Three Skipper efficiency

[Human Person]

Carry a payload to LKO, you may only use 3 Skipper engines on your first stage. Max payload wins.

you wouldn't believe how hard it is to balance this out between TWR and DeltaV.

You may have an empty fuel tank on your payload to drain leftovers from your last stage before detaching it. You may not use fuel from your payload to get into orbit. (Imagine the fuel crossfeed between payload and last stage works only in one direction, only into the payload)

There are 2 (3) Categories:

-Asparagus 

-Non asparagus

(-Delta IV Heavy Style: Non-asparagus and modular, wich means the boosters and core-stage are identical and you have to throttle down the core engine during ascend to save fuel.)

 

This main goal of this challenge is to determine how beneficial asparagus staging actually is. For this reason, please try to participate in both categories asparagus and non-asparagus.

pictures would be great, but simple stats are ok as well:

-Launch mass

-Payload mass (must be seperated from the core-stage)

-Booster configuration

 

Leaderboard:

Non asparagus

1. @Martian Emigrant: 32.79 t, modular core/booster and upper stage. I hope I got this right from the pictures, but it looks like he simply build a single first stage with 3 Skippers that burned out simultaneously.

2. Me: 31.867 t, modular core/booster, no upper stage, throttle control on the core

3. @MarvinKitFox: 27.1 t, throttle control on the core, no pictures 

 

Asparagus:

1. Me: 34.196 t, modular core/booster, no upper stage

2. @MarvinKitFox: 31.1 t

3. @Martian Emigrant: 30.36t, modular core/booster and upper stage. Extremely low TWR after booster sep lead to a shallow launch profile with presumably lots of drag losses.

Edited April 15, 2017 by Physics Student

[Numerlor]

Are you sure it is worth it to throttle something that big?

Edited March 29, 2017 by Numerlor

[Human Person]

14 hours ago, Numerlor said:

Are you sure it is worth it to throttle something that big?

If you don't, your boosters and core will burn out simultaneously, so you basically have a single stage. My Delta Heavy would have had only 3000 m/s if i wouldn't have saved some fuel on the core.

Edited March 30, 2017 by Physics Student

[Human Person]

My entry. I think this will be easily beaten

1st the Delta Heavy

Payload: 31.867 t

2nd the asparagus rocket (same rocket, bigger payload)

Payload 34.196 t

Having an empty fuel Tank on your payload to drain leftovers from your core stage is legitimate.

 

 

So, It seems like asparagus staging isn't all that beneficial. Prove me wrong!

Edited March 30, 2017 by Physics Student

[Gordon Fecyk]

Just on a cursory attempt with this craft:

http://www.antiwindowscatalog.com/media/ksp/LifterChallenge1-1.zip

...I'm getting a better result with asparagus staging than without. This is Stock KSP 1.2.2, no FAR, dev build or otherwise.

Here are the flight instructions for this one:

1. Full throttle and SAS Hold before launch
2. Launch, and hit SAS Prograde at precisely T +22s. The craft should be at 45 degrees pitch by 10 km up, at least in Asparagus mode.
3. Stage side tanks when empty.
4. Climb to AP (80 km for example), cut engines, close orbit at AP.

You can adjust the craft's mass by adding or removing ore. This one has two large ore tanks offering 20 to 37 tonnes final mass at LKO. Note the launch angle is not 90 degrees, so I could eliminate as many human variables as I could. I don't use MechJeb, but you might be able to eliminate other human variables with it.

To use Asparagus mode, enable fuel crossfeed at the decouplers. To use Modular mode, disable crossfeed and adjust throttle limiter on middle engine as appropriate. Bring up the monitors for the tanks to observe fuel use so you know when to stage the boosters away.

In Asparagus mode I have 1000+ OX when I hit 80 km LKO and 20 t post-separation mass. In Modular mode I have 600+ OX, but it might be that after months of Asparagus rocketry I don't know how to fly this without it.

[Avo4Dayz]

On 30/03/2017 at 11:43 AM, Physics Student said:

If you don't, your boosters and core will burn out simultaneously, so you basically have a single stage. My Delta Heavy would have had only 3000 m/s if i wouldn't have saved some fuel on the core.

Attach fuel lines from outside tanks back to the centre tank. This results in full throttle the whole time and the core stage has full fuel at the moment the strap ons are jettisoned. (Same was Space X plans for falcon heavy and I imagine Delta Heavy would do this to, but not certain)

[Human Person]

25 minutes ago, Avo4Dayz said:

Attach fuel lines from outside tanks back to the centre tank. This results in full throttle the whole time and the core stage has full fuel at the moment the strap ons are jettisoned. (Same was Space X plans for falcon heavy and I imagine Delta Heavy would do this to, but not certain)

That's called asparagus staging and it's what this challenge is all about. The point I want to make here is that even in it's most simplistic form, with only one pair of boosters, it isn't all that beneficial in terms of payload.

Edited April 4, 2017 by Physics Student

[Avo4Dayz]

6 minutes ago, Physics Student said:

That's called Asparagus staging and it's what this challenge is all about. Read again.

I did read, just was always confused on definition of asparagus staging given I saw soo many just using drop tanks haha...

Besides I usually specialise in SSTO VTVL rockets.... Hoping some of that can work here to. I used a single twin boar (plus 2 orange tanks) to lift 19t and return the rocket back, so maybe 3 skippers can lift 20-25 t (non returnable)..building now

Edited April 4, 2017 by Avo4Dayz

[Brent Kerman]

I have a Delta IV Heavy using skippers in one of my saves, but it was accurate and had an upper stage. I don't think it could get much of anything to orbit without it.

[Human Person]

23 hours ago, Brent Kerman said:

I have a Delta IV Heavy using skippers in one of my saves, but it was accurate and had an upper stage. I don't think it could get much of anything to orbit without it

I might be wrong but I believe that you won't be able to get a better result with such a configuration. The 3 Skippers put a pretty hard limit to your launch mass. Carrying that extra upper stage migt be worse than carryimng more fuel on the lower stages.

I'll change the rules to only 3 Skippers on the first stage.

[Martian Emigrant]

Hi.

Did 2 test flights.

Album

Spoiler

 

First flight:

Launch: 165.150t

Payload: 32.79t

Configuration: 1core+2boosters, 2nd stage

 

Second flight:

Launch:165.950t

Payload 30.36t

Configuration:

Asparagus core+2boosters, 2nd stage.

 

In my secod flight (The asparagus one) the lost of 2 engines resulted in a lost of altitude.

 

The tanks actually produced lift and the rocket started climbing again after gaining speed.

On the above picture you can see it's climbing though the TWR is only 0.56

It took forever to get to 73km but once there only ~73m/s were require to raise the Pe to orbit.

In this configuration the lost of 2 engines was very detrimental (Lost of 2/3 of the thrust while still at 1/2 mass).

I have had good results with asparagus in the past. But right now I am at a lost to explain....

Except perhaps at these higher weight, 2 booster with a core powered with a much larger engine

or four boosters down to 2, down to one bigger engine might be a better approach.

 

ME

 

Edited April 7, 2017 by Martian Emigrant

[Human Person]

17 hours ago, Martian Emigrant said:

In this configuration the lost of 2 engines was very detrimental (Lost of 2/3 of the thrust while still at 1/2 mass).

That's quite challenging, isn't it. Possible approaches are:

-Choose a higher launch path (more gravity losses)

-Make your boosters bigger and the core smaller (now your boosters burn longer (and you have to carry that dead weight for longer))

 

I'll do the leaderboard when i get home.

Edited April 7, 2017 by Physics Student

[MarvinKitFox]

Maybe you guys use a better ascent profile, maybe my KSP is a slightly differing version than yours.

 

Basic lifter, with a bit of throttle control on the core, gives me payload on orbit of 27.1 ton

Basic asparagus, same design just with fuel feed, give payload = 29.9 ton

Asparagus with droptanks before dropping the outer engines, gives me 31.1 ton

 

I wouldn't call an increase of (29.9-27.1)/27.1 = 10.3% in payload, simply by toggling crossfeed, to be a bad deal at all!?

With almost no added cost, just some complexity, i'm able to increase the Payload by 14.7%

 

You yourself achieve a 7.1% increase in payload.

[Human Person]

On 9.4.2017 at 7:19 PM, MarvinKitFox said:

Maybe you guys use a better ascent profile, maybe my KSP is a slightly differing version than yours.

That's why I'm interested in the statistics, but I definitely need more entries for doing such things. Also you should bare in mind that this is just the most simple asparagus design and the benefit per stage drops rapidly with an increased number of stages. People are building asparagus rockets with 20 stages to LKO, being maybe 0.01% more efficient than a asparagus design with 4 stages.

Many people are glorifying asparagus staging or stating it's a "must have", so I think showing that it increases your payload by just -insert statistics result here- is quite something and surely surprising for many people. We're doing science here.

"Asparagus with droptanks before dropping the outer engines" what do you mean by that?

Edited April 12, 2017 by Physics Student

[Gordon Fecyk]

On ‎4‎/‎12‎/‎2017 at 3:50 PM, Physics Student said:

"Asparagus with droptanks before dropping the outer engines" what do you mean by that?

A craft can drop empty tanks instead of dropping both empty tanks and engines. Here's an example from an older Scott Manley tutorial. Skip ahead to 2:36 to see the craft design. To accomplish the same thing in KSP 1.2.2 without using fuel lines, you can enable crossfeed on the decouplers and set a higher tank priority on the external tanks.

[Nicias]

I find that that is a good approach. I'll often do a twin boar with two orange drop tanks and two orange + skippers. The skippers, twin boar & fuel work to get time to Ap up to 50s, and then skippers & their tanks are dropped (if I get the tankage just right.) Then the rocket continues on mostly full throttle twin boar until the navball switches from surface/orbit . This requires a throttle up to keep time to Ap at 50 and at this time the orange tanks are dropped. Then the twin boar mostly takes me to orbit.