Carl L. Howlett

Measurements of ultraviolet radiation from a 5-km/s bow shock

Ultraviolet emission from a 5.1-km/s re-entry bow shock was measured in a sounding rocket experiment launched from the Barking Sands Research Range (Kauai, Hawaii) in February 1991 at 14:30 GMT. Optical data were obtained on the downleg portion of the flight as the pay load descended from 115 to 62 km in a very shallow trajectory at a nearly constant speed. The intensity of the ultraviolet spectrum (A200-400 nm), and the vacuum ultraviolet resonance radiation emitted by atomic oxygen and hydrogen at A130.4 nm and A121.5 nm, respectively, were measured. Data from optical instruments in the 200-400-nm spectral region is presented here. Langmuir probe measurements provided data on the total plasma density and electron temperature in the boundary layer over a limited altitude range.

Comparison of theory with experiment for the bow shock ultraviolet rocket flight

Comparison is made between the results obtained from a state-of-the-art thermochemical nonequilibrium flowfield and radiation code and data obtained from a recent experiment. The experiment obtained the first measurements of ultraviolet radiation from the shock-heated gas in the nose region of a 0.1016-m nose radius vehicle traveling at about 3.5 km/s at altitudes between 37-75 km. The preflight computations agree at low altitudes but underpredict the data at high altitudes. Postflight flowfield and radiation sensitivity studies suggest improvements for the models at high altitudes. Specifically, excitation mechanisms that contribute to production of NO gamma-band emission need to be revised. Altitude dependence of the radiation observed from the OH radical can be understood in terms of nonequilibrium chemistry in the flow.

Flight measurements of low-velocity bow shock ultraviolet radiation

The ultraviolet spectrum, atomic oxygen 130.4-nm radiation intensity, total plasma density, and electron temperature of a Mach 12 bow shock were obtained by a sounding rocket experiment launched from the Wallops Flight Facility (WFF) on April 25, 1990 at 12:32 a.m. Eastern Standard Time (EST). A two-stage, Terrier Malamute rocket which attained an apogee of 720 km was used in this experiment. Optical data in the 200400-nm wavelength range were obtained from 37 to 75 km at a vehicle velocity of 3.5 km/s at various locations on the 0.1016-m radius hemispherical dome. Electron probe and VUV OI 130.4-nm measurements were obtained near nose cone ejection at 37 km. This article presents a discussion of the instruments used and the key data obtained.

In Situ Plume Radiance Measurements from the Bow Shock Ultraviolet 2 Rocket Flight

The ultraviolet spectrum (200-400 nm) of the plumes generated by the second- and third-stage engines of a Strypi XI rocket and of the Mach 17 re-entry bow shock were obtained by a sounding rocket experiment launched from the Barking Sands Research Range (Kauai, Hawaii) on February 18, 1991, at 14:30 GMT. The re-entry optical data were obtained as the payload descended from 120 to 65 km with a vehicle velocity of 5.1 km/s. The intensities of the vacuum ultraviolet resonance radiation emitted by atomic oxygen and hydrogen in the bow shock at 130.4 and 121.5 nm, respectively, were also measured. Complementary Langmuir probe measurements provided data on the total plasma density and electron temperature in the boundary layer.

Theory of plume radiance from the bow shock ultraviolet 2 rocket flight

A computational fluid dynamics algorithm is used to simulate the flow field and solid rocket motor plume about the bow shock ultraviolet 2 flight vehicle. A new computationally efficient algorithm to model two-phase gas and particulate flow is developed. The flow over the complete rocket geometry and its interaction with the particle-laden plume is simulated. The computed plume radiance is compared with radiometric and spectroscopic data and good agreement with radiance magnitudes and spectral characteristics is obtained for the intrinsic core rocket exhaust data. The computation underpredicts the observed signal from the far-field photometers by many orders of magnitude. Based on the particulate flow simulations developed here and new experimental data, we hypothesize that the far-field radiation is due to molecular emission. Use of the CO Cameron band spectra obtained on this flight provides an estimate of the governing temperature of such radiation.

Utilizing UV and visible sensors on micro-satellites to demonstrate target acquisition and tracking

The Distributed Sensing Experiment (DSE) program is a technology demonstration of target acquisition, tracking, and three-dimensional track development using a constellation of three micro satellites. DSE will demonstrate how micro satellites, working singly and as a group, can observe test-missile boost and ballistic-flight events. The overarching program objective is to demonstrate a means of fusing measurements from multiple sensors into a composite track. To perform this demonstration, each DSE micro satellite will acquire and track a target, determine a two-dimensional direction and movement rate for each, communicate observations to other DSE satellites, determine a three-dimensional target position and velocity, and relay this information to ground systems. A key design parameter of the program is incorporating commercial off-the-shelf (COTS) hardware and software to reduce risk and control costs, while maintaining performance. Having completed a successful Critical Design Review, the program is currently in fabrication, integration, and test phase. The constellation of satellites is scheduled for launch in CY2009. This paper describes the status and capabilities of the UV and visible sensor payloads, as well as the algorithms and software being developed to achieve the DSE mission.