Halp me, I'm just some noob player :(

[Wᴏʟꜰʀᴀᴍ]

I wanted to get better. Could you guys please answer my questions that I can't answer on my own. There'll be more after this first one : I tried calculating the TWR of the rocket above. I started by multiplying its mass (28) to Earth's gravity (9.8). Then I divided its thrust (115) to the answer I got. The result was 0.419. It's almost correct (the 4 should be on the left of the decimal point as shown above) but I don't know what did I do wrong.

 

[SupremeDorian]

Altaïr Horus Lupercal

 

[Altaïr]

Hi Wolfram,

The calculation is correct, but the problem is that the engine thrust is given in tons instead of kN. The Hawk engine has a thrust of 1150 kN. This value will give you the good result.

Actually, Stef chose to display thrusts in tons after 1.4. That's practical because if thrust is 115 tons, it means that it can make lift off a launcher that weighs less than this.

For information, Stef didn't do the conversion well because he used a factor 10 instead of 9.8, so a Hawk has actually a thrust of 117.3 tons.

 

[Horus Lupercal]

View attachment 17927 I wanted to get better. Could you guys please answer my questions that I can't answer on my own. There'll be more after this first one : I tried calculating the TWR of the rocket above. I started by multiplying its mass (28) to Earth's gravity (9.8). Then I divided its thrust (115) to the answer I got. The result was 0.419. It's almost correct (the 4 should be on the left of the decimal point as shown above) but I don't know what did I do wrong.

You're using the right ish numbers, but in the wrong sequence.

You have to think of 'mass' as a downwards force. Essentially gravity is accelerating you into the floor. TWR is the rockets acceleration in the opposite direction to potentially give you enough speed to get away from Earth (lift).

So, you first find out what acceleration the rocket is capable of. And this number applies in a no gravity, vacuum.

The engine you're using is the Hawk, and the tooltip says it generates 115t of thrust. To put this into a unit of measure we can use, we need to convert this in kN. Fortunately for ease, the game does it wrong and rather than using the universal gravitational constant like you would do in the real world (9.811blahblahblah), it uses 10 instead which works out as 1150kN of thrust.

So, acceleration, in vacuum, no gravity, is 1150kN (thrust) / 28 (mass) = 41.07.

Now, for TWR.

TWR is location depending. Your TWR on the moon will be different to Earth and different again to Mars because TWR is your acceleration upwards against local gravity downwards.

In the case of Earth in game, it's 9.8

So, you divide your acceleration (41.07) / against local g (Earth, 9.8) = your TWR at launch 4.1909.

 

[Lt. Snakestrike]

Yeah, they've already said it, but basically, the Mass is pretty much the weight in this case (that's how I think of it anyway, although probably not correct). Because it's the weight it already accounts for the gravity, so you don't need to do that yourself.

 

[Wᴏʟꜰʀᴀᴍ]

You're using the right ish numbers, but in the wrong sequence.

You have to think of 'mass' as a downwards force. Essentially gravity is accelerating you into the floor. TWR is the rockets acceleration in the opposite direction to potentially give you enough speed to get away from Earth (lift).

So, you first find out what acceleration the rocket is capable of. And this number applies in a no gravity, vacuum.

The engine you're using is the Hawk, and the tooltip says it generates 115t of thrust. To put this into a unit of measure we can use, we need to convert this in kN. Fortunately for ease, the game does it wrong and rather than using the universal gravitational constant like you would do in the real world (9.811blahblahblah), it uses 10 instead which works out as 1150kN of thrust.

So, acceleration, in vacuum, no gravity, is 1150kN (thrust) / 28 (mass) = 41.07.

Now, for TWR.

TWR is location depending. Your TWR on the moon will be different to Earth and different again to Mars because TWR is your acceleration upwards against local gravity downwards.

In the case of Earth in game, it's 9.8

So, you divide your acceleration (41.07) / against local g (Earth, 9.8) = your TWR at launch 4.1909.

Horus Lupercal, now I may sound like an idiot but that rocket's delta v is 2523 m/s, right? But why did it only get 1799 m/s here?

 

[Danny Batten]

Horus Lupercal, now I may sound like an idiot but that rocket's delta v is 2523 m/s, right? But why did it only get 1799 m/s here? View attachment 17935

Drag

 

[Horus Lupercal]

Horus Lupercal, now I may sound like an idiot but that rocket's delta v is 2523 m/s, right? But why did it only get 1799 m/s here? View attachment 17935

I've got your Dv as 2530m/s. Don't worry about that though, its just my calculator works out ISP itself rather than relying on the tooltip which is wrong.

But, nope, you're not going crazy or looking at things wrong.

It's generally accepted that it takes upwards of 2800-3000m/s of Dv to achieve LEO purely because of (as Danny puts it) drag and its effects on launch, despite it only needing about 1667m/s to make a circle at 30km.
We're (as in, the actual great minds on the forum) still trying to figure out how to calculate the exact Dv cost to break the atmosphere but the sheer amount of variables make it very complex without using simulations and at the minute its just a case of best guess and experience

 

[Wᴏʟꜰʀᴀᴍ]

Hey umm I have an another question. Could you guys please show me a step-by-step procedure of getting the Total ISP or Average ISP or whatever it's called of this rocket? Sorry for the inconvinience

 

[Horus Lupercal]

Hey umm I have an another question. Could you guys please show me a step-by-step procedure of getting the Total ISP or Average ISP or whatever it's called of this rocket? Sorry for the inconvinience View attachment 17943

That'd depend on how you're intending on flying said rocket, but assuming you're going to burn everything at once then the calculation is like so:

Firstly, figure out how much fuel all that is going to use per second.

• Hawk. 0.468t per second x 2 = 0.936 tons per second
• Broadsword = 0.145 tons
  • = 1.081 tons per second

Take the gravitational constant 9.8 and multiply it by 1.081 tons = 10.5938

Add up the combined thrust of all 3 engines in kN.

• Hawk. 1150kN x 2 = 2300kN
• Broadsword = 400kN
  • Total = 2700kN

Then take your total thrust (2700) and divide it by 10.5938 to get your combined ISP of...(drum roll)...254.86 seconds.

On a side note, that number only counts whilst all 3 engines are burning. As soon as the boosters with the Hawks cut out after...38.46 seconds, the remainder of the flight (147.74 seconds) under the broadsword will be at ISP 281.49 seconds.


For further reading on Specific Impulse, i waffle at great length about it here...

ISP
Specific Impulse

Sticking with the car theme, ISP is simply how fuel efficient an engine is. In car terms, that’s distance/fuel (miles per gallon for example). In space, that doesn't work because theoretically once you're in deep space with no forces acting on you, then you will continue in motion forever at a constant speed covering all the distance in the universe for free. (I know technically that’s the same for a car but you have drivetrain resistance, rolling resistance, drag etc. all acting on the car, trying to slow it, thus you need to keep applying fuel to maintain a speed).
ISP is essentially a measure of how much of fuel quantity it takes to produce an amount of thrust. The less fuel an engine burns to achieve a specific impulse, the more efficient it is.
Now, 2 things about ISP

1. It's measured in seconds
2. It does take gravity into account.

Why seconds, and not lbs, kg, N or whatever? Because NASA, when they were working all this stuff out, was a mix of 'borrowed' German scientists and Americans. One side (Zee Germans) wanted to use Metric. The Americans wanted to use Imperial. After what I'd like to assume was a good natured fight involving a lot of spanners and slide rules, they decided on a unit of measurement everyone knew, but wasn’t in either system. Seconds.
And with gravity, you use Earths gravity 9.8 regardless of where you are. Why? Because its used as a constant, a benchmark for comparison. It allows you to compare an ISP of say a Rocketdyne F1 Engine with a titan without worrying if someone has used...Mars...as a constant for the titan.
How to work out ISP then. Easy, the information pops up when you select an engine will tell you its ISP. And as long as you only use that engine, regardless of how many, the rockets ISP will be that number.
Things get complicated when you're using engine combinations, or boosters with different engines. Even though each engine is using is own ISP, when it comes to working out the Delta V (coming soon...) of that rocket, you need a combined ISP of the engines that are being used at the time.
There are 2 ways of doing this.
Hard Way:

1. you need the exhaust velocity of an engine. To work this out, you multiply thrust by fuel consumption.
2. Then, you multiply that, by g (9.8) to get an individual engine ISP
3. Do that for all engines
4. Now, for each individual engine, divide its force by its own ISP. Do this for all of the engines and add the totals together. Then take the combined total of all the thrust your engines create and divide that by the all the totals you've just worked out.

Or

Easy Way.

1. Add up the combined thrust of your engines
2. Add up the combined fuel consumption of your engines.
3. Take your gravitational constant (9.8) and multiply it by your total consumption.
4. Finally, take your combined thrust and divide it by the answer you just got.
5. BOOM. ISP Baby.

 

[Wᴏʟꜰʀᴀᴍ]

That'd depend on how you're intending on flying said rocket, but assuming you're going to burn everything at once then the calculation is like so:

Firstly, figure out how much fuel all that is going to use per second.

• Hawk. 0.468t per second x 2 = 0.936 tons per second
• Broadsword = 0.145 tons
  • = 1.081 tons per second

Take the gravitational constant 9.8 and multiply it by 1.081 tons = 10.5938

Add up the combined thrust of all 3 engines in kN.

• Hawk. 1150kN x 2 = 2300kN
• Broadsword = 400kN
  • Total = 2700kN

Then take your total thrust (2700) and divide it by 10.5938 to get your combined ISP of...(drum roll)...254.86 seconds.

On a side note, that number only counts whilst all 3 engines are burning. As soon as the boosters with the Hawks cut out after...38.46 seconds, the remainder of the flight (147.74 seconds) under the broadsword will be at ISP 281.49 seconds.


For further reading on Specific Impulse, i waffle at great length about it here...

Sheesh that's why the ISPs I calculated were only around 20 to 30, because I should've used kN instead of t. I've already read your "novel" but your solution above was the one that helped me more. Anyway thanks for your time and your kindness. And you're a very great person by the way

 

[Roosterbooster]

Also, something you might want to use in your rockets (put a docking port above the parachute, don't mind how the parachute connects to the port, i'm in a previous version)

 

[Altaïr]

Can't say better than Horus Lupercal

There are several spreadsheets available on this forum to make all those calculations. Here is mine:
https://docs.google.com/spreadsheet...zOEbB5pSJMOjeiR-ES4y0HOzxy8/edit?usp=drivesdk
It's simple, but it can only handle one stage at once.
Horus Lupercal has one much more complete.
Other members also did one, they are all valid, it's just a matter of choice

Beyond that, you shouldn't focus too much on delta-V during the lift-off phasis: the formula behind that supposes that you're not fighting gravity (and drag). The TWR is way more relevant for that part.
For example, a rocket with ion engines could have more than 10000 m/s of delta-V, but it would be unable to lift off.

 

[Horus Lupercal]

I've already read your "novel" but your solution above was the one that helped me more.

Yeah, I've always found answers to a specific question a lot easier to understand than someone waxing lyrical about something like my Basics post as even if they're delivered the same way, they're more relate-able and can then be altered to suit other problems. That's very much how I learned from Altair walking me hand-in-hand almost through it all,

rather than looking at the Wikipedia/KSP forums/google absolutely dumbstuck at symbols and un-related data sets (especially KSP).

Anyway thanks for your time and your kindness.

That's not a drama dude. Ask away if you've got more.

 

[Wᴏʟꜰʀᴀᴍ]

Yeah, I've always found answers to a specific question a lot easier to understand than someone waxing lyrical about something like my Basics post as even if they're delivered the same way, they're more relate-able and can then be altered to suit other problems. That's very much how I learned from Altair walking me hand-in-hand almost through it all,

View attachment 17954

rather than looking at the Wikipedia/KSP forums/google absolutely dumbstuck at symbols and un-related data sets (especially KSP).



That's not a drama dude. Ask away if you've got more.

I was about to ask something, then I came up with the answer as I try to interpret my question... LOL

 

[Horus Lupercal]

I was about to ask something, then I came up with the answer as I try to interpret my question... LOL

What was the question?

Also, from your perspective what else topics wise would think would be handy for new players to know for my 'novel'?

 

[Wᴏʟꜰʀᴀᴍ]

What was the question?

Also, from your perspective what else topics wise would think would be handy for new players to know for my 'novel'?

The question I was gonna ask is:
In a 2-stage rocket, does the delta v of the 2nd stage adds up to the velocity generated by the 1st stage?

Yesterday I saw an article in Fandom about some equations and of course, as a newbie, I can't understand it. I think it would be nice to add this to your thread

https://spaceflight-simulator.fandom.com/wiki/Equations

 

[Wᴏʟꜰʀᴀᴍ]

Can't say better than Horus Lupercal

There are several spreadsheets available on this forum to make all those calculations. Here is mine:
https://docs.google.com/spreadsheet...zOEbB5pSJMOjeiR-ES4y0HOzxy8/edit?usp=drivesdk
It's simple, but it can only handle one stage at once.
Horus Lupercal has one much more complete.
Other members also did one, they are all valid, it's just a matter of choice

Beyond that, you shouldn't focus too much on delta-V during the lift-off phasis: the formula behind that supposes that you're not fighting gravity (and drag). The TWR is way more relevant for that part.
For example, a rocket with ion engines could have more than 10000 m/s of delta-V, but it would be unable to lift off.

How do I enter values into the spreadsheet?

 

[Horus Lupercal]

The question I was gonna ask is:
In a 2-stage rocket, does the delta v of the 2nd stage adds up to the velocity generated by the 1st stage?

They're accumulative. So the Dv of stage one is added to the Dv of stage 2 to create a total rocket Dv. So like your rocket at the top of the thread is sat at 1799m/s and out of fuel. If you had a second stage on top of that with 1000 m/s of Dv to play with, you can alter your current velocity by another 1000, potentially increasing your velocity to 2799m/s, or bringing you down to 799m/s, or any combination inbetween.

Yesterday I saw an article in Fandom about some equations and of course, as a newbie, I can't understand it. I think it would be nice to add this to your thread

The majority of those I've not put into the Basics thread as they go way beyond the bounds of a basic spaceflight and into more advanced flight planning like rather than just 'put satellite into orbit', orbital periods/velocity allows you to work out the Dv cost to go from one area in LEO to another setting up potentially geo sync orbits, higher ends of the Earths orbit etc, Keplers Law then allows you to not just work out a different orbit, but a specific distance onto that orbit creating equal distance constellations like the GPS system.

i am working on making the suicide burn maths work for landings but am getting similar drag issues that are experienced on take off so that may take some more time.

That being said, I have worked nearly all the equations on the wiki equations page above and it's all on my spreadsheet on various pages as required. Use the updated one, rather than the first one.

 

[Wᴏʟꜰʀᴀᴍ]

They're accumulative. So the Dv of stage one is added to the Dv of stage 2 to create a total rocket Dv. So like your rocket at the top of the thread is sat at 1799m/s and out of fuel. If you had a second stage on top of that with 1000 m/s of Dv to play with, you can alter your current velocity by another 1000, potentially increasing your velocity to 2799m/s, or bringing you down to 799m/s, or any combination inbetween.



The majority of those I've not put into the Basics thread as they go way beyond the bounds of a basic spaceflight and into more advanced flight planning like rather than just 'put satellite into orbit', orbital periods/velocity allows you to work out the Dv cost to go from one area in LEO to another setting up potentially geo sync orbits, higher ends of the Earths orbit etc, Keplers Law then allows you to not just work out a different orbit, but a specific distance onto that orbit creating equal distance constellations like the GPS system.

i am working on making the suicide burn maths work for landings but am getting similar drag issues that are experienced on take off so that may take some more time.

That being said, I have worked nearly all the equations on the wiki equations page above and it's all on my spreadsheet on various pages as required.

Eyyy see? I answered myself correctly!

Give me some time to think for topics

 

[Altaïr]

How do I enter values into the spreadsheet?

Ah, it's in read-only mode, because otherwise everybody would work on the same instance. You have to do your own copy, then you can use it with google sheets (there's an application for that if you play on a phone).

The question I was gonna ask is:
In a 2-stage rocket, does the delta v of the 2nd stage adds up to the velocity generated by the 1st stage?

Yesterday I saw an article in Fandom about some equations and of course, as a newbie, I can't understand it. I think it would be nice to add this to your thread

https://spaceflight-simulator.fandom.com/wiki/Equations

Same as Horus, but just to make sure you don't make things wrong, the first stage delta-V must be calculated by taking into account the second stage's mass. You can't calculate the delta-V for the first stage alone and add it to the second stage.

Don't bother with the equations to be honest, and let that to the nerds like us
We precisely work on making them understandable.
The most important is to understand how it works in practice, the concepts behind this... Then if you want to go further (and if you like maths), you can have a look and toy with the equations.

 

[Wᴏʟꜰʀᴀᴍ]

Ah, it's in read-only mode, because otherwise everybody would work on the same instance. You have to do your own copy, then you can use it with google sheets (there's an application for that if you play on a phone).



Same as Horus, but just to make sure you don't make things wrong, the first stage delta-V must be calculated by taking into account the second stage's mass. You can't calculate the delta-V for the first stage alone and add it to the second stage.

Don't bother with the equations to be honest, and let that to the nerds like us
We precisely work on making them understandable.
The most important is to understand how it works in practice, the concepts behind this... Then if you want to go further (and if you like maths), you can have a look and toy with the equations.

I'm into Science really but I can't call myself good in Science if I'm not good in Math since Science involves Math too so I'm trying my best to improve myself in this field.

Anyway Horus Lupercal, what if you make a guide on landing and making an orbit on the Galilean Moons, especially Europa?

 

[Roosterbooster]

I'm quite similar to you, wolfram.

Interested in science and such but not too good with math.

 

[Wᴏʟꜰʀᴀᴍ]

I'm quite similar to you, wolfram.

Interested in science and such but not too good with math.

Everybody loves hearing science facts but most of those science facts were made possible by complex maths, which everybody (not all) hates. The irony

 

[Altaïr]

Ah, too bad... But even when being good at maths, it's still better to first understand how it works in practice.

We can still explain a particular equation if you wish, but as equations are not especially popular I didn't really think it was worth it to make a thread for that.
And some phenomenons can be understood in a way simpler way with experience: the gravitational slingshot is a good example for this. The maths behind that are painful, but in practice it's a similar phenomenon to shooting a ball at a moving truck