Package: kspalculator
kspalculatoris a tool which determines thebestrocket
propulsion designs for one stage of a rocket, given a set ofconstraintsandpreferences.Constraintsare properties of the spacecraft which have to be
fulfilled. These are the possible payload and the Delta-v as well as the
minimum acceleration which is reached in an environment with given air
pressure.Preferencesare further properties a propulsion design might
fulfill in order to be preferred. Examples for preferences are the thrust
vectoring angle, the radial size, whether the engine is able to generate
electric power, etc.Which is thebestdesign depends heavily on the specific application.
A design might be better than another one, if it is cheaper or has a
lower mass, but it might also be considered better if it is buildable
using less technology or if it better fulfills some of the given
preferences. Obviously, it is impossible to sort all propulsion designs
by their “goodness”, so there might be more than one which is the best
at least by some criteria. This tool presents exactlyallbest
designs.There is an official web frontend for kspalculator at:https://kspalculator.appspot.com/.Featureskspalculator evaluates all possible designs, checks whether they fulfill
the user’s requirements, and then checks whether it is the best design
using the relation “Ais better thanBiffAis better thanBbyanyof the user’s criteria”. Only thebest designsare then
presented to the user. This way, the user has maximum flexibility to use
the type of propulsion which serves best his needs, still without being
spammed by non-optimal solutions.The stage might have different requirements for minimum acceleration fordifferent *flight phases*through different air pressures and
different Delta-v requirements. For example you might require the vessel
accelerating by 1000 m/s with an acceleration of 3 m/s², and later 500
m/s with an acceleration of 7 m/s².Besides considering theclassic liquid fuel enginesas well assolid fuel boosters, kspalculator also considers using theLV-N
Nerv Atomic Rocket Motor, theIX-6315 Dawn Electric Propulsionand
theO-10 Puff MonoPropellant Engine.Considered criteria to decide whether a design is better than another
one areMass,Cost,Whether it is buildable with easier
available technology,Whether gimbal (thrust vectoring) is available,
or Thrust Vectoring Range,Whether it uses MonoPropellant as fuel,
which is also used by Reaction Control System (RCS) thrusters,Whether its engine generates electric power,The length of the
engine, as might be meaningful when building landers,Whether it
meets user’s radial size preference.Even though calculating this sounds highly sophisticated, the best
designs are presented to the user usually withinless than a second.
The information shown about each design includes a detailed listing of
theperformance characteristics, i.e. theactually reachable
Delta-v(which might be slightly more than required, because of
rounding to tank sizes), theacceleration at full thrustas well as
themassat beginning and end of eachflight phase.UsageGUIThere is an official web frontend for kspalculator at:https://kspalculator.appspot.com/.Here we explain how to use the kspalculator command line tool, but the
basic concepts don’t vary.InstallationMake sure you havePython, at least
version 3.4 installed.If you havepipinstalled, you
may install kspalculator usingpip3 install kspalculatorAlternatively, fetch the most recent version of kspalculator athttps://github.com/aandergr/kspalculator/releases. Installation is then
done by unzipping the archive and callingpython3 setup.py installBasic Usagekspalculator is invoked on the command line. Syntax iskspalculator [--boosters] [--cost] [preferences] <payload> <Delta-v[:acceleration[:pressure]] [...]>wherepayloadis the payload in kg andDelta-v[:acceleration[:pressure]]are tuples of required Delta-v in
m/s, acceleration in m/s² and environment pressure in ATM (0.0 = vacuum,
1.0 = kerbin sea level pressure) for each flight phase. You have to
specify at least one of these tuples. Acceleration and pressure are
optional and default to zero.If you add--boosters, kspalculator will consider adding solid fuel
boosters. This is very useful for launcher stages.Options forpreferencesare:--preferred-radius{tiny,small,large,extralarge}: Preferred radius
of the stage. Tiny = 0.625 m, Small = 1.25 m, Large = 2.5 m (Rockomax),
ExtraLarge = 3.75 m (Kerbodyne),--electricity: Prefer engines
generating electricity,--lengthor--lander: Prefer engines
which are short or radially mounted,--gimbal: Prefer engines
having gimbal. If you specify this option twice, a higher gimbal range
is considered better.--rcsor--monopropellant: Prefer
engines using RCS fuel (monopropellant), i.e. prefer the O-10 Puff
engine.In contrast to the constraints, preferences aren’t hard requirements for
a design suggestion to be shown up. Adding preferences only adds
criteria under which designs may be considered better than others. This
means, specifying more preferences,moredesigns will be suggested.If you specify--cost, results will be sorted by their cost instead
of their mass.For a brief reference for options, callkspalculator--help. To
display the version of the tool as well as the corresponding version of
Kerbal Space Program, callkspalculator--version.Note that kspalculator calculates optimal designs for one stage only (or
two if you allow boosters, where the first is a stage only utilizing
solid fuel boosters). It will never split up your design into multiple
stages.ExampleImagine we build a light Mun lander, having a payload of 1320 kg. That
is a Mk1 Command Pod, four LT-05 Landing Struts, a Parachute, a Heat
Shield, a Stack Decoupler and Solar Panels. We want to have two stages:
the upper one flying from Low Kerbin Orbit to Mun, landing there, and
then flying back to Kerbin; and the lower one launching the lander stage
from Kerbin Space Center to Low Kerbin Orbit.After having determined the payload of the stage, we need to figure out
Delta-v requirements, acceleration requirements and air pressure at the
different flight phases.In this case air pressure is easy: As the Mun does not have any
atmosphere and the stage starts its way already being in orbit, it is
clear that the lander will be designed to fly through vacuum only.Needed Delta-v can be easily read at Delta-v maps or calculated by
calculation tools found in the internet (see links section later in this
document). We find out, that we need 1170 m/s from Low Kerbin Orbit to
Low Mun Orbit, then 580 m/s for landing at Mun, 580 m/s for starting at
Mun and later 310 m/s for returning to Kerbin. Additionally, in this
example we want to have 700 m/s Delta-v as a reserve.Now let’s think about acceleration. As we land and start on Mun, we
indeed have constraints regarding minimum acceleration, because we need
to counteract Mun’s gravity. In this example, we want to have at least
2g= 3.3 m/s² acceleration when starting to land at Mun (i.e. when
having reached Low Mun Orbit), and 3g= 5.0 m/s² to launch at Mun,gbeing Mun’s surface gravity, which is about 1.65 m/s² as can be
found out in the in-game knowledge base.Do we have any preferences? Yes we do. We’re building a lander utilizing
LT-05 Micro Landing Struts, which are quite bad, so it would be nice to
prefer engines which have a short length. Thus, we add--lengthflag
to kspalculator invocation. Additionally, our Payload has radial sizesmall, so it would be cool if the propulsion system also had this
radius. We add-Rsmall. Note that adding preferences doesnotprevent the listing of solutions which do not meet these preferences,
i.e. adding preferences always leads to more output.Doing so, we get:$ kspalculator 1320 -R small --length 1170 580:3.3 580:5.0 310 700
48-7S Spark
    Total Mass: 6145 kg (including payload and full tanks)
    Cost: 1670
    Liquid fuel: 840 units (4725 kg full tank mass)
    Requires: PropulsionSystems
    Radial size: Tiny
    Gimbal: 3.0 °
    Engine is short enough to be used with LT-05 Micro Landing Struts
    Performance:
    [...]

LV-909 Terrier
    Total Mass: 6320 kg (including payload and full tanks)
    Cost: 1190
    Liquid fuel: 800 units (4500 kg full tank mass)
    Requires: AdvancedRocketry
    Radial size: Small
    Gimbal: 4.0 °
    Engine is short enough to be used with LT-05 Micro Landing Struts
    Performance:
      1:  1170 m/s @ vacuum     9.49 m/s² - 13.42 m/s²    6.3 t -   4.5 t
      2:   580 m/s @ vacuum    13.42 m/s² - 15.92 m/s²    4.5 t -   3.8 t
      3:   580 m/s @ vacuum    15.92 m/s² - 18.90 m/s²    3.8 t -   3.2 t
      4:   310 m/s @ vacuum    18.90 m/s² - 20.72 m/s²    3.2 t -   2.9 t
      5:   700 m/s @ vacuum    20.72 m/s² - 25.48 m/s²    2.9 t -   2.4 t
      6:    51 m/s @ vacuum    25.48 m/s² - 25.86 m/s²    2.4 t -   2.3 t

[...]

LV-T30 Reliant
    Total Mass: 11008 kg (including payload and full tanks)
    Cost: 2825
    Liquid fuel: 1500 units (8438 kg full tank mass)
    Requires: GeneralRocketry
    Radial size: Small
    Engine generates electricity
    Engine is short enough to be used with LT-2 Landing Struts
    Performance:
    [...]

[...](Output was shortened)Of the suggested designs, all are the best by some criteria. The first
one, using Spark engine, is the one having the lowest total mass, but in
this example we do not want to use it, for example because we did not
research “Propulsion Systems” yet. We choose the Terrier design as we
think it serves best our needs. Note that the tool also suggests the
Reliant because of lower technology requirements, as well as some other
nice designs which we skipped in this document to save space.Now build the stage adding the 800 Unit Fuel Tank and the Terrier engine
under your payload. Then add a stack decoupler (which weights 50 kg) as
we’re building the launcher stage.The payload for the launcher stage is 6370 kg (i.e. the lander stage
plus 50 kg stack decoupler). Safe Delta-v and acceleration requirements
for a launch to Low Kerbin Orbit have been found out to be 905 m/s with
13 m/s² at 1 ATM and then 3650 m/s with 13 m/s² at 0.18 ATM.We want to use solid fuel boosters for the launch, so we add--boosters. Additionally, we prefer engines with thrust vectoring as
it may be helpful to counteract turbulences during launch, so we add--gimbal.Smallis still our preferred radial size. Now we
determine best launcher designs:$ kspalculator 6370 --boosters --gimbal -R small 905:13:1 3650:13:0.18
RE-I5 Skipper
    Total Mass: 89320 kg (including payload and full tanks)
    Cost: 18258
    Liquid fuel: 5600 units (31500 kg full tank mass)
    Requires: HeavyRocketry
    Radial size: Large
    Gimbal: 2.0 °
    Engine generates electricity
    Radially attached 2 * S1 Kickback SFB
    SFBs mounted on TT-70 Radial Decoupler, Advanced Nose Cone, 2 * EAS-4 Strut Connector each
    Performance:
     *1:   905 m/s @ 1.00 atm  13.30 m/s² - 21.35 m/s²   89.3 t -  55.6 t
     *2:   213 m/s @ 0.18 atm  23.59 m/s² - 26.08 m/s²   55.6 t -  50.3 t
      3:  3437 m/s @ 0.18 atm  15.55 m/s² - 47.68 m/s²   40.9 t -  13.3 t
      4:   107 m/s @ 0.18 atm  47.68 m/s² - 49.37 m/s²   13.3 t -  12.9 t

4 * Mk-55 Thud, radially mounted
    Total Mass: 108520 kg (including payload and full tanks)
    Cost: 19467
    Liquid fuel: 4600 units (25875 kg full tank mass)
    Requires: HeavyRocketry
    Radial size: Small
    Gimbal: 8.0 °
    Engine is short enough to be used with LT-05 Micro Landing Struts
    Radially attached 3 * S1 Kickback SFB
    SFBs mounted on TT-70 Radial Decoupler, Advanced Nose Cone, 2 * EAS-4 Strut Connector each
    You might limit SFB thrust to 79.5 %
    Performance:
     *1:   905 m/s @ 1.00 atm  16.42 m/s² - 26.35 m/s²  108.5 t -  67.6 t
     *2:   637 m/s @ 0.18 atm  29.12 m/s² - 39.36 m/s²   67.6 t -  50.0 t
      3:  3013 m/s @ 0.18 atm  13.15 m/s² - 36.68 m/s²   35.8 t -  12.9 t
      4:     2 m/s @ 0.18 atm  36.68 m/s² - 36.71 m/s²   12.9 t -  12.8 t

[...](Output was shortened)The asterisks in the performance tables indicate that the phase of
flight is done by solid fuel boosters. The SFB thrust limit suggestion
is the minimum thrust required to fulfill your acceleration constraints.Now build one of the launchers being suggested by kspalculator and we’re
ready to do a giant leap for kerbinkind.Helpful LinksOfficial web frontend for kspalculator:https://kspalculator.appspot.com/.Nice cheat sheet, especially containing maps with required Delta-v:http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheetThere is athread in the Kerbal Space Program
forumsabout kspalculator.In case you find any problems or have suggestions, please help us
improving this tool by reporting them at:https://github.com/aandergr/kspalculator/issues