Dr. Ojakangas has had a long history studying orbital debris for the NASA Johnson Space Center Orbital Debris Program (https://www.orbitaldebris.jsc.nasa.gov/). He worked full time at JSC as an orbital debris scientist for three years, under then-director Donald Kessler (see Kessler Syndrome). Ojakangas then left to pursue a career in academia, but he has continued to work as a consultant on an as-needed basis for more than 20 years.
This page just shows a few brief examples of some of his work for NASA.
Having helped develop NASA’s original full-scale model of the orbital debris population in orbit about the earth, his consultant work has involved hunting for errors in the massive EVOLVE code (which has since been replaced by another program). At the right, Dr. Ojakangas hunts for an error in the massive EVOLVE program.
Below: Catalogued debris objects shown at a particular date, orbiting the earth. These debris are currently generating a slow runaway, whereby collisions between objects generate hundreds to thousands more dangerous debris objects, which in turn collide with others with kinetic energy similar to that released by high explosive.
Generally, at a particular time, the probability of collision between objects in two different orbits is zero, because the orbits don’t touch. However, primarily due to the non-spherical mass distribution of the earth, orbits about the earth precess (or drift) , in a few different ways. This drift causes them to sweep out volumes in orbital space, leading to a nonzero collision probability when averaged over time, in many cases. The sum of the collision probabilities between all pairs of orbits determines the probable rate of collisions in earth orbit at any time. These collisions are of major concern to active satellites as well as manned missions, since each major collision generates typically hundreds to thousands of new debris objects, leading to runaway growth of the orbital debris population. The graphic at the left was created to graphically represent the probability of collision between two specific precessing orbits. [source: G.W. Ojakangas, on contract for NASA]
As a debris object orbits the earth, it also rotates, and as it does so, it reflects sunlight. Usually these objects are too far away and/or too small to resolve in a telescope, but telescopes can be used to measure the total amount of sunlight received at the telescope aperture versus time. This is known as a light curve. Dr. Ojakangas’ most recent work for the JSC orbital debris program involved simulating the light curves for various laser-scanned and other model debris objects as they rotate in outer space. The graphic on the left (top) shows the diffuse (red) and specular (i.e. mirror-like, yellow) light curves for a “flake-like” fragment, simulated in Matlab. Unit quaternions are four-dimensional complex numbers that lie on the surface of a 4D sphere, each point of which represents a unique orientation. The three-dimensional projection of all of these orientations is a solid sphere(lower right). For a given solar phase angle, the graphic on the lower right shows all possible orientations, color-coded by their brightness. The yellow curve is a trajectory of orientations for the object as it rotates [source: Dr. Ojakangas under contract with NASA].
Orbital debris objects of modest size, under the influence of solar radiation torque, exhibit rapidly varying rotational characteristics. The graphic at the left displays some of these.[source: Dr. Ojakangas under contract with NASA].
At one point, NASA officials were so impressed by the graphical depictions of space debris Ojakangas was routinely creating, that they framed some of them and gave them to the Chinese government on a diplomatic mission. One of these graphics is shown on the left. This graphic depicts the catalogued debris from the explosion of a Chinese Long March rocket body while in orbit. Obviously, these gifts were given to the Chinese for more than their artistic value. Orbital debris is a growing problem that must be addressed by all space-faring nations.
Right: This figure shows results of a model developed by Ojakangas in order to describe the growth over time of three sizes of space debris objects – large (>1m), medium (10cm – 1m) and small (< 10cm). In this simplified model, the debris population evolves (yellow curves are examples) toward the point of intersection of the three surfaces shown.
On the left is a graphic showing simulated light curves (top) for a synthetic pinwheel-shaped orbital debris object created by Ojakangas in a mathematical simulation. Under the influence of solar radiation pressure, the pinwheel-shaped orbital debis object undergoes complex orientation changes described using three-dimensional projections of four-dimensional unit spheres called quaternions (bottom). This graphic was part of a powerpoint presentation given by Ojakangas, for NASA, at the the world-premiere space situational awareness conference in Maui, known as the AMOS conference in 2011.