Revisiting an old, simple one: The 10 fuel tank challenge.

[khyron42]

Long ago, I made a "10 tank" challenge. Back then, there was only one kind of tank, and only two engines to choose from.

The tanks and engines have changed drastically, and I think it's time to once more determine the most efficient configuration. To make this a valid challenge with 0.16's fuel bug, the "full throttle until burnout" rule will be more important.

Jeb #1291 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 FL-T400 tanks survived the carnage. Jeb, of course, made it to space and died happy when the last 10 boosters exploded beneath him.

Jeb #1292 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.

Entries will be ranked on three categories...

Category 1: Get the highest speed at burnout. (speed efficiency) - Current leader, Nao with 6117 m/s.

Category 2: Get the highest altitude at burnout. (fuel efficiency) - Current leader, Nao with 1933 km.

Category 3: Most efficient launch, as measured by some kinda rocket science, Jeb #1292 doesn't care about the details (specific orbital energy) - current leader, Nao with 17.316 MJ/kg.

For category 3, it will be measured with this equation: .5*(final velocity in km/s)^2 - 3530.461/(600.00 + final altitude in km) = specific orbital energy in MJ/kg (provided by Kosmo-not)

The limitations:

- You have 10 of the FL-T400 fuel tanks (or the same amount of fuel in other stock rocket tanks), plus an unlimited number of all other parts, subject to the other limitations.

- Stock Parts only.

- No Solid Boosters, RCS tanks, and no spaceplane jets/tanks.

- Continuous full-throttle burn. Obviously, we'll have to take you at your word on this one, but this is both to avoid the fuel consumption bug in 0.16 and to keep Jeb happy.

- Anything goes as far as staging, angling to take advantage of orbital speed, etc.

- post a screenshot showing your craft's altitude and speed at burnout.

Example:

10 tanks in 3 stages, with 4 small LV-909 engines and one LV-T45 engine.

Burnout speed & altitude information

burnout speed: 3131 m/s

burnout altitude: 199 km

Specific orbital energy: .5*(3.131^2) - 3530.461/(600.00 + 199) = 0.482 MJ/kg

Edited August 14, 2012 by khyron42

[hen3ry]

Well, here's my entry

http://imgur.com/a/3s2C3

Burnout altitude 178,350 km

Burnout velocity 4543.7 m/s

Fancy Math (if I'm doin this correctly: used Google for 0.5*(4.5437)^2-(3530.461/(600+178.35)) = 5.78678 MJ/kg.

[Ziff]

I used mechjeb for tracking of speed and altitude, if that is not allowed I have no problems yanking it off and flying the mission again. Anyway, here's my first off the cuff attempt.

Pre-launch photo op.

Half a moment before burnout.

[dikkjo]

Hi,

here is my attempt. I restaged ziff design to have the 6 external tanks burn first and i tried to launch opposite to kerbin's orbital trajectory but failed of 20-30°

Final speed = 4340.0 m/s

Final height = 236km *

0.5*(4.340)^2-(3530.461/(600+236)) = 5.195 MJ/kg

(* i think it was more but screenshot say otherwise, and i would not have more than 5.32 anyway)

[Clouds]

Final speed = 6866m/s

Height at burnout ~ 243,900m

Orbital energy ~ 19.387MJ/kg

[trekkie_]

Altitude: ~521,000 Meters

Velocity: 1575.7 m/s

Total flight time - 8:15

I achieved the height by gravity turning at 15KM to line up to go into orbit at 100km, which kept me from losing some velocity and allowed me to gain some, then pointed straight away from the planet for the remainder of the flight. full burn from lift off to finish, immediate staging separation as well.

IMO using Jet engines is cheating.

Edited August 7, 2012 by trekkie_

[khyron42]

It's not cheating, but I'll record attempts that used jets as a first stage separately.

Good work everyone, and I'll update the first post with the current bests when I get a chance - rushing off to work right now!

[Apotheosist]

Are half-tanks allowed, even if it still alla dds up to 10 tanks?

[Koschei]

I would think that half tanks count as 0.5 of a tank.

[khyron42]

All the tanks are mostly equivalent now, but not quite. There's one key factor that makes number of tanks important: every one of them has 0.2 drag. This means that, while mass and fuel would be the same for 10 FL-T400's or 20 FL-T200's, the smaller tanks would have twice the total drag while in atmosphere. Likewise, using the larger tanks would give you a free ride by reducing overall drag during early flight. Because it would have different results, I'd prefer to keep this challenge to the FL-T400's only.

I notice that most of the front-runners currently are using the aerospike engines; interesting that it's such a huge difference!

Edited August 7, 2012 by khyron42

[Apotheosist]

I thought the drag values indicated the drag coefficient or something. If you drop two half tanks and one full tank in the atmosphere, they fall at the same rate. I think this explains also why empty tanks fall at the same rate as full tanks. The drag is probably modelled as drag per unit mass. Another example of this would be the big and small parachutes. They both have the same deployed drag value of 500, but the bigger one still slows down your capsule more. This is probably because the bigger chute is 3 times the mass of the small chute, which would give it three times more slowing force.

[trekkie_]

I notice that most of the front-runners currently are using the aerospike engines; interesting that it's such a huge difference!

I'm the only front runner in distance

that's why I said jet engines are cheating. while they do have their disadvantages, such as usable altitude, they can lift a lot of weight almost effortlessly and consume fuel VERY slowly.

I used jet engines to move this...

and they can lift this to several thousand meters and more in a short time. it weighs 50 tons. in comparison, an F-15 weighs only about 22 tons fully loaded.

Edited August 7, 2012 by trekkie_

[khyron42]

Hmm... the drag thing requires testing for confirmation then. Best test: fly to 10 km altitude with identical designs with the only difference being the fuel tanks (flying at full throttle.) Note time of reaching 10 km and speed at that mark. Any speed/time differences will be due to drag differences.

Design: pod, ASAS, 5 FL-T400 tanks, LV-T45 small engine. 1:29 time to 10 km, 238.9 m/s speed.

Same design with 10 FL-T200 tanks. 1:29 time to 10 km, 238.3 m/s speed.

With 1 FL-T16 and 1 FL-T400: 1:29 time to 10 km, 239.2 m/s speed.

The small differences were just a measurement issue - I was hitting escape to pause the game when I crossed 10 km. Cool, I learned something new about the game today!

So I guess any (non-jet) stock tank combination is okay as long as the total fuel is 4000. The jet tanks are horribly unbalanced compared with the four "normal" tanks.

Edited August 7, 2012 by khyron42

[TheDarkStar]

Here's my entry. It's not the highest, but it's fast. It uses the aerospike engines only, so no jets.

On the launchpad: There are 4 aerospike engines and 10 fuel tanks. Part is hidden in the image.

Another image that shows it better.

At burnout:

I boosted straight up until 20km or so, then tilted.

Total mass is 12.935.

Edited August 8, 2012 by TheDarkStar

[Clouds]

OK, here's the same design as I used before, only minus the jet engines (everything else identical).

5,460m/s

~149,000m

~10.19MJ/kg

[khyron42]

Well, if you can't beat the aerospikes, might as well join 'em. But the last two tanks being on the littlest engine gets you a really prolonged burn in space.

Shortly after launch:

Right after burnout (you can still see the flame fading):

2430 m/s

1037 km

only 0.80 MJ/kg

[TheDarkStar]

Does the efficiency equation follow order of operations?

Edit: No matter what I do, my answer makes no sense. Could someone check for my entry to see what I should be getting?

Edited August 8, 2012 by TheDarkStar

[khyron42]

Yes, it does. The really detailed notation would be (.5*(final velocity in km/s^2)) - (3530.461/(600.00 + final altitude in km))

Yours should come out to (0.5*(4.782^2)) - (3530.461/702.9) = 6.411 MJ/kg.

The equation on wikipedia for Specific Orbital Energy takes the form:

Here we're using the first portion of that. v is your velocity, r is the radius of your orbit (altitude + kerbin's radius), and u (3530.461) is the Kerbin's mass multiplied by the gravitational constant used in the game.

Any positive-number specific orbital energy means you're above escape velocity.

Edited August 8, 2012 by khyron42

[TheDarkStar]

Thanks, I found why I was having trouble.

[simplemunrockets]

I present to you the longest and spindliest rocket ever to grace the face of Kerbin.

If you can't tell, the bottom stage is 8 tanks of fuel, 1 aerospike, and 2 gimballing engines. Upper stage is the capsule (duh), an ASAS, 2 fuel tanks, and the tiny engine.

It actually broke the height record.

Here's the pic:

The Mun ended up doing some pretty and weird stuff to my trajectory at one point.

Height: 1110 km

Speed: 3811.2 m/s

Specific Energy: 5.198025643976608 MJ/kg

Edit: I just realized how similar my rocket is to khyron's. Huh.

Edit2: Here's the weird stuff getting captured by the Mun does to you:

The "Escape Mun" point kept going around in circles.

Edited August 9, 2012 by simplemunrockets

[trekkie_]

I present to you the longest and spindliest rocket ever to grace the face of Kerbin.

If you can't tell, the bottom stage is 8 tanks of fuel, 1 aerospike, and 2 gimballing engines. Upper stage is the capsule (duh), an ASAS, 2 fuel tanks, and the tiny engine.

It actually broke the height record.

Here's the pic:

The Mun ended up doing some pretty and weird stuff to my trajectory at one point.

Height: 1110 km

Speed: 3811.2 m/s

Specific Energy: 5.198025643976608 MJ/kg

Edit: I just realized how similar my rocket is to khyron's. Huh.

Edit2: Here's the weird stuff getting captured by the Mun does to you:

The "Escape Mun" point kept going around in circles.

that's not a 10 tank design, it's 11 tanks. now we could argue if whether it's a handicap for you or not, but there is also a benefit on weight when it comes to escape trajectories, gravity turns, speeds, and rocket design. see, even though those 2 half tanks add the same fuel, they also allow you to add 2 extra engines, the thrust of which negates any extra drag. if you were to add 2 engines with the standard full size tanks, you would have to take away essentially a whole tank from your center fuselage of tanks, which does make a difference in pretty much every aspect, especially since those two engines 1) balance your weight distribution, and 2) add more initial thrust. 3) allows you to keep more fuel in the center for the aerospike or 20 thrust lv909 engine.

all in all I would say this would mean a disqualification. and honestly, I don't really believe the distance either. the fuel simply couldn't burn that long at full throttle continuously, and that's taking into account your 20 thrust final stage engine. from my experimentation with all different types of combinations and flight trajectories in the 10 tank challenge, it simply doesn't add up. in fact, I took your design for a spin and did not get as far, whether going straight up or ascending at an angle to gain speed, etc.

and the irony is, I actually did break the distance record with it (even though it's disqualifiable anyways)....just not the distance you listed. (i.e. you cheated and lied...perhaps even used a different design outside of the rules, because even coasting or throttling wouldn't get you that far in a time frame of 15 minutes). tsk tsk. you should be ashamed of yourself.

total flight time, full burn immediate decouple: 14:56

your flight time: 15:12

Edited August 11, 2012 by trekkie_

[TheDarkStar]

His is not 11 tanks. The two from the first stage are both half tanks.

[trekkie_]

His is not 11 tanks. The two from the first stage are both half tanks.

perhaps you didn't pay attention. the point is by having 2 half tanks, he was able to add an extra engine and have weight balance.....had he used the regular full tanks, he would have to of taken an entire fuel tank from the center mass in order to add 2 extra engines.

the point of using 10 of the same fuel tanks is not only being limited by fuel....but also being limited in how you can design your rocket and what stages get X amount of fuel, how the weight is balanced, etc. for example, to add 2 side engines with 2 full size fuel tanks to attach them to, he would of for example, had to of taken a full tank off of the 20 thrust lv909, which would have severely limited his distance later on in the launch. (if we didn't follow strict rules, we could just use any tank as long as it came up to the equivalent amount of fuel, which would give a severely mixed bag of results) after all it's called the 10 tank challenge, not the 9 normal tank and 2 half tank challenge.

not to mention I timed the amount of the time it would take to burn through all of his fuel at full throttle the entire flight with immediate decoupling.....which took about 14:56 ......however he ran out of fuel at 15:12, which is a HUGE discrepancy. so either he cheated by using a different design than he showed, or an extra booster, or didn't decouple/coasted for well over 16 seconds at some point, which is unacceptable. either way he didn't follow the rules in multiple instances. what's the point of participating in a challenge if you're not going to follow the rules of it?!

Edited August 11, 2012 by trekkie_

[Ziff]

His is not 11 tanks. The two from the first stage are both half tanks.

He has 9 full tanks and 2 half tanks, that makes 11 tanks. It is a 10 tank challenge, not a 20 half-tank challenge, which would be totally different because it allows you to add twice as many engines and means many more configuration possibilities.

[sal_vager]

Two 1/2's equals 1