Low thrust problems present a number of mathematical challenges. In some mission models, the objective function is relatively insensitive to changes in some of the independent mission variables, with the result that the overall convergence can be difficult. The forces involved with interplanetary missions have a greater impact on low thrust simulations than on high thrust simulations simply based on the thrust magnitude. For instance, multiple gravitational bodies acting on a spacecraft can have a significant impact when low thrust propulsion is used, but with lessening effect as the thrust level increases .

All potential customers emphasize the need for consistency in analysis of low thrust propulsion missions. Therefore, the low thrust community has recognized the need to develop a tool or a suite of tools that takes the best capabilities from each of the current tools and combine them into a new tool or suite of tools that can be used by all NASA centers. This is not an easy task. The first step is to perform a gap analysis of all the tools in existence to identify their potential benefits and shortcomings.

Several low thrust propulsion tools are already in existence. The more widely used among them are: OTIS (Optimal Trajectories by Implicit Simulation), an aircraft and spacecraft trajectory simulator and optimizer developed and maintained by GRC/Boeing, and SNAP, a GRC developed high fidelity N-body trajectory/orbit integration code that provides the user a great measure of freedom in mission modeling. To name a few other low thrust propulsion tools: CHEBYTOP (Chebyshev (Polynomial) Trajectory Optimization Program), an approximate low-thrust interplanetary optimization code, SEPSPOT (Solar Electric Geocentric Transfer with Attitude Constraints Program for Optimization of Trajectories), a planetocentric low-thrust optimization code which uses an averaging technique, VARITOP (Variational Calculus Trajectory Optimization Program) and SEPTOP (Solar Electric Propulsion Trajectory Optimization Program), which are low-thrust interplanetary optimization codes which use calculus of variations. Each of these tools has strengths and weakness in solving the low thrust problem. However, with all these tools available the different NASA centers tend not to use the same ones.

Low thrust propulsion tool development is a current objective that will enhance NASA's analysis capabilities. An objective identified by the low thrust community is the development of a tool or suite of tools that is fast and accurate, user friendly, and versatile. These tools need to be fast and accurate in order to perform tasks in a timely and efficient manner where the turnaround time is short. It needs to be user friendly and versatile so that all the NASA centers can utilize this new tool or set of tools and the consistency boundary can be met.

7820 Participation

OTIS and the Low Thrust Trajectory Tool Project

Members of the branch are involved in a multi-year effort to modify and otherwise upgrade the OTIS trajectory optimization program so that it will more easily and robustly (less sensitivity to initial guesses of optimization variables) handle low thrust trajectory problems. Partners in this effort include the Boeing Phantom Works (Steve Paris), the University of Illinois (Dr. Bruce Conway), and the Naval Postgraduate School (Dr. Mike Ross).

Steve Paris' work, to date, has focused on improving the computational aspects of OTIS' strength, use of implicit integration. Building on the research Bruce Conway and his students have done, Steve has developed a mathematical framework for vastly improving the accuracy of the implicit solution without greatly increasing execution time or memory requirements.

Drs. Ross and Conway are supporting the development effort by exploring how alternate methods of implicit integration and pseudo-spectral methods can benefit OTIS.

Here at GRC, we hope to continue developing a Java based graphical user interface for OTIS. We are also working on improving several user interface issues in order to reduce the number of inputs required to do interplanetary problems. We are also adding many interplanetary trajectory features that SNAP and VARITOP currently provide. Participants at Glenn Research Center include John Riehl (lead), Waldy Sjauw, Les Balkanyi, Dave Smith, and Lisa Lambert (OTIS GUI).

The new OTIS should be fully developed and documented by October, 2005. Marshall Spaceflight Center is providing the funding for this work as part of the Low Thrust Trajectory Tool Project, a NASA wide effort to consolidate and provide a suite of low thrust software tools. Larry Kos is overall project leader.

Points of Contact

7820

John Riehl (John.P.Riehl@grc.nasa.gov)

Les Balkanyi (Leslie.R.Balkanyi@grc.nasa.gov)

Mike Martini (Michael.C.Martini@grc.nasa.gov)

HTML Contributions

Corinne Kellerman Summer Intern '04

• 1999-01-2449.pdf
• AIAA-93-4170.pdf
• AIAA-95-2812.pdf
• AIAA-96-2810.pdf

• AIAA-97-2956.pdf
• AIAA-98-3591.pdf
• AIAA-98-3883.pdf
• NASA_CR-198427.pdf

• NASA_CR-198517.pdf
• NASA_CR-204666.pdf
• NASA-TM-106406.pdf
• NASA-TM-1990-103234.pdf

• NASA-TM-2000-210243.pdf
• NASA-TM-2002-211314.pdf
• NASA-TM-2002-211599.pdf
• NASA-TM-2002-211871.pdf

• NASA-TM-2002-211892.pdf
• NASA-TM-2002-211893.pdf
• NASA-TM-2003-212227.pdf
• NASA-TM-2003-212315.pdf
• STAIF-2003-177.pdf