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Virginia Tech RockSat-X Payload


   

Virginia Tech RockSat-X Payload


Feb. 4, 2013 –

By: Stephen Noel and Robbie Robertson

Virginia Tech’s RockSat-X team is tasked with designing and building a sounding rocket payload, Nitric Oxide and Dust Detector Experiment (NODDEX), for launch in the 2012 RockSat-X Program. NODDEX will include an optical Nitric Oxide (NOx) sensor, a Piezo Dust Detector (PDD) CubeSat instrument, two inertial measurement units (IMU’s), and an aperture vacuum seal release mechanism for the Space Barometer (S-Bar) CubeSat instrument. The RockSat-X program is a low cost opportunity to launch university funded payloads into space on a sounding rocket. Coordinated by the Colorado and Virginia and Space Grant Consortia in cooperation with NASA Wallops, this program strives to give undergraduate students the opportunity to build spacecraft payloads and perform interesting and relevant experiments in Earth’s upper atmosphere and space. Design of the payload requires strict adherence to NASA guidelines in addition to communication and cooperation with the principal investigators of each experiment.

Developed by Dr. Rene Laufer’s group at Baylor University, the PDD will collect data on small dust and debris particles in LEO. The PDD uses multiple piezo sensor elements and charged detection grids to collect data on dust particle velocities, impact energy, number of impacts, and time and relative direction of particle impacts. The PDD detects dust particles between nominal diameters of 1 μm and 1 mm with velocities of less than 12 km/s. The current model provides a data rate of 150 kBytes/day and runs on less than 3 W while designed to fit in half of one CubeSat Unit (500 cubic centimeters). The flight heritage provided by the RockSat-X flight will assist Baylor University in flight qualification of the PDD.

The NOx sensor has flight heritage (two flights) on RockSat-C sounding rocket missions, but this summer’s RockSat-X flight will mark the first time the NOx sensor will have a full un-obscured field of view of Earth’s upper atmosphere. The NOx sensor uses an optical bandpass filter which passes only light in a small band around 220 nm, a custom sensor housing designed by our team, and a UV photodiode to collect NOx concentration data at various points in the upper atmosphere. Electronics for the NOx sensor include a high gain transimpedance amplifier from Femto Corp. followed by a second amplification board designed by our team to create three separate final output signals. Each of the three output signals will be amplified versions of the single input using a different gain factor, with the three gain factors optimized to provide the best balance of measurement resolution and robustness. Design, testing, and implementation of the NOx sensor are being carried out under the advisement of Dr. Scott Bailey, the primary investigator for the NOx sensor.

One of the two NODDEX IMU’s, the Memsense μIMU, has been flown on three Virginia Tech RockSat-C payloads with success each time. The second NODDEX IMU is a VectorNav VN-100 Rugged. The VectorNav VN-100 Rugged is the world’s smallest IMU that provides real-time 3D orientation data. The performance of the VN-100 in the space environment is important to us because Dr. Henderson is interested in using it for CubeSat attitude determination. The NODDEX flight will allow us to compare data from the proven Memsense IMU and the unproven VectorNav IMU to evaluate its effectiveness in the space environment.

S-Bar is a technology demonstrator CubeSat instrument being developed in Dr. Greg Earle’s Space Plasma Instrumentation Lab at Virginia Tech. The instrument is part of the joint Virginia Tech and University of Illinois LAICE CubeSat which recently won a launch through NASA’s ELaNa program. The instrument must remain vacuum sealed until on orbit, at which point the vacuum seal over the aperture to the instrument must be released and removed from the field of view of the aperture. A vacuum cap release mechanism has been designed, prototyped in plastic, and tested. The NODDEX flight will include a finalized, aluminum mock-up of the top surface of the S-Bar instrument with the aperture and vacuum cap release mechanism. At the apogee of the rocket flight, NASA will activate a timed power line and a thermal knife on the release mechanism will melt a release cord. The release cord will break, allowing four latches compressing the vacuum cap to flip back. The vacuum cap will be pulled off of the aperture by a spring loaded arm composed of a hinge, torsion spring, and flexible spring-steel strip. Detector switches will be used to determine the exact timing of each of these events. Success of the S-Bar release mechanism through NASA testing at Wallops and the RockSat-X flight will significantly increase the technical readiness level (TRL) of the S-Bar instrument for CubeSat flight.