I have a question about the Proton rocket design

[Firemetal]

So a few months ago, I got interested in the Proton design and did some research on it. I was surprised to see that its first stage had engines only one its "Strap-on boosters". I mean it doesn't have strap on boosters! But only today, I found a video that kinda annoyed me.

This guy's Proton was incredibly unrealistic as it had six solid rocket boosters and a main tank which the real Proton doesn't. But that brought up a question. Why doesn't it use those six engine holder booster thingys as actual strap on booster with a middle engine? I mean it works in Kerbal Space Program!

But jokes aside, why did the soviet union choose to build it like this?

Also if anyone doesn't know how the Proton works, here:

 

Also here is a replica I made tonight:

So does anyone know why this is?

Thanks

Fire

 

[Gaarst]

Because using as strap-on boosters would be more complicated and useless. It would require more engines than it currently has and more complicated designs around them. Having liquid fueled boosters of this size is just throwing money away (LF engines are expensive) and the USSR was never fond of SRBs.

What is hard to realise when only having KSP as a reference for rockets, is that in real life, fuel and oxidiser tanks are separated. You don't just have a bit of both here and there as in KSP, but you have one oxidiser tank, and below or above one "fuel" tank.

The Proton is a special case. The core of the first stage is an oxidiser tank (NTO) while the 6 side tanks are fuel (UDMH).

It was designed this way for a simple reason: to fit in the trains. 4.1m is about the largest diameter that the Soviet railroads could transport making stages with a greater diameter harder, and therefore more expensive to move to Baikonur (the Proton is built by Khrunichev which has its facilities near Moscow). It turns out that 4.1m is the diameter of the Proton core, having the fuel tanks mounted on the side allows the rocket to fit on the railway (the side tanks are transported separately and assembled at Baikonur where they don't have this problem) and therefore allows it to be bigger without increasing its diameter and having to rebuild half of Russia's railway.

[Nibb31]

What Gaarst said. In addition, the side tanks (they are not boosters) were originally cannibalized from an existing ICBM design.

[DDE]

2 hours ago, Nibb31 said:

What Gaarst said. In addition, the side tanks (they are not boosters) were originally cannibalized from an existing ICBM design.

Actually, the UR-500/Proton is part of a family of common designs and was supposed to be composed of four two-stage UR-200s topped off by another UR-200. That was kind of a trademark of the Chelomei-Glushko team - their designs were very Kerbal; here's UR-700, and there even was a UR-900 on the drawing board. The third stage is based on the Proton's first stage.

http://www.friends-partners.org/partners/mwade/lvfam/ur.htm (Astronautix link)

[todofwar]

8 hours ago, DDE said:

Actually, the UR-500/Proton is part of a family of common designs and was supposed to be composed of four two-stage UR-200s topped off by another UR-200. That was kind of a trademark of the Chelomei-Glushko team - their designs were very Kerbal; here's UR-700, and there even was a UR-900 on the drawing board. The third stage is based on the Proton's first stage.

http://www.friends-partners.org/partners/mwade/lvfam/ur.htm (Astronautix link)

I thought the only real reason to have side bound stages was so you can fire the center rocket at the same time, but that schematic seems to show them only firing the outer rockets until burnout. Or am I misreading that?

[Kryten]

51 minutes ago, todofwar said:

I thought the only real reason to have side bound stages was so you can fire the center rocket at the same time, but that schematic seems to show them only firing the outer rockets until burnout. Or am I misreading that?

Plenty of rockets have staging like that, e.g. Titan 3C. Means your assembly building doesn't have to be as large/tall, and that the aerodynamics are easier.

[DDE]

1 hour ago, todofwar said:

I thought the only real reason to have side bound stages was so you can fire the center rocket at the same time, but that schematic seems to show them only firing the outer rockets until burnout. Or am I misreading that?

Nope, simultaneous firing, R-7 style, and fuel crossfeed, Falcon Heavy-style.

[softweir]

3 hours ago, DDE said:

Nope, simultaneous firing, R-7 style, and fuel crossfeed, Falcon Heavy-style.

No, not fuel crossfeed Falcon-Heavy Style. The Falcon Heavy may (if they get the tec working) feed fuel and oxidiser from the strap-on stages to power the core stage until separation. In the Proton oxidiser is fed out to the ring of engines while fuel feeds down, and they have arranged things so the fuel and oxidiser empty more or less simultaneously.

As posts above have described, the Proton is designed this way so the large and heavy first stage can be transported by rail. If they built the fuel tanks on to the core then it would all be too big to fit the railways used to transport it from the manufacturing site to the assembly/launch site. Instead, the strap-on fuel tanks and engines go on one set of carriages, while the core is just narrow enough to be carried on its own carriage.

[kerbiloid]

Those gaps between radial blocks are just crying to put landing gears there.

P.S.
Afaik, the railway compatibility was caused not especially by Baikonur, but because originally Proton is ICBM with space option.

Edited October 31, 2016 by kerbiloid

[DDE]

7 hours ago, softweir said:

No, not fuel crossfeed Falcon-Heavy Style. The Falcon Heavy may (if they get the tec working) feed fuel and oxidiser from the strap-on stages to power the core stage until separation. In the Proton oxidiser is fed out to the ring of engines while fuel feeds down, and they have arranged things so the fuel and oxidiser empty more or less simultaneously.

I was talking about the UR-700 and not the UR-500.

15 minutes ago, kerbiloid said:

Afaik, the railway compatibility was caused not especially by Baikonur, but because originally Proton is ICBM with space option.

Yes, it's an ICBM that would launch from Baikonur's pads, R-7-style; the US would have given it a PGM- designation if it were theirs.

Rail compatibility was always important for the Soviet Union; they tried to build the N-1 without it, and look what happened. Plus it's the reason Vostochny can't use Protons even if it had pads; and just because Baikonu can, there are plans for a fatter version of the Zenit called the Sunkar.

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

[kerbiloid]

16 minutes ago, DDE said:

Yes, it's an ICBM that would launch from Baikonur's pads

It's an ICBM that would launch from SILOs.

[magnemoe]

2 hours ago, DDE said:

I was talking about the UR-700 and not the UR-500.

Yes, it's an ICBM that would launch from Baikonur's pads, R-7-style; the US would have given it a PGM- designation if it were theirs.

Rail compatibility was always important for the Soviet Union; they tried to build the N-1 without it, and look what happened. Plus it's the reason Vostochny can't use Protons even if it had pads; and just because Baikonu can, there are plans for a fatter version of the Zenit called the Sunkar.

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

Rail compatibility is useful everywhere, both the shuttle srb and falcon 9 is sized for it. The Israeli tank is wider than other as it don't have to be transported by rail. 
For Russia is even more important as they can not use boats to the launch site. 

[kerbiloid]

So, a horse retrograde part rules in space.

[Nibb31]

2 hours ago, kerbiloid said:

So, a horse retrograde part rules in space.

Urban legend: http://www.snopes.com/history/american/gauge.asp

[ElWanderer]

1 hour ago, Nibb31 said:

Snopes link in reply to Kerbiloid

Indeed... and the Russian gauge (1520mm) used in most of the former Soviet Union is wider than standard gauge (1435mm). Larger horses?

Plus the limitation on transporting something by rail is really down to the loading/structure gauges (how far the tracks are from obstructions, as opposed to the distance between the two rails).

[softweir]

8 hours ago, DDE said:

I was talking about the UR-700 and not the UR-500.

Oops! Sorry.  That'll teach me to read posts more carefully.

[kerbiloid]

3 hours ago, ElWanderer said:

and the Russian gauge (1520mm) used in most of the former Soviet Union is wider than standard gauge (1435mm).

1524 mm (5 ft) is an old American standard used since XIX, because of the first chief engineer.

That's Russia who is still using standard gauge!

3 hours ago, ElWanderer said:

Larger horses?

Wider.

 

What's strange: both American and Soviet/Russian space techs use more or less the same 4.1-4.2 m (up to 4.5).
Probably, not the gauge decides, but distance between parallel railways (and lightpoles).

[cfds]

2 hours ago, kerbiloid said:

Probably, not the gauge decides, but distance between parallel railways (and lightpoles).

That is exactly what "loading gauge" means.

[magnemoe]

15 minutes ago, cfds said:

That is exactly what "loading gauge" means.

Makes sense, note that Russia uses and tricks then transporting some oversized stages, they offset them to the left, this way you can transport wider stuff but can not meet other trains, it require that its nothing between the tracks. 
US double load containers, works as they don't use electrical power for trains and underpasses are high enough. 

[DDE]

15 hours ago, kerbiloid said:

It's an ICBM that would launch from SILOs.

Except that the work on silos was cancelled before it was even started, and certainly before UR-500 hit the launch pads.

[kerbiloid]

3 hours ago, DDE said:

Except that the work on silos was cancelled before it was even started, and certainly before UR-500 hit the launch pads.

http://militaryrussia.ru/blog/topic-799.html

Quote

На стадии проектирования (1961-1964 г.г.) прорабатывалась и шахтная пусковая установка для боевого варианта ракеты УР-500. Макет ШПУ был продемонстрирован Н.С.Хрущеву в 1964 г. во время его визита на Байконур.

During the design phase (1961-1964) also there was being designed SILO for the combat version of UR-500 rocket. The SILO mockup was presented to N.S.Khrushchev in 1964 during his visit to Baikonur.