Reach highest possible altitude with 7 Solid Boosters and cargo.

[Krenn]

The Challenge:

This challenge is to see who can make the most efficient use possible of 7 solid booster rockets, by reaching the highest possible altitude

Cargo

Your cargo is 1 command module, 1 parachute, and 1 SAS module.

Engines

You have exactly Seven Solid Fuel Boosters. you may using as many stock couplers, de-couplers, and struts as you like.

Goal

The goal is to reach the highest altitude possible, using any staging series you like. Stock parts only.

Background:

When reading through the thread on calculating ideal first stage thrust/mass ratios, http://kerbalspaceprogram.com/forum/index.php?topic=2230.0 I realized that firing three SRB's one after another in the lower atmosphere was probably more efficient than firing all three at once.

Then, when I was designing a rocket to test that, I noticed that an 'expended' solid rocket booster weighs 0.36, but a radial decoupler weighs 0.4, and a stack decoupler weighs 0.8.

I figured that might mean that discarding a solid rocket booster after use might be LESS efficient than discarding it later, since you would need to ration how much weight of decouplers you were willing to carry.

Thus, this challenge. What is the most efficient order to fire solid rockets in, and what is the most efficient way to discard them?

[frogger]

Hi All First post.

Well its by no means going to be the highest altitude im sure. but i managed to get 35,387m.

Warning large photos.

ok so heres how i did my first attempt.

On the launch Pad

separation

2nd Separation

Bill was slightly worried about the temperatures of the rocket

dropped off some more weight

They were lovin it!

At the top boys

some stats for people who like stats

landing was rough with only one parachute carrying the pod + SAS + booster, but they lived! ;P

[Krenn]

I reached 42,955, but in order to do it, I had to time things so my third stage engine would explode from overheat on it's last second of fuel. Which was convenient, since i didn't have any other way to seperate it so the fourth stage could fire.

if my timing was off, I would only make it to about 36,000.

I noticed that frogger staged his engines as 2-2-1-1-1. My staging was 3-2-1-1, although i tried several other configurations before settling on that one.

images:

on the launchpad

after dropping the second stage, I count to EIGHT before igniting the third stage, otherwise the engine will overheat too early.

This engine is going to explode at exactly the right moment.

at peak altitude

[McLuv]

Hehehe, KSP Director to Jeb: 'In order to rid ourselves of as much weight as possible, we've had to get rid of a decoupler separating these two boosters. I trust it to you to find a way of disconnecting them before the one on top fires, elsewise have fun!'

I'll have a go at this challenge.

[Krenn]

Actually, the third stage rocket was so close to overheating no matter what i did, that I could get away with firing the fourth stage WITHOUT detaching.. the third stage would blow up in seconds anyway. it just cost me delta-V if i did it that way.

[McLuv]

Krenn I took your biproduct about a step further, for my current design uses no bulky decouplers, be they radial or stack, yet still manages to get rid of the dead weight from the dry boosters. My design can make it to 46181m!

Although it does come at the expense of looking rather... well... nevermind =P

In the VAB

At peak altitude

In order to shrug off the dead weight, I force them to overheat by starting the booster above anywhere between 1 to 5 seconds before the booster's burn time ends, depending on how hot it already is. Unfortunately, I couldn't get completely away with no extra weight, because my initial forced overheats were too rapid (well before the boosters were half depleted!), so I was forced to add struts to absorb the heat, about 0.3 mass units in total.

Sorry for no staging pics, all my effort went in to squeezing every last ounce of thrust from this design.

Edit: Attached craft files. Props to you if you can get it any higher.

[Krenn]

cool. can we get a launchpad photo, or a copy of the the ship file? I'm interested to see what you used.

[DoctorEvo]

I saw boosters and got excited, but then I saw that an SAS was required - in the FINAL STAGE, no less.

LAME.

(Also, you're right - the weight of added decouplers kinda defeats the purpose of optimizing gravity- and aero-drag, since it increases both anyways. A certain amount of moderation and staging is beneficial, but it's important not to overdo it.)

[andydouble07]

The best I can do is 39 km

[Krenn]

huh. you're also firing your rockets in 2-2-1-1-1 . I wish i knew what staging the current record holder used.

[McLuv]

Alright, I've attached the ship parts, What I did was 3-1-1-1-1, except that the middle of the bottom three has to start burning a second later, because I need to force it to overheat before it ends it's burn, and if the two others are still going, they just fly up and kill you :-*

[kirra]

60009 meters

[Tiberion]

BAH, I was just coming in to post 58,900.. thought I was gonna be winning.

I think I can refine my rocket and beat that. BRB

[Tiberion]

Hah, Success!

66,287 meters!

7 boosters, 6 radial decouplers, no stack decouplers.

Just to be sure, I did it again without the modded SAS, the stock one can hold it just fine:

Fired 2-2-2-1

And that is the 'normal' C7 command pod, same stats as the default.

If you really wanna be strict I'll redo it with the default pod, but it takes so long to load

Going to run further tests to see if carrying the added weight of 2 decouplers for the 1st stage is better than carrying 2 dead tanks for stage 2 and then jettisoning 4 tanks...

[Jarnis]

Beaten.

66879m Edit: Final number is actually 66880m

Fired 3-2-1-1. I'm pondering if I should show the config or not... 8)

Screenshots below.

Edit: Config added. Yes, I drag 3 empty boosters for a bit. Still ends up ahead.

[Jarnis]

And before you have time to beat that... Beaten! By a mile!

New record: 68463m

Same base build, but with slight refinement by adding 2 radial decouplers - I now jettison two side boosters after the first stage burnout, pulling up only the empty core stage with two direct-connected boosters firing as stage 2.

3-2-1-1 > 2-2-2-1 - Lower atmosphere is just such a drag... and it follows the general principle of multi-stage rockets better: Thrust of Stage 1 engines > Stage 2 engines > Stage 3 engines. You'd prefer something like 9-3-1 ratio of thrust but that isn't possible here, so 3-2-1-1 it is.

[Jarnis]

Beaten, for the third time.

...so the rocket wasn't Kerbal enough and lacked Boom, so I ripped off some unneeded mass and removed the two decouplers between core stages. Time for some 'strategic overheat staging' and the little thing just kept going and going until...

70415m - outside the atmosphere!

Granted, this method takes several attempts as stage 3 and stage 4 has to be fired just at the right time so the stage below goes boom the moment it runs out of fuel. I also consider 'firing an engine through a lower stage' to be bit of a cheat. But hey... that's what Jeb would do, right?

That's enough of record-breaking for tonight 8)

(and in case you are wondering, the two struts from stage 3 to stage 2 are there to transfer heat - without them stage 2 would go Kaboom prematurely, greatly reducing the altitude at the end of burn and there would be excess jettisoning of waste material into the spacesuit by Jeb. And we can't have that.)

[kirra]

Come at me bro.

[Tiberion]

Well thats a bit cheesy, exploding tanks like that

I can do 2-1-1-1-1-1 in the same way, but only got 74,286 - just a little short.

I tip my hat to you, for now

[Jarnis]

Pretty nice. I can see how, after shedding decouplers completely, the 3-1-1-1-1 might get the thing even higher. With decouplers there is just too much dead weight for that configuration so I didn't consider it.

I wonder if this one is the ultimate optimization or if yet another config could be found. If blowing up empty stages is okay, this might be it.

Edit: Ah, no. Sorry, 'that's a negative'. 3-2-1-1 is the optimal configuration, just as I thought.

At 74k you should still be going at 250m/s. I call your 74k and raise by 5k:

79465m

All that was needed was some Kerbal ingenuity in configuring the booster layout so there is no need to haul up the spent core stage. Granted, this configuration can only blow up the third stage through overheating, but even with a coupler and two radial couplers, it handily beats the all-boom design.

I await your puny attempts at beating this 8)

[kirra]

3211 Does indeed work better than my previous design. I'll experiment some more with this.

New record is 81411m

[Jarnis]

Nice piloting of the design. I knew it was probably possible to push past 80km by just timing things better, but I never thought by that much...

:ponder:

I'm giving you the preliminary 'you won' certificate, but I reserve the right to confiscate it in case I come up with another design...

Cancel that... :rips up the certificate:

The new record now stands at 81797m Edit: Several additional tries inched that up to 83425m!

I tried to optimize the piloting as much as I could but there just wasn't much extra to be found there... your flight profile appeared perfect. Then I went back to the design and tried to think of something. 'What would Jeb do?'.... hmm... 'Add more boosters!'. Sorry, can't do that.

'Well, then take out something that isn't needed to save weight'.

I tried looking into a way of leaving Bill and Bob on the beach and save weight that way but KSP doesn't allow that. :-\

Then I looked at the part list, looking at each part and their weights. Nothing obvious there... Jeb wouldn't like if I left the parachute on the VAB floor and the rules of the challenge required it. Then I read the first post of this thread which mentions that an empty SRB weights less than a radial decoupler. And this design had two of them.

What if I take them out? I'm going to end up hauling two empty cans for the duration of stage 3 burn which is not good. Then again, doing so would allow me to leave two extra bits of metal on the VAB floor - bits that weighted more than those empty cans, and would be around for the ride for the whole first and second stage burns - and you really really really want to get off that pad and into thinner air in a hurry. I considered doing some math to figure it out but then decided that Jeb would just haul the design to the pad and light it up and see what would happen. To the VAB, then!

After a quick radial de-coupler de-mounting and some SRB-to-SRB welding, off it goes... higher and faster than ever before!

Success!

Again, the firing of stage 4 is very tricky - you want every ounce of thrust out of stage 3 but you also need to blow it (and the empty cans of stage 2) off the ship. Too late and it won't overheat, too soon and precious fuel is lost in the fireworks display. After several tries that clearly showed promise (80km+), I finally got the timing just right. ;D

I also removed the struts between stage 3 and 4 - they were no longer needed as stage 3 now had a 'free' pair of heatsinks around it. Every gram counts...

I could say 'beat this' but it is possibly beatable by split-second timing differences in staging. Stage 4 firing off by less than a second can mean 10-15m/s less speed at burnout which turns into more than 1000m in height.

But I do not thing there is a build that is better. This is now optimized to death. It really has only 7 boosters, the designated cargo and a single decoupler that simply cannot be removed from the design without changing the burn sequence and I'm quite convinced that 3-2-1-1 is the optimal.

So says Rocket Science, according to the Way of Jeb. 8)

[andydouble07]

86,641 m

your move

could probably get a couple km more out of this exact model

[Tiberion]

Huh, 2-1-1-1-1-1... I tried it like that but didn't have much success.

Nice piloting

[kirra]

3211 sucks.

New record is 90080