Optical PAyload for Lasercomm Science (OPALS) - 07.19.17

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

ISS Science for Everyone

Science Objectives for Everyone
The Optical PAyload for Lasercomm Science tests the potential for using a laser to transmit data to Earth from space. Instead of being broadcast on radio waves, data is packaged onto beams of laser light and hardware on the International Space Station will point the laser to a receiver station on the ground. Radio waves transmission is limited by the speed that it can transfer data, but beaming information packages with lasers can greatly increase the amount of information transmitted over the same period of time.
Science Results for Everyone
Straight outta science fiction, lasers can beam information from space to Earth. Turbulence in Earth’s atmosphere can distort such data transmission, but now researchers have solved that problem using adaptive optics, or a system that corrects the received signal to compensate for distortions. This adjustment potentially increases the speed at which laser data can be transmitted and is particularly important when attempting to send data at high rates during times of high atmospheric turbulence. Overall, the investigation indicates that high speed space to ground optical communications are possible from a fast moving spacecraft.

The following content was provided by Baris I. Erkmen, and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: OPALS

Principal Investigator(s)
Michael Kokorowski, Jet Propulsion Laboratory, Pasadena, CA, United States

Co-Investigator(s)/Collaborator(s)
Abi Biswas, Jet Propulsion Laboratory, Pasadena, CA, United States

Developer(s)
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Information Pending

ISS Expedition Duration
March 2014 - March 2016; March 2016 - April 2017

Expeditions Assigned
39/40,41/42,43/44,45/46,47/48,49/50

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • The Optical Payload for Lasercomm Science (OPALS), which is part of the JPL Phaeton early career employee hands-on training program, aims to demonstrate optical communications technology. This is accomplished by transferring a video from hardware onboard the ISS to our ground receiver at JPL’s Optical Communications Telescope Laboratory (OCTL) in Wrightwood, California. To aid the ISS investigation in accurately pointing the downlink laser to the ground telescope, a laser beacon is transmitted from the OCTL to the ISS investigation, which is tracked by the investigation as the ISS travels across the sky. Each demonstration lasts for approximately two minutes during which the ISS and ground telescope maintain line of sight. The OPALS instrumentation gathers technical data during these demonstrations, which is then studied to determine hardware performance, with the goal of improving the design of next-generation optical communications systems.
  • The scientific instruments in near-Earth and deep space missions increasingly require higher communication rates to transmit acquired data back to Earth, or to support high-data-rate applications (e.g., high-definition video streams). Optical communications (also referred to as lasercomm) is an emerging technology in which the data is modulated onto lasers to transmit the information. Because laser beams are significantly narrower than radio-frequency (RF) beams, optical communications offers the promise of delivering much higher power, and thereby achieving much higher data rates than the state of the art with RF beams. However, because laser beams are very narrow, the spacecraft must be able to very accurately point the laser beam to the receiving telescope on Earth as it travels across the sky, which is one of the primary challenges of lasercomm.
  • Optical communications has the promise of meeting the high data rate expectations of future scientific instruments flying on NASAs missions, and improving the interconnectivity between near-Earth assets, such as the ISS, and Earth. OPALS is one of NASAs first demonstrations of an optical communications link from near Earth, and is designed to help chart the path for enabling optical communications in future missions. OPALS collects sensor data during the demonstrations to determine the performance of its laser link. The investigation team plans to use this data to advance the design and performance of future lasercomm links built to support NASAs space endeavors. Additionally, OPALS is used to educate a team of early career employees being trained as the next generation of JPL/NASA employees to develop space-based technologies.

Description
The Optical Payload for Lasercomm Science (OPALS), which is part of the JPL Phaeton hands-on training program, aims to demonstrate free-space optical communications technology. During the technology demonstration, a video file from the investigation on the International Space Station (ISS) is transmitted to JPLs Optical Communications Telescope Laboratory (OCTL) located at Wrightwood, California. A digital video file, encoded with forward error-correction to protect against bit errors during transmission, is modulated onto the downlink laser using on-off keying (OOK); a simple form of present vs. absent carrier wave modulation. A beacon-assisted pointing architecture is used to achieve robust and accurate pointing and includes: a camera with a wide angular view used on the ISS investigation to detect the laser beacon transmitted from the OCTL, and an on-board feedback algorithm that actively tracks this beacon as long as line-of-sight is maintained. This enables reliable transfer of the video file in the presence of many disturbances, such as the ISS motion, gimbal jitter, turbulence and background noise. Because the focus of OPALS is to demonstrate end-to-end functionality of an optical communication link, the information transfer rate is chosen conservatively as 10 megabits-per-second or higher.

The OPALS Flight System refers to the optical communications investigation assembly that is externally-mounted on the ISS. It consists of a gimbal-mounted optical head, and a sealed container to hold the electronics, laser and motor drivers. The optical head houses a camera to track the beacon and a lens collimator system to transmit the data laser. The Flight System autonomously detects, acquires and tracks the uplink beacon that is transmitted from the ground telescope as a pointing reference, and uses an on-board feedback system to mitigate external disturbances. The Ground System refers to the receiver system that is located at the OCTL. It utilizes the OCTL one-meter aperture primary telescope to receive the downlink signal and transmit the reference beacon. The received optical signal is acquired and focused onto a photodetector, which converts the optical signal to a baseband electrical current. After digitization, synchronization, error-correction and post-processing, the video file is displayed on a monitor. The OCTL telescope uses ISS orbital predicts, as well as azimuth and elevation profiles to follow the ISS as it traverses its path across the sky.

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Applications

Space Applications
Modern spacecraft orbiting Earth and other planets are equipped with advanced science instruments collecting large amounts of data, which can take a long time to send back. Optical communications uses laser beams to transmit data instead of radio waves. Laser beams are more narrowly focused than radio waves and they can transmit data at a faster rate. A primary challenge is accurately pointing the laser beam from space to its target on Earth.

Earth Applications
The fastest commercial communication links on Earth use optical (or laser) fiber to transmit information. Using laser in space without this fiber is another method.  Fast laser communications between Earth and spacecraft like the International Space Station or the Mars rover Curiosity could enhance their connection to the public.  OPALS is also used to educate and train NASA personnel.
 

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Operations

Operational Requirements and Protocols

After OPALS is installed and ready for operation on the ISS, a 90-day mission begins. During these 90 days, OPALS must downlink a video from the ISS to the JPL Optical Communications Telescope Laboratory (OCTL) via an optical communications link. Opportunities for a downlink demonstration occur once every three days on average. One successful downlink of a video file is required to fulfill OPALS technical mission success requirement.
 
OPALS operations begin with the mission operations team identifying when the ISS is predicted to pass within the field of view of the OPALS ground telescope located at the OCTL (Optical Communication Telescope Laboratory). Optical communication can only be accomplished through a direct line-of-sight during these times. The mission operations team works with an ISS operations officer to ensure that ongoing on-orbit activities (e.g., robotic, extravehicular activity (EVA) or vehicle maneuvering) do not interfere with this line of sight.
 
After confirming that OPALS can safely and feasibly operate during a given timeframe, the mission operations team determines the predicted ISS trajectory in the sky over OCTL. A profile of local azimuth and elevation angles is delivered from the mission operations team to the OCTL operator for tracking the ISS pass. The OCTL is then readied to point towards the ISS during this timeframe.
 
Just prior to a pass occurring, the mission operations team powers up the OPALS Flight System and proceeds with several calibration procedures. The team then uploads pointing products to ensure the Flight System knows where to look for the OCTL. The OCTLs uplink beacon is then turned on, and the Flight System attempts to lock onto and track this uplink beacon for the purpose of downlinking the video file during the pass.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

​The use of an Adaptive Optics (AO) test bed hardware supplied by the Boeing Company which was incorporated into the OPALS ground telescope system, was successful in demonstrating its ability to correct wave-front distortions induced by random atmospheric turbulence on the optical downlink from the ISS to the ground receiving system. This demonstrated the potential for increasing the data rate of the laser data transmission received from the orbiting ISS OPALS hardware by using a small area detector in the ground receiver. The use of the AO to perform this correction on an optical link from a fast slewing low Earth orbiting spacecraft underscores its critical role, particularly when attempting to achieve high data rates for daytime operations when high levels of atmospheric turbulence are present. This indicates that potential high data rate space to ground optical communications are possible for operational use in future designs.

 

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Results Publications

    Wright MW, Morris JF, Kovalik JM, Andrews KS, Abrahamson MJ, Biswas A.  Adaptive optics correction into single mode fiber for a low Earth orbiting space to ground optical communication link using the OPALS downlink. Optics Express. 2015 December 28; 23(26): 33705-33712. DOI: 10.1364/OE.23.033705. PMID: 26832033.

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Ground Based Results Publications

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ISS Patents

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Related Publications

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Related Websites

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Imagery

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NASA Image: ISS048E052292 - Optical PAyload for Lasercomm Science (OPALS) installed on ExPRESS (Expedite the Processing of Experiments to Space Station) Logistics Carrier-1 (ELC-1).

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NASA Image: ISS048E057073 - Optical Payload for Lasercomm Science (OPALS) installed on ExPRESS (Expedite the Processing of Experiments to Space Station) Logistics Carrier-1 (ELC-1).

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Rendering of OPALS on ELC1.  Image courtesy of ISS CAMMP.

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Rendering of OPALS from Starboard.  Image courtesy of ISS CAMMP.

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Rendering of the Optical Payload for Lasercomm Science, or OPALS, laser beaming down to Earth from the International Space Station. Image courtesy of NASA's Marshall Space Flight Center.

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image Optical PAyload for Lasercomm Science (OPALS) Flight System. Image courtesy of NASA/JPL-Caltech.
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image Optical PAyload for Lasercomm Science (OPALS) Flight System hardware. Image courtesy of NASA/JPL-Caltech.
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image Optical PAyload for Lasercomm Science (OPALS) Flight System. Image courtesy of NASA/JPL-Caltech.
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image Full ISS Rendering showing OPALS integrated with ELC1. Image courtesy of ISS CAMMP.
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