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

[Wᴏʟꜰʀᴀᴍ]

Well done!

(It's crazy how a game like this can make anyone do maths for recreation. )

I think I'm now ready to conquer Venus, along with the help of the informations above

 

[Horus Lupercal]

Horus Lupercal, look! I did everything right. Calculating the ISP, TWR, and the delta v. I'm beginning to understand things View attachment 18096 View attachment 18097

Ha, looks like you're not far off at all.

Well done!

(It's crazy how a game like this can make anyone do maths for recreation. )

Yeah, you couldn't force it on someone at school. Here, yeah, let's throw some numbers downrange

 

[Wᴏʟꜰʀᴀᴍ]

Well, thanks for the answer .
Another question: I'm using mix first stages with 4 frontiers and 4 titans... If, during the ascent, I shut down the titans in pairs, im actually increasing ISP and dV, right?

Horus Lupercal, please explain this to me

 

[Pink]

I'm not Horus, but I'd like to try....
The Frontier engines have higher isp than the Titans. Which means more dV from the same amount of fuel, right?
But that's useless if the Frontier engines are not powerful enough to get your rocket off the launch pad. (aka the TWR is too low).
So what you do is you add some Titans to give your rocket a TWR boost at launch (yes, you turn on the Frontiers at the same time).
And then, when the rocket burns enough fuel to be light enough for the Frontiers to carry it without the help of the Titans, you shut down the Titans and keep going on just the Frontiers, for a little dV boost.
Some more maths is required to figure out when to shut down the Titans

 

[Wᴏʟꜰʀᴀᴍ]

I'm not Horus, but I'd like to try....
The Frontier engines have higher isp than the Titans. Which means more dV from the same amount of fuel, right?
But that's useless if the Frontier engines are not powerful enough to get your rocket off the launch pad. (aka the TWR is too low).
So what you do is you add some Titans to give your rocket a TWR boost at launch (yes, you turn on the Frontiers at the same time).
And then, when the rocket burns enough fuel to be light enough for the Frontiers to carry it without the help of the Titans, you shut down the Titans and keep going on just the Frontiers, for a little dV boost.
Some more maths is required to figure out when to shut down the Titans

It makes sense, yep it absolutely does. Thanks! It's like those jets that are placed in a slingshot to take off from a warship

 

[Horus Lupercal]

Horus Lupercal, please explain this to me

I'm not Horus, but I'd like to try....
The Frontier engines have higher isp than the Titans. Which means more dV from the same amount of fuel, right?
But that's useless if the Frontier engines are not powerful enough to get your rocket off the launch pad. (aka the TWR is too low).
So what you do is you add some Titans to give your rocket a TWR boost at launch (yes, you turn on the Frontiers at the same time).
And then, when the rocket burns enough fuel to be light enough for the Frontiers to carry it without the help of the Titans, you shut down the Titans and keep going on just the Frontiers, for a little dV boost.
Some more maths is required to figure out when to shut down the Titans

It's all about the efficiency. Once I've cooked some food I'll run you some numbers and show what Mooncrasher means. And an example of why staging/boosters are better than big SSTO type vehicles

 

[Horus Lupercal]

Hmmm... ribs.

Anyway, where were we...?

I'm not Horus, but I'd like to try....
The Frontier engines have higher isp than the Titans. Which means more dV from the same amount of fuel, right?
But that's useless if the Frontier engines are not powerful enough to get your rocket off the launch pad. (aka the TWR is too low).
So what you do is you add some Titans to give your rocket a TWR boost at launch (yes, you turn on the Frontiers at the same time).
And then, when the rocket burns enough fuel to be light enough for the Frontiers to carry it without the help of the Titans, you shut down the Titans and keep going on just the Frontiers, for a little dV boost.
Some more maths is required to figure out when to shut down the Titans

Horus Lupercal, please explain this to me

Imagine we have a fuck hewg rocket. 1289 tons worth to be exact, in an SSTO configuration.

• All up - 1289 tons
• fuel total - 1109 tons
• Dry mass - 186.5
• 4 titans
• 3 Frontiers

So, if we press launch on this, we'd have

• TWR - 1.21
• ISP - 252.79 seconds
• Burn time - 177 seconds
• Dv - 4789.32m/s

Right. what Mooncrasher wants to do is sequentially turn off the Titans to increase its efficiency. And he is absolutely right.

Turning 2 of them off gives you a ISP of 258.13 seconds. Turning off the last pair brings that up to 285.71 seconds.

The problem with that, as Mooncrasher also rightly put it, is TWR. The Titans are generating 4/5ths of the overall thrust and just turning them off willy nilly is going to book you a crash course with the planet.

So. When to turn them off?

Now that involves a fair amount of maths, a bit of trial and error. Luckily for you good souls, my spreadsheet has a trial and error page that allows theoretical flights like this without much hassle.

So, as the rocket passes 68% fuel (that's 56.9 seconds into the flight, having burnt 352 tons and used 792.26m/s of Dv), you've lightened the rocket just enough to be able to turn off the outer most Titans.

Lets do the comparison then.

Say we continue on as normal, without shutting down the Titans (flight plan A)).

• Thrust - 15360 kN
• TWR - 1.67
• ISP - As above)
• Remaining fuel - 749.2 tons
• Consumption - 6.2 tons per second
• Remaining burn time - 120.9 seconds
• Dv - 3997.06 m/s

Or, we shut them down (Flight plan B).

• Thrust - 9360 kN
• TWR - 1.02 (like I said, just)
• ISP - 258.13 m/s
• Remaining fuel - As above
• Consumption - 3.7 tons/second
• Remaining burn time - 202.6 seconds
• Dv - 4081.46 m/s

As you can see, we've gained an extra 84.4 m/s just by turning them off at the right time.

What about that last pair then? Lets keep going.

So, to turn off those last Titans, we're gonna need to go right down to 14% fuel (154.35 tons left)

Again, lets compare.

Plan A (4 titans, 3 Frontiers throughout).

• Thrust - Still 15360 kN
• TWR - 4.59
• ISP - Still 252.79 Seconds
• Remaining fuel - 154.35 tons
• Consumption - 6.2 tons/Sec
• Remaining burn time - 24.89 seconds
• Dv remaining - 1493m/s

or

Plan B (dropping from 2 Titans and 3 frontiers to just the 3 frontiers)

• Thrust - 3360 kN
• TWR - 1.005
• ISP - 285.71 seconds
• Remaining fuel - 154.36 tons
• Consumption - 1.2 tons
• Remaining burn time - 128.63 seconds
• Dv remaining - 1688m/s.

We gain another 195 m/s again just for turning off the last Titans. Interestingly if we left just those pair on, the Dv for that last part is 1525.55m/s. The reason for the huge jump is because of the huge jump in efficiency because we're no longer using the thirsty titans anymore.

All that ^^^ waffle means that by turning off your less efficient engines at the right times (in this instance) raises your Dv from 4789.32 to 5068.72m/s and is the more efficient way of using your SSTO.

Next. Boosters and how fat-shaming your rocket into losing weight makes it more efficient in flight.

 

[Horus Lupercal]

Lets assume everything else is the same on Fuckhewg rocket. Except now, we're making it a quad boosted monstrosity with the Titans on giant columns of fuel and a core powered by the frontiers.
And the reasons why we're using boosters rather than staging in this example is it means we can have the same amount of thrust, consumption, fuel weights, ISP etc as earlier at each flight part, the only difference is rather than just turning off Titans, we're going to be getting rid of them and the empty fuel tanks in a more direct comparison.
And I will label them Fuckhewg SSTO and Fuckhewg boosted.

So.
FuckHewg SSTO has hit just enough fuel burn as before (68%) to turn off the outer Titans and continues on like this.

• Thrust - 9360 kN
• Wet Mass - 936t
• Dry Mass - 186t
• TWR - 1.02
• ISP - 258.13 m/s
• Remaining fuel - 749.2 tons
• Consumption - 3.7 tons/second
• Remaining burn time - 202.6 seconds
• Dv - 4081.46 m/s

All very similar to above.

FuckHewg boosted however, is going to shed some weight at this point. It's going to lose the Titans and the empty tanks that had contained the 352 tons of fuel. That's a mass saving of 55.2 tons. And that comes, more importantly, off the dry mass side of the Dv calculation as well as the wet side.

• Thrust - 9360 kN
• Wet Mass - 881t
• Dry Mass - 131t
• TWR - 1.08
• ISP - 258.13 m/s
• Remaining fuel - 749.2 tons
• Consumption - 3.7 tons/second
• Remaining burn time - 202.6 seconds
• Dv - 4815.52m/s

You can see where this is going? We added 84m/s turning them off earlier, instead now we've added 734m/s by kicking them off at exactly the same time in flight. And nothing else has changed. Same fuel amount, same specific impulse, same engines. Just a lot less weight.

Lets continue this.

FuckHewg SSTO at 14% fuel after flying with 2 titans turned off as of Plan B earlier and is now down to 3 frontiers burning for the rest of the flight.

• Thrust - 3360 kN
• Wet Mass - 340.86t
• Dry Mass - 186.5t
• TWR - 1.005
• ISP - 285.71 seconds
• Remaining fuel - 154.36 tons
• Consumption - 1.2 tons
• Remaining burn time - 128.63 seconds
• Dv remaining - 1688.54m/s.

FuckHewg boosted is going to now get rid of the remaining titans and all of the dead weight in fuel tanks attached. That's another 20 tons in engines and 59.5 tons in empty tank weight.

• Thrust - 3360 kN
• Wet Mass - 206.16t (That's the SSTOs weight (340), minus the first set of boosters (55.2) and the second set (79.5))
• Dry mass - 51.8t (Ditto)
• TWR - 1.66
• ISP - 285.71 seconds
• Remaining fuel - 154.36 tons
• Consumption - 1.2 tons
• Remaining burn time - 128.63 seconds
• Dv remaining - 3867.57m/s

A 2179.03m/s difference. Again, absolutely no difference in ISP, engines, whatever. Just weight savings.

 

[Blazer Ayanami]

Hmmm... ribs.

Anyway, where were we...?





Imagine we have a fuck hewg rocket. 1289 tons worth to be exact, in an SSTO configuration.

• All up - 1289 tons
• fuel total - 1109 tons
• Dry mass - 186.5
• 4 titans
• 3 Frontiers

So, if we press launch on this, we'd have

• TWR - 1.21
• ISP - 252.79 seconds
• Burn time - 177 seconds
• Dv - 4789.32m/s

Right. what Mooncrasher wants to do is sequentially turn off the Titans to increase its efficiency. And he is absolutely right.

Turning 2 of them off gives you a ISP of 258.13 seconds. Turning off the last pair brings that up to 285.71 seconds.

The problem with that, as Mooncrasher also rightly put it, is TWR. The Titans are generating 4/5ths of the overall thrust and just turning them off willy nilly is going to book you a crash course with the planet.

So. When to turn them off?

Now that involves a fair amount of maths, a bit of trial and error. Luckily for you good souls, my spreadsheet has a trial and error page that allows theoretical flights like this without much hassle.

So, as the rocket passes 68% fuel (that's 56.9 seconds into the flight, having burnt 352 tons and used 792.26m/s of Dv), you've lightened the rocket just enough to be able to turn off the outer most Titans.

Lets do the comparison then.

Say we continue on as normal, without shutting down the Titans (flight plan A)).

• Thrust - 15360 kN
• TWR - 1.67
• ISP - As above)
• Remaining fuel - 749.2 tons
• Consumption - 6.2 tons per second
• Remaining burn time - 120.9 seconds
• Dv - 3997.06 m/s

Or, we shut them down (Flight plan B).

• Thrust - 9360 kN
• TWR - 1.02 (like I said, just)
• ISP - 258.13 m/s
• Remaining fuel - As above
• Consumption - 3.7 tons/second
• Remaining burn time - 202.6 seconds
• Dv - 4081.46 m/s

As you can see, we've gained an extra 84.4 m/s just by turning them off at the right time.

What about that last pair then? Lets keep going.

So, to turn off those last Titans, we're gonna need to go right down to 14% fuel (154.35 tons left)

Again, lets compare.

Plan A (4 titans, 3 Frontiers throughout).

• Thrust - Still 15360 kN
• TWR - 4.59
• ISP - Still 252.79 Seconds
• Remaining fuel - 154.35 tons
• Consumption - 6.2 tons/Sec
• Remaining burn time - 24.89 seconds
• Dv remaining - 1493m/s

or

Plan B (dropping from 2 Titans and 3 frontiers to just the 3 frontiers)

• Thrust - 3360 kN
• TWR - 1.005
• ISP - 285.71 seconds
• Remaining fuel - 154.36 tons
• Consumption - 1.2 tons
• Remaining burn time - 128.63 seconds
• Dv remaining - 1688m/s.

We gain another 195 m/s again just for turning off the last Titans. Interestingly if we left just those pair on, the Dv for that last part is 1525.55m/s. The reason for the huge jump is because of the huge jump in efficiency because we're no longer using the thirsty titans anymore.

All that ^^^ waffle means that by turning off your less efficient engines at the right times (in this instance) raises your Dv from 4789.32 to 5068.72m/s and is the more efficient way of using your SSTO.

Next. Boosters and how fat-shaming your rocket into losing weight makes it more efficient in flight.

Actually it was my idea

 

[Horus Lupercal]

Actually it was my idea

Ha, my bad. I've been looking at numbers the past...3 and half hours.

EVERYONE, IT WAS The Blazer's IDEA!

Better?

 

[Altaïr]

Does a rocket with large TWR (like 4) wastes more delta v than an another rocket with lower TWR, given that the throttle is at maximum? For example, a rocket with 1.4 TWR has a delta v of 2000 m/s but it lost 500 m/s due to the drag while a rocket with 4 TWR which has a delta v of 3000 m/s lost 750 m/s. Is that accurate?

With such a high TWR you will generate a ton of drag, and you will waste fuel.
For example, let's suppose you're lifting off from Venus, and quickly hit a limit speed due to drag. If your TWR is 4, it means that 25% of your thrust are used to compensate for gravity, while the remaining 75% feed drag. That's huge!

Something very important about drag is that it increases as the speed squared: doubling your speed will multiply drag by 4
That's why I said trying to fight drag with brute force will be a losing battle.
I once calculated that if your TWR is greater than 2 (which can occur in flight as you consume fuel) and you're hitting a limit speed (your speed doesn't significantly evolve anymore), then you'd better slightly reduce your throttle. Your speed will decrease of course, but not as much as your fuel consumption, so it's still interesting in the end.

Ingame, as long as the atmosphere is thick, it's better to raise vertically, and to do your gravity turn when pressure is low enough.

Also, an interesting way to deal with Venus' atmosphere is to remember that at a given height (let's call it h), the pressure is roughly the same than on Earth at h - 5 km.
For example, the atmosphere on Venus at 10 km is the same than on Earth at 5 km.
Generally, 8-10 kilometers is a good height to start your gravity turn on Venus.

 

[Wᴏʟꜰʀᴀᴍ]

With such a high TWR you will generate a ton of drag, and you will waste fuel.
For example, let's suppose you're lifting off from Venus, and quickly hit a limit speed due to drag. If your TWR is 4, it means that 25% of your thrust are used to compensate for gravity, while the remaining 75% feed drag. That's huge!

Something very important about drag is that it increases as the speed squared: doubling your speed will multiply drag by 4
That's why I said trying to fight drag with brute force will be a losing battle.
I once calculated that if your TWR is greater than 2 (which can occur in flight as you consume fuel) and you're hitting a limit speed (your speed doesn't significantly evolve anymore), then you'd better slightly reduce your throttle. Your speed will decrease of course, but not as much as your fuel consumption, so it's still interesting in the end.

Ingame, as long as the atmosphere is thick, it's better to raise vertically, and to do your gravity turn when pressure is low enough.

Also, an interesting way to deal with Venus' atmosphere is to remember that at a given height (let's call it h), the pressure is roughly the same than on Earth at h - 5 km.
For example, the atmosphere on Venus at 10 km is the same than on Earth at 5 km.
Generally, 8-10 kilometers is a good height to start your gravity turn on Venus.

Eyyy, another useful info for my Venus quest

 

[Blazer Ayanami]

Ha, my bad. I've been looking at numbers the past...3 and half hours.

EVERYONE, IT WAS The Blazer's IDEA!

Better?

Well, you don't have to be angry, and maybe you misunderstood. I'm not refering to your calculations. I'm refering to when you said

Right. what Mooncrasher wants to do is sequentially turn off the Titans to increase its efficiency. And he is absolutely right.

When some posts ago I had said

Well, thanks for the answer .
Another question: I'm using mix first stages with 4 frontiers and 4 titans... If, during the ascent, I shut down the titans in pairs, im actually increasing ISP and dV, right?

So, Its basically me who suggested the idea, not Mooncrasher.

You see? Its not a big deal, and here there is no problem at all. Like I said, you probably misunderstood. I should quote better.

 

[Blazer Ayanami]

And I'm sorry If I've offended you somehow

 

[Horus Lupercal]

Well, you don't have to be angry, and maybe you misunderstood. I'm not refering to your calculations. I'm refering to when you said

Horus Lupercal said:
Right. what @Mooncrasher wants to do is sequentially turn off the Titans to increase its efficiency. And he is absolutely right.

When some posts ago I had said

The Blazer said:
Well, thanks for the answer .
Another question: I'm using mix first stages with 4 frontiers and 4 titans... If, during the ascent, I shut down the titans in pairs, im actually increasing ISP and dV, right?

So, Its basically me who suggested the idea, not Mooncrasher.

You see? Its not a big deal, and here there is no problem at all. Like I said, you probably misunderstood. I should quote better.

And I'm sorry If I've offended you somehow

Ha, I wasn't angry dude. Or offended. You're right, it's not a big deal and in the midst of figuring out how I was going to demonstrate the lesson, design the rocket, run everything through the sheets as accurately as I could for 3 different profiles at gone midnight, I'd completely forgotten about your initial question as you seemed pretty content with the initial non-maths answer and only went this deep cos Wolfram requested a bit more substance.

It was only afterwards when you mentioned it I was like 'aaaah yeah, whoops'.

Ha, my bad. I've been looking at numbers the past...3 and half hours.

EVERYONE, IT WAS The Blazer's IDEA!

Better?

This was me messing around saying it is no big deal and it isn't a problem, as long as we all learned something...

 

[Blazer Ayanami]

Ha, I wasn't angry dude. Or offended. You're right, it's not a big deal and in the midst of figuring out how I was going to demonstrate the lesson, design the rocket, run everything through the sheets as accurately as I could for 3 different profiles at gone midnight, I'd completely forgotten about your initial question as you seemed pretty content with the initial non-maths answer and only went this deep cos Wolfram requested a bit more substance.

It was only afterwards when you mentioned it I was like 'aaaah yeah, whoops'.



This was me messing around saying it is no big deal and it isn't a problem, as long as we all learned something...

Okay, no problem, we're fine.

 

[Horus Lupercal]

Okay, no problem, we're fine.

Yeah, course. And feel free to ask more. Its been a while since I've done any teaching and this keeps my mind occupied

 

[Blazer Ayanami]

Yeah, course. And feel free to ask more. Its been a while since I've done any teaching and this keeps my mind occupied

Okay, now that you mention it, I do have a question. It was a friend 's question and I couldn't give him a proper mathematical explanation. I was just like: "Do THIS, because I say Its better than THAT." <XD

Okay, So the question is: Let's say that I have a single Titan on my first Stage. That gives me a determined amount of Delta V....
So now let's assume that I Add a single Ion engine, and that I have enough RTG's on my upper stages to keep it running. I told my friend that ISP is all, and that this will increase the Delta V of the first Stage dramatically... And he told me: "How? The Ion's fuel consuption and thrust is insignificant compared to the Titan's..."
Could you give me some maths to show him?

 

[Horus Lupercal]

Okay, now that you mention it, I do have a question. It was a friend 's question and I couldn't give him a proper mathematical explanation. I was just like: "Do THIS, because I say Its better than THAT." <XD

Okay, So the question is: Let's say that I have a single Titan on my first Stage. That gives me a determined amount of Delta V....
So now let's assume that I Add a single Ion engine, and that I have enough RTG's on my upper stages to keep it running. I told my friend that ISP is all, and that this will increase the Delta V of the first Stage dramatically... And he told me: "How? The Ion's fuel consuption and thrust is insignificant compared to the Titan's..."
Could you give me some maths to show him?

So basically running Ions alongside a Titan to increase its ISP? Yeah, that's pretty easy to be fair.

A single one won't make a huge impact, but enough of them will. In fact, I was talking about it a few hours ago. 15 of them will raise the ISP from 244 ish to 267ish (the conversation was about simulating the Rocketdyne F-1s ISP for a more real world scenario).

Gimme a minute, and I'll demo it.

 

[Altaïr]

It depends, if you don't shut down the Titan it will change practically nothing.
My calculator gives me an Isp of 246.4 seconds for a Titan and an ion engine, instead of 244.9 for a Titan alone.
Actually you would even lose some delta-V because of the mass added by the ion engine and its energy source.

This is because it also depends on fuel consumption, and as the Titan's one is huge, it "weighs" much more in the calculation.

If you want to calculate the global Isp of 2 engines, you can do it that way:
Isp = (F1×Isp1 + F2×Isp2)/(F1 + F2)
With F being the fuel consumption.

You can see that if F1 is much greater than F2, then Isp1 will have much more impact on the final result.

In practice, what will happen is that the Titan will quickly drink all the fuel way before the ion engine can do anything significant.

 

[Horus Lupercal]

Imagine you created a 110t rocket with a Titan on the bottom.

• Thrust - 3000kN
• Wet - 110t
• Dry - 20t
• Fuel - 90t
• Burn Time - 72 secs
• Consumption - 1.25t/ sec
• TWR - 2.78
• ISP - 244.34
• Dv - 4091.39m/s

Now, if we avoid the extra weight issue and just add an Ion into the mix...

• Thrust - 3024kN
• Wet - 110t
• Dry - 20t
• Fuel - 90t
• Burn Time - 71.86 secs
• Consumption - 1.2524t/ sec
• TWR - 2.80
• ISP - 246.89
• Dv - 4116.22m/s

It does help, but a single Ion, in naked terms, doesn't do much.

What about weight then? The lightest way to run an Ion is with a solar array which with the engine adds 2.6t

• Thrust - 3024kN
• Wet - 112.6t
• Dry - 22.6t
• Fuel - 90t
• Burn Time - 71.86 secs
• Consumption - 1.2524t/ sec
• TWR - 2.74
• ISP - 246.89
• Dv - 3877.52m/s

Ha, as usual, Space Stig is correct. The weight added does make it less efficient than the ISP can compensate for

Lets go full mythbusters though, and see if the rumour can be made real? And the way I'm gonna try that is increasing rocket mass first, to see if I can't bury the extra weight, or add loads of Ions to increase the ISP so much it isn't negligible.

Without an Ion...

• Thrust - 3000kN
• Wet - 280t
• Dry - 37t
• Fuel - 243t
• Burn Time - 194.4 secs
• Consumption - 1.25t/ sec
• TWR - 1.09
• ISP - 244.89
• Dv - 4857.29m/s

With one, plus the Array

• Thrust - 3024kN
• Wet - 282.6t
• Dry - 39.6
• Fuel - 243t
• Burn Time - 194.02 secs
• Consumption - 1.2524t/ sec
• TWR - 1.09
• ISP - 246.38
• Dv - 4745.10m/s

Waa Waa Waaaaaa. Still not viable.

More Ions. In this case, 10 of them. Plus 10 arrays to power them.

• Thrust - 3240kN
• Wet - 306t
• Dry - 63
• Fuel - 243t
• Burn Time - 190.73 secs
• Consumption - 1.274t/ sec
• TWR - 1.08
• ISP - 259.5
• Dv - 4019.35m/s

Oh dear... That's not good.

Fuck it.

MOAR IONS!!!! (100 of them. And arrays.)

• Thrust - 5400kN
• Wet - 540t
• Dry - 297t
• Fuel - 243t
• Burn Time - 163.08 secs
• Consumption - 1.49t/ sec
• TWR - 1.02
• ISP - 369.81 seconds
• Dv - 2166.65m/s

Conclusion.
Yeah, Ions help ISP, but adding them just for that purpose with the associated furniture carries a weight penalty that isn't worth while. However, if your SSTO type thing has them (Like my dropships do) already in addition to all the other engines fitted, then there's no reason not to turn them on as well at launch as the weight is already there, you may as well benefit from the ISP bonus.

 

[Blazer Ayanami]

Imagine you created a 110t rocket with a Titan on the bottom.

• Thrust - 3000kN
• Wet - 110t
• Dry - 20t
• Fuel - 90t
• Burn Time - 72 secs
• Consumption - 1.25t/ sec
• TWR - 2.78
• ISP - 244.34
• Dv - 4091.39m/s

Now, if we avoid the extra weight issue and just add an Ion into the mix...

• Thrust - 3024kN
• Wet - 110t
• Dry - 20t
• Fuel - 90t
• Burn Time - 71.86 secs
• Consumption - 1.2524t/ sec
• TWR - 2.80
• ISP - 246.89
• Dv - 4116.22m/s

It does help, but a single Ion, in naked terms, doesn't do much.

What about weight then? The lightest way to run an Ion is with a solar array which with the engine adds 2.6t

• Thrust - 3024kN
• Wet - 112.6t
• Dry - 22.6t
• Fuel - 90t
• Burn Time - 71.86 secs
• Consumption - 1.2524t/ sec
• TWR - 2.74
• ISP - 246.89
• Dv - 3877.52m/s

Ha, as usual, Space Stig is correct. The weight added does make it less efficient than the ISP can compensate for

Lets go full mythbusters though, and see if the rumour can be made real? And the way I'm gonna try that is increasing rocket mass first, to see if I can't bury the extra weight, or add loads of Ions to increase the ISP so much it isn't negligible.

Without an Ion...

• Thrust - 3000kN
• Wet - 280t
• Dry - 37t
• Fuel - 243t
• Burn Time - 194.4 secs
• Consumption - 1.25t/ sec
• TWR - 1.09
• ISP - 244.89
• Dv - 4857.29m/s

With one, plus the Array

• Thrust - 3024kN
• Wet - 282.6t
• Dry - 39.6
• Fuel - 243t
• Burn Time - 194.02 secs
• Consumption - 1.2524t/ sec
• TWR - 1.09
• ISP - 246.38
• Dv - 4745.10m/s

Waa Waa Waaaaaa. Still not viable.

More Ions. In this case, 10 of them. Plus 10 arrays to power them.

• Thrust - 3240kN
• Wet - 306t
• Dry - 63
• Fuel - 243t
• Burn Time - 190.73 secs
• Consumption - 1.274t/ sec
• TWR - 1.08
• ISP - 259.5
• Dv - 4019.35m/s

Oh dear... That's not good.

Fuck it.

MOAR IONS!!!! (100 of them. And arrays.)

• Thrust - 5400kN
• Wet - 540t
• Dry - 297t
• Fuel - 243t
• Burn Time - 163.08 secs
• Consumption - 1.49t/ sec
• TWR - 1.02
• ISP - 369.81 seconds
• Dv - 2166.65m/s

Conclusion.
Yeah, Ions help ISP, but adding them just for that purpose with the associated furniture carries a weight penalty that isn't worth while. However, if your SSTO type thing has them (Like my dropships do) already in addition to all the other engines fitted, then there's no reason not to turn them on as well at launch as the weight is already there, you may as well benefit from the ISP bonus.

It depends, if you don't shut down the Titan it will change practically nothing.
My calculator gives me an Isp of 246.4 seconds for a Titan and an ion engine, instead of 244.9 for a Titan alone.
Actually you would even lose some delta-V because of the mass added by the ion engine and its energy source.

This is because it also depends on fuel consumption, and as the Titan's one is huge, it "weighs" much more in the calculation.

If you want to calculate the global Isp of 2 engines, you can do it that way:
Isp = (F1×Isp1 + F2×Isp2)/(F1 + F2)
With F being the fuel consumption.

You can see that if F1 is much greater than F2, then Isp1 will have much more impact on the final result.

In practice, what will happen is that the Titan will quickly drink all the fuel way before the ion engine can do anything significant.

Wow, Thank you much for your calculations and time, guys.
So, I see. Its not enough just to Add an Ion.

So, I have a final question for you two. I want to optimize a rocketship to make it ideal for both LEO and interplanetary Missions. It has 3 Stages, for a total weight of 2500 tons, however, they all burn at the same time.

Stage 1 weights 1600 tons and its powered by 6 Titans, 2 Frontiers and 2 Ions. Three of these Titans are shutdown during ascent to increase ISP, the same way than in our previous example.

Stage 2 weights 400 tons and it has 4 Frontiers. Both of these stages are just fuel and engines.

Stage 3 Its the One that holds the payload. Weights 500 tons, but its a little more complex. Only 450 tons of fuel, the rest is necesary equipment. It has 2 Frontiers and 6 Ions...

If this situation is too complicated I can open a conversation with you guys and send the .bp.

Now, what I want to know Is If I'm using the correct engine disposition. And If I'm not, how can I optimize it for two different situations:

1- "The Stack" All 3 Stages to LEO, with a payload of 500 tons.
2- 3rd Stage is in Orbit fully fueled and wants to send 2500 to Venus (just for a flyby trajectory).

Like I said I want to know If I can do something with the engine layout to optimize Its performance on the two different situations described above. I'll be very pleased If you can do the calculations and I will totally understand If you can't. Thanks.

 

[Horus Lupercal]

Wow, Thank you much for your calculations and time, guys.
So, I see. Its not enough just to Add an Ion.

So, I have a final question for you two. I want to optimize a rocketship to make it ideal for both LEO and interplanetary Missions. It has 3 Stages, for a total weight of 2500 tons, however, they all burn at the same time.

Stage 1 weights 1600 tons and its powered by 6 Titans, 2 Frontiers and 2 Ions. Three of these Titans are shutdown during ascent to increase ISP, the same way than in our previous example.

Stage 2 weights 400 tons and it has 4 Frontiers. Both of these stages are just fuel and engines.

Stage 3 Its the One that holds the payload. Weights 500 tons, but its a little more complex. Only 450 tons of fuel, the rest is necesary equipment. It has 2 Frontiers and 6 Ions...

If this situation is too complicated I can open a conversation with you guys and send the .bp.

Now, what I want to know Is If I'm using the correct engine disposition. And If I'm not, how can I optimize it for two different situations:

1- "The Stack" All 3 Stages to LEO, with a payload of 500 tons.
2- 3rd Stage is in Orbit fully fueled and wants to send 2500 to Venus (just for a flyby trajectory).

Like I said I want to know If I can do something with the engine layout to optimize Its performance on the two different situations described above. I'll be very pleased If you can do the calculations and I will totally understand If you can't. Thanks.

Send me the .bp on a pm dude. I'll do something similar to what I did with Dannys Paladin, copy it onto my sheets and play with the numbers.

Looking at it very early on though, you're gonna need more titans. Even with everything firing at once you're only just breaking even TWR wise (1.09)

My assumption is your third stage is an interstellar pusher vehicle for this 2500t mass you want to deliver to Venus? And needs to arrive at say...100km LEO without burning any of its fuel?

 

[Horus Lupercal]

Send me the .bp on a pm dude. I'll do something similar to what I did with Dannys Paladin, copy it onto my sheets and play with the numbers.

Looking at it very early on though, you're gonna need more titans. Even with everything firing at once you're only just breaking even TWR wise (1.09)

My assumption is your third stage is an interstellar pusher vehicle for this 2500t mass you want to deliver to Venus? And needs to arrive at say...100km LEO without burning any of its fuel?

And stage 2 wet mass is just shy of a kiloton. That's definitely gonna need titans as 4 frontiers isn't even half of what that needs lift wise.

 

[Blazer Ayanami]

Send me the .bp on a pm dude. I'll do something similar to what I did with Dannys Paladin, copy it onto my sheets and play with the numbers.

Looking at it very early on though, you're gonna need more titans. Even with everything firing at once you're only just breaking even TWR wise (1.09)

My assumption is your third stage is an interstellar pusher vehicle for this 2500t mass you want to deliver to Venus? And needs to arrive at say...100km LEO without burning any of its fuel?

And stage 2 wet mass is just shy of a kiloton. That's definitely gonna need titans as 4 frontiers isn't even half of what that needs lift wise.

I should better send you the .bp So you see it by yourself.