OpNom: OPALSExperiment Overview
The Optical Payload for Lasercomm Science (OPALS) aims to demonstrate and test optical communications technologies from a space based platform. This is accomplished by transferring video data from the OPALS hardware on the International Space Station (ISS) to a ground receiver at the Jet Propulsion Laboratory’s (JPL’s) Optical Communications Telescope Laboratory (OCTL) in Wrightwood, California. Optical communication is an emerging technology wherein the data is modulated onto laser beams, which offers the promise of much higher data rates than what is achievable with radio-frequency (RF) transmissions.Principal Investigator(s)
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Technology Demonstration Office (TDO)Research Benefits
Information PendingISS Expedition Duration:
September 2013 - September 2014Expeditions Assigned
37/38,39/40Previous ISS Missions
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.
The scientific instruments in near-Earth and deep space missions increasingly require higher communication rates to transmit the growing amount of data back to Earth. Optical communications can support the current typical data rates from much farther distances than RF (i.e., useful for communicating with deep-space assets), or can support much higher data rates than RF from the same distance (i.e., useful for communicating with near-Earth assets).Earth Applications
Here on Earth people strive for more interconnectivity with our deep space and near-Earth space assets. For example, high-definition video streams from the ISS, or eventually Mars or the moon only enhances our experience and interaction with these locations here on Earth. Optical communications has the potential to support these high-data-rate applications, and improve our interconnectivity with space assets. OPALS is also a part of the JPL Phaeton early career employee hands-on training program, which engages new scientists in ongoing real-time investigations.
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.Operational Protocols
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.
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.
Optical PAyload for Lasercomm Science (OPALS) Flight System. Image is credited to NASA/JPL-Caltech.
OPALS will be mounted externally on the International Space Station (ISS) in a nadir position on an ExPrESS Logistics Carrier (ELC). Image is credited to NASA/JPL-Caltech.
Optical PAyload for Lasercomm Science (OPALS) Flight System hardware. Image is credited to NASA/JPL-Caltech.