Lunar Terrain Vehicle

I was the Lead Mobility Engineer on NASA's Lunar Terrain Vehicle- Ground Test Unit (LTV GTU). The LTV-GTU is a feature-rich ground test vehicle designed to be reconfigurable for ground testing and conceptual operations development for various NASA and contractor payloads.

As the Lead Mobility Engineer I was responsible for the architecture, design, manufacturing, integration, and testing of the vehicles mobility system, avionics boxes, and a majority of the crew interface hardware.

I was the sole designer of the vehicles propulsion actuator that contained the following features:

Dual Parker Hannifin frameless BLDC motor per wheel (4 motors per wheel module)
27:1 planetary geartrain
1200 Nm output torque per wheel
Frameless resolver sensor for motor commutation
Custom fail-safe brake disc and caliper on backside of motor
Integrated temperature sensors
Novel threaded bearing ring locking geometry currently being patented by NASA
Output drives wheel through center-lock nut with torque studs

As the Lead Mobility Engineer I was also responsible for the success of the suspension and steering actuators. Two other engineers did the initial 80% of the design of each actuator and I completed the final 20% to prepare both actuators for manufacturing. This included all of the tolerance analysis, manufacturing drawings and creating assembly tools and fixtures.

The active suspension actuator contained the following features:

Parker Hannifin frameless BLDC motor
9322:1 overall gear ratio
Custom planetary inside of strain-wave gearset driving a worm gearset
15,000 Nm output torque
Frameless resolver for motor commutation
Zettlex frameless inductive encoder for absolute position
Shock drive arm pushes and pulls the shock and spring to raise and lower vehicle
Vehicle ground clearance range of 8-24 inches
Series-elastic actuator utilizes sensors measuring the position of the active arm and sensor measuring the position of the lower control arm to determine load on each wheel module.

The steering actuator contained the following features:

Parker Hannifin frameless BLDC motor
1000:1 overall ratio
Dual stage planetary gearset driving worm gearset
600 degrees of rotation with hard-stops on each end utilizing rotary cascading hard-stop.
Frameless resolver for motor commutation
Zettlex frameless inductive encoder for absolute position
Propulsion assists the steering actuator in high load cases

I was also the sole designer of the vehicles avionics boxes. Each wheel module had its own avionics box installed in the suspension tower. The avionics box has the following features:

Houses six Elmo Gold Solo Triple Twitter motor controllers
Custom bus bars connect all motor controllers
Houses vehicle distributed Up board computers
Houses custom low voltage switching and shunt circuit boards
Integrated Amphenol Aerospace power and data connectors
Heat sink with forced air duct to cool motor controllers
Water tolerant and electrically bonded to vehicle ground

NASA VIPER MISSION

I served as a Mechanisms Design Engineer on NASA's VIPER mission. VIPER is launching to the lunar south pole in late 2027.

I worked on the Structures and Mechanisms team designing structure and launch lock mechanisms for the rovers navigation and communication gimbals.

Re-designed all communication gimbal structures to meet natural frequency requirements to withstand violent launch loads.
Integrated non-explosive actuators with custom cup-cone launch lock interface on both communication and navigation gimbals.
Designed spring retracted navigation gimbal arm that retracts launch lock actuator after landing on the lunar surface.
Designed torque transfer interface for coaxial cable rotary joint mechanism.
Designed extremely thermally isolated interface for RF communication switch to prevent heat leaking into surrounding structure during vehicle's hibernation phase.
Produced dozens of Flight engineering drawings

All hardware has completed all environmental testing and vehicle is awaiting shipment to Kennedy Space Center for lander integration.

Dust Tolerant Mechanisms

While serving as the Lead Mobility Engineer I worked with the NASA Kennedy Space Center "Swampworks" robotics group to build my propulsion actuator designed for the Chariot Unpressurized Rover project. The Dust Tolerant Mechanisms project was formed to test the lunar regolith dust sealing strategy developed at Johnson Space Center for the VIPER mission. This actuator was tested in thermal vacuum, with recirculating lunar dust, while a dynamometer was load testing against both actuator outputs.

My DTM actuator had the following features.

Dual output actuator designed to drive Chariot Unpressurized Rover "Dually" wheels
Two Parker Hannifin frameless BLDC motors per side of actuator
100:1 three stage planetary gearset
Integrated heaters and temperature sensors to warm actuator to operating temperature
First use of locking-pin threaded ring technology widely used on the LTV rover
Frameless resolver for motor commutation
Integrated Kendrion fail-safe brake on backside of motor stack
Spring-energized teflon seal and nomex felt seal with labyrinth to prevent dust intrusion

Mobile Utility Transporter

The Mobile Utility Transporter (MUT) is a self-propelled cart for early lunar surface missions. Designed to carry lunar samples, tools, science experiments, and double as an Incapacitated Crew Rescue (ICR) cart in the event of a medical emergency.

MUT went from conceptualization to functional prototype demo in less than 4 months to prove lunar surface capabilities in the rapidly changing Artemis program.

I served as the Lead Chassis and Integration Engineer as well as a subject matter expert for actuator design. The MUT propulsion actuator has the following features

Dual brushed motor per wheel
Custom 23:1 Cycloidal gearbox with dry-film lubricant
Brushed motors chosen so that no active electronics were needed to relieve schedule pressure
Dog-gear mechanism allows wheel to freewheel in case of actuator failure
Brass cup-cone brake that also functions as a heat transfer path to remove heat from motor
Designed to survive lunar night with no heaters

The chassis had the following features:

Low mass, heavily pocketed aluminum box tube framing
Thin sheet-metal fenders to prevent dust build-up on space suit
Sheet metal payload deck with dimple-dies for stiffness
Integrated ramp for incapacitated crew rescue

Space Exploration Vehicle

The Space Exploration Vehicle (SEV) is a prototype lunar pressurized rover used by NASA for crew evaluation, conceptual operations, field tests, protocol development, and asset integration.

The SEV was originally built in 2009 for NASA's Constellation program which was cancelled in 2011. After this cancelation the vehicle no longer received maintenance and upgrades.

In 2022 NASA planned a Desert Research and Technology Studies (DRATS) at Black Point Lava Flow, Arizona to test to evaluate planned features for the JAXA pressurized rover. The SEV was upgraded and refurbished in the months leading up to the field test. I designed new steering components that resolved fatigue issues in the main steering shaft and implemented changes that prevented over loading the Harmonic Drive gearsets used in the steering actuators. I also designed new payload and sensor hardware and lead the maintenance program that was performed between each of the 4 simulated missions we ran in the desert.

Since the end of the DRATS test we have continued to implement design changes to make the mobility system more robust with the help of interns participating on NASA's Robotics Academy each summer.

Micro-Chariot Rover

Micro-Chariot was my first rover project and my first custom actuator. The project was created as an early-career project to enable young engineers to gain experience across an array of disciplines ahead of NASA re-starting the human lunar rover program shortly after the start of the Artemis Program.

I had a unique opportunity to become the Lead Mobility Engineer for human rovers in the Robotics Systems Technology Branch at NASA JSC when I was only 20 years old. Many of the more experienced engineers were working on the Resource Prospector flight mission and the Chief Engineer for the Space Exploration Vehicle program decided to build a team of young engineers who had FIRST robotics experience. The team we built went on to design and build the Lunar Terrain Vehicle, Dust Tolerant Mechanisms actuator, Mobile Utility Transporter, and refurbished the Space Exploration Vehicle for its return to operational status for the Desert Research and Technology program.

The Micro-Chariot rover is a 30kg skateboard chassis designed to be used as a single-crew transporter to be used at an improved lunar base as well as a flatbed payload transporter for moving cargo across a lunar base.

I was the Lead Engineer on Micro-Chariot, responsible for the initial vehicle concept and architecture. I also designed a majority of the chassis and all of the propulsion actuator. The propulsion actuator has the following features:

Parker Hannifin frameless BLDC motor with integrated hall sensors
30:1 Harmonic Drive Gearset
Heaters and temperature sensors to bring actuator to operational temperature in vacuum
Carbon-Graphene thermal strap to sink heat into chassis

Ryan Stockton