Why are R-7 boosters inset?

[NFunky]

Hey guys, I've been searching the internet, but haven't been able to find the answer to this.  Maybe I'm using the wrong keywords or something, but then I remembered the well informed people on this forum, so I thought I'd ask here.

 

Why do the R-7 family of rockets have their liquid boosters inset?  What I mean is, most other rockets I see with boosters just strap cylindrical boosters to a cylindrical core, but R-7/Soyuz have a tapering core that has the boosters far closer together.  I assume this makes it more aerodynamic, but how much difference does it actually make, and are there other considerations I don't know about?

 

Thanks!

[Phineas Freak]

Because of the A-4 (V-2) heritage. TL;DR version:

http://astronautix.com/r/russia-earlisticmissiles.html

The idea was to strap multiple A-4-like booster cores around a single sustainer core (air igniting a rocket engine was a big no-no back then):

http://www.russianspaceweb.com/r3.html

This just got bigger as time passed (and nuclear warheads grew in mass):

http://www.russianspaceweb.com/r6.html

But the engines were not up to task. So, they were upgraded, increasing the diameter of the stages, leading to the R-7 design (and from there to Molniya, Vostok, Soyuz etc).

Edited March 7, 2018 by Phineas Freak

[ment18]

Warning: Mostly guesswork

I think the main reason is to reduce the height of the rocket.  The taller the rocket, the more mass you have to spend to prevent it from being destroyed by wind, so a shorter rocket can be a bit lighter from slightly reduced forces.  If the r-7 was meant to launch from a silo, launch size would want to be reduced, so having a small core stage bottom reduces horizontal size and then the expanding top allows for a shorter rocket.  In addition, it also allows for shorter additional stages.  There might also be something about the force transmission from the booster to the core.  With the slight overhang from the expansion, it might make the booster attachment force transmission easier.

[MaxwellsDemon]

I think part of it is also holdover from the V-2-influenced R-1, R-2, and following... the V-2/A-4 was of an 'ogive' (sort of ellipsoid) shape, as were the followons, though as Korlev and company went to work on them they started to straighten out.  The V-2 heritage is most obvious in the shapes of the strapons.

[p1t1o]

One could easily ask the question "Why are most strap-on boosters the same shape as the central core?"

Just in terms of optimal packing, conical shapes are better. This could potentially reduce drag due to a lower "wetted area" (put very simply: amongst everything else, drag is also proportional to surface area.)

So swings and roundabouts basically, different design heritage puts it on a slightly different track to western designs.

Edited March 7, 2018 by p1t1o

[wumpus]

From Ment18's picture, there appears to be significant aerodynamic issues as well.  It looks like they keep the cross-section constant-ish, which is critical in transonic and supersonic flight.
- not sure why they boosters keep tapering after the sustainer stops.  Could be for manufacturing, or it could be that a too sharp bend was worse than violating the cross section.

[p1t1o]

19 minutes ago, wumpus said:

From Ment18's picture, there appears to be significant aerodynamic issues as well.  It looks like they keep the cross-section constant-ish, which is critical in transonic and supersonic flight.
- not sure why they boosters keep tapering after the sustainer stops.  Could be for manufacturing, or it could be that a too sharp bend was worse than violating the cross section.

Cross section should not remain constant, it should just avoid sharp changes and optimally, should approximate the cross-section/length profile of a Seers-Haack body.

Conical parts do seem to help make smooth changes (where the sudden change in radius at the end of a cylindrical section would be quite different).

[NSEP]

R-7 was made during the dawn of spaceflight, when orbital rockets are were completely new. There was no other orbital rockets to compare it to, and that ends up in pretty odd designs. Just look at any early rocket design. The Juno I for example was a ballastic missle and had multiple solid rocket upper stages. Its like fireworks strapped together.

Eventually the most efficient and effective rockets stayed, and thats why most rockets are just cilinders with cones. But the R-7, just kind of sticked around, because it worked and there is no need for a replacement.

Edited March 7, 2018 by NSEP

[magnemoe]

4 hours ago, NSEP said:

R-7 was made during the dawn of spaceflight, when orbital rockets are were completely new. There was no other orbital rockets to compare it to, and that ends up in pretty odd designs. Just look at any early rocket design. The Juno I for example was a ballastic missle and had multiple solid rocket upper stages. Its like fireworks strapped together.

Eventually the most efficient and effective rockets stayed, and thats why most rockets are just cilinders with cones. But the R-7, just kind of sticked around, because it worked and there is no need for a replacement.

Pretty much this, except that the r-7 design is not stupid. I thought the tapering was closer to engines and that it was more like the R-7 style KSP rockets we can make with the tapered fuel tanks and nose cones. One bonus is that the booster force is put at top, you see that the booster tips are very heavy duty. 
At the time of booster separation you should be pretty much done with aerodynamic anyway. 
If I was to change anything with R-7 it would be an engine upgrade. 

[YNM]

8 hours ago, magnemoe said:

If I was to change anything with R-7 it would be an engine upgrade.

Small wonder it held for decades !

 

But yeah, I didn't thought R-7 had anything to do with A-4. I thougt it had more with streamlining or something.

13 hours ago, NSEP said:

The Juno I for example was a ballastic missle and had multiple solid rocket upper stages. Its like fireworks strapped together.

The upper stages were cruise missiles I think ? Or is it the "ship-launched missile" thing, or the cluster missile off trucks thing... IMO Juno is basically a mix-and-match approach, esp. for the launch of Explorer 1, they just scramble through the inventory and see what they could put together, after the failure of Vanguard.

They do reserve honorary mention though, as S-I and S-IB are descended from Redstone tankage.

Edited March 8, 2018 by YNM

[DerekL1963]

18 hours ago, magnemoe said:

If I was to change anything with R-7 it would be an engine upgrade. 

Keep in mind that the current Soyuz launcher is a descendant of the R-7...  The engine (among other things) has already been upgraded, multiple times.  Or, to put it another way, the belief widely held in the space fandom community that "the Russians have flown the same design for over fifty years" is nonsense.

[NSEP]

2 hours ago, DerekL1963 said:

Keep in mind that the current Soyuz launcher is a descendant of the R-7...  The engine (among other things) has already been upgraded, multiple times.  Or, to put it another way, the belief widely held in the space fandom community that "the Russians have flown the same design for over fifty years" is nonsense.

But they are still somewhat simulair, more simulair than the Atlas. Atlas V is completely unrecognizable from the SM-65 Atlas, from the engines to the fuel tank. The R-7 (first stage and boosters) and its derivatives, from what i know, only had changes in the rocket engines and maybe a few other small changes that lowered mass and increased performance, but nothing extremely drastic, unlike the Atlas wich went from Semi-SSTO balloon to a Soviet-American frankenstein machine throughout its life time. I think its safe to say the R-7 is the orbital rocket with the least changes through its over-a-century lifespan.

Saying its the same design is somewhat of an overstatement but saying its 'just of the same family' is an understatement.

Edited March 8, 2018 by NSEP

[IncongruousGoat]

40 minutes ago, NSEP said:

But they are still somewhat simulair, more simulair than the Atlas. Atlas V is completely unrecognizable from the SM-65 Atlas, from the engines to the fuel tank. The R-7 (first stage and boosters) and its derivatives, from what i know, only had changes in the rocket engines and maybe a few other small changes that lowered mass and increased performance, but nothing extremely drastic, unlike the Atlas wich went from Semi-SSTO balloon to a Soviet-American frankenstein machine throughout its life time. I think its safe to say the R-7 is the orbital rocket with the least changes through its over-a-century lifespan.

Saying its the same design is somewhat of an overstatement but saying its 'just of the same family' is an understatement.

Ditto this. Sure, the R7 family has evolved somewhat over time, but if you compare it to any other rocket family it's practically unchanged. For an extreme example, take the Delta family. It started off as a kerolox IRBM with a hypergolic upper stage strapped on to enable satellite launches, which after lots and lots of changes has ended in an all-hydrolox HLV (Delta IV Heavy is almost certainly going to be the last Delta rocket).

Also, consider the fact that Soyz only upgraded from analog to digital avionics in the 1990s. If that's not re-using the same design far past its sell-by date I don't know what is.

[DerekL1963]

46 minutes ago, NSEP said:

I think its safe to say the R-7 is the orbital rocket with the least changes through its over-a-century lifespan.

That's a true statement, but obscures the fact that the current Soyuz rocket differs greatly from the original R-7 ICBM.  The engines have been upgraded, the electronics have been upgraded, unlike the R-7 the Soyuz has a second stage, etc... etc...  I does look kinda like the original if you squint and tilt your head just right, but that doesn't make it the original.

Myself, I don't care to obscure facts.  YMMV.

The Soyuz launcher isn't an R-7, and the Russians aren't flying a fifty year old design.  Those are the facts.  You want to play semantic games, feel free.  Having introduced the facts I have no further interest in games.

 

[magnemoe]

7 minutes ago, DerekL1963 said:

That's a true statement, but obscures the fact that the current Soyuz rocket differs greatly from the original R-7 ICBM.  The engines have been upgraded, the electronics have been upgraded, unlike the R-7 the Soyuz has a second stage, etc... etc...  I does look kinda like the original if you squint and tilt your head just right, but that doesn't make it the original.

Myself, I don't care to obscure facts.  YMMV.

The Soyuz launcher isn't an R-7, and the Russians aren't flying a fifty year old design.  Those are the facts.  You want to play semantic games, feel free.  Having introduced the facts I have no further interest in games.

The Soyuz is evolved on the R-7 its not an R-7. I think it still used H2O2 to run the turbo pumps who is V2 technology. On the other hand the engines used in the N-1 is among the most advanced in the world. 
If its not broken don't fix it is another principle, or how the B52 is still in active use and its older than the Soyuz

[linuxgurugamer]

Just now, magnemoe said:

On the other hand the engines used in the N-1 is among the most advanced in the world. 

except that they never worked right.  4 launches of the N-1, 4 failures.  Different causes, but most tied back to the engines

 

[DerekL1963]

7 minutes ago, linuxgurugamer said:

4 launches of the N-1, 4 failures.  Different causes, but most tied back to the engines

It's not that simple.

Only one of the four failures can be directly tied to an engine failure - the second, in which a turbopump exploded.  The first was a failure due to POGO, the third was a failure of the KORD control system (but the booster was likely already doomed even without KORD's intervention), the fourth could go either way...  You  could blame the fire caused by water hammer bursting pipes or the explosion of engine #4 (which may or may not have been caused by the water hammer).
 

21 minutes ago, magnemoe said:

If its not broken don't fix it is another principle, or how the B52 is still in active use and its older than the Soyuz

To be fair, and grossly off-topic, the B-52 is still flying because once (or more accurately, each time) the USAF decided on a replacement, it turned out to be too expensive/low performance/whatever to actually replace the B-52 and as a result was either cancelled or at best produced in limited numbers.   And kind of back on topic, it's not clear to me how much of the current B-52's is actually original....  Between upgrades, modifications, overhauls, repairs, and routine maintenance, and awful lot has been replaced on any given aircraft.

[NSEP]

22 minutes ago, DerekL1963 said:

That's a true statement, but obscures the fact that the current Soyuz rocket differs greatly from the original R-7 ICBM.  The engines have been upgraded, the electronics have been upgraded, unlike the R-7 the Soyuz has a second stage, etc... etc...  I does look kinda like the original if you squint and tilt your head just right, but that doesn't make it the original.

I agree that the original R-7 isn't flying today, but i wasn't saying it is.

[YNM]

2 hours ago, IncongruousGoat said:

Sure, the R7 family has evolved somewhat over time, but if you compare it to any other rocket family it's practically unchanged. For an extreme example, take the Delta family...

Both Delta and Atlas no longer have any element of the ICBMs they were based on. The last one was Titan IV, Delta III and Atlas II.

Edited March 8, 2018 by YNM

[shynung]

The Soyuz rocket family are transported to its launch pad in Baikonur by train, fully assembled. The central core was tapered to make room for the side boosters, so as to fit the train's maximum load dimensions.

[YNM]

2 hours ago, shynung said:

The central core was tapered to make room for the side boosters, so as to fit the train's maximum load dimensions.

They could've "undone" them though, Energia was much, much larger yet runs on (almost) the same rails Soyuz runs on.

Commonality would make slightly more sense, the limits between the straight sections and the angled one made sense for fuel and oxidizer I think.

Edited March 9, 2018 by YNM

[monophonic]

19 minutes ago, YNM said:

They could've "undone" them though, Energia was much, much larger yet runs on (almost) the same rails Soyuz runs on.

Commonality would make slightly more sense, the limits between the straight sections and the angled one made sense for fuel and oxidizer I think.

"Almost" the same rails... just two parallel pairs of them!

 

[DerekL1963]

5 hours ago, shynung said:

The Soyuz rocket family are transported to its launch pad in Baikonur by train, fully assembled. The central core was tapered to make room for the side boosters, so as to fit the train's maximum load dimensions.

I'm not entirely sure I buy that...  It's a dedicated set of rails between the assembly building and the pad, so there's no obstructions that have to be cleared.  So long as the load is balanced, sticking out a meter or so on each side shouldn't be a particular problem.

[p1t1o]

9 minutes ago, DerekL1963 said:

I'm not entirely sure I buy that...  It's a dedicated set of rails between the assembly building and the pad, so there's no obstructions that have to be cleared.  So long as the load is balanced, sticking out a meter or so on each side shouldn't be a particular problem.

Its be weird to make the rocket fit the train, and not the other way around, too.

"We cant go to space, our....trains are too small?"

[shynung]

13 minutes ago, DerekL1963 said:

I'm not entirely sure I buy that...  It's a dedicated set of rails between the assembly building and the pad, so there's no obstructions that have to be cleared.  So long as the load is balanced, sticking out a meter or so on each side shouldn't be a particular problem.

I'd imagine there would be balance problems. Imagine holding a wide object while walking on a fence.