# Paul CefolaUniversity at Buffalo, The State University of New York | SUNY Buffalo · Department of Mechanical and Aerospace Engineering

Paul Cefola

Ph.D, Mechanical Engineering/Dynamics and Control

## About

133

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Introduction

**Skills and Expertise**

Additional affiliations

April 2001 - September 2004

July 1975 - March 2001

## Publications

Publications (133)

View Video Presentation: https://doi.org/10.2514/6.2022-1998.vid Rapid technical innovation in the aerospace field challenges the United States Air Force and Space Force. Just as the United States faced a perceived “missile gap” in the 1950s, the potential of a military “technology gap” is growing. Global competitors are investing heavily in aerosp...

The paper presents an open-source orbit determination application based on the Draper Semi-analytical Satellite Theory (DSST) and a recursive filter, the Extended Semi-analytical Kalman Filter (ESKF). The ESKF reconciles the conflicting goal of the DSST perturbation theory (i.e., large step size) and the Extended Kalman Filter (EKF) theory (i.e., r...

Space agencies generally use numerical methods to meet their orbit determination needs. Due to the ever increasing number of space objects, the development of new orbit determination methods becomes essential. DSST is an orbit propagator based on a semi-analytical theory. It combines the accuracy of numerical propagation and the speed of analytical...

The main goal of this research is to optimize low-thrust collision avoidance maneuvers for both the probability-of-collision between satellites and the propellant expenditure considering a J 2 perturbation model. As a first step, an indirect control method integrated with the current DSST software platform is presented in this paper. We apply numer...

Catalog maintenance for Space Situational Awareness (SSA) demands an accurate and computationally lean orbit propagation and orbit determination technique to cope with the ever increasing number of observed space objects. As an alternative to established numerical and analytical methods, we investigate the accuracy and computational load of the Dra...

The study presents an analysis of accuracy of observations which are contributing to the maintenance of space object catalogue. After quantifying the uncertainties in optical and radar measurements, the second part of the study presents the error within the mean element orbit determination procedure. A batch least square orbit determination method...

The study presents an analysis of the orbit determination process for maintenance of the space object catalogue. After quantifying the uncertainties in optical and radar measurements, the second part of the study presents the error within the mean element orbit determination procedure. A batch least square orbit determination method which makes use...

Among existing orbital propagation techniques, semi-analytical methods are of great interest: by separating the computation of long-term evolution from one side and the short-term variations from the other side, they tend to be significantly faster than classical numerical methods while keeping similar accuracy. The implementation of the Draper Sem...

The Hansen coefficients are one of the most important tools in the analytical or semi-analytical methods of celestial mechanics. The problem of efficient computation was investigated in detail in many papers, but this subject is still open and to date there are not standard algorithms to generate the Hansen coefficients with accuracy and good compu...

To ensure safe space operations, a catalogue with good ephemeris quality is required. Maintaining such a catalogue requires an accurate and precise orbit propagator that is not computationally resource consuming. Object densities in LEO, MEO and HEO regions are very high, which comprises of ∼85% of the current catalogued objects. For the purpose, D...

Semi-analytical propagation techniques are of great interest, as they aim to combine the accuracy of numerical techniques with the speed of analytical methods. Amongst them, the Draper Semi-Analytical Satellite Theory (DSST) stands out, with its extensive treatment of perturbations, its
exibility and also its maturity. Unfortunately DSST was for l...

Galileo operational orbits are slightly affected by the 3 to 5 tesseral resonance, an effect that can be much more important in the case of disposal orbits. Proceeding by canonical perturbation theory we show that the part of the long-term Hamiltonian corresponding to the non-centralities of the Earth's gravitational potential can be replaced by an...

High fidelity orbit propagation requires detailed knowledge of the solar radiation pressure (SRP) on a space object. The SRP depends not only on the space object's shape and attitude, but also on the absorption and reflectance properties of each surface on the object. These properties are typically modeled in a simplistic fashion, but are here desc...

The goal of the Draper Semi-analytical Satellite Theory (DSST) Standalone Orbit Propagator is to provide the same algorithms as in the GTDS orbit determination system implementation of the DSST, without GTDS's overhead. However, this goal has not been achieved. The 1984 DSST Standalone included complete models for the mean element motion but trunca...

Astrodynamies encompasses phenomena on diverse and disparate time scales. That solar electromagnetic atmospheric density proxies are developed every few hours demonstrates phenomena on that scale. In the most simple two body Newtonian formulation that includes only inverse square gravitation, there are equilibrium solutions that persist forever. Ti...

On time scales of interest for mission planning of GNSS satellites, the qualitative motion of the semimajor axis and the node evolves primarily from resonances with the Earth’s gravitational field. The relevant dynamics of GPS orbits, which are in deep 2 to 1 resonance, is modeled with an integrable intermediary that depends only on one angle, the...

Verification of the java Orekit implementation of the Draper Semi-analytical Satellite Theory (DSST) is discussed. The Orekit library for space flight dynamics has been published under the open-source Apache license V2. The DSST is unique among analytical and semi-analytical satellite theories due to the scope of the included force models. However,...

Currently, the number of space debris particles is about 33,500, out of which approximately 1100 are in geosynchronous orbits, which are tracked and whose orbital data are provided from US Space surveillance network, with instances of colliding and increasing the number of space debris. To further not exacerbate this situation, it is important to t...

With an increasing dependence on space systems in all areas of society, the need for accurate and robust Space Situational Awareness (SSA) is paramount. Despite this, software tools have been slow to progress; many systems remain in legacy languages, based on deprecated design principles. The Draper Semianalytic Satellite Theory (DSST) is one such...

The long-term effects of a distant third-body on a massless satellite that is orbiting an oblate body are studied for a high order expansion of the third-body disturbing function. This high order may be required, for instance, for Earth artificial satellites in the so-called MEO region. After filtering analytically the short-period angles via avera...

Orekit is a library for space flight dynamics. It was released under an open-source license in 2008 and has since gained widespread recognition. It has already been used operationally, it has been selected as the basis of new generation systems in agencies, it has been used for several studies and ground systems developments by various industrial a...

Global constellation coverage has been a topic of interest for many years. The Draim four-satellite continuous global coverage constellation offers improvement over traditional coverage constellations. We re-look at this constellation using new analytical search techniques, computational methods to assess the dynamic performance, and graphical depi...

A scalable second-order analytical orbit propagator program (AOPP) is being carried out. This AOPP combines modern and classical perturbation methods in function of orbit types or the requirements needed for a space mission, such as catalog maintenance operations, long period evolution, and so on. As a first step on the validation and verification...

We revisit the seminal 1961 paper of G. M. Clemence in light of the advances in the intervening 50 years. We review progress on the unsolved problems identified by Clemence, discuss the supporting technology now available, and give a list of currently unsolved problems. We note that the 1961 status still prevails in some current systems, denying si...

Two-line element sets have been in regular use for decades. As space centers have largely transitioned to numerical operations, the role of TLE's as an initial estimate tool seems only slightly diminished. Use in conjunction and other operations often requires a covariance, which is unavailable. The accuracy can be limited, but advancements have be...

The semi-analytical theory for the motion of a space object replaces the conventional equations of motion with two formulas: (1) equations of motion for the mean equinoctial elements, and (2) expressions for the short periodic motion in the equinoctial elements. Very complete force models have been developed for the mean element equations of motion...

An initiative within the realm of Space Surveillance Awareness (SSA) is to create an open source software suite that can provide all space actors access to the basic SSA analysis tools needed to operate safely and efficiently in space. These applications include observation compression, orbit propagators, state transition matrix, weighted least squ...

The technology of map projections is used to provide a new, reduced-distortion color visualization of the coverage characteristics of a multiple-satellite constellation vs. user earth-fixed latitude and longitude. While global visualization plots are exhibited in this paper, the method can also be "zoomed" to provide regional plots, such as only ov...

This paper shows an approach to improve the statistical validity of orbital estimates and uncertainties as well as a method of associating measurements with the correct resident space objects and classifying events in near realtime. The approach involves using an adaptive Gaussian mixture solution to the Fokker-Planck-Kolmogorov equation for its ap...

There is a growing international need for Space Situational Awareness (SSA), defined as knowledge of objects in Earth orbit and the space environment. Up until recently, the majority of SSA has primarily been done by the United States and Russia, which currently operate significant space surveillance tracking net-works and maintain catalogs of spac...

The accuracy of the orbital data products used for space situational awareness is affected by the evolution of the sensors collecting the data, the knowledge and control of the errors in the sensor network, the knowledge of the space environment, the available computing resources (both hardware and software), and the number of space objects to be m...

The semi-analytical theory for the motion of a space object replaces the conventional equations of motion with two formulas: (1) equations of motion for the mean elements, and (2) expressions for the short periodic motion. Very complete force models have been developed for the mean element equations of motion and for the short periodic motion. Ther...

This study used Optimal Control Theory to model the perturbations caused by continuous thrust. Fuel-optimal trajectories were calculated using numerical optimization techniques. Software was developed to calculate the optimal trajectories and associated thrust plans. A new force model was implemented in GTDS to accept externally generated thrust pl...

The NRLMSISE-00 density model and density corrections found using the dynamic calibration of the atmosphere process were implemented in GEODYN, the NASA GSFC Precision Orbit Determination and Geodetic Parameter Estimation Program. These updates are used in an attempt to improve the orbit precision of GEOSAT Follow-on (GFO). The corrections used in...

The threat of a tsunami in coastal communities is considerable, especially in the Pacific and Indian Oceans. Presently, the method of detection relies on bottom-pressure recorders connected to buoys. Another type of detection, which relies on microwave radiometry for deep-ocean sensing of tsunami, is proposed. Microwave radiometers are proposed tha...

Not long afterward, this model of the upper atmosphere became an integral part of the motion model for ballistic support of the international Apollo-Soyuz experiment. In 1977, the government standard USSR GOST 22721-77 "Upper Atmosphere Model for Ballistic Calculations" was drafted and approved. The standard established a method of calculating atmo...

Satellite maneuver detection is an important component of Space Situational Awareness. This report summarizes work done in an effort to develop a near-real time automated maneuver detection algorithm. Discussion and results for intermediate algorithms leading up to a chosen hybrid maneuver detection algorithm are included. Results for the hybrid al...

A spin-stabilized attitude determination capability was developed as a new feature in the Braxton Technologies Inc. Astro-Dynamics Environment (ADE). The attitude determination capability was implemented as a multiplicative extended Kalman filter. Because the design goal was to provide the maximum flexibility in solving for a fully dynamic spin sta...

The threat of a tsunami in coastal communities is considerable, especially in the Pacific and Indian Oceans. Current warning systems consist of two networks: (1) a network of seismometers, and (2) a network of sea level gauges and bottom pressure recorders. Bottom pressure recorders communicate with ocean surface buoys, which send the data to proce...

Satellite systems provide the most efficient and possibly the only means of achieving two-way global communications with mobile systems (ships, aircraft, and vehicular traffic). To date, such systems have used only circular orbits, either GEO or LEO. Medium altitude elliptical constellations, on the other hand, can provide an efficient and affordab...

This paper compares a selection of satellite constellations for possible future multimedia communications systems serving European customers. Systems considered include the LEO, MEO and GEO altitude ranges, and include both circular and elliptic arrays. The latitude range for European coverage was assumed to be 35N to 70N. The minimum elevation ang...

Since 1994 US and Russian space surveillance experts have held six space surveillance workshops. The 1994, 1998 and 2000 workshops were held at the US Naval Observatory in Washington, DC, the 1996 workshop was held in Poznan, Poland (in conjunction with the IAU Dynamics and Astrometry of Natural and Artificial Celestial Bodies Colloquium) and the 2...

This paper describes several recent developments in the field of elliptical Cobra Teardrop constellations, These eight-hour satellite constellations contain time-coordinated active arcs that merge at handover points to provide a continuous track in space so that no satellite-to-satellite antenna slewing is required. To a mid-latitude ground user, t...

The goal of this effort is to apply atmospheric density corrections to the NRLMSISE-00 model to provide a significantly more accurate orbit prediction and determination capability. Given that these corrections are statistical in nature, the end user must apply the corrections in a manner consistent with the way the corrections were generated. The c...

The operation of constellations in non-GEO space creates risks falling into three major categories: (1) physical collisions between operating satellites. (2) physical collisions with debris, and (3) electronic interference events. Electronic interference can be either up-link or down-link. For GEO systems frequency re-use is made possible by longit...

Repeat-ground track elliptic constellations present a viable way to provide coverage of mid to high latitude locales for broadband data communications. However, using electric propulsion for station keeping on these types of constellations is not yet well characterized. An automated technique formulated in equinoctial elements for determining a sta...

Errors in the upper atmosphere density models have a significant influence on the accuracy of orbit prediction and, specifically, on the accuracy of the prediction of the reentry time of space objects. The determination of current time corrections to the atmosphere density and their use in orbit prediction are proposed as a method for increasing th...

Elliptical, non-geostationary satellite orbit (NGSO) satellite constellations have been proposed as a solution to the problem of the shortage of slots in the Geostationary Ring for new communications satellites. These elliptical constellations have the potential to greatly multiply the available space real estate without interfering with the existi...

This study is intended to improve orbit determination accuracy for 3-axis stabilized geosynchronous satellites via an improved radiative force model. The macro-model approach, developed earlier at NASA GSFC for the TDRSS spacecraft, has been adapted for the UNIX version of the Goddard Trajectory Determination System (GTDS) at the MIT Lincoln Labora...

The unpredictable effects of atmospheric drag are the dominant error source in orbit determination and prediction of low altitude satellites. One prospective direction for increasing the accuracy of position prediction for these satellites is the organization of an upper atmosphere monitoring service. This would be the analog of the weather service...

This paper explores the characteristics of retrograde, Sun-synchronous elliptic orbits with line of apsides lying in or near the equatorial plane. Coverage plots for a five-satellite ring showing the number of satellites in view and elevation angle data versus latitude and local time are presented. Stability of the orbit is discussed. Also analyzed...

This paper begins an effort to compare the accuracy and timing characteristics of the Draper Semianalytical Satellite Theory (DSST) developed in the USA and the Universal Semianalytical Method (USM) developed in Russia. The DSST and the USM share several characteristics: Both employ the Generalized Method of Averaging (GMA) Perturbation Theory Both...

This paper investigates the properties of a new figure-of-merit for single-satellite orbits proposed by Draim: The coverage provided per unit of launch δV. This study limits orbits to critically inclined repeat ground track orbits. The coverage aspect of the figure-of-merit was investigated and found to exhibit complex behavior for certain cases. C...

Many inaccuracies in the determination and prediction of satellite orbits in the low earth orbit (LEO) range are due to errors in atmospheric drag modelling. These errors can theoretically be reduced by using observational data in realtime to enhance an existing atmospheric density model. An algorithm has been developed to compute a linear correcti...

In order to avoid mutual electronic interference between GEO satellites, the international regulatory bodies have allocated them to ‘slots’ separated by roughly 2 degrees in longitude. By contrast, no such standardization yet exists for the newer non-geostationary (NGSO) constellations. As a consequence, the widely differing periods, inclinations,...

Several theories have been presented in regard to creating a neutral density model that is corrected or calibrated in near-real time using data from space catalogs. These theories are usually limited to a small number of frequently tracked “calibration satellites” about which information such as mass and cross-sectional area is known very accuratel...

Many inaccuracies in the determination and prediction of satellite orbits in the low earth orbit (LEO) range are due to errors in atmospheric drag modelling. These errors can theoretically be reduced by using observational data in realtime to enhance an existing atmospheric density model. An algorithm has been developed to compute a linear correcti...

Elliptical, non-geostationary satellite orbit (NGSO) satellite constellations have been proposed as a solution to the problem of the shortage of slots in the Geostationary Ring for new communications satellites. These elliptical constellations have the potential to greatly multiply the available space real estate without interfering with the existi...

Atmospheric drag model inaccuracies can result in large errors in the determination and prediction of satellite orbits in low earth orbit (LEO). Improvements to any atmospheric density model can be made by incorporating observation data in near-real time. An algorithm has been created which uses estimated ballistic factors from observational data t...