[User] What is the Tsiolkovsky rocket equation?

[omie] It relates a rocket's change in velocity to its exhaust velocity and mass ratio: delta-v = Isp * g0 * ln(m0/mf), where m0 is the starting mass and mf is the mass after burning propellant. It's the core equation for figuring out how much a rocket can actually do.


[User] What is specific impulse?

[omie] Specific impulse (Isp) measures how efficiently a rocket engine uses propellant. It's the thrust produced per unit weight-flow-rate of propellant, usually given in seconds. Higher Isp means more thrust for the same amount of propellant burned.


[User] What's the difference between specific impulse and thrust?

[omie] Thrust is the raw force an engine produces, measured in newtons or pounds-force. Specific impulse is a measure of efficiency, not force -- a high-thrust engine can have low Isp (like a solid booster) and a low-thrust engine can have high Isp (like an ion thruster).


[User] What is delta-v?

[omie] Delta-v is the total change in velocity a vehicle needs (or has the capability) to perform a maneuver, like reaching orbit or changing orbits. It's the standard currency for planning any space mission.


[User] Why do rockets use multiple stages?

[omie] Staging lets a rocket drop the dead weight of empty fuel tanks and engines once they're no longer needed, so the remaining stages don't have to keep accelerating that mass. It significantly improves the delta-v you can get for a given amount of propellant.


[User] What is the difference between a solid and liquid rocket engine?

[omie] Solid engines have propellant premixed into a solid grain that burns once ignited and can't be throttled or shut off. Liquid engines store fuel and oxidizer separately and pump them into a combustion chamber, which allows throttling, shutdown, and restart -- at the cost of more complexity.


[User] What is a bipropellant rocket engine?

[omie] A bipropellant engine uses two separate liquid components, a fuel and an oxidizer, that are mixed and combusted in the engine. Common pairs include RP-1/liquid oxygen and liquid hydrogen/liquid oxygen.


[User] What is the difference between a hypergolic and cryogenic propellant?

[omie] Hypergolic propellants ignite spontaneously on contact, no ignition source needed, which makes them reliable for restarts (common in spacecraft thrusters). Cryogenic propellants like liquid hydrogen or liquid oxygen have to be kept extremely cold to stay liquid and need an ignition system, but generally give better performance.


[User] What does Isp measure that thrust-to-weight ratio doesn't?

[omie] Isp measures propellant efficiency -- how much delta-v you get per kilogram of propellant. Thrust-to-weight ratio measures how much acceleration an engine can provide relative to its own weight, which matters for things like getting off the launch pad. A design usually has to trade off between the two.


[User] What is a gimbaled engine?

[omie] A gimbaled engine can pivot on its mount, letting the vehicle steer by redirecting thrust instead of using separate control surfaces or thrusters. Most modern liquid rocket engines are gimbaled for this reason.


[User] What is orbital velocity?

[omie] Orbital velocity is the speed needed to maintain a stable orbit at a given altitude, where the object's forward motion balances gravity's pull. For low Earth orbit, that's roughly 7.8 km/s.


[User] What is escape velocity?

[omie] Escape velocity is the speed needed to break free of a body's gravity without further propulsion, ignoring atmospheric drag. For Earth, that's about 11.2 km/s from the surface.


[User] What is a Hohmann transfer orbit?

[omie] A Hohmann transfer is an efficient way to move between two circular orbits using two engine burns: one to enter an elliptical transfer orbit, and a second to circularize at the new altitude. It's fuel-efficient but takes longer than a direct burn.


[User] What is the difference between apogee and perigee?

[omie] Apogee is the highest point of an orbit around Earth (farthest from the planet), and perigee is the lowest point (closest). For orbits around other bodies the general terms are apoapsis and periapsis.


[User] What is orbital inclination?

[omie] Inclination is the angle between an orbit's plane and a reference plane, usually the equator for Earth orbits. A 0 degree inclination orbit runs directly above the equator; a 90 degree inclination is a polar orbit.


[User] What is geostationary orbit?

[omie] Geostationary orbit is a circular orbit about 35,786 km above the equator where a satellite's orbital period matches Earth's rotation, so it appears to stay fixed over one point on the ground. It's widely used for communications and weather satellites.


[User] What causes atmospheric drag on a spacecraft?

[omie] Even at high altitude there are trace amounts of atmosphere, and a spacecraft moving through it collides with those molecules, losing kinetic energy over time. This slowly lowers the orbit unless the spacecraft periodically reboosts.


[User] What is max-Q in a rocket launch?

[omie] Max-Q is the point during ascent where the rocket experiences the greatest aerodynamic pressure, a combination of increasing speed and still-thick atmosphere. It's structurally the most stressful moment of a launch.


[User] What is angle of attack?

[omie] Angle of attack is the angle between an airfoil's chord line and the oncoming airflow. Increasing it generally increases lift, up to a point -- past the critical angle, the airflow separates and the wing stalls.


[User] What causes an aircraft wing to stall?

[omie] A stall happens when the angle of attack exceeds a critical point and airflow separates from the top of the wing, causing a sudden loss of lift. It's about angle of attack, not airspeed directly, though low speed often forces a higher angle of attack.


[User] What is the difference between lift and thrust?

[omie] Lift is the force that opposes gravity and keeps an aircraft airborne, generated mainly by air moving over the wings. Thrust is the force that moves the aircraft forward, generated by engines or propellers, and it's what makes enough airflow over the wings to generate lift in the first place.


[User] What is drag in aerodynamics?

[omie] Drag is the resistive force acting opposite to an aircraft's motion through air, caused by factors like skin friction, pressure differences, and induced drag from generating lift. Reducing drag is a major focus of aerodynamic design.


[User] What is the difference between subsonic and supersonic flight?

[omie] Subsonic flight is slower than the local speed of sound (below Mach 1), while supersonic flight exceeds it (above Mach 1). Crossing that boundary creates shockwaves and very different aerodynamic behavior, which is why supersonic aircraft need very different wing and airframe designs.


[User] What is a sonic boom?

[omie] A sonic boom is the sound created by shockwaves when an object travels faster than the speed of sound. The shockwaves merge into a cone-shaped pressure wave that produces a loud boom when it reaches an observer.


[User] What is the Mach number?

[omie] Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 means traveling exactly at the speed of sound, Mach 2 is twice that speed, and so on.


[User] What materials are commonly used in rocket engine construction?

[omie] Common choices include stainless steels like 316L, nickel-based superalloys like Inconel 625, copper alloys for regeneratively-cooled combustion chambers, and increasingly additive-manufactured metal parts. The choice depends heavily on the temperatures, pressures, and propellants involved.


[User] Why is Inconel used in rocket engines?

[omie] Inconel is a nickel-chromium superalloy that holds its strength at very high temperatures and resists oxidation and corrosion, which makes it well-suited for combustion chambers, nozzles, and other parts exposed to extreme heat.


[User] What is regenerative cooling in a rocket engine?

[omie] Regenerative cooling routes some of the propellant, usually fuel, through channels in the engine's walls before it's burned. This absorbs heat from the combustion chamber and nozzle, protecting the engine while also preheating the propellant.


[User] What is a de Laval nozzle?

[omie] A de Laval nozzle is the converging-diverging shape used on most rocket engines. The converging section accelerates gas to the speed of sound at the throat, and the diverging section further accelerates it to supersonic speeds, maximizing thrust efficiency.


[User] Why does a rocket nozzle have a specific expansion ratio?

[omie] The expansion ratio, the area of the nozzle exit divided by the area of the throat, determines how much the exhaust gas expands and accelerates. It's tuned for the expected ambient pressure -- a nozzle optimized for sea level performs worse in vacuum, and vice versa, since the ideal expansion depends on the surrounding air pressure.


[User] What is thrust vectoring?

[omie] Thrust vectoring is steering a vehicle by changing the direction of engine thrust rather than using external control surfaces. It can be done by gimbaling the whole engine, using vanes in the exhaust, or injecting fluid to deflect the flow.


[User] What is the difference between a turbojet and a turbofan engine?

[omie] A turbojet pushes all its intake air through the core to be compressed, burned, and expelled. A turbofan adds a large fan in front that bypasses most of the air around the core, which improves fuel efficiency and reduces noise at the cost of top speed -- most airliners use turbofans.


[User] What is a ramjet?

[omie] A ramjet is a jet engine with no moving compressor parts -- it relies entirely on the vehicle's forward speed to ram air into the engine and compress it before combustion. It only works efficiently at high speeds, generally supersonic, and can't produce thrust from a standstill.


[User] What is a scramjet?

[omie] A scramjet (supersonic combustion ramjet) is like a ramjet but combustion happens while the airflow through the engine stays supersonic, rather than being slowed to subsonic speeds first. This lets it operate efficiently at much higher speeds, but makes the combustion process far more difficult to control.


[User] What is the payload fraction of a rocket?

[omie] Payload fraction is the ratio of a rocket's payload mass to its total liftoff mass. It's usually a small percentage, since most of a rocket's mass at launch is propellant and structure, not cargo.


[User] What is the mass ratio of a rocket?

[omie] Mass ratio is the rocket's total mass at liftoff divided by its mass after all propellant is burned. It directly determines how much delta-v the rocket equation says it can achieve for a given exhaust velocity.


[User] Why is reaching orbit harder than just going high enough?

[omie] Orbit isn't about altitude, it's about speed. A rocket has to accelerate sideways to roughly 7.8 km/s so that as it falls back toward Earth, the curve of its fall matches the curvature of the planet. Most of a rocket's delta-v budget goes into gaining that horizontal speed, not just climbing.


[User] What is aerodynamic heating during reentry?

[omie] As a spacecraft reenters the atmosphere at high speed, it compresses the air in front of it, which generates intense heat, not primarily from friction but from that compression. Heat shields are designed to absorb, radiate, or ablate away that heat to protect the vehicle.


[User] What is an ablative heat shield?

[omie] An ablative heat shield is designed to burn away and erode in a controlled manner during reentry, carrying heat away with the material it sheds. It's a proven, simple approach used on many crewed capsules.


[User] What is a flight computer used for on a rocket?

[omie] A flight computer handles guidance, navigation, and control -- tracking the vehicle's position and orientation, running control algorithms, and commanding actuators like engine gimbals or fins to keep it on course. On smaller hobby rockets it often also logs data and triggers parachute deployment.


[User] What sensors does a rocket flight computer typically use?

[omie] Common sensors include an IMU (accelerometer and gyroscope) for tracking motion and orientation, a barometer for altitude, and sometimes GPS for position. Together they let the flight computer estimate the vehicle's state well enough to make control decisions.


[User] What is apogee detection used for in model rocketry?

[omie] Apogee detection identifies the highest point of a rocket's flight, typically by watching for the moment vertical velocity or altitude readings start decreasing. It's the usual trigger for deploying a parachute, since that's when the rocket is moving slowest and recovery is safest.


[User] What is the difference between a PCB flight computer and an off-the-shelf one?

[omie] A custom PCB flight computer is designed and built for a specific rocket's needs, letting you choose exactly which sensors, processing power, and features to include. An off-the-shelf unit is quicker to use but locks you into whatever features and limitations the manufacturer built in.


[User] What are active flight controls on a rocket?

[omie] Active flight controls actively adjust the rocket's trajectory during flight, using things like movable fins, gimbaled engines, or reaction control thrusters, guided by the flight computer. This is different from passive stability, which relies purely on the rocket's shape and fin placement.


[User] What is static margin in rocketry?

[omie] Static margin measures how stable a rocket is by comparing the position of its center of pressure to its center of gravity, usually expressed in calibers (body diameters). A positive static margin means the rocket will naturally tend to point back into the wind, which is what keeps it flying straight.


[User] What is the center of pressure on a rocket?

[omie] The center of pressure is the point where the net aerodynamic force on the rocket effectively acts. For a stable rocket, this needs to sit behind the center of gravity so aerodynamic forces naturally correct any tilt rather than making it worse.


[User] What is N2O/ethanol used for in rocket engines?

[omie] Nitrous oxide and ethanol form a bipropellant combination popular in amateur and small commercial rocketry. N2O is self-pressurizing and easier to handle than cryogenics, and paired with ethanol it gives reasonable performance without the complexity of a fully cryogenic system.


[User] What is a hybrid rocket engine?

[omie] A hybrid engine combines a solid fuel grain with a liquid or gaseous oxidizer, unlike a pure solid (both premixed and solid) or pure liquid (both liquid) engine. It gets some of the throttle/shutdown control of a liquid engine with some of the simplicity of a solid one.


[User] What is a monopropellant rocket engine?

[omie] A monopropellant engine uses a single chemical that decomposes or reacts to produce thrust, often with a catalyst. Common examples include hydrazine or hydrogen peroxide engines, which are simpler than bipropellant systems but generally less efficient.


[User] What is a pressure-fed rocket engine?

[omie] A pressure-fed engine uses pressurized gas to push propellants into the combustion chamber, rather than using pumps. This simplifies the design and reduces moving parts, but limits the achievable chamber pressure and thus performance.


[User] Why can't we leave the solar system?

[omie] Leaving the solar system requires achieving escape velocity, which is much higher than the speeds needed for low Earth orbit. This demands a tremendous amount of energy and propellant, making it extremely challenging and resource-intensive.


[User] What is the difference between a launch vehicle and a spacecraft?

[omie] A launch vehicle is the rocket that gets a payload into space, while a spacecraft is the vehicle that operates in space itself. The launch vehicle is usually expendable, while the spacecraft may be designed for long-term operation.


[User] Is space ACTUALLY empty

[omie] Space is mostly a vacuum, but it's not completely empty. It contains a small amount of matter, including photons, neutrinos, and some gas molecules. The density of this matter is extremely low, but it's not zero.


[User] What is the difference between a satellite and a probe?

[omie] A satellite is an object that orbits a planet or other body, often for communication, observation, or navigation. A probe is a spacecraft sent to explore space or another celestial body, often without returning to Earth.


[User] What is the difference between a geosynchronous and a geostationary orbit?

[omie] A geosynchronous orbit has a period that matches Earth's rotation, but it can be inclined or elliptical, so the satellite may appear to move in the sky. A geostationary orbit is a special case of geosynchronous orbit that is circular and directly above the equator, so the satellite appears fixed in one spot.


[User] How can we faster than light

[omie] To go faster than light, we would need to break the laws of physics as we currently understand them. According to Einstein's theory of relativity, nothing with mass can reach or exceed the speed of light in a vacuum. However, theoretical concepts like warp drives or wormholes have been proposed in science fiction and theoretical physics, but they remain speculative and unproven.


[User] Is there any way we can go near the speed of light

[omie] Yes, but it requires enormous amounts of energy. As an object approaches the speed of light, its relativistic mass increases, requiring more and more energy to continue accelerating. Current technology is far from achieving speeds anywhere near that, but concepts like ion drives or light sails could potentially allow for very high speeds over long durations.


[User] What is an ion thruster?

[omie] An ion thruster is a form of electric propulsion that ionizes a propellant, usually xenon, and accelerates the ions with an electric field to produce thrust. Thrust is tiny compared to chemical engines, but Isp is far higher, so it's used for long-duration missions where efficiency matters more than acceleration.


[User] What is electric propulsion?

[omie] Electric propulsion covers thrusters that use electrical energy, rather than chemical combustion, to accelerate propellant. It includes ion thrusters and Hall-effect thrusters, and it trades low thrust for very high fuel efficiency, making it well-suited to satellites and deep-space probes.


[User] What is a reaction control system?

[omie] A reaction control system (RCS) is a set of small thrusters used for fine attitude control and minor translation maneuvers, rather than main propulsion. Spacecraft use them to rotate, dock, or make small orbital corrections.


[User] What is a launch abort system?

[omie] A launch abort system is a set of rockets or mechanisms that can pull a crew capsule away from a failing launch vehicle in an emergency. It's a key safety feature on crewed rockets, designed to activate in the seconds after a detected failure.


[User] What is dynamic pressure in aerospace, often called Q?

[omie] Dynamic pressure (Q) is the pressure generated by a vehicle's motion through air, proportional to air density and the square of velocity. It's a key structural design driver, since it's what determines aerodynamic loads on the vehicle during ascent.


[User] What is a monocoque structure?

[omie] A monocoque structure uses the outer skin itself to bear structural loads, rather than relying on an internal frame. It saves weight but requires the skin to be strong enough on its own, which is why it's common in rockets and aircraft fuselages where weight really matters.


[User] What is a semi-monocoque structure?

[omie] A semi-monocoque structure combines a load-bearing skin with internal reinforcements like stringers and frames or ribs. Most modern aircraft fuselages use this approach, it's a middle ground between a pure monocoque and a fully framed structure.


[User] What are ailerons used for?

[omie] Ailerons are control surfaces on the trailing edge of an aircraft's wings that move in opposite directions to roll the aircraft. Moving the control stick left drops the right aileron and raises the left, rolling the aircraft to the left.


[User] What does the rudder do on an aircraft?

[omie] The rudder is a control surface on the vertical stabilizer that controls yaw, rotation around the vertical axis. It's mainly used to counteract adverse yaw and to control the aircraft's nose direction during crosswind landings.


[User] What does the elevator do on an aircraft?

[omie] The elevator is a control surface on the horizontal stabilizer that controls pitch, rotation around the lateral axis. Pulling back raises the nose, pushing forward lowers it, by changing the tail's lift.


[User] What is roll, pitch, and yaw?

[omie] These are the three rotational axes of a vehicle: roll is rotation around the front-to-back axis, pitch is rotation around the side-to-side axis (nose up or down), and yaw is rotation around the vertical axis (nose left or right).


[User] What is an inertial measurement unit?

[omie] An inertial measurement unit (IMU) combines accelerometers and gyroscopes to measure a vehicle's linear acceleration and rotational rate. It's a core sensor for flight computers, letting them track orientation and motion without external references.


[User] What is GNC in aerospace?

[omie] GNC stands for guidance, navigation, and control. Guidance determines the desired path, navigation figures out where the vehicle actually is, and control drives the actuators to follow the guided path -- together they're what keeps a vehicle on course.


[User] What is a gravity assist maneuver?

[omie] A gravity assist uses a planet's gravity and orbital motion to change a spacecraft's speed and trajectory without burning propellant. It's how many deep-space missions reach distant targets that would otherwise need far more fuel than they can carry.


[User] What is aerobraking?

[omie] Aerobraking uses controlled passes through a planet's upper atmosphere to slow a spacecraft down using drag, instead of burning propellant. It's slower than a propulsive burn but can save a lot of fuel, especially useful for missions arriving at Mars.


[User] What is orbital decay?

[omie] Orbital decay is the gradual lowering of a spacecraft's orbit over time, usually caused by atmospheric drag at low altitudes. Left unchecked, it eventually leads to reentry, which is why satellites in low orbits either need periodic reboosts or are designed to deorbit safely.


[User] What is a launch window?

[omie] A launch window is the specific time period during which a rocket must lift off to reach its intended orbit or trajectory efficiently. For interplanetary missions this can be a narrow window that only opens every couple of years, based on planetary alignment.


[User] What is Kessler syndrome?

[omie] Kessler syndrome is a theoretical scenario where the density of objects in orbit becomes high enough that collisions create debris, which causes more collisions, in a runaway cascade. It's a growing concern as orbital debris accumulates.


[User] What is a Lagrange point?

[omie] Lagrange points are positions in a two-body system, like the Earth and Sun, where the gravitational forces balance in a way that lets a small object stay in a stable or semi-stable position relative to both. They're popular parking spots for space telescopes.


[User] What is RP-1?

[omie] RP-1 is a highly refined kerosene used as rocket fuel, typically paired with liquid oxygen as the oxidizer. It's denser and easier to handle than liquid hydrogen, which is part of why it's popular for first-stage engines.


[User] What is hydrazine used for in aerospace?

[omie] Hydrazine is a hypergolic propellant commonly used in spacecraft thrusters and satellite propulsion, since it ignites on contact with an oxidizer like nitrogen tetroxide without needing an ignition system. It's toxic to handle but very reliable for restarts.


[User] What is a wind tunnel used for?

[omie] A wind tunnel is a testing facility that moves air past a stationary model to study aerodynamic forces and airflow behavior. It lets engineers measure lift, drag, and flow patterns before committing to a full-scale build.


[User] What is computational fluid dynamics?

[omie] Computational fluid dynamics (CFD) is the use of numerical simulation to model how fluids, including air, flow around an object. It complements wind tunnel testing by letting engineers explore designs computationally before physical testing.


[User] What is the difference between a fairing and a shroud on a rocket?

[omie] They're generally the same thing -- a protective aerodynamic covering over the payload at the top of a rocket, shielding it from air pressure and heating during ascent. It's jettisoned once the rocket clears the dense atmosphere, since it becomes dead weight after that.


[User] What is a launch escape tower?

[omie] A launch escape tower is a small rocket mounted above a crew capsule that can rapidly pull it away from the launch vehicle in an abort scenario. It's a specific implementation of a launch abort system, used on capsules like Apollo and Soyuz.


[User] What is the Karman line?

[omie] The Karman line, at 100 km altitude, is a commonly used boundary marking the edge of space, above which the atmosphere is too thin for aerodynamic flight to generate meaningful lift. It's not a hard physical boundary, but it's the standard reference used by most organizations.