Rocket Science Terms and Basics in KSP - Simplified for Beginners

[Gianni1122]

[Originally a reply to StifMeister]

*Looks OVERWHELMING but it's 'some' basics of ROCKET SCIENCE SIMPLIFIED*
-KSP Veterans Please Don't Be Snarky-


First off, I HIGHLY recommend beginners use the Kerbal Engineer Redux mod. It shows you vessel info like DeltaV, TWR, Mass, Fuel, etc. and does the math so you don’t have to.


WHEN BUILDING ROCKETS USING Kerbal Engineer Redux, YOU WILL SEE:

-TWR (THRUST TO WEIGHT RATIO):
Basically tells you if the engines you're using are strong enough to lift the weight of your rocket above the ground. A TWR of 1.00 your rocket will hover. If it's less than 1.00 it will sink. A TWR of 1.50-2.00 is ideal and your rocket will lift off.

-DELTA-V:
Not to be confused with fuel, delta-V is one of the most important things in rocket science. It is a bit complicated but to put it as simply as I can, Delta-V is the "miles per gallon" that your rocket can get. Just like a cars mile per gallon (mpg) rating determines how far a car can travel on one gallon of fuel, a rockets delta-V (measured in meters per second) determines how far a rocket can travel using different engine and fuel combinations.

Every trip you make into space and every maneuver you do require a certain amount of Delta-V to complete. For example, you need roughly 3,000-4,500m/s of Delta-V to get into orbit around kerbin.

-WHEN CHOOSING ENGINES:
With or without the mods I mentioned, hover over an engine before selecting it and you will see its stats. There are three stats that are most important for beginners. "Max Thrust (Vac.)" and "Max Thrust (ASL) and "fuel Consumption"

1.) Max Thrust (Vac.)= Max Thrust in a 'Vacuum' (space)

2.) Max Thrust (ASL)= Max Thrust 'At Surface Level' (on the ground where there is more gravity)

3.) Fuel Consumption= How many 'units of fuel per second' an engine uses

These stats basically tell you how efficient an engine will be in space and at the surface of a planet (mainly Kerbin)

For Example:

LV-909 Terrier Engine
Max Thrust (Vac.)= 60.00
Max Thrust (ASL)= 14.78
Fuel consumption= 3.54 fuel/sec

LV-T30 Reliant Engine
Max Thrust (Vac.)= 215.00
Max Thrust (ASL)= 200.67
Fuel Consumption= 14.60 fuel/sec

Since the Reliant engine has more thrust ("power"), it is better to use for lifting off the GROUND because you need more power to fight gravity. The Terrier engine is better to use in SPACE because it uses less fuel/sec than the Reliant and since there is hardly any gravity in space, power is less important than fuel consumption.

i.e.
On the ground, you want engines with more thrust.
In space, you want engines with less fuel consumption.




*I could try explaining more terms and concepts in a simplified form upon request.*
*If any KSP Vets want to add SIMPLIFIED explanations of things I left out, please do.*


Cheers
- Gianni

[Gamer]

Next thing to add would be ISP.

[Gianni1122]

*This is not a "must know" for beginners trying to build rockets in KSP. However,


-ISP (Specific Impulse):
The Isp of an engine, or more specifically, "an engine's specific impulse", is how efficiently said engine converts fuel into thrust in order to propel a rocket. It determines how much thrust the engine will produce using one unit of fuel

In Simple Terms:
Isp is how good an engine is at turning fuel into thrust.

For Example:
A Hummer with 1 gallon of gas cannot travel as far as a Honda Accord can with the same amount of fuel because the Honda's engine uses gas more "efficiently" than the hummer's engine does.

The higher the Isp, the more efficiently the engine uses fuel. (Higher Isp = More Efficient Engine)

*Isp is used in the in the mathematic formula that calculates delta-V

[=BB= Misophist]

Useful knowledge bits:
SSTO (Single Stage to Orbit) to low orbit is the best way to launch.
Unless its a low orbit sat, bring a transfer stage.
Disposable fuel tanks are a must for interplanetary missions. More fuel, less weight.
Always include a fixed solar panel. Extendable ones need power to extend.
Dont use mechjeb until you can manually land on the moon.
Planes are fun in sandbox, annoying in career, and useless in science.
Dont use ion engines for anything that isnt a .625 unmanned probe.

I'll add more as I think of them.

[Manwith Noname]

I kind of like your analogy for delta v to miles per gallon but you should perhaps include what it actually translates as too, which is "change in velocity".

[Gianni1122]

Sir Panache,
Keep em comin! Thanks! Don't forget to elaborate so as to make it easier for beginners. I.e. SSTO=Single Stage To Orbit

Manwith Noname,
Thanks. I was hoping that analogy would be understandable. I left out things like delta-V literally meaning "velocity change" and so on to keep it as simple as possible. It was really difficult for me to find 'very basic' explanations when I first got in to KSP.

[ghpstage]

Originally posted by Gianni1122:

Manwith Noname,
Thanks. I was hoping that analogy would be understandable. I left out things like delta-V literally meaning "velocity change" and so on to keep it as simple as possible. It was really difficult for me to find 'very basic' explanations when I first got in to KSP.

The trouble is that without the basic definition of dV the term is meaningless as you can't even see it without a mod. I think you are in danger of causing confusion through oversimplification here.

Also,

2.) Max Thrust (ASL)= Max Thrust 'At Surface Level' (on the ground where there is more gravity)

Is just wrong.

ASL is At Sea Level not surface level. More importantly it has nothing to do with gravity.
Its atmospheric pressure that is important as this reduces both engine efficiency and thrust. Its also Kerbin specific, if you land on Duna or Laythe you will have a higher ISP and thrust at 'sea' level, but if you land on Eve then they are going to be much, much lower.

Non atmospheric bodies use the vacuum ISP and thrust values whether you are in orbit of them or sitting on the surface.

[Gianni1122]

Thats why I said, "WHEN BUILDING ROCKETS USING Kerbal Engineer Redux..."

In realality ASL means SEA level, in KSP It means SURFACE level because of the lack of water bodies on planets with atmosphere... I'm pretty sure anyway

Either way, whether I'm right or wrong, I guess you didnt see the "snarky" part

By the way, it's rocket science. it all has to do with gravity..

[ghpstage]

Originally posted by Gianni1122:

Thats why I said, "WHEN BUILDING ROCKETS USING Kerbal Engineer Redux..."

In realality ASL means SEA level, in KSP It means SURFACE level because of the lack of water bodies on planets with atmosphere... I'm pretty sure anyway

Even when using KER the analogy still doesn't explain it very well without the basic definition, plus its much closer to range than MPG, you even state this yourself!
Personally I prefer the "dV is the currency of spaceflight" analogy anyway.

ASL values in KSP is specific to Kerbin sea level pressures, it is completely meaningless on other bodies regardless of their having an atmosphere or not so their existance doesn't change what it means.

[Gianni1122]

The point of an analogy is to express a different way to interpret a correlation of the thing being interpreted without using the "basic definition". The anology I used applies. if you can't comprehend that specific correlation I'd be glad to lay it for you in more laymans terms

[TreeCase]

Originally posted by Gianni1122:

By the way, it's rocket science. it all has to do with gravity..

Thrust has nothing to do with gravity, and everything to do with pressure. To quote Wikipedia: "Rocket thrust is caused by pressures acting in the combustion chamber and nozzle. From Newton's third law, equal and opposite pressures act on the exhaust, and this accelerates it to high speeds."

"As exit pressure varies from the ambient (atmospheric) pressure, a choked nozzle is said to be underexpanded (exit pressure greater than ambient), perfectly expanded (exit pressure equals ambient), overexpanded (exit pressure less than ambient; shock diamonds form outside the nozzle), or grossly overexpanded (a shock wave forms inside the nozzle extension)."

Citation[en.wikipedia.org]

[Gianni1122]

If you're seriously implying that an object creating thrust doesn't need to inversely act upon the PRINCIPAL force keeping it from independantly moving in the first place, then I can't help you. However, maybe Wikipedia can...

"In astrodynamics and rocketry, gravity drag (or gravity losses) is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field. In other words, it is the cost of having to hold the rocket up in a gravity field.

It is the difference between the delta-v expended and the theoretical delta-v for the actual change in speed and altitude, plus the delta-v for other losses such as air drag, that are experienced by a thrusting spacecraft."

[ghpstage]

Drag, losses and flight are not what is being talked about.

2.) Max Thrust (ASL)= Max Thrust 'At Surface Level' (on the ground where there is more gravity)

This is whats being discussed.
Here you are stating (intended or not) that gravity affects the thrust output of an engine, which isn't true, while neglecting to mention atmospheric pressure which is the actual cause of the change in thrust.

[Gianni1122]

I siad (in simplified terms BTW), "Max thrust (ASL)=" the maximum amount of thrust capable for a given engine to achieve while ""ASL""...

In the interest of keeping things simple, I was not trying to delve into the concept of ISP and how propulsion works in and out of an atmosphere

You are inferring that I was talking about specific impulse when in fact all I was doing was using an analogical correlation of Isp to explain why an engine with more thrust is better where there is more gravity.

I was trying to simplify the core mechanics of rocketry without involving concepts that BEGINNERS do not need, such as Isp.

Btw, I know you don't know what gravity is but are you familiar with the term "snarky"? Because one of the first things I said was, "KSP Veterans Please Don't Be Snarky"... I would emphasize the words "please don't" but I guess it's too late for that.

It's people like you that made me want to create this thread in the first place. It was such a pain when I was trying to learn these things because almost all of the info out there is written by a bunch of smart asses who cant wait to show off how they can explain big words by using even bigger words.

[TreeCase]

Originally posted by Gianni1122:

I siad (in simplified terms BTW), "Max thrust (ASL)=" the maximum amount of thrust capable for a given engine to achieve while ""ASL""...

The only thing gravity affects is the TWR. Certainly, the rocket has to overcome gravity(which is what the TWR shows), but gravity does NOT affect thrust. If you'll kindly take a look at the equation for thrust, it is:

F = qVe+(Pe-Pa)Ae

Where:
F = Thrust
q = Flow rate of propellant
Ve = Ejection speed of propellant
Pe = Exhaust gas pressure
Pa = Ambient atmospheric pressure <-!!!
Ae = Area of nozzle exhaust

This equation has a distinct lack of gravity.
Meanwhile, TWR is calculated by dividing the thrust of the vehicle by its weight(which is only possible with gravity).

Source for thrust equation[www.braeunig.us]
Source for TWR equation[en.wikipedia.org]

[Docsprock]

Too bad that to understand this, you need a mod.