efficient fuel at 250k

[fommil]

I'm trying to work my way up the tech tree towards space planes, because my designs tend to require a fuel stop in Kerbin orbit.

But until I get there, I have to make do with wasteful trips to my station at 250km.

I've considered building an ore refinery on Minmus, but it sounds like a lot of work.

I have a design that delivers about 1,700 units of Liquid Fuel (and matching Oxidiser) at a price of 47.9 per unit. I tried experimenting with recoverable rockets, e.g. by adding 12 parachutes to my design, but the recovery cost didn't make any sense when return costs were factored in (500 liquid fuel left in for deceleration, plus apoapsis/mass losses on the way up due to the parachutes). I was getting about 10,000 - 15,000 recovery.

I challenge you to do better, my refuel ship is attached! (has an Engineer Redux) https://gist.github.com/fommil/272ef721db825ee8e1d4a458c219922d

This translates into 75.85 / unit at 100km orbit of the Mun (I can send 6480, with 4092 arriving).

Edited January 2, 2017 by fommil

[Aegolius13]

You could consider moving your station to a lower orbit.  Your heavy fuel shuttles would have less work to do to get there, and would use less fuel to get to a survivable reentry.  Also, your ships bound for elsewhere would use less fuel when launching from a lower orbit, thanks to Oberth.  

Mining ships can be expensive, but aren't really all that much work.  You can do a one-piece mining/refueling rig that has drills, an ISRU, enough solar panels and radiators to keep it going, a tiny ore tank to buffer, as much fuel capacity as you can lift, and a Klaw or docking port to transfer the fuel.  Then just plunk the thing down somewhere nice on Minmus and go at it!  Unless you're playing on hard mode, any old spot is likely to have enough ore concentration to be viable, so resource scanning is not necessary.  

[DunaRocketeer]

1 hour ago, Aegolius13 said:

 Also, your ships bound for elsewhere would use less fuel when launching from a lower orbit, thanks to Oberth.  

Not a rocket scientist here, but I think the Oberth effect is about burning your engines at periapsis (fastest point) rather than the fuel advantages of different types of orbit. Someone feel free to correct

[fommil]

1 hour ago, Aegolius13 said:

You could consider moving your station to a lower orbit.   

That is an interesting thought, I've picked this orbit only because it's easy to rendezvous with. Perhaps there is a better sweet spot.

But I don't think it saves much: especially on recovery the dv is all to slow down at 50k to avoid burning up. I'd have to land on the launchpad to make the recovery cents worthwhile. And I don't think the outbound ships save anything here, indeed I think that might make it more expensive to break SOI of Kerbin.

[LordKael]

37 minutes ago, DunaRocketeer said:

Not a rocket scientist here, but I think the Oberth effect is about burning your engines at periapsis (fastest point) rather than the fuel advantages of different types of orbit. Someone feel free to correct

Oberth effect is the idea that making a burn closer to the gravity source (planet/star) will net more dV than making an identical burn further away from the gravity source. The simplified version is that burning at periapsis is the most efficient. 

[Ruedii]

First, there is no shame in using drop tanks on a spaceplane.  It's a lot cheaper than discarding entire rockets. 

Second, a good way to boost your fuel efficiency is to reduce wing area, thus reducing drag in the atmosphere.  This has the unfortunate effect of also increasing takeoff and landing speeds and decreases your ability to decelerate during reentry, so it has to be balanced.  Also, try to have the minimum number of intakes you need, and select ones optimized for supersonic/hypersonic flight speeds.  (If your engines can't run full power on takeoff, that's fine, considering how overpowered many space planes are.  You may only want your first pair of engines on until you attain takeoff and sufficient speed to feed air to all the engines.)  You can't compensate for the near-zero oxygen at high altitude with more intakes anymore, so fewer intakes may be better.

Third, try to rapidly ascend and not exceed Mach 2.2 until you reach a good altitude, of 12Km to 18km.  Then you can make your run up to hypersonic speeds at a slight incline and curve upward to a near suborbital flight path, before entering a gravity turn.

 

Edited January 2, 2017 by Ruedii

[GoSlash27]

fommil,

 So you're saying it's costing you over $4,000 per tonne to orbit fuel? Or is my math wrong?

 If that's the case, yeah... your launcher is extremely inefficient.

Check here for ideas to help you out:

 

Good luck!

-Slashy

3 hours ago, Aegolius13 said:

Also, your ships bound for elsewhere would use less fuel when launching from a lower orbit, thanks to Oberth.  

Aegolius,

 Not necessarily. It depends on where you're going. Every destination has an ideal "gate orbit" where DV costs for the transfer are minimized. Oberth doesn't always trump being further down in the gravity well.

Best,
-Slashy

[Aegolius13]

38 minutes ago, GoSlash27 said:

Not necessarily. It depends on where you're going. Every destination has an ideal "gate orbit" where DV costs for the transfer are minimized. Oberth doesn't always trump being further down in the gravity well.

Yeah, but that's only looking at the amount of fuel consumed after the refueling, right?  If we're talking about fuel that's been hauled up from Kerbin, rather than "free" fuel from a lunar mining station, it seems that the most fuel-efficient overall scheme would be to have the refueling station as low in orbit as you can get away with.  Just like if you were launching one ship without refueling, you would not want to circularize into the gate orbit before going interplanetary.  OP is doing basically the same thing, just launching the fuel and the ship separately from Kerbin.  

[Carl]

10 hours ago, fommil said:

I'm trying to work my way up the tech tree towards space planes, because my designs tend to require a fuel stop in Kerbin orbit.

But until I get there, I have to make do with wasteful trips to my station at 250km.

I've considered building an ore refinery on Minmus, but it sounds like a lot of work.

I have a design that delivers about 1,700 units of Liquid Fuel (and matching Oxidiser) at a price of 47.9 per unit. I tried experimenting with recoverable rockets, e.g. by adding 12 parachutes to my design, but the recovery cost didn't make any sense when return costs were factored in (500 liquid fuel left in for deceleration, plus apoapsis/mass losses on the way up due to the parachutes). I was getting about 10,000 - 15,000 recovery.

I challenge you to do better, my refuel ship is attached! (has an Engineer Redux) https://gist.github.com/fommil/272ef721db825ee8e1d4a458c219922d

This translates into 75.85 / unit at 100km orbit of the Mun (I can send 6480, with 4092 arriving).

Try giving screenshots. You have non-stock parts in there so those of us without the specific mod can't even look at it. I should not i could quick modify an already shared design of mine to pull 48 a unit or better, (the current payload is a lot more expensive than just fuel).

Edited January 2, 2017 by Carl

[Aegolius13]

9 hours ago, fommil said:

I challenge you to do better, my refuel ship is attached!

Here's a basic idea for a very cheap fuel lifter.  For your payload stage, put in an orange tank and top with a probe core, electricity, orbital maneuvering, nose cone/aero and other needs.  For the stage below that, put in two more orange tanks and then a TwinBoar below that.  Add two Kickbacks with nosecones on radial decouplers to the sides.  This should start out with a comfortable TWR, have enough delta-v to get your payload tank to orbit, and cost under $50k for the basic parts.  If you need a little more thrust or delta-v, consider adding a little more fuel for the TwinBoar, another set of Kickbacks starting at 50% thrust, and/or some radial liquid boosters attached to Reliants. 

As a general matter, TwinBoars are stupidly good when you want to lift a heavy payload for cheap.  And SRBs are great for adding more cheap thrust, provided they don't overwhelm your ability to direct your rocket.  

Edited January 2, 2017 by Aegolius13

[fommil]

28 minutes ago, Aegolius13 said:

Here's a basic idea for a very cheap fuel lifter.  

What efficiency do you get for this?

The thread is a challenge to do better, you can't compete if you don't take your own score :-p

Delivering any less than 1500 units of liquid fuel (plus oxidiser) don't count... too much game repetition.

2 hours ago, Ruedii said:

First, there is no shame in using drop tanks on a spaceplane.  

I've not reached spaceplanes yet ;-) read the question again

1 hour ago, GoSlash27 said:

fommil,

 So you're saying it's costing you over $4,000 per tonne to orbit fuel? Or is my math wrong?

 If that's the case, yeah... your launcher is extremely inefficient.

If you think you can do better, why not try to put something together ;-) 1500+ liquid fuel plus oxidiser rendezvous at 250km. No spaceplanes or ore mining.

40 minutes ago, Carl said:

Try giving screenshots. You have non-stock parts in there so those of us without the specific mod can't even look at it. I should not i could quick modify an already shared design of mine to pull 48 a unit or better, (the current payload is a lot more expensive than just fuel).

Ok, I'll upload pics and a non-mod ship when I'm at my computer tomorrow. It's basically a huge fuel tank with a docking port, with a rhino surrounded by as many big solid boosters as can fit. Solid boosters go up 68k.

[Carl]

Ok i manged to dig through and find the modded parts and strip em (Engineer part, which i assumed is KES or somthing, and KAS.C.Port). First you math is hugely off, your getting 36 per unit since it's an 80k cost and under mechjeb ascent delivers just over 2k to orbit.. That said no RCS for docking. You can improve it slightly by making the fairing pointyier. However your clearly using a very modded game a for me the booster burned out at 23k.

 

Also sorry if i came off a bit aggressive about the modding btw :). Working on my own fuel truck for you.

Edited January 2, 2017 by Carl

[GoSlash27]

32 minutes ago, fommil said:

If you think you can do better, why not try to put something together ;-) 1500+ liquid fuel plus oxidiser rendezvous at 250km. No spaceplanes or ore mining.

fommil,

 I already have "done better' in the link I posted. I shared it to give you ideas on how to improve your lifter, not to make you feel bad about what you've made or to get into a competition. Having said that... I will share a "cheap disposable" example to help you along. What is your current tech level? Do you have any facility restrictions (part count, mass, etc)?

1 hour ago, Aegolius13 said:

Yeah, but that's only looking at the amount of fuel consumed after the refueling, right?  If we're talking about fuel that's been hauled up from Kerbin, rather than "free" fuel from a lunar mining station, it seems that the most fuel-efficient overall scheme would be to have the refueling station as low in orbit as you can get away with.  Just like if you were launching one ship without refueling, you would not want to circularize into the gate orbit before going interplanetary.  OP is doing basically the same thing, just launching the fuel and the ship separately from Kerbin.  

Aegolius,

 If the OP wants to save as much fuel as possible, then yes. If the OP wishes to make a lighter and more compact ship for the journey, then no.

Best,
-Slashy

 

[Ruedii]

Oh, reread the post.

In that case, you generally want at least two stages in your rocket designs.   Not doing so wastes a lot of fuel hauling dead weight.  Generally I use a standard 3 stage design with a deep gravity turn by using a launch angle of between 5 degrees and 15 degrees depending on launch TWR.  (5 degree for 2.0-2.5, 10 degree for 2.5-3.0 and 15 degree for 3.0-3.5) I hold prograde for the launch starting at 50m/s to 100m/s (

First is the Booster stage, 2.5-3.5 TWR for 25 sec (often utilizing radially attached boosters)  This gets the craft past the lower atmosphere as fast as possible.
Second is the maintainer stage.  This has 1.2-2.0 TWR for 1 minute 30 sec.   This extends the apoapsis to 70km
Third is the circularization stage.  I usually use this combined with the orbital maneuver stage unless the craft is very heavy.  This is especially so if the craft is designed to do long distance flights, and thus needs lots of fuel capacity in it's orbital maneuver stage and will be refueled.

Sometimes I adjust the size of the maintainer stage to handle much of the circularization this reduces the need for refueling.

For smaller craft you can do away with the second stage, and just have a single ascent stage.

Edited January 2, 2017 by Ruedii

[Carl]

Okay, here's mine Craft file first, note despite the screenshots showing MJ this version of the craft file has it stripped :). Efficiency is 25.87 a fuel unit. Do note however that could probably be improved a touch by swapping the R32 Rockomax tanks for Jumbo's in  couple of places, if you do that note both manual struts and auto strut settings or it will go unstable, but that should save you 2k more on costs, (each upper radial booster can swap it;s 2 rockormax's for jumbo's, and the 3 on the bottom could be changed to 1 jumbo and 1 32, technically you might be able to make it 2 Jumbo's on the bottom, but i have stability questions about that so didn;t try it.

Pictures one on VAB, one in orbit, note MJ accent guidance settings, the turn altitude and stage delays are especially important if you don't want bangs due to parts catching or getting hit by exhaust. Note in the on orbit shot that the boosters drifting away still had all of 6m/s of d/v left in them.

 

@GoSlash27: looks to me like he has everything tech wise. The problem is his Rhino while a very good engine is burning a lot of fuel finishing the 24km to orbit stage, so whilst it's only 80k a shot, it's using a lot of the fuel it carries. I'm sure you'll have pithy things to say about my little thing above though too.

[GoSlash27]

Carl,

He said he's still trying to unlock the tech for space planes, so I assumed he hadn't unlocked everything yet.

Actually, I'm hard pressed to make heads or tails from either one, so I'll refrain from commenting just yet.

Best,
-Slashy

 

 

 

 

[Vanamonde]

This discussion of how to play the game has been Moved to Gameplay Questions Discussions. 

[Carl]

Pics of his design below, mine, you can find the tourist version with much more detail in the spacecraft exchange here. I just adapted it by swapping the payload.

 

EDIT: hit post a tad too soon, second pic of it in orbit once it's done processing at imgur.

Edited January 3, 2017 by Carl

[GoSlash27]

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.

Best,
-Slashy

 

[AeroGav]

7 hours ago, Ruedii said:

Second, a good way to boost your fuel efficiency is to reduce wing area, thus reducing drag in the atmosphere.  This has the unfortunate effect of also increasing takeoff and landing speeds and decreases your ability to decelerate during reentry, so it has to be balanced. 

 

With more wing you need less thrust - this was a  3 engine challenge.

Does the OP have nuclear engines yet?    If so, his interplanetary ship does not need much oxidizer.

[fommil]

9 hours ago, Carl said:

Ok i manged to dig through and find the modded parts and strip em (Engineer part, which i assumed is KES or somthing, and KAS.C.Port). First you math is hugely off, your getting 36 per unit since it's an 80k cost and under mechjeb ascent delivers just over 2k to orbit.. That said no RCS for docking. You can improve it slightly by making the fairing pointyier. However your clearly using a very modded game a for me the booster burned out at 23k.

 

Also sorry if i came off a bit aggressive about the modding btw :). Working on my own fuel truck for you.

I totally forgot about the KAS port. I like to have those incase of emergencies. Stripping that off could be enough to get me into space with the solid stage.

Boosters burn out low yes, but the apoapsis just about hits space.

I can dock with this setup: I have vernors to slow down. It saves mass not to take RCS and mono fuel.

Very interesting about pointier shells, I didn't realise this is how the physics engine works! I will experiment.

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.

Looking forward to your fuel bus!

8 hours ago, Carl said:

Okay, here's mine Craft file first, note despite the screenshots showing MJ this version of the craft file has it stripped :). Efficiency is 25.87 a fuel unit.

@GoSlash27: looks to me like he has everything tech wise. The problem is his Rhino while a very good engine is burning a lot of fuel finishing the 24km to orbit stage,

Nice! I agree about that Rhino must be the killer, despite its awesome LSP. I was so excited about getting two stage: maybe dropping down the tech tree and getting higher on earlier stages with slower burns off lighter engines is more sensible after all.

Edited January 3, 2017 by fommil

[fommil]

6 hours ago, GoSlash27 said:

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

Which engines are you using there? (also what is that in units of liquid fuel, not mass... units are easier to count because that's what the resource panel shows).

[fommil]

8 hours ago, Ruedii said:

8 hours ago, Ruedii said:

Oh, reread the post.

In that case, you generally want at least two stages in your rocket designs...

But what efficiency are you getting for the challenge? The Gauntlet has been laid down :-P

8 hours ago, GoSlash27 said:

I already have "done better' in the link I posted. I shared it to give you ideas on how to improve your lifter, not to make you feel bad about what you've made or to get into a competition. Having said that... I will share a "cheap disposable" example to help you along. What is your current tech level? Do you have any facility restrictions (part count, mass, etc)?

 

But friendly competition is the point of this thread :-D

No restrictions except no spaceplanes or ore mining (I've not unlocked the rapier yet and I don't want any plane design spoilers... so I'm ignoring those kinds of designs posted here).

[fommil]

10 hours ago, Carl said:

Okay, here's mine Craft file first, note despite the screenshots showing MJ this version of the craft file has it stripped :). Efficiency is 25.87 a fuel unit.

Awesome stuff! This is exactly the kind of thing I was hoping to see :-D

I did a test flight and messed up my circularisation angles, but I got into 250km orbit to deliver 5872 units, giving an efficiency of 38.76... but I'm not counting the recovery costs of the earlier stages and of course this trajectory could be optimised.

A few questions:

1. how do you see how much you are recovering from parachutes on the earlier stages? I wonder if my solid boosters can survive an apoapsis of 70km...
2. you don't have any RCS, so docking is... tricky
3. you put your reaction wheels in a utility bay: why did you do that?

I'm going to have to rethink my entire rocket design ethos... but at this scale of up-front cost, it might bankrupt me in Hard Career mode! (it'd be cheating for me to use your design, but I'll certainly learn from it)

[GoSlash27]

3 hours ago, fommil said:

Which engines are you using there? (also what is that in units of liquid fuel, not mass... units are easier to count because that's what the resource panel shows).

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

 

Edited January 3, 2017 by GoSlash27