Side Mount vs Inline Mount launch configuration

T.Neo

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I still don't believe the viability of the sidemount, or that the people who suggested it aren't RisingFury's "McExperts". RisingFury is pretty knowledgable about aerodynamics (more so than myself), I doubt he is just talking nonsense.

Furthermore, in lieu of complaining about Energia-Buran's engineless sidemount;



There are various spaceplane designs that sit atop launch vehicles; while none of them might be quite as large, in relative terms, as Eridanus, I don't see why they wouldn't create "dangerous shockwaves on the boosters in transonic and supersonic flight", if that was a problem.

The major problem I can see with the in-line configuration is as RisingFury mentioned:

The problem then becomes instability... wings will start acting like canards. Even a small deflection that cannot get corrected by elevons will topple the space craft over.

I don't see why that couldn't be corrected with elevator trim/thrust vectoring.

A mounting point for an inline vehicle should not be a problem; interstages and payload mounts, are not really problems. In fact, you could even reduce mass by minimising asymmetric forces.

And remove the TPS shield, and whatever fairing you seem to have on top of the propellant tanks.

It should be noted that both Energia and STS have the vehicle center of mass quite close to the bottom of the tank/stage. Side-mount Eridanus is quite far away from the engines. I can't help but thinking, that this mass is trying to buckle over the tank structure, on the pad and during launch. Think almost, of a tall tower; attach a mass to the base of the tower, and things will be fine (more or less). Attach the same amount of mass to the top of the tower, and the tower will have far more of a tendency to bend over.

It should be noted that Eridanus has quite large wings (as opposed to vehicles such as Avatar or Hermes), larger in proportion than those on STS, but STS also has pretty large wings, because of its large crossrange requirements (for AOA from polar orbit).

The one area where a sidemount might be better than an in-line configuration, is payload handling, because the payload bay is lower down. You might, in some cases, be able to load the payload into the vehicle at an earlier stage in processing.
 
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fausto

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The Eridanus mass is 1/15 of the total mass.. and in addition to that, you must consider that the direction of the ascent profile and following pitching down balances the buckle over problem that you mentioned.. the upper fairing is a good way to fix that problem: it rises up the centre of gravity in z direction.

We have to consider now the advantages: we have shield protection against debris and that position allows us to use an escape tower.. more bending over, more saftey! :)
 

T.Neo

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The Eridanus mass is 1/15 of the total mass.. and in addition to that, you must consider that the direction of the ascent profile and following pitching down balances the buckle over problem that you mentioned.. the upper fairing is a good way to fix that problem: it rises up the centre of gravity in z direction.

Of the wet mass, yes. ;)

Of course most of the propellant mass is contained safe within the propellant tank itself. Eridanus is hanging off the side.

The fairing just adds mass. It can't negate the fact that the mass of Eridanus is exerting an asymmetric force on the propellant tank. The only way to fix that, is a sufficiently massive counterweight on the other side of the tank.

And that of course would also increase the total force on the propellant tank... and make it impossible for the vehicle to reach orbit.

We have to consider now the advantages: we have shield protection against debris and that position allows us to use an escape tower.. more bending over, more saftey!

Wait... buckling your propellant tank over is a sign of safety? I did not know this. :blink:

You only need the debris protection, because you have a debris problem. An in-line vehicle will not have this problem, because there is no possibility of a foam or ice strike from the propellant tank. The risk of a damaging birdstrike, for example, is likely pretty low, while foam strikes every once in a while seem to be a certainty. And of course an in-line design means you can save some 7 tons for other things, such as safety systems, extra payload, more capable spacecraft systems, or even a more durable TPS or repair systems.

EDIT:

It should also be noted that an in-line configuration would increase safety as the escape capsule would be further away from the propellant tank and thus less likely to be damaged and/or destroyed in a vehicle disintegration.
 
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fausto

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The right way to know who is right is trying to precisely calculate how much the ascent is effected by this configuration.. can someone help us? :facepalm:

---------- Post added at 09:47 AM ---------- Previous post was at 07:55 AM ----------



This is a erlier space shuttle design, made by NASA of course.. i think Eridanus to be very similar..
 

T.Neo

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The right way to know who is right is trying to precisely calculate how much the ascent is effected by this configuration.. can someone help us?

It is not only about the effect on the ascent, but the forces straining the vehicle structure as well. And the mass wasted on fairings and ascent shields.

This is a erlier space shuttle design, made by NASA of course.. i think Eridanus to be very similar..

You also have to realise the reasons for that configuration. First and foremost the ground handling and wing-lifted flight aspect:

 

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T.Neo, only few words: 134 successful STS launches and 2 successful Energia launches are a valid reference for our design. But, if you don't like it... the download is not mandatory. :tiphat:
 

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If you want inline, slap it on top of a Velcro stack. :shrug:
 

T.Neo

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You know, I am just trying to help you, with feedback on plausibility. I have explained the problems others and myself have seen in your design and why I think it could be suboptimal, and I've explained why various other designs were the way they are.

Using STS as a design justification, is just silly, because the SSMEs could never have been ignited at launch in an in-line stack. :facepalm:

If you don't care about having a plausible addon, then that's fine. But in that case, you might as well attach DeltaGlider engines to it. It just makes no sense, from a realism point of view.
 

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Using STS as a design justification, is just silly, because the SSMEs could never have been ignited at launch in an in-line stack. :facepalm:

T,

I know what you are saying, and I agree there is room for argument, your input is valuable:thumbup:, but...

What SSMEs? These are RS-25E engines, disposable, light and cheap.:hello:
The STS design is not silly, its a proven concept for 30 years, if it's so bad why did Russia build one? One iteration complements another, and thus we get evolution. Perhaps this IS evolution. Buran was canceled due to funding issues, not purpose or practice.

The whole system uses liquid propellants. Lots of rockets do.:)

Igniting the boosters and core stage may be accomplished at the same time, hold down to achieve thrust, and release the stack for launch. Nothing new about this technique. It works.:thumbup:

The space-plane has nothing to do with launch, which makes it a payload canister with wings. Side-mounting a payload is an acceptable practice. Most of the lift on the wings is negated by the ET, just like STS and Buran.:thumbup:

IMHO the inline stack up has a higher chance of folding in half from stresses than this side-mount stack. We both know the highest chance of that is at low altitude under 70,000 ft. and high mach speed where lift from the body and wings is the greatest.:thumbsdown:

IMHO the only argument against the idea, is the turbulence, and from what I've seen, the concern is minimal and acceptable. It has been compensated for, using the roll and pitch maneuvers after launch, just like STS and Buran. Once above 70,000 feet, turbulence, drag and lift are minimal as the atmosphere thins out, overall weight reduces near upper atmosphere just like STS and Buran. Throttling occurs. :thumbup:

I'm no rocket scientist:idk:, but I think these guys have done a great job short of building the real thing. It's realistic, not real! Even if this has an in-simulation failure rate of 25%, it's still low, because it's not real.:tiphat:

It may be that, the closer you make this thing perform like the real thing, as you would have it do, the higher the failure rate. That's just incentive to improve the add-on. Scientists call that "trial and error" and it's a valid scientific method. It's because we just don't know, that makes it fascinating.:cheers:

At least in simulation no one dies for real and we get to be a part of the experiment and improvement process.:hailprobe:

I gently suggest we just see where it takes us, and enjoy the moment.:)
 

T.Neo

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What SSMEs? These are RS-25E engines, disposable, light and cheap.

Igniting the boosters and core stage may be accomplished at the same time, hold down to achieve thrust, and release the stack for launch. Nothing new about this technique. It works.

No no, I'm not saying the inline technique is bad in and of itself;

If you took the STS Orbiter, and mounted it atop the ET, were would the SSMEs burn to? ;)

It is just that particular design.

The STS design is not silly, its a proven concept for 30 years, if it's so bad why did Russia build one? One iteration complements another, and thus we get evolution. Perhaps this IS evolution. Buran was canceled due to funding issues, not purpose or practice.

Frankly, I don't know. But I can put forward several reasons:

- Payload handling. The vehicle is lower down on the tank, and thus easier to service with payloads.

- Abort modes. I have no idea what the abort modes were for Buran, but they might have involved a seperation from the core, that would work better in a sidemount configuration. Eridanus uses a LES, and is arguably safer in an in-line configuration.

- Imitating STS. Ok, I know, maybe it does not make a lot of sense- but it does make some sense otherwise.

It should be noted that other Energia designs mounted the payload in an inline configuration, though I'm not sure if this was ever done with the Energia launcher otherwise as-is... Polyus was launched sidemount, but that could arguably be explained as a means to save costs over unecessarily modifying the Buran design.

Maybe they had future plans to bring the core stage to orbit with the OMS... or they had future plans to mount engines on the Buran itself (I know, that also doesn't make sense, but... maybe).

Side-mounting a payload is an acceptable practice.

Nobody side-mounts out of absolute choice, it seems (save for the Russians, for some reason). If a vehicle is sidemount, it usually is because of some other technical reason for it to be so- see the "Not Shuttle-C" SDHLLV.

IMHO the inline stack up has a higher chance of folding in half from stresses than this side-mount stack. We both know the highest chance of that is at low altitude under 70,000 ft. and high mach speed where lift from the body and wings is the greatest.

Lift force that you can negate with aerosurfaces, of course.

You cannot negate mass. The sidemount will always want to bend the stack over.

IMHO the only argument against the idea, is the turbulence, and from what I've seen, the concern is minimal and acceptable. It has been compensated for, using the roll and pitch maneuvers after launch, just like STS and Buran. Once above 70,000 feet, turbulence, drag and lift are minimal as the atmosphere thins out, overall weight reduces near upper atmosphere just like STS and Buran. Throttling occurs.

You also have the asymmetric mass, and thus asymmetric weight. And you can only throttle down so much- the SSME can only throttle down to about 64%, AFAIK. Not sure how the RS-25E differs there.

The original Eridanus design was inline.. we decided to change it because of criticism on Forum Astronautico, an italian forum where we discuss with guys involved in ASI projects (ASI is the italian space Agency)

I believe their wisdom, but I'm skeptical of their reasoning. Maybe they are even more Shuttle-nostalgic, than I am, that they would rather want a launcher that looks a bit like the STS stack. :lol:
 
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K_Jameson

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And the mass wasted on fairings and ascent shields.

fairing is not a waste of mass: it can accommodate large secondary payloads (up to 7 meters of diameter), as the external tank aft cargo carrier designed for STS and never used.
 
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T.Neo

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fairing is not a waste of mass: it can accommodate large secondary payloads (up to 7 meters of diameter), as the external tank aft cargo carrier designed for STS and never used.

Did you ever see a space shuttle launch with an aft cargo carrier, without any payload inside? ;)

You can implement a similar system in an inline configuration- with a payload in a specially designed cargo version of the connective interstage between the launch vehicle and Eridanus.
 

K_Jameson

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Did you ever see a space shuttle launch with an aft cargo carrier, without any payload inside? ;)

No, as written.
Just for the record:
http://beyondapollo.blogspot.com/2011/03/space-shuttle-with-aft-cargo-carrier.html

You can implement a similar system in an inline configuration- with a payload in a specially designed cargo version of the connective interstage between the launch vehicle and Eridanus.
obviously.

---------- Post added at 11:52 AM ---------- Previous post was at 11:38 AM ----------

T,

I know what you are saying, and I agree there is room for argument, your input is valuable:thumbup:, but...

What SSMEs? These are RS-25E engines, disposable, light and cheap.:hello:
The STS design is not silly, its a proven concept for 30 years, if it's so bad why did Russia build one? One iteration complements another, and thus we get evolution. Perhaps this IS evolution. Buran was canceled due to funding issues, not purpose or practice.

The whole system uses liquid propellants. Lots of rockets do.:)

Igniting the boosters and core stage may be accomplished at the same time, hold down to achieve thrust, and release the stack for launch. Nothing new about this technique. It works.:thumbup:

The space-plane has nothing to do with launch, which makes it a payload canister with wings. Side-mounting a payload is an acceptable practice. Most of the lift on the wings is negated by the ET, just like STS and Buran.:thumbup:

IMHO the inline stack up has a higher chance of folding in half from stresses than this side-mount stack. We both know the highest chance of that is at low altitude under 70,000 ft. and high mach speed where lift from the body and wings is the greatest.:thumbsdown:

IMHO the only argument against the idea, is the turbulence, and from what I've seen, the concern is minimal and acceptable. It has been compensated for, using the roll and pitch maneuvers after launch, just like STS and Buran. Once above 70,000 feet, turbulence, drag and lift are minimal as the atmosphere thins out, overall weight reduces near upper atmosphere just like STS and Buran. Throttling occurs. :thumbup:

I'm no rocket scientist:idk:, but I think these guys have done a great job short of building the real thing. It's realistic, not real! Even if this has an in-simulation failure rate of 25%, it's still low, because it's not real.:tiphat:

It may be that, the closer you make this thing perform like the real thing, as you would have it do, the higher the failure rate. That's just incentive to improve the add-on. Scientists call that "trial and error" and it's a valid scientific method. It's because we just don't know, that makes it fascinating.:cheers:

At least in simulation no one dies for real and we get to be a part of the experiment and improvement process.:hailprobe:

I gently suggest we just see where it takes us, and enjoy the moment.:)

Thanks for your words! :tiphat:
 

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T.Neo sorry again for my bad english, I try to explain, as well as I can, why we choose this configuration.
Speaking with Giuseppe Di Chiara (a.k.a. Archipeppe on http://www.forumastronautico.it) he explained us that build a in-line spaceplane could be a mistake because the wings made some big turbolence on the rocket tail, expecially during transonic passage. This is the real motivation why NASA developed Space Shuttle as we know today. Giuseppe is a flight controller of one of ISS experiments (now he works at ESA Center in Cologne, Germany), he also has a bachelor in astronautics science so if he told us that the sidemount configuration is better than in-line I must only believe him.
 

T.Neo

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Yes, I know. My point is that, as far as I know, nobody suggested flying the ACC empty.

Speaking with Giuseppe Di Chiara (a.k.a. Archipeppe on http://www.forumastronautico.it) he explained us that build a in-line spaceplane could be a mistake because the wings made some big turbolence on the rocket tail, expecially during transonic passage. This is the real motivation why NASA developed Space Shuttle as we know today. Giuseppe is a flight controller of one of ISS experiments (now he works at ESA Center in Cologne, Germany), he also has a bachelor in astronautics science so if he told us that the sidemount configuration is better than in-line I must only believe him.

I believe his qualifications, but I'm not following his reasoning.

Now, I know this image might not be that clear, and I am certainly light-years away from being any sort of aerodynamicist, but I don't really see a major shockwave coming off the wings here;



The image depicts the STS stack at mach 2.46, not transonic speeds though.

Also, saying that the reason STS was sidemount, is because of shockwaves, makes absolutely no sense. It is sidemount because of propulsion, aerodynamics is only a secondary factor.

During development, it became important to reuse the SSMEs. Obviously, because of their cost, etc. And this also meant having to mount them on the Orbiter vehicle. This creates a bit of a payload penalty, but is far more convenient. The other option would obviously be some sort of breakaway engine pod, that would have to be recovered and fitted seperately, incurring higher costs.

Here we can see why you need a side-mount configuration for a parallel burn configuration:



You need the engines on the side, you can't mount them inline. Because if you mount them inline, on the top of the vehicle, then obviously, you cannot use them.

EDIT:

This image is also of interest, though the ratio of stage length/vehicle length might be too different:
 
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T-Neo, sorry, in Italy there is a proverb that tell: "If you want to shave a donkey, you waste your soap, the water and your time". Try to explain you why we made Eridanus sidemount is the same thing. You have your idea, and no one can change it. Why do you wrote about motors, if I wrote that at transonic speed (TRANSONIC, not at 2.5 mach) you have a big turbolence on your rocket tail? What's about it?
Ok, at this point I repeat what Andrew (K_Jameson) wrote yesterday:
134 successful STS launches and 2 successful Energia launches are a valid reference for our design. But, if you don't like it... the download is not mandatory. :tiphat:
 

T.Neo

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T-Neo, sorry, in Italy there is a proverb that tell: "If you want to shave a donkey, you waste your soap, the water and your time". Try to explain you why we made Eridanus sidemount is the same thing. You have your idea, and no one can change it. Why do you wrote about motors, if I wrote that at transonic speed (TRANSONIC, not at 2.5 mach) you have a big turbolence on your rocket tail? What's about it?
Ok, at this point I repeat what Andrew (K_Jameson) wrote yesterday:

Listen, I never said anything against TRANSONIC shockwaves being a program (I'd love to see a simulation or wind tunnel test of the STS stack at TRANSONIC velocities, btw).

I'm explaining, part of the rationale behind why the STS stack is the way it is. If you want to just ignore that (and it is really so plainly simple) and say that it is because of shockwaves, then... yeah, I dunno. You can't mount the engines on the STS vehicle and have an in-line configuration at the same time, it is entirely impossible.

Using an STS comparison to justify a design choice, on a totally different vehicle with totally different features, does not make sense. Maybe using Energia-Buran as a reference would make more sense, but... that is also a different stack (and it's only one launch- Polyus was no spaceplane, it was just... whatever a Polyus is).

And I also urge you to consider this thing...


Whatever it is. It has a large spaceplane vehicle with large wings, atop a core stage and a set of boosters. If anything, shockwaves here are not a problem.

I find the issue of unwanted lift force, and lateral aerodynamic forces increasing with AOA, far more compelling than the shockwave issue. Also when the STS stack has stuff casting shockwaves onto other stuff, anyway... :shifty:

But hey... that image is made in China. Maybe it should not be trusted that much. :lol:
 

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Maybe using Energia-Buran as a reference would make more sense, but... that is also a different stack (and it's only one launch- Polyus was no spaceplane, it was just... whatever a Polyus is).

First of all, Energia/Buran is an analogous concept as Quasar/Eridanus. Different stack? Oh yes, is not the SAME stack, but, i repeat, is substantially analogous.

And IT WORKS. Has performed a successful flight, yes or not?
That "chinese thing" has performed a successful flight? For now, is only a paper rocket. A flight-proven rocket is a more solid reference. And, i repeat again, i'm a FAN of the in-line configuration and was reluctant to move the Eridanus on the sidemount... i'm not a STS-nostalgic.

ciao.
 
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Cras

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The STS was a side mounted oribter for more reasons than just the SSMEs need a place for its exhaust to go.
 

T.Neo

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And IT WORKS. Has performed a successful flight, yes or not?

Is it even an optimal configuration? At least Energia did not have to add an extra dead-weight fairing on the front...

That "chinese thing" has performed a successful flight? For now, is only a paper rocket. A flight-proven rocket is a more solid reference. And, i repeat again, i'm a FAN of the in-line configuration and was reluctant to move the Eridanus on the sidemount... i'm not a STS-nostalgic.

This is also a paper rocket. I don't see why relying on other paper rockets is a particularly bad thing, if they are a good enough design. All other "flight proven" designs have their differences, and fail as comparisons somewhere.

But- even as a sidemount, you can already improve things a good deal. For example, you can ditch the payload fairing, that is just sitting there eating payload, and use an ogive nose-shape instead. And you can also work towards having a more durable TPS, and different ways of insulating the core stage, instead of a 7+ ton shield.

And you can even attach the engines to the orbiter vehicle itself, and recover them for reuse- I know, this messes around with some other aspects of the vehicle, and reuse is not magic, but if your recurrent costs per engine for flight are 25% the original cost of the engine, and your engine is $50 million, then you could potentially save 70% of your costs and boost your payload capability by being able to afford more efficient engines.

The STS was a side mounted oribter for more reasons than just the SSMEs need a place for its exhaust to go.

Yes, but that is the primary reason. Can you really think of anything more critical than not having your rocket exhaust pointed directly onto the end-dome of your external tank? :lol:

Also, what are these other reasons? I can think of some, but I really can't believe that this shockwave stuff is so universally limiting, just because some guy on the internet talked about it. I don't care who he is, or what his job is, or what degrees he completed, if he just said it, then it might as well just be apocryphal. Where is there any documentation that discusses this? Where is the documentation, that discusses flight loads on the shuttle stack as it was actually built? Where is the word, of someone who actually worked on the STS program themself?

Especially that basic layout was estabilished long time ago.

It is a pretty silly layout, when your vehicle has a payload fairing that does nothing but add mass, and a TPS shield that adds a whole seven tons of payload penalty.
 
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