Descriptions, and suggestions for new rules...
Until the 2060s, spacecraft used classical telescopes and dish-shaped radars and communicators. With the development of nanotechnology, it became increasingly cheaper to build high-resolution phased-array detectors, which have gradually replaced the older systems in most modern designs.
Phased-array systems make use of the interference principle; technically, they work on the same principles as mirrors do. The atoms and molecules in mirrors absorb light waves and re-emit them in all directions with phase differences that depend on their positions. As a result these waves cancel each other in all direction but one, so that mirrors reflect incident light toward only one angle.
In the case of phased arrays, the electromagnetic waves are either transmitted or received by thousands of micro- or nano-elements. Changing the phases between the elements modifies the interference pattern and allows the beam to be steered while the array itself is immobile. When transmitting, the phases are controlled by emitting the pulses with a precise time shift between each; while reception works by filtering the incoming signals in narrow time windows. Because the elements are independent, they can be assigned by groups to different directions, or even to reception or transmission at the same time, though this results in lower resolution.
Compared to dish detectors, phased arrays have many advantages: no mechanical parts, thus no inertia or after-motion vibrations and no mechanical imprecision nor failure. They can be instantaneously oriented with high accuracy and allow for simultaneous multi-targeting.
The oldest phased-array systems are series of flat rectangular or circular matrices located all around spacecraft, each of them having an approximate 60° by 60° field of view. Since the 2080's, phased arrays have been increasingly found in compact semi-spherical geometry, each covering half the sky.
Radars are centimeter-wavelength phased array transmitters-receivers. They light up targets with short impulses of a narrow beam (typically half a degree) and measure the reflected signal. In the Well, this signal is weaker than thermal emissions, or even reflected sunlight and radar are not used much. Radar systems also work in passive mode so that they can detect other radars' emissions.
The typical imaging resolution of a radar is about 1%, e.g. is 10 miles at a distance of 1000 miles, which is useful for planet cartography, in particular because radar wavelengths traverse clouds and even a few yards of soil or water. Although the resolution is poor and makes small objects appear like simple spots, the accuracy of a radar, or the ability to locate exactly where this spot is, is sufficient for targeting purpose in combat. In addition, the shape of a target subtly alters the return signal and provides a typical signature usable to identify the class of spacecraft by comparison with a database. Additionally, the return signal changes with the angle, making possible the reconstruction of the orientation of a spacecraft. Radar also provide targets' range and radial velocity information. Radars see through non-conducting materials and can be fit behind anti-laser shielding.
Ladars are low-power, multi-wavelength, phased-array free-electron laser emitters/receivers. They work in a way similar to radars: the laser beam is reflected on targets and the return signal is detected with the same array or with a PESA, allowing for measurement of range and radial velocity. The resolution is much better: of the order of 0.00001% or approximately 1' at 1,000 miles, allowing for very good imaging. A spectral analysis of the return signal can be done for precise study of chemical composition of surface material, such that ladars can be used as chemscanners (p. TS151). Finally, they can also be used as narrow headlights, in which case a pseudo-white color is created by merging the three base colours.
PESAs include three distinct arrays: high-resolution, multi-wavelengths optical phased-array telescopes (sensitive to infrared up to 25 µm, visible light, and ultraviolet down to 200 nm), low resolution bolometers (heat-sensitive resistors) sensitive to far infrared (20 µm and up) and a set of microwave to long-wave radio antennae. PESAs can also be used as electromagnetic field scanners (p. TS151). In watch mode, the optical arrays continuously scan the sky and can detect objects approaching or in a suspect trajectory up to magnitude 18. They cannot directly measure the range of a target nor its velocity, but these can be estimated if the target is monitored during a long time and if its magnitude is changing quickly. The imaging resolution can be as high as lasers'.
Aside from PESAs, radars, and ladars descried in the books, spacecraft are also fit with arrays of secondary sensors (included in the cost). Deep-space vessels have a dust collector to measure density and composition of dust when around asteroids and comets. Aside from spectral analysis, it makes possible to estimate the loss of delta-V due to the minute friction forces, or the push due to vapor geysers, as well the dust deposition on optical detectors.
Along with this, a micro-meteoroid collector can estimate the integrated damages of the hull over the years. Several gyroscopes calculate the orientation of the vessel and measure kinetic attacks or meteoroid impacts.
Cosmic ray sensors buried inside the hull monitor high-energy particles going through the vessel and measure the intensity of solar flares, radiation belts or particle accelerator attacks.
X/γ-ray sensors also detect external radiation such as from fusion drives, but their standard resolution of only 0.1% does not permit them to locate a spacecraft at better than about 100,000 miles at 1 AU).
Mining equipment also comes with various geological probes either measuring the natural radioactivity of rock, activating it with neutrons or γ-rays, or using nuclear magnetic resonance techniques (NMR) to map the ground in 3D. These probes must be in contact or introduced into the rock after drilling. Asteroids are roughly homogeneous and surface tests are sufficient to know their compositions.
PESA optical arrays and ladars are too fragile to be used at full potential in combat, the delicate elements would immediately be destroyed by laser weapons. They cannot be effectively shielded with wavelength-selective material either, as free-electron laser weapons are tunable. They are consequently folded most of the time during combat, opened only a few seconds per turn to calibrate the radar signal with the much greater resolution they provide.
Radars are protected behind layers of heat-resistant plastic and graphite transparent to radio waves. Because of their low resolution, aiming at a single spot on a target spacecraft is very difficult. The GM could allow the gunner a +2 bonus if the shot is made with optical detectors fully deployed (at the risk of being shot off).
Three main sources of radiation allow for spacecraft detection. The sunlight reflected or absorbed and re-emitted as thermal infrared, the heat mostly due to the life-support system, and that due to the space drive. Weapons also generate heat, but they are normally used at the same time as the space drive. Electronics uses very low power in 2100.
Fusion drives release an enormous amount of energy in the form of X- and soft γ-rays, which can easily be detected from anywhere in the Solar System. However, high-energy sensors have too low resolution to be able to locate the source with precision because this radiation cannot be focused like light. Fusion also emits ultraviolet, visible, and infrared light, but in lower amount than the radiators that cool the drive. Even when the drive is off, the life-support system, sunlight reflection and heating radiate enough visible and infrared light to be detectable from very long distances by PESAs.
| A common meme suggests that great powers, such as China, the E.U. or the USA, and perhaps Duncanite security companies, continuously scan the sky with large telescopes and high-energy sensors to keep track of every spacecraft in the Solar System. |
The Detection Table shows the distance of detection for typical detectors: an object becomes easily detectable when it is at the distance listed or closer. If looking through atmosphere, subtract -6 for a radar or a ladar or -12 for a PESA. Add the Size Modifier of the target if the object is "cold": asteroid, wreck, or a "silent" spacecraft. If the orientation with respect to the Sun or to the detector is not known, use the average value of the vessel's size modifiers, discarding that of liquid-droplet radiators as they are not being used. Spacecraft trying to hide show their smallest side to the Sun, so the lowest SM should be used. Stealth military spacecraft have an angular geometry and a mirror coating (see New Design Options) so that sunlight and detector beams have very little return signal (typically a millionth on the incident energy). Detecting these vessels is done with a penalty of -18.
Box hull share some of the angular features of a stealth spacecraft, though most spacecraft are equipped with protuberant devices that reduce the effect. As a result, box-hull spacecraft are detected with a modifier of only -3. On the contrary, spherical hulls reflects light isotropically and can be detected with a bonus of +3.
The default numbers in the Detection Table correspond to the thermal re-emission and sunlight reflection of an object at 1 AU from the Sun. The further away from the Sun, the less light the object re-emits and reflects, and the more difficult it is to detect. The following bonuses and penalties should apply according to the distance. The modifiers below can be used for the listed planetary distances. The numbers in brackets are the distances to the Sun in AUs.
| Orbit | Distance (AU) | Modifier |
|---|---|---|
| Mercury | 0.4 | +3 |
| Venus | 0.7 | +1 |
| Earth | 1 | 0 |
| Mars | 1.5 | -1 |
| Asteroids | ~3 | -3 |
| Jupiter | 5.2 | -4 |
| Saturn | 9.5 | -6 |
| Uranus | 19.2 | -8 |
| Neptune | 30.1 | -9 |
| Pluto | ~39.5 | -10 |
The energy of the life-support system is spent heating and recycling water and air. When hiding, it should be turned off while the passengers survive on the supplies for some time: two man-days per passenger place in the spacecraft (two per cabin, four per bunkroom, plus one per seat and one to eight in the control room). The temperature aboard the spacecraft would drop by 10°F per 1 hour × greatest SM of the vessel, but a minimum heating can be kept with low thermal emissions. If the spacecraft uses life-support, the detection bonus is +3 if there is only one crewman, +1 for a factor 2 above, +2 for a factor 4 and +3 for each factor of 10, etc.. (2 crewmen: +4, 4: +5, 10: +6, 20: +7, 40: +8, etc..) Radiothermal Generators (p. HF142) can not be turned off.
There are other ways to hide. A silent spacecraft in daylight can stand very close or in front of an asteroid or orbit about a planet at very low altitude. The back-lighting from the body then dazzles PESAs, which makes difficult to spot the reflected light: apply a -10 modifier. Orbiting a planet, this technique cannot last longer than half a period of revolution about the planet as the dazzling ends when reaching the horizon. Radars and ladars have no back-lighting issues.
Though γ- and X-rays sources are difficult to locate with precision, the infrared emitted by a fusion drive cooling system can easily be spotted. When the drive is in use, the SM of a spacecraft is not taken into account, but a detection bonus is added (see table Detection Modifier.)
| Modifier | Range | Notes | Modifier | Range | Notes | |
| +30 | 150 mi | +49 | 1 ls | medium PESA | ||
| +31 | 200 mi | +50 | 1.5 ls | |||
| +32 | 300 mi | +51 | 2 ls | large PESA | ||
| +33 | 450 mi | +52 | 3 ls | |||
| +34 | 700 mi | +53 | 4.5 ls | |||
| +35 | 1,000 mi | +54 | 7 ls | |||
| +36 | 1,500 mi | very small radar/ladar | +55 | 10 ls | ||
| +37 | 2,000 mi | +56 | 15 ls | |||
| +38 | 3,000 mi | +57 | 20 ls | |||
| +39 | 4,500 mi | +58 | 30 ls | |||
| +40 | 7,000 mi | +59 | 45 ls | |||
| +41 | 10,000 mi | small radar/ladar | +60 | 70 ls | ||
| +42 | 15,000 mi | very small PESA | +61 | 100 ls | ||
| +43 | 20,000 mi | medium radar/ladar | +62 | 150 ls | ||
| +44 | 30,000 mi | +63 | 200 ls | |||
| +45 | 45,000 mi | large radar/ladar | +64 | 300 ls | ||
| +46 | 70,000 mi | +65 | 1 AU | |||
| +47 | 100,000 mi | small PESA | +66 | 1.5 AU | ||
| +48 | 150,000 mi | +67 | 2 AU |
Detection Modifiers (use only the highest bonus, if two or more are equal, add +1):
The modifiers below are for 1 space of drive, add +1/+2/+3 for a factor 2/4/10:
For example, a Sudbury-class (p. TS193, average SM: +8) coasting in the asteroids (sun distance modifier: -3) can be easily detected from a distance of 7 light-seconds with a medium PESA (+49) if running without life-support. If it is trying to reduce its emissions by facing the Sun, the SM of +6 is used (total +3), for a detection distance of 3 light-seconds, which is safe in the Belt. If only the heaters are on and assuming 10 passengers, the bonus is +3, equal to that due to the heating and light reflection from the Sun. So adding +1 for a total of +4, the Sudbury is detectable at 4.5 light-seconds. If the full life-support system is on for 10 passengers (+6), the heat release becomes much higher than the radiation due to the Sun, and the vessel can be detected up to 10 light-seconds. Finally, if the engines are switched on (100 Pulse Drive), the bonus jumps to +17, which makes possible to spot the spacecraft up to 1.5 AU. However, the X and γ radiations can be seen from anywhere in the Solar System.
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