- EA — Electronic Attack
- The division of electronic warfare involving offensive use of electromagnetic energy, directed energy, or anti-radiation weapons to degrade, neutralise, or destroy enemy combat capability and equipment.
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- EA (Engagement Area) — Engagement Area
- A designated area where the commander masses fires and obstacles to destroy enemy forces. Always named (e.g., EA RAIDER) for command-and-control clarity. Distinct from EA (Electronic Attack) in EW doctrine.
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- EAB — Emergency Air Breathing
- A shipboard system supplying breathable air via masks during smoke or contamination casualties.
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- EAC
- Estimate at Completion — the forecast total cost based on performance to date.
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- EAR — Export Administration Regulations
- US export control regime (Commerce Dept) governing dual-use items on the Commerce Control List. Less restrictive than ITAR but still imposes significant compliance requirements.
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- EAS — Equivalent Airspeed
- Calibrated airspeed corrected for compressibility effects at a particular altitude.
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- EASA — European Union Aviation Safety Agency
- The European Union agency responsible for civil aviation safety regulation and certification.
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- Eb/N0 — Energy per Bit to Noise Power Spectral Density Ratio
- A normalised signal-to-noise measure independent of bandwidth and symbol rate. The fundamental x-axis of BER-vs-SNR plots used to compare modulation and coding schemes.
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- Eb/No
- Energy per bit to noise power spectral density ratio. The fundamental measure of signal quality in digital communications, independent of data rate and bandwidth. Higher Eb/No yields lower BER.
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- EbN0 — Energy per bit to Noise power spectral density ratio
- A normalized SNR per bit used to compare digital modulation and coding performance.
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- ECAM — Electronic Centralized Aircraft Monitor
- An Airbus system that monitors aircraft systems and displays status, warnings, and corrective procedures.
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- ECC — Elliptic Curve Cryptography
- Public-key cryptography based on the algebraic structure of elliptic curves over finite fields. Provides equivalent security to RSA with much shorter keys: a 256-bit ECC key offers comparable security to a 3072-bit RSA key.
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- Eccentric Anomaly
- An auxiliary angle used in Kepler's equation (M = E − e·sin E) to relate mean anomaly to true anomaly. Geometrically defined on an auxiliary circle circumscribing the elliptical orbit.
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- Eccentricity
- An orbital element describing the shape of an orbit, ranging from 0 (circular) to just below 1 (highly elliptical). Determines the ratio of apogee to perigee altitude.
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- ECCM — Electronic Counter-Countermeasures
- Techniques used by radar and communication systems to resist jamming and deception. Includes frequency agility, pulse compression, sidelobe cancellation, and adaptive nulling. Now formally part of Electronic Protection (EP).
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- ECDIS — Electronic Chart Display and Information System
- A navigation system displaying electronic charts integrated with position and sensor data.
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- ECEF — Earth-Centered Earth-Fixed
- A reference frame that rotates with the Earth. The X-axis passes through the intersection of the prime meridian and equator. Used for ground-based positions and ground tracks.
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- Echelon
- A level of military command within a hierarchical force structure. From smallest to largest: fire team, squad, platoon, company, battalion, brigade, division, corps, field army, theater. Each echelon has defined command authority and capabilities.
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- ECI — Earth-Centered Inertial
- A non-rotating reference frame centered at Earth's center with axes fixed relative to the stars. The X-axis points toward the vernal equinox. Standard frame for orbit propagation.
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- Eclipse
- The period during which a satellite passes through Earth's shadow. Affects power generation (no solar input), thermal control (rapid cooling), and communications (potential signal blockage).
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- ECLSS — Environmental Control and Life Support System
- The crewed-spacecraft subsystem providing breathable atmosphere, water recovery, waste management, thermal control, and fire detection. ISS ECLSS recovers ~93% of water and ~50% of oxygen; lunar/Mars architectures push for closed-loop operation.
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- ECM — Electronic Countermeasures
- Use of electromagnetic energy to deny an adversary effective use of the electromagnetic spectrum. Includes noise jamming, deception jamming, and chaff/flare dispensing.
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- ECP — Engineering Change Proposal
- A formal proposal to change an approved configuration item, with rationale and impact analysis.
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- ECS — Environmental Control System
- The aircraft system that provides cabin pressurization, air conditioning, and temperature control.
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- ECSS — European Cooperation for Space Standardisation
- The framework of standards governing European space programmes covering management, engineering, product assurance, and sustainability.
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- EDL — Entry, Descent, and Landing
- The phase of a mission during which a spacecraft enters an atmosphere, descends, and lands on a surface.
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- EDR — Endpoint Detection and Response
- Cybersecurity technology that continuously monitors endpoint devices for suspicious activity, provides visibility into threats, and enables rapid investigation and response to incidents.
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- EEFI — Essential Elements of Friendly Information
- Critical aspects of a friendly operation that, if known by the enemy, would compromise the mission.
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- EEI — Essential Elements of Information
- The most critical information requirements about the enemy and environment needed by a commander.
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- EEZ — Exclusive Economic Zone
- A sea zone extending up to 200 nautical miles where a coastal state has special resource rights.
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- Effects Synchronisation
- The deliberate timing of capabilities (kinetic, non-kinetic, information) across domains so that their effects converge on the adversary at the decisive time and place. The synchronisation matrix is the planner's primary deconfliction tool.
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- EFIS — Electronic Flight Instrument System
- A cockpit display system that presents flight and navigation data on electronic screens instead of mechanical gauges.
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- EFP — Enhanced Forward Presence
- NATO’s multinational battlegroups deployed to eastern member states to deter aggression.
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- EGM — Earth Gravitational Model
- A high-order model of Earth's gravity field used for precise orbit propagation and geoid definition.
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- EGM2008 — Earth Gravitational Model 2008
- A high-resolution geopotential model providing an improved global geoid for height reference.
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- EGM96 — Earth Gravitational Model 1996
- A geopotential model defining a geoid used to convert ellipsoidal heights to mean-sea-level elevations.
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- EGPWS — Enhanced Ground Proximity Warning System
- An enhanced terrain-warning system that uses a worldwide terrain database to provide predictive terrain alerts.
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- EHF — Extremely High Frequency
- Radio band from 30 to 300 GHz used for high-bandwidth and low-probability-of-intercept links.
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- EICAS — Engine Indicating and Crew Alerting System
- A display system that shows engine parameters and system alerts to the flight crew.
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- EIGRP — Enhanced Interior Gateway Routing Protocol
- A Cisco advanced distance-vector routing protocol using the DUAL convergence algorithm.
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- EIRP — Effective Isotropic Radiated Power
- The product of transmitter power and antenna gain, representing the power that would need to be radiated isotropically to produce the same signal strength in the direction of maximum gain.
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- Eisenhower Matrix
- A priority framework classifying tasks on urgent × important axes into four quadrants. Attributed to Dwight D. Eisenhower: "What is important is seldom urgent, and what is urgent is seldom important."
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- EKF — Extended Kalman Filter
- A recursive nonlinear estimator that fuses sensor data to determine spacecraft attitude and orbit state.
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- Electric Propulsion
- Propulsion using electrical energy to accelerate propellant (ions/plasma) to very high exhaust velocities. Isp of 1,000-10,000 s but very low thrust, suited for station-keeping and spiral orbit transfers.
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- Elevation Mask
- The minimum elevation angle below which a satellite or aircraft is considered unusable due to multipath, atmospheric noise, or terrain blockage. Typical GPS receivers mask below 5–10°; precision survey work tightens this to 15°.
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- ELF — Extremely Low Frequency
- The radio band from 3 to 30 Hz, used for submarine communication through seawater.
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- ELINT — Electronic Intelligence
- Intelligence derived from non-communications electromagnetic emissions, primarily radar. Characterises emitter parameters (frequency, PRI, pulse width, scan type) to identify and locate threat systems.
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- ELNOT — Electronic Intelligence Notation
- Standardized alphanumeric code that identifies a specific radar emitter signal in ELINT databases.
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- ELT — Emergency Locator Transmitter
- A device that transmits a distress signal to aid search and rescue in locating a downed aircraft.
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- EMC — Electromagnetic Compatibility
- The ability of a system to operate without causing or suffering from unacceptable electromagnetic interference. EMC testing verifies conducted and radiated emissions/susceptibility per MIL-STD-461G or ECSS-E-ST-20-07.
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- EMCON — Emission Control
- The selective and controlled use of electromagnetic emitters to minimise detection by adversary electronic support systems. Ranges from Level I (all emissions off) to Level III (unrestricted).
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- EMD — Engineering and Manufacturing Development
- The acquisition phase that develops, integrates, and demonstrates a system before production.
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- EME2000 — Earth Mean Equator and Equinox of J2000
- The standard inertial reference frame tied to the mean equator and equinox at the J2000 epoch.
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- EMI/EMC Chamber
- Shielded enclosure for testing electromagnetic emissions (EMI — does the system radiate excessively?) and susceptibility (EMC — can it tolerate external fields?). Qualification per MIL-STD-461 / DO-160. Typical sizes 3×3×3 m to 10×10×10 m.
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- EMS — Electromagnetic Spectrum
- The range of electromagnetic frequencies used and contested for sensing, communications, and effects.
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- EMSO — Electromagnetic Spectrum Operations
- Coordinated military activities to exploit, attack, protect, and manage the electromagnetic operational environment.
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- EMT — Emergency Medical Technician
- A trained provider who delivers basic emergency medical care and transport for the sick and injured.
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- EMW — Expeditionary Maneuver Warfare
- A naval concept combining maneuver from the sea with expeditionary operations ashore.
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- EN1 / EN2 — Enemy Position 1 / 2
- Sequentially numbered enemy positions identified on the far side of a breach or within an engagement area. Used to coordinate suppressive fires and assault objectives.
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- Encryption
- The transformation of plaintext into ciphertext using a cryptographic key, such that only key-holders can recover the original. Symmetric (AES, ChaCha20) and asymmetric (RSA, ECC) flavours; modern systems combine both via hybrid schemes.
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- END STATE — End State
- The set of conditions that defines achievement of the commander’s objectives and mission success.
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- Engagement Area
- An area along an expected enemy avenue of approach where the commander intends to concentrate fires to destroy an enemy force. Typically defined in defensive operations with pre-planned fires, mines, and obstacles.
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- Engineering Ethics
- The application of ethical principles to engineering practice — public welfare, honesty, competence, conflicts of interest. Codified by ABET, NSPE, IEEE, and discipline-specific bodies. Mandatory study area in most accredited engineering programmes.
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- ENOB — Effective Number of Bits
- A measure of an analog-to-digital converter’s real resolution accounting for noise and distortion.
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- ENU — East-North-Up
- Local tangent-plane coordinate frame variant with Z pointing up. Preferred in western C2 systems and most mapping/GIS tools where positive altitude is intuitive.
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- EO — Earth Observation
- The acquisition of information about Earth's surface and atmosphere from space using optical, infrared, or radar sensors. Applications include mapping, agriculture, disaster monitoring, and climate science.
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- EO-IR — Electro-Optical / Infrared
- Combined visible-band and thermal-infrared sensor suite typical of ISR payloads on UAVs, gunships, and satellites. EO provides imagery and motion; IR adds night/obscurant penetration and thermal contrast.
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- EO/IR — Electro-Optical / Infrared
- Combined visible-light and thermal-infrared sensor payload. EO provides daytime imagery and identification; IR detects thermal contrast for night, smoke, and camouflage penetration. Standard ISR payload on tactical UAS and gimbals.
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- EOB — Electronic Order of Battle
- Catalog of an adversary electronic emitters, their locations, characteristics, and associated platforms or units.
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- EOBT — Estimated Off-Block Time
- The estimated time at which an aircraft will begin moving away from the gate for departure.
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- EOC — Emergency Operations Center
- A facility that coordinates response and support during emergencies and defense support of civil authorities.
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- EOD — Explosive Ordnance Disposal
- The detection, identification, evaluation, rendering safe, and final disposal of unexploded ordnance, including IEDs. EOD teams work with robots and protective suits to minimise personnel exposure.
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- EOH — Engine Operating Hours
- The cumulative running hours logged by an engine, used to schedule maintenance and track life.
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- EOIR — Electro-Optical/Infrared
- A combined sensor suite spanning visible and infrared bands for day/night imaging and targeting.
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- EOL — End of Life
- Spacecraft performance/condition at the end of its operational lifetime.
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- EOOW — Engineering Officer of the Watch
- The officer in charge of the engineering plant and propulsion during a watch.
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- EOP — Earth Orientation Parameters
- Measured quantities (polar motion, UT1-UTC) needed to transform precisely between inertial and Earth-fixed frames.
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- EOQ — Economic Order Quantity
- The order size that minimizes the combined cost of ordering and holding inventory.
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- EOR — Earth Orbit Rendezvous
- Mission architecture assembling/refuelling in Earth orbit before departure.
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- EP — Electronic Protection
- The division of electronic warfare comprising measures to protect friendly use of the electromagnetic spectrum from adversary EW. Includes ECCM, LPI/LPD techniques, emission control, and spectrum management.
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- EPA — Environmental Protection Agency
- The U.S. agency that develops and enforces regulations to protect human health and the environment.
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- EPF — Expeditionary Fast Transport
- A high-speed shallow-draft catamaran for rapid intra-theater sealift of troops and cargo.
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- EPLRS — Enhanced Position Location Reporting System
- A US Army secure, jam-resistant data radio network for position reporting and tactical data.
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- EPS — Electrical Power System
- Generates, stores and distributes spacecraft electrical power.
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- EPT — Electrothermal Propulsion Thruster
- A thruster that electrically heats propellant, such as a resistojet or arcjet, for modest efficiency gains.
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- EPW — Enemy Prisoner of War
- A captured enemy combatant detained and afforded protections under the law of armed conflict.
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- EQ — Emotional Intelligence
- The ability to recognise, understand, and manage one's own emotions and those of others. Core competencies: self-awareness, self-regulation, motivation, empathy, social skills.
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- ERP — Effective Radiated Power
- Total power radiated by an antenna relative to a reference antenna, accounting for antenna gain.
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- ES — Electronic Support
- The division of electronic warfare involving passive search, intercept, identification, and localisation of electromagnetic emissions for intelligence, threat warning, and targeting. Inherently covert as it requires no transmission.
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- ESA — European Space Agency
- Intergovernmental organisation of 22 member states coordinating European civil space activities. Programmes include Copernicus, Galileo, science, and human spaceflight.
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- ESB — Expeditionary Signal Battalion
- A battalion that provides deployable communications and network support to a force.
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- ESCORT — Escort (Screening) Operations
- The protection of high-value or merchant ships by combatants screening against threats.
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- Escort Jamming
- Jamming by dedicated aircraft (EA-18G Growler, EC-130H Compass Call) protecting a strike package. Projects high-power noise or deception at longer range to suppress threats before the strike enters their envelope.
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- ESD — Electrostatic Discharge
- A sudden flow of electricity between two electrically charged objects caused by contact, short-circuit, or dielectric breakdown. In space, surface charging from plasma can cause ESD arcing that damages electronics and solar cells.
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- ESG — Expeditionary Strike Group
- An amphibious task group combining amphibious ships, escorts and an embarked Marine unit.
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- ESM — Effects Synchronisation Matrix
- A joint planning tool that maps all planned effects (kinetic, cyber, EW, information) against timelines and target sets across domains. Ensures deconfliction and coordinated timing.
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- EsN0 — Energy per symbol to Noise power spectral density ratio
- A normalized SNR per symbol used to characterize modulation performance.
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- ESPA — EELV Secondary Payload Adapter
- A standardised ring adapter between launch vehicle upper stage and primary payload, providing ports for up to six secondary payloads of ~180 kg each.
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- ESSM — Evolved Sea Sparrow Missile
- Medium-range semi-active/active radar homing ship-launched surface-to-air missile providing area defense against anti-ship missiles and aircraft.
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- ESTRACK — European Space Tracking Network
- ESA's network of ground stations (Kiruna, Redu, Cebreros, Malargüe, New Norcia).
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- ETA — Estimated Time of Arrival
- The predicted time a vessel will arrive at a destination or waypoint.
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- ETC
- Estimate to Complete — the forecast cost of the remaining work.
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- ETD — Estimated Time of Departure
- The predicted time a vessel will get underway from port or a station.
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- Ethical Leadership
- A leadership style centred on integrity, fairness, ethical decision-making, and visible role-modelling of values. Shown in research to cascade — middle managers replicate the ethics they observe from the top, for better or worse.
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- ETOPS — Extended-range Twin-engine Operations
- Rules permitting twin-engine airliners to fly long over-water routes.
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- ETS — Expiration Term of Service
- The date on which a service member’s current enlistment contract ends.
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- ETSI — European Telecommunications Standards Institute
- A European standards organization producing telecom standards including GSM and TETRA.
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- Euler Angles
- Three successive rotations (roll, pitch, yaw) describing the orientation of one coordinate frame relative to another. Subject to gimbal lock when pitch approaches ±90°.
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- EV
- Earned Value — the budgeted cost of the work actually completed so far.
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- EVA — Extravehicular Activity
- Crewed activity outside a spacecraft's pressurised volume — a "spacewalk" on ISS, "moonwalk" on Apollo. Drives suit pressure, joint mobility, thermal control, and tether/SAFER-jetpack design. ISS EVAs typically run 6–7 hours.
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- EVM — Earned Value Management
- A project management methodology integrating scope, schedule, and cost data. Key metrics: SPI (Schedule Performance Index), CPI (Cost Performance Index), EAC (Estimate at Completion).
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- EW — Electronic Warfare
- Military operations involving the use of the electromagnetic spectrum to attack (EA), protect (EP), or surveil (ES). Includes jamming, deception, anti-radiation weapons, and signals intelligence.
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- EWSK — East-West Station Keeping
- Maneuvers correcting the longitude drift of a geostationary satellite within its assigned box.
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- EXORD — Execute Order
- An order issued by proper authority to initiate a military operation or transition to a new phase.
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- Expeditionary Basing
- Operating from austere, dispersed locations rather than permanent main operating bases. Reduces targeting vulnerability and complicates adversary planning at the cost of logistics and sustainment overhead.
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