To completely describe the orientation of an object in three-dimensional space requires three angles, the most commonly known of which are called Euler angles. The device in the video on the left is our first three-axis gimbal system. Initially made of PEX pipe and PVC, Drury University physics major Miles Moser added DC motors with optical encoders to each axis. Slip rings pass power and data to and from the inner rings. A model object is fixed within the inner ring (in this case a globe of the earth), and with commands sent from an Arduino, and feedback from the optical encoders, the system allows the user to put the object into any desired rotation state. Rotation about each axis is governed by a PID controller. The best thing about it is that it looks really cool in operation. However, our acquisition of a 3D printer allowed for a higher fidelity version (see below).
Below: the original gimbal system holds a glowing earth ball.
Right: Drury student Miles Moser presents the motorized device at the Republic Middle School Science Night event. (February, 2016)
One goal for the Drury Observatory is to gather light curves (total light versus time) of catalogued debris objects as they pass over the site, and to compare them with simulations created using the Drury Optical Measurements Lab (see below), in order to attempt to determine the rotation state of the observed object. Such data is critical if NASA is to perform Active Debris Removal of such objects in the future. The video on the left is a simulation of a cylindrical rocket body in a specific orbit, passing over an observatory located at specific coordinates on the earth. The magenta, yellow, and green lines show the rotation axis, the direction toward the sun, and the direction toward the observatory, respectively. The yellow and red graphs on the right represent the expected specular (mirror-like) and diffuse light curves (total light versus time) received by the telescope. This simulation was produced with Matlab by Dr. Ojakangas under contract with NASA.
A proposal was made to the Missouri Space Grant Consortium in the Fall of 2016 for funding with which to pursue the goals described here, using the Drury University Observatory together with the Drury Optical Measurements Lab. A copy of that proposal is here. This was an innovative proposal that would leverage the needs of Drury students to achieve valuable information. The proposal was denied, with no explanation whatever, despite repeated requests for such data.
Above three images: Drury student and 3D printing guru Sage Kaneko works on the 2nd generation gimbal system, which was originally designed by Miles Moser, under the direction of Dr. Ojakangas. The video on the right shows the machine in motion. The new version uses stepper motors instead of DC motors. With plentiful help from Sage Kaneko and others, the device was displayed at the Republic Middle School Science night a few years ago. The white object in the middle is a 3D printed model of an SL-8 rocket body — a common type of large discarded object orbiting the earth. A primary reason for the new gimbal system is for research into the rotation states of orbital debris objects (see below).
Drury Optical Measurements Lab (DOML)
DOML consists of the experimental equipment shown in Figure 1. At the center is a system of three motorized gimbals; small models of catalogued LEO debris objects are conceived in Autodesk Fusion 360, printed using a Taz6 3D printer, and hand-painted appropriately. They are suspended in the innermost ring with thin, dark colored wires. The three gimbal rings are made of black printer material so as to reflect a minimal amount of light. A prototype of this device was recently constructed at Drury University. In its final form, a xenon arc lamp, simulating the sun, will be mounted on a rotatable arm, driven by a stepper motor and Arduino microcontroller so that the lamp can be moved by computer commands to chosen locations in a 360° angular range. Figure 2 (far right) shows the plan for using this system to better understand light curves from catalogued orbital debris objects.
Using the physics program’s Taz 6 3D printer, several students have created scale models of known space debris types (left) , the largest of which are rocket bodies. These are suspended in the inner ring of the gimbal system and illuminated by an artificial sun residing in a chosen location. As the object rotates in a prescribed manner, images are taken by a digital camera through a long cardboard tube, the inside of which is painted black. All pixels in each image are added together, creating a simulated light curve, for comparison with actual data collected at the Drury University Observatory. The camera is identical to one in use in the observatory.
Right: Drury University students Cale Martin and Jaxon Adams use the Drury University Optical Measurements Lab (DOML) to gather images as a model rocket body rotates.
