Rules of Thumb for Building Cheap and Cheerful Rockets

Norcalplanner · October 7, 2015

Welcome to my first-ever tutorial thread. I've picked up a lot of knowledge and formed some definite opinions about KSP ever since I started playing back in 0.23.5. I thought it was time to give back to the community and let others profit from my experience.

What is Cheap and Cheerful?

Cheap and Cheerful (hereinafter abbreviated C&C) is what I've come to call my philosophy for cost-effective rocket design in KSP. It's based on a British idiom for Ã¢â‚¬Å“something that is costing little money but is attractive, pleasant, or enjoyableÃ¢â‚¬Â. Another definition is Ã¢â‚¬Å“not of bad quality, or otherwise enjoyable, despite being cheapÃ¢â‚¬Â.

When looking at payload fraction and cost per ton to orbit in KSP, the smart crowd tends to gravitate toward SSTO space planes. They make a lot of sense, if your temperament is compatible with their design and operation. But it takes longer to get to orbit, your ascent profile needs to be closely managed, and designing a craft which is stable and controllable throughout the flight profile (ascent, descent, with cargo, without cargo, full tanks, empty tanks) can be an exercise in frustration for those not well-versed in KSP aerodynamics. The best space plane parts aren't available until relatively late in the tech tree, and the funds investment per craft can be quite high. The cargo bay dimensions limit the size of what you can lift with a single craft. Recovery economics dictate that you have to land fairly close to KSC and in one piece. There has to be another way - dare I say it, an easier way.

Enter Cheap and Cheerful. C&C is about rockets - practical rockets that exist at the intersection of cost, capability, part count, ease of operation, and tech requirements. Building a rocket that has almost as much capability as an optimized design, while having a lower part count and costing a fraction of the funds Ã¢â‚¬â€œ this is the C&C way.

In the entries to follow, I'm going to set forth what I've learned in a number of "Rules of Thumb" for doing things the C&C way. Those wanting pretty graphs and detailed analysis may be disappointed. Healthy debate and alternate viewpoints are welcome. Snarky comments and trolling are not. While the majority of the discussion will be about lifters, we'll also talk about other types of craft.

To demonstrate what I'm talking about, I've inserted below the namesake Cheap and Cheerful lifter which was the inspiration for this thread. It was a 1.0.2 entry in Red Iron Crown's payload mass fraction challenge, and got 20.9 tons of inert payload into LKO. The entire rocket, including payload, was 36,775 funds, while still getting over 20% payload mass fraction to orbit.

Please note that this tutorial is intended for those who already know the basics, and have successfully landed on the Mun or Minmus and returned. If you're still struggling to get to orbit, other threads may be more helpful. Also, this thread is going to be a work in progress for at least the next few weeks. I'll add new posts with additional Rules of Thumb (RoT) on a quasi-regular basis regarding different aspects of KSP rocket design. If anyone has questions regarding a particular topic I haven't covered yet, feel free to chime in and I'll do my best to get to that topic sooner rather than later. Similarly, if anyone needs more/better/any illustrations for a particular concept, let me know and I'll do my best to provide pretty pictures to help explain these concepts.

Table of Contents

7. Command and Control

8. Docking

9. Stage Recovery

Exotic Propulsion Discussion

Examples

200K Fueler

Docking Port Attachment/Orange Tank Refueler

Double Orange Tank Refueler

Edited January 2, 2016 by Norcalplanner
modified table of contents

Norcalplanner · October 7, 2015

1. SRBs

Any discussion of Cheap and Cheerful design has to start with SRBs. They're one of the cornerstones of C&C design. Here are my Rules of Thumb (RoT) for SRBs.

RoT 1.1 - Use SRBs in your designs, but generally only as part of the first stage.

SRBs are cheap for the thrust that you get. They're also heavy, and their vacuum Isp stinks. Use them where these disadvantages are minimized, which is the first stage. Sure, you can use them as a second stage, particularly early in career mode or when cheaply lofting a satellite into orbit; but generally, keep them on the first stage where they belong.

RoT 1.2 - Use fewer, larger SRBs whenever possible.

SRBs are more useful as they get larger. The Flea isn't good for anything, IMHO, other than providing a "holy crap what is happening" moment for new players the first time they launch a rocket in career. Hammer starts to get useful, BACC is definitely useful, and the Kickback is awesome. Not only does the cost go down on a unit of thrust per unit of time basis with the larger rockets, but mounting hardware costs stay the same - i.e., both the Hammer and the Kickback can be attached with a single radial decoupler, and possibly a nose cone. But one provides 227 kN of thrust for 24 seconds, and the other provides 670 kN of thrust for over a minute. Radial decouplers and nose cones are always justified for Kickbacks, sometimes for BACCs, and rarely for Hammers and Fleas.

RoT 1.3 - Keep SRB costs low by taking advantage of surface attachment.

SRBs are awesome in that they combine an engine and a fuel tank into a single surface attachable part. While it may take a little experimentation, it's entirely possible to create bottom stages made entirely out of SRBs radially attached to a center SRB or LFO tank, with the whole mess connected to the next stage via a single stack decoupler.

RoT 1.4 - It's generally a good idea to tweak SRB thrust levels in the VAB.

It's a rare occasion when it's appropriate to use an SRB full throttle. Generally you should tweak the thrust levels so that you have an appropriate initial SLT TWR (generally somewhere between 1.2 and 1.5, depending on a variety of factors). This may be difficult if you don't use MechJeb or Kerbal Engineer Redux to have accurate TWR info in the VAB. Another benefit of tweaking thrust is that it reduces the chance of overheating, which can happen when you're surface attaching SRBs.

Rot 1.5 - Put a larger payload on top of an SRB-only first stage if you're having problems.

Many players have tried using an SRB-only first stage. It can work well in early career, but things can be difficult once the BACC and Kickback are tried. One of the problems is the huge difference in TWR levels between a full SRB and an empty one. The solution is easy, but not entirely intuitive - put more payload on the SRB. If you don't have enough, you'll accelerate really quickly in the lower atmosphere, potentially with overheating and control problems. But if you give it a larger payload, TWR swings are minimized.

- - - Updated - - -

2. Non-Part Mods

Before I get any further, I think it's a good idea to talk about mods. I don't think anyone should hesitate to use mods which give you information which is critical to designing and constructing your rockets, or give you more flexibility in rocket design. With that in mind, consider the following mods.

RoT 2.1 - MechJeb or KER give you useful TWR and Delta V readouts when designing rockets.

This may seem obvious to most, but I'll come out and say it anyway - use KER or MechJeb for TWR and Delta V readouts when designing rockets. They form a critical part of the feedback loop during the iterative process of rocket design, instantly showing how the change you just made will affect rocket performance. Pay special attention to the Sea Level Thrust (SLT) TWR number for the first stage or two to make sure you've got a design which is going to get off the pad.

RoT 2.2 - Editor Extensions gives you a lot of options in design.

While it's possible to eyeball things, wouldn't it be better to hit a key that will automatically center a part vertically or horizontally? Wouldn't it be great to do 7-way symmetry if that's the exact number of SRBs you need? Wouldn't it be great to do angle snap at a bunch of other angles besides 15 degrees? Editor Extensions does all of this. Seriously - if you're into rocket design and want to build things precisely, get Editor Extensions.

RoT 2.3 - Kerbal Joint Reinforcement will not only make your rockets more solid, it will reduce your part count and increase rocket and game performance.

I know that KJR was occasionally buggy in the past, but all the kinks appear to have been worked out now. While making rockets more solid is always appreciated, I think it's just as helpful in reducing part count, particularly struts. Reducing the part count reduces cost, drag, and the load on your CPU when flying the rocket. KJR is a C&C builder's friend.

Edited October 14, 2015 by Norcalplanner
typos, links

Specialist290 · October 7, 2015

This looks like it's going places. I'll be keeping an eye on your progress

Highguard · October 8, 2015

Every one of these points is excellent advice, and I like the thrust of the whole idea.

Constructive criticism - a bit 'masterclass' at the moment? People who can appreciate your points will appreciate the wisdom but a beginner simply might not understand the whys and wherefores?

(Re-reading I'm not really able to stand back and look at this objectively. You explain each point very well, for me, and each point is, for me, a useful one. For some reason though I have the feeling that a lot of people just won't "get it" anyway.)

Norcalplanner · October 8, 2015

Highguard,

Thanks for the feedback. The plan is to do a few more posts covering major systems (aero, command and control, LFO engines and tanks, electrical, and rocket geometry) then add some imgur albums with annotated photos illustrating various concepts and how it all fits together.

Part of the reason for doing this is that my actual KSP time is limited due to RL travel. I figured that jotting down "lessons from the trenches" was something useful I could do without having KSP actually in front of me.

Regarding beginners, I don't really see them as the target audience. I should probably make that clearer in the OP. If I start explaining every acronym, then I start stomping on the toes of folks like Pecan who have created some very good newbie-friendly material.

Norcalplanner · October 8, 2015

3. LFO Engines

Liquid Fuel and Oxidizer engines (LFO for short) have a crucial role in C&C design, although they may be used slightly differently than in more traditional applications.

RoT 3.1 - Almost always use gimbaling LFO engines.

One of the major strengths of LFO engines compared to stock SRBs is their ability to gimbal, i.e. steer the rocket using off-axis thrust. Gimbaling engines provide strong positive control authority in both atmosphere and vacuum. The exceptions to this rule are for very small engines (such as the Ant) where the probe core or capsule provides enough attitude control, and the LVT-30 in the early game when you don't have anything better. Once you have gimbaling engines unlocked, they should be just about the only LFO engines you use.

RoT 3.2 - Match tank and engine diameters for lifters.

Whenever you change diameters in a rocket stack, you end up using extra parts (adapters, fairings) which drive up the price, along with additional aerodynamic considerations. In general, keep all your tanks and lifters the same diameter (i.e., 1.25m engines under 1.25m tanks, 2.5m engines under 2.5m tanks, etc.) for each stack. Minimizing the extra "bits and bobs" which add cost and weight is a key part of C&C design. Once you're out of the atmosphere, this rule is much less important.

RoT 3.3 - Run your LFO engines for at least two minutes in your lifters.

LFO engines are more expensive than SRBs for the same thrust. To maximize the return on your engine investment, it's important to fire those LFO engines for as long as you reasonably can. The RoT is to put enough fuel tanks on top of each engine so that it will run for at least two minutes, possibly longer. If this reduces your TWR to a level which is too low, then it's time to bring in the SRBs. Also note that this RoT can be averaged in the case of asparagus lifters (which are not the first choice for C&C design, BTW) where the center stack ends up firing for a very long time.

RoT 3.4 - LFO transfer stages should have a TWR between 0.3 and 1.

If your TWR is too low, you're going to have trouble making an accurate transfer in a single burn and will start incurring major steering losses. If your TWR is too high, then you either brought too much engine (and made your rocket too expensive) or aren't pushing enough fuel for the thrust you have (and aren't maximizing the return on your LFO engine).

RoT 3.5 - Most LFO landers should have an initial TWR between 2 and 5 for the body that they're landing on.

It's always exciting when landing on the Mun or Minmus for the first time. Those new to the game or not well versed in design will frequently overbuild their landers, hauling around way more engine mass than they need. Slapping a Terrier on the bottom of a Rockomax 16 works great as the power section for a Mun lander, while a Minmus lander can get away with just a Spark under a Rockomax 8. Keep those initial TWRs low.

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

In order to get maximum return from your first stage LFO engine, you need to stack a lot of fuel on it - at least two orange tanks for a Mainsail, and at least 3/4 of an orange tank for a Skipper. When you do stage, the next engine should be substantially less powerful. In addition, the need for higher thrust levels goes down towards the end of a burn to LKO. So long as the first part of the launch has a healthy TWR, the last 500 to 700 m/s to reach orbit can be at a TWR which is significantly below 1. The lowest I've gone is 0.42, but 0.5 or 0.6 should be workable in most situations. This can actually be a bit of a problem with 3.75 meter rockets, since one engine is half the thrust of the other.

RoT 3.7 - 2.5m engines are in the sweet spot.

Many C&C lifters will use 2.5m LFO engines, since they tend to occupy the happy middle ground between cost, performance, and tech requirements. There is nothing wrong with a rocket which uses only Mainsails, Skippers, and Poodles. They can also be augmented with a small number of SRBs, (such as two Kickbacks with a Skipper) which keeps the decoupler and nose cone costs down.

Edited October 11, 2015 by Norcalplanner

silent_prtoagonist · October 8, 2015

This reminds me a bit of the big dumb booster concept, I like it. Looking forward to reading more.

Norcalplanner · October 9, 2015

There's more than a little overlap between BDB and C&C. It's a case of synchronicity in this instance, because I started building this way long before I had ever heard of BDB. :-)

Next entry should be tonight or tomorrow.

Norcalplanner · October 10, 2015

4. Electrical

Most craft need electrical power, whether it's for transmitting science results, running a science lab, scanning a planet, powering reaction wheels, or just keeping a probe core running. Here are the Cheap and Cheerful Rules of Thumb for electricity on a craft.

RoT 4.1 - Use solar panels as much as you can.

Perhaps this is obvious to many, but solar panels give you the best bang for the buck when it comes to power, as long as they're receiving enough light from Kerbol to function. Fuel cells are heavier, more expensive, and slowly use up your craft's fuel supply. RTGs are horrendously expensive, heavier, and not available until the end of the tech tree. Stick with solar panels as far out as Dres, and possibly Jool for craft with lower power requirements.

RoT 4.2 - Stick with Z-100 and Z-1K batteries.

While capacity of a battery scales linearly with weight, it does not scale linearly with cost. Z-100s and Z-1Ks are your best bargain. Stick with them for most craft unless you're using a lot of power while on the dark side of a planetary body (like a science lab) or need the 2.5m form factor and lower part count of the Z-4K.

RoT 4.3 - For early craft only going to LKO, put fixed panels on the E and W sides of your craft.

Putting panels on the E and W sides of the craft as it sits on the pad will ensure that one panel or the other will point at the sun as long as the craft doesn't rotate around its long axis. The opposite rule applies for deployable panels, which should be placed on the N and S sides of the craft, Kerbal ladder access permitting.

RoT 4.4 - For complete coverage with fixed panels, mimic the faces of a die.

In order to get complete coverage with fixed panels, the most efficient method is to mimic the arrangement of faces on a platonic solid, such as dice with 8 or fewer faces, i.e. a D4, D6, or D8. That way, no matter which way the craft is pointed, at least one or more panels will always be generating power. BTW, the angles in between faces are approximately 70 degrees, 90 degrees, and 110 degrees for each of these configurations.

RoT 4.5 - Default to placing 3 deployable panels on the widest part of the payload.

If in doubt, put deployable panels using 3x symmetry on the widest part of the payload. (Panels on narrow parts of the craft are more likely to be blocked by other parts of the craft.) If the craft is a satellite or deep space vessel that will never enter an atmosphere, use the unshielded versions. If you're going to enter an atmosphere, use the shielded versions. This configuration will always generate power no matter the orientation of the craft.

Album with examples

Edited October 12, 2015 by Norcalplanner
Added imgur album

Norcalplanner · October 10, 2015

5. LFO Tanks

It's impossible to run an LFO engine without LFO tanks. The rules for tanks are few and straightforward.

RoT 5.1 - Use fewer, larger tanks wherever possible.

Using fewer tanks keeps the part count down, and the larger tanks are slightly less expensive per unit of fuel. The old mass penalty that the white tanks had no longer exists, so there's no reason to avoid using them.

RoT 5.2 - Put enough tanks in each stage to run the engines for a long time.

As previously mentioned in RoT 3.3, you should run your LFO engines for as long as you reasonably can to extract the most value from your investment, generally at least two minutes per engine. This translates to a minimum of 2 white tanks for a Mammoth, 1 white tank for a Rhino, 2 orange tanks for a Mainsail, 3/4 of an orange tank for a Skipper, 1/4 of an orange tank for a Poodle, two FLT-800s for a Swivel or Reliant, and an FLT-400 for a Terrier. Once you're in space and no longer have to maintain a higher minimum TWR, the tankage per engine can increase. I've made plenty of rockets that have 3/4 of an orange tank attached to a Poodle as a transfer stage.

RoT 5.3 - Fuel Tanks Plus gives you a lot more options.

One of my favorite mods is Fuel Tanks Plus by Necrobones. It's a stockalike mod (actually slightly better than stock, IMHO) that gives you additional lengths in each tank diameter. For example, the 2.5m tanks include the Rockomax 48, 96, and 128, representing 3/4 of an orange tank, 1 1/2 orange tanks, and 2 orange tanks of LFO capacity. Each tank also has multiple setups (such as holding just LF to power an LV-N) and multiple skins to allow a customized rocket appearance. Using this mod will allow a reduced part count and improved appearance for all your LFO rockets. Be sure to check out the video which demonstrates the 1.0 version of the mod in the thread's OP.

Norcalplanner · October 11, 2015

6. Aerodynamics

Aerodynamics is one of the areas where Cheap and Cheerful can depart a bit further from standard design. When discussing aerodynamics, I'm specifically talking about nosecones, fairings, fins, and conical rocket parts. From a C&C perspective, aerodynamic features can add significant cost and weight, and must be considered not only on their merits, but holistically as part of the entire rocket system.

RoT 6.1 - Put your best nosecone on the center stack.

Just as it's a good idea to run your LFO engines as long as possible to extract maximum value from them, it's also a good idea to put your best aerodynamic nosecone on the center stack, where it will be used for the longest. Depending on how long a radial stage is burning, it may make sense to have the same nosecone as the center stack. It's generally worthwhile to put an advanced nosecone on a Kickback, and a basic nosecone on a BACC. Hammers may or may not be worthy of a nosecone. Fleas are... well, I'll just repeat my earlier statement that Fleas are useless, IMHO.

RoT 6.2 - Rarely use fairings; but if you do, don't skimp.

Fairings are fairly (ba-dum) expensive in KSP, and should generally be avoided. If you have just a few things attached radially on your payload (science experiments, small solar panels) then a fairing isn't justified. When you start having larger items (Gigantor solar panels, docking ports, landing legs) on the side of your payload, it may be time for a fairing. This is especially true if you're also having problems with the rocket flipping. Once you do decide to use a fairing, go ahead and cover everything you reasonably can, and make it fairly pointy - the vast majority of the cost is in the fairing base, not the fairing itself.

Rot 6.3 - Rarely use fins. If you do need them, try the cheapest ones first.

Many rockets need no fins whatsoever. If you have a reasonably aerodynamic front end of the rocket, and some workable level of control authority (gimbaling engine or substantial reaction wheels) then there shouldn't be any need for fins. If you do have trouble with your rocket flipping over, despite using a proper flight profile (staying close to the prograde marker), then try adding four of the smallest fixed fins to the very bottom of the rocket. Only if that doesn't work should you go for the larger and more expensive fins. Keep in mind that the cost of fins (particularly controllable fins) can quickly add up, and should be weighed against the cost of other solutions.

RoT 6.4 - Fins should generally be used in groups of four. If you use three, place the first fin on the E or W side of the rocket.

If you do need fins, the best arrangement is to use them in groups of four, mounted on the cardinal directions of the rocket (N-S-E-W). Not only does it track straighter, but the computer seems to be able to predict what the craft will do better. If you do decide to go down to three fins, place the first fin (the one you're controlling with the mouse) on the E or W side of the rocket. If you place it on the N or S side, then things will get a little weird when you start your gravity turn. Also note that you can vary the amount of authority the fins have by altering the height they're mounted on the rocket. If you're finding it too hard to turn with fixed fins, move them up higher on the rocket.

RoT 6.5 - Use the C7 conical tank as much as you can.

The C7 conical tank, which smoothly transitions your rocket from 1.25m to 2.5m, has the same fuel capacity and cost as an FLT-800 or a Rockomax-8. Compared to the Rockomax adapter for the same diameters, which costs 500 funds and doesn't contribute anything to the rocket's power, it's a no brainer. Unless you're using a mod that has 2.5m SRBs, all of your 2.5m radial stacks should have a C7 conical tank and a 1.25m nosecone on top. In my testing, the combination of the C7 tank plus an advanced nose cone was the best performer for 2.5m stacks.

RoT 6.6 - Look at aerodynamics as part of a larger system. Not every aerodynamic problem is worthy of attention, and some solutions don't involve aerodynamic parts.

Because the cost of aerodynamic parts is relatively high for something that produces no thrust, you have to consider what makes the most sense. For example, an advanced nosecone costs 320 funds, while a Hammer costs 400. In some situations, it may make more sense to surface attach Hammers and power through the aerodynamic losses instead of trying to minimize them with a nosecone. You may be able to live with suboptimal aero on your ejected stages, particularly if they're being ejected before you go supersonic. If you have an ascent that is too vertical because you don't have any fins and are relying on reaction wheels for an SRB-only first stage, you have to weigh the cost of the fins against the cost of increasing the fuel in a subsequent stage to compensate for the steering and aero losses.

RoT 6.7 - Look at Fuel Tanks Plus for aerodynamic fuel tanks, including nosecones.

I know I already plugged it once, but I would be remiss in not mentioning the aero components of Fuel Tanks Plus. The mod includes fueled nosecones in every diameter, and conical tanks in every diameter. Check it out.

Edited October 11, 2015 by Norcalplanner
typos

Norcalplanner · October 11, 2015

Time for an Example

I still have a few areas to cover, but I thought it might help people to see a number of these concepts put into action with a real rocket.

This is the 200K Fueler Mk11. I made it for a challenge to see how much fuel I could get to a 90 km orbit with a rocket using only stock parts and physics for less than 200k funds. The craft is available on KerbalX if you want to try it out. Note that this design includes struts because KJR was prohibited for the challenge - normally I'd use KJR, omit the struts, and see if I can use the savings in cost and drag to increase the payload.

Just to walk through some of the design decisions:

Although it's an asparagus design, it only uses 2x2 staging to minimize the total number of stacks.

All five LFO engines are Mainsails at 13,000 funds each.

All six SRBs are Kickbacks at 2,700 funds each.

Each radial stack is the same diameter as the engine.

Each Mainsail has at least 2.75 orange tanks worth of fuel stacked on top of it.

Each stack uses a C7 conical tank and an advanced nosecone on top.

No fins.

No fairings.

All stages are absolutely level thanks to Editor Extensions, which means we don't need any launch clamps.

MechJeb allows for precise TWR and Delta V information.

Just one 1.25m reaction wheel. (I haven't covered command and control yet, but I'll give you a sneak peak - fewer reaction wheels are better.)

The lone docking port is a standard 1.25m clamp-o-tron under the advanced nosecone at the top of the rocket, where it creates no drag. (We'll get to docking and docking ports too.)

Final stage used for circularization has a TWR less than 1.

This design got 2.08 large white tanks worth of fuel to a 90 km orbit, plus the hardware to allow it to function as a fuel depot, for less than 200K.

Welcome to Cheap and Cheerful.

Edited October 11, 2015 by Norcalplanner
typos

Norcalplanner · October 12, 2015

7. Command and Control

Every rocket needs some means to control it, either a probe core or a manned capsule. There also needs to be a way to translate those control inputs into motion in the craft, whether through dedicated reaction wheels, RCS thrusters and monoprop, or integrated reaction wheels in a probe core or capsule. Here are the Cheap and Cheerful Rules of Thumb for Command and Control.

RoT 7.1 - Use only the OKTO and RC-001S probe cores.

The OKTO should be the only core you ever use on small probes. It's available early in the tech tree, gives you basic SAS capability, is cheap, is light, and has a small integrated reaction wheel. If you're using MechJeb, then SmartASS provides all the capability (holding prograde/retrograde, etc.) of the more expensive probe cores. The only time you shouldn't use the OKTO is when you really need the 1.25m form factor, such as on the front of a manned capsule and/or beneath a docking port. In those cases, use the RC-001S. The only other probe core you should even consider is the RC-L01, and then only when the craft needs the 2.5m form factor (such as being inline close to the center of a space station).

RoT 7.2 - Use only a single 1.25m or 2.5m reaction wheel.

The smallest (0.625m) reaction wheel has a strength of 5. The 1.25m reaction wheel has twice the mass and cost, but triple the strength (15). The 2.5m reaction wheel has twice the mass and strength of the 1.25m wheel, but less than twice the cost. Avoid using the tiny reaction wheel, and stick with the medium and large diameter versions, assuming that you need one at all. Try to use only one whenever possible. Yes, you can break this rule for something big that you're going to be interacting with a lot, such as a Jool mothership weighing several hundred tons. But for most craft less than 75 tons in vacuum, a single reaction wheel will give you sufficient attitude control while minimizing part count, cost, and mass.

RoT 7.3 - Don't use RCS for attitude control.

RCS costs mount quickly - four of the standard RCS blocks cost 2,480 funds, and will go through a finite resource (monoprop) that you have on board. Save the cost and part count, and only put RCS on craft that will be docking. And remember to empty any monoprop out of your capsule in the VAB if you're not going to use it.

RoT 7.4 - Stick with the Mk1 Command Pod as long as you can stand it.

The first capsule that you get is the cheapest. It's also tied for the highest heat tolerance, is the second lightest, and is somewhat aerodynamic. Use it on as many craft as you can for as long as you can. If you need a standard size docking port on top, then move up to the 1-man lander can. Once you do decide to move to a 2- or 3-person capsule or cockpit, they're all markedly inferior in one way or another. Use the Mk1-2 if you're going to be doing a high-speed reentry, and the 2-man lander capsule for vacuum operations and gentle LKO reentries. The 2-man lander also presents some unique opportunities due to its form factor, as it's the only stock capsule or cockpit that can have a Sr. docking port on top.

Edited October 14, 2015 by Norcalplanner
Making format consistent

Norcalplanner · October 14, 2015

8. Docking

Docking is simultaneously one of the most challenging and rewarding things for a new player to master. It allows landers to depart from and return to orbital motherships or stations, the transfer of personnel, and the transfer of fuel and resources. It also allows the player to assemble craft in orbit which would be difficult or impossible to launch with a single rocket. Here are the Cheap and Cheerful Rules of Thumb for docking and docking ports.

RoT 8.1 - Stick with the standard docking port.

The standard 1.25 meter Clamp-o-tron docking port should be your mainstay port. It's the cheapest and the second lightest, and provides enough strength for most docking jobs. It should be the only docking port for the majority of your craft. Only use the smaller ports if they're intended for a very small 0.625 meter probe, where every ounce counts, and only use the large ones for assembling large stations and motherships. Both other port sizes are significantly more expensive.

RoT 8.2 - Only put thruster blocks on craft which are a) going to dock and undock, and weigh more than 2 tons.

Smaller probes and landers can get away with not having any RCS thruster blocks - it's just a matter of zeroing out relative velocity between the two craft using the main engine, then having each craft point its docking port at the other craft's docking port. If you're slightly off and wobble a bit before locking on, then that's fine - the mass and cost savings for not putting RCS blocks and tanks on your small craft is well worth the extra docking effort.

RoT 8.3 -Try to use only a single group of four RCS thruster blocks.

If it's possible to do so, figure out what the most likely fuel load will be during a typical docking maneuver for a craft, then put only a single group of 4 RCS blocks around the center of mass for that fuel load as shown in the VAB. Yes, you may get a bit of wobble every now and then, but you've saved 2,480 funds and four parts by having only a single group of thrusters. Only put on a second group of thrusters if you're having trouble with a lot of wobble, or will be docking with vastly different fuel states. Also note that the location of the RCS blocks does not matter for a craft that is only pushing back - in other words, don't worry about having RCS thrusters near the "full tanks" center of mass for the craft. Location only matters when translating, not going forward or backward. Also consider deliberately placing the RCS blocks off center if it means that they'll be on the part of a craft which will be recovered.

RoT 8.4 - Don't use a monoprop tank unless you have to. If you do need one, use a single inline tank.

Most manned capsules carry enough monopropellant on board to dock and undock at least four or five times, so long as you're using proper docking technique. Only add monoprop tanks if you don't have a manned capsule, or if the manned capsule is on a massive craft. Also note that certain docking ports also contain monoprop, such as the stock Mk2 inline docking port, as well as some mod docking ports (such as those in Nertea's Stockalike Station Parts Expansion mod). If you do decide you need some additional monoprop, use a single inline tank. Yes, it won't look as cool as that ring of smaller radial tanks, but the inline tanks cost less per unit of monoprop, have a better full/empty mass ratio, and result in a lower part count.

RoT 8.5 - Use them as decouplers, where feasible.

Anything with an axial attachment node can be stuck to the "out" side of a docking port, and then be detached one time while in flight - just right click on the port, and choose "decouple node". They can be used as cheaper stack decouplers, so long as you disable crossfeed so you don't accidentally drain your upper stage tanks. They can also be used to temporarily attach smaller craft or satellites which won't reattach (such as resource scanning satellites attached to an orbital station going to a distant location). I've also planted satellites with a docking port on top upside down on a radial LV-N stack, just as a convenient place to park the satellite as part of the launch that will already be underneath a fairing. One of my favorite uses is to make a satellite with a docking port on top, then send multiple stacked versions of the satellite to a distant location as part of a single craft (such as two satellites to Duna/Ike, or six satellites to Jool).

RoT 8.6 - Check out SpaceY for even bigger docking ports and RCS blocks.

SpaceY is another mod by Necrobones that contains a number of large rocket parts, including 2.5 meter SRBs and 5 meter LFO tanks. For docking, the critical addition is the inclusion of 3.75 meter and 5 meter docking ports. It also has a number of powerful RCS thruster blocks. If you're looking at joining some truly massive things together in orbit, check out SpaceY. When used in combination with Kerbal Joint Reinforcement, you can have some very large, solidly constructed craft with very few struts.

- - - Updated - - -

Pause for Q & A

At this point, I think the next step is to clean up the format of what I've got and put in a table of contents. After that, the plan is to start putting up some some sample C&C craft for typical scenarios (and hopefully posting them all to KerbalX) to show how all this fits together. The idea is to have a tangible visual reference for reference and discussion craft for different mission profiles.

Before I do, does anyone have any questions, comments, feedback, or alternative viewpoints? I'd like to make sure that I'm explaining things clearly enough, and answering questions that you actually have, rather than questions that I think that you have.

Edited October 14, 2015 by Norcalplanner
Clarified a few things

passinglurker · October 14, 2015

I'm curious under what conditions it would be best to use exotic propulsion(monoprop, nuclear, ion, etc...) according to your cheap and cheery logic.

I'm also curious since you referred to a mod in the latest post how RLA-Stockalike would factor into docking as well since it includes a variety of RCS related parts.

Finally after crunching all these numbers what would you change about the stock balance to cut down on money saving tricks that seem more hacky like using docking ports as decouplers?

Norcalplanner · October 14, 2015

Passinglurker, these are all good questions.

Regarding exotic propulsion, I think these are very different cases. I'm not aware of any scenario where it would make make sense to use a monoprop engine in a stockish game, but I'm not familiar with some of the hybrid monoprop/electric engines that I just saw are in RLA.

For ion, it would depend on the total delta V requirements and the cost of the payload. Once you have 50,000 funds worth of instrumentation on a probe, the difference between 2,000 and 20,000 for the drive section doesn't seem to be as large. In terms of pure efficiency, I think you would need to be doing a multi-year, multi-planet probe flying a flight path that requires more than 8,000 m/s of delta V for an ion drive to start to make sense. Essentially, you would need to look at how much it would cost to achieve the same science objectives using one or more chemical rockets and whether or not you can recover the instrumentation anywhere near KSC after the end of its flight. The initial cost difference in lifting a 1 ton ion probe vs. an 8 ton multi-stage LFO probe isn't all that great, but the chemical one would require more engines and decouplers, which drives up the price a little bit.

Nuclear really comes into its own when there's a large payload involved. Without a payload, an FLT-800 with a Terrier has approximately the same delta V as an LF-only tank of the same size being pushed by an an LV-N, and the Terrier setup is 1/8 the cost and 2.5 tons less to orbit. Once you start adding larger payloads though, so that the greater weight of the LV-N ceases to be such a disadvantage, then it makes more sense to go nuclear. This is especially true if it's a station or mothership that is going to be used for many missions. I just did a quick test - five LV-Ns pushing an 81-ton payload required a 40-ton LF tank to have over 2,000 m/s of delta V. The same solution using LFO and a Rhino required over a hundred tons of LFO tankage for the same Delta V. The nuclear solution was 27,000 funds more, but it would cost more than 27,000 funds to loft the additional 60 tons of LFO tanks, so a nuclear solution is superior in this scenario. One thing I would add is that the nuclear TWR was only 0.23, and would need to use multiple periapsis kicks if it was doing a transfer to Jool, whereas the Rhino could do it in a single burn. Of course, if you have a good mining and refining setup and can refuel things in orbit cheaply, then things change again, and not in entirely predictable ways.

On RLA, I've only ever used that mod as part of RSS/RO, so I don't know its strengths and weaknesses in the standard Kerbal universe. Give me a few days to play with it and I should be able to form an opinion.

Regarding balance issues, I agree that using and abusing docking ports is gamey, and I wouldn't do it in a RP situation (such as my Apollo Applications Program save for that particular challenge). In terms of balance, it seems to me that the easiest thing would be change things so that that docking ports can only connect to a decoupler, stack separator, or another docking port. I'd also look at increasing the price of the 1.25m docking port so that it's not significantly cheaper than a 1.25m stack decoupler. Are there any other hacky tricks you're thinking of?

Thanks again for all the great questions. I'll see if I can get you an answer on the RLA issue sometime soon.

Addendum - After doing some testing with LFO probes and ion probes, including the cost of their respective launchers, I've been able to refine things a bit. If you've unlocked the entire tech tree, then it makes financial sense to use an ion-powered probe if your flight plan needs more than 9,000+/- m/s of delta V and you can make the whole thing work with only solar panels and batteries (no fuel cells). Otherwise, it's better to use a multi-stage 8- to 10-ton LFO probe. I would also note that the parts for the LFO probe are available earlier in the tech tree, that it has better TWR than the ion probe, and has better burn capabilities out past Dres. In terms of lifter cost, the LFO probe's lifter costs $15K, while the ion probe's lifter costs $4K. The entire ion probe rocket (including lifter) is $3K more expensive than the LFO probe rocket, but the ion version had 500 m/s more delta v.

Addendum No. 2 - After playing around with RLA a bit, I've come to some conclusions: 1) whoever made the mod really loves probes and monoprop; 2) there's some overlap with SpaceY in terms of 0.625 meter fuel tanks, RCS thruster blocks, and SRBs; 3) there are some nice probe cores that fill out the range a bit; and 4) several of the monoprop engines seem OP compared to stock. Because of the lower empty tank mass fraction of monoprop compared to xenon, and the much lower price of monoprop, several configurations I tested with hybrid electric/monoprop engines were superior to xenon at a lower price. However, even the straight monoprop engines had a very high vacuum Isp (340) compared to stock. On the whole, I'd say that the straight monoprop engines are slightly OP, and the hybrid monoprop engines are much closer to Near Future Propulsion than they are to stock.

Edited October 15, 2015 by Norcalplanner
more ion info, clarified a few things, added RLA info

passinglurker · October 17, 2015

On RLA I believe the higher vacuum isp of the monoprop engines was an effort to find a niche for the engine type since the real world advantages of this type of engine can't be simulated in KSP (reliability and no boil off) as a result compared to LFO a monoprop system with equivalent DV would have less mass but also less TWR (classic thrust for isp trade off that bridges the gap between chemical and nuclear) I hadn't considered the xenon angle before its high cost because they tried to emulate a real world element instead of an abstract resource like the rest throws a lot of wrenches in the works in terms of game balance (for example you can't ISRU xenon because you could fund your space program just drilling ore on kerbin.) though as you've shown you can make LFO probes on par with xenon cost wise already, but without the inconveniently low twr so one could argue they are already essentially obsolete especially for a late game career with maxed buildings, ISRU, and a healthy budget so knowing the engines leave xenon in the dust I'm curious how they stack against nuclear and chemical. Though really I asked about RLA in the first place because I was wondering if it's probe sized rcs, or 5 way ports made a difference for adding rcs to small payloads.

Are docking tugs economical? on paper a single set of rcs ports for your whole station and its visitors would sound great though in practice the tug may grow expensive and beefy to haul around its payloads and it may mean adding multiple docking ports to everything.

As for other gamey tricks its been noted that some parts simply become obsolete (like the lv-t series of engines, or what we just covered with xenon even without RLA). ram is precious there isn't room for obsoleteness so taking the most useless parts you have time to ponder about how could they be altered to not seem to be a waste of ram either by buffing them or nerfing the parts that obsolete them? Another thing is crewed parts these are a big gaping hole in the balance as you said the either the ugly old mk1pod or the mighty mk1landercan are essentially the best pods in terms of all around practicality (until you combine the mk3 crew cabin with a probe core anyway, but where are you gonna take 16 kerbals?) so what would it take for the other pods to make sense in more cases than just looks?

Norcalplanner · October 17, 2015

Passinglurker,

Lots more good questions. Since Cheap and Cheerful design tends to be part agnostic (i.e., it's a philosophy for making the most cost-effective and practical use of whatever parts you have available), I don't want to delve too deep into responses for fear of turning this thread into a part balance discussion. However, I can answer in a few generalities.

I don't think small craft ever need RCS ports, since existing reaction wheels provide sufficient control authority for less cost and the magnetic docking ports have a wide tolerance for slightly-off approaches for lightweight craft.

I don't think xenon is obsolete, it just has a particular niche that it fills that perhaps isn't as large as many people thought.

Docking tugs can be economical, depending on the amount of docking you're doing. The trick is being able to deal with the asymmetric RCS thrust during translation. I tend to not use them that much because I'm comfortable launching very large payloads that require minimal docking - for example, I launched this 700-ton station in two pieces, so there was only one orbital docking maneuver to make.

If you're using a spaceplane for construction of an orbital station or have otherwise placed some restrictions on your rocket design so that you'll be bringing up more numerous smaller modules, then go ahead and include a tug. Otherwise, fewer larger launches using cheap SRBs can result in a lower total cost and part count for a station.

Regarding parts becoming obsolete, I'm OK with that. It gives the player something to shoot for with larger/better parts. That said, I nearly always play with SpaceY, which includes a more powerful 1.25m engine, 0.625m SRBs, 1.875m SRBs, 2.5m SRBs, 5m LFO engines and tanks, and other goodness. In terms of filling in the gap in capsules, I'm also a big fan of Nertea's mods, including Near Future Spacecraft, because it includes a Gemini-ish 2-Kerbal capsule that weighs less than the stock 2-kerbal lander can but has better reaction wheels and heat tolerance. There are also a small number of nice engines in Randazzo's VX Series Vanguard Engines pack, including a 40 kN 1.25m vacuum engine and a 120kN 2.5m vacuum engine which I use all the time.

RL beckons, so I have so sign off. I should be able to post some more example craft later today.

Norcalplanner · October 18, 2015

Example - Small Science Satellite

Here's a small satellite that follows C&C design principles. It's essentially a Terrier-powered single-stage craft that needs an SRB for the initial kick. Lots of information is in the descriptions.

Please note that this is only meant to demonstrate one way of doing things the C&C way. It is by no means the only way.

Edited October 18, 2015 by Norcalplanner
Added clarification

Waxing_Kibbous · October 18, 2015

I've been playing for 3-4 weeks now and this is a real eye opening thread, thanks a ton. A couple of things:

Docking ports: I could use some clarification on their use- it seems there is a sort of hidden attribute, where they can be used once by themselves (as in, not in a pair to attach), eg. I feel as though I watched a video where someone used a docking port to attach directly to a heat shield during gameplay. Was I just imagining things or is this a possibility with them?

Would it be possible to assemble this excellent writeup into a doc or pdf in the OP for printing?

Thanks again :cool:

Norcalplanner · October 18, 2015

Waxing_Kibbous,

Thanks for the kind words. I'm glad you're finding the thread helpful.

I should have some more examples posted later today which show how to use docking ports as you describe, among other things.

Once all the entries are complete, I'll likely reorganize things a bit. Converting to PDF is a definite possibility. However, I think I still have a few more entries to make before taking those final steps.

Norcalplanner · October 19, 2015

Docking Port Attachment Examples

Here are some photos of how to use docking ports in a manner similar to decouplers. While there are advantages to doing things this way (including the fact that 1.25m docking ports are lighter and cheaper than 1.25m stack decouplers) I don't recommend using them for anything which will be separating while under power and/or in atmosphere, such as with a lifter. Not being able to activate them as decouplers through the standard staging sequence can have calamitous unintended consequences.

- - - Updated - - -

Orange Tank Refueler Example

Here are some photos of a refueler with enough hardware to either be a passive depot or an active tanker going to a craft which is out of fuel. Includes a demonstration of how to figure out where to place a single group of four RCS thruster blocks around the CoM of the craft.

Norcalplanner · October 20, 2015

Double Orange Tank Refueler Example

"But Norcal, my ship needs two orange tanks worth of fuel. How can that be done in a Cheap and Cheerful way?"

Funny you should ask. Meet the Double Orange Tank Refueler. The basic Orange Tank Refueler design is tweaked to add another orange tank to the payload, and 5/8 of an orange tank of fuel to the lifter. Oh, and one little detail - eight more Kickbacks are surface attached to the existing four, making a total of 12 SRBs in the first stage. Remember, SRBs are cheap. This example gives fuller expression to many C&C design principles, effectively doubling the payload for only a 61% increase in cost. More information is in the descriptions.

Edited October 20, 2015 by Norcalplanner
typos

Meithan · October 21, 2015

Excellent guide, Norcal! I couldn't but nod and nod as I read along. It seems I've converged to a very similar set of rules of thumb, which should be an indication of their general validity.

I just have one question regarding RCS: what's your take on the linear ports? They're cheaper than the RCS blocks, even if you need 6 of them to get 3-axis control. Part count is a con, I guess? There's also having to place the front/back-facing ports, which is not always easy (I usually place two in the front/back directions; 8 linear ports cost slightly less than 4 blocks). They have twice the thrust, though, so they provide the same overall thrust.

Edited October 21, 2015 by Meithan

Norcalplanner · October 21, 2015

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

Honestly, I've only used linear ports once, and that was a long time ago. But now that I'm looking at the stats and thinking about the geometry, I think there could be a scenario where they would work. 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.

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.

Rules of Thumb for Building Cheap and Cheerful Rockets

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