Any way to recover the old forum blog posts?

[cicatrix]

Hello, this question could have already been answered, but this is kind of important to me so I dare to ask -

Is there any way I could recover some of my blog posts on the old forum engine? I know they have been discarded during the upgrade but still there might have been some old backup left or something? Unfortunately I have discovered that I lost the original files of my translations of some articles that I posted as blog entries here and these posts were the only one left.

I judged that according to the old Internet saying that 'once posted it's there forever' I can always use them if I need to, but this situation proves that every rule has an exception.

 

[KasperVld]

Hmm, if you could provide me with some information such as the title of the blog I can have a look. No promises that I'll find it, though.

[magico13]

You might try using the wayback machine to see if it was archived: https://web.archive.org/web/20151123012829/http://forum.kerbalspaceprogram.com/blog.php?s=dda1a4bc16d507a57b9760ba0d42e4c4

[cicatrix]

1 hour ago, KasperVld said:

Hmm, if you could provide me with some information such as the title of the blog I can have a look. No promises that I'll find it, though.

There were a total of 5 translations titled 'Hidden complexities of rockets' (parts 1 through 5).

 

Here, even with links (There's a thread where the links to all 5 parts are listed - it's still here, but the links are obviously lead to nowhere).

 

Edited March 3, 2016 by cicatrix

[magico13]

Looks like you can find them with the link I provided and just copy+paste them into the new forum! (you probably will need to make a few manual tweaks. Also I don't know why this is bolded)

Spoiler

 

Hidden complexity of rockets. Part 1

2 Comments

by 

cicatrix

, 2nd December 2014 at 07:45 (2774 Views)

Translation notice: the text below was originally published in Russian here:

http://geektimes.ru/post/208048/

I only translated in into English.

 

The article so far consists of 5 parts, here is the first one.

 

Following parts:

 
Part 2: Solid fuel engines 

(Original here:

 http://geektimes.ru/post/209242/ 

)

Part 3: Types of liquid fuel, geometry, transportation 

(Original here:

 http://geektimes.ru/post/211054/ 

)

Part 4: More about engines and fuel tanks 

(Original here:

 http://geektimes.ru/post/215959/ 

)

Part 5: Launchpad facilities 

(Original here:

 http://geektimes.ru/post/220977/ 

)

Hidden complexity of rockets. Part 1

 

Assembly and operation of rockets is a ‘black team’ of cosmonautics in a peculiar way. It’s a big and difficult work that is being done quietly and all the credits go to those who build payloads. We keep forgetting of the difficulties that are being resolved during research and development of launch vehicles. This article serves to display the importance of this subject and bring a small bit of insights to those who would want to know ‘how it flies’.

Introduction

 

Even a small company can make its own satellite but only eleven countries in the world so far managed to build rockets that delivered their payloads to the orbit. Given that, it should be mentioned, for example, that South Korea has bought the first stage from Russia and got it as a ‘black box’. Why there’s so few? Because building a launch vehicle requires a very sophisticated technology and a great deal of money.

 

We should probably start with this video:

 

 

It’s been seventy years already since the first launches of V-2 but rockets are still go out their way to fall. They do it less frequently today and failed launches are measured by mere per-cents, not tens of per-cents, but this industry’s difficulties play along.

Engines

 

Even the simple educational diagram the rocket engine looks quite sophisticated. What can be said then about real diagrams?

 

Why so much complexity? All these crafty turbine pumps, regenerative cooling, closed cycle operation and other techniques serve to raise the engine efficiency. You can make the simplest LFE in literally in your garage (

monopropellant MosGIRDa (link in Russian) 

or simply

 3d-printed

), but this engine font fly farther than your hobby.

Turbine pump assembly (TPA)

 

Its main task is to pump fuel and oxidizer. To accomplish that one has to spend some amount of fuel energy by burning it in a small gas generator combustion chamber.

Left: diagram of TPA RD-107108 for R-7 family, Right: TPA for RD-180 (Athlas-V)

 

Turbine pump operates in quite severe conditions. For example, explosive rupture of TPA was behind two failures of Soviet ‘moon’ N-1 rocket.

Combustion chamber

 

Fuel and oxidizer are injected into the chamber through pulverizing nozzles. One of the major problems the engineers face is instability of burning. Any random change of flow through the nozzles can cause a pressure peak which in turn would detonate the components instead of their uniform combustion. This alone can cause a catastrophic failure. The only solution that ultimately worked was separation of the combustion chamber into smaller sections isolated by protruding nozzles or curtains.

Left: RD-107/108, Center: RD-180, Right: F-1 (the first stage of Saturn-V )

Nozzle

 

And here the main problem is heat dissipation. The temperature in the combustion chamber can reach up to 2000 °C (3632 °F) with the heat transfer rate of 1-20 MW/m2.

 

The best solution to handle that was so called ‘regenerative cooling’. A fuel component (usually fuel itself) is pumped through the cooling ‘jacket’ along the outer surface of the nozzle. In USA they designed a system of pipes and in USSR – corrugated spacers and milled notches:

Left: RD-10, first experiments in 1933, Center: notches chart for RD-107/108, Right: LR-87, Titan-2

Aside from that, additional ejector nozzles are placed along the walls that eject fuel thus creating a curtain from the flame. There can even be several of such curtains (for example, the V-2 engine had 4 such curtain belts). Here’s a 3-belt curtain example for RD-170:

1. Gas duct
2. Middle floor of the intermixing head
3. Frontal (combustion) floor of the intemixing head
4. Injectors that form anti-pulsating barriers (54 total)
5. Main injectors
6. Ignition composition feed (4 injectors are fed from a separate manifold)
7. Top curtain belt manifold
8. Fuel feeding manifold for cooling of the cyllindrical part of the combustion chamber
9. Collectors for the middle (26) and the bottom (26) curtain belts
10. Main combustion chamber fuel feed manifold
11. Outer (load-bearing) wall of the combustion chamber
12. Nozzle cooling circuit exit manifold
13. Inner wall of the combustion chamber
14. Intake manifold for nozzle cooling circuit
15. Nozzle
16. Fuel flows towards the nozzle edge along the even (for example) channes and returns along the odd ones
17. Intake manifold for cooling of the nozzle exit
18. Fuel feed from the pump
19. Fuel feed to the middle and lower curtain belts
20. Separating barrier
21. Cyllindrical part of the nozzle
22. Intermixing head
23. Central injector
24. Gas chamber of the intermixing head
25. Perforated back floor of the intermixing head
26. Middle curtain belt
27. Bottom curtain belt


Efficiency

 

It’s virtually impossible to discuss the efficiency rocket engine considering it to be an integral parameter because the engine and the stage it carries is a result of a complex tradeoff between many parameters such as: technological complexity of the design/upgrade/manufacture, cost of the design/upgrade/manufacture, thrust, specific impulse, pressure in the combustion chamber, well-established reliability and many others. All these parameters are in constant conflict with each other. A simple to manufacture and low-cost under-loaded engine will have mediocre thrust or specific impulse and, at the same time, an engine having a very high specific impulse will turn out to be complex, unreliable or too expensive. It’s quite common a situation when it’s easier to use an existing engine having non-optimal characteristics because it’s right there and does not require any investments in developing a new one. For example, the “Kosmos-2” rocket had to be filled with six different liquids because its first stage used-to be a middle-range ICBM, and its second one was developed many years later and different fuel components were used.

 

This situations gets even more complex because up to the present time our technology approached quite closely to the physical limit of chemical fuels and any new engine using know principles would not be considerably better than the old ones.

Control system

 

The control system has two difficult tasks – maintaining a stable flight and transportation of the payload to the necessary point in space.

Maintaining a stable flight

 

Nearly all rockets are aerodynamically unstable:

Another name for this problem is ‘reverse pendulum’. The control system constantly maintains unstable equilibrium by negating all disturbing effects.

Orbit injection accuracy

 

A modern digital ‘Proton-M’ has the

 following (link in Russian) 

injection accuracy:

• Perigee: ± 2 km
• Apogee: ± 4 km
• Inclination: ± 1.8 minutes
• Injection time: ± 3 s

 

If you have never played Orbiter or Kerbal Space Program it would be quite difficult to explain about how high this precision is. Imagine you close your eyes then drive a car for 9 minutes and, with the precision of ± 3 seconds, you drive in a box that is only 8 cm longer and only 2 cm wider than your car.

And how does it work?

 

You might ask, why had I had to close my eyes in the previous example? Because in space you do not have any road markings and modern systems do not use any external guidance information, they work completely autonomous. Inertial navigation system records the attitude and acceleration changes and sends control signals to service mechanisms. Such control system has a so called gyro-stabilized platform where the gyroscopes that record attitude and accelerometers that record acceleration are mounted. The platform itself is suspended in such a way that allows it to maintain its orientation.

 

Here’s how it looks like:

Left: a computer model of the platform made by Pilyugin’s Science Centre (link in Russian), Center: the platform of “Oka” missile complex", Right: the platform of the American “Peacekeeper” ICBM

.

 

Today, thanks to the development of digital technology, gyro-stabilized platforms gradually recede into the past. Traditional gyroscopes have nearly universally been replaced with

 laser 

ones, and rotating platforms are being replaced with platform-less systems where gyroscopes and accelerometers are mounted on the hull and their data is processed by a computer. By the way, gyroscopes in consumer electronic gadgets are neither rotational nor laser – they work on

 vibration

. They are not very precise, but they are small and cheap.

Reliability

 

In our imperfect world not only a complex rocket engine can fail, but even a simple cable, sensor or valve. Because of that, special reliability measures are employed, such as:

• All actuation mechanisms are doubled: when the main unit fails, the reserve one takes action. The STS-112 Space Shuttle mission barely escaped a catastrophe during liftoff when the main pyrobolt detonators that held the side solid fuel boosters did not work in time. Fortunately, reserve detonators worked and pyrobolts broke in time.
• All instruments are tripled: routinely three sets of instruments are installed and they take votes. In case one of them fails, the two remaining ones continue to provide correct information. There was an incident in aviation when two of the three gyroscopic horizons failed and the autopilot plunged the craft into a dive. Fortunately, the pilots took action and prevented the catastrophe. Nowadays, when computers became common, sometimes the fourth ‘vote’ is added (or the third one in place of one instrument) – it represents a mathematic model of ‘how it should be’.

Conclusion

I hope you’ve just got more acquainted with hidden complexity of rockets.

 

 

Edited March 3, 2016 by magico13