3 ms·

> purpose-built ABM systems use infrared imagers for terminal guidance What kind of optical window for the IR imager gets used for this application?

by zkms 9y ago

jandrewrogers 9y ago
The materials tech is pretty amazing, and they've been building it since the early 90s. At least in the past, they were using sapphire crystals and diamond films that have tiny cooling conduits drilled through them with lasers so that you can run (IIRC) liquid helium through the crystals as a coolant. Even in this configuration, the ablation and thermal loading due to hypersonic transit through the atmosphere has proven to be so high that the optical window is covered in ablative shielding for the first part of the flight, where the terminal guidance package is not much use anyway. Once the missile is within terminal range, the ablative shield is removed and it switches to homing mode. Early tests didn't have the ablation shield, and the damage to the optical window was sufficiently high that the imager lost effectiveness. The performance envelope within atmosphere of the rocket motors they use for ABM is high enough that it really pushes materials engineering to the breaking point.
- killjoywashere 9y ago
  > sapphire crystals and diamond films that have tiny cooling conduits drilled through them with lasers so that you can run (IIRC) liquid helium through the crystals Citations, pleeeeassse! I neeeeed it!
  - joshwa 9y ago
    A reference to "seeker cryo-cooldown" in this video about a THAAD test: https://youtu.be/0z0l0NsMduQ?t=233 https://youtu.be/0z0l0NsMduQ?t=233
    - kijiki 9y ago
      That is probably about cooling the sensor. High-sensitivity IR sensors need to be cooled so thermal noise from the sensor itself doesn't wash out a weak IR signal. Fighter aircraft provide liquid nitrogen to captive IR missiles.

3 ms·

> purpose-built ABM systems use infrared imagers for terminal guidance What kind of optical window for the IR imager gets used for this application?

by zkms 9y ago

> purpose-built ABM systems use infrared imagers for terminal guidance What kind of optical window for the IR imager gets used for this application?

jandrewrogers 9y ago
The materials tech is pretty amazing, and they've been building it since the early 90s. At least in the past, they were using sapphire crystals and diamond films that have tiny cooling conduits drilled through them with lasers so that you can run (IIRC) liquid helium through the crystals as a coolant. Even in this configuration, the ablation and thermal loading due to hypersonic transit through the atmosphere has proven to be so high that the optical window is covered in ablative shielding for the first part of the flight, where the terminal guidance package is not much use anyway. Once the missile is within terminal range, the ablative shield is removed and it switches to homing mode. Early tests didn't have the ablation shield, and the damage to the optical window was sufficiently high that the imager lost effectiveness. The performance envelope within atmosphere of the rocket motors they use for ABM is high enough that it really pushes materials engineering to the breaking point.
- killjoywashere 9y ago
  > sapphire crystals and diamond films that have tiny cooling conduits drilled through them with lasers so that you can run (IIRC) liquid helium through the crystals Citations, pleeeeassse! I neeeeed it!
  - joshwa 9y ago
    A reference to "seeker cryo-cooldown" in this video about a THAAD test: https://youtu.be/0z0l0NsMduQ?t=233 https://youtu.be/0z0l0NsMduQ?t=233
    - kijiki 9y ago
      That is probably about cooling the sensor. High-sensitivity IR sensors need to be cooled so thermal noise from the sensor itself doesn't wash out a weak IR signal. Fighter aircraft provide liquid nitrogen to captive IR missiles.