Dr. Mortari is working on the field of spacecraft dynamics and control. Current research efforts include developing novel constellations (such as Flower Constellations), space debris removal (TAMU Sweeper), spacecraft attitude estimation and k-vector range searching. He is also developing optical planetary-based navigation under NASA for use in the Orion capsule.
The need for more complex, versatile and powerful satellite systems today and in the future is increasingly being noticed. Dr. Mortari, with collaboration with M. P. Wilkins, C. Bruccoleri and J. J. Davis invented a new way of determining and designing satellite constellations, termed Flower Constellations.
The design of artificial satellite constellations is gaining importance both for classical applications, such as telecommunications and global navigation (GPS or GPS-like), and for the more innovative concepts of very large aperture interferometry in space (SAR and InSAR systems). It is expected that the next generation of satellites will feature more cooperation of smaller, redundant, and less expensive spacecrafts. The cooperation of a number of spacecrafts can be accomplished using formation flying or constellation schemes. The real difference between the two concepts of formation flying and constellation is actually unclear. However, the terminology commonly used identifies a constellation when the inter-satellite distances are very great (higher than a few kilometers), while formation flying identifies much shorter inter-satellite distances (lower than a few kilometers). We have adopted the name of “Flower Constellations” (FCs) because – theoretically – there is no upper limit to the inter-satellite distances.
A literature research on the constellation subject reveals that constellations have been used in order to assure coverage of an area on the ground for communications (COBRA, LOOPUS), for global navigation GPS, Galileo, and for surveillance (i.e. Molnyia Orbits). During the last two decades a number of new constellation concepts, similar in nature, have been developed. Mainly these constellations are built upon a subset of the existing many categories of satellite orbits: Low Earth Orbits (LEO), Molniya (a subset of Highly Eccentric Orbits – HEO), TUNDRA orbits, Geosynchronous/Geostationary Earth Orbits (GEO). However, up to now, no general theory of constellations exists that helps the engineers in achieving the desired coverage or to satisfy a different specific mission target.
Due to the inherent complexity of the general constellation design, the Walker constellations, which use circular orbits, became so popular and are the most common type encountered in practice, while HEO based constellations are rarely used.
The theory of Flower Constellations poses no constraint in the kind of orbits to be used. The Flower Constellations can be made using circular or elliptical orbits, and equatorial or inclined orbits. The resulting dynamics present interesting features that the Flower Constellations Visualization and Analysis Tool (FCVAT) greatly help to exploit. These FCs are of interest in the telecommunications industries for their ability to address global and regional telecommunications coverage in those areas where there is poor reception from GEO satellites (i.e. Northern Europe).
Mortari et al, have introduced the Flower Constellations as a general theory for the design of very wide class of constellations. It has been also proved that many of the previous constellations, including but not limited to the GPS and Galileo, can be easily reproduced as Flower Constellations.
Below is a video of a proposed wide coverage constellation. The video illustrates the coverage provided on a Cartesian projection of Earth.
This other video provides the same constellation’s satellites’ viewed from above Earth.
Space Debris Removal through TAMU Sweeper
Orbital debris is a well established and universal concern for space flight, and forecasts predict the problem will grow exponentially worse. China’s successful anti-satellite test in 2007, and the collision of Cosmos 2251 and Iridium 33 in 2009 have illuminated the issue in the public eye. In LEO alone, 500,000 pieces of manmade clutter larger than 0.04 inches endanger human and craft alike. Addressing this issue is nontrivial. Traditional satellites and mission structures are not efficient enough; successively transferring orbits to collect debris consumes excessive fuel. Several ideas have been proposed to interact with debris at a distance (such as lasers and ion guns); however, they are often viewed as potential weapons, eliminating them as options due to political sensitivity.
To remedy this situation, the recently proposed TAMU Sweeper mission structure plans to put a twist on traditional missions that will improve their fuel economy to make them feasible. In the same way that gravity assists take advantage of existing momentum in the broader system to extend the capabilities of a spacecraft, TAMU Sweeper steals momentum from the debris field to save fuel. The key to unlocking the advantages of these opportunistic methods is executing specific and well timed maneuvers. Our objective in this paper is to establish the cornerstone of this technique: a trajectory sequence optimization method that effectively and efficiently interacts with debris for removal.
Below is a video that describes TAMU Sweeper operations.
K-Vector Range Searching
The k-vector search technique is a method designed to perform extremely fast range searching of large databases at computational cost independent of the size of the database. k-vector search algorithms have historically found application in satellite star-tracker navigation systems which index very large star catalogs repeatedly in the process of attitude estimation. Recently, the k-vector search algorithm has been applied to numerous other problem areas including non-uniform random variate sampling, interpolation of 1-D or 2-D tables, nonlinear function inversion, and solution of systems of nonlinear equations. In instances where these tasks must be performed repeatedly on a static (or nearly-static) data set, k-vector-based algorithms offer an extremely fast solution technique that outperforms standard methods.
For more on k-vectors, click here.
In addition, Dr. Mortari has taught at the School of Aerospace Engineering of Rome’s University, and at Electronic Engineering of Perugia’s University. He received his doctor degree in Nuclear Engineering from University of Rome “La Sapienza”, in 1981. He has published about 250 papers, holds U.S. patent, and has been widely recognized for his work, including receiving best paper Award from AAS/AIAA, two NASA’s Group Achievement Awards, the 2003 Spacecraft Technology Center Award, and the 2007 IEEE Judith A. Resnik Award. He is AAS Fellow, AIAA Associate Fellow, IEEE Senior Member, IEEE Distinguish Speaker, and Honorary Member of IEEE-AESS Space System Technical Panel.
Dr. Mortari is Associate Editor of AAS The Journal of the Astronautical Sciences, of International Journal of Navigation and Observations, of IEEE Transactions on Aerospace and Electronic Systems, of Frontiers in Aerospace Engineering, and of Theory and Applications of Mathematics & Computer Sciences.