## Concept explanation A rocket engine works as a connected **system**: the **fuel tank** and **oxidizer tank** store the propellants, the **feed lines** carry them downward, the **valves** regulate how much flows, the **combustion chamber** releases energy by burning them together, and the **bell nozzle** turns that hot, high-pressure gas into a fast exhaust jet. That downward jet creates **thrust**, pushing the rocket the opposite way. ## What you see You are looking at a simple 3D cutaway of a rocket engine arranged from top to bottom, so you can follow the path from storage to exhaust. Each major part is labeled, and when you select one, it brightens while glowing animated markers trace the flow associated with that component. The short card at the lower left changes with your selection so you can connect each physical part to its job in the engine. ## Try it yourself - **Click the fuel tank** and watch the glowing markers move inside it, then notice that its role is storing one of the two propellants. - **Click the oxidizer tank** and compare it with the fuel tank to see that both are needed before combustion can happen. - **Select the feed lines** to follow how the system connects the tanks to the engine core. - **Choose the valves** and notice that they sit in the path of the liquids, showing how flow can be controlled before burning. - **Click the combustion chamber** to see where the two propellant streams come together and become hot gas. - **Select the bell nozzle** and watch the exhaust path continue downward, showing how gas expansion produces thrust. - **Use the Selected part menu** to jump directly between components and review the engine in system order. - **Adjust the Flow speed slider** to speed up or slow down the glowing motion and make the sequence easier to follow. - **Toggle Auto rotate** or **drag to rotate** so you can inspect the cutaway from different angles. ## Concept explanation A rocket engine works only when both **fuel** and **oxidizer** are delivered into the combustion chamber at the right time and in the right amounts. Because there is no air in space to supply oxygen, the engine must carry its own oxidizer in a separate tank. The injectors mix the two propellants at the chamber top, and the combustion gets stronger when the propellant **flow rate** increases, because more material is entering the chamber each second. ## What you see You are looking at a 3D cutaway of a rocket engine feed system. The blue tank and stream represent fuel, and the green tank and stream represent oxidizer. Both travel through separate pipes into injectors above the chamber. As flow rises, the colored streams move faster and the chamber glow becomes brighter and fuller, showing that the engine depends on controlled propellant delivery rather than just having propellants stored in tanks. ## Try it yourself - **Move the flow-rate slider upward** and notice how both colored streams speed up together. - **Lower the flow rate toward `0%`** and watch the injectors weaken and the chamber activity fade. - **Set the flow rate near `100%`** to see the chamber fill with brighter swirling gas. - **Drag to orbit the model** and inspect how each tank feeds its own pipe into the injector plate. - **Adjust the view-angle slider** to compare the side tanks, the injector region, and the chamber interior. - **Press Reset** to return to the default operating view and flow setting. ## Concept explanation When **fuel** and **oxidizer** burn together in a combustion chamber, the chemical reaction releases heat very quickly and creates **hot gas**. Because that gas is both very energetic and trapped inside the chamber, it expands and builds **pressure** against the walls. That pressure is stored energy the rocket engine can use: the chamber holds the gas at high pressure so it can later rush out through the nozzle and produce thrust. ## What you see You are looking at a transparent 3D combustion chamber. Blue and teal sprays enter from the injector side, mix near the center, and—after ignition—turn into a bright turbulent fireball. The glowing gas cloud grows denser and brighter as pressure rises, while teal arrows around the chamber show the gas pushing outward on the chamber walls. The wall-force meter in the control panel gives a simple readout of how strongly the hot gas is pressing outward. ## Try it yourself - **Click `Ignite`** and watch the two propellant sprays turn into a bright hot gas cloud in the chamber. - **Drag the `pressure` slider** upward and notice how the combustion region becomes denser, brighter, and more energetic. - **Compare low and high pressure settings** to see that higher chamber pressure means stronger outward force on the walls. - **Watch the teal arrows and wall-force meter** as you change pressure to connect hot expanding gas with stored pressure energy. - **Drag the chamber to rotate it** and inspect how the sprays mix and where the burning gas forms inside the transparent volume. - **Click `Reset`** and repeat the sequence to test your own predictions about what changes when pressure increases. ## Concept explanation A rocket nozzle turns **chamber pressure** into **exhaust velocity**. Inside the combustion chamber, hot gas particles are crowded together and push in all directions. As that gas is forced through the narrow **throat** and then into the expanding bell, pressure energy is converted into directed motion, so the gas stream speeds up and shoots out the back as a fast exhaust jet. ## What you see You’re looking at a 3D cutaway of a rocket engine from the chamber to the bell nozzle. The glowing particles represent hot gas: they start dense and jostling in the chamber, then squeeze through the throat, and finally stretch into a tighter, faster plume leaving the nozzle. The brighter chamber glow and longer exhaust core at higher settings help you see how more pressure feeds a stronger, faster jet. ## Try it yourself - **Drag the chamber pressure slider** upward and notice how particles enter the throat faster and the exhaust plume extends farther behind the nozzle. - **Lower the pressure slider** and watch the gas linger in the chamber longer, with a shorter, dimmer plume. - **Adjust the gas supply slider** to change how many particles are circulating, then compare a sparse chamber with a densely packed one. - **Drag the nozzle model** to rotate the cutaway and inspect how the stream narrows at the throat before expanding downstream. - **Press `Reset view`** to return to the starting angle and repeat the comparison at low and high pressure. ## Concept explanation **Thrust** is the upward reaction force produced when an engine pushes **exhaust** downward at high speed. This is an example of **Newton’s third law**: if the rocket forces gas downward, the gas forces the rocket upward. When you increase throttle, the engine throws more exhaust downward and usually throws it faster, so the upward thrust grows. If that thrust becomes larger than the pull of gravity, the rocket rises. ## What you see You are looking at a hovering rocket above a launch pad, with its engine underneath and a bright exhaust plume blasting downward. The teal arrow shows the upward thrust force from the engine. As the rocket produces more thrust, the plume gets longer and brighter, the force arrow grows, and the rocket lifts higher. The readout card helps you compare throttle, thrust, and height at the same time. ## Try it yourself - **Drag the throttle slider** upward and notice how the exhaust plume becomes longer and brighter. - **Watch the teal thrust arrow** as you increase throttle and see how a stronger downward exhaust produces a larger upward force. - **Lower the throttle** until the rocket can no longer hold itself up, then observe how gravity wins. - **Raise the gravity slider** and test how much more throttle is needed to hover at the same height. - **Drag across the rocket view** to rotate the simple 3D perspective and inspect the engine and plume. - **Press `Reset hover`** and then **try to find a near-hover setting** where thrust almost balances gravity. ## Concept explanation A rocket engine’s performance depends on **mixture ratio**: the balance between **fuel flow** and **oxidizer flow** entering the chamber. Even if the total propellant flow is high, thrust is weaker when one ingredient is in excess because not all of the propellant can react efficiently. When the two flows are well matched, combustion is hotter, steadier, and more complete, which produces a brighter flame and a stronger exhaust jet. ## What you see You’re looking at a 3D cutaway of a rocket engine. The blue pipe feeds fuel, the green pipe feeds oxidizer, and both streams enter the injector plate before burning inside the chamber. The live status card tracks the current burn condition, while the flame shape, chamber glow, and exhaust plume respond immediately to the slider settings: compact and bright when balanced, cooler and weaker when slightly off, and visibly pulsing when the imbalance becomes severe. ## Try it yourself - **Set both sliders near the same value** and notice how the flame becomes short, bright, and concentrated while the exhaust plume grows stronger. - **Lower both sliders together** to see that a balanced mixture can still burn steadily, but with less overall energy and thrust. - **Raise fuel flow while keeping oxidizer lower** and watch how extra fuel cannot burn efficiently, shifting the engine toward a cooler or unstable state. - **Raise oxidizer flow far above fuel flow** and compare the result: the total flow is still large, but the combustion quality drops because the mixture is badly matched. - **Push the sliders far apart** to trigger the unstable burn and look for pulsing inside the chamber, which represents rough, inefficient combustion. - **Press `Reset`** and then **drag to orbit** so you can inspect how the two separate feed lines meet at the injectors before entering the chamber. ## Concept explanation A rocket nozzle works by turning hot, high-pressure gas into a fast-moving exhaust jet. The key idea is **expansion**: the gas should leave the nozzle at a pressure close to the **outside air pressure**. If the nozzle is too wide for dense air, the exhaust **over-expands** and gets squeezed back inward. If the nozzle is too narrow for thin air, the exhaust **under-expands** and keeps spreading after it leaves, which means some possible thrust is left unused. The best nozzle shape depends on altitude because atmospheric pressure falls as you go higher. ## What you see You’re looking at a cross-section of a rocket engine with the chamber, throat, bell nozzle, and visible exhaust plume. The right-side altitude control changes the surrounding atmosphere from thick near sea level to thin near vacuum. The bell-width control changes the nozzle exit size, and the plume responds by pinching inward, flowing out smoothly, or spreading outward. The dashed guide marks the exit size that best matches the current outside pressure, and the efficiency bar shows how closely the nozzle is matched to that altitude. ## Try it yourself - **Move the altitude slider** from low to high and watch how the outside pressure drops while the plume naturally wants to spread more in thinner air. - **Keep altitude low, then widen the bell nozzle** until the plume gets squeezed inward and shock patterns appear: that is over-expansion. - **Keep altitude high, then narrow the bell nozzle** and notice how the plume continues expanding outside the nozzle: that is under-expansion. - **Adjust both sliders together** until the plume leaves the nozzle smoothly and the efficiency bar rises toward `100%`. - **Drag the nozzle rim directly** on the drawing to change the bell width and compare that hands-on adjustment with the bell-width slider. - **Press `Reset`** and try matching the nozzle to several different altitudes to see why real engines are designed for specific operating conditions.