The document describes a robotic arm subsystem for a free-flying robot on the International Space Station. It provides an overview of the free-flying robot and its components, including a robotic arm. Key requirements for the arm subsystem are listed, such as a mass limit of 1kg, range of motion specifications, grasping capabilities, and electrical safety standards. The task is to decompose the arm subsystem and document the process.

1. Systems Description Document
Robotic Arm for Free Flyer Robot on the International Space Station
The task is related to the Arm Sub-system described in detail in section 2. A description of the
entire system free flyer system is provided first in order to set the context for the operational
scenario of the Arm sub-system.
1.0 Robotic Free Flyer Robot Overview
Astronauts and robots currently work together to perform a number of different tasks supporting
reseach, operations and maintance on board human space flight vehicles like the International
Space Station. One type of robot NASA is developing is a next generation free flying robot for
testing and operation on board the International Space Station. A free flyer robot is one that has
the capability to move around inside the space station on it’s own without interfacing or
interfering with the space station. This type of robot can perform a number of tasks that can be
routine, repetitive, or simple but long duration such as surveys and inspections, serving as a
mobile sensor platform, or even as a mobile camera to film activites or special events like
astronauts speaking to school children. Although not considered a fully capable robot, NASA
currently has a platform named SPHERES on the International Space Station -
http://www.nasa.gov/spheres. The new free-flyer robot being developed will have many new
capabilities but one of the principle additions is a robotic arm. At the highest level, the overall
robotic free flyer system includes the robot, a dock/resupply station for replenishing power, and
hardware and software for communication, control and data transfer (Figure 1).
The free flyer robot element consists of structure, propulsion, power, guidance, navigation &
control (GN&C), command and data handling (C&DH), avionics, communications, dock
mechanism, and robotic arm subsystems. The robot element is designed to be self-contained and
capable of autonomous localization, orientation, navigation and holonomic motion as well as
autonomous resupply of consumables while operating inside the International Space Station.
1.1 Typical example Use Case Scenario
A typical use case scenario would be for an operator on the ground to run a plan that commands
the robot to fly autonomously to a specified location while under operator supervision. The
robot would then use its arm subsystem to grip onto a specified handrail along the walls of the
International Space Station and standby until its next command. The operator would then
command the robot to begin recording video and downlink its live video stream. If needed, the
operator could adjust the camera orientation from the perched location, using the arm subsystem,
to ensure unobstructed video is being captured. If desired, the operator could also command the
robot to un-perch (release the grip) and then tele-operate or command it to autonomously
relocate to change the perspective of the camera. When the task is complete, the operator would
then command the robot to return to its docking location either via a new plan or tele-operation.
1.2 Safety Challenge for Overall System
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2. Many of the challenges faced by the robot and the development of its arm stem from operation
on-board the International Space Station. In particular, operating in close proximity to astronauts
and critical systems on the International Space Station requires special attention. The robot and
arm subsystem’s design must strike a delicate balance between meeting performance
requirements and providing an inherently safe system and sub-system.
2.0 Overview of Arm Sub-System
A robot such as this also needs a way to hold still, grip, and/or grasp objects to conserve energy,
maintain a specific position, or to carry out a task. The proposed method for this would be a type
of robotic arm sub-system that, must have at least a compliant 2 Degree-of-Freedom (DOF)
capability plus an ability to grasp, which would allow it to grab handrails and hold its position
without using its propulsion system, minimizing power required. An overview of the handrails
can be found at https://grabcad.com/challenges/nasa-handrail-clamp-assembly-challenge.
2.1 Requirements
Here is a summary list of requirements for the Arm Sub-system
General Requirements
Shall remain within the mass allocated of 1kg.
Shall remain within the volume allocated of approximately 6 x 4 x 10 inches.
Shall be capable updating software and firmware.
Range of Motion Requirements
Shall pan at 90 degrees in 15 seconds.
Shall tilt at 90 degrees in 15 seconds.
Shall have joint angle resolution of 1 degree.
Shall have minimum bend radii of 3mm.
Shall pan at least -90 to +90 out from center while perched.
Shall tilt at least -30 to +90 out from center while perched.
Attachment Requirements
Shall be capable of grasping ISS IVA handrails. (see https://grabcad.com/challenges/nasa-
handrail-clamp-assembly-challenge)
Shall allow crew to manually perch arm and gripper to handrail without requiring power from
actuators.
Shall release when the Free Flyer is impacted at 556 newton.
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3. Shall remain perched while experiencing a force of 4 newtons.
Shall change position with less than or equal to 8 lbs-force.
Mechnical Interface and Crew Safety Requirements
Shoud be packaged as replaceable modular components or as an entire unit as a minimum.
The connector from the free flyer to the arm sub-system will use the following 30-pin payload
connector at https://www.samtec.com/ with the following part number:
* Free Flyer side: Samtec IPS1-115-01-L-D
* Arm sub-system side: Samtec IPT1-115-01-L-D
Should minimize the number of mechanical attachment screws for components.
Shall only use capture screws.
Shall protect crewmembers from sharp edges, protrusions, etc., during all crew operations.
Translation paths and adjacent equipment shall be designed to minimize the possibility of
entanglement or injury to crewmembers.
The Arm Sub-system exposed surfaces shall be free of burrs.
Shall protect crewmembers from pinch hazard at arm joints.
Power and Electrical Safety Requirements
Shall support 6 hours of non-flight, perched activity.
Shall remain within the power allocated of 1W with peak power 5W (moving).
Shall comply with ISS safety standards for electrical per station interface circuit protection and
wire sizing requirements of SSP 57000, applicable module Interface Control Document. (For
this requirement please just note any element in your decomposition that is likely to contain
wiring)
Shall comply with ISS safety standards for mating/demating per the low power criteria (32V or
less, and less than or equal to 3A maximum available upstream current). (For this requirement
please just note any element in your decomposition that is likely to contain a connector)
Shall be designed such that it can be removed or returned to its stowed configuration by the
crew with hand operations and/or standard IVA tools within 10 minutes.
The unpowered Arm Sub-system shall not be damaged by Electrostatic Discharge (ESD) equal
to or less than 4,000 V to the case or any pin on external connectors. EPCE that may be
damaged by ESD between 4,000 and 15,000 V shall have a label affixed to the case in a
location clearly visible in the installed position. Labeling of EPCE susceptible to ESD up to
15,000 V shall be in accordance with MIL-STD-1686, Electrostatic Discharge Control Program
for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding
Electrically Initiated Explosive Devices). These voltages are the result of charges that may be
accumulated and discharged from ground personnel or crewmembers during equipment
installation or removal.
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4. 3.0 Task Description
Robotic arms or manipulators are common in many industrial, commercial, and hobby
environments. The form a robotic arm can take varies greatly. Also the approach that teams
take to build those arms can vary and the approaches can potentially limit the implementation
options of those arms.
The approach for designing a robotic arm would start by generating a system architecture. In
other words, what are all the parts of the sytem, how do they interact with each other, what are
the requirements and how are they related to all the parts of the system. When determining the
parts of the system, engineers typically use the process of decomposition which results in an
breakdown of all the parts. This decomposition process, including the design trades that are
made, requires the designer to break down and the decompose the system into a basic breakdown
structure that enables each function and capability to be addressed methodically. There are many
approaches to this process and different disciplines engaging in this process will result in many
answers for any given system. We are interested in exploring the differences in the way people
go through this process and the resulting decompositions they come up with.
For this task we are asking you to go through the decomposition process using whatever method
you choose. We just ask that you deliver a set of products to show your decomposition and
describe how and why you determined the resulting system architecture.
3.1 Task Delvierables
1. A graphical depiction of the decomposed structure with any interdependencies noted.
Examples are provided.
2. A written description demonstrating completeness of the decomposition – Please note
any flow down of requirements from one element to another.
3. A written description of the decision process on why the decomposed structure was
chosen.
4. A written description for each decomposed element of the system stating the
knowledge and skills required to design and build that element with a mapping to the
Freelancer skill category(s) that it could be posted under
(https://www.freelancer.com/job).
5. A completed Final Survey.
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5. 3.2 Example
There are potentially many ways you could decompose a system to perform the functions and
meet the requirements noted above. We want to explore as many decompositions as possible.
For starters we are providing one example below for the complete arm system that also shows a
partial list of the interdependencies between the elements of the system. This example only
includes samples of the products to meet deliverable number one. It is not complete. Your
products should include the other written descriptions as well. Examples of names of parts could
include joint or boom. Examples of subparts could include connector, actuator.
3.2a - Example
1.
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6. 1.2
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7. 2
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