National Aeronautics and

Space Administration

Educational Product

Educators Grades 5-12

EB-2001-04-004-JSC

Educational Brief

Humans and Robots

Following the remarkable successes of the Apollo

Moon landings and the Skylab space station program,

many space experts began reconsidering the role of

humans in space exploration. In a healthy debate on

exploration strategies, some experts concluded the goals

of the future would be best served by robotic spacecraft.

Human space travelers require extensive life support

systems. With current propulsive technologies, it would

just take too long to reach any destination beyond the

Moon. Robots could survive long space voyages and

accomplish exploration goals just as well as humans.

Other space experts disagreed. Humans have an

important place in space exploration, they contended.

Robots and humans are not interchangeable. Humans

are far more adaptable than robots and can react better to

the unexpected. When things go wrong, humans can

make repairs. This, they pointed out, was demonstrated

conclusively during Skylab, when spacewalkers made

repairs that saved the mission.

Today, new exploration strategies are at work. The

goal is no longer humans or robots. It is humans and

robots working together. Each bring important

complimentary capabilities to the exploration of space.

This has been demonstrated time and again with the

Space Shuttle Remote Manipulator System (RMS) robot

arm. The arm, also called Canadarm because it was

designed and constructed by Canada, has been

instrumental to the success of numerous space missions.

The 15-meter-long arm is mounted near the forward end

of the port side of the orbiter’s payload bay. It has seven

degrees of freedom (DOF). In robot terms, this means

that the arm can bend and rotate in seven different

directions to accomplish its tasks. Like a human arm, it

has a shoulder joint that can move in two directions (2

DOF); an elbow joint (1 DOF); a wrist joint that can roll,

pitch, and yaw (3 DOF); and a gripping device (1 DOF).

The gripping device is called an end effector. That

means it is located at the end of the arm and it has an

effect (such as grasping) on objects within its reach. The

RMS’s end effector is a snare device that closes around

special posts, called grapple fixtures. The grapple

fixtures are attached to the objects the RMS is trying to

grasp.

On several occasions, the RMS was used to grasp

the Hubble Space Telescope and bring the spacecraft into

the orbiter’s payload bay. After the spacecraft was

locked into position, the RMS helped spacewalking

astronauts repair the telescope and replace some of its

instruments. During operations, the RMS is controlled

by an astronaut inside the orbiter. The RMS actually

becomes an extension of the operator’s own arm.

Television cameras spaced along the RMS permit the

operator to see what the arm is doing and precisely target

its end effector. At times, during the Hubble servicing,

one of the spacewalkers hitched a ride on the end

effector to gain access to parts of the telescope that were

difficult to reach. The arm became a space version of

the terrestrial cherry picker.

Mobile

Transporter (MT)

Mobile Remote

Servicer Base

System (MSB)

Special Purpose

Dexterous Manipulator

(SPDM)

Space Station

Remote Manipulator

System (SSRMS)

Truss Beam

International Space Station

Mobile Servicing System

(MSS)
Humans and Robots 2 EB-2001-04-004-JSC

Robots on the International Space Station

The International Space Station (ISS), currently

under construction in Earth orbit, will have several

robots to help astronauts complete their tasks in space.

Five of the ISS international partner nations are

developing robotic systems for the station. Japan is

developing the JEM Remote Manipulator System. The

European Space Agency and the Russian Space Agency

are developing the European Robotic Arm. Canada and

the United States are developing the Mobile Servicing

System (MSS). Detailed information on each of these

systems can be obtained at the website listed below.

Mobile Servicing System

The most complex robotic system on the ISS is the

MSS. It consists of the Space Station Remote

Manipulator System (SSRMS), the Mobile Remote

Servicer Base System (MBS), the Special Purpose

Dexterous Manipulator (SPDM), and the Mobile

Transporter (MT). The MSS will be controlled by an

astronaut working at one of two Robotics Work Stations

inside the ISS.

The primary functions of the MSS robotic system on

the ISS are to:

• assist in the assembly of the main elements of the

station (e.g. aligning newly delivered modules to the

structure)

• handle large payloads

• replace orbital replacement units (plug-in equipment

designed to be periodically replaced with newer units)

• support astronauts during extravehicular activities

• assist in station maintenance

• provide transportation around the station

The main component of the MSS is the 17-meterlong SSRMS robot arm. It is similar to the Shuttle RMS

but will ride from one end of the station to the other on

the mobile transporter, which will glide along the giant

truss beam. After arriving at a worksite, the arm will

grasp payloads, modules, or other structures with its wire

snare end effector. If a work location is too distant for

the arm to reach while still attached to the transporter,

the arm can connect to an intermediate grapple fixture.

Electrical power will be rerouted through that fixture.

The SSRMS will then release its other end and

“inchworm” itself through successive fixtures until it

reaches the desired site. The SSRMS is also able to pick

up and connect to the SPDM. This unit consists of a pair

of 3.5-meter, 7-joint arms connected to a single joint

base. The SPDM can pick up small tools for repair or

servicing activities or effect delicate manipulations of

smaller objects than the SSRMS can handle.

Latching End

Effector "B”

Camera, Light Assembly

Joint Electronics Unit

B End Indicator

Stripe

Wrist Joint

(roll, pitch, yaw)

Camera Light,

Pan/Tilt Unit

Backup Drive

Arm Computer

Unit

Latching End

Effector "A"

Camera Light,

Pan/Tilt Unit Elbow

(pitch)

Space Station Remote

Manipulator System

Grapple Fixture

Interface

Electronic Units

Arm Interface Latch/Umbilical

Mechanism (4)

Latching End Effector

Power and Data

Grapple Fixture
Humans and Robots 3 EB-2001-04-004-JSC

Latching End

Effector

Body Joint

Electronic Unit

Tool

Holsters (4)

Joint

Electronics

Unit

Power/Data

Grapple

Fixture

ORU/Tool Change

Out Mechanism

Force Moment

Sensor

Wrist Joints (3)

(roll, pitch, yaw)

Elbow Joint

(pitch)

Shoulder Joints (3)

(roll, pitch, yaw)

Arm Computer

Unit (2)

Camera, Light and

Pan/Tilt Unit (2)

Body Joint

Special Purpose

Dexterous Manipulator

Robotic Work

Station

The Future

Advanced robotic systems

are under development for use

on the ISS. The ISS provides

an exceptional laboratory

for testing new

robots such as

NASA’s

Robonaut.

Robonaut will feature end

effectors based on the human hand and

will be capable of handling detailed and

complex tasks. It will interface with the MSS and serve

as a spacewalker’s assistant or surrogate for tasks too

dangerous for humans.

When astronauts return to Earth’s Moon and set foot

on Mars, they will not be alone. Robots will be there as

assistants and partners in the exploration of space.

Robotic research and application on the ISS will lead the

way for the advanced intelligent robotic systems of the

future.

Classroom Activity – Making and Using an ISS End Effector

Materials and Tools

Styrofoam coffee cups (2 each)

String - 12-cm pieces (3 each)

Cellophane tape

Plastic picnic knives (serrated)

Objectives:

• Students will learn how the end effectors for the

robotic arms used on the Space Shuttle and the

International Space Station work.

• Students will design and construct a grapple fixture that

will enable the end effector to pick up an object.

National Standards:

Science Content

• Abilities of technological design

Technology Education Content

8. Students will develop an understanding of the

attributes of design

9. Students will develop an understanding of engineering design

10. Students will develop an understanding of the role of

troubleshooting, research and development, invention and innovation, and experimentation in problem

solving

11. Students will develop abilities to apply the design

process

Teaching Plan:

In this activity, students can work

singly or in small groups of two or

three. Have students use a sawing

motion to cut through the cups. It is

easier to cut through the outer cup

first and then the inner cup.The

important part about cutting

the two cups is that their

cut-off ends lie flush

with each other when

the cups are nested.

Use the knives as scrapers

to smooth the cut edges.

Upon completing the end

effector, have your students design a

grapple fixture. The idea here is to

design something that the end effector can grab onto

without slipping off. After grapple fixtures are

completed, tell students to compare their fixture to those

created by two other students or groups. Ask them to

create a table or a chart comparing the strong and weak

points of the fixtures they evaluated. They should

summarize their

results with a

statement about

how they can

improve the

fixture they

designed.

Open - Close

Resources: For more information about robots on the International Space Station,

refer to the reference section of this web site. http://spaceflight.nasa.gov/station
Humans and Robots 4 EB-2001-04-004-JSC

Making the End Effector:

1. Nest the two cups together and cut through both cups

where indicated in the diagram by the dashed line.

Smooth the cut edges by scraping them with the

picnic knife edge.

2. Cut three pieces of string 12 centimeters long each.

3. Tape the end of the first string to the inside of the

inner coffee cup just below the cut edge. Tape the

other end of the string to the outside of the cup but do

not press this piece of tape tightly yet.

4. Repeat step 3 twice more, but place the strings about

1/3 of the way (120 degrees) around the cup from the

first string.

5. While holding the rim of the inner cup, rotate the

outer cup until the three strings cross each other. The

strings will have some slack. Pull the end of the

strings on the outside until they are straight and

intersect exactly in the middle of the opening. Press

the tape on the outside to hold the strings.

Using the End Effector:

1. Use the end effector to pick up an object such as a

pencil. Have someone hold a pencil upright. Open

your end effector so that the strings are not crossing

each other. Slip the end effector over the pencil so

that the pencil extends down the center and not

through any of the loops. Rotate the outer cup until

the strings grasp the pencil. Pick up the pencil.

2. You may find that the pencil is too slippery to be held

securely. How might you modify the pencil so that it

can be held? Design a standard grapple fixture that

can be mounted to other objects so that they can be

picked up.

3. Compare your grapple fixture to two other grapple

fixtures designed by your classmates. Which one

works the best? Why? Create a chart or a table that

evaluates the strong and weak points of each grapple

fixture you compared. How can you improve your

design?

Assessment:

Review the tables or charts created by your students.

Pay special attention to the ideas students have for

improving their grapple fixtures.

Extensions:

Search robot sites on the Internet and review

different end effector designs. How does the design of

an end effector enable it to pick up and manipulate

various objects?

Tape string loop

from outside to

the inside

Open Position Rotate Outer Cup Continue Rotating to

Close Snares

Saw through

both cups

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