Make a Spacecraft Motion Simulator!

Abstract

How do you practice landing a spacecraft on another planet or docking it with a space station? With a spacecraft motion simulator here on Earth! In this engineering project, you will design and build your own cable-driven spacecraft motion simulator that lets you move a model spacecraft around in three-dimensional space.

Summary

Areas of Science

Space Exploration
Mechanical Engineering

Difficulty

Method

Engineering Design Process

Time Required

Short (2-5 days)

Prerequisites

None

Material Availability

Readily available

Cost

Low ($20 - $50)

Safety

No issues

Credits

Ben Finio, PhD, Science Buddies

Thanks to Ryan Caverly and James Flaten at the University of Minnesota for help developing this project.

This publication was supported by an agreement with Cornell University, under Prime Agreement MCS2107‑23‑01 from the Department of Defense, Office of Local Defense Community Cooperation. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of Cornell University nor those of Sponsor.

Science Buddies is committed to creating content authored by scientists and educators. Learn more about our process and how we use AI.

https://www.youtube.com/watch?v=_bKn2_AAMnU

Objective

Build a spacecraft motion simulator and use it to simulate maneuvers like landing or docking. 

Introduction

Docking a spacecraft with the International Space Station (ISS) or landing it on another planet is hard. You only get one chance to get it right! Scientists can practice docking and landing maneuvers here on Earth using a spacecraft motion simulator, but it is difficult to move a large, heavy object around in three-dimensional space in Earth's gravity. One solution to this problem is to use a cable-driven simulator. The payload (spacecraft or other object) is suspended in the middle of a large, empty room by cables instead of a traditional robotic arm (which resembles a human arm with joints). These cables are attached to winches driven by powerful motors that can rapidly wind or unwind the cables. Watch this video for an example of a human-sized, cable-driven motion simulator:

https://www.youtube.com/watch?v=cJCsomGwdk0

By building artificial terrain on the floor or mounting a model docking port on the wall (Figure 1), scientists can use a motion simulator to practice landing and docking maneuvers. 

Image Credit: Ryan Caverly

Figure 1. Diagram of a cable-driven spacecraft motion and docking simulator.

Designing these systems is complicated. For example, the motions of all of the motors must be synchronized so that two cables do not try to pull in opposite directions at the same time, and scientists must make sure the cables do not collide with each other or the spacecraft as they move around. In this project, you will build your own manually-driven spacecraft motion simulator like the one in Figure 2. You will control it just by pulling on the strings—no motors required. 

Image Credit: Ben Finio / Science Buddies

Figure 2. An example of what you will build in this project. A model satellite is suspended by four strings above a printout of the lunar surface with a red X marking the desired landing location.

For this project, you will need to decide how many degrees of freedom you want your model spacecraft to have. An object's number of degrees of freedom determines how many independent motions it can make in different directions. Degrees of freedom can be translational (back and forth in a line) or rotational (rotating about an axis). For example:

• An object that is constrained to move back and forth on a rail, like a train, only has one degree of freedom. It cannot move sideways or up and down, and it cannot rotate at all. So, it has one translational degree of freedom and zero rotational degrees of freedom.
• An object that is constrained to slide around on a surface has three degrees of freedom. Imagine sliding a magnet around on a refrigerator or whiteboard. You can slide the magnet in two different directions: horizontal or vertical. Any diagonal motion can be done as a combination of these two motions, so the magnet has two translational degrees of freedom. The magnet also has one rotational degree of freedom. You can twist it about a single axis, but in order to remain flat against the surface, it cannot rotate about the other two axes. The magnet has three degrees of freedom total.
• An object that is free to move in three-dimensional space has six degrees of freedom: three translational (typically called X, Y, and Z) and three rotational (typically called roll, pitch, and yaw).

Building a full six-degree-of-freedom spacecraft motion simulator and coordinating all the cable motions can be quite challenging, so in this project, we recommend starting out with two or three degrees of freedom. Keep reading to get started!

Terms and Concepts

• Motion simulator
• Cable-driven
• Payload
• Winch
• Degree of freedom
• Translational
• Rotational
• Roll
• Pitch
• Yaw

Questions

• What are the differences between a cable-driven robotic system or simulator and a "traditional" robotic arm?
• What are some advantages and disadvantages of cable-driven systems?
• How many separate cables do you think you need to achieve full control over a certain number of degrees of freedom?

Materials and Equipment

The materials listed here can be used to build a tabletop-sized, portable frame as shown in the project's procedure. To build a larger frame, you will need to scale up your materials (use thicker pipe, rope instead of string, etc.).

• 1/2" diameter PVC pipe (12 feet total - you can purchase smaller pieces; they will be cut into 12 one-foot pieces)
• 3-way PVC 90° elbow connectors (8)
• Small screw eyes (8)
• String (at least 20 feet). String that will glide smoothly will work better than rough material like twine or yarn. Diameter must be small enough to fit through your screw eyes and tie to your model spacecraft.
• Tape measure
• Small, heavy objects to act as weights you can tie the strings to
• An object to use as your spacecraft that you can tie, tape, or glue strings to; or materials to build one (building toys such as LEGO® or K'Nex® etc.)
• An object or surface for your spacecraft to land on or "dock" with, such as a target drawn on a piece of paper or the side of a cardboard box
• Saw for cutting PVC pipe
• Scissors
• Drill with small drill bit (for pre-drilling holes for screw eyes) 

This project follows the Engineering Design Process. Confirm with your teacher if this is acceptable for your project, and review the steps before you begin.

1. Build something to use as your spacecraft. Make sure it includes tie points where you can attach string. Figure 3 shows several example LEGO® vehicles. You can use building toys or craft supplies. 
2. Make something for your spacecraft to land on or dock with. This could be as simple as a target drawn on a piece of paper, but you could also print out an aerial photo of the Martian or Lunar surfaces, or build a docking interface. Figure 3 shows a LEGO® spacecraft that can magnetically dock with a "space station."

Image Credit: Ben Finio / Science Buddies

Figure 3. Assorted model spacecraft made from LEGO bricks. From left to right: a small satellite with two tie points, a larger satellite with four tie points, a rectangular payload with eight tie points (four top and four bottom), and a spaceship that can magnetically dock with a space station.

3. Cut your PVC pipe into 12 one-foot sections.
4. Assemble your PVC frame. Connect the 12 sides to the 8 corners (elblow connectors) to form a cube, as shown in Figure 4.

Image Credit: Ben Finio / Science Buddies

Figure 4. The cube-shaped PVC pipe frame.

5. Set up your spacecraft motion simulator to test using just two strings (cables).
   1. Pick an outer side of your cube. Drill small pilot holes for the screw eyes in the left and right top corners and screw them in (Figure 5).
   2. Cut two pieces of string, each about 3 feet long.
   3. Tie one end of each piece of string to your model spacecraft.
   4. Pass one string through each of the screw eyes.
   5. Tie the other ends of the strings to small, heavy objects. The objects should be heavy enough that they can hold your spacecraft up in the air when the strings are pulled tight (Figure 6).

Image Credit: Ben Finio / Science Buddies

Figure 5. Close-up of a screw eye screwed into the PVC frame.

Image Credit: Ben Finio / Science Buddies

Figure 6. A model satellite suspended by two strings, which pass through screw eyes screwed to the outer top corners of the PVC frame and are tied to spools of wire that act as weights.

6. Practice maneuvering your spacecraft by controlling the two strings.
   1. Can you make your spacecraft move straight up and down? Hint: try pulling on (or loosening) both strings at the same time.
   2. Can you make your spacecraft move left to right? Hint: try pulling on one string while loosening the other. 
   3. Can you make your spacecraft move diagonally?
   4. How does your spacecraft's rotation change as it moves around? Can you independently control the rotation? Is it possible to keep the same horizontal and vertical position and have the spacecraft rotate in place?
7. Set up your spacecraft motion simulator to test with three cables.
   1. Connect three more screw eyes to form a triangle around the undersides of the top pieces of your PVC frame (Figure 7).
   2. Cut or untie the strings you initially tied to your spacecraft.
   3. Reconnect your spacecraft with strings passed through the three new screw eyes and tied to three weights.

Image Credit: Ben Finio / Science Buddies

Figure 7. Model satellite suspended from strings (orange yarn is used for better visibility) that pass through three screw eyes that form a triangle around the top edge of the frame.

8. Practice maneuvering your spacecraft by controlling the three strings. Since you only have two hands, you can use the weights to hold the strings in place and move the strings incrementally instead of pulling on them (or loosening them) continuously.
   1. Can you make your spacecraft move left to right or front to back while maintaining a constant altitude (distance from the ground)?
   2. Can you move your spacecraft up and down while maintaining a constant horizontal position?
   3. Can you independently control the rotation of your spacecraft while maintaining a constant horizontal and vertical position?
9. Once you have figured out how to control your spacecraft, practice your landing or docking maneuver. How easy is it to control your spacecraft and move it into the position and orientation that you want?
10. Can you think of ways to improve your cable-driven motion simulator by adding more cables and/or changing where the cables are attached to your model spacecraft? See the Variations section for more suggestions.

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Post a Question

Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.

Variations

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