ISS: OPALS and HDEV
ISS Utilization: OPALS (Optical PAyload for Lasercomm Science) and HDEV (High Definition Earth Viewing)
OPALS is a NASA/JPL optical technology instrument to be flown to the ISS (International Space Station) in the spring of 2014. The objective is to demonstrate optical communication by transferring a video from the OPALS payload on the ISS to a ground receiver at JPL's OCTL (Optical Communications Telescope Laboratory) in Wrightwood, California. As the ISS travels across the sky, a laser beacon will be transmitted from the ground telescope to OPALS and be tracked. While maintaining lock on the uplink beacon using a closed loop control system and a two-axis gimbal, the OPALS flight system will downlink a modulated laser beam with a formatted video. Each demonstration lasts for approximately 100 seconds as the ISS payload and ground telescope maintain line of sight. 1) 2)
Figure 1: OPALS mission architecture (image credit: NASA/JPL)
OPALS, which is part of the JPL Phaeton early career employee hands-on training program, aims to demonstrate free-space optical communications technology. During the technology demonstration, a video file from the investigation on the ISS is transmitted to JPL's OCTL. 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 Mbit/s or higher.
Figure 2: OPALS concept of operations (image credit: NASA/JPL)
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 1 m 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.
Figure 3: OPALS experiment processed at Kennedy Space Center in July 2013 (image credit: NASA)
Figure 4: Alternate view of the OPALS instrument at NASA/KSC in July 2013 (image credit: NASA) 3)
Launch: OPALS is manifested to launch on the third ISS resupply mission; it is the primary payload on the CRS-3 (Cargo Resupply Services-3) flight provided by SpaceX CRS-3 spacecraft in March 2014. It will be the fifth flight for SpaceX's uncrewed Dragon cargo spacecraft and the third SpaceX operational mission contracted to NASA under a Commercial Resupply Services contract. The launch vehicle is the Falcon-9v.1.1 of SpaceX and the site is Cape Canaveral, FL. 4) 5)
Orbit: Near-circular orbit, altitude of ~400 km to ISS, inclination =51.6°.
The second external payload launching on SpaceX-3 is the HDEV (High Definition Earth Viewing) package, which consists of four commercial HD video cameras which will film the Earth from multiple different angles from the vantage.
In addition to the primary payload, a Dragon cargo capsule resupply space transport mission to the ISS, the CRS-3 Falcon 9 mission will carry the following secondary payloads:
• All-Star/THEIA, a 3U CubeSat of COSGC (Colorado Space Grant Consortium), 2401.700 MHz
• Hermes-2, a 1U CubeSat of COSGC, 437.425 MHz
• Ho’oponopono-2, a 3U CubeSat of the University of Hawaii, 427.220 MHz, 9.6 kbit/s, FSK / GMSK
• LMRSat (Low Mass Radio Science Transponder Satellite), a 2U CubeSat of JPL (Jet Propulsion Laboratory)
• SporeSat, Santa Clara University, 437.100 MHz and 2401.2-2431.2 MHz
• TechCube-1 (Technology Demonstration CubeSat-1), a 3U CubeSat of NASA/GSFC, Greenbelt, MD
• TSAT (TestSat-Lite), Taylor University
OPALS system description:
1) Flight System:
The optical flight system is composed of three main elements:
• Sealed Container: houses all of the COTS (Commercial-of-the-Shelf) avionics boards, the laser, and custom power board pressured at 1 atmosphere with air. Connected to the optical gimbal transceiver via cable feedthroughs.
• Optical gimbal transceiver: an optical head that contains an uplink camera and laser collimator for the downlink sits on a two-axis gimbal.
• FRAM (Flight Releasable Attachment Mechanism): both the sealed container and Optical gimbal transceiver sit on the FRAM, which provides a standard mechanical and electrical interface to both the ISS and the launch vehicle.
Figure 5: Illustration of the OPALS flight system (image credit: NASA/JPL)
2) Ground System:
The OPALS ground system will be at the OCTL (Optical Communications Telescope Laboratory) at the JPL facilities on Table Mountain in Wrightwood, CA. It utilizes OCTL's 1m primary telescope aperture 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 baseband electrical current. After necessary digitization, synchronization, error-correction and post-processing, the video file is displayed on a monitor. The OCTL telescope relies on orbital predicts generated by JSC (Johnson Space Center) to follow the ISS as it traverses its path across the sky.
Figure 6: Photo of the OCTL ground station (image credit: NASA/JPL)
3) ISS (International Space Station):
OPALS will be mounted externally on the ISS in a nadir position on an ELC (ExPrESS Logistics Carrier).
Figure 7: Artist's view of the OPALS instrument integrated externally on the ISS with its laser beam pointed to the ground (image credit: NASA/JPL)
Operational requirements: 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 OCTL (Optical Communications Telescope Laboratory) 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 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 OCTL's 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.
HDEV (High Definition Earth Viewing)
The HDEV experiment places four commercially available HD cameras on the exterior of the space station and uses them to stream live video of Earth for viewing online. The cameras are enclosed in a temperature specific housing and are exposed to the harsh radiation of space. Analysis of the effect of space on the video quality, over the time HDEV is operational, may help engineers decide which cameras are the best types to use on future missions. High school students helped design some of the cameras' components, through the HUNCH (High Schools United with NASA to Create Hardware) program, and student teams operate the experiment. 6)
The HDEV investigation places four different commercial high definition cameras external to the ISS on the Columbus External Facility. The objective is to assess the camera hardware’s ability to survive and function in the extreme radioactive environment of LEO (Low Earth Orbit). Educational outreach has been an important component of the HDEV project through the entire projects life cycle. NASA HUNCH program students fabricated some of the HDEV flight components, and most of the HDEV operation will be performed by students teams.
Description: The HDEV primary objective is to validate the space-based performance of the cameras in a variety of operating modes to exercise and demonstrate the features and longevity of the COTS equipment for future ISS Program usage. This payload is an external earth viewing multiple camera system using a set of Commercial-off-the-shelf (COTS) cameras. The HDEV integrated assembly is composed of a camera system of four COTS cameras, integrated Command and Data Handling (C&DH) avionics (Ethernet), and a power data distribution box that allows the integration of the payload's components interface to the ISS Columbus module.
The HDEV visible HD video cameras are a fixed payload camera system that requires no zoom, no pan or tilt mechanisms. The four fixed cameras are positioned to capture imagery of the Earth’s surface and its limb as seen from the ISS (i.e., one camera forward pointed into the station’s velocity vector, two cameras aft (wake), and the other one camera pointing nadir). The video imagery is encoded into an Ethernet compatible format for transmission to the ground and further distribution. In this format, the video can be viewed from any computer connected to the Internet.
The HDEV does not record video on board the ISS, all video is transmitted to the ground in real-time; any desired recording of the video occurs as ground operations. The COTS cameras, COTS encoder and other electronics are enclosed in a pressurized box to provide a level of protection to the electronics from the space environment. The Enclosure contains dry nitrogen at Atmospheric pressure.
HDEV Design for Operations: The HDEV operates one camera at a time. The HDEV is designed so that when the system is initially powered on, after a 1-2 minute warm up period, the cameras are turned on one at a time in a repeating cycle. The Forward looking camera is powered first, followed by the Nadir and each aft looking camera, such that the HDEV video “follows” a location on the Earth as the ISS passes overhead. This auto-cycle mode of the HDEV does not require any input from ground operators, so the HDEV can be operated any time when the ISS power and data resources are available, without requiring a ground controller present to operate the payload. The only command required, is the initial “power on” command, which is performed by ESA’s Columbus Control Center as schedule by ISS Payload Operations.
Alternately as desired by ground controllers, the HDEV video can be commanded. Ground operators have the choice to change the cycle of the images noted in the auto-cycle mode (either changing which cameras that are powered on, or changing the length of time they are powered on), or, if desired, ground controllers can command a single camera to remain powered on and no auto-cycle to take place. — The HDEV is operated from a standard ISS TReK workstation with HDEV specific software installed.
Operations: Camera/system longevity performance — Initially when installed on orbit, the cameras are turned on and video is recorded (on ground) to establish initial camera image quality. Periodically during HDEV operations the camera video images are recorded and compared to previous video. The video image analysis over time will document how well each of the camera systems hold up in the space environment.
Public Relations: The HDEV video is available to the public over the Internet, at the ISS Imagery web site. The HDEV imagery is displayed next to an ISS location map (showing where the ISS is located over the Earth as the video is viewed). The majority of HDEV operations are performed by student teams through the life of the project.
Figure 8: Photo of the HDEV flight assembly (image credit: NASA)
Figure 9: Photo of the HDEV internal electronics (image credit: NASA)
Introduction of landing legs for Falcon-9 launch vehicles:
The SpaceX CRS-3 (Cargo Resupply Services-3) flight to the ISS is the first of the Falcon-9 launch vehicle, which will be equipped with a quartet of landing legs in a key test that will one day lead to cheaper, reusable boosters, as announced by Elon Musk, the company’s founder and CEO. 7) 8) 9)
The attachment of landing legs to the first stage of SpaceX’s new and more powerful, next-generation Falcon-9 rocket counts as a major step towards the firm’s eventual goal of building a fully reusable rocket. SpaceX believes a fully and rapidly reusable rocket is the pivotal breakthrough needed to substantially reduce the cost of space access.
Figure 10: 1st stage of SpaceX Falcon 9 rocket newly equipped with landing legs (image credit: SpaceX)
Although this Falcon-9 will be sprouting legs, a controlled soft landing in the Atlantic Ocean guided by SpaceX engineers is still planned for this trip. But SpaceX engineers will continue to develop and refine the technology need to accomplish a successful touchdown by the landing legs on solid ground back at the Cape in Florida. Extensive work and testing remains before a land landing will be attempted by the SpaceX company.
However, F-9 will continue to land in the ocean until SpaceX proves precision control from hypersonic thru subsonic regimes. Ocean recovery teams will retrieve the 1st stage and haul it back to port much like the Space Shuttle’s pair of Solid Rocket Boosters.
Figure 11: All four landing legs are mounted on Falcon-9 rocket being processed inside a hanger at Cape Canaveral, FL for a March launch (image credit: SpaceX)
Figure 12: Photo of a SpaceX Falcon-9 landing leg (image credit: SpaceX)
1) “Optical PAyload for Lasercomm Science (OPALS),” NASA/JPL, URL: http://phaeton.jpl.nasa.gov/external/projects/optical.cfm
2) “Optical PAyload for Lasercomm Science (OPALS),” NASA Fact Sheet, January 09, 2014, URL: http://www.nasa.gov/mission_pages/station/research/experiments/861.html
3) “NASA's OPALS to Beam Data From Space Via Laser,” NASA/JPL, July 11, 2013, URL: http://www.jpl.nasa.gov/news/news.php?release=2013-218
4) Joshua Buck, Stephanie L. Smith, George Diller, “NASA's OPALS to Beam Data From Space Via Laser,” NASA News Release 13-214, July 11, 2013, URL: http://www.nasa.gov/press/2013/july/nasas-opals-to-beam-data-from-space-via-laser/#.Ud-CeazODWI
6) “High Definition Earth Viewing (HDEV),” NASA News, Feb. 12, 2014, URL: http://www.nasa-usa.de/mission_pages/station/research/experiments/917.html
7) Ken Kremer, “Next SpaceX Falcon 9 Rocket Gets Landing Legs for March Blastoff to Space Station – Says Elon Musk,” Universe Today, Feb. 25, 2014, URL: http://www.universetoday.com/109721/next-spacex-falcon-9-rocket-gets-landing-legs-for-march-blastoff-to-space-station-says-elon-musk/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.