- V-Model
- A systems engineering lifecycle model where the left arm represents decomposition (requirements, design) and the right arm represents integration and verification, with testing tracing back to corresponding requirements.
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- DiagramTry it: Space Systems EngineeringTry it: Software Testing Guide
- V&V — Verification and Validation
- The pair of acceptance activities at every system level. Verification: did we build the system right (does it meet the specification)? Validation: did we build the right system (does it satisfy the user need)? Both are required for IV&V acceptance.
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- DiagramTry it: Waterfall Test GuideTry it: Space Standards GuideTry it: Requirements Elicitation+1 more
- VAC
- Variance at Completion (BAC − EAC) — expected over/under-spend at the end. Positive is good.
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- Validation
- The activity of confirming that a system / component meets its intended use. "Did we build the right system?" Often involves end-user trials, operational test, and stakeholder reviews. Pair of verification; both required for acceptance.
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- DiagramTry it: Ttps GuideTry it: Cultural Transformation SimulatorTry it: Waterfall Test Guide+1 more
- Van Allen Belts
- Zones of trapped charged particles (protons and electrons) held by Earth's magnetic field. Inner belt: ~1,000-6,000 km; outer belt: ~13,000-60,000 km. Hazardous to spacecraft electronics.
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- 3D modelTry it: Space Fundamentals GuideTry it: Space Environment Effects GuideTry it: Pnt Guide
- VASI — Visual Approach Slope Indicator
- A runway light system that provides visual glide slope guidance to pilots on final approach.
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- VBSS — Visit, Board, Search, and Seizure
- The boarding of a vessel to inspect it and, if warranted, seize personnel or contraband.
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- VCO — Voltage-Controlled Oscillator
- An oscillator whose output frequency is set by an input control voltage.
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- VDS — Variable Depth Sonar
- A sonar transducer lowered below the surface to exploit favorable acoustic layers for detection.
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- Vendor Selection
- The structured process of choosing suppliers based on weighted criteria — capability, capacity, quality, price, terms, risk. RFI → RFP → BAFO → award is the canonical sequence in formal procurement, with pass/fail gates and trade-off scoring.
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- DiagramTry it: Stakeholder Negotiation Sim
- Verification
- The activity of confirming that a system / component meets its specification. "Did we build the system right?" Includes inspection, analysis, demonstration, and test (IADT). Pair of validation; both required for acceptance.
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- DiagramTry it: Mbse Ontology SimulatorTry it: Software Testing GuideTry it: Cultural Transformation Simulator+1 more
- Vernal Equinox
- The direction in space where the Sun crosses the celestial equator moving northward (~March 20). Defines the reference direction for RAAN and other celestial coordinates.
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- DiagramTry it: Smad Orbit VisualizerTry it: Reference Frame VisualizerTry it: Orbital Perturbations+1 more
- VERTREP — Vertical Replenishment
- Helicopter-based transfer of supplies between ships or from ship to shore while underway. Faster than UNREP for light stores but limited by weather and helicopter availability.
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- 3D modelTry it: Ttps Guide
- VFR — Visual Flight Rules
- Regulations permitting flight by visual reference when weather conditions meet defined minimums.
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- VGPO — Velocity Gate Pull-Off
- Deception jamming that shifts a false Doppler return to pull a radar velocity gate off the target.
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- VHF — Very High Frequency
- Radio band 30-300 MHz. Used for amateur satellite comms, some military applications, and legacy systems. Long wavelength enables simple antennas but limits bandwidth.
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- 3D modelTry it: Defense Spectrum MapTry it: Space Spectrum MapTry it: Multi Domain Spectrum Planner+1 more
- VJTF — Very High Readiness Joint Task Force
- The spearhead element of the NATO Response Force capable of deploying within days.
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- VLAN — Virtual Local Area Network
- A logically segmented broadcast domain within a physical switched network.
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- VLEO — Very Low Earth Orbit
- Orbital regime below ~450 km where atmospheric drag requires active propulsion to maintain altitude. Attractive for high-resolution imaging, low-latency comms, and graceful self-disposal. Commercial focus from Skeyeon, ThinkOrbital, Redwire refueling concepts.
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- 3D modelTry it: Space Fundamentals GuideTry it: Constellation Guide
- VLOS — Visual Line of Sight
- Drone operations conducted where the remote pilot maintains direct unaided visual contact with the aircraft.
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- VLS — Vertical Launching System
- Shipboard missile launcher with individually sealed cells firing missiles vertically, enabling rapid multi-target engagement and mixed-load flexibility. Mk-41 (US, 8 or 24-cell modules) and CAMM Sea Ceptor are dominant Western designs.
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- 3D modelTry it: Defense Fundamentals GuideTry it: Orbat Guide
- VM — Vulnerability Management
- Continuous process of identifying, assessing, prioritizing, and remediating security vulnerabilities.
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- VMC — Visual Meteorological Conditions
- Weather conditions with visibility and cloud clearance sufficient for flight by visual reference.
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- VMF — Variable Message Format
- A bit-oriented tactical messaging standard for exchanging data over diverse military links.
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- VNB — Velocity-Normal-Binormal Frame
- Satellite-centered frame: V along velocity, N along orbit normal, B = V×N.
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- VNIR — Visible and Near Infrared
- The combined visible and near-infrared band, roughly 0.4–1.0 microns, common in imaging spectrometers.
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- VoIP — Voice over Internet Protocol
- Technology that transmits voice calls as data packets over IP networks.
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- VOR — VHF Omnidirectional Range
- Ground beacon giving aircraft a radial bearing for navigation.
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- VPN — Virtual Private Network
- Encrypted tunnel that extends a private network across a public network for secure remote access.
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- VSAT — Very Small Aperture Terminal
- Compact ground terminal for two-way satellite communications.
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- VSWR — Voltage Standing Wave Ratio
- A measure of impedance mismatch on a transmission line from reflected voltage waves.
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- VTOL — Vertical Take-Off and Landing
- Aircraft capable of hovering, taking off, and landing without a runway — helicopters, tiltrotors (V-22), some jets (F-35B), and emerging eVTOL urban air mobility designs. Pays a penalty in payload and cruise efficiency vs conventional take-off.
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- 3D modelTry it: Aerospace Defense Industry GuideTry it: Aerodef Standards Guide
- VV&A — Verification, Validation, and Accreditation
- DoD process for establishing the credibility of models and simulations. Verification: does the implementation match the specification? Validation: does the specification match reality? Accreditation: is the M&S fit for the intended decision?
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- Diagram
- VXLAN — Virtual Extensible LAN
- An overlay tunneling protocol that extends Layer 2 networks over a Layer 3 fabric.
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