On 28 October 2014, the International Space Station (ISS) Program approved development of the Debris Resistive Acoustic Grid Orbital Navy-NASA Sensor (DRAGONS) as an experiment to fly on the ISS, possibly as early as October 2016. The DRAGONS is a calibrated impact sensor designed to directly measure the ISS orbital debris environment for 2 to 3 years.
The sensor will have about 1 m2 of detection area mounted at an external payload site facing the velocity vector to maximize detections. As shown in Figure 1, it combines observation techniques to measure the size, speed, direction, time, and energy of small debris impacting the sensor. The front layer of DRAGONS is a thin film of Kapton with acoustic sensors and a grid of resistive wires. These acoustic sensors will measure the time and location of a penetrating impact, while a change in resistance on the grid when lines are broken will provide a size estimate of the hole.
The relationship between object size and hole size will be determined by hypervelocity testing under controlled conditions at the White Sands Test Facility in New Mexico and at the University of Kent at Canterbury, UK.
Located 15 cm behind the first layer is a second thin layer of Kapton with acoustic sensors to measure the time and location of the second penetration. Velocity is determined by dividing the distance travelled between the first and second impact points by the time it took to travel that distance. An instrumented back layer will stop the debris and measure the amount of energy in the collision. With energy (E) and velocity (v), we can solve for mass (m) in the equation: E = ½ m * v2. Finally, the density of the object can be estimated if we assume that the object volume is about the same as a sphere with a diameter determined from the hole size. Density is an important feature of debris because an object made of steel (7.9 g/cc) will do more damage than a similarly sized piece of aluminum (2.8 g/cc).
The DRAGONS should be able to detect debris as small as 50 microns and will collect statistics on objects below 1 mm, illustrated in Figure 2. Results from this experiment will update information previously obtained by inspecting hardware returned from space by the Space Shuttle. This flight demonstration will also prove the viability of the technology for future missions at higher altitudes where risks from debris to spacecraft can be greater than at the ISS altitude.
The decision by the ISS Program to fund and fly DRAGONS marks a major milestone in the history of the project. The DRAGONS team includes the NASA Orbital Debris Program Office, the NASA Hypervelocity Impact Technology group, the NASA/JSC Engineering Directorate, Jacobs, the United States Naval Academy, the Naval Research Lab, Virginia Tech, and the University of Kent. See our previous article on DRAGONS in ODQN, vol. 16, issue 3, July 2012, pp. 2-3 <http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ ODQNv16i3.pdf>.
Update since release in the ODQN, vol. 19, issue 1, January 2015: The Debris Resistive Acoustic Grid Orbital Navy-NASA Sensor (DRAGONS) will be renamed Space Debris Sensor once onboard the International Space Station.