Rules of Thumb for Building Cheap and Cheerful Rockets

[GoSlash27]

Norcalplanner,

I'm putting together a series of cheap disposable lifters and have a couple points to add on SRBs:

1) If you're building a 2 stage rocket, the first stage will be thrown away during launch with no recovery value (assuming you're playing without mods). Therefore your first stage should always be SRBs.

2) surface attached clusters of SRBs are very useful. You can adjust the throttle in opposing pairs of boosters to regulate the thrust throughout the launch.

My best disposable launcher at the moment can orbit 31t of payload and costs $35,000 (less if the payload controls the launch vehicle).

3) If you're going for ultimate cheapness, then the entire LV should be recoverable. Thus no staging and thus no SRBs.

Best,

-Slashy

[Starhawk]

This is wonderful stuff, Norcalplanner. Thank you.

A point about LFO tanks that I think might be salient. When using a stack that contains different lengths of tanks in a single stage, it is better to place the shorter tanks at the top of the stack. This improves where the CoM ends up when the stack is almost empty.

Happy landings!

Edited October 21, 2015 by Starhawk

[Meithan]

Thanks for the feedback, Meithan. Love your chart app, BTW.

Thanks!

If you had sufficient rotational control authority via reaction wheels, then four ports placed around the CoM should give adequate translation ability. You could use the main engine on the craft to thrust forward, and would need two symmetrical ports on the front of the craft, on either side of the docking port, to slow down and reverse. The six ports would give the same translation authority as four of the multi-directional ports (one port at 2 kN vs. two ports at 1kN each) at a slight savings in cost (1680 funds vs. 2480 funds) and weight (0.18 tons vs. 0.20 tons) but with two more parts. My gut tells me that wobble will be a bigger problem if the ports aren't right over the CoM. I'll need to test this in game before deciding if it's a good or bad idea.

Yup, I use the reaction wheel for rotation, and the RCS for translation only. I usually go with 8 linear ports (adding two back-facing ports), which comes at nearly the same cost and weight as 4 RCS blocks. I find that shutting down the main engine during docking is a good idea (I did have some accidents with that when I was learning to dock).

If your ship has a reaction wheel (and pretty much all my ships do), there's no point in spending your RCS fuel for rotation. Before I switched to linear ports, I used to alternate switching RCS on and off during dockings to save monoprop on rotations. With the linear ports + reaction wheel, I leave RCS on all the time during docking.

I may have to also try my other oddball RCS idea - that it's possible to dock a craft using only two multi-way RCS blocks. Since you'd only get translation in one axis, you'd have to rotate the craft around its long axis to align the thrusters with the needed translation vector for every correction. Sounds a bit crazy, but I bet that Jeb would be up for it. If he can get it to work, it would be the cheapest, lowest weight, and lowest part count solution for RCS-assisted docking.

It's entirely possible, but IMO it's just not worth the hassle. I think that even with Cheap and Cheerful, there should be cases when a little extra cost/mass/complexity is worth it if it makes life considerably easier. Full 3-axis control during docking is one of such things for me.

[wumpus]

Is Kerbal Engineer buggy, or is it just my installation (which should be current, but I had problems with it)? My copy has different values for TWR in the VAB and on the pad, with the pad values looking more accurate. I was trying to get data justifying higher TWRs, when I realized that what I thought my TWR was (as set in the VAB) was likely way higher anyway."

"RoT 3.6 - For serial staged LFO rockets, the upper stage should have thrust between 1/3 and 1/6 of the lower stage."

Usually (in non-kerbal guides) I see this written as "mass of upper stages should be around 1/4 of the lower stage". Going by thrust will have much higher mass, but should make up for it with much higher ISPs. A better rule of thumb (not seen enough in the kerbal community) is to keep the delta-v between stages roughly equal (which obviously doesn't come into play in C&C designs until you are using enough kickback SRBs to have much control over your stage 1 delta-v). Note that equal delta-v stages is only a rule of thumb and not always optimal.

Recovery also throws a monkey wrench into everything (assuming "cheap" equals "less cost" during career). One way to work it is to use SRBs for the first stage (jettisoned first stages landed before hitting 3000m seems a fools errand, although I'm curious if it works), followed by a recoverable second stage: stage 2 needs airbrakes, , and enough fuel/delta-v to get itself into orbit (once payload has taken off) and back to KSC. The key here is that once the payload is launched the remaining booster is light enough that circularizing takes very little fuel to get back to KSC. On the other hand, this gets sufficiently tiresome to burn me out of KSP for awhile (mechjeb is both too inefficient to land like I want it to land (low fuel usage) and too efficient to always hit the landing pad for 100% recovery when it does work).

[Norcalplanner]

Lots of good points here in the last few posts. I'll respond as soon as I can, which will probably be later tonight.

[Meithan]

Recovery also throws a monkey wrench into everything (assuming "cheap" equals "less cost" during career).

Yup, this is something that hasn't been mentioned (neither here nor in that other Delta-v vs. TWR discussion thread): recoverable launchers can substantially change the picture, I think.

All my launchers are recoverable single-stage with expendable SRBs designs. For instance, my Titan Heavy launcher can put 36 tonnes to ~80 km orbit. The central stage returns to Kerbin and lands on parachutes (it has landing legs to protect the engine on touchdown; it must land on solid ground, though). Recovery close to KSC gives back >95% of the cost of the stage, which has the expensive liquid engine, for <32k total expenditure per launch, yielding less than 900 funds per tonne of payload. And frankly I haven't spent much time optimizing it; I'm sure it can be made cheaper.

Anyway, I'll let Norcalplanner get to the previous topics before going into this.

[passinglurker]

On reusable lifters I'll just say that they may be "cheap" but they are not cheery what you save in funds you ultimately spend in time performing these recovery maneuvers.

[Norcalplanner]

Norcalplanner,

I'm putting together a series of cheap disposable lifters and have a couple points to add on SRBs:

1) If you're building a 2 stage rocket, the first stage will be thrown away during launch with no recovery value (assuming you're playing without mods). Therefore your first stage should always be SRBs.

2) surface attached clusters of SRBs are very useful. You can adjust the throttle in opposing pairs of boosters to regulate the thrust throughout the launch.

My best disposable launcher at the moment can orbit 31t of payload and costs $35,000 (less if the payload controls the launch vehicle).

3) If you're going for ultimate cheapness, then the entire LV should be recoverable. Thus no staging and thus no SRBs.

Best,

-Slashy

Slashy,

Thanks for your comments. I look forward to seeing your lifters. Seeing how other people do things can result in a healthy cross-pollination of ideas and techniques.

I agree that a Cheap and Cheerful lifter should always have SRBs in the first stage, but I'm a bit hesitant to say that it should "always and only" be SRBs, if I'm hearing you correctly. Part of the Cheap and Cheerful philosophy does include an ease of use factor, which is one of the ways it contrasts with the use of SSTO spaceplanes. (And yes, I feel moderately embarrassed to be saying this to one of the best SSTO spaceplane guys on the forums.)

We'll definitely need to include some examples of differential thrust limiting in launchers to manage TWR. I tend not to do it too much, but I have used it occasionally.

An SSTO rocket is generally the cheapest way in terms of cost, but the recovery time and skill required to "close the loop" and make it pencil out compared to a cheap disposable rocket means that it's not going to be everyone's cup of tea. I did it a couple of times, but it always involved a precise reentry profile, a powered final descent in addition to parachutes, and landing on engine bells. It was a bit too nail-bitey for me to do on a regular basis.

I think I need to write an entry regarding the different spots on the Cheap and Cheerful continuum, noting how there are frequently tradeoffs which need to be made based on the player's available time, patience, and piloting skill in addition to things like cost and part count. I also have some vague ideas running around in my head regarding a challenge, but it's been done many times before and trying to come up with "Cheap and Cheerful" rules that don't quash creativity would likely be difficult.

- - - Updated - - -

This is wonderful stuff, Norcalplanner. Thank you.

A point about LFO tanks that I think might be salient. When using a stack that contains different lengths of tanks in a single stage, it is better to place the shorter tanks at the top of the stack. This improves where the CoM ends up when the stack is almost empty.

Happy landings!

Starhawk,

Good observation. I think some players (hopefully not many at this point) still put small tanks on the bottom because of the old issue with orange tanks overheating. I'll either add your point to the LFO tank discussion, or fold it into the future post I'm formulating about rocket geometry. This is one of the reasons I love Fuel Tanks Plus, by the way - because it has tanks like the Rockomax 128 (a double-length orange tank as a single part), it's much easier to have the rocket maintain a desirable CoM during ascent. This is in contrast to the frequent problems with rockets becoming bottom-heavy due to the fuel flow rules when using stacked tanks in the first stage.

Edited October 21, 2015 by Norcalplanner
clarified a point

[mudkest]

Starhawk,

Good observation. I think some players (hopefully not many at this point) still put small tanks on the bottom because of the old issue with orange tanks overheating. I'll either add your point to the LFO tank discussion, or fold it into the future post I'm formulating about rocket geometry. This is one of the reasons I love Fuel Tanks Plus, by the way - because it has tanks like the Rockomax 128 (a double-length orange tank as a single part), it's much easier to have the rocket maintain a desirable CoM during ascent. This is in contrast to the frequent problems with rockets becoming bottom-heavy due to the fuel flow rules when using stacked tanks in the first stage.

another option when you use mods is, cant remember the name from top of my head, but goodspeed fuelpump or something and set tanks to drain bottom to top.

[Norcalplanner]

Is Kerbal Engineer buggy, or is it just my installation (which should be current, but I had problems with it)? My copy has different values for TWR in the VAB and on the pad, with the pad values looking more accurate. I was trying to get data justifying higher TWRs, when I realized that what I thought my TWR was (as set in the VAB) was likely way higher anyway."

"RoT 3.6 - For serial staged LFO rockets, the upper stage should have thrust between 1/3 and 1/6 of the lower stage."

Usually (in non-kerbal guides) I see this written as "mass of upper stages should be around 1/4 of the lower stage". Going by thrust will have much higher mass, but should make up for it with much higher ISPs. A better rule of thumb (not seen enough in the kerbal community) is to keep the delta-v between stages roughly equal (which obviously doesn't come into play in C&C designs until you are using enough kickback SRBs to have much control over your stage 1 delta-v). Note that equal delta-v stages is only a rule of thumb and not always optimal.

Recovery also throws a monkey wrench into everything (assuming "cheap" equals "less cost" during career). One way to work it is to use SRBs for the first stage (jettisoned first stages landed before hitting 3000m seems a fools errand, although I'm curious if it works), followed by a recoverable second stage: stage 2 needs airbrakes, , and enough fuel/delta-v to get itself into orbit (once payload has taken off) and back to KSC. The key here is that once the payload is launched the remaining booster is light enough that circularizing takes very little fuel to get back to KSC. On the other hand, this gets sufficiently tiresome to burn me out of KSP for awhile (mechjeb is both too inefficient to land like I want it to land (low fuel usage) and too efficient to always hit the landing pad for 100% recovery when it does work).

wumpus,

Not sure about Kerbal Engineer on the TWR readings - I've been using only MechJeb for the last few months.

When I'm going for optimal delta V design, I'll use that 1/4 rule that you're talking about. The staged LFO probe that was mentioned as part of the exotic propulsion discussion uses just such an arrangement, consisting of an FLT-100 with an Ant, on top of an FLT-400 with a Spark, on top of a Rockomax 16 with a Terrier. All those stages have approximately the same delta v, just like you said. I think what I was trying to say with that rule is that if the bottom stage is a Mainsail, it's better for the next stage to be a Poodle than a Skipper. The Skipper would be more appropriate on top of a Twin Boar or a Rhino. For a stage on top of a Skipper, I'd go with the Big Impulse 120 kN orbital engine from Randazzo's Vanguard VX engine pack, mentioned earlier, since a Poodle would be too big and a Terrier too small for the rule. I'd agree that there's lots of room for different designs which can all work.

Recovery is a whole other kettle of fish, which I'm now convinced needs its own entry as part of the Cheap and Cheerful discussion. Essentially, you have to decide what resources are most important to you, both in-game and in real life (such as your patience and time available to play the game). I discussed this a bit in a previous response - I'll come up with something that weighs the pros and cons of different levels of recovery and distills them into a few Rules of Thumb.

Thanks for the observations and for the real life Rules of Thumb regarding rocket stage mass and delta V.

- - - Updated - - -

Yup, this is something that hasn't been mentioned (neither here nor in that other Delta-v vs. TWR discussion thread): recoverable launchers can substantially change the picture, I think.

All my launchers are recoverable single-stage with expendable SRBs designs. For instance, my Titan Heavy launcher can put 36 tonnes to ~80 km orbit. The central stage returns to Kerbin and lands on parachutes (it has landing legs to protect the engine on touchdown; it must land on solid ground, though). Recovery close to KSC gives back >95% of the cost of the stage, which has the expensive liquid engine, for <32k total expenditure per launch, yielding less than 900 funds per tonne of payload. And frankly I haven't spent much time optimizing it; I'm sure it can be made cheaper.

Anyway, I'll let Norcalplanner get to the previous topics before going into this.

Yep - definitely need to have a discussion and Rules of Thumb for various levels of recovery. Maybe that could be a challenge - lowest cost to orbit for various categories of rocket recovery - SSTO, SSTO with disposable SRBs, and disposable staged. Still need to think about that some more, especially since I got burned out on running my other challenge.

- - - Updated - - -

On reusable lifters I'll just say that they may be "cheap" but they are not cheery what you save in funds you ultimately spend in time performing these recovery maneuvers.

While I agree, I don't think everyone would. I'll fold this into the recovery discussion, which hopefully will be ready in a day or two.

[Sanic]

SRB spam works!

[GoSlash27]

Slashy,

Thanks for your comments. I look forward to seeing your lifters. Seeing how other people do things can result in a healthy cross-pollination of ideas and techniques.

I agree that a Cheap and Cheerful lifter should always have SRBs in the first stage, but I'm a bit hesitant to say that it should "always and only" be SRBs, if I'm hearing you correctly. Part of the Cheap and Cheerful philosophy does include an ease of use factor, which is one of the ways it contrasts with the use of SSTO spaceplanes. (And yes, I feel moderately embarrassed to be saying this to one of the best SSTO spaceplane guys on the forums.)

We'll definitely need to include some examples of differential thrust limiting in launchers to manage TWR. I tend not to do it too much, but I have used it occasionally.

An SSTO rocket is generally the cheapest way in terms of cost, but the recovery time and skill required to "close the loop" and make it pencil out compared to a cheap disposable rocket means that it's not going to be everyone's cup of tea. I did it a couple of times, but it always involved a precise reentry profile, a powered final descent in addition to parachutes, and landing on engine bells. It was a bit too nail-bitey for me to do on a regular basis.

I think I need to write an entry regarding the different spots on the Cheap and Cheerful continuum, noting how there are frequently tradeoffs which need to be made based on the player's available time, patience, and piloting skill in addition to things like cost and part count. I also have some vague ideas running around in my head regarding a challenge, but it's been done many times before and trying to come up with "Cheap and Cheerful" rules that don't quash creativity would likely be difficult.

Norcalplanner,

Not a problem. Thanks for starting the thread!

Unfortunately, my back problems make it impossible for me to "fly" every day so development is slow. Here's the "Cheep31" (still tweaking):

http://wikisend.com/download/177932/cheep31.craft

Launch profile is simply "hit spacebar and hold D until the first stage is expended".

For disposable 2 stage launchers, the key to being "cheap" is in using SRBs exclusively for the first stage. No LF tank and engine combo can match the SRB in terms of cost effectiveness. But having said that, it can impact the "cheerful" factor if not done right because SRBs don't throttle, thrust- vector or generate electricity.

That is easily remedied with staggering the thrust, a couple tailfins, and a battery if needed.

This results in a cheap booster stage that isn't any more difficult to get to the injection phase than a LF&O booster would be.

And FWIW I agree with you about the SSTOs. Not only do they require recovery, they also carry a risk of failure because they cost so much more to build and there's a chance of destroying them. SSTOs are a whole lot cheaper, but also a whole lot less cheerful.

[Meithan]

On reusable lifters I'll just say that they may be "cheap" but they are not cheery what you save in funds you ultimately spend in time performing these recovery maneuvers.

An SSTO rocket is generally the cheapest way in terms of cost, but the recovery time and skill required to "close the loop" and make it pencil out compared to a cheap disposable rocket means that it's not going to be everyone's cup of tea. I did it a couple of times, but it always involved a precise reentry profile, a powered final descent in addition to parachutes, and landing on engine bells. It was a bit too nail-bitey for me to do on a regular basis.

Recovery is a whole other kettle of fish, which I'm now convinced needs its own entry as part of the Cheap and Cheerful discussion. Essentially, you have to decide what resources are most important to you, both in-game and in real life (such as your patience and time available to play the game).

Agreed. As a guy who is currently running entirely on recoverable single-stage rockets, I'll attest to how much of a pain it can become. I've had quite a lot of practice now, and I can land close to KSC (usually some kilometers west of KSC) with little effort, and landing legs mean I don't need powered descent. Even so, it's very time-consuming. I think the reentry and landing take more time than the launch itself, so I'm more than doubling the times to launch stuff to orbit.

I'm planning a 12-ship Duna flotilla for my next launch window and I'm definitely not looking forward to recovering all those lifters.

Honestly, I'm hoping for you guys to convince me to go disposable two-stage again. I'll cheerfully spend more per tonne to orbit just to get rid of the chore of returning the rockets. And staging a stack is cool - I miss it.

Yep - definitely need to have a discussion and Rules of Thumb for various levels of recovery. Maybe that could be a challenge - lowest cost to orbit for various categories of rocket recovery - SSTO, SSTO with disposable SRBs, and disposable staged. Still need to think about that some more, especially since I got burned out on running my other challenge..

Hasn't there been a "classic-rocket lowest cost per tonne" challenge in 1.0? I'd be surprised, but a quick forum search didn't find any. RIC is still hosting a Payload Fraction Challenge, but those designs are not meant to be Cheap and Cheerful (and that's the new official name of my preferred design philosophy ).

Edited October 22, 2015 by Meithan

[Norcalplanner]

9. Stage Recovery

Recovery of dropped stages, up to and including SSTO rocket lifters, can reduce funds expenditures dramatically for your space program. It can also result in additional costs, both in-game and in real life. Here are the Cheap and Cheerful Rules of Thumb for Stage Recovery.

RoT 9.1 - Recovery of lifter stages can reduce the amount of funds per ton of payload to orbit, but it isn't for everyone.

Choosing to recover stages represents a conscious choice to move the needle closer to "Cheap" and further away from "Cheerful". It will require more time, patience, and piloting skill to achieve recovery success at a high level. Because each launch and recovery will take at least twice as long as a launch with a disposable rocket, it will reduce the amount of launches you'll be able to do during a KSP play session. (It's very similar to RSS in that regard.) Weigh the impacts to your sanity and your available KSP time before committing to a high level of recovery in your space program.

RoT 9.2 - Recover your lifter parts as close to KSC as you reasonably can.

If you're a reentry pilot extraordinaire and can land your recoverable stages on the launch pad or the runway, you'll achieve the lofty goal of 100% funds recovery for that stage. For the rest of us, it's better to just try to get within a couple of kilometers of KSC, which will get you 95% recovery with a much bigger target to aim for. This means that your lifter has to have enough stamina (particularly electricity) to orbit Kerbin at least once before landing. Including airbrakes on your rocket can you help fine-tune your descent (especially along the E-W axis) and achieve a landing closer to KSC.

RoT 9.3 - Partial recovery is a viable option. Feel free to discard SRBs and only recover the LFO core.

Recovery is not an all or nothing affair. It's generally more worthwhile to recover the core of your lifter, with the expensive LFO engines, than it is to recover cheaper parts like SRBs. (SRBs have an additional strike against them in that they nearly always go into a suborbital arc, landing far away from KSC for a lower recovery percentage.) Don't be afraid to split the baby and go with a partially recoverable rocket, which can move the needle back toward "Cheerful". Discarding SRBs without concern for recovery also allows for a better balanced, easier to fly rocket due to the TWR drop after staging.

RoT 9.4 - Balance the cost of recovery hardware against the cost of the recovered stage.

Consider the full cost of the required recovery hardware, including funds, weight, and drag, when deciding whether to recover a stage. We'd all agree that putting a Mk-16XL parachute (850 funds) on top of a Hammer (175 funds when empty) makes little sense. Even the largest SRB, the Kickback, is only worth 1,140 funds when empty. When combined with the need for a probe core if the stage will drop out of physics range while in atmosphere, along with the reduced recovery percentage for a stage that lands hundreds of kilometers from KSC, only the largest, most expensive stages (typically LFO cores and asparagus stages) are worthy of recovery. The only real exception to this RoT is when using Kerbal Construction Time, where there is additional value assigned to recovered parts (time saved in building the next rocket), no matter where they come down.

RoT 9.5 - SSTO rockets can be appealing on paper, but they have drawbacks - and you have to stick the landing.

A pure SSTO rocket offers the potential for the highest level of funds recovery, but there are some big drawbacks. They're more expensive to construct initially than a disposable or partially recoverable rocket, and have a lower payload mass fraction. It can be difficult to fly an SSTO rocket to orbit with an efficient ascent profile when there's no staging and a constantly increasing TWR. The lack of a heat shield means you have to have a shallow reentry profile, which can make accurate landings more difficult. And because SSTO rockets tend to be tall with a narrow base, it's imperative to land someplace flat (yet still near KSC). If the rocket tips over, it's likely that at least some of it is going to explode, which will negatively impact the economics of your lifter.

RoT 9.6 - Mods can make recovery easier.

Some mods, particularly Stage Recovery, can help recover stages that would otherwise be lost. They can also partially automate the recovery operation itself, so you don't have to go into the Tracking Station after every flight and manually recover dropped parts. Stage Recovery is especially useful when used in combination with Kerbal Construction Time - it's almost as if both of them were created by the same modder...

- - - Updated - - -

Norcalplanner,

Not a problem. Thanks for starting the thread!

Unfortunately, my back problems make it impossible for me to "fly" every day so development is slow. Here's the "Cheep31" (still tweaking):

http://i52.photobucket.com/albums/g13/GoSlash27/Cheep31_zpsggouj1vi.jpg

http://wikisend.com/download/177932/cheep31.craft

Launch profile is simply "hit spacebar and hold D until the first stage is expended".

For disposable 2 stage launchers, the key to being "cheap" is in using SRBs exclusively for the first stage. No LF tank and engine combo can match the SRB in terms of cost effectiveness. But having said that, it can impact the "cheerful" factor if not done right because SRBs don't throttle, thrust- vector or generate electricity.

That is easily remedied with staggering the thrust, a couple tailfins, and a battery if needed.

This results in a cheap booster stage that isn't any more difficult to get to the injection phase than a LF&O booster would be.

And FWIW I agree with you about the SSTOs. Not only do they require recovery, they also carry a risk of failure because they cost so much more to build and there's a chance of destroying them. SSTOs are a whole lot cheaper, but also a whole lot less cheerful.

Slashy,

I've downloaded your craft, and will give it a whirl soon. My own experiences with SRB-only first stages have been somewhat mixed, so I'm curious to see what you've come up with.

- - - Updated - - -

Hasn't there been a "classic-rocket lowest cost per tonne" challenge in 1.0? I'd be surprised, but a quick forum search didn't find any. RIC is still hosting a Payload Fraction Challenge, but those designs are not meant to be Cheap and Cheerful (and that's the new official name of my preferred design philosophy ).

I looked too, and I didn't see one for the 1.0 era. The best match I could find is the 0.24 Cost-Effective Lifters Challenge, but that didn't have a very high level of participation. There was also the Heavy Lift Challenge a while ago, but that was about cheaply lofting a particular payload (orange tank plus some bits) than a pure funds/ton measurement for just rockets. If someone wants to run a 1.0.4+ Cheap and Cheerful Lifter Challenge, that would be fine by me. I'd even be happy to come up with the rules, but someone else would have to manage it and score the entries. My schedule is somewhat unpredictable these days with less free time, and people tend to get cranky when you don't score their entries for three or four days.

Edited October 23, 2015 by Norcalplanner

[celem]

Good observation. I think some players (hopefully not many at this point) still put small tanks on the bottom because of the old issue with orange tanks overheating..

Oh...

*scurries off to rebuild every 2.5m stack across 4 installations*

(otherwise...yeah, smaller tanks at the top)

Nice series of posts. Well thought out and adaptive to feedback, good stuff. Particularly interesting discussion on recovery, its not something I've really done for many many versions now. (havent really played since stock got heat and dont think i mucked about with recovery under DRE except at RSS scale).

StageRecovery mod was a lot of fun to use during my RSS career, but I found it mainly useful for the situations you list where other techniques dont work so well. Particularly 1st stage SRBs and early asparagus LFO cores. Once you get into the upper atmosphere and the later stages then stuff you drop is gonna burn up, I always suspected it was not allowing for orientation retrograde like a player would do to put the heat on the engine-bells. So I ended up letting StageRecovery take care of the first stage, and then manually re-enter the primary core for maximum refunds. This was my experience at RSS-scale at least, anything going sub-orbital will burn if you are not riding it, though the first stage does tend to land at 95% range even allowing for realistic (early) gravturns. Perhaps stock heat is less aggressive. Are you able to let stuff ride in from LKO unattended without the plugin declaring it incinerated?

[Sanic]

Just a small question about SRBs and staging.

I tend to fire my radial SRBs and then fire my LFO engine once the SRBs are burned out to save fuel.

Is this effective, just a waste of tome, or does it not matter?

[Norcalplanner]

Just a small question about SRBs and staging.

I tend to fire my radial SRBs and then fire my LFO engine once the SRBs are burned out to save fuel.

Is this effective, just a waste of tome, or does it not matter?

Sanic,

It works OK, but it's not as good as it could be. Any time you have an LFO engine that could be firing that currently isn't, you're giving up some efficiency. From a monetary standpoint, the cost of radial decouplers adds up quickly - if you're firing the SRBs first and then the LFO engine, save yourself some funds by making the entire first stage SRBs and then use a single stack decoupler. Doing it this way will also reduce drag caused by radially mounted decouplers and struts, and nearly eliminate any chance for SRB staging mishaps. If you want to post a photo of your rocket, I can probably provide some better comments.

The next (and possibly last) main post is going to have to do with rocket geometry and numbers - TWR, ratio of solids to LFO, how best to arrange the various parts for lower cost and higher performance, etc. I'll make sure to include an example that compares stacked SRBs to radial SRBs.

[Alshain]

SRB's have no gimbal, so generally speaking you want the LFO engine to fire at least at 1/4 throttle. Depends on the SRB you are using but if it's the Thumper or the Kickback you should be starting your gravity turn before they are finished, if not, something else is wrong.

[Norcalplanner]

Oh...

*scurries off to rebuild every 2.5m stack across 4 installations*

(otherwise...yeah, smaller tanks at the top)

Nice series of posts. Well thought out and adaptive to feedback, good stuff. Particularly interesting discussion on recovery, its not something I've really done for many many versions now. (havent really played since stock got heat and dont think i mucked about with recovery under DRE except at RSS scale).

StageRecovery mod was a lot of fun to use during my RSS career, but I found it mainly useful for the situations you list where other techniques dont work so well. Particularly 1st stage SRBs and early asparagus LFO cores. Once you get into the upper atmosphere and the later stages then stuff you drop is gonna burn up, I always suspected it was not allowing for orientation retrograde like a player would do to put the heat on the engine-bells. So I ended up letting StageRecovery take care of the first stage, and then manually re-enter the primary core for maximum refunds. This was my experience at RSS-scale at least, anything going sub-orbital will burn if you are not riding it, though the first stage does tend to land at 95% range even allowing for realistic (early) gravturns. Perhaps stock heat is less aggressive. Are you able to let stuff ride in from LKO unattended without the plugin declaring it incinerated?

celem,

Thanks for the feedback.

Regarding your question, it's been awhile since I've used Stage Recovery - I'll fire it up and make sure it still works the way I remember it does, then amend that post as necessary.

[Alshain]

For Stage Recovery, your upper stages aren't typically going to be worth the cost of recovery. Even at larger sizes you have to add so many parachutes, it outweighs the cost of the stage and even if the stage lands, it will be very distant from the KSC you don't get enough refund to warrant the chutes. SRB's are so cheap they aren't worth it either. I only put chutes on the first stage of my main stack. I don't use Asparagus (or Onion) at all, you can almost always build cheaper with a 2 stage stack and SRB radials, at least up until you start lifting the enormous payloads. So far my biggest lifter carries 100 tonnes to 100km, not a single fuel line in any of them, and for anything bigger I usually break them up into components at that point.

EDIT: Scratch that, I just got 120 tonnes to orbit. 1 Mammoth, 1 Rhino, 8 Kickbacks, 145,416 funds. No fuel lines.

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Edited October 25, 2015 by Alshain

[Norcalplanner]

For Stage Recovery, your upper stages aren't typically going to be worth the cost of recovery. Even at larger sizes you have to add so many parachutes, it outweighs the cost of the stage and even if the stage lands, it will be very distant from the KSC you don't get enough refund to warrant the chutes.

Alshain,

That's my gut feeling too, but I'm still going to play around with it a bit to see if I can improve on any of the Rules of Thumb I've already come up with.

[Alshain]

Alshain,

That's my gut feeling too, but I'm still going to play around with it a bit to see if I can improve on any of the Rules of Thumb I've already come up with.

Well the way it figures it, it takes the lowest percentile of speed or distance to KSC and that is your refund rate. So if your distance rate is 10% and your speed rate is 100%, you still get a 10% refund.

[Norcalplanner]

Well the way it figures it, it takes the lowest percentile of speed or distance to KSC and that is your refund rate. So if your distance rate is 10% and your speed rate is 100%, you still get a 10% refund.

STOP THE PRESSES!

Breaking news story...

It makes sense to recover Kickbacks using StageRecovery! More info at 11.

[celem]

Yeah thats how I understand it to reckon the numbers too, but I was finding (again...RSS scaled) that the SRBs have a tendency to come down nice and close. Im probably barely inclined when they get chucked (assuming stock ASL-tuned booster types).

Quite right that the recovery values need to be monitored, if it doesnt pay for the chutes its pointless..

In retrospect I imagine a lot of my different experience here has to do with NathanKell's RP-0 rebalance. My upper stages were not cheap, J-2s are shiny, and shiny stuff is always expensive.

The entire reason I got so heavily into StageRecovery during that particular career playthrough was the Rocketdyne F-1 in Saturn V config. You cannot ever afford to lose one of those motors as the driveblock has a 6-digit pricetag. Yes, I needed about 40 radial chutes to soft-land it, which drove the cost up even further....fine, but the engine bell must survive. There are very few pieces like that in the stock-game, even the 3.5m engines wont ruin you in that fashion if you pop them... But the one time I lost an F-1 it set me back years in the career (as i couldnt afford to launch anything interesting/heavy) and I then went looking for ways to avoid it.

Thanks for the feedback guys.

[Norcalplanner]

So here's what I did that caused me to change my position on recovering Kickbacks using StageRecovery.

I took Slashy's rocket, the cheep31, and modified it a bit. The cheep32 simply removed the Rockomax adapter, to reduce cost a little bit. That rocket cost 46,956 funds, and didn't have any appreciable change in performance from the original version.

A few iterations later, the cheep34 had eight radial parachutes on it, which added 3200 funds in cost, driving the price up to 50,156 funds.

Recovery of the bottom stage (7 Kickbacks, Rockomax decoupler, 2 Delta fins, and the 8 parachutes) was 115.44 km from KSC. Terminal velocity from the 8 parachutes was 7.95 m/s. At that distance and speed using stock StageRecovery settings, the recovery percentage is 82.8%, or 10,710 funds out of the total value of 12,930. Net cost of the rocket after the recovery was 39,446 funds.

That's 7,510 funds cheaper than the version without the parachutes.

Clearly more research is warranted and photos need to be put up, but it's late and I need to get up early in the morning. More information (including photos) should be posted tomorrow.