What's the most efficient way to get stuff into LKO?

[alverro]

Since I managed to make a fully reusable shuttle, I'd like to hear everyone's ideas a super - reusable launcher concept ( SRLC ).

[☭Woodsman☭]

efficiency and reusability are 2 different things. real life shuttles were barely reusable and not very efficient at all. the only difference between a reusable rocket and one that's not is leaving some extra fuel to land it and being more mindful of when they're released. efficiency comes down to getting your gravity turn right, which can be affected by the TWR, drag, maneuverability, and other things that might require adjustments to the turn. some of the least efficient builds I've done, for instance, forced me to shoot straight up longer, and reach a higher apoapsis before circularizing to ensure I didn't fall back into the atmosphere. The most efficient just required me to pitch toward 90 10-15 degrees at around 100 m/s and then set it to follow prograde marker and watch it follow perfectly until you cut the engines and prepare to circularize.

Usually there's always a compromise somewhere, between whether or not it's reusable, if you're able to drop stages at the ideal moment, if it follows prograde without much intervention, if you both have enough fuel but don't bring too much, etc. I have ships I've come back to and tweaked a bit here and there for a long time, and other times I start on something from scratch despite doing the same thing a million times before, just in case I accidently find a better way this time.

I should also mention using mechjeb is ridiculously more efficient than flying manually. You don't need to use it full stop with all the bells and whistles, just "manually" steering with the Smart A.S.S. feature is enough.

[alverro]

Originally posted by ☭Woodsman☭:

efficiency and reusability are 2 different things. real life shuttles were barely reusable and not very efficient at all. the only difference between a reusable rocket and one that's not is leaving some extra fuel to land it and being more mindful of when they're released. efficiency comes down to getting your gravity turn right, which can be affected by the TWR, drag, maneuverability, and other things that might require adjustments to the turn. some of the least efficient builds I've done, for instance, forced me to shoot straight up longer, and reach a higher apoapsis before circularizing to ensure I didn't fall back into the atmosphere. The most efficient just required me to pitch toward 90 10-15 degrees at around 100 m/s and then set it to follow prograde marker and watch it follow perfectly until you cut the engines and prepare to circularize.

Usually there's always a compromise somewhere, between whether or not it's reusable, if you're able to drop stages at the ideal moment, if it follows prograde without much intervention, if you both have enough fuel but don't bring too much, etc. I have ships I've come back to and tweaked a bit here and there for a long time, and other times I start on something from scratch despite doing the same thing a million times before, just in case I accidently find a better way this time.

I should also mention using mechjeb is ridiculously more efficient than flying manually. You don't need to use it full stop with all the bells and whistles, just "manually" steering with the Smart A.S.S. feature is enough.

True, I should've rephrased.
Efficiency does indeed corrolate with Reusability, but they are not the same thing.

[andylaugel]

I deleted my last two screenshot laden posts as providing too many unasked-for examples and getting off-topic.

Reusable lifters can make sense, but there are trade-offs and risks.

First, lets look at the completely disposable solution. We’ll put our payload into orbit using disposable stages—SRBs and/or a disposable Liq/Ox rocket. The SRBs are dropped once expended. The disposable rocket stage usually achieves the target Ap altitude and expends the rest of its fuel on approaching orbital speed—but not enough for the Pe to leave the atmosphere. Once dropped, the payload supplies the last few hundred m/s dV for a stable orbit.

Then there is the completely reusable solution, in which our ship needs to be a single-stage to orbit. We have more mass that requires more dV because it has to achieve a stable LKO, and then a little extra to de-orbit itself. If we use wings for reentry, that imposes a dV tax in the form of drag with the atmosphere on take-off. And it’ll be more expensive, as the return vessel needs to control itself and be able to land. If anything explodes during re-entry or landing, we lose the refund for the lost parts. And we want to control our landing, because while we get 100% part refund on KSC’s runway, we might only get 13% landing on the opposite side of the planet. And of course, the player needs to spend time and attention on recovering the reusable stage. And if you use a spaceplane, the change in weight distribution from spent fuel and detached payload can turn a stable aircraft into an unstable one.

And there are hybrid solutions that fall in the middle, like accepting sunk costs in some SRBs on a mostly recoverable lifter.

Depending on your skill and luck, the difference in cost between these solutions can be close. Whether the investment in time and attention is worth it is up to you. Personally, I tend to use the disposable option most often. But I do enjoy my SSTO spaceplanes I can reliably land on KSC’s runway as a cheap means of moving kerbals and experiments into and out of orbit.

That said, I really go reusable after achieving LKO. Mining can generate fuel on almost any world. And once you’ve got that, you can maintain a fleet of spacecraft capable of going almost anywhere and back for no additional costs past their initial launches. … Okay, so it’ll also take time and attention in the form of refueling and docking, but I don’t mind that.

[andylaugel]

Here are some problems you might experience when using a recoverable stage to put yourself into LKO.

• The recoverable stage was dropped in atmosphere on a suborbital path, causing KSP to believe it was a lost cause prematurely and destroying it entirely.
  
• Control lost because the battery ran dry and can't recharge.
  
• Commnet is enabled, but you don't have the signal required for control.
  
• Insufficient means of turning around in orbit for the de-orbit burn.
  
• Ran out of fuel achieving LKO.
  
• Payload ran out of fuel, because the reusable stage drained it on take-off without you noticing.
  
• Aerobraking caused parts to overheat and explode, like the control pod.
  
• Aerobraking didn't slow the craft enough to deploy parachutes before it crashed into the ground.
  
• The center of mass moved behind the center of lift, making the spaceplane to uncontrollable to land.
  
• You didn't account for the mountain blocking your path at that altitude. *crash*
  
• Landing on that 50-degree mountain slope caused you to gain speed sliding down, tumble, and crash.
  
• The very expensive engine exploded because we landed a touch faster than the engine's tolerance.
  
• Expensive parts exploded because the recoverable stage tipped over upon landing.
  
• The stage landed too far from KSC, resulting in a puny part refund.

[Lystent]

I just use a single-stage space plane, if low kerbin orbit is all I am after. They can get real small, or be a winged space station, and can return back to the surface without losing a single part (baring any accident from pilot/ design error).

[RoofCat]

LKO efficiency is weird thing. Because there are a few different, even contradicting efficiencies.

If you mean real time (your life) efficiency, it is rather quick, disposable vertical launch.

If you mean like cost efficient, this is probably cheapest way to get men in orbit. Even though you dispose Thumper, that's less than 1ooo and tiny heatshield is even cheaper as decoupler. So landing close to KSC you should still get around 1ooo back.
https://steamcommunity.com/sharedfiles/filedetails/?id=1399847529

If you mean delta v efficient, you have to use explosive, semi-horizontal launch. This is one of the lowest delta v I have managed to get to LKO. It's nowhere cheap or useful as for payload though as you can see. The delta v is an estimate as I have used average real Isp values over the course to be more accurate, but those still aren't perfectly accurate due to extended burn in the end and just 5 readings used for each stage to find approximate average (at 100-75-50-25-0 fuel). KER is even worse to do this math as it uses fixed Isp afaik, so there is that.
https://steamcommunity.com/sharedfiles/filedetails/?id=1421440591

If you mean for reusable, spending more initial costs on launch, spending a lot of real time to land it back on runway, but reaching 100% salvage besides fuel, of course you would choose RAPIER cargo planes. Simply because of Isp. You can go further and fuel at start those from mining station next to runway. So kind of zero costs. Refuel after landing again and make it profit. Well, if you enjoy being that stingy.
Sooner or later you will figure out even MK3 isn't large enough for some stuff and then MK3 cargo bays are also very heavy. So you could fool around with some launch systems with external cargo attachment. They aren't as simple due to more drag and balance issues, but the main isssue is structural rigidness as there aren't great parts to builld this stuff in KSP and also because structural loops aren't possible except for struts in KSP. Here is what my bored mind has created at some point just for some fun.
https://steamcommunity.com/sharedfiles/filedetails/?id=1307354079
https://steamcommunity.com/sharedfiles/filedetails/?id=935347445


Is it worth saving 1ooo$ in KSP at all? Well it's up to you.

[andylaugel]

For a bit of fun, I ran a practical experiment. In both cases the "payload" in both cases was mostly the same, a vessel that can grab a bit of space debris in LKO and return it to Kerbin's surface.

Please note this is based on my abilities and comfort level. I'm certain others can build more efficient rockets and spaceplanes.

The Disposable Launcher

https://steamcommunity.com/sharedfiles/filedetails/?id=1571235522
Net Cost to Put Payload into Orbit: 7,330 funds.

• 19,250 total vessel cost
  
• 11,920 payload cost

Time spent: 3 minutes, 6 seconds.
Note: The payload did use a few hundred dV circularizing its own orbit.

Reusable Launcher

https://steamcommunity.com/sharedfiles/filedetails/?id=1595517639
Net Cost to Put Payload into Orbit: 2,798 funds.

• 112,854 total vessel cost
  
• 12,580 payload cost
  
• 97,476 refund for spaceplane recovered while landed on KSC's runway

Time spent: 20 minutes, 8 seconds. Payload detached at 7 minutes, 7 seconds.
Note: This reusable spaceplane is a little overkill, and also carries two kerbals and some fuel it can offload in LKO.

Conclusions

The disposable launcher was 17 minutes faster, but cost 4,532 funds more--and didn't provide the option of tossing a couple of kerbals into LKO and back too. Assuming a perfect runway landing that is...

If the reusable solution is only recovered for 95.3% of its value though, it's break even on cost. Or a loss if you get even less back for the spaceplane.

[doum]

All the above or Alt f12.