How many Large Hydrogen Thrusters per 1,000,000 weight?

[Mad_House]

I'm experimenting with planets (Yes, it's going horribly) and I've found some difficulty putting together planet-capable ships. Playing vanilla, how many large hydro-thrusters do you need to lift a 1,000,000 ton ship off the ground? How many would you estimate an 8,000,000 ton ship?

[Thalyn]

A single Large Hydrogen Thruster can "hover" approximately 6,000kg, or 6 tonnes 600,000kg, or 600 tonnes. It's actually slightly higher than that, but the math is easier if you work of 1G = 10N/kg instead of 1G = 9.81N/kg and it's still close enough.

Thus a 1,000,000 tonne ship would require approximately 166,666 1,666 thrusters just to break even in 1G. 8,000,000 tonnes would naturally require 8x as many (approximately 1,333,333 13,333). To actually produce lift you simply need more than that - myself I like an extra 20% to allow stopping from 100m/s free-fall in about 2km.

Fuel usage would be astronomical with the default game. A single, full Hydrogen tank would last 0.00029 0.23 seconds with all those thrusters at full burn, and for every 1kg of Ice you process you'll get about 0.000000000348 0.000000276 seconds under the same conditions. Decrease this proportional to the amount of extra thrusters you add: eg If you add 20% more thrusters (6/5) you'll get only 84% (5/6) the flight time, 100% more thrusters (2/1) gets 50% (1/2) the flight time and so on.

Of course, if you meant 8,000,000kg (which is only 8,000 tonnes) than you can divide the number of thursters by 1,000 and multiply the expected fuel runtimes by the same.

[Mad_House]

Oh damn lol, I'm sorry Thalyn, I meant to say KG in place of the tons.

I'll go ahead and edit it now, but if you're still on, can you provide an algorithm for what the requirements per 1,000,000 KG would be?

I totally didn't mean to say tons lol.

[Mad_House]

Also, would large atmospheric thrusters be better to use?

[Thalyn]

As I mentioned, it's much the same but divide by 1,000.

So instead of 166,666 166 thrusters, you'd be looking at approximately 166 1.6 for "hover", but naturally you can't install part of a thruster (rounding down isn't a problem since we're already understating their output). You'd then get 2.3 198 seconds (I messed up earlier - dunno where the 9 came from, plus I'm out by a factor of 10, and it threw off my numbers) of full thrust per full Hydrogen tank, or approximately 0.00000276 0.000198 seconds per 1kg of Ice. The same applies for increasing the number of thrusters reducing the flight times accordingly, with exactly the same ratios.

Reaching 0g requires you to get 42km from the surface, so at maximum speed it will take you at least 420 seconds. If you're just holding in the up button than that's how much fuel you'll need to allow for - so around 183 2 and a bit full tanks, 152,173,913kg 2,121,212kg of Ice or a combination there-of (keeping in mind that each Oxygen Generator can process 167kg of Ice per second). And this is for the 100% mark, which you'll need to be over to fly.

But you can get away with substantially less fuel than that (probably 1/3 as much) if you take into consideration that you use less thrust to maintain speed than to accelerate, gravity starts to decrease at 6km above the surface and if you're using Ice your ship will get lighter as it's consumed. A launch script, or just pulsing (since there's no friction or air resistance) will be required for this.

Returning from 0g depends largely on the altitude you want to stop and how much thrust you're using to do it. If you're 20% over like I mentioned, that 2km in 1G takes about 40 seconds so you only need to allow that much fuel. But there's no cheaper way this time - that's 40 seconds of unavoidable 100% thrust, unless you like craters.

[Thalyn]

Large Atmos help, but they're useless for higher flight. Once you get to around 7-8km off the planet they basically can't lift their own weight, and that distance will actually be lower if you fly over a mountain (since your altitude is measured from surface, where their output is based on height above sea level).

Still, you can use them to get a nice boost while they're effective.

If you've no intention of taking the ship off-world, they're a much better idea. The logistics are far, far simpler and they're more power efficient.

[Mad_House]

That certainly blows my planet-capable ships out of the water, at least for the most part. I tried it a few times with my lightest ships, and it seems that the designs are too heavy for 4 atmo thrusters on the bottom to do anything. I guess these will just be meant for the moon...

Should I keep any of my hydrogen thrusters, or are they too inefficient and useless for space travel? I'm wanting my designs to be workshop convenient, so people can actually like them. If hydrogen thrusters aren't any good, or do you think people would rather I make these ships pure Ion thrust? Either way is fine, as long as these ships work well I'm happy doing either way.

And thank you so much for your contributions here, you've taken it to the real science of it all and I love that.

[Thalyn]

I have a sneaking suspicion... that I'm out in my math still. You remember that 9? Well, I don't think that's the only mistake I've made - I suspect I've actually understated the power of the thrusters by a factor of 100. In other words, a single LG-LHT isn't capable of lifting 6 tonnes but rather 600t.

However, given that's now two mistakes I'm reluctant to try again. It's hot and I'm unwell but I probably should have checked my numbers a little closer, so if anyone else can step in and correct me here I'd be most appreciative.

If I am wrong... which I believe I am... and if I'm out by as much as I think, then divide the number of thrusters by 100 and multiply the flight times accordingly.

Sorry, chief, but I'm perhaps not the best person to be assisting at the moment. Maybe tomorrow after some sleep but I think tonight might be a write-off for me when it comes to math.

I can say, however, that pure Ion would be a colossal undertaking. Those things are so weak in atmosphere and so damned heavy that using them as the sole, or even primary lift provider is basically impossible on any ship that has blocks other than thrusters on it.

[Tal Maru]

1 Newton of thrust will move 1 kilogram 1 meter in 1 second.
Gravity = 9.8 meters per second

you need 10 newtons of thrust to hover in a 1 gravity field.

Large Block Small Hydrogen Thrusters produce 900,000 N of thrust
1 Large Block Small Hydrogen Thruster can hover with 91,836 Kg

Large Block Large Hydrgoen Thrusters produce 6,000,000 N of thrust.
1 Large Block Hydrogen Thruster will hover with 612,244 Kg


You would need 10 small thrusters to lift a 1 Million Kg ship.
You would need 2 large thrusters to lift a 1 Million Kg ship.

You would need 80 small or 16 large to lift a 8 million kg.

[arbi186]

the game is so hard

[Thalyn]

Cheers, Tal Maru. Looks like I was off by a factor of 100 again, even re-working it. Comforting to know! I'll go back and do some editing, with a little preservation to remind myself not to do that again.

[Tericc]

Originally posted by Tal Maru:

1 Newton of thrust will move 1 kilogram 1 meter in 1 second.
Gravity = 9.8 meters per second

you need 10 newtons of thrust to hover in a 1 gravity field.

Large Block Small Hydrogen Thrusters produce 900,000 N of thrust
1 Large Block Small Hydrogen Thruster can hover with 91,836 Kg

Large Block Large Hydrgoen Thrusters produce 6,000,000 N of thrust.
1 Large Block Hydrogen Thruster will hover with 612,244 Kg


You would need 10 small thrusters to lift a 1 Million Kg ship.
You would need 2 large thrusters to lift a 1 Million Kg ship.

You would need 80 small or 16 large to lift a 8 million kg.

Hope you dont mind but i copy and pasted what you said in note pad for refrance.
Nice Help for future designs when i only needed just one more thruster

[jamnb]

soon the lag from using so many vanilla thrusters/gyros/reactors is far greater than the lag from just using modded stuff

[Anrock]

A side note: it's more convenient to use spreadsheets to calculate all this stuff - computer at least wouldn't accidentally divide or multiply by 10 :)
For ship calculations i'm using google spreadsheets for calculations + SE wiki as engine and weight reference + wikipedia as basic school physics reference.
There is also a huge spreadsheet to calculate absolutely everything, made by redditers from r/spaceengineers - https://docs.google.com/spreadsheets/d/156mIkBxN5k-rA0z5jD28CgNehFOM-Ib5enwpykIKAfU/edit?usp=sharing
But that's probably overkill.

[Mad_House]

Originally posted by Tal Maru:

1 Newton of thrust will move 1 kilogram 1 meter in 1 second.
Gravity = 9.8 meters per second

you need 10 newtons of thrust to hover in a 1 gravity field.

Large Block Small Hydrogen Thrusters produce 900,000 N of thrust
1 Large Block Small Hydrogen Thruster can hover with 91,836 Kg

Large Block Large Hydrgoen Thrusters produce 6,000,000 N of thrust.
1 Large Block Hydrogen Thruster will hover with 612,244 Kg


You would need 10 small thrusters to lift a 1 Million Kg ship.
You would need 2 large thrusters to lift a 1 Million Kg ship.

You would need 80 small or 16 large to lift a 8 million kg.

That's not that hard to do, I guess I have a little bit of refitting to do for my ship then! I offer a huge thank you to everyone here! You guys are the best!

https://www.youtube.com/watch?v=YRL4uIVzVWI

[Thalyn]

Originally posted by Anrock:

A side note: it's more convenient to use spreadsheets to calculate all this stuff - computer at least wouldn't accidentally divide or multiply by 10 :)

Hey! I resemble that remark!

Ugh... still feel bad about it the next morning. I know it's not that important, but it's year 9 physics at best - sucks to mess it up so badly.