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RLEP (Robotic Lunar Exploration Program) 6 DOF Simulation and Graphics

The project:

ATK Elkton LLC, in partnership with the Jet Propulsion Laboratory, is developing propellants for a low-cost flexible solid-propellant control system applicable to payload descent and spacecraft cruise phases for future Mars Exploration missions.

In a desire to leverage existing technologies, ATK Elkton wanted to market SOFTLAND™ (Solid Flextstage for extra-Terrestrial Landers) as a possible solution for Mars missions.  One of the primary goals for the SOFTLAND™ system is to provide flexible controlled descent at half the price of a competing liquid system. The SOFTLAND™ baseline design concept is to utilize 600-lbf-class fully throttle able solid thrusters (de rated to 200-lbf-class for smaller landers to provide axial and lateral control). The system uses manifolds and an array of gas generators to provide full spacecraft control capability in a modular design for future systems. This approach can minimize future system repackaging and redesign efforts when requirements change and new missions are identified.

In order to market SOFTLAND™ technologies for applicable Mars missions, such as RLEP (Robotic Lunar Exploration Program), ATK needed a high fidelity 6 Degree-of-Freedom simulation of their low-cost high-temperature proportional valve technologies being utilized in a typical RLEP mission. This simulation would be used to drive high fidelity animated graphics for visualization and capability demonstration to prospective partners and customers. With this in mind, ATK hired ATA to produce a 6 DOF simulation along with computer graphics of RLEP de-orbiting to the Lunar surface (The Lunar south pole) using ATK’s Gas Generators for powered flight during the descent.

The Challenge:

With key marketing meetings with JPL and NASA pending, ATK needed a 6 DOF simulation capability involving their Gas Generator technologies in use in a typical RLEP mission. The RLEP mission itself encompassed 4 phases; A large first burn using one of ATK’s Star series solid rocket motors of approximately 55 seconds in order to place the RLEP vehicle on a ballistic trajectory towards the Lunar surface; a vehicle reorientation phase using ATK’s Gas Generators to control vehicle attitude and reorient the vehicle for landing; a long coast phase prior to the powered descent; and the terminal phase using ATK’s Gas Generators for powered, 3 axis controlled descent to and “safe landing” on the Lunar surface. Mission planning and targeting needed to be performed outside of the 6 DOF simulation in order to place the simulated vehicle in the proper lunar orbit and target the lunar South Pole.

As stated above, the 6 DOF simulation would be used to demonstrate Gas Generator technology capability for use in mission, such as RLEP, and provide data for animated graphical depiction of the mission. The simulation and graphical capability needed to be very high-fidelity to impress technically oriented customers like JPL and NASA, and had to be produced on an expedited schedule, approximately 1 month.

The Solution:

To meet the challenge of high-fidelity, complex software being produced on an extremely condensed schedule, ATA turned to the LabVIEW programming environment and the stable of pre-tested flight dynamics simulation software from the ATA Aerospace Toolkit.

Because of the extreme schedule, ATA took a divide and conquer strategy. The 6 DOF simulation was developed in two pieces. The first piece was the de-orbit, attitude re-orientation, and coast. The second piece was the terminal 3 axis controlled powered descent using the Gas Generators. The two pieces of the simulation along with the graphics and targeting software were developed simultaneously by various members of the ATA team of engineers during the 1 month span of time. The two pieces of the simulation produced data representing their respective phases of flight, and were then pieced together to input into the graphics software to produce a high quality animated graphical depiction of the RLEP mission.

The ATA Aerospace Toolkit provided ready-made software for solving Lambert’s problem which made targeting and initial orbit calculation fast and relatively straightforward. The toolkit also provided software for attitude control (computing desired attitudes for desired vehicle pointing) and lunar gravitational modeling during the attitude re-orientation and coast phase of flight. The mathematical analysis software from the ATA Aerospace Toolkit provided numerical integration routines for integrating the equations of motion during the simulation, as well as necessary element set conversion routines for analyzing data (i.e. Kepler elements to Cartesian elements). The toolkit also provided orbit propagation functionality and coordinate system transformation capability needed in the simulation.

For the second part of the simulation, ATA leveraged already existing Gas Generator models built in LabVIEW during its long history of performing hardware-in-the-loop testing for other Gas Generator related projects for ATK.  LabVIEW was chosen for these projects because of the efficiency in interfacing with hardware.  LabVIEW's fast and efficient programming environment made developing the necessary additional functionality not provided by the ATA Aerospace Toolkit for 3 axis attitude controlled powered descent as fast and efficient as possible.

The Outcome:

Exactly one month after Authority To Proceed, A high fidelity animated graphical depiction of an RLEP vehicle landing on the south pole of the lunar surface was delivered to ATK. The graphical depiction was the center piece in numerous marketing meetings that followed.