Discussion LKS inspired shuttle concept.

[Urwumpe]

This is a mith that I read several times; while it is true that the safety standards weren't those of today and the Apollo missions faced countless problems, "a few mm away from catastrophe" is a bit exaggerated statement regarding the Saturn V launches, IMHO.

Well, for example, during Apollo 13, the center engine of the S-II vibrated so strongly because of excessive POGO, that its massive thrust bearing flexed 5.2 inches by 34G vibrations. It was actually calculated that, would the engine not have shutdown earlier, it would have destroyed the launcher. Luckily, the oscillations in the propellant lines grew so strong that they triggered a low-pressure switch designed to prevent the engine pumps running dry by a tank leak before structural damage occurred.

http://www.vibrationdata.com/Newsletters/October2008_NL.pdf

Because the mission had some lot of bad luck, it was really not considered that important, but for people deeper involved in the program, it was actually much more dangerous for future missions than the oxygen tank explosion.

Literally any mission of the Apollo program until Skylab had some more or less serious flaws, that often like for the Space Shuttle later only lucky coincidences prevented worse. Compare this episode of pogo for example to Gemini, where the milder pogo oscillations of the Titan 2 had been reason enough to delay the first launch until the vibrations had been low enough that a human astronaut could work in the capsule (for the performance of the ICBM, the pogo was never a problem)

If I recall correctly, the S-IVB engine on Apollo 6 performed poorly during the first burn and completely fails the in-orbit restart, forcing to use the Apollo SPS to raise the orbit.

Apollo 6 also had been the first launch to show significant pogo.

 

[K_Jameson]

Well, for example, during Apollo 13, the center engine of the S-II vibrated so strongly because of excessive POGO, that its massive thrust bearing flexed 5.2 inches by 34G vibrations. It was actually calculated that, would the engine not have shutdown earlier, it would have destroyed the launcher. Luckily, the oscillations in the propellant lines grew so strong that they triggered a low-pressure switch designed to prevent the engine pumps running dry by a tank leak before structural damage occurred.

Well, you stated previously that Apollo was "always" a few mm from catastrophe, and I don't agree with you, although surely was the case of Apollo 13. Even Apollo 12 was a nightmare during launch, although not for strictly tecnical deficiencies, and Apollo 15 had a potentially serious problem with S-IC that poses the risk of a collision during the first staging event; but Apollo 7, 8, 9, 10, 11, 14, 16, 17 and Skylab 2, 3, 4 and ASTP, as far as I remember, don't show really serious problems during launch, assuming that your statement concern only the launch (because we were talking about launchers) and not the entire flight (in this case it's a different matter!).

Because the mission had some lot of bad luck, it was really not considered that important, but for people deeper involved in the program, it was actually much more dangerous for future missions than the oxygen tank explosion.

Here I agree with you completely. That was really a serious problem. Glad to see that the Apollo 13 movie has covered that little known event, also showing the eventuality of an abort.

 

[Lmoy]

Alright, that makes a lot of sense. Thanks for the detailed explanation!

 

[Loru]

Sidemount and inline after some fuel / mass tweaks.

 

[K_Jameson]

In the end you decided for metholox boosters?

 

[Loru]

In the end you decided for metholox boosters?

Boosters (or in this case they're 1st stage) are kerolox.

 

[K_Jameson]

Oh, OK. I noticed that your core stage was small in comparison, so I thought that your boosters was LOX/LCH4. I forgot your air-lit core approach that saves a bit of tank volume.

Regarding this. With airstart, the core is dead weight in the first phase of the flight. So you has the disadvantages of a classical sequential staging rocket, plus the disadvantage of an higher drag determined by your larger cross section in comparison with an inline rocket (and higher dry weight of the first stage because is actually composed by two stages).

Regarding safety concerns : I still think that air-start is viable, as stated before, but Urwumpe can have a point if I think that, in the beginning of the flight, the delicate cryogenic engines of the core are exposed to the intense flux of air and to the heat by the boosters, and not protected as in a classical inline rocket.
This can (maybe) increase the chance of some problems at the point of ignition. Rocket with air-lit cores, as Titan, had hypergolic, that are FAR more simple engines and less prone to failures.
So in case of exposed, delicate cryoengines, ground start can be the best choice.
I think that a little more tank weight is worth for such a launch vehicles. Progress in materials allows very light tanks so the penality is not drammatic. Also, you can choice a common bulkhead and save additional weight, probably more than you saves with the air-lit approach.

At this point, if you want retain the air-start, reunite the two boosters in a single first stage at the bottom of the LH2 stage and you has a more efficient launch vehicle!

 

[fred18]

At this point, if you want retain the air-start, reunite the two boosters in a single first stage at the bottom of the LH2 stage and you has a more efficient launch vehicle!

Totally agree with this, i was about to write the very same thing when I read it

 

[Loru]

I'll be probably investigating hybrid booster / hydrolox core later today. In the mean time I've played a bit with shuttle itself to make landing gear.

---------- Post added at 05:01 PM ---------- Previous post was at 04:08 PM ----------

And 2nd narrow angle shot with crew for scale. She is 1.62 meter tall.

---------- Post added at 05:55 PM ---------- Previous post was at 05:01 PM ----------

This company claims to achieve 340s of ISP vac. from it's parafine / LOX engine. With little grain of salt (ISP reduced to 320s) I put some numbers into silverbird and came up with satisfactory result for "classic" core + boosters:

Now I need to do some estimations about size of such booster.

---------- Post added at 07:47 PM ---------- Previous post was at 05:55 PM ----------

Tank size estimation based on numbers below.

LV capacity is ~24 tons to 45 deg 185km x185km LEO from equator.

I think that's reasonable concept. What do you think?

---------- Post added at 08:59 PM ---------- Previous post was at 07:47 PM ----------

Tanks incorporated into actual stages:

Stack dimensions (orbiter coordinate system):

X: 11.6 meters
Y: 9.6 meters
Z: 31 meters

 

[fred18]

From just a visual point of view, if i think of the space shuttle it seems that this vehicle has a very "bigger" launch configuration: bigger tank/core and way larger boosters for smaller shuttle. Again, i didn't go through your numbers, it's just a "visual" observation, didn't mean to be scientific in any way!

 

[K_Jameson]

I share your observation. Yeah, honestly, even Eridanus is smaller than Shuttle in comparison with its launch vehicle. One reason are the liquid boosters, that are far larger than SRB.

I think that's reasonable concept. What do you think?

Honestly I don't like hybrid engines too much, but it's me.
Your core is still air-lit?

 

[Loru]

I think that's because STS Shuttle had enormous payload bay which bloated the size of the shuttle. Probably Booster to core ratio may give that effect. Also rockets don't scale in linear fasion. I'll play with exact shape more.

 

[K_Jameson]

I think that's because STS Shuttle had enormous payload bay which bloated the size of the shuttle.

Here the reason #2. The shuttle is big but it's internal is mostly empty space.

 

[Loru]

I share your observation. Yeah, honestly, even Eridanus is smaller than Shuttle in comparison with its launch vehicle. One reason are the liquid boosters, that are far larger than SRB.

Yes - SRBs are compact.

Honestly I don't like hybrid engines too much, but it's me.
Your core is still air-lit?

core is ground lit. I'll investigate SRBs also - they may look better, however I'm not fan of putting humans next to a firework.

 

[DaveS]

Yes - SRBs are compact.



core is ground lit. I'll investigate SRBs also - they may look better, however I'm not fan of putting humans next to a firework.

You could sacrifice payload to orbit in exchange for a reinforced orbiter structure to handle the sudden loss of thrust from the SRMs by implementing a Thrust Termination System (TTS). This way a fast sep can be achieved without losing the crew and/or the vehicle.

 

[K_Jameson]

core is ground lit. I'll investigate SRBs also - they may look better, however I'm not fan of putting humans next to a firework.

To me, SRB are a bad choice, especially big SRB + sidemount... We have discarded it on Eridanus for the same reason. Stay with LRB (or hybrid, if you like it more).

 

[DaveS]

Here the reason #2. The shuttle is big but it's internal is mostly empty space.

Well, when most people think of the orbiter they think of the cylindrical payload bay but it is just part of the midbody. In fact all of the orbiter's EPS live in it. The forward-most sections are home to the three fuel cells and further aft we have the cryogenic reactant sets (each set consists of one LOX tank and one LH2 tank, minimum flight set is two sets) that supplies the fuel cells. It is also home to the GN2 tanks that are used to pressurize the crew module (atmosphere is sea-level equivalent, 80/20 N2/O2 mix at 101.352 kPa) as well as the GHe tanks that used for MPS pressurization.

So there's alot of equipment living in the midbody.

 

[K_Jameson]

Thanks for your very competent precisation. We just wanted to say that the cargo bay increases greatly the overall volume of the spaceplane, and thus contribute (along with the relatively small SRB) to create the feeling of a "big" spaceship in relation to the launch vehicle, in striking contrast to the proportions of the Loru's vehicle (and partially of our Quasar/Eridanus).

 

[Loru]

After some tinkering with diameters I managed to make it look bit better. I'll play with asymetric LOX tank in booster tomorrow so I can see if I can reduce aparent booster size bit more.

 

[K_Jameson]

In case of abort the spaceplane is supposed to fly away with its own engines? Or will have some sort of LES, maybe small detachable SRB at the flanks of the fuselage? Or nothing at all?