10 fuel tanks - efficiency challenge

[khyron42]

While playing around with other challenges, I thought of an 'efficient design' one.

Jeb #291 took every booster from the booster factory used them in a single ship... which he launched from inside the factory because it was just too much work to move them to the launch pad. Every ready-to-launch booster and the factory itself was destroyed. The liquid fuel tank factory was destroyed too in the ensuing mayhem, but 10 tanks survived the carnage. Jeb, of course, made it to space and died happy when the last 10 boosters exploded beneath him.

Jeb #292 wants an immediate launch, and will settle for non-boosters if you can still get him moving really fast or keep the engines burning for a really long distance.

The Challenge:

• [li]Option 1: Get the highest speed at burnout. (speed efficiency) Current leader - Dashcunning, 6685 m/s[/li]
  [li]Option 2: Get the highest altitude at burnout. (fuel efficiency) Current leader - Godot, 800 km[/li]
  [li]Option 3: Most efficient launch, as measured by some kinda rocket science, Jeb #292 doesn\'t care about the details (total energy) Current leader - Dashcunning, 18.369 MJ/kg 'Specific orbital energy'.[/li]
  

Performance in the third category will need to be judged by plugging the numbers into this equation: .5*(final velocity in km/s)^2 - 3530.461/(600.00 + final altitude) = specific orbital energy

(thanks, Kosmo-Not!)

The Limitations:

• 
  [li]You have 10 of the FL-T500 fuel tanks, plus an unlimited number of all other parts, subject to the other limitations.[/li]
  [li]Stock Parts only.[/li]
  [li]No Solid Boosters.[/li]
  [li]Continuous full-throttle burn. Obviously, we\'ll have to take you at your word on this one![/li]
  [li]Anything goes as far as staging, angling to take advantage of orbital speed, etc.[/li]
  

This is kind of a combination of efficient design and efficient piloting. Post a screenshot taken just after burnout, ideally still showing the engine trail before it fades.

My initial attempt, trying for speed:

[Mr. Generic]

Here\'s my attempt:

[Kosmo-not]

Here\'s my first attempt:

I think scoring criteria should be based off of total energy after burnout. That way, we can actually do fuel efficient ascents and get appropriate credit for it.

[khyron42]

Is there an easy way to calculate that, though?

Besides, this is Jeb we\'re trying to please... but I could always add a third category if you can come up with an easy way to measure it.

[Kosmo-not]

It\'s easy to measure.

You have kinetic energy due to velocity: KE = .5*m*v²

And then there\'s the potential energy: PE = -m*(gravitational parameter)/r

Add them together and you get the total energy of the system.

Because mass can vary among different craft, we can use the specific orbital energy by dividing by mass. The equation for specific orbital energy for a Kerbin orbit is:

U/m = .5*v² - 3530.461/(600 + altitude)

velocity is in km/s, altitude in km

[Gruntzilla]

My little ole ship.

[khyron42]

I added the third category.

I think we still have a lot more than can be done in the second category, but these are all looking fun so far!

[DonLorenzo]

Hm I wanted to show my three tries, what\'s the spoiler tag so I can do that sensibly? For now they are in the attachments.

First try: 5551.2 m/s @ 426km. Had too much weigth in decouplers and engines

Second try: 5892,3 m/s @ 590km, Fused the top two stages, still not fast enough though.

Third try: 6009,8 m/s @ 632km, Lost the tri-coupler and made all engines fire all the time

It\'s easy to measure.

You have kinetic energy due to velocity: KE = .5*m*v²

And then there\'s the potential energy: PE = -m*(gravitational parameter)/r

Add them together and you get the total energy of the system.

Because mass can vary among different craft, we can use the specific orbital energy by dividing by mass. The equation for specific orbital energy for a Kerbin orbit is:

U/m = .5*v² - 3530.461/(600 + altitude)

The mass of my ship is 4.2 (pod @ 1, engine @ 2, 4x empty fuel tank @ 1,2)

taking the numbers from my third try

KE = .5*4.2*6.01^2 = 75.85

PE = what\'s the gravitational parameter?

That orbital specific energy = .5*6.01^2-3530.461/(600+632) = 15.2

I\'ve no idea if I\'ve done that correctly, or what the units are. But here\'s my go at rocket science 8)

edit: added rocket science

edit2: (hopefully) fixed rocket science

[Kosmo-not]

I forgot to mention that for the equation, velocity is in km/s and altitude is in km.

[DonLorenzo]

Updated it.

[Kosmo-not]

Oh, and to answer your question:

The gravitation parameter is the gravitational constant multiplied by the mass of the body. It is helpful to express this as the gravitational parameter because G*M comes up so often that we get tired of inputing two separate numbers, especially when one of those numbers is always the same. Saves paper, thus trees, thus the precious air we breath.

[khyron42]

DonLorenzo - you do 'spoiler' in brackets to start a spoiler and /spoiler to end it, or just click the Radiation symbol in the post toolbar.

Here was an attempt at just getting a good Option 2. I ditched the ASAS for a little less mass-to-orbit, but it\'s a pain to fly by hand for 6 & 1/2 minutes.

I think the only difference between this one and DonLorenzo\'s was using gimballing engines for the slightly longer burn times. I\'m sure this can be improved further if people want to try.

Let\'s see, total mass after burnout is 4.2. Speed 5.79 km/s at 716 km altitude.

Kinetic energy: .5*4.2*5.79^2 = 70.4

Potential energy: -4.2*3530.461/1316 = -11.267 ?

So, combined kinetic and potential of 59.133? or did I mess that up?

Specific orbital energy = .5*5.79^2 - 3530.461/1316 = 14.079

I find it amusing that there\'s no mass-of-the-ship term in the last bit (intiuitively it feels like it should be a factor.) Also, I was assuming that the third equation was supposed to give the same result as adding the first two\'s answers, but I guess not.

[DonLorenzo]

Hmm to do option 2 well it\'s far more important to stretch out the burn time as long as possible than to obtain a high speed. It\'s a bit artificial because you are restricted to burning at 100% and stats at cutoff count, but fun none the less.

I\'m gonna try a 2x2LFT booster and a 6 tank upper stage tonight, see how far that goes. In the mean time, well done on the 730-ish km

[Kosmo-not]

I find it amusing that there\'s no mass-of-the-ship term in the last bit (probably should be, but compared with the mass of Kerbin it\'s neglibible.) Also, I was assuming that the third equation was supposed to give the same result as adding the first two\'s answers, but I guess not.

The third equation does give the same result as adding the first two equations, it\'s just all divided by the mass. Two spacecraft with the same orbital parameters will have the same specific orbital energy. It is because the mass of the spacecraft is so tiny compared to the body it\'s orbiting. This is why I think using the specific orbital energy is the best method of calculating fuel efficiency.

[DonLorenzo]

Another photo finish. With the rocket described in the previous post I managed 730km at cutoff

found the spoiler button, thanks. Is it possible to insert images from attachments here? how? ty

[chaz]

6348m/s and change

[DonLorenzo]

Nice, clever design

[chaz]

Nice, clever design

your design pointed me in the right direction!

[jebbe]

This is a cool challenge!

I got:

Speed: 6064 m/s

Altitude: 679 km

Specific energy: 15.6 MJ/kg

My design:

Leaving out the ASAS makes flying a pain in the a**, but it gains me a little

It\'s interesting how close the three and the four engine designs get us - I would have expected one of them to perform a lot better than the other.

[DonLorenzo]

your design pointed me in the right direction!

Iteration is key

[chaz]

angling definitely gives an advantage to orbital speed.

[Gruntzilla]

Does this count?

The lander had to be able to touch down on the Mun and survive reentry with enough fuel to softly land. I don\'t think that I could have gotten back with the extra decoupler for the pod. I barely had enough fuel as it was.

[Guest TonyZ]

Think I got the first 2...

Design is 5 stages, 2 tanks and 2 small LFE\'s per stage. Wasted a bit of altitude and speed correcting the rockets attitude from lift-off to final stage MECO, but wow... add an aSAS and I have a new design to go to the Mun.

Withdrawn and apologies. I launched the wrong KSP. That particular icon was a balanced config. Will do over and re-submit. Sorry... Completely unintentional.

[Gruntzilla]

Think I got the first 2...

Design is 5 stages, 2 tanks and 2 small LFE\'s per stage. Wasted a bit of altitude and speed correcting the rockets attitude from lift-off to final stage MECO, but wow... add an aSAS and I have a new design to go to the Mun.

This craft won\'t even get off the ground with that stack order.

[dashcunning]

I\'m up to 6685 m/s.

Design is essentially the same as chaz\'s but with 2x3 outer tanks instead of 2x2 and 2x1. I don\'t think the savings you get from dropping 2 tanks earlier makes up for the weight from the 2 extra decouplers and fuel lines.

Edit:

Actually, after some more testing, there is a small but real improvement by dropping the 2 tanks early on. My higher end speed was achieved by flying closer to the horizon.