Soft Stewart Platform for Robotic In-Space Assembly Applications

SOFT STEWART PLATFORM FOR ROBOTIC IN-SPACE ASSEMBLY APPLICATIONS

A Thesis Presented

Samantha Helen Glassner

The Department of Mechanical Engineering

in partial fulfillment of the requirements for the degree of

Master of Science

in the field of

Mechanical Engineering

Northeastern University Boston, Massachusetts

May 2020

ABSTRACT

Research into controlling how robotic manipulation of materials can impart stresses into the system is a novel realm. Great robustness is needed to handle a variety of autonomous behaviors for the uncertainty of reaction from materials of different properties ranging from lightweight gossamer to stiffer truss structures. Currently robotic manipulation for space applications is done on a very case by case basis but in-space assembly (ISA) and servicing applications introduce a large number of possible uncertainties and anomalies that would be a departure from regular operations.

My mechatronics thesis project focused on the development a Soft Stewart Platform (SSP) robot with precise 6 Degrees of Freedom (DOF) position control. A platform such as this could provide high precision with compliance to handle a diversity of material strengths, from stiff heterogenous structures to soft goods. The SSP concept is comprised of six Soft

Linear Actuators (SLAs) with precision length control. An additional benefit of a SSP versus the conventional hard Stewart platform is the ability to store the robot in a compact state that is shorter than half the full actuator length, the limit for conventional electric linear actuators.

The main application selected for this SSP concept was as an end effector to robotically manipulate gossamer structures and mitigate the impartment of stress and conduct specified testing on space telescope sunshields for how this manipulation could benefit deployment and handle servicing of anomaly cases. Overall, my research would provide benefits to

NASA missions such as deploying, or recovering from failed deployment, of space telescope sunshields critical for astrophysics science such as exoplanet observations.

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The report will also provide a history of ISA, the current space telescope paradigm, and plans for the in-space construction of large telescopes. Bringing forth the recent advancements in robotic ISA ground demonstrations shows a promising ability to shift to a new robotic ISA paradigm to mitigate risk and enrich science over a longer lifetime of a space telescope therefore getting more value for the initial upfront cost of the mission.

TABLE OF CONTENTS

1. INTRODUCTION TO IN-SPACE ASSEMBLY ...... 1 2. BACKGROUND ...... 2

2.1. HISTORY OF HUMAN IN-SPACE ASSEMBLY: INTERNATIONAL SPACE STATION ...... 2 2.2. HISTORY OF HUMAN IN-SPACE REPAIR: HUBBLE SPACE TELESCOPE ...... 3 2.3. FUTURE OF IN-SPACE ASSEMBLED TELESCOPES ...... 3 2.3.1. Astrophysicists Desire for Large Space Telescopes ...... 3 2.3.2. James Webb Space Telescope ...... 4 2.3.3. Decadal Survey Telescope Proposals ...... 4 2.3.4. NASA in-Space Assembled Telescope Study ...... 5 2.3.5. Benefits of Robotic In-Space Assembly and Servicing for a Future Telescope Mission ...... 5 3. SPACE ROBOTICS STATE OF THE ART ...... 7

3.1. ROBOTIC PLANETARY SURFACE EXPLORATION ...... 8 3.2. ROBOTIC IN-SPACE OPERATIONS ...... 8 3.3. ROBOTIC IN-SPACE ASSEMBLY RESEARCH ...... 9 3.4. ROBOTIC TELESCOPE ASSEMBLY RESEARCH ...... 12 4. ROBOTIC IN-SPACE ASSEMBLY RESEARCH ...... 13

4.1. NASA LANGLEY RESEARCH CENTER ...... 14 4.2. NASA JET PROPULSION LABORATORY ...... 16 4.3. NASA IN-SPACE ASSEMBLED TELESCOPE STUDY ...... 17 5. SOFT LINEAR ACTUATOR (SLA) DEVELOPMENT ...... 18 6. SOFT STEWART PLATFORM (SSP) DESIGN ...... 20 7. TESTING PLAN ...... 25 REFERENCES ...... 27

LIST OF FIGURES

FIGURE 1: (LEFT) MARS CURIOSITY ROVER [17] AND (RIGHT) MARS INSIGHT LANDER [18] ...... 8 FIGURE 2: (A) CANADARM 2 CAPTURE OF CARGO VEHICLE [6], (B) DEXTRE ROBOT [7], AND (C) ROBONAUT 2 [8] ...... 9 FIGURE 3: A) ARCHINAUT CONCEPT ART, (B) CIRAS TALISMAN TESTING AT NASA LANGLEY, AND (C) DRAGONFLY CONCEPT ART [22] ...... 11 FIGURE 4: (A) RSGS TESTING AT NAVAL RESEARCH LABORATORY [19] AND (B) RESTORE-L CONCEPT ART [18] ...... 11 FIGURE 5: (A) TRUSS ASSEMBLY WITH JPL’S ROBOSIMIAN ROBOT [23], AND (B) AAREST CONCEPT ART [24] ...... 12 FIGURE 6: (A) SOLAR PANEL ASSEMBLY, LARC SUMMER 2016, (B) TRUSS ASSEMBLY, LARC SUMMER 2017, (C) STACKED STEWART PLATFORM DEVELOPMENT, LARC FALL 2017, (D) ISAT STUDY MEETING, JPL SPRING 2019 ...... 14 FIGURE 7: SLA INTERIOR STRUCTURE ...... 19 FIGURE 8: SLA PROTOTYPING ...... 20 FIGURE 9: SSP SECTION BREAKDOWN ...... 21 FIGURE 10: SLA COILED STORAGE AND PRECISION LENGTH CONTROL IN SSP TOP PLATFORM ...... 22 FIGURE 11: SSP PNEUMATIC ELECTRONIC CONTROL DIAGRAM ...... 23 FIGURE 12: GAZEBO MODEL OF SSP ...... 24 FIGURE 13: THE LEFT IMAGE SHOWS A STEWART PLATFORM (IPJR) AS AN END EFFECTOR FOR A LONG REACH MANIPULATOR (TALISMAN). THE RIGHT IMAGE SHOWS POSSIBLE APPLICATIONS FOR STACKING STEWART PLATFORMS. [25] ...... 24

NOMENCLATURE

Assembly of Space SystEMs By using Locomotion and Error-correction for ASSEMBLERS RobustnesS CIRAS Commercial Infrastructure for Robotic Assembly and Servicing EVA Extravehicular Activity HOME Highly Organized Multi-agent Enclosures HST Hubble Space Telescope IPJR Intelligent Precision Jigging Robots IRMA In-Space Robotic Manufacturing and Assembly ISA In-Space Assembly iSAT In-Space Assembled Telescope ISS International Space Station JPL Jet Propulsion Lab JWST James Webb Space Telescope LaRC Langley Research Center LEO Low Earth Orbit LSMS Lightweight Surface Manipulation System MSL Mars Science Laboratory NASA National Aeronautics and Space Administration NINJAR NASA Intelligent Jigging and Assembly Robot PROPS Persistent Robotically Operated Platform for Science RSGS Robotic Servicing of Geosynchronous Satellites SLA Soft Linear Actuator SSP Soft Stewart Platform STMD Space Technology Mission Directorate TALISMAN Tension Actuated Long-reach In-Space Manipulator TDM Technology Demonstration Missions TRL Technical Readiness Level V&V Verification & Validation

1. INTRODUCTION TO IN-SPACE ASSEMBLY

Every decade a new large space telescope mission is undertaken with the goal to answer the age-old questions like are we alone in the universe and can we detect life elsewhere.

To answer these questions NASA has been trying to design bigger and more complex space telescopes like the James Webb Space Telescope (JWST) but they are hitting problems trying to keep large missions within budget and on the desired schedule. For JWST these problems are largely driven by the difficulty required to design a complex system that can fold up the 6.5-meter diameter telescope to meet the size constraint of the launch vehicle

5-meter diameter fairing and light-weighting the design to meet the rocket’s mass requirements. [1] All this time and money for a mission with a planned 5-year mission lifetime that starts only after a series of 22 deployments must occur flawlessly for JWST to even become operational. Finally, there is the concern that if JWST requires servicing like the Hubble Space Telescope (HST) did that this repair won’t be able to be performed due to JWST’s orbit at Lagrange point 2 (L2), which is much farther away from Earth than

HST’s Low Earth Orbit (LEO) and therefore human servicing is not an option in a deployment failure or other anomaly occurs.

These concerns about meeting cost and time constraints for a mission while mitigating risk and ultimately having a long telescope lifetime to allow for more science leads to the idea of a new robotic In-Space Assembly (ISA) space telescope paradigm. By assembling the telescope in-space the mission is no longer constructed by the mass and size constraints of a single launch vehicle and does not have to spend design time trying to make a complex origami structure to fit everything into one rocket. Additionally, having robots on the

2 observatory allows for the ability to respond to anomalies and repair the telescope when needed and even have scheduled servicing planned to update science instruments. Overall this concept for a new ISA telescope paradigm would result in space observatories that have a longer lifetime and therefore allow for the gain of more science to answer the burning questions of the astrophysics community. To understand the validity of this new proposed paradigm first the history of ISA must be discussed and the recent innovations in the field that offer hope to a vibrate future of robotic ISA.

2. BACKGROUND

2.1. HISTORY OF HUMAN IN-SPACE ASSEMBLY: INTERNATIONAL SPACE STATION

The only in-space assembly of a large structure to date is the International Space Station

(ISS). [2] The ISS is a spacecraft that serves as an international laboratory that has been orbiting the Earth with humans onboard 24/7 since 2000. This space laboratory is approximately the size of a football field and took more than 100 international launches to bring up all the materials into orbit and carry up crew to assemble. More than 140 spacewalks were performed by astronauts to assemble and service the ISS. The reality is through it is difficult for humans to work in space; the longest Extravehicular Activity

(EVA), where an astronaut was in a space suit outside of the main spacecraft doing work in space, was around 9 hours. On average EVAs last around 6 hours, which is why so many needed to be carried out in order to construct the space station. In addition, astronauts usually only spend a limited amount of time in space, around 6 months. Longer duration missions have been taken, up to a year, but there are concerns for the health of humans

3 exposed to the microgravity and radiation of space. Robots on the other hand often exceed their expected duration of operation; such as Mars rover Opportunity which was supposed to operate ninety days but has been sending data back to earth for nearly fifteen years. The debate is can robotics and autonomy progress to a great enough level that a team of robots could assemble something in-space and deal with unexpected circumstances to the level or better of a human assembly team.

2.2. HISTORY OF HUMAN IN-SPACE REPAIR: HUBBLE SPACE TELESCOPE

In 1990, the Hubble Space Telescope (HST) [3] was deployed and it was discovered that there was an aberration in the primary mirror that caused the images the telescope could produce to be fuzzy. The Hubble Space Telescope required a total of five servicing missions to make it operational; these repairs were carried out by astronauts in a series of

Extravehicular Activity (EVA). The Hubble Space Telescope (HST) initially cost only 5 billion dollars but when it was discovered in orbit that the primary mirror had an aberration causing fuzzy images a series of five human servicing missions were conducted to repair the telescope to operational status and increased the overall project cost to 10 billion dollars. Robotic ISA has been considered in the past for repair missions such as Hubble but set aside due to concerns about increased cost.

2.3. FUTURE OF IN-SPACE ASSEMBLED TELESCOPES

2.3.1. ASTROPHYSICISTS DESIRE FOR LARGE SPACE TELESCOPES

Astrophysicists are asking for larger and larger space telescopes to advance their observations in topics such as the origins of galaxies and Exoplanets. JWST is the largest

4 space telescope designed and built currently but astrophysicists state that 10 – 16 meter- class space telescopes are desired for increased science capabilities. [4]

2.3.2. JAMES WEBB SPACE TELESCOPE

The United States government just invested over 10 billion dollars in the technology development, design, manufacturing, and soon launch of the James Webb Space Telescope

(JWST). [1] The James Webb Space Telescope (JWST) has an aperture size, diameter, of

6.5 meters is planned to be launched in a 5-meter fairing. Due to this size restriction the telescope and its sunshield, an umbrella like device to protect the telescope from the heat of the sun, will need to be folded up and fit into this smaller fairing for launch. Once the telescope is in its desired orbit it must perform 22 deployment events perfectly, to unfold its mirror and deploy its sunshade, in order for it to become an operational space telescope.

Scientists and engineers have performed all these deployment tests on the ground but there is no certainty they will be successful in space. The concern is that due to JWST’s orbit much farther away from Earth servicing is not an option as it was for HST. These assessments of risk bring many space scientists and engineers to question if building large telescopes in-space, and incorporating servicing and repair robotics, would be preferable to relying on a single launch and a series of perfect deployments to make a telescope observatory operational.

2.3.3. DECADAL SURVEY TELESCOPE PROPOSALS

The newest telescope proposals as a part of the 2020 Decadal Survey for the National

Aeronautics and Space Administration’s (NASA’s) Astrophysics Division all still have concepts based on the single launch, deployment reliant model of space telescope

5 production. Congress recently required these proposals to include a plan for servicing but based on their interim reports their servicing plans are not well developed and none of them incorporate robotic ISA into their mission plan. Robotic In-Space Assembly (ISA) and servicing could be utilized to optimize cost, mitigate risk, and increase science value of future space telescope missions.

2.3.4. NASA IN-SPACE ASSEMBLED TELESCOPE STUDY

The NASA in-Space Assembled Telescope (iSAT) Study was chartered to answer the question: “When is it advantageous to assemble space telescopes in space rather than to build them on the Earth and deploy them autonomously from individual launch vehicles?”

[5] The iSAT Study recommended to the 2020 Astronomy and Astrophysics Decadal

Survey that ISA be considered as a possible construction method of future large space telescopes for its possible risk, cost, and science benefits. By assembling the telescope in- space the mission is no longer constructed by the mass and size constraints of a single launch vehicle and does not have to spend design time trying to make a complex origami structure to fit everything into one rocket. Additionally, having robots on the observatory allows for the ability to respond to anomalies and repair the telescope when needed and even have scheduled servicing planned to update science instruments. Overall this concept for a new ISA telescope paradigm would result in space observatories that have a longer lifetime and therefore allow for the gain of more science to answer the burning questions of the astrophysics community.

2.3.5. BENEFITS OF ROBOTIC IN-SPACE ASSEMBLY AND SERVICING FOR A FUTURE TELESCOPE MISSION

Conceptually, the benefit of robotic ISA is that for the first mission it would not be able to beat the current space telescope paradigm in terms of cost but that it will reduce risk and increase science value.

2.3.5.1. ISA COST BENEFITS

For the first ISA mission the costs for technology development would cause it to either break even with the current paradigm or be slightly costlier. After the first ISA missions many lessons learned will allow the process to decrease in cost. ISA allows for a project to decide to use more launch vehicles, adding additional launch cost, to give the added benefit of not having to spend engineering time and dollars on light-weighting their system to fit into a single launch vehicle. is their mass Additionally, there are opportunities for mission costs to decrease down the line by reducing the standing army at any single time of the project by being able to have a flexible schedule where you only bring people onto the mission when needed.

2.3.5.2. ISA RISK REDUCTION

In terms of risk robotic ISA allows for repeatable assembly processes that can be tested on the ground and then carried out in space. The assembly line for manufacturing in factories have been revolutionized by robotics allowing for faster and more precise operations. This efficiently could be carried into the space robotic systems and with the integration of vision systems the operations could be overseen by human operators on the ground for added quality control. Assembling the components in their final operational environment also reduces the risk of replying on perfect deployments by replacing those complex systems with simpler system that are assembled together to make the final large system required.

Having these robots on the telescope also allows for anomaly resolution, the ability to service it if something goes wrong instead of just leaving it stranded in space. Also planned servicing could be scheduled to upgrade components and instruments when new technology is developed allowing for an adaptable telescope.

2.3.5.3. ISA ADDED SCIENCE VALUE

Since ISA could allow for the building of larger aperture telescopes in space that would greatly increase the possible science value because a larger aperture allowing for better observations. Additionally, with the option to upgrade instruments throughout time the telescope could serve more similar to a ground-based observatory where instruments can be swapped and upgraded allowing for a larger variety of science to be observed throughout time. This all culminates to the huge benefit for ISA to allow for the creature of a space telescope with a long lifetime that can adapt with the changes in science and decrease future costs for having to develop a new telescope every time the previous one ends its life.

3. SPACE ROBOTICS STATE OF THE ART

A key engineering development to enable the in-Space Assembled Telescope (iSAT) is leveraging the state of the art in space robotics for assembly and servicing of the space telescope. Space robotics concerns two primary domains: in space and on planetary surfaces. Planetary surface exploration includes reconnaissance, sample acquisition and analysis, and human exploration assistance. In-space operations involve assembly, inspection, maintenance and servicing, and human extravehicular activity (EVA) assistance.

3.1. ROBOTIC PLANETARY SURFACE EXPLORATION

Robotic space exploration dawned with a series of lunar spacecraft including probes, orbiters, and rovers such as Mariner, Surveyor, and Ranger. Robotic exploration of Mars has been favored in leu of human exploration. Mars has been studied by both landers, including Viking 1 and 2, Pathfinder, Phoenix, InSight, and rovers, Sojourner, the Mars

Exploration Rovers Spirit and Opportunity, and Curiosity. Today the state of the art for planetary surface exploration is Curiosity, the Mars Science Laboratory (MSL) rover with the next generation rover, Mars2020, set to launch this year.

FIGURE 1: (LEFT) MARS CURIOSITY ROVER [17] AND (RIGHT) MARS INSIGHT LANDER [18]

3.2. ROBOTIC IN-SPACE OPERATIONS

Robotic in-space operations have been focused around the Space Shuttle and International

Space Station (ISS). There are a variety of robotic arms on the ISS that can perform either gross manipulation such as cargo capture or dexterous manipulation such as changing scientific instruments. The gross manipulators include the Space Station Remote

Manipulator System (SSRMS), also known as Canadarm 2 and the Japanese Experiment

Module Robotics System (JEMRMS) main arm. The dexterous manipulators include

Dextre the Special Purpose Dexterous Manipulator (SPDM), the JEMRMS Small Fine

Arm, and the European Robotic Arm (ERA). There have also been tests with free-flying robots including the AERCam Sprint, a teleoperated free-flying camera tested in 1997 during STS-87, and more recently with robots such as SPHERES and Astrobee inside the

ISS. Additionally, the ISS has tested the humanoid Robonaut 2 (R2) robot utilizing its dexterous manipulation capabilities inside the station; development of the next generation of this robot Valkyrie (R5) is underway on the ground.

FIGURE 2: (A) CANADARM 2 CAPTURE OF CARGO VEHICLE [6], (B) DEXTRE ROBOT [7], AND (C) ROBONAUT 2 [8]

3.3. ROBOTIC IN-SPACE ASSEMBLY RESEARCH

Alongside the flight tests there have been developments in ground testing of space robotics for in-space assembly and servicing applications since the early 2000s with Skyworker robotics assembly, inspection, and maintenance at Carnegie Mellon [9] and Ranger testing at the Neutral Buoyancy Laboratory at University of Maryland [10].

In 2015 NASA’s Space Technology Mission Directorate (STMD) gave funding for the

Technology Demonstration Missions (TDM) program’s In-Space Robotic Manufacturing and Assembly (IRMA) project to select three ground-based ISA technology development demonstrations. [11] These three “tipping point” projects were focused on NASA and

10 industry partnerships completing a ground demonstration in two years to determine if similar technologies may be advanced enough for a flight demonstration. One of these projects was called Archinaut and was led by the company Made In Space Inc. and aided by NASA’s Ames Research Center. After the two years the Archinaut project conducted a successful test in the summer of 2017 of the first large-scale additive manufacturing in a vacuum and thermal conditions of space. [12] The Commercial Infrastructure for Robotic

Assembly and Servicing (CIRAS) project focused on assembling truss structures in space was led by Orbital ATK, and owned and operated by Northrup Grumman, and partnered with researchers at NASA’s Langley Research Center and US Naval Research Laboratory.

The project built the NASA Intelligent Jigging and Assembly Robot (NINJAR) in the summer of 2017 and successfully tested its abilities to precisely position the joints for a truss structure and have truss struts be adhered together with a welding analog. [13] Later on the project performed a demonstration of the other robot proposed to be used in assembling these large space truss structures, the Tension Actuated Long-reach In-Space

Manipulator (TALISMAN) successfully showed its capability to be used as a large robotic arm in simulated zero-g conditions in a testing facility. [14] The third tipping point was called Dragonfly and was run by the Space Systems Loral with partners at NASA Langley

Research Center, NASA Ames Research Center, Tethers Unlimited, and MDA US Systems

LLC. Dragonfly worked on enabling robotic satellites in Low Earth Orbit and successfully demonstrated the ability for its dexterous 3.5-meter robotic arm to install a delicate antenna onto a satellite in September of 2017. [15] Progress of these IRMA projects show that the robotic capability for ISA and in-space manufacturing is being developed and with more

11 funding could be tested more to get to a flight-ready state for a future ISA telescope mission. [16] [17]

FIGURE 3: A) ARCHINAUT CONCEPT ART, (B) CIRAS TALISMAN TESTING AT NASA LANGLEY, AND (C) DRAGONFLY CONCEPT ART [22] There have also been efforts in developing robots for satellite servicing in both NASA’s

Restore-L [18] and DARPA’s Robotic Servicing of Geosynchronous Satellites (RSGS) [19] programs.

FIGURE 4: (A) RSGS TESTING AT NAVAL RESEARCH LABORATORY [19] AND (B) RESTORE-L CONCEPT ART [18]

3.4. ROBOTIC TELESCOPE ASSEMBLY RESEARCH

There have even been focused robotic telescope assembly ground testing including very early robotically assembled truss testing at NASA Langley’s Automated Telescope

Assembly Lab (ASAL) in 2002 and newer testing as a part of their Robotic Assembly of

Modular Space Exploration Structures (RAMSES) project. [20] JPL has also performed a multitude of telescope assembly related testing including deployment of modular primary mirror backing structures [21] and autonomously assembling a 3m x 3m truss with JPL’s

RoboSimian robot. [22] Additionally, there has been collegiate research into the concept of autonomously assembled space telescopes including the Autonomous Assembly of a

Reconfigurable Space Telescope (AAReST) project out of Caltech and a Cornell run

2018 NIAC on a modular, self-assembling space telescope swarms.

FIGURE 5: (A) TRUSS ASSEMBLY WITH JPL’S ROBOSIMIAN ROBOT [23], AND (B) AAREST CONCEPT ART [24]

Looking at this heritage of space robotics all of the proposed robotic operations for iSAT are within the capabilities of the current state-of-the art long reach manipulators on the ISS.

As the capability of autonomous robotic assembly advances though ground testing and is verified though future flight tests these capabilities will further advance and offer the potential for more complex assembly and servicing endeavors.

4. ROBOTIC IN-SPACE ASSEMBLY RESEARCH

I have collaborated with researchers at NASA Langley Research Center (LaRC) and the

NASA Jet Propulsion Laboratory (JPL) to further ISA robotics research. At these centers

I gained experience leading teams of interns and contractors and developing the mechanical hardware, electrical systems, and software for robots used for various ISA demonstrations.

Our research has spanned many applications, including precision jigging robots for solar array assembly, heterogeneous teams of robots for truss construction, lunar crane development, modular soft robots, stacked Stewart platform manipulators, reconfigurable satellites with serviceable scientific payloads, robotic starshade assembly, and in-space assembly of telescopes.

(a) (b)

FIGURE 6: (A) SOLAR PANEL ASSEMBLY, LARC SUMMER 2016, (B) TRUSS ASSEMBLY, LARC SUMMER 2017, (C) STACKED STEWART PLATFORM DEVELOPMENT, LARC FALL 2017, (D) ISAT STUDY MEETING, JPL SPRING 2019

4.1. NASA LANGLEY RESEARCH CENTER

The very first project I worked on with NASA was the summer of 2016, after my freshman year, at NASA LaRC making Intelligent Precision Jigging Robots (IPJR) for the Robotic

Assembly of Solar Array Modules. During this summer I worked with two other interns to design, build, and test components for a teleoperated trial in which a team of robots,

15 consisting of LSMS (a long reach manipulator) and an IPJR, assembled solar array modules onto a backbone truss. This project required me to rapidly prototyped designs for the interfacing elements of the two robots, utilizing a MakerGear M2 3D printer, a waterjet,

Arduinos, and breadboards to allow for quick iteration of hardware and software, maximizing verification time. Our work on IPJR was summarized in the paper we published “Structure assembly by a heterogeneous team of robots using state estimation, generalized joints, and mobile parallel manipulators." [25]

The next time I went to NASA LaRC was the summer and fall of 2017. I worked on two projects, the Commercial Infrastructure for Robotic Assembly and Servicing (CIRAS) tipping point project and the Assembly of Space SystEMs By using Locomotion and Error- correction for RobustnesS (ASSEMBLERS) project. CIRAS allowed me to take on a leadership role over six other interns to develop the mechanical, electrical, and software for a robot called NASA Intelligent Jigging and Assembly Robot (NINJAR). We conducted a successful demonstration of NINJAR 2.0 in which it precisely positioned eight truss joints then team members attached struts between the joints to complete the truss bay within 5-mm and 3-deg of the reference truss. In addition, we conducted a more advanced demo – a tele-operated trial in which a truss bay was constructed by a team of three robots:

NINJAR, the Strut Assembly, Manufacturing, Utility & Robotic AId (SAMURAI), and the

Lightweight Surface Manipulation System (LSMS). Team members operated the robots with controllers: SAMURAI was an end effector of LSMS and handed off truss joints and struts to NINJAR. Our work on CIRAS was summarized in the paper we published

“Validation of Operations for the In-Space Assembly of a Backbone Truss for a Solar-

Electric Propulsion Tug.” [26] For ASSEMBLERS I designed and made renders for in-

16 space robotic assembly concepts using Creo Parametric and lead a team of interns and contractors in building two robots, each comprised of four Stewart platform units stacked on top of each other. Our work on ASSEMBLERS was summarized in the paper we published “A Reinforcement Learning Approach for the Autonomous Assembly of In-

Space Habitats and Infrastructures in Uncertain Environments. [27]

Finally, the summer of 2018 I worked with two other interns on a soft robotics project called Highly Organized Multi-agent Enclosures (HOME) to develop two soft robot modules that could move, join, shape, and rigidize. This project tied in very well with some preliminary prototyping I was doing for my master’s thesis of creating a soft Stewart platform robot which I will finish in Spring 2020. Additionally this past summer I lead a team of seven interns and contractors in completing a demonstration where a miniature version of the Lightweight Surface Manipulation System (LSMS-mini), small lunar crane, was mounted to the platform of a mock-lunar lander and performed tasks such as unloading payloads onto the back of a rover, swapping end effectors, charging the rover, and deploying ground solar panels.

4.2. NASA JET PROPULSION LABORATORY

I have also gotten the opportunity to work at the NASA JPL in the Robotic Vehicles and

Manipulators Group on a satellite servicing project called the Persistent Robotically

Operated Platform for Science (PROPS). I focused on designing and testing components for a hybrid passive isolation and active pointing system for the modular satellite’s pallet.

The summer of 2018, I designed, computationally validated, and created experimental testing plans for loop flexures used to passively mitigate high frequency motion. I

17 conceptualized an active disturbance eliminator system comprised of four actuators, used for active pointing to compensate for low frequency motion/drift, to effetely keep instruments “still” despite disturbances from the satellite truss that they are mounted to. I also designed the electrical motor controller system with encoder feedback for four pointing stepper linear actuators and prototyped an attitude measurement system using a commercially available camera and AprilTag markers as proxy for a star tracker and stars, respectively. The fall of 2019 I created a controls architecture and wrote the Python code to run the active precision pointing system I developed the previous summer, to maintain instrument attitude within ± 3 millidegrees while counteracting disturbances under 1

Hz. In addition, I conducted testing and created sequences for robotic arm maneuvers including end over end walking, instrument manipulation, and the complete autonomous assembly of a 2.5-meter starshade mockup. Our work on PROPS was summarized in the paper we published “Technologies for a Robotically Assembled and Maintained Science

Station for Earth Observations.” [28]

4.3. NASA IN-SPACE ASSEMBLED TELESCOPE STUDY

I was a member of the NASA in-Space Assembled Telescope (iSAT) study. This study was focused submitting a white paper, called “When is it Worth Assembling Observatories in

Space?” [5] to the National Academies’ 2020 Astronomy & Astrophysics Decadal Survey.

My role on the study was similar to that of a system engineer, I was part documentarian, part organizer. I took meticulous notes at weekly telecons and large face to face meetings and tied together the content generated from the various subsystems of subject matter experts (structures, optical, spacecraft, etc.). I also had the great opportunity to write the

18 final report of the study to support the white paper submitted to the decadal survey. This over 200-page report brings together all the work of the nearly two-year study and the various findings and recommendations of the study members for the opportunity ISA offers to future large space telescopes.

5. SOFT LINEAR ACTUATOR (SLA) DEVELOPMENT

The SLA is a pneumatic linear actuator with precise length controllability and a small stored length. I have found research on some soft linear actuators, but they are often just used to extend and retract from a beginning to a final distance but with low controllability of their length throughout the movement. My SLA concept, shown in Figure 7, involves an inner inflatable tube that can be inflated from an air source to extend the actuator. To control actuator length there will be a soft rack on the sides of the actuator that will interface with a pinion in the top platform of the SSP to control the extension and retraction of the

SLA. When the SLA reaches its desired length, it will be rigidized by causing laminar jamming by pulling vacuum on layers of paper between the exterior of the inflation tube and the interior of another larger tube. This SLA design works for terrestrial applications, for in-space applications a similar design could be used but there would be an exterior inflation tube and the laminar jamming effect would be caused by inflating both the inner and outer tubes and squeezing the section in-between them.

FIGURE 7: SLA INTERIOR STRUCTURE

One end of the SLA would have the pneumatic tubes to control inflation of the inner tube and vacuum on the outer layer. The other side of the SLA would be able to be coiled for storage. This allows the SLA to have a high full extension to full retraction ratio, shown in

Figure 8.

FIGURE 8: SLA PROTOTYPING

6. SOFT STEWART PLATFORM (SSP) DESIGN

Six SLAs can be used to form a SSP. The top platform of the SSP would house the system for SLA length control and coiling of the excess actuator for storage, while the bottom platform would house the pneumatic actuator and vacuum control, shown in Figure 9.

FIGURE 9: SSP SECTION BREAKDOWN

The system in the top platform would control the SLA length by having two pinions (one on either side of the SLA) on a motor that can rotate and interface with the racks on the sides of the SLA to control the extension and retraction of the SLA. Rollers will be used in between the pinions to compress the actuator layers and create a seal for the end of the

SLA. Then the excess actuator will be coiled inside the platform to maximize storage space.

FIGURE 10: SLA COILED STORAGE AND PRECISION LENGTH CONTROL IN SSP TOP PLATFORM

The bottom plate of the SSP will house the pneumatic control system. Six solenoid valves will be used, one for each SLA, to control when each individual SLA’s inflation tube is connected to the lab air supply for extension. Once the SSP gets into its desired position the vacuum pump connected to all the vacuum ports of the six SLAs will be turned on to rigidize the SSP position. This system will be controlled by an Arduino Mega with an XBee attached to allow for wireless control.

FIGURE 11: SSP PNEUMATIC ELECTRONIC CONTROL DIAGRAM

For controlling the SSP, the planned method was to use the Robot Operating System. In preparation for this a Gazebo model was created with circular plates and six prismatic joints connecting them, shown in Figure 12. A MATLAB model of the basic Stewart platform was used to determine the placement of joints connecting the ends of the linear actuators to the platforms by editing the radius of platform plates, spacing between joint pairs on plates, and height between plates of Stewart platform.

FIGURE 12: GAZEBO MODEL OF SSP

The SSP could be used as a soft end effector for a long reach manipulator to allow it to precisely interact with fragile materials such as Kapton used for sunshields or stacked to form a mobile robot that can maneuver around structures carefully. These possible applications for SSP robots are shown in Figure 13 below.

FIGURE 13: THE LEFT IMAGE SHOWS A STEWART PLATFORM (IPJR) AS AN END EFFECTOR FOR A LONG REACH MANIPULATOR (TALISMAN). THE RIGHT IMAGE SHOWS POSSIBLE APPLICATIONS FOR STACKING STEWART PLATFORMS. [25]

7. TESTING PLAN Due to COVID-19, completion of the final physical prototypes of the SLA and SSP were not possible and therefore testing on them could not occur. Planned testing for the SLA included a force test to measure the maximum force the SLA can impact during actuation.

An actuation precision and repeatability test would have measured the smallest distance the SLA could actuate and would have repeated the same command to extend or retract a specific distance to see if it reached the same end point each time. In addition, a speed test would have been conducted to measure the time for SLA to go from full retraction to full extension. Finally, a position duration test would have left the SLA actuated to a distance for a long time and see if it changes position through leakage. Once all six SLA’s were tested and their performance characterized, they would have been assembled into a full

SSP which could have then been run through the same test campaign to analyze the force output, actuation precision and repeatability, speed, and position duration.

8. CONCLUSION Robotic ISA is required if humanity wants to build large habitats or scientific equipment, such as the large space telescopes described which astrophysicists want to be on the order of 20-meters in magnitude, because no current single launch vehicle could have enough size or mass capacity to launch the telescope in a single launch. This report also highlighted how there are benefits to building a telescope though ISA even before it is strictly required.

A robotic ISA mission for a telescope might break even in terms of cost compared to the current space telescope paradigm but the added risk mitigation and science value opportunities are of such great value. No longer would a telescope mission be reliant on perfect deployments and have a short-projected lifetime, the government could invest in

26 more robotic ISA technology development like IRMA now so that the next large space telescope is built thought ISA and has very long lifetime filled with the ability to evolve the telescope with the changing science need.

The SSP, if developed and tested further, could prove a valuable tool in the robotic ISA toolbox to allow for delicate, high precision manipulation of a large variety of materials.

As a soft robot it could handle fragile, gossamer structures such as sunshield material without risk of puncture. In-addition the high storage compatibility of the SSP compared to standard rigid Stewart platforms would make it advantageous for launching into space where size and mass availability is very limited in launch vehicles.

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