The Distributed Extreme Environment Drive System (DEEDS)
What Is It? What Does it Do? How Does It Work?
The Distributed Extreme Environment Drive System (DEEDS) is an advanced space-rated avionic and actuation control system that addresses a wide thermal range of operations for harsh environments. This new technology development, undertaken by Motiv Space Systems (Motiv), addresses some of the most stringent environmental requirements of lunar and deep space exploration. It will enable sustained operations for critical systems like lunar rovers, robotics, cranes, offload equipment, ISRU processing equipment, and cargo manipulation systems. DEEDS was funded under NASA’s SBIR ‘Moon to Mars’ Sequential Program and builds on previously established cryogenic operating avionic SBIR-funded technologies that have been successfully commercialized for orbital and lunar lander systems.
DEEDS is made up of a highly capable avionic motion control system that is integrated with a modular mechanical drive system. A first of its kind, Motiv is driving technology maturation through a test and qualification program that will validate a scalable architecture benefitting any of the primary developers of lunar exploration equipment that needs to operate well beyond the typical single lunar cycle mission. DEEDS is intended to show operational thermal cycling lifetimes of greater than five years and become critically infused technology for Artemis and other deep space missions.
DEEDS’ avionics leverage decades of prior JPL/NASA/Industry research dedicated to identifying components that operate at -180°C and tolerate 125°C. Specific families of electronic components demonstrate normal functionality at cryogenic temperatures and allow for integrated systems to meet the functional needs of operating in Permanently Shadowed Regions (PSRs), Mars polar sites, or deep space ocean worlds such as Europa or Enceladus without the reliance upon survival heating. This “built-in resilience” yields savings in power and mass attributed to thermal management systems. Motiv has taken the approach of design for the environment to the extremes by qualifying hardware to sustain and operate through these harsh environments at the core technology level. The design objectives also include utilizing 100 krad components throughout.
The capabilities of the DEEDS controller section are significant, with a 28V-120V wide operating input bus voltage range. These voltages span typical spacecraft operational ranges for both robotic and human exploration critical systems. Total current production reaches up to 20A and approaches 2.5 kW of output power. Dual brake controls exist for either power-off systems, which require pull-in capabilities for operation, or power-on brakes used to energize restraint systems when utilized in systems that require active braking, such as human-driven rovers. The controller is also outfitted with dual resolver sensing for fine resolution when operations dictate fine positioning or velocity controls. Finally, the controller supports a variety of commutation schemes as required by the operation serviced.
Operational modes include a closed-loop control schema for velocity and position control. For specific torque control dominated operations, both current control and utilization of locally derived actuator torque sensing are available. The controller also supports motion profiling to execute various user-defined operations.
Bulk Metallic Glass
In addition to the cryogenic avionic operations, Motiv is leveraging the emergence of Bulk Metallic Glass (BMG) in the construction of the geared torque production system. The actuation system is a scalable, modular component that allows for multiple stages of planetary gearing, a power-off brake (typical for robotic operations), a power-on brake (equivalent to the brake pedal in a vehicle), fine resolution output resolver sensing, and a cryogenic brushless DC motor. This can be adjusted to meet specific output torque production needs as required by varied user applications. Recent developments in BMG materials used in planetary gear systems have shown excellent wear properties with specific alloys. Not only does the material wear well with minimal galling, but gears have been operated cryogenically without the need for lubricants. Demonstrating long-life operations, down to -180°C, through dozens of deep thermal cycles, consistent with a lunar rover mission of 5+ years, is a game-changing achievement.
While configurable to a multitude of operational cases and configurations, the initial DEEDS specification was based upon a popular “corner case” promoted by NASA’s LTV definition. The LTV specification is desirous of a 500 kg rover with a 500 kg payload capacity, >10 kmph traverse, and capabilities for cornering and driving up and down inclines. The extrapolated requirements established the electrical and mechanical requirements for an LTV wheel system supported by the DEEDS architecture.
Testing the DEEDS system will include a wide range of validation activities. A lifetime test program cycled through temperature extremes will exercise the actuation output to an equivalent set of revolutions to yield a minimum of 50 km and a goal of 250 km. Dynamometer testing at various thermal setpoints will also evaluate cross-moment loading capabilities and peak torque performance consistent with simulated lunar incline and cornering traverse models, as well as expectations for releasing from embedment conditions. Lastly, regolith incursion testing using simulants will be exercised to validate dust mitigation design practices to ensure the protection of rotating interfaces and long-life capabilities.
As the Artemis campaign has evolved, important themes have arisen which speak to the technology vector required to maintain a long-term presence on the Moon or Mars. The first is “To Survive the Lunar Night”. This goal speaks to creating methods that allow systems to robustly perform beyond the single lunar day missions. For Motiv, developing systems at all levels capable of performing in the extremes of the harsh lunar day/night cycle is a major step forward in delivering high-reliability capabilities that do not require augmented survival power or accommodations.
The other theme, “To Operate Through the Night,” is critical for standard operations in PSRs and supporting ISRU activities. The objectives of the Artemis mission are significant, and in order to achieve them, systems must not be limited to a maximum of 50% efficiency via means of hibernating during the lunar night. Strategies of power collection and storage must be coordinated to take advantage of maximum efficiency potentials. Continuous operations also reduce the total number of deep thermal cycles witnessed by these systems to execute any measure of work.
DEEDS offers unique architectural advantages in that it can be utilized in a completely distributed fashion. Classic architectures have been served in warm electronics boxes or have only been utilized for short-duration missions under favorable daytime environmental conditions. These techniques are inherently more massive and require ‘thermal maintenance’.
Serviceability is also a benefit of the DEEDS architecture. In the example of the LTV wheel drive system, the module can be serviced by humans once it has surpassed its operational life expectancy. This type of life extensible topology has been very successful with Orbital Replacement Units (ORUs) aboard ISS and will also be essential for minimizing large system degradation and maximizing operational life to support both robotic- and human-tended activities throughout a sustainable campaign.
It is anticipated that the technologies and techniques being developed for DEEDS will serve as the foundation for successful operations on the lunar surface, and many other harsh environments for years to come.
This article was written by Tom McCarthy, robotics expert and VP of Business Development, Motiv Space Systems, Inc. (Pasadena, CA). For more information, go here .