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How can you optimize rocket engine performance for human spaceflight safety?

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Rocket engines are the key components that enable human spaceflight, but they also pose significant challenges and risks. To ensure the safety and reliability of space missions, aerospace engineers need to optimize the performance of rocket engines, which depends on many factors such as design, materials, fuel, thrust, efficiency, and cooling. In this article, you will learn about some of the basic principles and methods that can help you improve the performance of rocket engines for human spaceflight safety.

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Dave Gingerich

Senior Staff Engineer at Lockheed Martin Space Systems Company

1 Design principles

The design of a rocket engine is based on the principle of conservation of momentum, which states that the total momentum of a system remains constant unless an external force acts on it. A rocket engine works by expelling a high-speed stream of exhaust gas from a nozzle, which creates a reaction force that propels the rocket forward. The performance of a rocket engine is measured by its specific impulse, which is the ratio of thrust to propellant mass flow rate. The higher the specific impulse, the more efficient the engine is. To increase the specific impulse, you need to increase the exhaust velocity and decrease the nozzle exit pressure.

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Dave Gingerich

Senior Staff Engineer at Lockheed Martin Space Systems Company
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Rocket engines are not based upon conservation of momentum. Different Newton's Law -- equal and opposite reaction. The efficiency of a rocket is measured by specific impulse, but that isn't a full measure of a rocket's performance. We already have efficient rockets with very high Isp's, but they can't get off the ground because their thrust is way too low. All rockets, regardless of type, do just two things; 1) Energize a propellant 2) Convert the energized propellant to a high speed exhaust. Optimization of a rocket doesn't mean producing the highest Isp possible. It means optimizing for the mission and that includes cost, schedule, complexity, reaching the required trajectory, and providing a ride that doesn't damage the payload

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2 Material selection

The material selection for a rocket engine is crucial, as it has to withstand extreme temperatures, pressures, and vibrations. The material properties that affect the performance of a rocket engine are strength, density, thermal conductivity, thermal expansion, and corrosion resistance. The material selection also depends on the type of fuel and oxidizer used, as some materials are incompatible or reactive with certain propellants. For example, liquid hydrogen and oxygen require cryogenic materials that can handle low temperatures and high thermal stresses. Some of the common materials used for rocket engines are aluminum, titanium, steel, nickel, copper, and carbon fiber.

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Dave Gingerich

Senior Staff Engineer at Lockheed Martin Space Systems Company
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The answer to the left presumes you're selecting material for a thermochemical rocket with a fuel and oxidizer. Material for thermonuclear and electrodynamic rockets is similar - have to pick materials that will produce and sustain the environment required. BTW, LOx and H2(l) presently are only used for ascent vehicles from Earth's surface. No one has demonstrated how to handle cryogenic fluids in outer space or how to produce it anywhere but Earth. NASA is working on that with the Cryogenic Demonstration Mission, CDM.

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3 Fuel choice

The fuel choice for a rocket engine is another important factor that influences its performance, as it determines the energy density, combustion temperature, and exhaust composition. The fuel choice also affects the safety and environmental impact of the rocket engine, as some fuels are more toxic, flammable, or polluting than others. The main types of fuels used for rocket engines are solid, liquid, and hybrid. Solid fuels are easy to store and handle, but have low specific impulse and are difficult to control. Liquid fuels have high specific impulse and are controllable, but require complex pumps and tanks. Hybrid fuels combine solid and liquid propellants, and offer some advantages of both.

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Dave Gingerich

Senior Staff Engineer at Lockheed Martin Space Systems Company
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True, for thermochemical rockets. Other rocket types use ions or Hydrogen as their propellant. Combustion or oxidization is not necessary. "All you have to do" is expel some mass at the highest speed possible. If you sat in a child's wagon and threw a brick out the back as fast (hard) as you could, you have just demonstrated what every rocket does - eject mass in a direction opposite from the desired velocity.

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4 Thrust control

The thrust control for a rocket engine is essential for achieving the desired trajectory, speed, and altitude of the rocket. The thrust control also affects the stability and maneuverability of the rocket, as well as the fuel consumption and safety. The thrust control can be achieved by varying the propellant flow rate, the nozzle area, or the direction of the exhaust. The propellant flow rate can be regulated by valves, pumps, or injectors. The nozzle area can be adjusted by movable parts, such as throat plugs or petals. The direction of the exhaust can be changed by gimbal mechanisms, jet vanes, or thrust vectoring.

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5 Efficiency improvement

The efficiency improvement for a rocket engine is a challenging task, as it involves reducing the losses and increasing the output of the engine. The losses can be caused by friction, heat transfer, pressure drop, incomplete combustion, or shock waves. The output can be improved by increasing the combustion temperature, the expansion ratio, or the nozzle shape. Some of the methods that can help you improve the efficiency of a rocket engine are using staged combustion, regenerative cooling, aerospike nozzles, or scramjets.

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Dave Gingerich

Senior Staff Engineer at Lockheed Martin Space Systems Company
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We've reached the end stage of improving thermochemical rockets. Tsiolkovsky's rocket equation is an impenetrable barrier that always defeats every effort to produce a rocket with more than tiny, marginal improvements. Every rocket. Every type. If you're expelling propellant at high speed, this physical limitation is a cruel, harsh limit. The rocket equation tells us how, but it also tells us you cannot get beyond this limit.

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6 Cooling system

The cooling system for a rocket engine is a vital component that prevents the engine from overheating and melting. The cooling system also affects the performance and weight of the engine, as it consumes some of the propellant and adds some mass to the engine. The cooling system can be classified into passive or active, depending on whether it uses external or internal sources of cooling. Passive cooling systems use insulation, radiation, or ablative materials to reduce the heat transfer to the engine. Active cooling systems use liquid or gas to circulate around the engine and remove the heat. Some of the common active cooling systems are film cooling, transpiration cooling, or dump cooling.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Dave Gingerich

Senior Staff Engineer at Lockheed Martin Space Systems Company
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The original question, "optimize rocket engine performance for human spaceflight safety" is out-of-date. A better, broader way that addresses the 'real problem' and isn't asking for marginal improvements on a method that was solved 50 years ago, would be "how can we improve (optimize) access to space manned and unmanned missions". Improvements include; higher safety, lower cost, increased launch frequency, heavier cargo, lower environmental impact, ...

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How can you optimize rocket engine performance for human spaceflight safety?

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4

5

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7

1 Design principles

2 Material selection

3 Fuel choice

4 Thrust control

5 Efficiency improvement

6 Cooling system

7 Here’s what else to consider

Aerospace Engineering

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How can you optimize rocket engine performance for human spaceflight safety?

1

2

3

4

5

6

7

1 Design principles

2 Material selection

3 Fuel choice

4 Thrust control

5 Efficiency improvement

6 Cooling system

7 Here’s what else to consider

Aerospace Engineering

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