RCS thrusters are mainly used in space flight, the reason why RCS is better than gimbal during space flight (not atmospheric!) is because it can apply torque more efficiently. In atmospheric flight, fins and gimbal are probably the best. Another method is to alter the direction a rocket nozzle is facing during flight(this is called GIMBAL, see d). These thrusters are alot less potent compared to your rocket engine, therefore, when traveling through an atmosphere where air drag dominates, RCS is not very effective. These thrusters are usually mounted perpendicular to the direction of the rocket(see e in picture below). One is to use aerodynamic fins(like flaps on an airplane), the other is to use RCS thrusters, which stands for reaction control system. To achieve stability, we have several options. If the mass is not well distributed, gravity acts heavier on the heavier sides, this creates torque, which displaces the rotation of the rocket. More on this later!ĭuring flight, we want the rocket to be as stable as possible. The amount of drag depends on the atmospheric pressure, shape and velocity of a craft. The only thing preventing the table from collapsing is because the atmospheric pressure is everywhere, it exists on top, and on the bottom, the forces cancel out! However, this does not mean you can't destroy the table, simply make the space below it a vacuum! By doing so, you disrupt the balance of force and effectively allow pressure to exert the force(10 tons)!īasically, drag is just air friction, it slows your craft down and generates heat! This is vital for liftoff and reentry. This, in literal terms, means that there are more than 10 tons of mass stacked on top of any table that has a surface area of 1m^2(1 meter by 1 meter). *the pressure units here are kilo pascals, 1kPa=1000Pa! Recall 1 Pa = 1 N/m^2Ītmospheric pressure is a bit of an odd thing, the atmospheric pressure on Earth at sea level is over 101,300 N/m^2. This is why compressed gas flows out fast and aerosol cans work!ĭue to the Earth's gravitational effects, air gets thinner as altitude increases, that is, air density decreases and so does atmospheric pressure. A familiar non-SI unit is PSI.Ī pressure difference causes particles to flow from a high pressured location to a low pressured location, the higher the difference, the faster the flow rate. The SI unit for pressure is Pascals(Pa) or N/m^2(force over area). What is pressure? Pressure is the measure of force applied to a surface. Not all planets within the Kerbal solar system have atmospheres! But it is an EXTREMELY important factor to consider in Kerbal Space Program! Landing and taking off from a planet with and without an atmosphere is very different! The unit for Isp is in seconds, this may seem weird, but it is the result of canceling units. You can see a rocket engine's Isp by hovering your mouse cursor over it! Having said all this, Isp is the measure of thrust produced per unit of fuel, or fuel efficiency. Exhaust particles ejected at high speeds HAVE to be accelerated to that speed, which means higher exhaust velocities equal more acceleration, which means more Force. This is because of F=ma, as discussed previously. In order to maximize the efficiency of a rocket, the exhaust velocities of each particle must be maximized as well. This is due to the fact that the mass of the particles coming out of the rocket nozzle is precisely the mass which the rocket loses. As you may know, a rocket loses mass as long as it is burning fuel. In rocketry, or any device or vehicle that generates thrust, we use specific impulse(Isp) to measure efficiency. The higher the temperature, the greater the motion. Temperature is proportional to average kinetic energy of an object, kinetic energy is the energy of motion! So particles within onjects are constantly in motion so long as they have temperatures above absolute zero. The pressure difference between the outside of the rocket nozzle and inside of the nozzle is what causes the particles to move out!(more on that later) Heated particles want to expand outwards, which is how a steam engine works. Thus, pressure within the chamber increases due to the increase in average kinetic energy of the particles. When chemical reactions occur within the combustion chambers of a rocket, heat is generated. How particles are accelerated by chemical reactions: With action comes reaction, since a force is being exerted on the particles coming out of the rocket, a force of equal magnitude is exerted in the opposite direction! This is why rocket propulsion works! In a rocket, exhaust particles are constantly being driven out of a rocket nozzle, that is, particles are being accelerated by the chemical reactions within the rocket. Thrust is measured in Newtons, which is the unit for force!įrom Newton's laws, we know that objects accelerate due to applied force, the mathematical illustration of this is Force=mass*acceleration or F=ma.
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