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Optimal Trajectories by Implicit Simulation
NASA Glenn Research Center
Cleveland, OH

Frequently Asked Questions

When and why was OTIS4 written?

What fidelity does OTIS4 have compared to other legacy codes that have been used for a long time?

What type of work for real-life launch vehicles has been done with OTIS4?

What type of 'advanced' mission and vehicle work has been done with OTIS4?

How many OTIS4 users are there anyway?

Should I use POST4, OTIS2D, or SORT?

How many people actually develop and maintain OTIS4?

How often do you change the program?

Describe your testing process.

Describe your configuration control.

Are there other programs that use collocation?

What platforms are supported by OTIS4, and what are the requirements?

Why do you only distribute Fortran source code?

How can I change the program to do what I need done?

When will there be an OTIS4 GUI?

How do I let you guys know about bugs and errors?

Where is the documentation?

What if I have trouble getting OTIS4 installed or have trouble with an OTIS4 case? Who can help me?

Can I share the program with other people?

Why is the program ITAR and what does that mean?

What do I get when I request from NASA?

Boeing originally developed OTIS1.2 and delivered it to the USAF. The goal was the development of an implicit trajectory optimization tool.

In 1992 NASA Glenn Research Center took over maintenance and distribution. NASA GRC sponsored OTIS3 in 1995. OTIS3 featured phase-based problem definitions, interplanetary capability, and the inclusion of SNOPT.

OTIS4, developed by NASA GRC and Boeing, was released in 2008. OTIS4 is a significant change over OTIS3.2, featuring among other things:
  • Standardization to Fortran namelist input with many new input names and metastrings for model building and problem definition.
  • Improved options for implicit integration schemes.
  • An overhauled installation and execution system.
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OTIS4 is used to support actual launches at the NASA Kennedy Space Center. The OTIS4 results compare extremely well to those of the legacy codes used by the Launch Vehicle providers to generate their final 'as-will-be-flown-tomorrow' trajectories. State vector comparisons in various frames such as Body Inertial, EME 2000, Flight Path, and Orbtial elements, all compare well. Detailed trajectory plots also show good comparisons of a wide range of trajectory/mission/vehicle parameters, including steering profiles.
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OTIS4 is used to support mission integration activities for near term NASA Expendable Launch Vehicle (ELV) launches: anywhere from early integration activities all the way through day of launch. As an example of an early integration activity: solving flight design issues, due to unusual constraints levied by the Spacecraft customer. Early in 2007 there was such a trajectory problem (in this case: special Spacecraft sun light requirements and Spacecraft telemetry requirements) that the Launch Vehicle (LV) contractor had some difficulties converging to optimal solutions using their own trajectory software. The basic mission design was already difficult and adding these constraints made for a real challenge. Complicating matters was the number of scenarios to be analyzed. OTIS4 readily handled the task and produced optimized trajectory results, in quick turnaround time, that were passed on to the LV contractor and the spacecraft customer. Those solutions were proven to be valid and feasible for the ongoing real life mission integration activities at hand. The LV contractor was subsequently able to duplicate those results with their own software and using the OTIS4 solution as a starting point.
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OTIS4 is used for feasibility analyses of upcoming missions and new launch vehicles. Specifically, OTIS4 has been used to perform mission design work for upcoming missions under consideration for procurement by NASA. OTIS4 has used to assess the feasibility of 'academic' missions. OTIS4 has also been used to simulate trajectories for new launch vehicles that are still in their development cycle. Where available, the OTIS4 results have been proven accurate when compared to those of the launch vehicle providers that are using tools other than OTIS4 for their analyses.
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At the last count there were approximately 130 registered OTIS users include over 60 for OTIS4.
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Given a knowledgable user, any of these program should be able to meet your needs. Choose the one you feel most comfortable and/or productive with, which seems to provide the best convergence for your problem.
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OTIS4 is maintained by a team of 4 characters. None of them work full-time on the program, but the contribute when possible.
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OTIS4 is constantly being refined now as the developers have a chance to refine and simplify. With OTIS4 , users can expect more updates than with past versions simply because we anticipate new users with new needs.
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OTIS4 contains a core set of relatively simple example problems that we test against when we develop a new release. This detects and glaring mistakes made by the developers before the code gets to our end users.

OTIS4 is also tested in a variety of Independent Verification and Validation (IV&V) tasks. For instance, OTIS4 has been used to verify launch vehicle trajectories generated by POST and found to match mass perfomance within 0.1%.

OTIS4 has also been used to verify the launch trajectory for the Mars Phoenix lander.

OTIS4 has also been used to conduct launch abort analysis of the Orion Crew Exploration Vehicle. The optimal control profiles determined by OTIS4 agree well with those generated by a closed-loop PEG guidance algorithm.

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The OTIS4 development team utilizes Subversion for configuration control. We maintain a 'trunk' version of OTIS4 that is the current development branch. Once we reach a stable point where we believe the program is worthy of release, we tag a release (e.g. OTIS4 .0.0). End users will have access to the latest tagged version.
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OTIS4 has been tested on a variety of Linux distributions, Windows 2000/XP, OS X, and Solaris. Any computer with more than 512 MB of RAM and a reasonably fast processor should be capable of running OTIS4, although faster machines will yield faster results.

OTIS4 is distributed with Makefiles designed for GNU Make. A project file for Intel Visual Fortran is also available. Currently we support the following operating system / compiler combinations.

  • g95
  • Intel Fortran
  • Absoft Fortran (v10 only)
  • Pathscale
    OS X
  • g95
  • IBM XL Fortran (PPC G5)
  • Intel Fortran (Mac Intel)
    Windows 2000/XP
  • g95
  • Compaq Visual Fortran
  • Intel Fortran
  • g95
  • Sun Fortran 95
OTIS4 also is distributed with a number of helper utilities, many of which are written in Python. While these are not necessary to use OTIS4, we believe they make for a far easier and convenient OTIS4 experience. Python comes standard with OS X and most Linux/Unix distributions.

Windows users can download Python from
GNU Make for Windows is available from

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We only distribute the source code for a few reasons. Some components of the OTIS4 source code are not maintained by us, require specific versions dependent upon the OS environment (SPICE toolkit), or are proprietary software requiring a license to be purchased by the end user (SNOPT).

We also distribute the source code in an effort to allow OTIS4 to run on as many platforms as possible. Given the small size of the development team, it's easier to allow the users to build OTIS4 on their particular platform than to maintain binary distributions for various flavors of Windows, Linux, OS X, etc. We've tried very hard to improve the build-system with OTIS4 , making it relatively easy to compile on the supported platforms.

Finally, by distributing the source code we empower you, the end users, to modify the source code to suit your needs, if you are so inclined.

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Great efforts have been made with OTIS4 to make it as generic as possible, such that code changes will not be necessary for the vast majority of trajectory optimization problems. However, if you find that you need a capability that does not exist currently within OTIS4, we distribute a Programmer's Manual that gives some insights into changing the source code. Simple changes include adding new variables or calculator functions, but you can change whatever you like. Be careful when adding new parameters to the common block ABLOCK. Consult the Programmer's Manual for this.
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The development effort on OTIS4 has been focused on developing the best possible optimization tool. Our desire is that any GUI development be cross-platform, allow as much flexibility as an input text file. When we develop such a GUI, rest assured you will hear about it here.
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The bug-reporting link on this website will allow you to notify the developers of possible bugs or issues. Please include a set of input files which exhibit the issue, and let us know what operating system, compiler, and version of OTIS4 you are using. The OTIS4 version or build number is output near the top of an .oto file.
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OTIS4 documentation consists of 4 volumes that cover virtually all aspects of using the program. They are searchable pdf files.
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If you're stuck on a problem feel free to contact the developers at NASA Glenn Research Center. We will do our best to help you in a timely manner.
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No. OTIS4 is covered by ITAR regulations (see the question below). OTIS4 may only be used in work sponsered by the U.S. Government.
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In short, OTIS4 is cover by ITAR regulations because it was originally developed under a USAF contract. It can be used in the development of weapons technology. This means that the distribution of OTIS4 to, or use of OTIS4 by non-U.S. persons is forbidden.
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NASA provides a tarball otis4.tar.gz and a document entitled "How to install OTIS4.doc". Upon opening the tarball, the following directory structure appears in the directory (folder) otis4:
doc examples libs obj spice utils ephem exe makefiles obj_debug src vs2k3
The doc directory contains the 4 volumes of OTIS4 manuals, a document with additional insights for Windows installation, and a copy of the SNOPT 7 manual. The src directory contains the OTIS4 source code and the libs directory contains the various support libraries used with OTIS4. The directory spice is where users place the spice software that user obtained from JPL for their systems and that OTIS4 requires.The directory examples contains many samples problems and their solution. These provide confidence that OTIS4 is running correctly and a template for solving new problems.
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Date of Last Site Update: May 2008