RLEP (Robotic Lunar Exploration Program) 6 DOF Simulation and Graphics
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.
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.
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.
chosen for these projects because of the efficiency in interfacing with
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.
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