Physics and Astronomy

Clemson Team Returns to Poker Flat Research Range for MTeX Mission

The Spring 2013 issue of Schrödinger’s Tiger described the Department’s participation in the newly awarded NASA sounding rocket experiment “MTeX,” led by the University of Alaska to study turbulence in the mesosphere-lower thermosphere region. During the holiday break of 2014/2015 I was fortunate enough to travel with Clemson coinvestigator Dr. Gerald Lehmacher to Fairbanks for a one-week period to see firsthand the preparation for the launch of two sounding rockets with MTeX science payloads at the Poker Flat Research Range. With the launch window opening a week after our visit, we mainly oversaw the assembly of the payloads and prepared the CONE ionization gauge before it became inaccessible under the nosecone. The MTeX mission aimed to explore ways in which meteorological conditions can influence the impact of solar radiation received by the atmosphere.

With neutral density as a tracer, turbulence measurements during specific atmospheric conditions of a mesospheric inversion layer allow us to identify a representative distribution of turbulence activity and, thus, better characterize turbulent transport in the upper atmosphere between 60 and 120 km. Two rockets were launched on January 26, 2015 at 00:13 and 00:46 a.m. in order to obtain in situ measurements of turbulence, density and temperature. With the CONE ionization gauge, turbulence is identifiable as small oscillations of 0.1 to 1% in the observed ion current, which is proportional to density. The remaining instruments in the science package (positioned on the four deployable booms) measured aspects of atmospheric plasma using different forms of Langmuir probes, as well as an impedance probe. As a significantly cheaper and as yet unproven method of measuring turbulence and density variations, a three-axis MEMS accelerometer was included in the payload, the subject of my research for the past few semesters. The plasma and accelerometer experiments were built by Embry-Riddle Aeronautical University. Working with Dr. Lehmacher, the Sounding Rocket Instrumentation Creative Inquiry section has explored how we might be able to use the output of the sensitive accelerometer to provide a further means of measuring the atmospheric drag and density. With micro-g resolution and 5 kHz sampling rate, I have previously characterized the amount of noise present in the signal by spectral analysis on data from drop tests performed from the breezeway, as well as at rest in the lab. With the rockets having recently flown we now have flight data and will use it to potentially verify some structures seen by CONE and later calculate drag coefficients of the rocket in flight. The observed accelerometer shows 35 seconds of in-flight measurements. During this period of time, the rocket is being configured for the upward leg science window of the flight. We first see a period of intense modulation from the rocket engine which tapers off as the second stage motor burns out. Then spin effects and precession of the rocket’s velocity vector are visible from 40 seconds to 50 seconds. At this point the nosecone is ejected from the payload. When the nosecone and its shroud clear all the instruments, it is pushed out of the same trajectory as the payload by ejecting a slug radially at high velocity. The despin stage then brings down the rotation rate to 2 Hz followed by booms deploying and payload separation in rapid succession. As final preparation for measurement, attitude control systems further adjust the spin rate and orientation.

Another part of my experience was the lidar which was also at Poker Flat. This technology was used to measure the telltale temperature structure indicative of a mesospheric inversion layer needed for launch. Using powerful pulsed solid-state and dye lasers, certain atmospheric constituents left from meteorite trails are excited and the resulting photons are collected or, (in case of a Rayleigh lidar), backscatter from nitrogen and oxygen is observed to determine counts and doppler shifts at heights from 40 km to over 100 km. With the Rayleigh lidar, a brilliant green beam was visible shooting into the atmosphere that was truly an amazing sight. The facility also operates an iron lidar, which requires an ultraviolet laser and is, thus, invisible to the human eye. We stayed into the night to watch as a team of graduate students and Dr. Richard Collins, who is also the principal investigator of MTeX, calibrated and operated the system and obtained a temperature profile in preparation for the launch window.

Lastly we did indulge in a bit of tourist allure on our expedition to the final frontier. Heavily layered and armed with a rudimentary knowledge of photography, we stayed late into the night atop Ester Dome to watch the aurora. The hours of 10 p.m. to 2 a.m. were filled with spurts of activity in green from atomic oxygen, as well as periods of nothing more than a dull glow. After tweaking a few camera settings, we obtained some reasonably picturesque scenes of green ribbons decorating the sky. Then as we gave up for the night already quite content with the show, we were blown away by striking white and pink streaks which writhed and darted about at a rapid pace. These colors only show up as a combination of the same green and a red also produced by atomic oxygen at higher altitudes only visible during periods of high solar fluxes.

– Brandon Burkholder, Graduating Senior 2015