

I've filmed the 2nd ship but won't be able to post it today. Rest assured, it got into a 28x25km orbit with (again) over 200m/s to spare, even though I screwed up the ejection bur and had to turn around and slow down a bit. Then I overshot THAT and had to speed up a little again. Probably 10-15 m/s total though so no bigs. I may have had 300m/s in the tank when all was said and done, which is actually better than the above monstrosity.

So you are saying that both of these ships are easy to turn, despite having only one reaction wheel at the top i.e. the worst point to turn the vehicle from? ....Maybe I am doing something wrong then... do you hold down the turn key or let the vehicle turn itself? I know you are supposed to bank 5-10 degrees instantly upon liftoff, but then you just leave the rocket alone or turn slightly (with a joystick or keyboard)?

I will build your crafts and fly them both ways...

Also, I will try firing my liquid engine during liftoff to see if that saves fuel since I am still below terminal velocity in FAR. For some reason, ShadowPlay stopped working for me (seems to happen every time there is a new driver or new version of NVIDIA Experience), so i wont be able to record it though...

[arkie87]

5thHorseman said:

Okay I reworked my rocket when I realized that the biggest SRBs were 3x the size of the mid sized ones, and not 2x as I mistakenly thought.

The entire rocket. It took quite a bit of finagling to get it under $10k.

[defunct site link removed by moderator]

Most of the finagling involved using the translate tool and cubic octagonal struts, something impossible in 0.25 and before.

[defunct site link removed by moderator]

Note the lack of struts here. I'm as surprised as you that this thing flew, and flew quite well. It got the payload into a sub-30k mun orbit with over 200m/s to spare. In other words, it could have done about half of the landing burn.

[defunct site link removed by moderator]

But the much nicer, redesigned rocket is so much cooler.

I call it "The Pencil" and it's as simple as it gets. The hardest part is actually falling East but it's pretty forgiving in the first 200m/s or so, so you can wrestle it into place so long as you don't let it wander too far. And you can't argue with the $9322 price tag (Including payload!)

[defunct site link removed by moderator]

I've filmed the 2nd ship but won't be able to post it today. Rest assured, it got into a 28x25km orbit with (again) over 200m/s to spare, even though I screwed up the ejection bur and had to turn around and slow down a bit. Then I overshot THAT and had to speed up a little again. Probably 10-15 m/s total though so no bigs. I may have had 300m/s in the tank when all was said and done, which is actually better than the above monstrosity.

I dont know if we can absolutely rely on KER deltaV readouts, but if we can, my craft has 4629 m/s deltaV, while your first craft has 4964 m/s and 4830 m/s, so the 200 m/s of remaining fuel could easily be because it started with more (though both are cheaper than mine, so that might not matter).

In terms of aesthetics though, i'd say mine wins Let me know how flying mine with a horizontal burn goes.... if you can do it, i'd like to learn what im doing wrong...(though if you could turn your monstrosities, then i assume i can turn mine...)

And FYI: for the last stage before the lander/payload, i had the same design using that smaller engine (rockomax 48-7s), but i noticed i actually get more deltaV from the LV-909 since its ISP is larger; the increase in mass of the LV-909 to the total package isnt significant enough to offset its increased ISP.

[Superfluous J]

Okay I lied. Or stayed up way too long putting the video together when I should have gone to bed

It's not quite ready yet but I'm going to bed now so am going to post the link. I don't show the whole 12 minute video, but I do show what is easily the hardest part of the gravity turn. I even get very scarily close to losing control on the early ascent but keep it together. I also seem to keep my cool through the whole thing but that's just because it's post commentary. In reality I was freaking out.

[arkie87]

Okay I lied. Or stayed up way too long putting the video together when I should have gone to bed

It's not quite ready yet but I'm going to bed now so am going to post the link. I don't show the whole 12 minute video, but I do show what is easily the hardest part of the gravity turn. I even get very scarily close to losing control on the early ascent but keep it together. I also seem to keep my cool through the whole thing but that's just because it's post commentary. In reality I was freaking out.

I never claimed vertical was always better.

I was wondering if it COULD be better with a high TWR in FAR. I dont see where all the animosity and condescension is coming from. Every time i say "could" or "might" people interpret that as "IS 100% WITHOUT A DOUBT" and i'm getting kind of sick of it...

Second, I also was trying to suggest that it definitely isnt as bad as people say-- my craft cost about 20% more and can do just about the same task (i also overshot and had to correct a few times, but those were minimal). 20% isnt the 100%+ inefficiencies that people claim. Plus, it happens to be loads more fun

That said, i dont think your pencil craft is particularly well suited to vertical launch due to low TWR. Can you give me details about how exactly your fly it so i can try to replicate it. If you can steer this pencil, then i should be able to steer all of the craft ive made, given they all have lower moment of inertia.

Also, please comment on my suggestion for improvement by using lv909 instead of 48-7s...

In an unrelated note, maybe its a good that this forum was moved to challenges so no one will come in and derail it...

Edited December 17, 2014 by arkie87

[Superfluous J]

IMO 20% is a massive inefficiency. If you one store is selling something for $100 and another $80, which one are you going to buy? For the record I stated that in stock aero, my testing found that it cost and extra 1000 dV (back then I didn't even think in terms of money because money was a non-issue). 1000 dV in an appoximately 6000 dV journey is far less than 20% and I considered that a massive inefficiency.

But remember that the payload itself cost $3122, so my LIFTER costs $9322-3122= $6200.

Your LIFTER costs $11352-3122= $8230

My LIFTER actually costs 25% less than your rocket, or to use marketing speak, your rocket is 33% MORE inefficient than mine. For every $3 I spend getting that payload to space, you spend $4. If 5/4ths the size of my rocket isn't bad enough, is 4/3rds? Maybe we need to define "massive inefficiency."

EDIT:

Adding an LV909 cut my total dV from 6972 to 6110, though it did raise that one stage from 1186 to 1235. So while it's better for that stage, it's worse for the rocket as a whole.

And I'll agree with one thing: it was nice to have this whole thing settled without interruption

Edited December 17, 2014 by 5thHorseman
Added to the first paragraph and also some stuff at the end.

[arkie87]

IMO 20% is a massive inefficiency. If you one store is selling something for $100 and another $80, which one are you going to buy?

But remember that the payload itself cost $3122, so my LIFTER costs $9322-3122= $6200.

Your LIFTER costs $11352-3122= $8230

My LIFTER actually costs 25% less than your rocket, or to use marketing speak, your rocket is 33% MORE inefficient than mine. For every $3 I spend getting that payload to space, you spend $4. If 5/4ths the size of my rocket isn't bad enough, is 4/3rds? Maybe we need to define "massive inefficiency."

That is all true.

But when conventional wisdom says "vertical is much worse" I dont think they mean by 25% or 33%. I think they mean by 100%+, no?

Besides, I might have an idea or two of how to further improve it...

And regardless, I have mentioned other advantages that vertical might have over horizontal, such as, (if it's stable during ascent) it is more foolrpoof/harder to mess up, but maybe i just need to learn how to do a proper FAR turn...

Edited December 17, 2014 by arkie87

[arkie87]

IMO 20% is a massive inefficiency. If you one store is selling something for $100 and another $80, which one are you going to buy?

But remember that the payload itself cost $3122, so my LIFTER costs $9322-3122= $6200.

Your LIFTER costs $11352-3122= $8230

My LIFTER actually costs 25% less than your rocket, or to use marketing speak, your rocket is 33% MORE inefficient than mine. For every $3 I spend getting that payload to space, you spend $4. If 5/4ths the size of my rocket isn't bad enough, is 4/3rds? Maybe we need to define "massive inefficiency."

An alternate launch approach I would like to investigate is first using a stage (or two) to blast vertically out of the atmosphere, and then burning horizontally into orbit, and then periapsis transfer to Mun... (i.e. "the gravity turn" that couldnt or didnt happen in atmosphere)

What do you think of that? Will extra cost be more or less than straight vertical approach?

Also, have you tried flying my craft horizontally? Does it work for you?

[Superfluous J]

That is all true.

But when conventional wisdom says "vertical is much worse" I dont think they mean by 25% or 33%. I think they mean by 100%+, no?

Besides, I might have an idea or two of how to further improve it...

While you were typing this I added to my post:

For the record I stated that in stock aero, my testing found that it cost an extra 1000 dV (back then I didn't even think in terms of money because money was a non-issue). 1000 dV in an appoximately 6000 dV journey is far less than 20% and I considered that a massive inefficiency.

[arkie87]

While you were typing this I added to my post:

For the record I stated that in stock aero, my testing found that it cost an extra 1000 dV (back then I didn't even think in terms of money because money was a non-issue). 1000 dV in an appoximately 6000 dV journey is far less than 20% and I considered that a massive inefficiency.

Yeah, but in stock the extra dV is gonna be a lot higher since terminal velocity is a lot lower...

Our dV's are within 2.5% of each other...

But i see your point... if 20% is too much for you, then it's too much...

I'm not saying its not for me, but at present, since i cannot do a gravity turn in FAR reliably, 20% extra might be worth it to not kill Jeb.

[Superfluous J]

An alternate launch approach I would like to investigate is first using a stage (or two) to blast vertically out of the atmosphere, and then burning horizontally into orbit, and then periapsis transfer to Mun... (i.e. "the gravity turn" that couldnt or didnt happen in atmosphere)

What do you think of that? Will extra cost be more or less than straight vertical approach?

Also, have you tried flying my craft horizontally? Does it work for you?

That's the way I used to launch when I started the game. It was a terrible waste of fuel.

I just tried your rocket one time, and my gravity turn was pretty bad but I ended up with an Ap over 200km when the SRBs conked out. I got my Pe over 75km and then burned to Mun. When I got the Pe at Mun at 25km, I made a maneuver node there and if I'd bothered to do it, KER says I'd still have 200dV in the tank. I never reached atmospheric efficiency but my rocket had all the firey goodness that we love in KSP.

[arkie87]

That's the way I used to launch when I started the game. It was a terrible waste of fuel.

I know. But that wasnt my question. My question is better or worse than the direct vertical launch? My guess is better, since it is somewhere in between vertical and horizontal... Maybe it will only cost 10% more...instead of 20%

I just tried your rocket one time, and my gravity turn was pretty bad but I ended up with an Ap over 200km when the SRBs conked out. I got my Pe over 75km and then burned to Mun. When I got the Pe at Mun at 25km, I made a maneuver node there and if I'd bothered to do it, KER says I'd still have 200dV in the tank. I never reached atmospheric efficiency but my rocket had all the firey goodness that we love in KSP.

A good measure of how good your gravity turn is is horizontal velocity at apoapsis... do you by any chance know how much horizontal velocity you had by the time you got to apoapsis? Or alternatively, the approximate angle your prograde vector had with the horizontal... i can never get mine anywhere near 45 degrees with my rockets when i try a gravity turn... Is that what you found too? If so, why wont my rockets do a gravity turn...

By atmospheric efficiency you mean terminal velocity, i presume?

And it sounds like you had more fun using my rocket