The simulation engine under xGEO: its physical models, the sources they rest on, how each is checked, and how to use it as an open-source tool

1Method and labels

The rule is that every number is either sourced or labelled. Each source claim carries one of four labels:

• V-TEXT The document was fetched and the passage read; the section, table or page is given.
• V-RECORD The work exists (publisher, DOI or official listing) but the passage was not read, because of a paywall or because it is a book. The equation used is the standard textbook form.
• UNVERIFIED Not confirmed. Treat it as unsourced.
• DERIVED Computed from verified inputs, with the method stated so it can be rerun.

Values chosen for play carry DESIGN VALUE. A design value is never presented as measured. Where possible, it is chosen inside a range that a source does support. The most important design values in CLOSE PASS are the inspector's plan (where it parks and for how long), the distances at which it gives way or leaves, the three hours of lost contact after which it withdraws (only with a Blue craft within 25 km of it), the tension costs, and the scenario's two days, against the weeks the real event took.

The game runs in Godot 4.7 (GDScript, with 64-bit arithmetic wherever precision matters). Its physics is tested by an external suite (§10), which reads the engine's own outputs. Python never reimplements the game in order to grade it.

2Frames, time and starting states

2.1 Reference frame and time

CLOSE PASS is centred on the Earth. Its axes are those of GCRF, the Earth-centred frame aligned with the ICRF: the Earth's mean equator and equinox of J2000 to within the frame bias of a few milliarcseconds. The Earth is an oblate body, 6,378.137 × 6,356.752 km (WGS 84), with GM = 398,600.4418 km³ s⁻² and J2 = 1.08262668×10⁻³ (EGM2008, as tabulated by Vallado¹⁸). The 3-D view uses a floating origin at the camera's focus, so positions keep their precision at any distance. The clock is UTC, starting at 21:00 UTC on 26 October 2026 and running two days. Leap seconds, TT − UTC and UT1 − UTC are ignored; §2.4 gives what that costs.

2.2 Starting states from public element sets

ICEYE-X36 (NORAD 59103, 2024-043F) starts on its real orbit. Its CelesTrak GP element set (epoch 26 October 2026, 21:06 UTC)¹⁶⁶ is propagated by SGP4 (Vallado et al. 2006¹⁶⁷), whose output is in the TEME frame, and then rotated into GCRF. The result is a near-circular orbit with semi-major axis 6,924.4 km: 549 km up, a period of 95.57 minutes and a speed of 7.584 km/s. SGP4 is used only for this starting state. From then on every craft is integrated under the force model of §3, which is how a real analyst would turn a catalogue orbit into a precise one.

Cosmos 2612 (NORAD 68762, 2026-083H) starts 5.1 km behind ICEYE-X36 and 140 m above it, where public element sets put it at 07:38 UTC on 18 October 2026 (KeepTrack's account of the rendezvous¹⁶⁸). It is placed on the path that does not drift away along-track, which is how an inspector holds station. Blue starts with Cosmos 2612's catalogued orbit, about 200 m off its true one (a design value). WATCHMAN-1, the notional US inspector, starts 20 km behind ICEYE-X36.

2.3 The Sun and the Moon

The Sun's position comes from JPL's approximate Keplerian elements for the Earth–Moon barycentre (Standish & Williams², Table 1, valid 1800–2050), reversed to give the Sun as seen from the Earth: 0.9938 AU at the start. The barycentre lies about 4,700 km from the Earth's centre, which turns the Sun's direction by under 7 arcseconds. The Moon comes from the low-precision lunar series of Montenbruck & Gill²⁰ (§3.3.2, eqs. 3.47–3.48), good to a few arcminutes, about 500 km at the Moon's distance. It is 367,065 km away at the start. GM values come from DE440³ (the Moon's 4,902.800118 km³ s⁻²). Planets are added only beyond the Earth's sphere of influence, where their pull starts to matter.

2.4 The turning Earth and its ground sites

The ground radars of §4.5 and Cosmos 2612's handler near Moscow sit on the turning Earth. A site's position is rotated from the Earth-fixed frame into GCRF by Greenwich mean sidereal time (GMST 1982, Vallado¹⁸ Alg. 15) and by IAU 1976 precession (Alg. 23), at the Earth's rate of 7.292115×10⁻⁵ rad/s. Nutation (under 20″), polar motion (under 0.5″) and UT1 − UTC (under 0.9 s) are omitted, so a site sits within about 1 km of where a full IERS reduction would put it. A radar measures what it sees from that point; a 1 km site error is about a thousandth of a typical range, and it is shared by every look from that site.

3Gravity and trajectory design

3.1 Force model and integration

The acceleration on a craft is the Earth's point mass, its J2 zonal term, and the Sun and the Moon as third bodies (direct minus indirect term; Montenbruck & Gill²⁰ §3.3, Cowell's method):

Integration is DOP853, the Dormand–Prince 8(5,3) pair with error control (Hairer, Nørsett & Wanner 1993), every step held to a relative 10⁻¹², so steps lengthen on quiet arcs and shorten near a close pass, with no step rule to tune. Against scipy's DOP853 at 10⁻¹³ on the same forces, the engine stays within 2.8 mm over a day, and within 0.13 m over a 20-day J2 arc. The classical fourth-order Runge–Kutta step stays in the code for tests. There is no atmospheric drag (§11). The same engine, run on its own, centres the world on Jupiter with the four Galilean moons as its third bodies; the external suite of §10 checks that world against JPL Horizons.

For the Earth, two checks run in Godot on every change. ICEYE-X36's orbital node turns 1.0395° per day, against 1.0400° from J2's first-order secular rate (Vallado eqs. 9-41/42). And a craft placed on the no-drift path beside it stays within 779 m of it over a whole orbit, which shows that the starting states and the forces agree.

3.2 Two-body tools

Kepler propagation uses universal variables (Curtis¹⁷ Alg. 3.3–3.4), with Danby's starter near e = 1 and Vallado's starter for long hyperbolic coasts (Vallado¹⁸ Alg. 8). Lambert's problem is solved by Izzo's method (Izzo 2015²³), including multi-revolution transfers. Across 111 test transfers it agrees with hapsira's Izzo solver to 7.3e-15, and it reproduces Curtis Example 5.2. An earlier build used Curtis Alg. 5.2; a loss of precision in its Stumpff function as z → 4π² made every transfer over 180° fail, which was one reason for the change.

3.3 Refining under full gravity

Over a 3-hour coast in low orbit, J2 alone moves a craft by kilometres, so a two-body Lambert solution misses a target only a few kilometres away. Every planned burn is therefore refined by differential-correction shooting through the full-gravity coast (Vallado¹⁸; single shooting as set out in NASA/TP-20220014814 §5.2.1). Newton's method starts from a two-body Jacobian and updates it with Broyden's method²⁴. A 3-hour move by WATCHMAN-1 from 20 km behind ICEYE-X36 to beside it is planned at 0.74 m/s and flies at 0.75 m/s.

3.4 The planner

The planner shows a porkchop plot: departure wait against time of flight, each cell a refined transfer coloured by the Δv to go and the Δv to match on arrival. Its grid steps are design values. Close to a target, the planner also offers station-keeping: holding a point a set distance ahead, behind, above or beside the target. A point 1 km out of ICEYE-X36's plane is held at 1.00 km.

3.5 Leaving Earth orbit

Where a scenario allows it, the planner plans between planets with patched conics (Curtis ch. 8; Vallado ch. 12). A heliocentric Lambert arc runs between the planets; the escape burn is fitted so its hyperbola leaves from the ship's actual position; and the plan is refined under full gravity. Spheres of influence follow Laplace, r = a(m/M)^2/5 (Curtis §8.4). From ICEYE-X36's orbit, the cheapest departure for Mars in the 400 days after the start costs 4.03 km/s. WATCHMAN-1 carries 259 m/s, Cosmos 2612 about 90. Interplanetary flight is switched off in CLOSE PASS, and these figures show it would be out of reach anyway.

4Radio and radar: antennas, links and detection

4.1 Antenna gain and patterns

The peak gain of a dish of diameter D at wavelength λ is G₀ = η(πD/λ)², with η = 0.55 throughout. That is 1.24 dB conservative against the DSN 34 m antenna at X band (68.24 dBi at 8425 MHz, DSN 810-005 Module 104 Rev. O Table 8³⁹). The beamwidth is about 70λ/D degrees (NAWCWD TP 8347 §3-1⁵⁴; ITU-R SA.509-3 §1.3³³) V-TEXT.

Off-axis gain follows the ITU reference envelopes: SA.509-3 for large dishes (D/λ ≥ 100), and S.465-5 Note 4 for small ones³⁴:

These are envelopes of sidelobe peaks, used in interference coordination, so they are conservative for a well-designed antenna. Note 2 of S.465 warns against using them below D/λ = 50, and every Red dish in the game is that small. They are still the most credible public pattern. Every emitter points. In CLOSE PASS, Cosmos 2612's command radio aims its 0.3 m dish at its handler near Moscow, and WATCHMAN-1 listens through a 0.5 m dish of its own. Warships and buoys in the engine's other world listen through four-face arrays that form beams in all directions (after the TDRS S-band multiple-access array, NASA TM-105422), with gain equal to the face's peak plus 10 log cos(scan).

4.2 Link budget and noise

Free-space loss is the exact 20 log(4πR/λ) of ITU-R P.525-4 eq. (3). The practical eq. (4) rounds its constant to 32.4 dB (exactly 32.448 dB), so the game differs from eq. (4) by 0.048 dB.

4.3 Detection of unknown bursts

Listeners don't know a burst's waveform, so they detect it with an energy (radiometer) detector (Urkowitz 1967⁵¹). The integrated SNR grows as √(Bτ). The chance of detection is:

The false-alarm rate is a DESIGN VALUE. This expression matches the exact chi-square distributions to 0.01 for n ≥ 10⁵ samples, and even odds come at 6.8 dB. Spreading a signal over a wider band costs an eavesdropper's energy detector √(B_old/B_new) in SNR at fixed power (the radiometer equation; Urkowitz 1967⁵¹). ITU-R SM.1055³⁸ §1 notes that spread signals are noise-like and not readily detected.

4.4 Direction finding and identification

A two-element interferometer measures a bearing with

This is the cross-correlation phase error for a noise-like signal. It follows from the Knapp & Carter (1976) Cramér–Rao bound in terms of coherence, γ² = s²/(1 + s)², in the narrowband limit; it is checked by a Monte Carlo of a two-element correlator to 3%. A 20 µrad floor is a DESIGN VALUE. Bearings from separated listeners are crossed by weighted least squares. Identification compares a recording's modulation and symbol rate against a threat library above a minimum SNR, a design-value gate. Specific-emitter identification is real: it recognises a device by imperfections in its analog circuitry (Danev et al.⁷⁸).

4.5 Ground radar

Five real radar sites track the three craft. Each look returns range, azimuth and elevation, each with Gaussian noise, every 10 seconds while the craft is above the site's elevation mask and inside its reach. The site's position follows the turning Earth (§2.4): PFISR, at 65.1° N, moves 704 km in an hour, at 0.1962 km/s: the Earth's rate times its 2,690 km distance from the polar axis on WGS 84 gives 0.1961 km/s (DERIVED). Range noise is published for three of the sites; angle noise and masks are notional.

A radar at a site differs from one on a ship in two ways that matter here. It sees a craft only for a few minutes per pass, so custody between passes rests on the filter's prediction (§7). And its range noise, tens of metres, is far smaller than its angle noise at 1,000 km (0.05° is 870 m across the line of sight), so a single pass fixes how far away a craft is much better than where across the sky.

5Electromagnetic attack and tension

The engine models jamming, spoofing, dazzling, high-power microwaves, cyber takeover and kinetic kills, and its other world uses them all. CLOSE PASS gives Blue none of them: WATCHMAN-1's only lever is its presence. The models are kept here because they are part of the engine, and because a scenario that adds a jammer would rely on them.

5.1 The jamming equation

Jamming a command uplink means being louder, at the victim's receiver, than its handler. Both paths are one-way, so the equation is Friis applied twice. This is the communications form of NAWCWD TP 8347 §4-9 V-TEXT, and Adamy's EW 101⁷⁵ gives it in dB form:

G_v(θ_j) is the victim's gain toward the jammer, at angle θ_j off its line to the handler, so geometry matters: a jammer near the handler's line faces the victim's main beam. The aim term means a loose track costs beam-pointing gain. Before the signal is identified, a jammer must spread its power across the whole allocation (barrage); once identified, it can put it all in the channel (spot). How much J/S breaks a link has no universal number. NAWCWD §4-7 (p. 4-7.3) says plainly that effectiveness "is not a direct mathematical function of J/S" V-TEXT. The engine requires +6 dB, a DESIGN VALUE inside the 0–10 dB band typical for FEC-coded BPSK.

5.2 Other effects

A kill breaks the wreck up by the NASA standard breakup model (Johnson et al. 2001¹³¹, as given in Frey & Colombo 2021 App. B¹³⁵). An impact is catastrophic above 40 J/g, and N(≥L_c) = 0.1 M^0.75 L_c^−1.71 fragments are drawn. Each fragment's area-to-mass ratio χ = log₁₀(A/M) follows App. B: the bimodal spacecraft law above 11 cm, the small-object law below 8 cm, and a linear blend in log L_c between 8 and 11 cm. Its speed follows log₁₀ Δv ~ N(0.9χ + 2.9, 0.4), Δv in m/s.

5.3 Escalation in the engine

Each effect carries an escalation cost, a design value: jamming 2 per hour, radar 1 per hour, spoofing 4, dazzling 8, cyber 10, high-power microwave 15, and a kinetic kill 45. Doctrine provides no escalation ladder (§8).

5.4 Tension in CLOSE PASS

CLOSE PASS has its own meter, because its only acts are approaches. Tension rises by 3 when Cosmos 2612 parks inside ICEYE-X36's 1 km keep-out, by 5 each time WATCHMAN-1 crowds it into giving way, and by 12 for every hour WATCHMAN-1 spends within 1 km of it. At 25, Cosmos 2612 turns cautious: it gives way once fewer before leaving, and it stops pushing in. At 50 it leaves at the next crowding. At 100 the confrontation has become open conflict and the scenario is lost. Every value is a DESIGN VALUE.

6Heat, infrared and visible signatures

6.1 Energy balance

Each craft has a skin and, if it carries a reactor, radiators. Skin temperature follows a single-node balance with heat capacity (Gilmore¹⁰³):

S = 1,361 W m⁻² at 1 AU (Kopp & Lean 2011¹⁰⁹), scaled by the inverse square of the Sun's distance, and f is the sunlit share (§6.4). The heat capacity is aluminium's at 298 K, 24.21 J mol⁻¹ K⁻¹ or 897 J kg⁻¹ K⁻¹ (NIST-JANAF, NIST Chemistry WebBook¹⁰⁵); Incropera¹⁰⁴ Table A.1 gives 903 J kg⁻¹ K⁻¹ at 300 K, 0.7% more. The 25% skin fraction is a DESIGN VALUE. WATCHMAN-1's skin has a time constant of about 1.5 hours (DERIVED: C = 897 × 0.25 × 600 kg = 134,550 J/K against 4εσT³A ≈ 25 W/K), so it cools noticeably during each pass through the Earth's shadow, which lasts up to about 36 minutes at 549 km. The Earth's own reflected sunlight (albedo 0.367) and its infrared glow (254 K as a black body) are not yet added to the heat balance (§11). Absorptance and emittance come from NASA RP-1121 (Henninger 1984⁹⁵).

The engine also models reactor radiators, after the 100 kWe Brayton plant of NASA Glenn's JIMO study (Mason 2003⁹⁶; Siamidis 2005⁹⁸), as two-sided Lambertian plates, I(θ) = εσT⁴A cos θ/π. No craft in CLOSE PASS carries a reactor.

6.2 Going dark

A reactor ship can stop radiating for a while by storing its heat in water it vents (2.5 MJ/kg) or ice it melts (333 kJ/kg, Leimkuehler 2011¹⁰²). This is part of the engine's other world; CLOSE PASS has no use for it.

6.3 In-band infrared detection

Telescopes work in NEO Surveyor's NC2 band, 6–10 µm (Mainzer et al. 2023¹¹⁵ V-TEXT). The in-band share of each body's emission comes from the Widger & Woodall series, which matches astropy to 6×10⁻¹¹. The 0.5 m LWIR's 1σ noise-equivalent irradiance is 7×10⁻¹⁸ W m⁻². That lies inside the 0.4–1.1×10⁻¹⁷ range derived from NEO Surveyor's S/N-5 sensitivity. A look detects with

Against the planet's disc, the background raises the NEI ×50, a DESIGN VALUE inside the ×26–92 derived for a background-limited sensor. Just off the disc, stray light raises it ×5, also a design value, out to three times the planet's apparent radius but never more than 20° past its limb. From low orbit the Earth fills almost half the sky, and three times its apparent radius would leave no sky at all; 20° is about the Hubble Space Telescope's bright-Earth avoidance angle. False alarms are Poisson, with a mean of 0.1 per sensor per look (design value), and only lines from two places at once start a track.

6.4 Shadows and reflected light

The Sun is a limb-darkened disc, I(μ) = 1 − u(1 − μ) with u = 0.6 (Allen's¹⁰⁶ §14.7), sampled by 397 rays in 12 rings. The sunlit share is the weighted fraction not blocked by the oblate Earth (6,378 × 6,357 km), the Moon, or, far out, a planet. This gives both umbra and penumbra (Montenbruck & Gill §3.4.2), within 0.019 of a dense numerical integration.

Sunlit hulls are also seen in visible light. The Sun's M_V = 4.81 (Willmer 2018) is scaled to the irradiance at the craft, and each hull is a Lambert sphere with phase law Φ(α) = (sin α + (π − α) cos α)/π. It returns a share p·Φ(α)·r²/R² of the sunlight at its distance R, with p the geometric albedo and r² = A/4π for a hull of surface area A (Madhusudhan & Burrows 2012 eq. 3¹²²). An earlier build used the cross-section πr² in place of r², which made every hull π times (1.24 mag) too bright and every visible range √π = 1.77 times too long. A 1 m GEODSS-class telescope reaches magnitude 22 (Stokes et al. 1996¹¹⁹; the free 1998 Lincoln Laboratory Journal account of the same tests gives magnitude 22 at S/N 4 in under 100 s). The game asks for S/N 5 at magnitude 22, a DESIGN VALUE. Visible telescopes look only where a track already exists, because reaching magnitude 22 takes about 100 s staring at one field.

6.5 What the scenario's sensors see

For the visible ranges the hull is a Lambert sphere (above). With a 1 m telescope the same hulls are seen at 583,270 km (ICEYE-X36), 623,542 km (Cosmos 2612) and 1,150,225 km (WATCHMAN-1), each √(1/0.3) = 1.83 times the 0.3 m range, because the limiting flux scales with aperture and flux falls as the square of range. These are long because the Sun at 1 AU is 27 times brighter than at Jupiter.

7Tracking

Every contact is a track: an estimate with a covariance, not ground truth. Bearings and ground radar looks (range, azimuth and elevation, §4.5) update it in three dimensions through an unscented Kalman filter (Julier sigma points, κ = 0, circular mean for angles), which matches filterpy to 3×10⁻¹². Prediction uses central-difference state transition matrices and white-noise acceleration (Bar-Shalom et al. 2001). Two cases needed special handling.

• Close in. With WATCHMAN-1 a few kilometres from Cosmos 2612, sigma points can straddle the sensor. Within a tenth of the range, a bearing therefore enters as a pseudo-linear measurement (Lindgren & Gong 1978; Aidala & Nardone 1982). Between craft in nearly the same orbit, range is unobservable from angles alone without a manoeuvre (Woffinden & Geller 2009). So without a recent radar range, the track keeps at least 0.5 × range of 1σ along the line of sight (design value).
• Unseen burns. A bearing whose normalised innovation passes the χ²(1) 99.9% point (10.83) is taken as a burn nobody saw, and widens the track (Bar-Shalom ch. 11). The 50 m/s and 10 min used are design values.

CLOSE PASS scores custody: Blue's track of Cosmos 2612 within 1 km of the truth for at least 80% of the time (design values). Between radar passes the track coasts on the force model of §3, so custody depends on how well the filter predicts. In the unattended 24-hour run of Fig. 12, with no orders and only the radar sites looking, custody held 94% of the time. Tracks also size the burns they see: a jump in a track's motion is reported as a burn of about so many m/s, give or take its uncertainty.

A track nobody has detected for 24 h, or whose 1σ exceeds 100,000 km, is dropped (after Blackman & Popoli 1999). Both thresholds are design values. Contacts are drawn after MIL-STD-2525D, with a dashed frame for a last known position.

8Doctrine and the kill chain

The game's verbs follow US joint doctrine, read from the published texts: JP 3-85 Joint Electromagnetic Spectrum Operations (2020)¹³⁹, JP 3-60 Joint Targeting (2018)¹⁴¹, AFDP 3-60 (2026)¹⁴² and the USSF Space Warfighting framework (2025)¹⁴³.

Under JP 3-85, a stealth ship going dark is practising electromagnetic protection: "multispectral low-observability" is one of its listed examples. Doctrine says nothing about TDOA/FDOA, look-through, own-platform jammer isolation, or an escalation ladder. JP 3-85, JP 3-60 and AFDP 3-60 never use the words "spoofing" or "reversible": their terms are intrusion and deception, and temporary or nonlethal effects. (The USSF framework does speak of reversible and nonreversible actions, pp. 5 and 9.) Nor does it treat crowding another craft as an act at all. The tension meter of §5.4 is therefore entirely a design value. Its ordering (reversible and deniable acts cheap, debris-generating acts ruinous) follows doctrine's escalation-of-force guidance qualitatively.

9The scenario and its real-world basis

CLOSE PASS is built on a real uncooperative rendezvous and proximity operation. In October 2026 the Russian satellite Cosmos 2612 approached ICEYE-X36, a commercial X-band radar-imaging satellite, and shadowed it at a few kilometres. It was reported from LeoLabs tracking data by Breaking Defense and The War Zone on 19 October 2026^158,159, and reconstructed from public element sets by KeepTrack¹⁶⁸. As reported, the sequence was: coplanar alignment; closing from long range; station-keeping within 5 km, then 1–2 km; a closest pass reported at 500 m (another report gives 26 m); and moves ahead of and behind the target. The scenario keeps the real craft and their real orbits. WATCHMAN-1, the US inspector the player commands, is notional, and so is everything Cosmos 2612 does after the start.

• Orbit. 549 km, a 95.57-minute period, 7.584 km/s (§2.2). Each orbit takes the craft through the Earth's shadow and over different radar sites.
• Cosmos 2612's plan. In the order LeoLabs reported the real one: close in from behind to 2 km, reposition 2 km ahead, then loiter 0.8 km behind. Each move takes 3 hours and each slot is held for 6. Distances and times are DESIGN VALUES.
• Coming closer. When no Blue craft is within 50 km of it, it takes its next slot at half the distance, but not under 0.5 km.
• Giving way. With a Blue craft within 5 km of it, it gives way to a slot 8 km on the far side of ICEYE-X36. Crowded again after two give-ways (one in the tutorial), it leaves: 4 m/s prograde, and gone once it is beyond 200 km.
• Its radio. An S-band (2.25 GHz) BPSK burst at 100 kbaud, 5 W into a 0.3 m dish aimed at its handler near Moscow (the Titov control centre is at Krasnoznamensk), two minutes long, every 3 to 6 hours and after each move. These are design values within ordinary practice.
• Losing its link. Cut off from its handler for 3 hours within 200 km of its target, and with a Blue craft within 25 km of it, it leaves. Cut off but alone, it holds its slot and waits. This is grounded in practice, not in a published rule: a Progress approach to the ISS was aborted on loss of its telemetry link in 2010¹⁶², and ESA's ATV carried RETREAT and ESCAPE modes for the same reason. The threshold and the burn are DESIGN VALUES.
• Score. Making it break off counts 40; keeping it outside 1 km of ICEYE-X36, 20; custody, 20; using no more than half of WATCHMAN-1's fuel, 10; staying below open conflict, 10. Design values.
• Timescale. The real event took weeks. The scenario runs two days from 21:00 UTC on 26 October 2026 DESIGN VALUE.

Left alone, the plan runs to completion. Fig. 12 is a real 24-hour run of the engine with no orders given: Cosmos 2612 parks 2 km behind ICEYE-X36 at +3 h, passes within 490 m of it at +10.3 h on its way to its slot 2 km ahead (+11.5 h), and at +19.8 h parks 0.8 km behind, inside the keep-out. The keep-out objective fails, while WATCHMAN-1, given no orders, drifts from 20 km to 41 km behind.

10Verification

A Godot script runs every test case through the engine's own functions and writes the results out. A Python suite (pytest) then compares them with independent references, each comparison carrying its own tolerance. JPL data is cached, so the suite runs offline. The suite exercises the engine on its own world, at Jupiter, where JPL Horizons gives an exact reference for every body; the models are the same ones CLOSE PASS runs at the Earth. On 1 November 2026 it made 681 comparisons across 64 tests; all 681 fall within tolerance, and 4 further rows report known simplifications.

The Earth's own numbers are checked by two Godot tests, earth_test and close_pass_earth_test, against textbook values. Both pass:

The suite has also found and fixed real errors. Moon longitudes were up to 114° off. DF σ was three times too large, because it was fed the integrated SNR. The barrage band was twice as wide as the real allocation. Long-way Lambert transfers failed. Two hulls were π times too bright in visible light. And the check of who sees whom had to learn the 20° cap on glare that the Earth brought in (§6.3). Kepler's equation lost accuracy near e = 1. Each fix and its effect on play is recorded in the project's verification log.

11Limits, simplifications and open questions

Not public, so notional

• Cosmos 2612's mass, engine, propellant, camera and radio. Only its orbit and its observed moves are public.
• WATCHMAN-1 as a whole. GSSAP's mass is reported; its sizes, thrusters and sensors were never published.
• Angle noise and elevation masks of the radar sites, and all of Space Fence's figures.
• The site and mask of Cosmos 2612's handler.

Not verified

• The closest approach of the real event: one report gives 500 m, another 26 m.
• HawkEye 360 geolocation accuracy; the Albersheim validity limits; specific-emitter identification accuracy; look-through duty cycles.
• The 2024 edition of JP 3-60 (the 2018 edition was read), and JP 5-0's definitions of MOE and MOP.
• MIL-STD-2525D was read through a reproduction of its tables, not the original PDF.

Simplifications

• No atmospheric drag. At 549 km it slows a small satellite by metres per second per year, depending on the Sun's activity; over two days it moves the three craft relative to each other by an amount that depends on their area-to-mass ratios, which are not public.
• No reflected sunlight or infrared from the Earth in the heat balance, though the Earth's disc does raise the infrared background (§6.3).
• A low-precision Moon (a few arcminutes) and an approximate Sun; no Earth gravity terms beyond J2.
• No nutation, polar motion or UT1 − UTC: ground sites sit within about 1 km of their true places.
• SGP4 is used only for the starting state; nothing is fitted back to element sets during play.
• The umpire's view: some kill-chain indicators still read ground truth rather than Blue's assessed belief.

12xGEO Core as an open-source tool

The models in this edition make up xGEO Core, the engine under the game. xGEO Live, the game, draws what Core computes and sends orders into it, and nothing more. Core runs with no window, and it is being prepared for release as an open-source simulation tool for teaching, concept studies and research. It is not a validated operational tool.

12.1 What is Core and what is Live

12.2 Running Core without the game

A command-line runner loads a scenario, steps time and writes what happens as JSON lines, one object per line:

godot --headless --path godot --script res://cli/run.gd -- \
      --hours=24 --step=600 --seed=4417 --out=run.jsonl

The first line describes the run (scenario, seed, start time, units). Each step line carries the time, escalation, Blue's ships (position, velocity and Δv left), Blue's tracks with their 1σ ellipses, and every log entry since the last step. The last line is the debrief. Tracks report Blue's belief, never the truth; --truth=true adds the true states for analysis. Units are kilometres, km/s and seconds, centred on the scenario's central body: the Earth in CLOSE PASS. Run with no scenario, Core loads its own sample world at Jupiter. The test suite runs it on every change.

12.3 Real, Projected and Notional

Every model and value carries one of three labels, which extend the source labels of §1:

• Real: sourced and checked against an independent reference (§10). The orbits, gravity, the radio and radar equations, Planck's law, the filter.
• Projected: near-future and grounded in programmes that exist today, such as nuclear-thermal drives at NASA's tested 900 s specific impulse.
• Notional: invented for a scenario, the way defence and industry studies fly notional systems: Red's classes and behaviour, equipment sizes, escalation scores, the compressed timescale.

A Real model fed Notional inputs gives a Notional answer: the jamming equation is exact, but a Red jammer's power is a design value, and so is the range it yields. The project's fidelity table (docs/FIDELITY.md) gives each model's label, what it was checked against and what it leaves out.

12.4 Status of the release

Licence (26 October 2026): xGEO Core, the code of the models, the runner, the tests and the verification, is released under the Apache License 2.0. Anyone may use it and change their own copy for any purpose, keeping the notices and not calling their version xGEO. The game, its art and story, and this document stay all rights reserved. Core is open source but not open to contributions: bug reports, physics corrections and feature requests are welcome as issues; pull requests are not accepted. Done: the asset licence audit, the Core and Live split with its check, the command-line runner, the fidelity table, and contribution, conduct and security guides. The jamming and counterspace models are built only from open, published sources, every one cited in this edition, and the owner has cleared them and the name for release. CLOSE PASS names real satellites, operators and radar sites from public records; WATCHMAN-1 and everything the scenario has them do after its start are notional. Still to do before release: a review of the repository's history, then making it public. Issues must cite public sources only.

References

Every source the game cites, in its code, data and tests, grouped by the model that uses it. A link opens the document itself, or a free copy where the publisher's is behind a paywall. Works with no readable copy online are listed without one.

Ephemerides and reference frames §2

1. JPL Solar System Dynamics Group. Horizons On-Line Ephemeris System. Jet Propulsion Laboratory, California Institute of Technology. JPL SSD
2. Standish, E. M. & Williams, J. G. (1992). Keplerian Elements for Approximate Positions of the Major Planets. JPL Solar System Dynamics (web edition). JPL SSD
3. Park, R. S., Folkner, W. M., Williams, J. G. & Boggs, D. H. (2021). The JPL Planetary and Lunar Ephemerides DE440 and DE441. Astronomical Journal 161(3):105. doi:10.3847/1538-3881/abd414 JPL SSD PDF
4. JPL Solar System Dynamics. Planetary Satellite Mean Elements (Jupiter: JUP365). JPL SSD
5. JPL Solar System Dynamics. Planetary Satellite Physical Parameters. JPL SSD
6. Jacobson, R. A. (2021). The Orbits of the Regular Jovian Satellites and the Orientation of the Pole of Jupiter (JUP365). Personal communication to Horizons/NAIF. Corroborated by: JPL Solar System Dynamics, Planetary Satellite Mean Elements (JUP365), which gives this reference JPL SSD.
7. Archinal, B. A., Acton, C. H., A'Hearn, M. F. et al. (2018). Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015. Celestial Mechanics and Dynamical Astronomy 130(3):22. doi:10.1007/s10569-017-9805-5 Corroborated by: NAIF/JPL (2022). Generic PCK kernel pck00011.tpc (IAU WGCCRE 2015 constants, citing Archinal et al. 2018) NAIF; Archinal, B. A. et al. (2019). Correction to: Report of the IAU WGCCRE: 2015. CMDA 131:61 (DLR repository copy) elib.dlr.de PDF.
8. IAU (2015). Resolution B3 on recommended nominal conversion constants for selected solar and planetary properties. XXIXth IAU General Assembly, Honolulu. See also Prša, A. et al. (2016). Nominal values for selected solar and planetary quantities: IAU 2015 Resolution B3. Astronomical Journal 152(2):41. iau.org PDF
9. Williams, D. R. Jupiter Fact Sheet. NASA Space Science Data Coordinated Archive (NSSDCA), Goddard Space Flight Center. nssdc.gsfc.nasa.gov
10. Williams, D. R. Jovian Satellite Fact Sheet. NASA Space Science Data Coordinated Archive (NSSDCA), Goddard Space Flight Center. nssdc.gsfc.nasa.gov
11. Peale, S. J. (1976). Orbital resonances in the solar system. Annual Review of Astronomy and Astrophysics 14:215–246. ADS scan PDF Corroborated by: Peale, S. J. & Lee, M. H. (2002). A primordial origin of the Laplace relation among the Galilean satellites. Science 298:593 (arXiv:astro-ph/0210589) arXiv.
12. Peale, S. J., Cassen, P. & Reynolds, R. T. (1979). Melting of Io by tidal dissipation. Science 203(4383):892–894. Corroborated by: Morabito, L. A. (2012). Discovery of volcanic activity on Io: a historical review. arXiv:1211.2554 arXiv.

Gravity and trajectories §3

13. Folkner, W. M., Iess, L., Anderson, J. D. et al. (2017). Jupiter gravity field estimated from the first two Juno orbits. Geophysical Research Letters 44(10):4694–4700. doi:10.1002/2017GL073140 iris.uniroma1.it PDF
14. Iess, L., Folkner, W. M., Durante, D. et al. (2018). Measurement of Jupiter's asymmetric gravity field. Nature 555:220–222. doi:10.1038/nature25776 weizmann.ac.il PDF
15. Durante, D., Parisi, M., Serra, D. et al. (2020). Jupiter's gravity field halfway through the Juno mission. Geophysical Research Letters 47(4):e2019GL086572. doi:10.1029/2019GL086572 cris.unibo.it PDF
16. Sicardy, B. (2010). Stability of the triangular Lagrange points beyond Gascheau's value. Celestial Mechanics and Dynamical Astronomy 107(1–2):145–155. doi:10.1007/s10569-010-9259-5 HAL
17. Curtis, H. D. (2020). Orbital Mechanics for Engineering Students, 4th ed. Butterworth-Heinemann (Elsevier). Corroborated by: Weber, B. Orbital Mechanics & Astrodynamics (open textbook, CC BY-SA 4.0) open textbook; Izzo, D. (2015). Revisiting Lambert's problem. CMDA 121:1-15 (arXiv:1403.2705) arXiv; NASA/TP-20220014814 (2022). Astrodynamics Convention and Modeling Reference for Lunar, Cislunar, and Libration Point Orbits. NASA NASA NTRS; JPL SSD, Approximate Positions of the Planets (Standish & Williams 1992 web edition) JPL SSD.
18. Vallado, D. A. (2013). Fundamentals of Astrodynamics and Applications, 4th ed. Microcosm Press. Corroborated by: hapsira (open-source poliastro fork), core/propagation/vallado.py, documented as Vallado's KEPLER algorithm GitHub; NASA/TP-20220014814 (2022). Astrodynamics Convention and Modeling Reference for Lunar, Cislunar, and Libration Point Orbits. NASA NASA NTRS.
19. Bate, R. R., Mueller, D. D. & White, J. E. (1971). Fundamentals of Astrodynamics. Dover Publications. Corroborated by: Weber, B. Orbital Mechanics & Astrodynamics (open textbook, CC BY-SA 4.0) open textbook.
20. Montenbruck, O. & Gill, E. (2000). Satellite Orbits: Models, Methods and Applications. Springer. Corroborated by: NASA/TP-20220014814 (2022). Astrodynamics Convention and Modeling Reference for Lunar, Cislunar, and Libration Point Orbits. NASA NASA NTRS.
21. Aarseth, S. J. (2003). Gravitational N-Body Simulations: Tools and Algorithms. Cambridge University Press. Corroborated by: Pelupessy, F. I., Jaenes, J. & Portegies Zwart, S. (2012). N-body integrators with individual time steps from hierarchical splitting. New Astronomy 17:711 (arXiv:1205.5668) arXiv.
22. Danby, J. M. A. (1987). The solution of Kepler's equation. III. Celestial Mechanics 40:303–312. ADS scan PDF Corroborated by: Zechmeister, M. (2018). CORDIC-like method for solving Kepler's equation. A&A 619:A128 (arXiv:1808.07062) arXiv.
23. Izzo, D. (2015). Revisiting Lambert's problem. Celestial Mechanics and Dynamical Astronomy 121(1):1–15. doi:10.1007/s10569-014-9587-y arXiv
24. Broyden, C. G. (1965). A class of methods for solving nonlinear simultaneous equations. Mathematics of Computation 19(92):577–593. ams.org PDF Corroborated by: Bindel, D. (2023). CS 4220 Numerical Analysis, lecture notes 2023-04-14 'Broyden'. Cornell University cs.cornell.edu PDF.
25. Press, W. H., Teukolsky, S. A., Vetterling, W. T. & Flannery, B. P. (1992). Numerical Recipes in C: The Art of Scientific Computing, 2nd ed. Cambridge University Press. nr.com reader
26. Press, W. H., Teukolsky, S. A., Vetterling, W. T. & Flannery, B. P. (2007). Numerical Recipes: The Art of Scientific Computing, 3rd ed. Cambridge University Press. numerical.recipes Corroborated by: Bindel, D. (2023). CS 4220 lecture notes 'Broyden'. Cornell University cs.cornell.edu PDF.

Propulsion §3

27. NASA Glenn Research Center. Ideal Rocket Equation. Beginner's Guide to Aeronautics (formerly Beginner's Guide to Rockets). grc.nasa.gov
28. Tsiolkovsky, K. E. (1903). Exploration of Outer Space by Means of Reaction Devices [Issledovanie mirovykh prostranstv reaktivnymi priborami]. Nauchnoe Obozrenie, no. 5. English translation as 'A Rocket into Cosmic Space (1903)' in Works on Rocket Technology, NASA TT F-243 (1965). tsiolkovsky.org PDF
29. Sutton, G. P. & Biblarz, O. (2016). Rocket Propulsion Elements, 9th ed. Wiley. Corroborated by: Reed, B. D. (2004). On-board chemical propulsion technology. NASA/TM-2004-212698, NASA Glenn NASA NTRS.
30. Borowski, S. K., McCurdy, D. R. & Packard, T. W. (2009). Nuclear Thermal Rocket/Vehicle Characteristics and Sensitivity Trades for NASA's Mars Design Reference Architecture (DRA) 5.0 Study. Nuclear and Emerging Technologies for Space (NETS) 2009, Atlanta. NTRS 20120012928. NASA NTRS
31. Borowski, S. K., McCurdy, D. R. & Packard, T. W. (2012). Nuclear Thermal Propulsion (NTP): A Proven Growth Technology for Human NEO/Mars Exploration Missions. IEEE Aerospace Conference, Big Sky, MT; NASA report E-18081, NTRS 20120003776. NASA NTRS
32. NASA (2023, January 24). NASA, DARPA Will Test Nuclear Engine for Future Mars Missions [news release]. Demonstration Rocket for Agile Cislunar Operations (DRACO), a DARPA/NASA program. nasa.gov

Radio: antennas, links and detection §4

33. ITU-R Recommendation SA.509-3 (12/2013). Space research earth station and radio astronomy reference antenna radiation pattern for use in interference calculations, including coordination procedures, for frequencies less than 30 GHz. ITU, Geneva. ITU PDF
34. ITU-R Recommendation S.465-5 (1993). Reference earth-station radiation pattern for use in coordination and interference assessment in the frequency range from 2 to about 30 GHz. ITU, Geneva. (Superseded by S.465-6, 01/2010.) ITU PDF
35. ITU-R Recommendation S.1428-1 (02/2001). Reference FSS earth-station radiation patterns for use in interference assessment involving non-GSO satellites in frequency bands between 10.7 GHz and 30 GHz. ITU, Geneva. ITU PDF
36. ITU-R Recommendation S.672-4 (09/1997). Satellite antenna radiation pattern for use as a design objective in the fixed-satellite service employing geostationary satellites. ITU, Geneva. ITU PDF
37. ITU-R Recommendation P.525-4 (08/2019). Calculation of free-space attenuation. ITU, Geneva. (Superseded by P.525-5, 11/2024.) ITU PDF
38. ITU-R Recommendation SM.1055-0 (07/1994). The use of spread spectrum techniques. ITU, Geneva. ITU PDF
39. JPL. DSN Telecommunications Link Design Handbook, 810-005: Module 201, Frequency and Channel Assignments, Rev. F (May 2022); Module 202, Doppler Tracking, Rev. D (Sept. 2021); Module 104, 34-m BWG Stations Telecommunications Interfaces, Rev. O (34 m X-band gain, Table 8; system temperatures, Table 11). Jet Propulsion Laboratory, Pasadena. JPL PDF
40. CCSDS 401.0-B-32 (October 2021). Radio Frequency and Modulation Systems, Part 1: Earth Stations and Spacecraft. Recommended Standard (Blue Book), Issue 32. CCSDS, Washington, DC. CCSDS PDF
41. IEEE Std 211-2018. IEEE Standard Definitions of Terms for Radio Wave Propagation. IEEE, New York (revision of IEEE Std 211-1997). Corroborated by: ITU-R P.372-17 (08/2024). Radio noise ITU PDF.
42. Friis, H. T. (1946). A note on a simple transmission formula. Proceedings of the IRE 34(5):254-256. doi:10.1109/JRPROC.1946.234568 Corroborated by: Naval Air Warfare Center Weapons Division (2013). Electronic Warfare and Radar Systems Engineering Handbook, 4th ed., NAWCWD TP 8347 (DTIC ADA617071) everyspec.com.
43. Shannon, C. E. (1949). Communication in the presence of noise. Proceedings of the IRE 37(1):10-21. doi:10.1109/JRPROC.1949.232969 Corroborated by: Modiano, E. MIT OCW 16.36 Communication Systems Engineering (Spring 2009), Lecture 2 MIT OCW.
44. Balanis, C. A. (2016). Antenna Theory: Analysis and Design, 4th ed. Wiley, Hoboken, NJ. Corroborated by: ITU-R P.525-4 (08/2019). Calculation of free-space attenuation ITU PDF; Naval Air Warfare Center Weapons Division (2013). Electronic Warfare and Radar Systems Engineering Handbook, 4th ed., NAWCWD TP 8347 (DTIC ADA617071) everyspec.com.
45. Skolnik, M. I. (2001). Introduction to Radar Systems, 3rd ed. McGraw-Hill, New York.
46. Skolnik, M. I. (ed.) (2008). Radar Handbook, 3rd ed. McGraw-Hill, New York. Corroborated by: Naval Air Warfare Center Weapons Division (2013). Electronic Warfare and Radar Systems Engineering Handbook, 4th ed., NAWCWD TP 8347 (DTIC ADA617071) everyspec.com; ITU-R SA.509-3 (12/2013) ITU PDF.
47. Barton, D. K. (2005). Radar System Analysis and Modeling. Artech House, Norwood, MA. Corroborated by: MIT Lincoln Laboratory, Introduction to Radar Systems lecture series: Tracking and Parameter Estimation (2008) MIT LL.
48. Richards, M. A. (2005). Fundamentals of Radar Signal Processing. McGraw-Hill, New York.
49. Albersheim, W. J. (1981). A closed-form approximation to Robertson's detection characteristics. Proceedings of the IEEE 69(7):839. doi:10.1109/PROC.1981.12082 Corroborated by: Naval Air Warfare Center Weapons Division (2013). Electronic Warfare and Radar Systems Engineering Handbook, 4th ed., NAWCWD TP 8347 (DTIC ADA617071) everyspec.com.
50. North, D. O. (1963). An analysis of the factors which determine signal/noise discrimination in pulsed-carrier systems. Proceedings of the IEEE 51(7):1016-1027 (reprint of RCA Laboratories Report PTR-6C, June 1943). doi:10.1109/PROC.1963.2383
51. Urkowitz, H. (1967). Energy detection of unknown deterministic signals. Proceedings of the IEEE 55(4):523-531. doi:10.1109/PROC.1967.5573 Corroborated by: Rashid, M. & Nanzer, J. A. (2024). Expectation Maximization Aided Modified Weighted Sequential Energy Detector for Distributed Cooperative Spectrum Sensing. arXiv:2403.19556 arXiv PDF; Condon, J. J. & Ransom, S. M. Essential Radio Astronomy, ch. 3 (NRAO / Princeton Univ. Press 2016, online edition) NRAO.
52. Dicke, R. H. (1946). The measurement of thermal radiation at microwave frequencies. Review of Scientific Instruments 17(7):268-275. doi:10.1063/1.1770483 Corroborated by: Condon, J. J. & Ransom, S. M. Essential Radio Astronomy, ch. 3 (NRAO / Princeton Univ. Press 2016, online edition) NRAO.
53. Wilson, T. L., Rohlfs, K. & Hüttemeister, S. (2013). Tools of Radio Astronomy, 6th ed. Springer, Berlin. Corroborated by: Condon, J. J. & Ransom, S. M. Essential Radio Astronomy, ch. 3 (NRAO / Princeton Univ. Press 2016, online edition) NRAO.
54. Naval Air Warfare Center Weapons Division (2013). Electronic Warfare and Radar Systems Engineering Handbook, 4th ed., NAWCWD TP 8347. Point Mugu, CA. (DTIC ADA617071, approved for public release.) DTIC PDF
55. Kerczewski, R. J., Yu, J., Walton, J. C., Perl, T. D., Andro, M. & Alexovich, R. E. (1992). Multiple-access phased array antenna simulator for a digital beam forming system investigation. NASA TM-105422 (Ninth International Conference on Digital Satellite Communications, Copenhagen, May 1992). NASA NTRS PDF
56. Gardner, W. A. (1991). Exploitation of spectral redundancy in cyclostationary signals. IEEE Signal Processing Magazine 8(2):14-36. doi:10.1109/79.81007 cyclostationarity.com PDF
57. Self, A. G. & Smith, B. G. (1985). Intercept time and its prediction. IEE Proceedings F (Communications, Radar and Signal Processing) 132(4):215. doi:10.1049/ip-f-1.1985.0052
58. Clarkson, I. V. L., Perkins, J. E. & Mareels, I. M. Y. (1996). Number/theoretic solutions to intercept time problems. IEEE Transactions on Information Theory 42(3):959-971. doi:10.1109/18.490557
59. Wiley, R. G. (2006). ELINT: The Interception and Analysis of Radar Signals. Artech House, Norwood, MA.
60. Pace, P. E. (2009). Detecting and Classifying Low Probability of Intercept Radar, 2nd ed. Artech House, Norwood, MA.
61. Torrieri, D. (2022). Principles of Spread-Spectrum Communication Systems, 5th ed. Springer, Cham.
62. Donkersley, J. (with Rouma, A.) (2022). SDR++ User Guide, for SDR++ up to version 1.1. SDR++ software by Alexandre Rouma. sdrpp.org PDF
63. GNU Radio Foundation / SigMF project. Signal Metadata Format (SigMF) Specification, version 1.2.x (v1.2.6 current). sigmf.github.io
64. AMD (2023). Zynq UltraScale+ RFSoC Data Sheet: Overview, DS889 (v1.14), 27 June 2023. docs.amd.com

Direction finding and geolocation §4

65. Knapp, C. H. & Carter, G. C. (1976). The generalized correlation method for estimation of time delay. IEEE Transactions on Acoustics, Speech, and Signal Processing 24(4):320-327. doi:10.1109/TASSP.1976.1162830 Corroborated by: Obo, H. et al. (2025). Noise Suppression for Time Difference of Arrival: Performance Evaluation of a Generalized Cross-Correlation Method Using Mean Signal and Inverse Filter. arXiv:2512.05355 arXiv PDF.
66. Thompson, A. R., Moran, J. M. & Swenson, G. W., Jr. (2017). Interferometry and Synthesis in Radio Astronomy, 3rd ed. Astronomy and Astrophysics Library, Springer, Cham. doi:10.1007/978-3-319-44431-4 Springer (open)
67. Poisel, R. A. (2012). Electronic Warfare Target Location Methods, 2nd ed. Artech House, Norwood, MA. Corroborated by: Thompson, A. R., Moran, J. M. & Swenson, G. W. (2017). Interferometry and Synthesis in Radio Astronomy, 3rd ed., Springer (open access) Springer (open) PDF; Herath, S. C. & Pathirana, P. N. (2013). Optimal sensor arrangements in Angle of Arrival (AoA) and range based localization with linear sensor arrays. Sensors 13(9):12277-12294. doi:10.3390/s130912277 (open access, PMC3821368) PMC (open).
68. Stein, S. (1981). Algorithms for ambiguity function processing. IEEE Transactions on Acoustics, Speech, and Signal Processing 29(3):588-599. doi:10.1109/TASSP.1981.1163621 Corroborated by: Fowler, M. L. EECE 522 Notes 15: ML for TDOA/FDOA (revised). Binghamton University course notes ws2.binghamton.edu PDF; Obo, H. et al. (2025), arXiv:2512.05355 (Knapp & Carter coherence CRLB) arXiv PDF.
69. Ho, K. C. & Chan, Y. T. (1997). Geolocation of a known altitude object from TDOA and FDOA measurements. IEEE Transactions on Aerospace and Electronic Systems 33(3):770-783. doi:10.1109/7.599239
70. Ho, K. C. & Xu, W. (2004). An accurate algebraic solution for moving source location using TDOA and FDOA measurements. IEEE Transactions on Signal Processing 52(9):2453-2463. doi:10.1109/TSP.2004.831921
71. Ho, K. C., Lu, X. & Kovavisaruch, L. (2007). Source localization using TDOA and FDOA measurements in the presence of receiver location errors: analysis and solution. IEEE Transactions on Signal Processing 55(2):684-696. doi:10.1109/TSP.2006.885744
72. Sarda, K., Roth, N., Zee, R. E., CaJacob, D. & Orr, N. G. (2018). Making the invisible visible: precision RF-emitter geolocation from space by the HawkEye 360 Pathfinder mission. 32nd Annual AIAA/USU Conference on Small Satellites, Logan, UT, paper SSC18-II-06. (Also presented at IAC 2018 as IAC-18-B4.4.1.) SmallSat 2018 PDF
73. ESA eoPortal. HawkEye 360 (satellite mission page). eoportal.org
74. Burt, E. A., Prestage, J. D., Tjoelker, R. L. et al. (2021). Demonstration of a trapped-ion atomic clock in space. Nature 595:43-47. doi:10.1038/s41586-021-03571-7

Electromagnetic attack and directed energy §5

75. Adamy, D. L. (2001). EW 101: A First Course in Electronic Warfare; (2004) EW 102: A Second Course in Electronic Warfare; (2009) EW 103: Tactical Battlefield Communications Electronic Warfare. Norwood, MA: Artech House. Corroborated by: Naval Air Warfare Center Weapons Division (2013). Electronic Warfare and Radar Systems Engineering Handbook, NAWCWD TP 8347, 'Support Jamming' section (public domain; RF Cafe reproduction) rfcafe.com.
76. Cummings, W. C. (1992). An adaptive nulling antenna for military satellite communications. The Lincoln Laboratory Journal 5(2):173–194. MIT LL PDF
77. Sabharwal, A., Schniter, P., Guo, D., Bliss, D. W., Rangarajan, S. & Wichman, R. (2014). In-band full-duplex wireless: challenges and opportunities. IEEE Journal on Selected Areas in Communications 32(9):1637–1652. doi:10.1109/JSAC.2014.2330193 arXiv
78. Danev, B., Zanetti, D. & Čapkun, S. (2012). On physical-layer identification of wireless devices. ACM Computing Surveys 45(1), article 6:1–29. doi:10.1145/2379776.2379782
79. Riyaz, S., Sankhe, K., Ioannidis, S. & Chowdhury, K. (2018). Deep learning convolutional neural networks for radio identification. IEEE Communications Magazine 56(9):146–152. doi:10.1109/MCOM.2018.1800153
80. Merchant, K., Revay, S., Stantchev, G. & Nousain, B. (2018). Deep learning for RF device fingerprinting in cognitive communication networks. IEEE Journal of Selected Topics in Signal Processing 12(1):160–167. doi:10.1109/JSTSP.2018.2796446
81. Kaushal, H. & Kaddoum, G. (2017). Optical communication in space: challenges and mitigation techniques. IEEE Communications Surveys & Tutorials 19(1):57–96. doi:10.1109/COMST.2016.2603518 arXiv preprint
82. Klein, B. J. & Degnan, J. J. (1974). Optical antenna gain. 1: Transmitting antennas. Applied Optics 13(9):2134–2141. doi:10.1364/AO.13.002134 Corroborated by: Safi, H., Wang, Z., Mast, S., Haas, H. & Tavakkolnia, I. (2026). Analytical channel modeling and stability aware optimization of optical inter-satellite links. arXiv:2609.17431 arXiv.
83. Papoulis, A. & Pillai, S. U. (2002). Probability, Random Variables and Stochastic Processes, 4th ed. New York: McGraw-Hill.
84. Benford, J., Swegle, J. A. & Schamiloglu, E. (2016). High Power Microwaves, 3rd ed. Boca Raton: CRC Press.
85. Zervas, M. N. & Codemard, C. A. (2014). High power fiber lasers: a review. IEEE Journal of Selected Topics in Quantum Electronics 20(5):219–241 (article 0904123). doi:10.1109/JSTQE.2014.2321279 Corroborated by: Hecht, J. (13 Apr 2016). Photonic Frontiers: High-efficiency optical pumping. Laser Focus World 52(4) laserfocusworld.com.
86. Lockheed Martin (28 Jan 2014). Lockheed Martin Demonstrates Weapons-Grade High Power Fiber Laser [press release]. Bothell, WA. news.lockheedmartin.com
87. Hecht, J. (13 Apr 2016). Photonic Frontiers: High-efficiency optical pumping: 'Going green' cranks up the laser power. Laser Focus World 52(4). laserfocusworld.com
88. Lockheed Martin (18 Aug 2022). Lockheed Martin Delivers Integrated Multi-Mission Laser Weapon System to the Navy [press release on HELIOS, 60+ kW class]. Related: Lockheed Martin (28 Jul 2023), Lockheed Martin to Scale Its Highest Powered Laser to 500 Kilowatts Power Level (OUSD(R&E) High Energy Laser Scaling Initiative, HELSI). news.lockheedmartin.com
89. Air Force Research Laboratory (30 Jul 2021). AFRL's drone killer, THOR will welcome new drone 'hammer' [news release on THOR and the Mjolnir follow-on]. CHAMP: Boeing/AFRL flight test, Utah Test and Training Range, 16 Oct 2012. afresearchlab.com
90. Missile Defense Agency (Jan 2024). Ground-based Midcourse Defense [fact sheet, 24-MDA-11677]. mda.mil PDF
91. L3Harris Technologies (Dec 2025). L3Harris Delivers First Meadowlands Production Unit to US Space Force [news release; Meadowlands is the upgraded Counter Communications System]. l3harris.com
92. Albon, C. (15 Apr 2025). Space Force 'Meadowlands' jammer ready for formal testing. Defense News. defensenews.com
93. NASA (2023). DSOC (Deep Space Optical Communications) Technology Demonstration [fact sheet, dated 15 Jun 2023]. NASA/JPL-Caltech. nasa.gov PDF
94. Speed, R. (30 Sep 2025). NASA's deep-space laser comms demo has left the chat. The Register. theregister.com

Power and heat §6

95. Henninger, J. H. (1984). Solar Absorptance and Thermal Emittance of Some Common Spacecraft Thermal-Control Coatings. NASA Reference Publication 1121, NASA Goddard Space Flight Center. NASA NTRS PDF
96. Mason, L. S. (2003). A Power Conversion Concept for the Jupiter Icy Moons Orbiter. NASA/TM-2003-212596 (AIAA 2003-6007, 1st International Energy Conversion Engineering Conference), NASA Glenn Research Center. NASA NTRS PDF
97. Mason, L. S. (2004). Power-Conversion Concept Designed for the Jupiter Icy Moons Orbiter. In Research and Technology 2003, NASA Glenn Research Center. NTRS 20050192432. NASA NTRS PDF
98. Siamidis, J., Mason, L., Beach, D. & Yuko, J. (2005). Heat Rejection Concepts for Brayton Power Conversion Systems. NASA/TM-2005-213337 (AIAA 2004-5654, 2nd International Energy Conversion Engineering Conference). NASA NTRS PDF
99. Poston, D. I., Gibson, M. A., Sanchez, R. G. & McClure, P. R. (2020). Results of the KRUSTY Nuclear System Test. Nuclear Technology 206(sup1):S89-S117. doi:10.1080/00295450.2020.1730673 OSTI PDF
100. Choi, M. K. (2012). Phase Change Material for Temperature Control of Loop Heat Pipe Compensation Chamber. 10th International Energy Conversion Engineering Conference (AIAA), NASA GSFC. NTRS 20120015405. NASA NTRS PDF
101. Choi, M. K. (2018). Thermal Assessment of Paraffin Phase Change Material Mini-Packs on IceCube 3U CubeSat in Flight. 2018 AIAA Propulsion and Energy Forum, NASA GSFC. NTRS 20180004470. NASA NTRS PDF
102. Leimkuehler, T. O., Stephan, R. A. & Hawkins-Reynolds, E. (2011). Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers. 41st International Conference on Environmental Systems (AIAA), NASA JSC. NTRS 20110008723. NASA NTRS PDF
103. Gilmore, D. G. (ed.) (2002). Spacecraft Thermal Control Handbook, Vol. 1: Fundamental Technologies, 2nd ed. The Aerospace Press / AIAA, El Segundo, CA. Corroborated by: Gaite, J. & Fernández-Rico, G. (2012). Linear approach to the orbiting spacecraft thermal problem. Journal of Thermophysics and Heat Transfer 26:511-522. arXiv:1202.4372 arXiv.
104. Incropera, F. P., DeWitt, D. P., Bergman, T. L. & Lavine, A. S. (2007). Fundamentals of Heat and Mass Transfer, 6th ed. Wiley. Corroborated by: Çengel, Y. A. & Ghajar, A. J. Heat and Mass Transfer: Fundamentals and Applications, Appendix 1, Table A-3 'Properties of solid metals' (free appendix PDF from McGraw-Hill) highered.mheducation.com PDF.
105. Chase, M. W., Jr. (1998). NIST-JANAF Thermochemical Tables, 4th ed., J. Phys. Chem. Ref. Data Monograph 9; as tabulated in the NIST Chemistry WebBook, SRD 69: Aluminum, solid-phase Shomate equation, 298–933 K (Cp = 24.21 J/mol·K at 298.15 K, 897 J/kg·K). NIST WebBook
106. Cox, A. N. (ed.) (2000). Allen's Astrophysical Quantities, 4th ed. AIP Press / Springer, New York. Corroborated by: Tripathi, A. K., Chaubey, S. & Singh, A. K. (2020). Study of Limb Darkening Effect and Rotation Period of Sun by using Solar Telescope. Journal of Scientific Research (Banaras Hindu University) 64(1). doi:10.37398/JSR.2020.640132 bhu.ac.in PDF.
107. Hanel, R. A., Conrath, B. J., Herath, L. W., Kunde, V. G. & Pirraglia, J. A. (1981). Albedo, internal heat, and energy balance of Jupiter: Preliminary results of the Voyager infrared investigation. Journal of Geophysical Research 86(A10):8705-8712. doi:10.1029/JA086iA10p08705 NASA NTRS PDF
108. Li, L., Jiang, X., West, R. A., Gierasch, P. J., Perez-Hoyos, S., Sanchez-Lavega, A., Fletcher, L. N., Fortney, J. J. et al. (2018). Less absorbed solar energy and more internal heat for Jupiter. Nature Communications 9:3709. doi:10.1038/s41467-018-06107-2 Nature (open)
109. Kopp, G. & Lean, J. L. (2011). A new, lower value of total solar irradiance: Evidence and climate significance. Geophysical Research Letters 38:L01706. doi:10.1029/2010GL045777 AGU (open)
110. Edwards, D. (2012). An Overview of the Jupiter Icy Moons Orbiter (JIMO) Mission, Environments, and Materials Challenges. NASA MSFC presentation, 12th International Symposium on Materials in the Space Environment. NTRS 20120016895. [Programme: NASA Project Prometheus, JIMO, 2003-2005.] NASA NTRS PDF

Infrared and optical sensing §6

111. Planck, M. (1901). Ueber das Gesetz der Energieverteilung im Normalspectrum. Annalen der Physik 309(3):553-563 (4. Folge, Bd. 4). doi:10.1002/andp.19013090310 Wikisource
112. Widger, W. K. & Woodall, M. P. (1976). Integration of the Planck blackbody radiation function. Bulletin of the American Meteorological Society 57(10):1217-1219. doi:10.1175/1520-0477(1976)057<1217:IOTPBR>2.0.CO;2 AMS (open) Corroborated by: Lewis, W. & McClarren, R. G. (2025). Fast, Accurate Numerical Evaluation of Incomplete Planck Integrals. arXiv:2503.08892 (University of Notre Dame) arXiv.
113. Hudson, R. D. (1969). Infrared System Engineering. Wiley, New York. Corroborated by: OpenStax, University Physics Volume 2, §1.6 Mechanisms of Heat Transfer (Rice University, CC BY) OpenStax.
114. Hecht, E. (2017). Optics, 5th ed. Pearson. Corroborated by: OpenStax, University Physics Volume 3, §4.5 Circular Apertures and Resolution, Eq. (4.5) OpenStax; Barbastathis, G. MIT OCW 2.71 Optics (Spring 2009), Lecture 17: Fraunhofer diffraction; Fourier transforms and theorems MIT OCW.
115. Mainzer, A. K., Masiero, J. R., Abell, P. A., Bauer, J. M., Bottke, W. et al. (2023). The Near-Earth Object Surveyor Mission. Planetary Science Journal 4(12):224. doi:10.3847/PSJ/ad0468 IOP (open)
116. NASA Jet Propulsion Laboratory. Near-Earth Object Surveyor (mission page). Accessed 2026. jpl.nasa.gov
117. Matsumoto, T., Tsumura, K., Matsuoka, Y. & Pyo, J. (2018). Zodiacal light beyond Earth orbit observed with Pioneer 10. Astronomical Journal 156(3):86. doi:10.3847/1538-3881/aad0f0 arXiv
118. Leinert, Ch., Bowyer, S., Haikala, L. K., Hanner, M. S., Hauser, M. G., Levasseur-Regourd, A.-Ch., Mann, I., Mattila, K. et al. (1998). The 1997 reference of diffuse night sky brightness. Astronomy and Astrophysics Supplement Series 127:1-99. doi:10.1051/aas:1998105 aas.aanda.org PDF
119. Stokes, G. H., Weber, R., Shelly, F. C., Beatty, D. E., Viggh, H. E. M., Rork, E. W. & Hays, B. (1996). Air Force Planetary Defense System: Initial Field Test Results. In Space 96: Proceedings of the Fifth International Conference on Space, Engineering, Construction, and Operations in Space V (ASCE), Albuquerque, 1-6 June 1996, pp. 46-53. doi:10.1061/40177(207)7 Corroborated by: Stokes, G. H., Evans, J. B., Viggh, H. E. M., Shelly, F. C. & Pearce, E. C. (1998). The Lincoln Near-Earth Asteroid Research (LINEAR) Program. Lincoln Laboratory Journal 11(1):27-40 MIT LL PDF.
120. U.S. Space Force. Ground-Based Electro-Optical Deep Space Surveillance (GEODSS) fact sheet (sites: Socorro NM, Maui HI, Diego Garcia). spaceforce.mil
121. Johnson, J. (1958). Analysis of image forming systems. In Proceedings of the Image Intensifier Symposium, 6-7 October 1958, U.S. Army Engineer Research and Development Laboratories, Fort Belvoir, VA, pp. 244-273 (DTIC AD220160). Corroborated by: Sjaardema, T. A., Smith, C. S. & Birch, G. C. (2015). History and Evolution of the Johnson Criteria. Sandia National Laboratories, SAND2015-6368. OSTI 1222446 OSTI PDF.
122. Madhusudhan, N. & Burrows, A. (2012). Analytic models for albedos, phase curves, and polarization of reflected light from exoplanets. Astrophysical Journal 747(1):25. doi:10.1088/0004-637X/747/1/25 arXiv
123. Willmer, C. N. A. (2018). The absolute magnitude of the Sun in several filters. Astrophysical Journal Supplement Series 236(2):47. doi:10.3847/1538-4365/aabfdf arXiv
124. Torres, G. (2010). On the use of empirical bolometric corrections for stars. Astronomical Journal 140(5):1158-1162. doi:10.1088/0004-6256/140/5/1158 arXiv

Tracking §7

125. Julier, S. J. & Uhlmann, J. K. (2004). Unscented filtering and nonlinear estimation. Proceedings of the IEEE 92(3):401–422. doi:10.1109/JPROC.2003.823141 Corroborated by: filterpy 1.4.5 documentation, JulierSigmaPoints (R. Labbe) filterpy.readthedocs.io.
126. Bar-Shalom, Y., Li, X. R. & Kirubarajan, T. (2001). Estimation with Applications to Tracking and Navigation. New York: Wiley. Corroborated by: Labbe, R. R. Kalman and Bayesian Filters in Python (open textbook, CC-BY 4.0) GitHub; Labbe, R. R. Kalman and Bayesian Filters in Python, ch. 14 'Adaptive Filtering' (open textbook) GitHub.
127. Lindgren, A. G. & Gong, K. F. (1978). Position and velocity estimation via bearing observations. IEEE Transactions on Aerospace and Electronic Systems AES-14(4):564–577. doi:10.1109/TAES.1978.308681 Corroborated by: Bu, S., Meng, A. & Zhou, G. (2021). A New Pseudolinear Filter for Bearings-Only Tracking without Requirement of Bias Compensation. Sensors 21(16):5444 PMC (open).
128. Aidala, V. J. & Nardone, S. C. (1982). Biased estimation properties of the pseudolinear tracking filter. IEEE Transactions on Aerospace and Electronic Systems AES-18(4):432–441. doi:10.1109/TAES.1982.309250 Corroborated by: Bu, S., Meng, A. & Zhou, G. (2021). Sensors 21(16):5444 PMC (open).
129. Woffinden, D. C. & Geller, D. K. (2009). Observability criteria for angles-only navigation. IEEE Transactions on Aerospace and Electronic Systems 45(3):1194–1208. doi:10.1109/TAES.2009.5259193
130. Blackman, S. & Popoli, R. (1999). Design and Analysis of Modern Tracking Systems. Norwood, MA: Artech House. Corroborated by: MathWorks. trackHistoryLogic (Sensor Fusion and Tracking Toolbox documentation), citing Blackman & Popoli 1999 mathworks.com.

Debris and breakup §5

131. Johnson, N. L., Krisko, P. H., Liou, J.-C. & Anz-Meador, P. D. (2001). NASA's new breakup model of EVOLVE 4.0. Advances in Space Research 28(9):1377–1384. doi:10.1016/S0273-1177(01)00423-9 Corroborated by: Frey, S. & Colombo, C. (2021). Transformation of satellite breakup distribution for probabilistic orbital collision hazard analysis. JGCD 44(1):88-105 (PoliMi IRIS open-access copy) re.public.polimi.it PDF; Krisko, P. H. (2011). Proper implementation of the 1998 NASA breakup model. ODQN 15(4):4-5 NASA ODPO PDF; Panarotto, S. (2024, a.y. 2023/24). Analisi del delta V di detriti spaziali generati a seguito di eventi di frammentazione in orbita. MSc thesis, Univ. Padova thesis.unipd.it PDF.
132. Krisko, P. H. (2011). Proper implementation of the 1998 NASA breakup model. Orbital Debris Quarterly News 15(4):4–5. NASA ODPO PDF
133. Joubert, W. & Tingay, S. (2020). Simulations of orbital debris clouds due to breakup events and their characterisation using the Murchison Widefield Array radio telescope. Experimental Astronomy 51(1):61–75 (issue dated 2021). doi:10.1007/s10686-020-09684-7; arXiv:2008.03657 arXiv
134. Thiele, S. & Boley, A. C. (2022). Investigating the risks of debris-generating ASAT tests in the presence of megaconstellations. The Journal of the Astronautical Sciences 69(6):1797–1820. doi:10.1007/s40295-022-00356-6; arXiv:2111.12196 arXiv
135. Frey, S. & Colombo, C. (2021). Transformation of satellite breakup distribution for probabilistic orbital collision hazard analysis. Journal of Guidance, Control, and Dynamics 44(1):88–105. doi:10.2514/1.G004939. Appendix B: the NASA standard breakup model as implemented. re.public.polimi.it PDF
136. Panarotto, S. (2024; academic year 2023/24). Analisi del delta V di detriti spaziali generati a seguito di eventi di frammentazione in orbita [Analysis of the delta-V of space debris generated by in-orbit fragmentation events]. MSc thesis (Laurea Magistrale, Ingegneria Aerospaziale), Università degli Studi di Padova; supervisor L. Olivieri. thesis.unipd.it PDF
137. NASA Orbital Debris Program Office (2007). Chinese anti-satellite test creates most severe orbital debris cloud in history. Orbital Debris Quarterly News 11(2):2–3. And: (2022). The intentional destruction of Cosmos 1408. Orbital Debris Quarterly News 26(1):1–4. NASA ODPO PDF
138. Anz-Meador, P. D., Opiela, J. N., Shoots, D. & Liou, J.-C. (2018). History of On-orbit Satellite Fragmentations, 15th ed. NASA/TM-2018-220037, NASA JSC Orbital Debris Program Office. NASA NTRS PDF

Doctrine §8

139. Joint Chiefs of Staff (2020). JP 3-85, Joint Electromagnetic Spectrum Operations, 22 May 2020. FAS PDF
140. Joint Chiefs of Staff (2018, incorporating Change 1, 26 Oct 2020). JP 3-14, Space Operations, 10 April 2018. FAS PDF
141. Joint Chiefs of Staff (2018). JP 3-60, Joint Targeting, 28 September 2018. esd.whs.mil PDF
142. U.S. Air Force, LeMay Center (2026). AFDP 3-60, Targeting, 1 May 2026. doctrine.af.mil PDF
143. U.S. Space Force (2025). Space Warfighting: A Framework for Planners. March 2025 (released April 2025). csps.aerospace.org PDF
144. U.S. Space Force (2025). Space Force Doctrine Document 1 (SFDD-1), The Space Force, signed 3 April 2025. spaceforce.mil PDF
145. Department of Defense (2014). MIL-STD-2525D, Department of Defense Interface Standard: Joint Military Symbology, 10 June 2014. jcs.mil PDF Corroborated by: milsymbol (spatialillusions), MIL-STD-2525D implementation test page reproducing the standard's tables cdn.jsdelivr.net.

The setting and the scenario §9

146. U.S. Space Force, Combat Forces Command (formerly Space Operations Command). Fact sheet: Mission Delta 2 - Space Domain Awareness (companion fact sheets: Delta 3 - Space Electromagnetic Warfare; Delta 9 - Orbital Warfare). ussf-cfc.spaceforce.mil
147. Combined Space Operations (CSpO) Initiative (2022). Combined Space Operations Vision 2031. Released February 2022. defence.govt.nz PDF
148. NATO. NATO's approach to space (official topic page; documents the December 2019 London Declaration recognising space as an operational domain and the October 2020 decision to establish a NATO Space Operations Centre at Allied Air Command, Ramstein). nato.int
149. UK Ministry of Defence (2021). UK Space Command (GOV.UK guidance page, published 1 April 2021; withdrawn 25 June 2026). gov.uk
150. U.S. Space Force. Fact sheet: Geosynchronous Space Situational Awareness Program (GSSAP) (current as of Oct 2020). spaceforce.mil
151. National Reconnaissance Office. SILENTBARKER/NROL-107 launch page (launched 10 September 2023; joint NRO-U.S. Space Force space domain awareness mission). nro.gov
152. U.S. Space Force / SAF Public Affairs (2 December 2023). US, UK, Australia announce trilateral Deep Space Advanced Radar Capability initiative. spaceforce.mil
153. Defense Intelligence Agency (2022). Challenges to Security in Space 2022 (follow-up to the February 2019 edition). dia.mil PDF Corroborated by: Joint Chiefs of Staff news (11 Feb 2019), 'Defense Intelligence Agency releases report on challenges to U.S. security in space' jcs.mil; Weeden, B. & Samson, V. (eds.) (2023). Global Counterspace Capabilities, Secure World Foundation SWF PDF.
154. Strout, N., Defense News (23 July 2020). Russia conducted anti-satellite test in space, says US Space Command. Reports the USSPACECOM statement that Cosmos 2543 released an object in a non-destructive on-orbit ASAT test on 15 July 2020. defensenews.com
155. Swope, C., Bingen, K. A., Young, M., Chang, M., Songer, S. & Tammelleo, J. (2024). Space Threat Assessment 2024. CSIS Aerospace Security Project, April 2024. aerospace.csis.org PDF
156. Weeden, B. & Samson, V. (eds.) (2023). Global Counterspace Capabilities: An Open Source Assessment. Secure World Foundation. Co-orbital inspection, including Luch/Olymp-K at GEO from 2014, Cosmos 2542/2543 shadowing USA 245 (2019–2020) and Shijian-21 towing Compass-G2 (2022). SWF PDF
157. Xinhua, via China Aerospace Science and Technology Corporation (20 March 2024). China launches new relay satellite for Earth-Moon communications (Queqiao-2). The original Queqiao (2018) operates in an Earth-Moon L2 halo orbit. english.spacechina.com
158. Hitchens, T., Breaking Defense (19 October 2026). Russian satellite stalked ICEYE spacecraft in potentially dangerous on-orbit maneuvers. breakingdefense.com
159. Trevithick, J. & Altman, H., The War Zone (19 October 2026). Russian Satellite's Unprecedented Shadowing Of A Very Particular Radar Imaging Satellite Is A Big Deal. twz.com
160. ESA Earth Online. ICEYE (mission description: X-band SAR constellation of sub-100 kg satellites). earth.esa.int
161. NASA/JPL (16 June 2016). NASA's Juno Spacecraft to Risk Jupiter's Fireworks for Science. News release. jpl.nasa.gov
162. Harwood, W., CBS News (2 Jul 2010). Progress docking aborted: Progress M-06M lost its telemetry link on final approach to the ISS and flew past. cbsnews.com

Units and constants

163. BIPM (2019). The International System of Units (SI), 9th edition (SI Brochure). bipm.org PDF
164. Tiesinga, E., Mohr, P. J., Newell, D. B. & Taylor, B. N. (2021). CODATA recommended values of the fundamental physical constants: 2018. Rev. Mod. Phys. 93, 025010. physics.nist.gov PDF
165. Thompson, A. & Taylor, B. N. (2008). Guide for the Use of the International System of Units (SI). NIST Special Publication 811, 2008 edition. nvlpubs.nist.gov PDF

CLOSE PASS at the Earth §2, §4.5, §9

166. CelesTrak. General perturbations (GP) element sets, ICEYE-X36 (NORAD 59103), epoch 26 October 2026 21:06 UTC. celestrak.org
167. Vallado, D. A., Crawford, P., Hujsak, R. & Kelso, T. S. (2006). Revisiting Spacetrack Report #3. AIAA/AAS Astrodynamics Specialist Conference, AIAA 2006-6753. Code: CelesTrak, SGP4 software. celestrak.org
168. KeepTrack. Cosmos 2612 / ICEYE-X36 rendezvous, an analysis from public element sets (19 October 2026, updated 23 October). keeptrack.space
169. Krebs, G. D. Gunter's Space Page: ICEYE (spacecraft entry).
170. McDowell, J. C. General Catalog of Artificial Space Objects (GCAT), release 1.8.
171. Nicolls, M. J., Vittaldev, V., Ceperley, D., Creus-Costa, J., Foster, C., Griffith, N., Lu, E., Mason, J., Park, I., Rosner, C. & Stevenson, M. (2017). Conjunction Assessment for Commercial Satellite Constellations Using Commercial Radar Data Sources. Advanced Maui Optical and Space Surveillance Technologies Conference (AMOS).
172. Stevenson, M., Nicolls, M. J., Park, I. & Rosner, C. (2020). Measurements of the Kiwi Space Radar. Advanced Maui Optical and Space Surveillance Technologies Conference (AMOS).
173. Federal Communications Commission. Experimental radio service licence WO2XME (LeoLabs, Arizona). FCC Office of Engineering and Technology, experimental licensing system.