Category: [TECHNOLOGY]
Type: [Starship Sensor System, Survey Instrument]
Canon Tier: Tier 2 (Expanded Universe; pending Council review)
Tags: [NEW-TECH] [PLOT-DEVICE]
A sensor mast is a folding boom with a cooled infrared imager at its tip and a pulsed lidar beside it. It is the eye of a small ship. The standard mast sees a warm radiator from a million kilometres and ranges a hull from 200 km; the survey mast adds a gamma-ray spectrometer, a bigger aperture and a deeper-cooled detector, and sees three times as far. Ships of the Terran Sphere have no radar-stealth to defeat and no way of hiding heat, so sensing is almost entirely passive infrared, and the lidar is used only when you want to be seen. Larger ships add a gravitational-wave “bell” detector, the only sensor that hears a slide.
| Parameter | Standard mast | Survey mast |
|---|---|---|
| Mass | 0.3 t | 0.5 t |
| Stowed envelope | 0.6 × 1.8 × 0.6 m | 0.8 × 2.4 × 0.8 m |
| Power and heat | 3 kW | 6 kW |
| IR aperture | 0.30 m | 0.50 m |
| IR detector | Cryocooled bolometer array | Deeper-cooled array |
| IR rated range | $1.0 \times 10^9$ m (10⁶ km) | $3.0 \times 10^9$ m |
| Lidar rated range | 200 km | 600 km |
| Gamma spectrometer | No | Yes |
| Components | IR imager, lidar, mast motor | IR imager, lidar, gamma spectrometer, mast motor |
Rated range (IR). The reference target is one Vari-E radiator panel at 600 K and ε = 0.8: $P = \epsilon\, \sigma T^4 A = 0.8 \times 5.67 \times 10^{-8} \times 600^4 \times 16 = 94$ kW. A Lambertian emitter delivers a power $P A_{ap} / (\pi d^2)$ onto the aperture $A_{ap}$:
| Mast | $A_{ap}$ | Rated range $d$ | Power on the detector at the rated range |
|---|---|---|---|
| Standard | 0.071 m² | $10^9$ m | $2.1 \times 10^{-15}$ W |
| Survey | 0.196 m² | $3 \times 10^9$ m | $6.5 \times 10^{-16}$ W |
Both are above the detector’s noise-equivalent power (about $10^{-16}$ W in 1 s, so SNR ≈ 10 or more). The same masts see other targets at different distances, because $d \propto \sqrt{P}$:
| Target | Emitted power | Standard mast | Survey mast |
|---|---|---|---|
| One Vari-E radiator panel (600 K, ε = 0.8) | 94 kW | $1.0 \times 10^9$ m | $3.0 \times 10^9$ m |
| A micro-torch drive wing at full thrust (1,800 K, ≈ 28 m², ε = 1 for a bare radiating surface, single-sided) | 16.7 MW | $1.3 \times 10^{10}$ m (0.09 AU) | $4.0 \times 10^{10}$ m (0.27 AU) |
| A ship running cold (hull 250 K, ε = 0.05, 226 m²) | 2.5 kW | $1.6 \times 10^8$ m (160,000 km) | $4.9 \times 10^8$ m (490,000 km) |
The last row is the point of cold-running: an ε of 0.05 and a shut-down drive cut the signature by a factor of 40 and the detection range by a factor of 6, to a distance a patient crew can steer clear of.
Lidar. A pulsed lidar gives range to centimetres and a cross-section. Round-trip time at the rated range is $2d/c$: 1.3 ms at 200 km and 4.0 ms at 600 km. It is active, so the target sees the lidar and learns your bearing: stealth ships use it rarely, port pilots use it constantly.
Gamma-ray spectrometer (survey mast). A scintillator crystal measures the gamma lines of a surface, which come from natural radioactivity (K, U, Th) and from cosmic-ray neutron capture (H at 2.22 MeV, Fe, Si, Mg, O). The signal falls with distance, so the useful altitude is about one body radius; a survey crew orbits low, and a mapped asteroid takes tens of minutes to hours per pass.
Gravitational-wave “bell” detector (L-class). A slide rings a gravitational-wave “bell” with strain $h \approx 10^{-15} (1\ \text{km} / r)$ for a 72 kt courier jump; scale by $\sqrt{E/72\ \text{kt}}$ for other hulls (×2.1 for a 3 kt freighter at 12c, ×5 for Atlas). A ship-borne detector with a sensitivity of $10^{-21}$ hears a courier within $10^6$ km. A port array with a sensitivity of $10^{-24}$ hears the same courier at $10^9$ km (6.7 AU), and with three or more arms in a network fixes time, bearing and mass. The detector is a pair of squeezed-light interferometers, like the ones in the Quantum-Optical Nav Array, folded into 10 km tethered arms: at $h = 10^{-21}$, 10 km of arm shifts by $10^{-17}$ m. It is an L-class module because the arms need a large hull to deploy from, and it is mounted in a spinal bay and not on a mast.
Space has no ambient light to hide in. Every drive, radiator and body is a point of heat against a 3 K background, and the whole fleet doctrine (Space Warfare Doctrine) comes from this: you cannot stop being seen, only delay it by running cold. The mast’s infrared imager works day and night, through no atmosphere, with no emissions of its own. A good sensor operator reads a heat picture the way a field hand reads a sky.
The mast folds flat against the hull and is raised by a motor on its mount. Raising takes seconds. It is retracted before a burn, since the torch plume (and even the RCS steam, within a kilometre) will cook a bolometer, and it is raised again when the dust has settled. A mast is a light, brittle part (health 60) and the first thing to go in a collision.
The survey mast is the tool of prospectors and the Dragonfly scouts that fly from them. The gamma spectrometer tells a miner whether a rock is ice, carbonaceous or metal before she commits a UniPod to it. It is also the instrument of salvage: a derelict’s reactor and fuel show up in the gamma spectrum at ranges where the infrared is blind.
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