the next step space robotics initiative skyworker pdr 9/10/99-1 skyworker preliminary design review...

The Next StepSPACE ROBOTICS INITIATIVE

Skyworker PDR 9/10/99-1

SkyworkerSkyworkerPreliminary Design ReviewPreliminary Design ReviewSkyworkerSkyworkerPreliminary Design ReviewPreliminary Design Review

Field Robotics Center

September 10, 1999

William “Red” WhittakerPeter StaritzChris Urmson



• Constellation of SSP satellites in GEO

• 1GW of energy to the ground via a microwave transmission antenna 1 km in diameter

• 150m wide and 10 to 15 kilometers in length

• Mass of 4800 MT (10X as massive as ISS)

• Assembled over 1 year, maintained for 30 years

• Need for robotic systems capable of Assembly, Inspection, and Maintenance (AIM) tasks

Space Solar Power (SSP) FacilitiesSpace Solar Power (SSP) FacilitiesSpace Solar Power (SSP) FacilitiesSpace Solar Power (SSP) Facilities



SSP Facility AIMSSP Facility AIMSSP Facility AIMSSP Facility AIM

• Solar array– Assembled through automated docking and deployment

• Microwave antenna– Requires completion of complicated assembly tasks

• Joining of deployable truss sections

• Attaching transmitter elements

• Coupling Power Management and Distribution (PMAD) system

• Entire facility will benefit from automated inspection and maintenance capabilities



Space Solar PowerSpace Solar Power

Automated Technology Roadmap Automated Technology Roadmap 2001-2005 2006-2010 2011-2015 2016-2020< 2000

Electrodynamic Propulsion Systems

FY99 FY00 FY01 FY02 FY03 FY04 FY05 FY06 FY07 FY08 FY09 FY10 FY11 FY12 FY13 FY14 FY15 FY16 FY17 FY18 FY19 FY20

LEGEND

R&D Result-Driven Decision Point

Major R&D Prm Milestone

Strategic Program Objective

Tether and Antenna Front Plane Maneuvering

Demonstration

single axis ED thruster

in uwave field

Autonomous Rendevous and Dock

Air-bearing precision

maneuvering

80% Reliable Fly-to-grapple and Robust Abort

Demo terminal guidance

sensing system

Trajectory planning and optimization

Robust control w/ attached

robot interaction

Force and Redundancy Control Strategies for Cooperative Systems

Learning/adapta-tion for unknown payloads&failure

90% Reliable Fly-to-grapple and Robust

Abort

Sensing/Perception

Stable Posture and gait

control w/ 4 cooperating

truss walkers

Perform mating tasks w/ 4 cooperating truss

walkers & flex. structure

Payload balancing w/ 6

cooperating truss walkers

Force-controlled free flyer payload

exchange

Joint failure compensation and increased

structural disturbance

Robust locomotion and free flyer interaction in dynamic

environment

Locate standard grabrail fixture under nominal conditions

Identify feducial mark scheme to simplify vision

Integrate high-bandwidth optical flow, range, and force to improve grasp reliability Develop compact flight

hardware implementation of high-rate vision

algorithmsDemonstrate

strategies to mitigate lighting effects

Borrowed from Automated Assembly, Maintenance, and Operations of a Space Solar Power System



Space Solar PowerSpace Solar Power

Automated Technology RoadmapAutomated Technology Roadmap2001-2005 2006-2010 2011-2015 2016-2020< 2000

FY99 FY00 FY01 FY02 FY03 FY04 FY05 FY06 FY07 FY08 FY09 FY10 FY11 FY12 FY13 FY14 FY15 FY16 FY17 FY18 FY19 FY20

LEGEND R&D Result-Driven Decision Point

Major R&D Pgm Milestone

Strategic Program Objective

Integrated Technology Demos

On-orbit walker/free flyer antenna assembly and repair demo

Autonomous grasp and

locomotion of antenna element

Multi. walker automated antenna assembly in neutral

buoyancy

Multi. walker/free-flyer antenna repair in neutral buoyancy

Prototype neutral

buoyancy truss walker

On-orbit multi. walker antenna assembly

demonstration

FY05 Decision on first flight

demo

Assembly and Maintenance Planning

Assembly activity planning for 4

cooperating truss walkers

Assembly activity planning for 4

cooperating truss walkers + free flyer

Simulation and visualization of

assembly activity

Demo automated Ground Segment

operations inc. power sales

Demo automated Space Segment operations inc.

maintenance flights Demonstrate 100% automation of space and

ground segment operations

Borrowed from Automated Assembly, Maintenance, and Operations of a Space Solar Power System



ObjectivesObjectivesObjectivesObjectives

• Demonstrate the viability of using robots for orbital construction

• Prove the validity of using structure walkers for orbital AIM

• Demonstrate SSP AIM relevant tasks using robotics

• Simulate prospective SSP AIM robots and tasks



Representative TasksRepresentative TasksRepresentative TasksRepresentative Tasks• Walk, turn, and transition across planes on a truss

structure

• Pick up and place a payload at arbitrary locations and orientations in space

• Carry a payload while walking, turning, and transitioning

• Conduct calibration and inspection tasks

• Connect power and communications cables

• Cooperatively carry massive or large payloads

• Perform tasks that require multiple robot collaboration



DemonstrationDemonstrationDemonstrationDemonstration

• Prototype Robot– Pick up and carry a model transmitting element the length of the

truss, turn while carrying, couple the element to the structure– Connect Power Management and Distribution (PMAD) to the

element– Perform a mock calibration

• Simulation– Large scale construction utilizing multiple robots– Coordinated installation of full scale transmitting elements– Demonstrate extended lifetime operations



Program PhilosophiesProgram PhilosophiesProgram PhilosophiesProgram Philosophies

• Design for Earth based demonstration, but always maintain a path to orbital application

• Accept a baseline environment (structure, tasks, etc..)

• Leverage heritage technologies when available

• Design and manufacture in house whenever possible

• Consider physical scalability of design

• Ensure robust software operation through incremental testing of components

• Maintain software scalability through Object Oriented Principles



Configuration - Key MetricsConfiguration - Key MetricsConfiguration - Key MetricsConfiguration - Key Metrics• Control Complexity

– The number of joints that must be actuated in synchrony

• Continuous Motion– System supports a gait in which the payload can maintain a constant

velocity

– How difficult it is to control that gait

• Cost– DOF, links, grippers, sensors, control complexity, gravity compensation

• Compatibility with gravity compensation– Possible to compensate with available resources, new system or

recycled heritage system

• Forces exerted / Forces experienced– Maximum forces and torques experience/exerted by the robot



Configuration - Key Metrics (Cont.)Configuration - Key Metrics (Cont.)Configuration - Key Metrics (Cont.)Configuration - Key Metrics (Cont.)

• Workspace– Effective working volume with one gripper attached to the structure

• Energy Consumption– The energy consumed by the machine to move a specified distance

and speed with a given payload

• DOF– Total number of joints– Number of different joint types

• Mass– DOF, links, grippers, sensors, constants

• Layout of available volume– Sufficient room for onboard components



ContendersContendersContendersContenders

DOF Grippers LinksM-type 12 3 4

N-type 11 3 4

S-type 12 4 7



N-typeN-typeN-typeN-type

• Key Features– Walking posture– Manipulating posture – Sufficient internal

volume to allow tetherless operation

– Fine motion / Transition Joint

• Inchworm Gait• Cable Mating



Configuration N-typeConfiguration N-typeConfiguration N-typeConfiguration N-type• Control Complexity

– At most 4 joints must operate in synchrony for standard gait

• Continuous Motion– System supports a continuous gait– Simplified gait, uncertainties in only one

dimension

• Cost– Lowest number of total components

affecting cost

• Compatibility with GC– Compatible with heritage system, only minor modifications

needed

• Forces Exerted / Forces Experienced– Normal stride exerts/experiences minimal torques



Configuration N-typeConfiguration N-typeConfiguration N-typeConfiguration N-type

• Workspace– N-type “unfolds” to become a 3 link

manipulator

• Energy Consumption– Continuous gait and fewer motors

needed for standard stride result in lower consumption

• DOF– 11 joints, 3 grippers

• Mass– ~35 kilograms

• Layout of available volume– Sufficient room for onboard

components



Gripper Design IssuesGripper Design IssuesGripper Design IssuesGripper Design Issues• Skyworker will move its own mass in

addition to a payload – Increased possibility of truss failure due

to point loads– Gripper faces will be extended and

shaped to match the structure (reducing point loads)

• Rotation about the longeron is a possibility– High coefficient of friction coatings

• Simple structure detection is necessary– Proximity sensors (capaciflectors)



JointsJointsJointsJoints

• 3 Joint types– 3 Axial revolute joints– 2 Offset revolute joint– 6 Inline revolute joints



Force AnalysisForce AnalysisForce AnalysisForce Analysis

Z2

X2

Y2

Z1

Y1 X1

Z0

X0

Y0

ZL

XL

Ft,2

Fn,2

Fy

Fx

Ft,1

Fn,1

Fn,L

Ft,L

Ry

Rx

T2

T1TT

Forces:-Payload Inertia-Arm’s Inertia

Given:-Payload Velocity-Payload acceleration

• Concept of “Walking lightly”

• Largest forces occur during a standard stride as opposed to during acceleration

• 2 forms of force analysis– Further analysis will

minimize the torque generated by the base joints



Maximum TorquesMaximum TorquesMaximum TorquesMaximum Torques

A

C

D

B

-4

-3

-2

-1

0

1

2

3

4

5

Torq

ue (N

m)

A B C DTorque (Nm) 4.12 .929 4.43 -3.57



Gravity CompensationGravity CompensationGravity CompensationGravity Compensation

• Allows for maneuvers not possible in normal gravity

• Passive compensation– Counterweight system– Transmission

• 10:1 ratio

– Active X-Y table– Heritage system



Power ElectronicsPower ElectronicsPower ElectronicsPower Electronics

• Tetherless operations

• 20 minute demonstration

• Less than 40 watt-hours of energy at a peak rate of 120W +/- 30%

• Mass Constraint 3kg (batteries/charger/converters)

• Volume Constraint



Battery RechargingBattery RechargingBattery RechargingBattery Recharging

• Onboard Charging Solution– Power obtained through special gripper– Contact with electrified terminal on demonstration structure– Inductively Coupled Charging a future possibility– All charging electronics/distribution onboard

• Battery Monitoring System– Automatically detects when charge is necessary– Returns to ‘Charging Station’ when needed– Disconnects and returns to work when fully recharged



Battery TechnologiesBattery TechnologiesBattery TechnologiesBattery Technologies

• Batteries we considered:

• NiCd batteries selected for prototype, different battery technology may be used in space applications.

NiCd NiMH Li-IonEnergy/kg Fair Good ExcellentEnergy/cm3 Fair Good ExcellentCharge Rate High Moderate LowEase of Charging Easy Difficult DifficultMax. Discharge Rate Extremely High Moderate LowCost/W Low Moderate HighMass/W Low Moderate HighVolume/W Moderate Moderate High

the next step space robotics initiative skyworker pdr 9/10/99-1 skyworker preliminary design review...

Documents