Lesson 28 Flashcards#
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1. State the multi-spectral fusion rule and what it means.
Detection is a union over bands, so the effective detection range is the largest band, not the average: \(R_\text{det} = \max_b R_b\). In plain terms — you are only as quiet as your loudest band.
2. Why is detection a union rather than an average across bands?
A fused defender is cued if any single band crosses its threshold. It needs only one band to succeed, so the band with the longest detection range decides when you are found.
3. What happens to \(R_\text{det}\) when you reduce a band that is not the limiter?
Nothing. The defender is still cued by the loudest band, so investment in a quiet band buys zero range — until that band actually becomes the limiter.
4. Why does \(R_\text{det}\) flatten as you cut the loudest band?
Cutting the loudest band lowers \(R_\text{det}\) only until it meets the next band, which then inherits the limit. Past that point more reduction on the old band does nothing — the curve flattens at the new limiter.
5. Name the two visual amplifiers that extend eye detection past a few km.
Contrails — engine water vapor freezing into a persistent, sky-wide ice trail — and glint, the brief but very bright specular flashes off the canopy, leading edges, and flat panels.
6. What counters the visual band, and what does not?
Tactics and finish counter it: contrail-avoidance routing and altitude, matte finishes, and low-reflectance paint to cut contrast. Radar-absorbing material does not — no coating hides a contrail.
7. Why is acoustic a minor band for a high-altitude bomber but dominant down low?
Sound is slow (~340 m/s) and lossy, fading with geometric spread and atmospheric absorption. A high-altitude slant range is long, so little reaches the ground; but low-altitude penetrators, helicopters, and UAS (blade-passage tones) are often heard first.
8. List L22's five IR signature components and their type.
Three emitters — hot parts (~700–900 K, MWIR), plume (CO₂ near 4.3 µm, MWIR), and aero-heated skin (LWIR) — and two reflectors — reflected solar (day) and reflected sky/earthshine.
9. Which IR band carries what, tail-on vs all-aspect?
MWIR carries the plume and hot parts, which dominate tail-on. LWIR carries the aero-heated skin, which is the all-aspect contributor.
10. What reads the IR signature, and why does it tie to L27's EMCON?
IRST and FLIR (L23) read all five components passively. Passive IR needs no emission of its own to intercept, so there is nothing for a radar-warning receiver to hear and nothing EMCON can deny it.
11. Why is EO/IR called "the band that never left"?
Radar can be shaped and absorbed and emitters can be silenced, but a hot engine glows on its own and a passive seeker collects that glow. Signature management can only manage which IR component is loudest, not remove the band.
12. What does thermal crossover hide, and what does it not?
It hides the LWIR aero-heated skin twice a day, when the skin temperature matches the background sky. It does not hide the MWIR plume, which is independent of the time of day.
13. How does this lesson's budget relate to L26 and L27?
It is the same loudest-first discipline, moved from within the RCS budget (L26) to across the whole spectrum. Cut the limiter, expect the problem to move to the next band, re-plan, and repeat — L27's materials and discipline being the last-decibel step within a band.
14. Which signature floors resist coatings entirely?
The eyeball floor — a contrail or a glint — and, tail-on, the engine plume. Below those there is nothing to coat, so further material investment buys no range.
15. Why is the loudest-band rule the core of Project 3?
Project 3 is a B-21 signature trade against a VHF surveillance radar, an X-band fire-control radar, and an IR MANPADS. The rule decides which investment actually buys survivability: spending on a non-dominant band is wasted, so the trade must attack the limiter and expect it to move.