Validation of a CubeSat Stellar Gyroscope System (SGSat) - 03.15.17

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Satellites in low Earth orbit experience drag from Earth’s atmosphere, which can cause them to slow down and fall back to Earth. Correctly using propulsion to keep the craft in orbit requires determining the satellite’s orientation as it moves through space. The Validation of a CubeSat Stellar Gyroscope System (SGSat/KySat-3) investigation uses pictures of star fields to orient a small satellite and tests new software to predict the satellite’s path as it experiences atmospheric drag.
Science Results for Everyone
Information Pending

The following content was provided by James E. Lumpp, Jr., Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom:

Principal Investigator(s)
James E. Lumpp, Jr., Ph.D., University of Kentucky, Lexington, KY, United States

Co-Investigator(s)/Collaborator(s)
Suzanne Weaver Smith, Ph.D., University of Kentucky, Lexington, KY, United States

Developer(s)
Space Systems Laboratory, University of Kentucky:Department of Electrical and Computer Engineering, Lexington, KY USA, Lexington, KY, United States
NASA Kentucky EPSCoR Program, Lexington, KY, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Space Exploration, Earth Benefits

ISS Expedition Duration
September 2016 - April 2017

Expeditions Assigned
49/50

Previous Missions
KySat-2 (predecessor) was launched into orbit on the Educational Launch of Nanosatellites (ELaNa) IV mission in November 2013.

^ back to top

Experiment Description

Research Overview

  • Current methods of determining a satellite’s movement through space involve star databases, large cameras, heavy power requirements, and large computational power. These aren’t conducive to small satellites, which are smaller and cheaper than their larger rivals.
  • Small satellites have historically been limited in utility partially because it is difficult to determine how they are moving, thus limiting how accurately they can be pointed – whether at earth features, space objects, or other small satellites.
  • The SGSat/KySat-3 investigation’s Stellar Gyroscope uses a small camera to take consecutive pictures of stars. A low-power computer on the satellite then analyzes those pictures, identifying the same star in both images, and measures how much the star moved in the pictures. This measurement is used to determine how the satellite moved between those consecutive images.
  • With the miniature physical scale of the Stellar Gyroscope and low power consumption of the process, this method of determining a satellite’s movement through space is more well-suited to small satellites, with their limited size and available power, than the more traditional options. • With knowledge of how a small satellite is moving through space, it can be more accurately pointed, increasing its scientific utility.
  • Due to the altitude of ejection from the International Space Station (ISS), the satellite’s “shuttlecock” shape from its deployable solar panels contribute to its movement against atmospheric drag.
  • The Smart Nanosatellite Attitude Propagator (SNAP) is a software tool developed at the University of Kentucky Space Systems Laboratory, and is used to characterize the satellite’s orbit due to this atmospheric drag.

Description

Small spacecraft typically use micro-electrical mechanical system (MEMS) gyroscopes to measure angular rate data to determine changes in the spacecraft’s attitude. However, MEMS gyroscope readings are subject to drift due to sampling and measurement noise, becoming unreliable after a few minutes, particularly at low angular rates. While not in eclipse, small spacecraft can use the sun vector to provide absolute attitude knowledge to reset such drift. However, in eclipse and without the sun vector, spacecraft are restricted to star trackers, which require a large database and high-quality optics, or infrared (IR) sensors to sense the Earth’s horizon, which require a cooling system and a rotation mechanism. Neither of these options is ideal for small spacecraft, which pose significant volume and power restrictions. The objective of the stellar gyroscope is to provide such an absolute attitude measurement to periodically reset this MEMS gyroscope drift in a package more suitable for small spacecraft.
 
The stellar gyroscope works by starting with two pictures of star fields. First, the brightest stars in the pictures are identified by filtering noise and applying a brightness threshold. Next, an algorithm called Random Sample Consensus (RANSAC) is applied to determine a proposed rotation matrix between the images. RANSAC works by comparing a random set of the brightest stars in both images, then calculating a rotation matrix between those stars, then testing that rotation matrix against the stars that weren’t randomly chosen. If a threshold percentage of the remaining stars in the first image match up to stars in the second image using that rotation matrix, then the test is completed and the stellar gyroscope reports the rotation matrix as the attitude propagation of the spacecraft.
 
The stellar gyroscope hardware consists of a single five megapixel camera and a Beagleboard-xM single-board Linux computer. This hardware was previously flown on KySat-2, an identical CubeSat to the Validation of a CubeSat Stellar Gyroscope System (SGSat/KySat-3), on the ELaNa IV mission in November 2013. All subsystems were verified as operational on that mission; however, uplink problems at the ground stations and suspected radiation damage prevented the team from validating the stellar gyroscope. Lessons learned from that mission are applied to improve the operations of SGSat/KySat-3 to enhance the chances of successful validation of the stellar gyroscope.
 
In addition to the stellar gyroscope for determining the spacecraft attitude while in orbit, SGSat/KySat-3 also verifies the utility of using atmospheric drag as a passive attitude control method. SGSat/KySat-3’s deployable solar panels enhance the atmospheric drag experienced by the spacecraft at the ISS altitude. By using the onboard camera to visually sense the Earth’s horizon, as well as onboard sensors, it can be determined if the spacecraft’s attitude is stabilized by atmospheric drag. This design is predicted to shape the spacecraft’s attitude profile like a shuttlecock, based upon previous theoretical research conducted by the University of Kentucky. This orbit was predicted by the Smart Nanosatellite Attitude Propagator (SNAP) software tool, developed by the University of Kentucky; verification of the spacecraft attitude profile on-orbit also verifies the predictive capabilities of SNAP.

^ back to top

Applications

Space Applications
People have used the stars for navigation for thousands of years. Star fields can determine a satellite’s attitude in orbit, but this usually requires advanced computers to complete the calculations. SGSat tests a simple method for determining attitude for small spacecraft, and tests a new software tool that predicts the satellite’s future path. Accurate prediction of a satellite’s orbital trajectory benefits small-satellite programs at universities, private industry and at NASA.

Earth Applications
Small satellites can dramatically reduce the risk and cost of accessing space, but they can also be difficult to maneuver, because their small size limits their power supplies and capacity for navigation. SGSat tests new Smart Nanosatellite Attitude Propagator (SNAP) software, developed by a team of undergraduate and graduate students at the University of Kentucky, that improves satellite orbit tracking and prediction. This benefits small-satellite programs used for Earth observation, telecommunications and research.

^ back to top

Operations

Operational Requirements and Protocols

No crew interaction is required for this investigation, other than ensuring ejection from ISS. Due to battery life of the lithium ion cells, it is requested (though not required) that ejection occur during the first six months on-orbit.
 
No on-orbit procedures from the crew are required. Once ejected, SGSat completes a self-checkout to ensure functionality of all subsystems, conducts a preliminary stellar gyroscope test involving comparing a calculated attitude propagation to the measured attitude propagation from a high-fidelity MEMS gyroscope for a short duration, and transmits the results of this test until contact is made with University of Kentucky ground stations. After contact, the team at the University of Kentucky ground station transmits commands to replicate stellar gyroscope test results and conducts further, more complicated tests to fully validate the stellar gyroscope. The team also uses the onboard camera to visually sense the Earth’s horizon to provide feedback on whether the spacecraft’s “shuttlecock” design is effectively using atmospheric drag for stability.

^ back to top

Decadal Survey Recommendations

Information Pending

^ back to top

Results/More Information

Information Pending

^ back to top

Related Websites
NASA Kentucky Space Grant & EPSCoR Programs
Space Systems Laboratory
NASA Education - Experimental Program to Stimulate Competitive Research

^ back to top


Imagery

image
KySat-3 is a 1-Unit CubeSat designed to measure the spacecraft movement through space using the apparent motion of stars in a small camera’s field of view. Image courtesy of the University of Kentucky.

+ View Larger Image


image
University of Kentucky students Timothy Lim and Zachary Porter perform subsystem upgrade testing for a CubeSat that will be launched into orbit from the International Space Station to test an experimental stellar gyroscope method for small spacecraft attitude determination developed by the UK Space Systems Lab.  Image courtesy of the University of Kentucky.

+ View Larger Image


image
The Smart Nanosatellite Attitude Propagator (SNAP) software tool predicts a small satellite’s attitude profile on orbit. This software was created by the University of Kentucky Space Systems Laboratory, and is used by researchers and satellite designers around the world.  Image courtesy of the University of Kentucky.

+ View Larger Image