## Astronautics (AEM 360)

**acceleration**- Acceleration is the rate that velocity is changing with respect to time. Acceleration is a vector quantity, i.e. it has a magnitude and direction. Typical units: m/s² (SI) or ft/s² (USCS).

**aerodynamics**- Aerodynamics is the study of the interaction between a surface and the flow of a fluid over the surface.

**apogee**- The highest altitude achieved for a suborbital flight or the point along an orbital path where the position of the orbiting object is furthest from the object it orbits.

**astronautics**- Astronautics is the science/engineering of systems capable of flight beyond a planetary atmosphere; including launch vehicles, spacecraft, and other space related technology.

**atmosphere (standard)**- The standard atmosphere is a static model of the Earth's atmosphere that can be used as a common reference for calculations of pressure, temperature, density, and viscosity. Standard atmosphere models divide the atmosphere into zones of constant or linearly-varying temperature and model the pressure as a hydrostatic column of air. The 1976 U.S. Standard Atmosphere is one of several standard atmosphere models.

**attitude**- the orientation of an object in a specified frame of reference, i.e. the orientation in space of a spacecraft or rocket.

**booster**- rockets, typically jettisoned during launch, that are used to increase a launch vehicle's take-off thrust and/or payload capacity.

**bus**- the infrastructure (structure, electric power, attitude, communications, propulsion, etc) that allows a spacecraft to perform the specified mission.

**center of gravity (CG)**- The center of gravity is an imaginary point in an object where the total “weight” of the object can be considered to be concentrated. An object may be balanced at its CG, the CG is the point where there is no torque due to gravitational forces acting on the body. For a uniform acceleration due to gravity, g, the CM is at the same location as the CG. When g is not contact over the entire object, then the CM and CG will be at different locations.

**center of mass**- an imaginary point within a body that if acted on by an external source will cause it to move without rotation, same as the center of gravity in a uniform gravitational field.

**CubeSat**- a low-cost miniaturized satellite based on the "CubeSat Standard". The standard unit for a CubeSat is 1U and a 1U CubeSat will measure 10 cm x 10 cm x 10 cm and will have a mass of no more than 1.33 kg. Note that CubeSats may be configured using multiple standard units. For example, a common configuration is a 6U CubeSat, where 6 standard CubeSat units are combined to form a single 6U CubeSat.

**delta-V**- a term referring to the change in the speed of a rocket during flight.

**design methodology (**

**engineering**

**)**- The engineering design methodology is the iterative process that, based on customer-driven specifications and model/prototype testing, is used to develop technology capable of solving a previously identified problem.

**drag**- Drag is one of the 4 principal forces acting on an aircraft or any aerospace system that operates within a planetary atmosphere. Drag is the aerodynamic force (a vector quantity) exerted on an aircraft in the direction rearward and parallel to the relative wind. The effect of the drag force is to decelerate the aircraft. Typical units: N (SI) or lbf (USCS)

**drag coefficient**- The drag coefficient is a dimensionless number that is proportional to the drag force over a surface or body.

**dynamic pressure**- Dynamic pressure is the kinetic energy per unit volume of a fluid element, defined as one-half the product of the density times the square of the freestream fluid speed. Typical units: Pa (SI) or psi (USCS).

**engine**- An engine is a device that convert thermal energy to mechanical energy (work/power); engine-driven propeller uses aerodynamic forces to produce thrust, jet engine converts thermal energy & pressure to kinetic energy to produce thrust.

**engineering**- Engineering is the profession that uses mathematical, computational, and/or physical models to create, design, test, analyze, and/or predict the behavior of technology and technological systems. It is a profession that is fundamentally about creating practical knowledge and problem solving.

**fins**- aerodynamic surfaces on a rocket that can be used to change the path of the rocket, fins will also lower the center of pressure of the rocket and thus affect stability.

**flight**- Flight is the process of moving through the atmosphere (aeronautics) or beyond the atmosphere (astronautics).

**force**- A force is the push or pull experienced by an object during its interaction with another object. When the forces acting on an object are not in balance, i.e. not in equilibrium, the object will accelerate. Force is a vector quantity, i.e. it has a magnitude and a direction. Typical units: N (SI) or lbf (USCS). In a much broader sense, a force may refer to any phenomenon that is capable of changing the state of the system.

**free body diagram**- A free body diagram is a schematic representation of the forces and moments acting on an object (including the direction of the forces/moments and ideally the relative magnitude of the forces). Such diagrams are used to conceptualize the impact that support structures, weight, drag, lift, thrust, etc. have on an object.

**fuel**- Fuel is one of the 3 needed components for combustion to occur (the others being an oxidizer and a heat source),

**equilibrium**- A system is in equilibrium when all the phenomena that can cause the state of a system to change are in balance. For example, mechanical equilibrium implies that there are no unbalanced forces acting on a system.

**launch vehicle**- a system that employs rocket propulsion as the sole means of achieving flight.

**lift**- Lift is one of the 4 principal forces acting on an aircraft or any aerospace system that operates within a planetary atmosphere. Lift is the aerodynamic force (a vector quantity) exerted on an aircraft in the direction upward and perpendicular to the relative wind. Lift is used to overcome the weight of the aircraft during flight. Typical units: N (SI) or lbf (USCS)

**liquid propellant rocket engine**- a chemical rocket propulsion system that employs 2 separate tanks for the fuel and the oxidizer, such engines allow for the control of thrust during flight, i.e. the a liquid propellant rocket engine can be throttled.

**Mach number (Ma)**- The Mach number is a dimensionless ratio of the speed of an object to the speed of sound, where the speed of sound is how fast a pressure disturbance will move through a material. Flows can be classified as subsonic (M<1), supersonic (M>1), transsonic (M approximately equal to one), and hypersonic (M approximately equal to or great than 5).

**mass**- Mass refers to the amount of matter in an object. Typical units: kg (SI) or lbm (USCS)

**Micrometeorite and Orbital Debris (MMOD)**- MMOD are man-made or naturally occuring "small" objects in space that can cause severe damage to a spacecraft.

**momentum**- An object's momentum, a vector quantity, is the product of its mass times its velocity. Typical units: kg*m/s (SI) or lbm*ft/s (USCS).

**moment (also known as torque)**- Moment, a vector quantity, is defined as the product of the force acting on an object times the distance between where the force is applied and a reference point in space. Typical units: N*m (SI) or ft*lbf (USCS).

**Newton's First Law of Motion**- An object will remain at rest or will remain in motion with the same speed & direction, i.e. velocity, unless acted upon by an unbalanced force.

**Newton's Second Law of Motion**- The sum of the forces acting on object (a constant mass system in an inertial reference frame) is equal to the rate that the object's momentum is changing with respect to time. The object's momentum is the product of the object's mass times its velocity. In simplest terms, Newton's Second Law of Motion says that the sum of the forces acting on an object is equal to the object's mass times its acceleration.

**Newton's Third Law of Motion**- For every action, there is an equal and opposite reaction. In other words, if an objects exerts a force on a second object, then the second object also exerts a force of equal magnitude and opposite direction on the first object.

**nose cone**- A nose cone is a cone shape structure at the "top" of a rocket, used to improve aerodynamic efficiency of the rocket (payloads are typically housed in the nose cone).

**nozzle**- A nozzle is a device used to increase the kinetic energy of a flow, a converging-diverging (CD) nozzle can be used to achieve supersonic flows, CD nozzles used to produce high speed jet flows provide thrust for rockets.

**orbit**- An orbit is the path followed by an object as it revolves around another object due to the gravitational interaction between the 2 objects.

**o-ring**- An o-ring is an o-shaped gasket used to provide a mechanical seal between 2 cylindrical shaped structures.

**oxidizer**- An oxidizer is one of the 3 components needed for combustion to occur (the others being a fuel and a heat source).

**payload**- The payload of a rocket is the cargo, items, and/or passengers carried by a launch vehicle that serve as the motivation for the launch.

**perigee**- The point along an orbital path where the position of the orbiting object is closest to the object it orbits.

**propulsion**- Propulsion refers to the technology used to produce a thrust force on an object. Jet propulsion produces this force by the expulsion of mass (Newton's Third Law) and both aircraft and spacecraft employ jet propulsion to produce thrust.

**Reynolds number (Re)**- Reynolds number is a dimensionless quantity that represents the ratio of inertial forces to the viscous forces. The Reynolds number is used to characterize whether a fluid flow is laminar or turbulent.

**scalar**- A scalar is a quantity that has only a magnitude. Temperature, area, density (mass per unit volume), mass, and volume are all scalar quantities.

**solid rocket motor**- A solid rocket motor is a chemical rocket propulsion system where the fuel, oxidizer, and a binder are mixed to form what is known as the grain, the grain burns during the operation of the solid rocket motor. The thrust of a solid rocket motors is determined by the internal shape of the grain.

**stability**- Stability refers to how an aircraft or spacecraft responds to a small change in the forces acting on the vehicle (stable - a small change in the forces acting on a vehicle will not cause a significant change in vehicle's behavior | neutrally stable - the change in the vehicle behavior is proportional to the size of the change in the forces acting on the vehicle | unstable - a small change int he forces acting on a vehicle will cause a significant change in the vehicle's behavior).

**state**- The state of a system is specified by the set of properties needed to fully describe the condition of the system in equilibrium. For example, the thermodynamic state of a "simple compressible" system is completely specified by knowledge of only 2 intensive (or specific) properties. Knowledge of these properties allows one to determine all the other properties of the system.

**temperature**- Temperature is a measure of energy and is proportional to the average internal energy of matter. Typical units: °C, K (SI) or °F, °R (USCS)

**terminal velocity**- Terminal velocity is the speed of a falling object that occurs when the weight of the object is equal to the drag force exerted on the object (in the absence of forces other than weight and drag). At terminal velocity, the object will no longer accelerate as it falls.

**thrust**- Thrust is one of the 4 principal forces acting on an aerospace system. Thrust is the force (a vector quantity) acting on an object that is forward and generally taken to be parallel to the relative wind. The effect of the thrust force is to accelerate an aerospace system, thrust is used to overcome drag (and possibly weight depending on the flight direction). Typical units: N (SI) or lbf (USCS).

**time**- Time is a measurable period during which an event or process occurs. Typical units: s (SI) or s (USCS)

**torque**- see the definition for moment.

**vector**- A vector is a quantity that has both a magnitude and a direction. Force, velocity, and acceleration are examples of vectors.

**velocity**- Velocity is the rate that position is changing with respect to time. Velocity is a vector quantity, i.e. it has a magnitude and direction. Typical units: m/s (SI) or ft/s (USCS).

**weight**- Weight is one of the 4 principal forces acting on an aerospace system. Weight is the force (a vector quantity) acting on an object in the presence of a gravitational force field. The magnitude of the weight is equal to the product of the mass times the acceleration due to gravity, i.e. W=mg. Weight always acts in the same direction as the vector associated with the acceleration due to gravity, i.e. "downward." Typical units: N (SI) or lbf (USCS).

**wing span**- Wing space refers to the distance from the tip of one wing to the tip of the other wing.