L23 Pre-flight

L23 Pre-flight#

Block 3: IR EW and Signature Management — Lesson 23: IR Seekers, IRST, and FLIR Work this before L23. Pre-flights are never collected — in class, anyone may be cold-called to present any question at the board, and that recitation is the participation grade.

Assumed pre-class reading#

  • L22 wrap-up (five signature components, in-band intensity ranking rule, aspect and thermal crossover)

  • The Jupyter Book Reading page for L23 — the seeker / IRST / FLIR division of labor, reticle vs imaging seekers, why IRST is a passive radar with a ranging problem, and the passive detection range rule.

Quiz questions (5 items, ~5 minutes)#

Q1. (Multiple choice) A reticle seeker tracks a target by:

  • [ ] (a) Forming a full image and matching the target’s shape frame to frame

  • [ ] (b) Chopping the target’s energy with a spinning patterned disk and reading the modulation

  • [ ] (c) Transmitting a laser pulse and timing the return

  • [ ] (d) Comparing the target’s radar and IR returns

Q2. (Multiple choice) Why did imaging (FPA) seekers fundamentally change the countermeasure game compared with reticle seekers?

  • [ ] (a) They see a shape with spatial, spectral, and temporal structure, which a flare struggles to fake

  • [ ] (b) They detect at longer wavelengths where flares do not radiate at all

  • [ ] (c) They are active sensors, so decoys cannot blind them

  • [ ] (d) They have a wider field of view than any reticle seeker

Q3. (Multiple choice) An IRST is often called a “passive radar.” Which pairing correctly gives its biggest operational advantage and its biggest limitation?

  • [ ] (a) Advantage: high-resolution imagery; limitation: needs a human interpreter

  • [ ] (b) Advantage: emits nothing for the target’s RWR to detect; limitation: angles come easy but range does not

  • [ ] (c) Advantage: unaffected by weather; limitation: rear-aspect only

  • [ ] (d) Advantage: longer wavelength than radar; limitation: cannot track more than one target

Q4. (Short answer) In one or two sentences: using the rule \(R_{\max} \propto \sqrt{J\,\tau/\text{NEI}}\) and radar’s \(R_{\max} \propto \sigma^{1/4}\), explain why IRST systems are attractive against low-observable (stealth) aircraft.

Q5. (Multiple choice) Early IR missiles could only be fired from the target’s rear hemisphere, while later ones became all-aspect. What made the difference?

  • [ ] (a) Faster rocket motors that could catch a crossing target

  • [ ] (b) Larger warheads that removed the need for precise aim

  • [ ] (c) Cooled MWIR detectors that could see the exhaust plume, not just hot metal

  • [ ] (d) Radar mid-course guidance added to the missile

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