Space Shuttle V2 Thought Experiment

[RocketSquid]

8 hours ago, DerekL1963 said:

Then why haven't you shown your design despite being asked for it?  Why has it been like pulling teeth to obtain those numbers?
 

o.0  No, you can't know the TWR unless you know the mass.  I cannot repeat and emphasize this enough, it's one of the most basic axioms of rocket design.  (You can assume the TWR, but that's treading on very, very thin engineering ice.)  The mass is the starting condition for the booster and the foundation for all other calculations.
 

That's not an alternative method - it's the only method.  That being said, those numbers look way off, two tons of aeroshell (even without TPS) isn't going to buy you much in the way of structure.   (And I wouldn't be surprised if your thrust web ended up eating a significant fraction of that.)  And are the control surfaces included in that?  Where is your recovery system (parachutes and landing gear) in your weight estimates?  For that matter, what is your recovery method?

Your tank estimates seem similarly off - you can't use conventional rocket numbers as these tanks will have to take stresses in directions that a conventional rocket doesn't, meaning your tanks will be heavier as will your structure.
 

I have tried repeatedly to offer constructive criticism, only to be shot down because you don't seem to grasp what I'm saying.   Serious question, is English your native language?  Because we have a communications gap, and it's either language or you really don't grasp the engineering as well as you think you do and don't (or won't) grasp the existence of the gap.  (And no, this is not ad hominem.  I have yet to make such an "attack", nor do I plan to.   Pointing out the errors in your design process is not an attack.)

1. I will try to get an image uploaded. 
2. If I cannot start with the TWR, where can I start? If you had told me this earlier, instead of just shouting about how "you can't do that", that would've been constructive criticism.
3. This was the first time you talked about the structural problems, and I thank you for bringing the problem of the elevons to my attention. I realized that the dry mass would need to be higher after sevenperforce commented earlier, and I had a few doubts about the TPS.
4. See #3.
5. English is my first language, however, I am an inexperienced engineer at best (probably related to being a high school freshman). I apologize for the comment about ad hominem attacks, I was getting rather annoyed about you saying I was wrong without giving alternatives, and may have misinterpreted your post.

[fredinno]

On February 15, 2016 at 9:03 AM, RocketSquid said:

Fine. You think I'm just rattling off words that sound cool. However, I can explain it in simpler terms.

Simpler Terms:

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It is re-usable, therefore, it can be used again. A linear aerospike is a real engine concept that has been extensively developed. Blended wing bodies and Lifting bodies are both real things that actually work. It holds fuel, and lands with parachutes. If you do not know what those are, you should not be on the KSP forums talking about rockets. Passively cooled TPS means that its thermal protection system does not ablate or have coolant pumps.

Simplest terms (using the XKCD simplewriter)

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This space engine has fire shooters that have three sides, and can be used again. It has stuff inside for burning. After it falls off of the space car, it flies with wings or can land with a big sheet that slows it down. It is controlled by a computer, and has an outside that cools itself down as it falls. It has a special shape that gives it lift, and its wings are part of its body.

Also, I have some back-of-the-envelope stats:

Dry mass: ~2.394 t

Wet mass: ~61.8 t

Delta v: ~9398 m/s without cargo

Propellants: LOX/RP-1

Thrust: ~909 kN

TWR: 1.5, fully fueled, but without cargo.

Two of these would be almost capable of satisfying this challenge.

Well, with 9398 m/s Delta V, you'll definately be missing the payload capacity requirement, even using 2 strapped together.

23 hours ago, sevenperforce said:

Peroxide and hydrazine pumped into a single combustion chamber have a crappy ISP, true. But staged/induced supersonic shockwave combustion carries a lot more promise; I did a little iterative optimization by hand and got a vacuum ISP of 414s at a 2:3 molar ratio (N2H4/H2O2).

Even if the supersonic combustion mode can't manage efficiencies quite as high as, say, the SSMEs, the exhaust velocity is still going to be on the order of 3700-4000 m/s, with T/W comparable to the SRBs and extraordinarily compact, lightweight tankage. Plus, monoprop fuels make pre-preburning turbopumps super simple.

You'd probably want an open aerospike of some kind...

Why not just use a H2 Lox engine at that point? Hydrazine is toxic...

[RocketSquid]

11 minutes ago, fredinno said:

Well, with 9398 m/s Delta V, you'll definately be missing the payload capacity requirement, even using 2 strapped together.

I understand that, it's a booster, not my actual entry, I was simply pointing out that two of them could lift the 60 t payload without any other engines, but it of course wouldn't be able to lift them into orbit.

[sevenperforce]

9 minutes ago, fredinno said:

Why not just use a H2 Lox engine at that point? Hydrazine is toxic...

Well, I realized I was using SL ISP for H2/LOX rather than vacuum ISP. The actual ISP of the dual-mono engine is going to be closer to 440 s.

Advantages: higher T/W ratio; lower tankage volume and weight. Dramatically. 

[shynung]

6 minutes ago, sevenperforce said:

Well, I realized I was using SL ISP for H2/LOX rather than vacuum ISP. The actual ISP of the dual-mono engine is going to be closer to 440 s.

Advantages: higher T/W ratio; lower tankage volume and weight. Dramatically. 

This seems awfully optimistic. Higher TWR, maybe, but 440 seconds?

Edited February 16, 2016 by shynung

[sevenperforce]

2 minutes ago, shynung said:

This seems awfully optimistic. Higher T/W, maybe, but 440 seconds?

Yep. Could be higher, actually. I need to re-run my optimization algorithm with the correct vacuum specific impulse at various H:O ratios instead of SL specific impulse. But it's going to be hella high.

[shynung]

Just now, sevenperforce said:

Yep. Could be higher, actually. I need to re-run my optimization algorithm with the correct vacuum specific impulse at various H:O ratios instead of SL specific impulse. But it's going to be hella high.

Can I see your calculations?

[sevenperforce]

3 minutes ago, shynung said:

Can I see your calculations?

Sure thing. I'll detail them out in the dedicated thread. 

[DerekL1963]

4 hours ago, RocketSquid said:

If I cannot start with the TWR, where can I start? If you had told me this earlier, instead of just shouting about how "you can't do that", that would've been constructive criticism.

I didn't just "shout" "you can't do that".  I told you multiple times that you need to know the mass before you could calculate TWR.   This is now the fifth time I've said this.  You start with the mass.

You can start with an estimated or target TWR (what you keep calling a known TWR), but then you have to determine (or estimate) the mass and use that with the thrust of your chosen engine to calculate the actual TWR.  If the latter doesn't equal or exceed the former, you iterate.   You choose a new level of engine performance or you start slashing your weight.  Now that we've seen your masses, we know that your estimates are likely on the low side - time to iterate.  Something has to give or change.
 

4 hours ago, RocketSquid said:

This was the first time you talked about the structural problems, and I thank you for bringing the problem of the elevons to my attention. I realized that the dry mass would need to be higher after sevenperforce commented earlier, and I had a few doubts about the TPS.

That's because it's the first time you've given the information I asked for in my very first response to you, the information I needed in order to analyze your design - before you provided the numbers I had no idea what you had or hadn't taken into account in calculating your dry mass.  (And wasn't going to assume a priori that you hadn't.)  In the same vein, you'll note that specific criticisms (like sevenperforce's) are in response to actually posting numbers.
 

4 hours ago, RocketSquid said:

English is my first language, however, I am an inexperienced engineer at best (probably related to being a high school freshman). I apologize for the comment about ad hominem attacks, I was getting rather annoyed about you saying I was wrong without giving alternatives, and may have misinterpreted your post.

Squid, I gave you alternatives in every single post (see the first line of this reply), and you just kept repeating the same thing back to me.  That's very frustrating and why I went close to going too far.

[RocketSquid]

3 hours ago, DerekL1963 said:

I didn't just "shout" "you can't do that".  I told you multiple times that you need to know the mass before you could calculate TWR.   This is now the fifth time I've said this.  You start with the mass.

You can start with an estimated or target TWR (what you keep calling a known TWR), but then you have to determine (or estimate) the mass and use that with the thrust of your chosen engine to calculate the actual TWR.  If the latter doesn't equal or exceed the former, you iterate.   You choose a new level of engine performance or you start slashing your weight.  Now that we've seen your masses, we know that your estimates are likely on the low side - time to iterate.  Something has to give or change.
 

That's because it's the first time you've given the information I asked for in my very first response to you, the information I needed in order to analyze your design - before you provided the numbers I had no idea what you had or hadn't taken into account in calculating your dry mass.  (And wasn't going to assume a priori that you hadn't.)  In the same vein, you'll note that specific criticisms (like sevenperforce's) are in response to actually posting numbers.
 

Squid, I gave you alternatives in every single post (see the first line of this reply), and you just kept repeating the same thing back to me.  That's very frustrating and why I went close to going too far.

Okay, I think this has just been a communication error, I interpreted your post on me not being able to get the mass from the TWR as meaning that it was an invalid estimation method, not that I needed to mark the TWR I was using as a target TWR and iterate. Meanwhile, my posts may not have made it clear that the values I gave were preliminary as opposed to final values. I was under the impression that I had given the numbers you asked for very early on, but I may have missed something. And of course when someone else reads your post they may get a very different impression than you had originally intended.

[Emperor of the Titan Squid]

Stop arguing.We aren't NASA, ok, not everything has to be perfect.What fuel is best? I don't know that much about fuels.

[fredinno]

5 hours ago, Emperor of the Titan Squid said:

Stop arguing.We aren't NASA, ok, not everything has to be perfect.What fuel is best? I don't know that much about fuels.

It depends on what you want.

[Emperor of the Titan Squid]

Storability, power.Also, have we chosen a design? Does anyone like air augumented SERV?

[shynung]

You mean this?

Interesting.

[DerekL1963]

A mechanical nightmare... 

[fredinno]

3 hours ago, DerekL1963 said:

A mechanical nightmare... 

Not to mention it would need new factories to build.

[sevenperforce]

Ditch the jet engines in favor of throttleable linear aerospike central-bypass ducted rockets positioned around the payload bay, and you'd have something.

Edited March 1, 2016 by sevenperforce
dammit

[fredinno]

6 hours ago, sevenperforce said:

Ditch the jet engines in favor of throttleable jet engines, use three linear aerospike central-bypass ducted rockets positioned around the payload bay, and you'd have something.

Wait, aren't jet engines usually throttleable?

[sevenperforce]

3 hours ago, fredinno said:

Wait, aren't jet engines usually throttleable?

Why in the world did I say that?