(Re)building rockets for economic efficiency

[Thomas Cook]

Hello everybody.

I've been playing KSP for about two months now and I love it. Currently I've been training a lot to get the basic maneuvers right, and it goes very well lately. Always within the Kerbin boundaries though, but currently I'm thinking about making a fleet to get my first steps to Duna.

However since 0.21 I'm aware that in a future release, you will get to build rockets within financial limits. Until now I just grabbed everything off the shelf whatever I needed, overkill or not. Lately I've been looking at all the rockets I've built. All of them did the job decent to very nicely. However I've noticed that I haven't built my rockets very efficient from an economic standpoint. I can also see that in the following situations.

Examples:

1. Having to ditch a lot of my launcher stages in sub/lower orbit with a lot of fuel left in them.

2. Returning from a mission to Kerbin atmosphere with a tonload of fuel left, something you dragged along all that time.

3. Having to ditch a pretty big ship on the Kerbin surface. Only the command module with the Kerbals in them needed to be saved with parachutes. The rest will be unrecoverable as it crashes.

Do you have some more information how to build or rebuild rockets to make them do "the same with less"? Or if you build a new rocket for a mission, what do you do to keep your rocket lean and cheap? Do you take into consideration if you want to recover as much as possible for example and how?

I know this is not a technical question that can be answered with a single answer. However I do think that a mixture of answers can make my rockets much simpler, better and cheaper.

As an extra info:

I'm not making use of MechJeb, and not planning to in the near future. Currently I only make use of the Kerbal Engineer and the Subassembly Manager.

My sincere thanks in advance for all the input you give.

Edited September 10, 2013 by Thomas Cook

[SaturnVee]

Using Kerbal Engineer, when you are designing your ships in the VAB make them so that the delta-v they possess is the amount required for the mission at hand, so that you don't end up with a bunch of leftover fuel at the end worth a thousand or two surplus delta-v. You can find out how much delta-v it takes to get to x and y and then return online.

Edited September 8, 2013 by SaturnVee

[zekes]

ive found that as re-usability (and efficiency) of a rocket increases, the gross tonnage to orbit decreases. So bigger payloads mean more costs, and smaller payloads can be brought up with only the cost of the fuel.

[Johnno]

Since you're using Engineer the route I'd suggest is pretty straightforward. Start by finding a delta-v map (this one courtesy of the wiki for example), I also personally like using alexmoon's planner.

Then design your mission/flight backwards, that is first figure out what do you need to return from whatever location. 3-man pod, bit of fuel, engine, power, doesn't take much really. Next, build the lander, for that one as well you can do it as a singlestage or do it in several stages, in which case work backwards there as well; what do you need to return to orbit for docking, what do you need for descent.. etc.

Next figure out what do you need to get that whole lot there, ie interplanetary stage. You can build one by placing a 'dummy mass' above that simulates the mass of your lander + return craft, then adjust fuel/engines to have enough delta-v to get you from Kerbin orbit to your location.

If you've built all this light enough, you can get it all up in one go, in which case you simply build a launch vehicle with 4500-5000 m/s delta-v to get the whole lot into Kerbin orbit. Alternatively, assemble the different parts in orbit.

[rpayne88]

When they introduce career mode, which I think you're preparing for, if they include maintenance costs, it may be cheaper to use expendable systems. One of the major price tags for the shuttle program was the refurbishment of the orbiter follower each launch. When you think about it, oxidizer is corrosive and TPS tiles had to be replaced. The SRBs had to be recovered and refurbished.

If you play stock and still want re-usability, just strap chutes to every thing. If you use mods, it might be might be easier to place them inside decouplers.

As far as determining efficiency, take the mass of your payload divided by the cost of your rocket. This will give you the cost of pound to orbit (or kilogram, ton, ect.) The lower the number, the more economically efficient your design is.

[Thomas Cook]

Since you're using Engineer the route I'd suggest is pretty straightforward. Start by finding a delta-v map (this one courtesy of the wiki for example), I also personally like using alexmoon's planner.

Then design your mission/flight backwards, that is first figure out what do you need to return from whatever location. 3-man pod, bit of fuel, engine, power, doesn't take much really. Next, build the lander, for that one as well you can do it as a singlestage or do it in several stages, in which case work backwards there as well; what do you need to return to orbit for docking, what do you need for descent.. etc.

Next figure out what do you need to get that whole lot there, ie interplanetary stage. You can build one by placing a 'dummy mass' above that simulates the mass of your lander + return craft, then adjust fuel/engines to have enough delta-v to get you from Kerbin orbit to your location.

If you've built all this light enough, you can get it all up in one go, in which case you simply build a launch vehicle with 4500-5000 m/s delta-v to get the whole lot into Kerbin orbit. Alternatively, assemble the different parts in orbit.

Thanks fo your input Johnno. That was very interesting. I'll definitely take it into consideration. In that way you really build the thngs you need, instead of what you think you need. Also by using 'dummy mass' you can also test if the ship works as a total, unlike each part seperately. I'll test this whole process comparing a new mun rover lander with an old one I've made. See if I can make it smaller and cheaper.

[Captain Sierra]

Though not super economical, my new Guppy orbiter lineup is small, effective, and efficient. It is based heavily on 1.25m parts over 2.5m parts so it is considerably cheaper than a system of equal power and capability made from 2.5m parts.

http://forum.kerbalspaceprogram.com/showthread.php/49222-Holy-flying-fish%21-It-s-Guppies%21-Guppy-series-orbiters-from-SSI

[Thomas Cook]

When they introduce career mode, which I think you're preparing for, if they include maintenance costs, it may be cheaper to use expendable systems. One of the major price tags for the shuttle program was the refurbishment of the orbiter follower each launch. When you think about it, oxidizer is corrosive and TPS tiles had to be replaced. The SRBs had to be recovered and refurbished.

If you play stock and still want re-usability, just strap chutes to every thing. If you use mods, it might be might be easier to place them inside decouplers.

As far as determining efficiency, take the mass of your payload divided by the cost of your rocket. This will give you the cost of pound to orbit (or kilogram, ton, ect.) The lower the number, the more economically efficient your design is.

Thanks rpayne88. That is indeed the meaning of the question. Career mode can introduce some new aspects I haven't taken into consideration at all unitl now. Ofcourse it also depends what Squad will have in store for us. Do they introduce maintenance or repair costs for broken parts? Payrolls for Kerbals you hire? Costs for R&D?

One thing for sure is rocket building costs, and I want to lean up my building style. At least getting more aware of it.

Your idea of the "Cost to Weight" ratio is awesome.

[Thomas Cook]

Hey Johnno. I've just finished a simple mission I've played about 6 weeks ago, rebuilding the whole ship again from scratch. It was fun to do and it taught me quite a while. I did play it in version 0.20 though, instead of 0.21 as I didn't move my ships to 0.21 yet.

The mission back then was to send a 2 Kerbal landing ship with a simple rover to the mun.

Image of original lander.

Old ship design.

When I made it I was pretty proud I achieved it. Keep in mind that when I built this I was way less experienced. When I look at this now I almost feel ashamed to share it. The ship had 147 parts, weighed 310.15 tonnes and cost around 142,260.

Once I had the delta-v map and your process of how to build your ship efficiently, I quickly realised I didn't need the "interplanetary" vessel in the middle at all. Since the lander only had to operate in space or on the mun, I just needed about 300 units of fuel extra. The four LV909 engines had more than enough thrust and are pretty efficient since they only needed to land on the mun.

A whole simplification process began, ending in the following ship:

New ship design.

As you can see it just has the lander on a +/- 5000 delta-v lifter.

Lander design.

The lander got a decoupler, and an extra tank with three small engines, just to bring me back to Kerbin.

The total rocket now has 93 parts, weighed around 197.7 tonnes and cost around 92,370. That was a 100 tonnes and 50K reduction. Awesome.

There was some stuff left unrecoverable in 0.21, but I think I can find solutions to that as well:

1. as mentioned: adding parachutes to the lifter stages.

2. adding parachutes to the lander so I can fly the whole thing back to kerbin and save it.

3. Need to find a way to redock the rover to the lander, to bring it back along to Kerbin.

I think I start to get the hang of this. Thanks.

[SRV Ron]

Some things to consider on a budget;

1. The smaller the payload, the less rocket is needed to get them into orbit.

Example, this launched a satellite into orbit with enough fuel to place into Mun orbit.

2. SRB first stages are cheaper then liquid fuel. (Especially recycled ones that NASA used for the Minotaur mission.)

This was my example with a large SRB;

3. Experiment. Start small and work up.

This one landed a probe on Duna. The probe has been since redesigned for less weight and better stability.

Edited September 8, 2013 by SRV Ron

[Vanamonde]

You can do the deltaV math to keep things from getting out of hand during construction, but practice never perfectly matches the math. So I approach efficiency by making a design intentionally a bit bigger than it needs to be, test it, and then pare down the design wherever testing reveals a surplus.

But there's another approach. Make the whole ship reuseable, so that it doesn't matter how much it originally costs because you can just keep refuelling it and using it for mission after mission, like this: http://forum.kerbalspaceprogram.com/showthread.php/48610-My-roundtrip-ships-for-download.

[Dispatcher]

@ Johnno: thanks for the link to alexmoon's interactive site. The results look like porkchop charts and there is a ton of info with each result. More charting info can be found at http://www.projectrho.com/public_html/rocket/mission.php#porkchop but the alexmoon site is all that's needed to calculate the delta V for any particular mission.

[tizalee]

I really don't know anything about it. But pictures you have posted are awesome. A little I know is that it is necessary to rebuild rockets for economy efficiency. By this we will be able to save precious money for some other causes.

[el_coyoto]

Some things to consider on a budget;

1. The smaller the payload, the less rocket is needed to get them into orbit.

Example, this launched a satellite into orbit with enough fuel to place into Mun orbit.

2. SRB first stages are cheaper then liquid fuel. (Especially recycled ones that NASA used for the Minotaur mission.)

This was my example with a large SRB;

3. Experiment. Start small and work up.

This one landed a probe on Duna. The probe has been since redesigned for less weight and better stability.

Agreed.

I've recently discovered the pleasure of building small, reusable and efficient probes launchers (using Mission Controller as an incentive), and I noticed that there were many cheap staging options to launch probes that I hadn't considered before :

- SRB as a first stage can do wonders (don't forget the winglets! )

- A LV-909 has more than enough thrust to lift a small probe (including its engines and fuel), and can bring it very high in Kerbin atmosphere. I often used them as the 1st or 2nd stage (if I have a SRB underneath) of my launchers. You don't always need a LV-T45 to launch a small probe.

- Rockomax 48-7S DOES pack quite a punch and is a very powerful addition to the game. For small probes it is very efficient and is an excellent choice for a probe orbital injection stage.

Of course, the last step towards a fully reusable space program is adding parachutes to all your stages and making sure they land softly, thanks to this wonderful online parachute calculator : http://ksp.freeiz.com/.

Cheers!

[SRV Ron]

Some of the Nova Punch mods have inexpensive alternatives including a liquid fueled booster that is cheaper then a SRB. But, be aware that it has no vectoring built in. The small probe launcher uses an engine similar to the LV-909 with a bit more thrust.

So far, I have not needed fins in 021 although I do need an SAS controller below the small probe stage since the StayPutNik SAS is not strong enough to stabilize the larger boosters. The SAS becomes dead weight past its use on the first stage causing shake and forcing me to disable it.

Until career mode allows for recovery cost, it remains cheaper to use small boosters once. (Although you can return probes to Kerban via parachutes and recover them.)

Edited September 9, 2013 by SRV Ron

[Thomas Cook]

You can do the deltaV math to keep things from getting out of hand during construction, but practice never perfectly matches the math. So I approach efficiency by making a design intentionally a bit bigger than it needs to be, test it, and then pare down the design wherever testing reveals a surplus.

But there's another approach. Make the whole ship reuseable, so that it doesn't matter how much it originally costs because you can just keep refuelling it and using it for mission after mission, like this: http://forum.kerbalspaceprogram.com/showthread.php/48610-My-roundtrip-ships-for-download.

Thanks Vanamonde. It's true that you should never match exactly the amount of delta-v shown on maps, because I would always like to have some extra margin for errors or mistakes. Construction is something I got under control the last mission. Now I'm going to try (as you said) to build the mission as reusable as much as I can. I need to be able to salvage:

1. The skipper boosters on the side.

2. The lander part of the lander. I think I can save it by adding parachutes and a bit more fuel to bring it back to Kerbin.

[EDIT]

3. The rover. I need to get it reattached to the lander once I'm done. Maybe some RCS can do the trick.

[Thomas Cook]

Some things to consider on a budget;

1. The smaller the payload, the less rocket is needed to get them into orbit.

Example, this launched a satellite into orbit with enough fuel to place into Mun orbit.

2. SRB first stages are cheaper then liquid fuel. (Especially recycled ones that NASA used for the Minotaur mission.)

This was my example with a large SRB;

3. Experiment. Start small and work up.

This one landed a probe on Duna. The probe has been since redesigned for less weight and better stability.

Thanks SRV Ron. This is indeed a very good way to start cheap with smaller ships or satellites.

However do you also think the SRB's could be usefull on bigger vehicles?

[SRV Ron]

Thanks SRV Ron. This is indeed a very good way to start cheap with smaller ships or satellites.

However do you also think the SRB's could be usefull on bigger vehicles?

Not only are they useful on bigger rockets as strap on or first stage. the Nova Punch pack has some real monsters in SRB to experiment with for your interplanetary designs. Again, only useful for first stage or boosting your first stage during launch. They are too heavy otherwise for upper stage use.

Be sure to brace them so they don't wobble and fly off. They also tend to be hard to steer so are best for boosting your rocket straight up to 5,000 meters.

Edited September 9, 2013 by SRV Ron

[Superfluous J]

I'm not bothering to worry about cost until they give me - in game - a way to easily see the cost of a ship, its total and dry mass, and its delta-v. Preferably those last 3 should be visible in the VAB (and SPH) and in-flight at any time with the push of a button.

Until then, I just try to build so I end up at my destination with as little fuel as is possible, and call it efficient.

Regarding putting parachutes on everything: That doesn't seem to work well because as soon as the objects go to on-rails physics, they disappear because they're in the atmosphere. Unless something it added to the game to auto-recover anything in atmosphere with deployed parachutes, I don't see the reason for adding the extra mass.

[SRV Ron]

An extreme example of added boosters. This is under an onion stage Eve probe lander. Not a recommend setup. Cross bracing is a must for stability during launch and flight or it will tip over. The six boosters reach about 5K at burnout. The asparagus hit Kerban escape velocity with 1/2 a tank in the core stage. The design did not spin, with or without those six boosters. Without the SRB, the design reaches 100k orbit just as the core stage ran dry.

Edit;

Experimenting with the asparagus stage rocket. With three boosters instead of the asparagus, I got a good results with the probe capable of reaching Duna under ideal conditions. With 4 boosters, I had 20 more units of fuel on the second stage for orbit. With six boosters, an additional 20 units. Not much bang for the extra bucks. There is an ideal number in which doubling them yields little additional benefits for a given design. Same for liquid fueled boosters unless they are asparagus staged which cannot be done with SRB.

Edited September 10, 2013 by SRV Ron

[Thomas Cook]

As a last post before I change this to "answered".

I've redone the mission again. The only difference is instead of just bringing home the capsule, I tried to bring back the entire lander back to Kerbin.

It all went pretty well except the landing on Kerbin, where something odd happened.

Reentry picture of the original lander

Since I had very little fuel left (about 182 units) I transfered all the remaining fuel to 2 of my engines, opposite of each other to keep stability.

Image of parachutes deployed

I deployed my parachutes and they deployed very well. However I saw that I was still dropping at 15m/s, which is too fast to keep the lander intact.

So at the last 100 meters I fired up my engines to slow down to 8m/s. However the whole shuttle crashed in the ocean breaking everything, including the command pod.

I don't really know why it happened, as 8m/s is an acceptable landing speed in my experience.

However that's another question apart from this one. I think I got the basics covered in how to build efficient rockets, and I'm definitely going to use it more because it was a lot of fun to work on this. Everybody that added their input I thank you all.

[el_coyoto]

As a last post before I change this to "answered".

I've redone the mission again. The only difference is instead of just bringing home the capsule, I tried to bring back the entire lander back to Kerbin.

It all went pretty well except the landing on Kerbin, where something odd happened.

Reentry picture of the original lander

Since I had very little fuel left (about 182 units) I transfered all the remaining fuel to 2 of my engines, opposite of each other to keep stability.

Image of parachutes deployed

I deployed my parachutes and they deployed very well. However I saw that I was still dropping at 15m/s, which is too fast to keep the lander intact.

So at the last 100 meters I fired up my engines to slow down to 8m/s. However the whole shuttle crashed in the ocean breaking everything, including the command pod.

I don't really know why it happened, as 8m/s is an acceptable landing speed in my experience.

However that's another question apart from this one. I think I got the basics covered in how to build efficient rockets, and I'm definitely going to use it more because it was a lot of fun to work on this. Everybody that added their input I thank you all.

In my experience, splashdowns in KSP don't work very well : I've seen designs that could withstand rough landings on earth explode when touching the ocean at roughly the same speed.

Also, during my own take on a reusable space program, I noticed that the SpaceX approach to reusing boosters works wonders.

My medium and heavy lifters often use asparagus staging. The "stalks" receive parachutes, but I usually design my core booster so that it can put the payload in LKO with a bit of fuel left. Once free from its heavy payload, the core booster needs only fumes of fuel to deorbit and soft land (less weight -> more delta-V and more TWR).

Despite the probe and power needed to control the core booster during re-rentry and landing, it seems more efficient than parachutes. I just let the booster slow down to terminal velocity over KSC, then "suicide burn" at the last moment (using the very high TWR) before touching down.

Showing off a bit...