Glossary

Plain-language definitions of the terms used in Kshana. Each entry starts with a one-line "in plain terms" and then adds the precise meaning where it helps. Abbreviations not defined in a section are in the A-to-Z table near the end, Every other abbreviation, A to Z.

Navigation & timing#

PNT — Positioning, Navigation, and Timing. Knowing where you are, which way you are going, and what time it is — precisely. Modern PNT mostly comes from satellite signals (GNSS, the global navigation satellite systems defined next); Kshana studies what happens to time and position when those signals are lost.

GNSS — Global Navigation Satellite System. The satellite constellations that provide PNT: GPS (the Global Positioning System, USA (United States of America)), Galileo (EU), GLONASS (Russia's Global Navigation Satellite System), BeiDou (China). A receiver that can see ≥ 4 satellites can compute a full 3D position and time fix.

GNSS outage / denied / degraded / jammed. When the satellite signals are unavailable (blocked, jammed, or out of view). During an outage the system must "coast" on its own onboard sensors. Kshana's whole purpose is to measure how well it coasts.

Holdover. In plain terms: how long the clock can keep good time on its own after it loses GNSS. A better clock holds longer before its error crosses the allowed limit.

Dead-reckoning. In plain terms: estimating where you are by adding up your measured motion, with no outside reference. Errors accumulate, so a better inertial sensor drifts more slowly.

Spec / threshold. The maximum error you are allowed before the solution counts as "out of spec" — e.g. "timing must stay within 20 ns" or "position within 100 m".

The sensors Kshana compares#

Clock (atomic clock). A device that keeps time by counting an atom's natural oscillation. Two examples here:

• CSAC — Chip-Scale Atomic Clock. A small, deployed, commercial clock (the "classical" reference). Good, but drifts noticeably over a long outage.
• Optical lattice clock (e.g. strontium). A far more stable "quantum" clock; the state of the art in laboratories, not yet flown in space.

Accelerometer. Measures acceleration (change in motion). Integrated twice, it gives position — so any error grows quickly. Cold-atom accelerometer is the quantum version with much better long-term stability; navigation-grade is the classical one.

Gyroscope. Measures rotation. A small rotation error tilts the platform, which leaks gravity into the horizontal direction and corrupts the position estimate.

IMU — Inertial Measurement Unit. The accelerometer-and-gyroscope package itself: three axes of each, reporting specific force and angular rate. It measures motion; on its own it does not know where it is.

INS — Inertial Navigation System. An IMU plus the "mechanization" that integrates its output into attitude, velocity and position. The INS is what dead-reckons through a GNSS outage, and its accuracy is set by the IMU error processes listed below.

Time transfer. Sending a precise time signal between two places (e.g. satellite to satellite). Optical links are far more precise than RF (radio-frequency) links.

How errors are modelled (clock noise)#

Clock error is built from standard "noise types", each with a known signature:

White FM (white frequency modulation). In plain terms: fast, random jitter in the clock's rate. Averaging it down improves with time. Parameter q_wf.

Random-walk FM. In plain terms: the clock's rate slowly wanders. This dominates long outages. Parameter q_rw.

Flicker FM (1/f noise). In plain terms: a stubborn noise floor the clock can never average below. It is flat across averaging times. Parameter flicker_floor.

Aging / drift. A slow, predictable change in rate over time; because it is predictable, Kshana's estimator removes it. Parameter drift.

VRW — Velocity Random Walk. The accelerometer equivalent of white noise: random kicks to velocity that build up into position error. Parameter q_va.

ARW — Angular Random Walk. The gyroscope equivalent: random kicks to orientation. Parameter q_arw.

How stability is measured#

Allan deviation (σ_y(τ)). In plain terms: the standard way to state how stable a clock is over a given averaging time τ. A clock datasheet quotes, e.g., σ_y(1 s) = 3×10⁻¹⁰. Kshana validates its clock model by computing the Allan deviation of its own output and checking it matches the published number. (Reference: Riley, NIST SP 1065 — National Institute of Standards and Technology Special Publication 1065.)

PSD — Power Spectral Density. How a noise's power is distributed across frequencies; the formal way to specify white / random-walk / flicker noise.

The figures of merit (how a run is scored)#

The six operational PNT figures of merit Kshana reports (see the README "Output" table):

FoM — Figure of Merit. One number that scores one aspect of a run, reported with its unit and whether it is validated or modelled. The six below are Kshana's operational FoMs.

• Positioning / Timing performance — the size of the error, as RMS (root mean square, the quadratic average) and as the 95th percentile.
• Autonomy — the holdover duration (how long it stays in spec without GNSS).
• Resilience — how fast the error grows once GNSS is lost.
• Availability — the fraction of the run that has an in-spec solution.
• Integrity — can you trust the system's own estimate of its error? Kshana reports the fraction of outage samples whose true error stays inside the filter's protective bound.
• Security — robustness to spoofing: a clock-stability-based spoof-detectability score (since v0.3.0), meaningful only when a spoofing-attack scenario is configured. It is not aviation-grade integrity: it computes no horizontal or vertical protection level (HPL/VPL) and runs no receiver autonomous integrity monitoring (RAIM), advanced or otherwise. Those come from the separate integrity and ARAIM (advanced RAIM) scenario kinds and are defined under "Integrity & augmentation" below. Export-sensitive.

Terms used alongside the figures of merit:

Spoofing. In plain terms: a fake satellite signal that lies about position or time. A spoofer feeds the receiver a plausible but wrong answer, which is worse than jamming because the receiver may not notice.

1-DOF — one degree of freedom. A single axis. Kshana's scenario-pack position error is single-axis; a full 3-D answer needs the three-axis model.

Monte Carlo ensemble. Running the same scenario many times with different random seeds and reporting the spread of the results rather than one run.

CI — confidence interval. The range a statistic is expected to fall in at a stated probability (for example 95 %). In the README's tables and badges "CI" more often means continuous integration — the automated build-and-test run on every change; the context says which.

k-sigma bound. A bound set at k standard deviations of the filter's own uncertainty; the Integrity figure of merit counts how often the true error stays inside it.

CEP / 2DRMS — circular error probable / twice the distance root mean square. Two standard ways of stating 2-D horizontal accuracy: CEP is the radius holding 50 % of fixes; 2DRMS is twice the root-mean-square horizontal error. The library can compute both from a position covariance (src/fom.rs), but no scenario kind reports them yet.

Reading a result: the terms in the output#

These are the names you meet in a result file or the playground's summary, in plain terms first.

Holdover (holdover_s). In plain terms: how many seconds the system stayed inside its error limit after GNSS was lost. Kshana reports the shortest such coast across all outages in the run, measured on the run's time grid, so it is a lower bound at the time-step resolution. A holdover equal to the outage length means the limit was never crossed.

p95 (timing_p95_ns). In plain terms: 95 % of the time, the timing error was this small or smaller. It is the 95th percentile of the error over the outage. A very small value can display as 0.0 in a short summary; the result JSON (JavaScript Object Notation) file holds the full-precision number.

Integrity (integrity). In plain terms: how often the system's own error estimate was honest. It is the fraction of outage samples whose true error stayed inside the filter's k-sigma bound (defined below). A value near 1 means the estimator did not understate its error. It is not an aviation protection level; see "Integrity & augmentation" below and INTEGRITY.md.

Security score (security). In plain terms: how likely a spoofing attack is to be caught. It is the probability that the configured attack is detected — one minus the missed-detection probability P_md — derived from the clock's stability. It only means something when the scenario configures a spoofing attack. With no attack configured, the one-line summary prints security n/a (no attack) and the result marks the figure applicable: false in its figure_tiers block; the value stays in the document and means "not applicable", not "zero security".

PDOP — position dilution of precision (keys such as pdop_min). In plain terms: how much the satellite geometry magnifies ranging error into position error. Position error is roughly PDOP times the ranging error, so lower is better. See DOP under "Estimation & geometry".

sigma_y (σ_y(τ), the Allan deviation). In plain terms: how much a clock's rate wobbles when averaged over a time τ. A datasheet line such as sigma_y(1 s) = 3e-10 means the rate, averaged over one second, varies by about 3 parts in 10¹⁰. Smaller is a more stable clock. See "How stability is measured" above.

q_wf — white-frequency noise intensity. In plain terms: the strength of the fast, random jitter in a clock's rate. It is the coefficient in σ_y²(τ) = q_wf / τ for white frequency noise, so a scenario sets q_wf = sigma_y(1 s)² from the datasheet's one-second Allan deviation. Its companions are q_rw (random-walk frequency noise) and drift (ageing); see "How errors are modelled" above.

Telecom timing terms#

Telecom networks distribute time over packet networks (Precision Time Protocol) from a GNSS-fed reference clock, and the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) sets limits on the time error each clock may add. These terms appear in the telecom-timing kind; see TELECOM-TIMING.md.

TE — time error. In plain terms: how far a clock's time is from the reference time, at one instant. Positive or negative, usually in nanoseconds.

max|TE| — maximum absolute time error. In plain terms: the worst time error seen over the measurement, ignoring its sign. It is the headline limit most masks set.

cTE — constant time error. In plain terms: the steady offset part of the time error — the average error that does not change over the measurement.

dTE — dynamic time error. In plain terms: the wobbling part of the time error — what is left after the constant offset is removed. It is judged with MTIE and TDEV.

MTIE — maximum time interval error. In plain terms: the largest swing in time error seen within any window of a given length. For each window length it slides a window along the record and takes the biggest peak-to-peak change; a mask gives the largest allowed value per window length.

TDEV — time deviation. In plain terms: the typical (root-mean-square) wander of the time error at a given averaging time, after short-term jitter is averaged out. It is a time-domain cousin of the Allan deviation and, like MTIE, is checked against a mask.

PRTC — primary reference time clock. The clock at the top of a telecom timing chain, normally steered by GNSS. Its performance limits are in ITU-T Recommendation G.8272.

ePRTC — enhanced primary reference time clock. A PRTC with a tighter time-error limit, backed by a highly stable local atomic clock so it can hold time through a long GNSS loss. ITU-T Recommendation G.8272.1.

T-BC — telecom boundary clock. A network clock that receives time from upstream and passes it on downstream, adding a little time error of its own. ITU-T Recommendation G.8273.2.

T-TSC — telecom time slave clock. The clock at the end of the chain that receives time and serves it to the equipment that needs it (for example a radio base station). Also covered by ITU-T Recommendation G.8273.2.

OCXO — oven-controlled crystal oscillator. A quartz oscillator kept at a constant temperature inside a small oven, which makes it much more stable than an ordinary quartz oscillator. A common holdover clock in network equipment; it ages (drifts) noticeably over days.

CSAC — chip-scale atomic clock. A very small atomic clock (see "The sensors Kshana compares" above). More stable over long holdovers than an OCXO, at higher cost and power.

Evidence tiers: VALIDATED, MODELLED, PARTNER#

Every capability in the machine-checked verification matrix (VERIFICATION-MATRIX.md) carries one of three tiers.

VALIDATED. In plain terms: checked against someone else's answer. The capability's output was compared with an independent external oracle — real measured data, an independent library written by someone else, or published reference values — and agreed within a stated tolerance. A continuous-integration check refuses a VALIDATED row that names no external oracle.

MODELLED. In plain terms: built from sound physics and checked for internal consistency, but not yet compared with an outside answer. The figures are meaningful for comparison and design trades; they are not evidence that a real device will perform that way. MODELLED-RATIONALE.md explains why each such row is modelled.

PARTNER. In plain terms: this part belongs to a hardware or product-assurance partner, and Kshana claims nothing about it. The row exists so the gap is visible rather than silent.

Spectrum and interference terms#

These terms appear in the spectrum kind; see SPECTRUM.md.

• BPSK(n) — binary phase-shift keying at n × 1.023 Mchip/s. The rectangular-chip modulation of GPS L1 coarse/acquisition (C/A) and L2 civil (L2C) (n = 1) and GPS L5 and Galileo E5a (n = 10). Its spectrum is a sinc² with nulls every n × 1.023 MHz.
• BOC(m, n) — binary offset carrier. A spreading code at n × 1.023 Mchip/s multiplied by a square-wave subcarrier at m × 1.023 MHz, which splits the spectrum into two lobes either side of the carrier.
• MBOC(6,1,1/11) — multiplexed binary offset carrier. The power spectral density 10/11 × BOC(1,1) + 1/11 × BOC(6,1), agreed for Galileo E1 open service and GPS L1C; Galileo transmits it as composite BOC (CBOC).
• CW — continuous wave. An unmodulated carrier: a single tone.
• J/S — jammer-to-signal ratio. Received jammer power over received signal power, in decibels.
• SSC — spectral separation coefficient. κ = ∫ G_s(f) G_j(f) df over the receiver band: how much of a unit-power interferer's spectrum lands where the signal's does. The effective carrier-to-noise density is [1/(C/N₀) + (J/S)·κ]⁻¹.
• Noise figure. How much a receiver adds to the thermal noise, as a ratio F in decibels; the system noise temperature is T_ant + 290 K × (F − 1).
• Waterfall. A time-frequency picture of a spectrum: frequency across, time down, colour for power.
• Welch estimate. A power spectral density estimated by averaging windowed, overlapping periodograms (Welch 1967).
• SigMF — Signal Metadata Format. An open recording format: a JSON .sigmf-meta file describing a raw .sigmf-data file of samples (here complex cf32_le, ci16_le or ci8).
• IQ — in-phase and quadrature. The two components of a complex baseband sample.

LEO-PNT signal terms#

These terms appear in the leo-signal kind and the multi-band spectrum scenarios; see LEO-SIGNAL.md.

• LEO-PNT — low Earth orbit positioning, navigation and timing. Navigation signals broadcast from satellites a few hundred to about 1200 km up: stronger and faster-moving than GNSS from medium Earth orbit.
• RNSS, RDSS, MSS, EESS — Radio Navigation Satellite Service, Radio Determination Satellite Service, Mobile Satellite Service, Earth Exploration-Satellite Service. ITU (International Telecommunication Union) service allocations a band can sit in.
• Pilot, data and acquisition components. The parts of one signal: a data-free pilot for ranging, a data component that carries the navigation message, and a short, low-rate acquisition component that is easy to find.
• FDMA — frequency-division multiple access. Components or satellites separated by carrier frequency rather than by code.
• Gabor (RMS) bandwidth. β = √(∫ f² G df / ∫ G df) over the receiver band: the spread of a signal's power in frequency, which sets how finely it can range.
• DLL — delay lock loop. The code-tracking loop; its early-late correlator spacing and noise bandwidth set the thermal-noise ranging jitter.
• EFQPSK — enhanced Feher quadrature phase-shift keying. A constant-envelope modulation (Xona Pulsar); approximated here by a rectangular-chip spectrum.
• OFDM — orthogonal frequency-division multiplexing. A multicarrier waveform (the Starlink downlink); drawn here as a flat band.
• TEC — total electron content. Electrons per square metre along the path; 1 TECU = 10¹⁶ el/m². The first-order ionospheric delay is 40.3·TEC/f² metres.
• EIRP — effective isotropic radiated power. Transmit power times antenna gain toward the receiver.

Integrity & augmentation#

Integrity is the trust question: not "how big is my error?" but "can I bound it, and will I be told when the bound is broken?" These are the aviation terms for that.

RAIM — Receiver Autonomous Integrity Monitoring. In plain terms: the receiver checks the satellites against each other. With more satellites than the four a fix needs, the leftovers (the residuals) should be small; a large residual means one satellite is lying, and the receiver can say so without help from the ground. Implemented in src/raim.rs.

ARAIM — Advanced Receiver Autonomous Integrity Monitoring. The modern, dual-frequency multi-constellation form of RAIM. It is fed an integrity support message stating each satellite's assumed error and fault probability, and returns protection levels rather than a pass/fail flag. Full treatment, with every assumption, in ARAIM_REFERENCE.md.

SISRE — Signal-in-Space Range Error. In plain terms: how far off a satellite's broadcast orbit and clock make the range a typical user measures. The orbit error is split into radial, along-track and cross-track parts and weighted by how much each shows up along an average line of sight, then combined with the clock error (Montenbruck et al. 2018). For a low Earth orbit satellite the along- and cross-track parts weigh far more than for GPS, because users see it from far off nadir. Used by the leo-navmsg kind.

RAC — Radial, Along-track, Cross-track. The three directions an orbit error is resolved into: out from the Earth's centre, along the direction of flight, and perpendicular to the orbit plane. The leo-navmsg kind's kepler-rac model adds a correction polynomial in each.

SVID — Space-Vehicle Identifier. The number a navigation message uses to name the satellite that sent it.

IOD — Issue of Data. A counter that changes whenever a satellite's navigation message content changes, so a receiver can tell a new message from a repeat. (Not to be confused with an in-orbit demonstration, also abbreviated IOD, as in ESA's Celeste IOD.)

TOW — Time of Week. Seconds since the start of the current GNSS week (Sunday 00:00).

CRC-24Q — 24-bit cyclic redundancy check (Qualcomm polynomial). The error-detecting check RTCM 10403 and Galileo messages carry: a 24-bit remainder of the message bits divided by the polynomial 0x1864CFB. A receiver recomputes it and discards a message that does not match.

URE — User Range Error. In plain terms: how wrong a satellite's own broadcast orbit and clock make every range to it. Also called the signal-in-space error (SISE); it is the per-satellite error budget ARAIM and RAIM are fed (sigma_ure_m in src/raim.rs).

MHSS — Multiple Hypothesis Solution Separation. The method ARAIM uses. For each way the constellation could be faulted it forms a solution that excludes the suspect satellites, and bounds how far that sub-solution can sit from the all-in-view one.

HPL / VPL — Horizontal / Vertical Protection Level. In plain terms: the radius the system promises the true error is inside, at a stated integrity risk. It is a bound the algorithm computes, not a measured error. A run is available when the protection level stays under the alert limit the operation allows (VAL, the vertical alert limit; HAL, the horizontal one).

SBAS — Satellite-Based Augmentation System. A ground network that watches GNSS, computes corrections and integrity bounds, and broadcasts them from geostationary satellites. WAAS — Wide Area Augmentation System is the United States one; EGNOS (the European Geostationary Navigation Overlay Service) is the European equivalent. Kshana computes protection levels in the DO-229E weighted-least-squares form (DO-229E is the RTCA minimum operational performance standard for SBAS receivers; RTCA was formerly the Radio Technical Commission for Aeronautics) (src/sbas.rs).

Estimation & geometry#

Estimator. The algorithm that predicts the true position/time during an outage from the sensor model. Kshana has an analytic holdover predictor and a Kalman filter.

Kalman filter. In plain terms: an algorithm that tracks a quantity and also tracks how uncertain it is. Kshana uses its uncertainty bound to compute Integrity.

EKF — Extended Kalman Filter. A Kalman filter for a non-linear problem: it linearises the model about the current estimate at every step. The standard choice for coupling GNSS to an INS.

UKF — Unscented Kalman Filter. The same job without linearising: it pushes a small set of deterministically chosen sample points through the true non-linear model and rebuilds the mean and covariance from where they land. Better behaved when the non-linearity is strong, which is why the orbit determination uses it.

DOP — Dilution Of Precision. In plain terms: how much the satellites' geometry amplifies ranging error into position or time error. Position error ≈ PDOP × ranging error, so a low number is good geometry. The family: GDOP (geometric — position and time together), PDOP (position), HDOP (horizontal), VDOP (vertical), TDOP (time).

Walker constellation. A standard way to describe a satellite constellation by its number of orbital planes and satellites per plane (GPS is roughly a 24/6 Walker shell).

Elevation mask. The minimum angle above the local horizon at which a satellite is considered usable; signals too low are excluded.

Occultation. When the Earth physically blocks the line of sight to a satellite.

CTI — Composed Timing Integrity. Protection levels for time rather than position, computed across a hand-over between different time sources — for example from a satellite-checked (RAIM-available) clock to a free-running one in holdover — so the bound stays valid through the transition (src/integrity/mod.rs).

TIB — Timing Integrity Benchmark. A yardstick for other people's timing monitors: it injects a menu of faults and checks whether the monitor's stated protection level actually bounded its error. It makes no accuracy claim of its own, so it cannot overstate one (src/benchmark/mod.rs).

Orbits & cislunar#

CR3BP — Circular Restricted Three-Body Problem. The Earth–Moon system treated as two bodies on circular orbits about their common centre of mass, plus a spacecraft too light to pull back. Near the Moon, a two-body Kepler ellipse is simply the wrong shape; the CR3BP is the cheapest dynamics that is right (src/cr3bp.rs).

NRHO — Near-Rectilinear Halo Orbit. A periodic CR3BP orbit that swings close over one lunar pole and far out over the other, so it is almost a straight line end-on — hence "near-rectilinear". It is the orbit chosen for the lunar Gateway, and it keeps near-continuous line of sight to Earth.

DRO — Distant Retrograde Orbit. Another CR3BP family: a large, stable orbit that circles the Moon backwards as seen in the rotating frame.

EOP — Earth Orientation Parameters. The measured, slightly irregular wobble and spin of the Earth (polar motion, UT1 (Universal Time 1, Earth-rotation time)−UTC — Earth-rotation time minus Coordinated Universal Time — and length of day) that is needed to turn an Earth-fixed position into an inertial one to better than metres. The IERS (International Earth Rotation and Reference Systems Service) publishes them; Kshana reads its finals2000A file via --eop.

Standards, formats & organisations#

The abbreviations the README and the package pages use for standards, file formats, time scales, frames and the bodies behind them. Each is also spelled out at its first use in those pages.

Orbits, frames and time

• SGP4 / SDP4 — Simplified General Perturbations 4 / Simplified Deep-space Perturbations 4. The standard analytic propagators for published satellite orbits.
• TLE — two-line element set. The public orbit format SGP4 reads.
• LEO / MEO / GTO / IGSO — low Earth orbit / medium Earth orbit / geostationary transfer orbit / inclined geosynchronous orbit. Orbit regimes; most GNSS satellites fly in MEO.
• LMO — low Mars orbit.
• ECI / ECEF — Earth-centred inertial / Earth-centred, Earth-fixed. A frame that does not rotate with the Earth, and one that does.
• TEME — true equator, mean equinox. The frame SGP4 outputs in.
• GCRS / ITRS / ITRF — Geocentric Celestial Reference System / International Terrestrial Reference System / its realisation, the International Terrestrial Reference Frame. The modern inertial and Earth-fixed frames.
• CIO — Celestial Intermediate Origin. The reference point of the modern, equinox-free Earth-rotation chain.
• LVLH — local vertical, local horizontal. A frame that moves with the spacecraft.
• WGS-84 — World Geodetic System 1984. The Earth ellipsoid GPS uses.
• UTC / TAI / TT / UT1 / TDB — Coordinated Universal Time / International Atomic Time / Terrestrial Time / Universal Time 1 (Earth-rotation time) / Barycentric Dynamical Time.
• LTC / TCL — Lunar Coordinate Time (Temps-Coordonnée Lunaire). The proposed time scale for the Moon.
• OD — orbit determination. Recovering an orbit from tracking measurements.
• CR3BP, NRHO and DRO are defined under "Orbits & cislunar" above.

File formats and messages

• SP3 — Standard Product 3. The precise-orbit file format of the International GNSS Service (IGS), in versions c and d.
• RINEX — Receiver Independent Exchange Format. The standard file format for GNSS observations and broadcast ephemerides.
• IONEX — IONosphere map EXchange format.
• OEM / OMM / TDM — Orbit Ephemeris Message / Orbit Mean-elements Message / Tracking Data Message. Standard messages for orbits and tracking data from the Consultative Committee for Space Data Systems (CCSDS).
• TOML — Tom's Obvious, Minimal Language. The plain-text format of Kshana scenarios.
• KIF — Kshana Interchange Format. Kshana's versioned, self-describing result envelope.

Standards

• DO-229E / DO-316. RTCA minimum operational performance standards for SBAS receivers and for GPS airborne equipment with aircraft-based augmentation.
• IS-GPS-200 / IS-GPS-705. The GPS interface specifications (the second covers the L5 signal).
• NIST SP 1065. The National Institute of Standards and Technology Handbook of Frequency Stability Analysis.
• TRL — technology readiness level. A 1-to-9 scale of hardware maturity.

Organisations

• ESA / ESOC / ESTRACK — the European Space Agency, its European Space Operations Centre, and its European Space Tracking network.
• NASA / JPL / NAIF / DSN — the US National Aeronautics and Space Administration, its Jet Propulsion Laboratory, its Navigation and Ancillary Information Facility (which publishes the SPICE — Spacecraft, Planet, Instrument, C-matrix, Events — toolkit), and its Deep Space Network.
• IGS — the International GNSS Service. IERS — the International Earth Rotation and Reference Systems Service. IAU — the International Astronomical Union (whose SOFA library, Standards of Fundamental Astronomy, and its open port ERFA, Essential Routines for Fundamental Astronomy, are Kshana's frame references).
• CCSDS — the Consultative Committee for Space Data Systems. AIAA — the American Institute of Aeronautics and Astronautics. RTCA — formerly the Radio Technical Commission for Aeronautics.

Software and supply chain

• CLI — command-line interface. MCP — Model Context Protocol, the protocol Kshana's agent server speaks. IDE — integrated development environment.
• SBOM — software bill of materials. SLSA — Supply-chain Levels for Software Artifacts, the build-provenance framework Kshana's releases are attested under.

Every other abbreviation, A to Z#

Every abbreviation used in the repository documentation (docs/ and the four READMEs) that no section above defines, plus a few that one does, repeated for lookup. Each page also spells its abbreviations out at first use; this table is the one place to look them all up. A few entries are identifiers or names rather than abbreviations, and say so.

Reproducibility & licensing#

Reproducible (deterministic). The same input always gives bit-for-bit identical output — scenario + seed + version → identical result. No hidden randomness.

Seed. The number that initialises the (deterministic) random generator, so runs are repeatable.

Open core. The business model: the engine is free and open source (AGPL-3.0, the GNU Affero General Public License defined below; dual-licensed commercially); the sustaining business is support, integration, commercial licences, and proprietary add-ons — not seat fees on the open engine.

AGPL-3.0. The GNU Affero General Public License v3 — an OSI-approved (Open Source Initiative), strong copyleft open-source licence. Like the GPL (GNU General Public License), but with an extra clause (§13) covering software offered to users over a network: a modified version reached over a network must offer those users its corresponding source. Kshana's open licence.

Dual-licensing. Offering the same code under two licences so users choose: here, the AGPL-3.0 (open, copyleft) or a commercial licence from Ashforde OÜ (an Estonian private limited company; OÜ = osaühing) for proprietary/closed use the AGPL does not suit. See LICENSING.md.

Also used on kshana.dev

Abbreviations the website uses that are not in the repository's glossary above.

GPS

Global Positioning System

C/N₀

carrier-to-noise density, in dB-Hz

L-band

the 1 to 2 GHz radio band GNSS uses

C/A

coarse/acquisition code of GPS L1

AFS

augmented forward signal (lunar)

MEMS

micro-electromechanical systems

UAS

uncrewed aircraft system

PL · AL

protection level · alert limit

APV-I

approach with vertical guidance, level I

LEO · GEO

low Earth orbit · geostationary orbit

OEM · OMM · TDM

CCSDS orbit ephemeris, orbit mean-elements and tracking data messages

IGRF

International Geomagnetic Reference Field

DSN

Deep Space Network

VLBI

very long baseline interferometry

LLR

lunar laser ranging

TCXO · OCXO

temperature-compensated · oven-controlled crystal oscillator

RAFS

rubidium atomic frequency standard

PHM

passive hydrogen maser

USO · DSAC

ultra-stable oscillator · deep space atomic clock

MTIE · TDEV

maximum time interval error · time deviation

PRTC · ePRTC

primary reference time clock · enhanced PRTC

ADEV · σy(τ)

Allan deviation at averaging time τ

ITU-T

International Telecommunication Union, Telecommunication Standardization Sector

NIS · NEES

normalised innovation squared · normalised estimation error squared

IEEE

Institute of Electrical and Electronics Engineers

WASM

WebAssembly

JSON · CSV · SVG

JavaScript Object Notation · comma-separated values · Scalable Vector Graphics

CLI · API · IDE

command-line interface · application programming interface · integrated development environment

SBOM · SLSA

software bill of materials · Supply-chain Levels for Software Artifacts

NDA

non-disclosure agreement

DOI

Digital Object Identifier

C/N₀ waterfall

a chart of carrier-to-noise density per satellite over time

HPL · VPL

horizontal · vertical protection level

LROC

Lunar Reconnaissance Orbiter Camera