Side Mount vs Inline Mount launch configuration

[Cras]

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, at least, of someone who actually worked on the STS program themself?

Well, the Shuttle really was always thought of being a side mount from the beginning in one form or another. The initial plane had it being flown to high altitude by another aircraft and then let go so it can boost itself into space.

Also the Shuttle was supposed to really be a space plane with a set of turbine engines for powered approach to the landing site.

But then someone at NASA noticed how the Air Force had already shown the vailidity of the un-powered approach utilizing the the steep slope to the TDZ compared to one that is normally utilized in powered approch, which is generally 3.0 degrees.

No turbines, less weight, so NASA went with that, but it was soon determined that a ship of this size with the giant delta wings and stabilizer was going to have to deal with pressure during ascent in a manner much different than with the capsules that came before. The shockwave and pressures but on the orbiter are a very serious thing, that is after all what destroyed the Challenger.

This pressure also required the SSMEs to be able to throttle.

Next would be the shear size of the stack. The Orbiter is the size of a DC-9, and having it sit on top of anything would be immensly unstable during the first parts of the flight, however brief.

Also the taller that stack the more pronounced the sandwhiching of the stack when the mains are fired. A real issue with the Saturn Vs, when the bottom of the stack and the F1s are fired, they want to fly through everything above them. Of course the stack was designed for this, and thus the whole rocket squished and then released that tension as things got underway, but with STS, the goal here was reusability, so that kind of action would certainly work against that.

One thing you metioned was how a side mounted orbiter causes the stack to pitch onto its backside. For the STS this is a plus. That tendency allows for greater course accuracy during ascent. Same as with the twang when the mains fire while the solids are still bolted to the pad.

By having the stack fall back, that eliminates a whole direction required for corrections. All the computers have to worry about is how slowly to let the pitch rise, slowly from zero to about 70 degrees over onto the back.


Now you are certainly right on safety. Orbiter ontop of the tank is many times safer. The biggest issues in STS safety was due to the side-mounted nature of the Orbiter, from the foam strikes and damage they did, the umbilical system to feed the fuel into the orbiters systems for the SSMEs was very problematic. Remember STS-133 being delayed time and again because it kept leaking. Thankfully it was noticed (not saying there was much of a chance it wasn't going to be, but hypothetically). And the ability for aboarts. The STS probably had some of the worst and craziest ideas for abort modes every concieved (aside from the ATO). Nothing could be done until the solids were burnt out, the mains had to still remain on during that time to keep the pressure normalized, then it was either pitch over on its side and burn the mains at 109 to kill velocity and establish a vector back to KSC, which is nuts, so nuts that when John Young heard that this was going to be the plan for STS-1, he said he would not do it.

With the top mount, more reasonable aborts could be managed, such as what has been demonstrated the Eridanus will simulate, with the rocket tower jet pulling the crew module away from the stack.

 

[T.Neo]

Next would be the shear size of the stack. The Orbiter is the size of a DC-9, and having it sit on top of anything would be immensly unstable during the first parts of the flight, however brief.

Why? Where? How?

And how would you expect a vehicle to be able to have engines on its own airframe, and use them at launch, with a propellant tank below the airframe? :uhh:

Also the taller that stack the more pronounced the sandwhiching of the stack when the mains are fired. A real issue with the Saturn Vs, when the bottom of the stack and the F1s are fired, they want to fly through everything above them. Of course the stack was designed for this, and thus the whole rocket squished and then released that tension as things got underway, but with STS, the goal here was reusability, so that kind of action would certainly work against that.

No sandwiching... but there are now asymmetric forces, just from the orbiter hanging off the tank, as well as during the twang, and launch, of course.

One thing you metioned was how a side mounted orbiter causes the stack to pitch onto its backside. For the STS this is a plus. That tendency allows for greater course accuracy during ascent. Same as with the twang when the mains fire while the solids are still bolted to the pad.

By having the stack fall back, that eliminates a whole direction required for corrections. All the computers have to worry about is how slowly to let the pitch rise, slowly from zero to about 70 degrees over onto the back.

Various in-line SDLV proposals show that a twang isn't necessary for correct launch timings and positionings in those systems.

And that method of controlling attitude is nice... but doesn't remove the asymmetric forces on the vehicle.

Now you are certainly right on safety. Orbiter ontop of the tank is many times safer. The biggest issues in STS safety was due to the side-mounted nature of the Orbiter, from the foam strikes and damage they did, the umbilical system to feed the fuel into the orbiters systems for the SSMEs was very problematic. Remember STS-133 being delayed time and again because it kept leaking. Thankfully it was noticed (not saying there was much of a chance it wasn't going to be, but hypothetically). And the ability for aboarts. The STS probably had some of the worst and craziest ideas for abort modes every concieved (aside from the ATO). Nothing could be done until the solids were burnt out, the mains had to still remain on during that time to keep the pressure normalized, then it was either pitch over on its side and burn the mains at 109 to kill velocity and establish a vector back to KSC, which is nuts, so nuts that when John Young heard that this was going to be the plan for STS-1, he said he would not do it.

With the top mount, more reasonable aborts could be managed, such as what has been demonstrated the Eridanus will simulate, with the rocket tower jet pulling the crew module away from the stack.

Yeah. STS had no LES, at least this does. But still, I question the safety difference between a side-mount and inline vehicle, using a LES.

I also wonder, if fins cannot stabilise the vehicle during launch. I know Quasar already has fins, but I'm talking larger fins, that counter the asymmetric forces, obviously. Of course those fins would add mass, but it might be less mass than required for a useless fairing and 7-ton TPS shield...

The Grumann shuttle proposal had fins on the ET, on the opposite side from the orbiter vehicle.

 

[Cras]

Well you have already made the big point, and that in STS, the Orbiter had three main engines fired during launch, while Eridanus does not, it is more or less being dragged on the side of the launch vehicle throught the atmosphere.

If I were to chime in and comment on that, it would be still based on my initial reactions. I do in fact suffer from STS-nostalgia, and it is one reason whey so many of these space plane add-ons do nothing for me. This one however seems to be different. It has a very shuttle like payload by with RMS, OBSS, cameras.

My only things are,
One, not having any engines on the oribter but instead having them mounted on the ET. It does make the orbiter dead weight during launch, and there is going to be massive stress on the vehicle and its connections to the LV.
Two, the nose cone docking system. It just doesnt make sound sense to me why so many of these space planes, the XR2, this one, basically vehicle that require the payload bay doors to be open (the XR2 Mk1 doesnt but it looks like the Mk2 wil have solar panels on the inside of the doors, and the Eiranus seems to be likewise with maybe some sort of radiator there as well), why not have the docking port in there dorsal style? Having a nose cone that can be opened and closed just seems to be needlessly complicated and just adds another thing that can go wrong to prevent successful launch and re-entry.

The asymmetric forces thing does not really transfer over across the Eridanus and STS examples. It if anything becomes more prononced in Eridanus becaus of the lack of main engines during ascent. STS being designed around the ET as the backbone to the whole structure gets over this issue quite well, as it has been said 134 successful launches. And Challenger was not unsuccesfull because it bailed over to far over its head, it was the twisting from when one of the SRBS connections to the ET broke and the whole stack went sideways into the dynamic pressure.

But after all this, I will say I like the Eridanus side mounted, mainly because it looks better to me, and looks more like STS. I am so vain I know.

 

[T.Neo]

If I were to chime in and comment on that, it would be still based on my initial reactions. I do in fact suffer from STS-nostalgia, and it is one reason whey so many of these space plane add-ons do nothing for me. This one however seems to be different. It has a very shuttle like payload by with RMS, OBSS, cameras.

Hey, there is nothing wrong with STS-nostalgia. I am probably the worst STS-nostalgic person here. :lol:

My only things are,
One, not having any engines on the oribter but instead having them mounted on the ET. It does make the orbiter dead weight during launch, and there is going to be massive stress on the vehicle and its connections to the LV.

Yes. Of course, after SRB sep, the whole ET is hanging off the shuttle. By then the vehicle is more-or-less in a vacuum, but that mechanical stress is still there.

If you can eliminate those stresses, it's a good thing.

Two, the nose cone docking system. It just doesnt make sound sense to me why so many of these space planes, the XR2, this one, basically vehicle that require the payload bay doors to be open (the XR2 Mk1 doesnt but it looks like the Mk2 wil have solar panels on the inside of the doors, and the Eiranus seems to be likewise with maybe some sort of radiator there as well), why not have the docking port in there dorsal style? Having a nose cone that can be opened and closed just seems to be needlessly complicated and just adds another thing that can go wrong to prevent successful launch and re-entry.

Payload bay doors being open on-orbit, makes a lot of sense. It is a way to expose things to space, but maintain aerodynamics once the vehicle lands. You need only one opening for it, really. And it makes sense to put your power collection and radiators there too, so you not only want your radiators to be open, you need them to be open, too.

There are several advantages to nosecone docking. The Grumman shuttle proposal had nosecone docking. But I think, without anything to justify it specially, it is just something to add mass and complexity. Fitting a docking port in the payload bay, doesn't remove a lot of payload capability, is easier to install, and relies on the same payload bay doors as a cover.

The asymmetric forces thing does not really transfer over across the Eridanus and STS examples. It if anything becomes more prononced in Eridanus becaus of the lack of main engines during ascent. STS being designed around the ET as the backbone to the whole structure gets over this issue quite well, as it has been said 134 successful launches. And Challenger was not unsuccesfull because it bailed over to far over its head, it was the twisting from when one of the SRBS connections to the ET broke and the whole stack went sideways into the dynamic pressure

There is Energia, after all.

I don't really think the asymmetric forces are a problem in and of themselves, they're just a potential inefficiency in the design.

 

[Hlynkacg]

The problem with this is, if you think about it, that the lift of the wings in a side-mount stack points 90 degrees normal to the velocity vector. This screws up your ascent profile, or am I wrong?

The ET and SRBs disrupt the airflow over the wings thus minimizing this problem.

 

[Xyon]

OF Staff Note: These posts were moved from Space Plane Eridanus, final development steps thread and as such some aspects may not make sense in their current context.

 

[RisingFury]

DISCLAIMER:

"McExperts" is not my original term. I picked it up from potholer54.

Now I'm actually gonna go read this thread and see if I have anything useful to contribute...

---------- Post added at 14:19 ---------- Previous post was at 14:12 ----------

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.

He may be an expert at the ISS experiment he runs, but that doesn't make him an expert on Shuttle aerodynamics... and his reasoning in this case is incorrect. You just can't stick the Shuttle anywhere else then where it is (was) now.

 

[K_Jameson]

He may be an expert at the ISS experiment he runs, but that doesn't make him an expert on Shuttle aerodynamics... and his reasoning in this case is incorrect.

Points of view... his reasonig was generally shared in the italian forum. Just for the record and not for polemic:

one significant background of this guy was his involvement in the "Aries/Moonlight" projet, an old, but serious proposal to ASI, ESA and NASA for a range of reusable spacecrafts/spaceplanes, along with a lunar exploration/exploitation scenario.

currently, is involved in the development of the IRENE reentry vehicle, another real space program of ASI.

he know the matter. :tiphat:

 

[T.Neo]

I've never heard of this "Aries/Moonlight proposal"...

Of course he is not infallible. What of shockwaves from boosters on the Orbiter vehicle? Or from fairings or nosecones onto boosters and/or parallel-burn stages? Or from smaller in-line spaceplanes? Is there a magic size at which a spaceplane suddenly doesn't give off shockwaves?

Also, if he is claiming that aerodynamics is the main reason for the Shuttle's sidemount, I don't really think he is making sense, because the reason for STS's sidemount design is clear, aerodynamics or not:

Of course, a sidemount also makes pad handling easier- if STS was mounted inline, it could easily result in a vehicle around 100 meters tall. And of course you then have to have the white room and the RSS up so much higher. But it otherwise depends on the dynamics of the whole system, for example STS sits on the pad for a relatively long time, you could have other launchers which don't have such intensive payload handling (or don't need it). Or simply don't have it, even though it might be advantageous.

 

[RisingFury]

Points of view... his reasonig was generally shared in the italian forum.

And does the whole Italian forum have a Ph. D. in trans-sonic aerodynamics?

Where are you gonna stick the Space Shuttle, other then at the bottom? the ET is shuttle's fuel tank so it can't be anywhere else but on the side and the SRBs just provide enough lift to get the Shuttle off the ground. Any aerodynamics gains from the configuration are a moot point.


Here is a basic description of what the problems are with a un-powered shuttle. I hope you can read my hand writing and don't make too much fun of my über-1337 drawings...

I cannot go into aerodynamics because they vary from vehicle to vehicle and are generally calculated numerically. One more point I need to add...
If you're using the engines to turn you into the correct trajectory, then you can mount the shuttle lower on that stack. That will increase the angle arctan(b/a) (sorry for using Alpha in both cases) and the torque on the vehicle will increase.

If the wings of the shuttle are small and the vehicle can take the stress of having a large payload on top, then it would make more sense to mount the vehicle on top of the booster. But anything with large wings would best be mounted on the side - if the wings do produce lift negative lift, it's to your benefit. But if they don't, then you've gained stability with the loss of some performance. The cross section of the booster is exposed to the airstream creating more drag. But in neither case your booster will tip over.

 

[K_Jameson]

Of course he is not infallible.

Of course. NOBODY is infallible. :hello:

---------- Post added at 05:01 PM ---------- Previous post was at 04:38 PM ----------

And does the whole Italian forum have a Ph. D. in trans-sonic aerodynamics?

Where are you gonna stick the Space Shuttle, other then at the bottom? the ET is shuttle's fuel tank so it can't be anywhere else but on the side and the SRBs just provide enough lift to get the Shuttle off the ground. Any aerodynamics gains from the configuration are a moot point.


Here is a basic description of what the problems are with a un-powered shuttle. I hope you can read my hand writing and don't make too much fun of my über-1337 drawings...

I cannot go into aerodynamics because they vary from vehicle to vehicle and are generally calculated numerically. One more point I need to add...
If you're using the engines to turn you into the correct trajectory, then you can mount the shuttle lower on that stack. That will increase the angle arctan(b/a) (sorry for using Alpha in both cases) and the torque on the vehicle will increase.

nice analysis. I made something similar some time ago, taking account of the real dimensions and weights of my stack. The resulting AoA / gimbal angle is around 0,9° in the worst case. Rough calculation with the energia/buran stack shows similar data. This was comfortable. :thumbup:

If the wings of the shuttle are small and the vehicle can take the stress of having a large payload on top, then it would make more sense to mount the vehicle on top of the booster.

another URSS-example: the LKS project, a mini-Buran launched with a Proton, was an in-line stack. The LKS was a little vehicle (roughly 1/4 of the Buran) with small, folding wings.

 

[T.Neo]

nice analysis. I made something similar some time ago, taking account of the real dimensions and weights of my stack. The resulting AoA / gimbal angle is around 0,9° in the worst case. Rough calculation with the energia/buran stack shows similar data. This was comfortable.

Wasn't that based on COG alone? I'm incapable of reading some of RisingFury's handwriting, but I believe he's talking in part about aerodynamic forces.

another URSS-example: the LKS project, a mini-Buran launched with a Proton, was an in-line stack. The LKS was a little vehicle (roughly 1/4 of the Buran) with small, folding wings.

Here is an interesting .pdf on the LKS vehicle. Dimensions aren't given, but it is stated to mass "20-25 tons" at liftoff.

The Dyna-Soar and its launcher are pretty interesting as well;

 

[RisingFury]

The Dyna-Soar and its launcher are pretty interesting as well;

These would work. First two rockets have a large fin at the bottom to ensure stability. The second I imagine has enough engine gimball to prevent the stack from tipping over...

 

[n0mad23]

Thanks T. Neo for starting this timely thread.

I'm wondering at what altitude do these issues fade? Both ""dangerous shockwaves on the boosters in transonic and supersonic flight" and "wings...acting like canards" are lower atmosphere problems, right? Where exactly (or approximately) are neither a problem?

 

[RisingFury]

I'm wondering at what altitude do these issues fade?

Well, there's no magic line that you have to cross (like you do in KSP) to get out of the atmosphere and the atmosphere is not to be underestimated even at high altitudes, but above 30 km altitude you've passed all the thick crap...

 

[T.Neo]

When researching a whole lot of old concepts, I came across the original von Braun Ferry Rocket:

I realised that the ferry rocket has exactly the same problem as has been discussed: a spaceplane, mounted atop a rocket, causing instability.

I know that this is without any strict aerodynamic analysis (as far as I know), and I know it comes from the very early days of spaceflight theory, but I have trouble believing that the problem would be totally lost on von Braun.

The second obvious feature of the Ferry Rocket is that it has very large fins:

While fins are found on other vehicles of the time period and are not particularly special in and of themselves, the Ferry Rocket has very large fins. Clearly von Braun believed that such large fins could stabilise the vehicle, or that they were necessary.

A later version with a delta-winged upper stage had smaller fins, perhaps because of an increased trust in the ability of engine gimbaling:

Is stabilisation of a top-mounted spaceplane really impossible? Does it add enough ot a disadvantage to warrant a side-mount design?

In our age of finless launch vehicles, does a fin-equipped top-mount spaceplane-launching launch vehicle make sense?