efficient fuel at 250k

[Carl]

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How on earth is mech getting 2k to orbit? I'm circularising to about 80k, then one prograde to rendezvous, a speed adjustment, then trivial fuel to dock.

Let me go refly it and i'll show you the MJ settings, your real problem is your letting the booster burn out then letting it just go straight up from the sounds of it instead of immediately kicking the rhino in and building velocity to orbit.

 

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Fommil, It's just a Twin- Boar with 6 Kickback boosters. Nothing fancy. 60 tonnes is 5400 fuel and 6600 oxidizer; a little over twice the fuel delivered in Carl's design.

It's better cost certainly, mine delivers 7200 fuel though, under MJ control ofc. (that actually makes my efficiency 31.6, i accidently used oxidizer to calculate my efficiency previously). Surprise your design flies though. a twin boar should not have a positive TWR once the boosters burn out...

 

it's the main issue i've been fighting with my designs, how to get enough TWR it will not just dump all velocity after the boosters burn out.

[GoSlash27]

11 minutes ago, Carl said:

Surprise your design flies though. a twin boar should not have a positive TWR once the boosters burn out...

Carl,

 The Isp and thrust improve once you get out of the thicker air. By the time the boosters burn out, it's almost in a vacuum. Also, you don't need a lot of acceleration in the transstage. As your rocket tips horizontal during the gravity turn it's no longer fighting gravity.

Best,
-Slashy

[GoSlash27]

57 minutes ago, Carl said:

It's better cost certainly, mine delivers 7200 fuel though, under MJ control

Carl,

 Oh, sorry. I got the 2 confused. I meant fommil's design.

Best,
-Slashy

[Carl]

Quote

Carl,

 Oh, sorry. I got the 2 confused. I meant fommil's design.

Best,
-Slashy

Hahaha. No worries .

 

Also i'm curious when do the boosters burn out? My experiance is they almost never last high enough that you don;t need a positive TWR, (not highly so ofc), to not suffer massive inefficiency penalties. Even the design i posted has some issues with that, but it's a modification of a mid tech design before i had mainsails.

 

 

[GoSlash27]

Carl,

 I didn't optimize or tweak that one in any way, just put it together as a quick demo. It is what it looks like, so you could just slap one together and try it out.

IIRC The SRBs burn out at 13km and 450 m/sec. At that point it has *just enough* thrust to keep it going.

Best,
-Slashy

[fommil]

3 hours ago, GoSlash27 said:

Fommil, It's just a Twin- Boar with 6 Kickback boosters. Nothing fancy. 60 tonnes is 5400 fuel and 6600 oxidizer; a little over twice the fuel delivered in Carl's design. I guess that's $15.75 per fuel unit? I'm not interested in participating in a competition, so I'll bow out.

Best,
-Slashy

 

just ONE twin-boar? wow, that's pretty awesome. You may well bow out, after taking the prize! 

2 hours ago, Carl said:

Let me go refly it and i'll show you the MJ settings, your real problem is your letting the booster burn out then letting it just go straight up from the sounds of it instead of immediately kicking the rhino in and building velocity to orbit.

I'm very interested in what you have to show here! To keep things simple, I always pick a solid booster that gets me to space, then burn horizontal with my stage 2. I keep reading about gravity turns but I've always found them to be more hassle than they are worth. I play career in Hard mode, so for me safety of the crew is more important than cost, so I've perhaps erred too much on the side of stable rockets that don't rely on aerodynamics too much.

BTW, you might have missed my response to your design here: 

 

Edited January 3, 2017 by fommil

[fommil]

13 hours ago, GoSlash27 said:

How about something like this:

It'll put 60t of fuel into a 250x250 orbit for $85,000 launch cost. Just dispose of it when you're done.

 

Slashy, I built this rocket using the engines that you said in a later post, but it doesn't go anywhere for me:

1. it doesn't have any stability on the way up, so I added two reaction wheels in the middle
2. the solid boosters burn out at 3500m with a velocity of 150m/s
3. the twin boar doesn't have enough TWR to take it up any higher

did I misunderstand something in your design? Are you using any mods, like FAR? I'm using Kerbal 1.2.2

[GoSlash27]

fommil,

 No, it is what it looks like, no mods. Are you sure you're not clipping the engines?

Best,
-Slashy

[fommil]

11 minutes ago, GoSlash27 said:

fommil,

 No, it is what it looks like, no mods. Are you sure you're not clipping the engines?

Best,
-Slashy

I added a second row of boosters and that is much better... this is pretty neat! The twin boars can then kick in when the solid boosters burn out at about 20k.

Are you maybe firing all engines from the launch pad?

I had very little aerodynamic stability on the way up (I moved the reaction wheels to the top because it's weak in the middle, like in yours, but I have two instead of one) so my ascent was terrible. Nevertheless, I got 4488 units of liquid fuel to 250km round orbit at an efficiency of $28/unit! I'll try adding some aerodynamic stability to get that down to the teens that you're seeing.

I'd never really appreciated the usefulness of the twin boar until now... I've opted for high space LSP and used the solid boosters to get me into space, completely ignoring atmospheric LSP.

[GoSlash27]

8 minutes ago, fommil said:

Are you maybe firing all engines from the launch pad?

fommil,

 Affirmative. I'm guessing that's why you were having issues.The Twin-Boar is a wonderfully cheap and useful booster. Isp is pretty good across the board.

Best,
-Slashy

 

[fommil]

13 minutes ago, GoSlash27 said:

 Affirmative. I'm guessing that's why you were having issues.The Twin-Boar is a wonderfully cheap and useful booster. Isp is pretty good across the board.

Ah, ok... well I tried with just one row of solid boosters and igniting the twin boar on the launchpad. I got 3242 to 250k, giving an efficiency of $31/unit. Which is still far better than I was getting... but I don't know how you're getting almost half this.

I probably held onto the solid booster shells for too long (they impact the twin boars if released when they are spent), and didn't gravity turn early enough. The impact on efficiency of the gravity turn is much higher than I had thought it would be. This certainly deserves further investigation...

EDIT: I tried again with the gravity turn (and a really lucky disengagement of the solid boosters... that is the tricky bit) by turning to 10 degrees reasonably early on then tracking prograde once the solid boosters burnt out and I got down to $20/unit. That's pretty amazing!

Edited January 3, 2017 by fommil

[GoSlash27]

fommil,

 All of the above. I attach the decouplers high on the SRBs and anchor them at the bottom with struts so they do a Korolev cross. Ditch the SRBs as soon as they're spent. My gravity turn was initiated at 110 m/sec. Get the prograde vector to 85° pitch and then just follow prograde. It should end up floating at 45km until Ap is established.

HTHs,
-Slashy

[fommil]

4 minutes ago, GoSlash27 said:

fommil,

 All of the above. I attach the decouplers high on the SRBs and anchor them at the bottom with struts so they do a Korolev cross. Ditch the SRBs as soon as they're spent. My gravity turn was initiated at 110 m/sec. Get the prograde vector to 85° pitch and then just follow prograde. It should end up floating at 45km until Ap is established.

HTHs,
-Slashy

I think you just changed how I design rockets... a bit of practice with this gravity turn in sandbox mode and I might start swapping over my designs in career mode (where iterating this kind of thing is very expensive). Kinda cheating, but as long as I don't copy the `.craft` files I think it's fair enough  Proves the value of R&D!

oh, lol, the irony. My scientists on the Mun just finished giving me enough science points to build spaceplanes... but I'm sure this experiment in efficient fuel buses is not wasted.

Edited January 3, 2017 by fommil

[fommil]

wow, ok, picking a cheaper probe core and getting the hang of the gravity turn (turning to 10 degrees straight away then following surface prograde, auto switching to orbital prograde) I'm getting 5895 to 250k orbit at an efficiency of $16/unit! This makes my design look like a hunk of junk.

That Korolev cross is a pretty neat move! It is the game changer for using multiple stages in the atmosphere.

Edited January 3, 2017 by fommil

[GoSlash27]

23 minutes ago, fommil said:

I think you just changed how I design rockets... a bit of practice with this gravity turn in sandbox mode and I might start swapping over my designs in career mode (where iterating this kind of thing is very expensive). Kinda cheating, but as long as I don't copy the `.craft` files I think it's fair enough  Proves the value of R&D!

oh, lol, the irony. My scientists on the Mun just finished giving me enough science points to build spaceplanes... but I'm sure this experiment in efficient fuel buses is not wasted.

fommil,

 Lots of good ideas like that in the cheap 'n' cheerful challenge I linked upstream. I'm glad it's worked out for you.

Release the hounds,
-Slashy

[fommil]

only way I can see to improve on this would be to recover the solid stage shells, but they are moving too fast for parachutes to deploy so I'll need to tune the minimum pressure.

[GoSlash27]

fommil,

 If you stagger the thrust of the SRBs and stage them off in pairs, you can save a considerable amount of payload at the other end. You can also set up a pseudo- asparagus arrangement where the SRBs haul fuel tanks to carry the fuel burned by the core.

 You might also want to look at adding a 3rd low thrust vacuum stage.

Best,
-Slashy

[Carl]

DoH! took the shot forgot to upload it .

 

Here you go. Seriously go get CKAN  and grab MJ, if your rough at flying rockets and like me find it more of a chore than the effort to get good is worth it's great. Do note you'll need to customise the accent profile for each rocket as each needs different.

 

Also  yes i saw your post, just not much comment to make, glad it worked for you :).

 

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IIRC The SRBs burn out at 13km and 450 m/sec. At that point it has *just enough* thrust to keep it going.

Huh, i probably will have to build it and try, i was stuck not able to game much when i wrote that though ;). Waiting on deliveryman.

 

 

Also that MJ settings:

 

[GoSlash27]

fommil,

 Here's a really crazy one. My favorite design from the c'n'c challenge:

http://s52.photobucket.com/user/GoSlash27/slideshow/KSP/CnCRocketFactory/Cheep135

If you modify it to your purpose and tweak it out, it should get you roughly $10 per unit.

Best,
-Slashy

[Superfluous J]

9 hours ago, Carl said:

massive inefficiency penalties

There's inefficiency and there's inefficiency. Burning off prograde or taking an air drag hit is very frequently offset by not having to carry more engines. I've no math to back it up, but it seems that generally the less engine you bring, the better right up to the point where you literally cannot get into orbit.

[Carl]

Nah there is a point before that where you hit the penalties, experienced it trying to build my 22 man tourist mun shot orbiter design. Using 2 stages of engines worked much better. But i will agree it's a narrow band and hard to judge at a glance usually. Slashy's design caught my attention because it looks close to the line so to say.

[Superfluous J]

8 hours ago, fommil said:

I keep reading about gravity turns but I've always found them to be more hassle than they are worth.

 

7 hours ago, fommil said:

I tried again with the gravity turn (and a really lucky disengagement of the solid boosters... that is the tricky bit) by turning to 10 degrees reasonably early on then tracking prograde once the solid boosters burnt out and I got down to $20/unit. That's pretty amazing!

ONE OF US ONE OF US

[GoSlash27]

17 minutes ago, 5thHorseman said:

 

ONE OF US ONE OF US

 

Looking at it from a purely DV perspective, it's worth it to accelerate as rapidly as possible. *But* from a dollars- per- tonne perspective it is far better to pick a lighter cheaper engine.

Best,
-Slashy