Kerbal Rocketeering 101 - By Professor Lynch [1.0.2]

[Lynch]

This is a brief introduction to rocket mechanics.

All my calculative posts include;

Kerbal Aerodynamics 101 - By Professor Lynch [1.0.0]

Kerbal Rocketeering 101 - By Professor Lynch [1.0.2]

Kerbal Orbital Mechanics 101 - By Professor Lynch [1.0.4]

Beneath is my excel file which allows you calculate and build your own specific rocket for desired payloads.

You want a TWR above 1.6

Most rockets are capable of carrying %15 paylaod at max efficiency

You need 3650-4000dV depending on your gravity turn quality for Kerbin 75km orbit

1) Summing all these, I made a quick excel spreadsheet so that you can first type in your payload,

2) Then type in the asparagus booster count

3) Then play with the Core and Booster engine count so that it stays in the appropriate ranges

4) Then play with the Liquid fuel mass so that it stays in the appropriate ranges

The result is, you will know what engines to use, and how much fuel to use for 2 stage launcher of your "x" tonnes payload.

Remember to make your core engine thrust higher than your asparagus to reach high efficiency.

Technique of Gravity Turn used in reaching these values is,

1) Vertical until 8,000m

2) Start your gravity turn earliest 8,000 or latest 20,000 ; earliest the better but needs more wings to withstand aerodynamics.

3) Gravity turn is done by slowly pushing towards 90HDG and following the tip of your PROGRADE's more horizontal line (not this but+this side)

4) Try to be horizontal no matter what altitude you are IF your Altitude > 30,000 AND your Apoapsis > 45,000

5) Depending on your TWR, decide to stop burning until you reach your Apoapsis -30seconds, and keep continuing until you circularise.

This must take between 3300 and 4000 dV, in most cases which I experimented, and also out of my experiments, in videos of average Kerbonauts; it will take 3900m/s for a 70,000 and 0 eccentric 0 inclination Kerbin orbit.

If you want to make a plane which is only and only useful to fly on Kerbin below atmosphere for visual temperature and pressure experiments; refer to Kerbal Aerodynamics 101 - By Professor Lynch

however it is outdated and I am not thinking to update it anytime soon.

Download Link

Any questions?

Thanks

Edited October 14, 2015 by Lynch
adding picture

[cwalrus]

I have a question! How do you download from Megafile without signing up?

If you email me I can host the tiny file on my site and send you the perma-link...

[Champ]

Hi

There are a few things i dont understand, and a few things i think are wrong :

First, what is the purpose of your spreadsheet ? Forgive me if i misunderstood, but it seems like you take your payload weight, assume you will always use the same engine, and "play" with the number of boosters and the liquid fuel to get the desired caracteristics for your rocket (mainly TWR). Why would you want to do that ? Seems like nonsense to me, that's why i think i misunderstood something.

That was the "i dont understand" part.

Now, the "i could be wrong, but i think you are wrong" part :

"You want a TWR above 1.6" : No. This was true in the old days, but not now. 1.6 TWR at launch is plenty.

"2) Start your gravity turn earliest 8,000 or latest 20,000" : this really depends on your rocket and design payload. For my simplest rockets, i give just a little impulse east just after launch (approx 1000m altitude), disable SAS and let the gravity do the job. For my very hard to fly and very unstable "put-a-space-station-in-orbit-in-one-launch" rocket, i started my gravity turn at 30 000m (this is a very extreme example : you DONT want to do that). "earliest the better" is absolutely true, by the way.

[GoSlash27]

Lynch,

I like how you've laid out this spreadsheet visually.

My spreadsheet works backwards from this, effectively automating the process. I give it the mission parameters and it designs a booster using each engine so I can see which design is lightest and/ or cheapest.

I wonder if your visual layout might benefit my model...

Here you see my inputs in yellow and the outputs for each engine type in green. Number of engines, mass of empty tanks, mass of fuel, and total stage mass.

Best,

-Slashy

Edited June 19, 2015 by GoSlash27

[Lynch]

I have a question! How do you download from Megafile without signing up?

If you email me I can host the tiny file on my site and send you the perma-link...

.

Dear helpful Kerbonaut Mr cwalrus' date=' it is as easy to download as clicking slow download or low, since file is 12kB it ll be 1 sec. Once clicking the same pagr comes, dont know why, but click again and there it downloads tried it myself and it worked, tell me if any problems occur

I have therefore added a photo to my original post for you to show how to download

First, what is the purpose of your spreadsheet ? Forgive me if i misunderstood, but it seems like you take your payload weight, assume you will always use the same engine, and "play" with the number of boosters and the liquid fuel to get the desired caracteristics for your rocket (mainly TWR). Why would you want to do that ? Seems like nonsense to me, that's why i think i misunderstood something.

.

Mr champ, my spreadsheet helps you design how many of which engines you attach to core and aka to boosters to lift the payload and also the fuel needed for orbit.

Also, I have only used Terrier Swivel and Skipper because on the time I was playing Hard Mode Career with no save or quicksave or revert, so I had only those 3 engines opened, well a few little ones but these were suitable for this purpose you can always make it wider once you have my spreadsheet and understand it by reading. It involves quite a lot of math and differential equations.

Gravity turns are a highly discussed subject, after my wide online research I come up to that using that always consumes 3,850dV of me for orbit, higher the twr lower the dV, nonetheless I recently learnt that lowest can go do 3650dV

Lynch' date='[/color']

I like how you've laid out this spreadsheet visually.

My spreadsheet works backwards from this, effectively automating the process. I give it the mission parameters and it designs a booster using each engine so I can see which design is lightest and/ or cheapest.

I wonder if your visual layout might benefit my model...

.

Mr GoSlash27, can you please share the spreadsheet link please? I like as many data as possible. Thanks

Edited June 19, 2015 by Lynch

[FancyMouse]

I can't even get my rocket horizontal at 30km when I start my turn at 1km

8km vertical then 30km horizontal? wow

[cwalrus]

Hi Lynch,

tried clicking again and again, in chrome and in firefox- no luck yet! I think I'll try registering to see if that works...

GoSLash- Yes please share link to that spreadsheet!

thanks

[Lynch]

I can't even get my rocket horizontal at 30km when I start my turn at 1km

8km vertical then 30km horizontal? wow

Dear FancyMouse, horizontal at 30km if and only if your apoapsis is 45,000 or more; if not, try to go more vertical.

Hi Lynch,

tried clicking again and again, in chrome and in firefox- no luck yet! I think I'll try registering to see if that works...

GoSLash- Yes please share link to that spreadsheet!

thanks

Dear cwalrus, I have a little problem in the excel sheet which is, dv calculations are only for Skipper, now I am updating it for Terrier Swivel Skipper Mainsail and Twin Boar. I must have made a mistake forgive me Where would you like me to upload the new spreadsheet?

[cwalrus]

anywhere that works is great! (I'm surprised we can't put small text attachments here in the forum..)

[Lynch]

anywhere that works is great! (I'm surprised we can't put small text attachments here in the forum..)

Would you please name a site, I am bad at this; and my next update is a ground breaker, I have put in the concept of combined engines, and had a factoring with advanced math in order to come up with a nice constant to balance the equations.

[cwalrus]

Hmmm... I don't know because I usually just use my own company's site. Try Rapidshare? Dropbox? GoogleDrive?

[GoSlash27]

Oh wow sorry guys...

I wasn't trying to post my spreadsheet as an alternative to the OP. I was just looking for suggestions on how I can make mine visually cleaner.

My spreadsheet has a lot of experimental content that's not quite ready for primetime and I wasn't planning on distributing it.

Sorry for the confusion!

-Slashy

*edit*

Mesklin has a spreadsheet similar to mine here:

http://forum.kerbalspaceprogram.com/threads/122407-Optimal-engine-selector-for-v-1-0-2

Edited June 19, 2015 by GoSlash27

[cwalrus]

what? You terrible tease! You show us and then don't share !!

Mesklin's looks good, even though half of it is in russian.

BTW Lynch, he shared it as a google doc.

[Lynch]

Done, uploaded and fixed the spreadsheet feel free to use and comment

My twitch profile:

http://www.twitch.tv/professorlynch/profile

[GoSlash27]

what? You terrible tease! You show us and then don't share !!

Mesklin's looks good, even though half of it is in russian.

BTW Lynch, he shared it as a google doc.

Yeah, I suck

If you'd like, I can walk you through the math and you can make your own version. It ain't hard.

As mine currently stands, it's got too much content that's in an unfinished state.

[Lynch]

Yeah, I suck

If you'd like, I can walk you through the math and you can make your own version. It ain't hard.

As mine currently stands, it's got too much content that's in an unfinished state.

Id like to hear your math

[GoSlash27]

Lynch,

Sure thing. I have limited time this morning, so I may need to come back this afternoon to fill in the blanks.

The idea is to start with a mission requirement and end up with a design derived from it.

-Mission requirement: Payload mass, required DV, minimum acceleration

-Design result: Number of engines, mass of fuel, mass of empty tanks.

We set up the math for one engine and then copy & paste for all others so that we can see the result for all engines simultaneously. This allows us to compare designs so we can pick the best design.

Step #1: How much total mass can a single engine of this type accelerate at our minimum rate?

I define the acceleration in Gs and reference it to the local gravity, such as .5 Gs on Kerbin

We take the thrust in KN and divide it by the local gravity and Gs acceleration.

Step #2: What fraction of this total mass must be fuel in order to achieve the desired DV?

This uses the rocket equation in reverse; e^(DV/9.81Isp)-1

Step #3: From step 2, derive the mass of fuel and tanks for our single engine reference.

Multiply the fuel fraction by total stage mass to yield the mass of fuel. Multiply the fuel mass by 1/8 to yield the tank mass.

Step #4: Find the payload mass of our single engine reference.

Total stage mass-engine mass-fuel mass-tank mass=payload mass.

Step #5: Scale it up to fit our need.

Payload mass required/ reference payload mass= number of engines needed for the full scale stage. Use the roundup(x,0) function to yield an integer value.

At this point, we could simply use the scaled numbers and call it good, but because we have to round up to the nearest whole number of engines, we have a little more mass than the model expects and this will hurt our total DV. We have to reiterate with our total engine mass and payload in order to find our fuel load and tankage.

Step #6: Compute tankage mass for final vehicle.

6a: e^(DV/9.81Isp)= Rwd

6b:

(Rwd-1)(NMe+Mp)

_______________ = Mt The mass of your required fuel tank in tonnes when empty.

(9-Rwd)

where

N= number of engines

Me= mass of an individual engine

Mp= mass of payload

6c: Mt*8= Mf; the mass of your fuel and oxidizer.

So now you have everything you need. Number of engines, amount of fuel, and tankage. From here you can figure out total vehicle mass and cost so that you can directly compare results from different engines.

I design my missions backwards this way with later stages+couplers entered as payload for previous stages.

For a first stage lifter I'll use the sea level thrust and an Isp mid-way between Vac and Isp. For all others I use the vacuum numbers.

It only takes a few minutes to design a multistage rocket this way, and then I build it IAW the numbers. Takes all the guesswork out of the process and assures that my design is cheap, efficient, and will do exactly what I need it to do.

Best,

-Slashy

Edited June 24, 2015 by GoSlash27

[Lynch]

Best regards to Slashy on his answer to my post, I am preparing a new post up on calculations; for whom interested I await you on the links of the 1st post of this thread. =)

[Kerbart]

A brave attempt to make our lives easier is always appreciated. Critiquing positive efforts to improve the life of the KSP community members should always be met with positive critique I think, even if you don't agree (positive ≠ attaboys)

• Color coding is good as it helps us to identify good/bad. But if overpowered is considered bad, I wouldn't color it green. Maybe red/yellow/green/blue, with red for a TWR <1, yellow for a positive TWR that's insufficient (whatever that number is), green for a TWR in the desired range and blue for the overpowered range?
  
• What does the spreadsheet add compared to just building inside the VAB and using, say, Kerbal Engineer? This seems to be a kumbersome (<- ) way to design a rocket. I'm sure designing the spreadsheet was a fun exercise but I'm not sure what you'll get out of it if you didn't build the tool, so to say
  
• One approach is to use the optimizer in Excel. As Slashy mentioned: my payload is x, my required dV is y. I want a two-stage launchers. Go! and the model would tell me what the most optimal choice is within those constraints. That's pretty tough to build though
  
• So what about a "build analyzer"â€â€you give it the configuration of your rocket, and the model shows various alternatives. Instead of 3 mansails I'd get more DV with one mainsail and two skippers? Should or should I not use a nuclear engine? Those are interesting questions to answer.
  

I think that where the model gets interesting is when you quickly want to see how various configurations stack up against each other.

[Lynch]

A brave attempt to make our lives easier is always appreciated. Critiquing positive efforts to improve the life of the KSP community members should always be met with positive critique I think, even if you don't agree (positive ≠ attaboys)

• Color coding is good as it helps us to identify good/bad. But if overpowered is considered bad, I wouldn't color it green. Maybe red/yellow/green/blue, with red for a TWR <1, yellow for a positive TWR that's insufficient (whatever that number is), green for a TWR in the desired range and blue for the overpowered range?
  
• What does the spreadsheet add compared to just building inside the VAB and using, say, Kerbal Engineer? This seems to be a kumbersome (<- ) way to design a rocket. I'm sure designing the spreadsheet was a fun exercise but I'm not sure what you'll get out of it if you didn't build the tool, so to say
  
• One approach is to use the optimizer in Excel. As Slashy mentioned: my payload is x, my required dV is y. I want a two-stage launchers. Go! and the model would tell me what the most optimal choice is within those constraints. That's pretty tough to build though
  
• So what about a "build analyzer"â€â€you give it the configuration of your rocket, and the model shows various alternatives. Instead of 3 mansails I'd get more DV with one mainsail and two skippers? Should or should I not use a nuclear engine? Those are interesting questions to answer.
  

I think that where the model gets interesting is when you quickly want to see how various configurations stack up against each other.

True, im just trying my best to contribute to the society though; as much as i can. =)