Landing Area and Rocket Plume Diagnostics

Systems & Processes Engineering Corporation (SPEC) proposes a Plume Diagnostic Coherent LADAR, composed of a pair of orthogonally mounted, high rep rate, spectrally tuned, coherent wind LADARs to perform a 3D mapping and diagnostics of the rocket plume and landing area debris, and plume and debris velocities during a rocket vertical descent/ SPEC has developed several wind LADARs and other long range coherent LADARs and our most recent LADAR development uses technology developed for SPEC's MDA next generation missile intercept sensor, a coherent LADAR with 200km range with Inverse Synthetic Aperture LADAR (ISAL) imaging capability. The LADAR uses 1550nm eye-safe wavelength with narrow band, 1kHz seed fiber and transmits a phase encoded pseudo random number (PRN) pulse.  Our MDA program studying forward looking LADAR transmission through hypersonic plasma has shown this transmit frequency operates between emission lines and, due to its narrow bandwidth and tight field of view, has minimum bremsstrahlung radiation interference.  This effect was also shown by 1550nm LADAR imaging through fire balls at the Texas A&M University (TAMU) fire lab.   SPEC is developing a multi-channel, long-range Wind Measurement LADAR System for measuring wind fields with high temporal resolution and fidelity. The planned system has roots in single-channel fiber optic-based, eye-safe wind LADAR, initially designed by SPEC for UAV systems and brought to a breadboard level on Army and NASA programs. The system uses telecom fiber components to optimize the combination of performance, low cost and miniature sizing. The sensor assembly is composed of a SPEC wind LADAR using a fiber optic transceiver consisting of a narrow band seed, acousto-optic modulator (AOM) for frequency shifting, an optical modulator for pulse forming, a three-stage rare-earth doped fiber amplifier, and a coherent receiver, all operating at an eye-safe wavelength of 1550 nm. The LADAR uses phase-encoded pulse trains, which support a signal to noise improvement of 13:1 over conventional LADAR operation by utilizing a Barker-13 pulse compression code. In the current system, a new higher bandwidth receiver will allow for a 1023-pulse long waveform with pseudo random number (PRN) pulse encoding, yielding a 1000:1 improvement in signal to noise. This LADAR achieves air current Doppler detection beyond 6 km.  This latest generation will use 16 channels combined with a high speed Risley prism scanner to accomplish video rate 3D imaging of wind, dust and solid objects, including their velocities.  The key to capturing the dynamics of the rocket plume is fast frame rate and high velocity resolution.  Obviously, the doppler resolution drops to zero if the wind/dust is perpendicular to the line of sight.  By using two LADARs with perpendicular lines of sight, all voxels (volume pixels) can be viewed and high accuracy velocity can be measured.