To demonstrate laser or optical communications from a distance as great as Mars, NASA is conducting the ground-breaking Deep Space Optical Communications (DSOC) experiment.
On Friday, October 13, DSOC will launch with NASA's Psyche mission to a metal-rich asteroid with the same name, where it will test crucial technologies that will allow future missions to send denser scientific data and potentially broadcast video from Mars.
The goal of the new laser space communication system called Deep Space Optical Communications (DSOC) is to boost communication speeds by a factor of 10 to 100 compared to radio frequency technology without increasing size, weight, or energy consumption.
From locations outside of cislunar space, DSOC will be able to provide high-bandwidth downlinks. The Jet Propulsion Laboratory (JPL) at NASA's headquarters in Pasadena, California, is in charge of the mission.
High-definition pictures, live video feeds, and real-time data transfer over deep space may be necessary for future human missions to provide for timely guidance and updates throughout the long-distance travels.
The Mars Reconnaissance Orbiter (MRO) takes 7.5 hours to transmit its entire onboard recorder and 1.5 hours to send a single HiRISE picture to be processed back on Earth, even at its highest transmission rate of 5.2 megabits per second (Mbps). The introduction of new high-resolution hyperspectral imagers puts more strain on their network and necessitates increased data transfer speeds.
In 2022, NASA's robotic Psyche mission will go to the massive metal asteroid 16 Psyche to provide the technological demonstration for this optical transceiver. A ground-based telescope at California's Palomar Observatory will pick up the spacecraft's laser signals. The Table Mountain Observatory in California has a smaller telescope that will send laser beams to the spaceship.
This groundbreaking technology harnesses the potential of advanced lasers operating within the near-infrared region (approximately 1.55 µm) of the electromagnetic spectrum. The fundamental architecture of this system revolves around the transmission of a laser beacon from Earth.
This beacon plays a crucial role in facilitating line-of-sight stabilization and pointing for the downlink laser beam. To ensure flawless communications, the DSOC system employs highly efficient codes. However, it must also contend with the challenge of correcting background noise, particularly scattered light originating from Earth's atmosphere and the radiant Sun.
The anticipated performance of the uplink segment is a data rate of 292 kbit/s at a distance of 0.4 astronomical units (AU), where 1 AU is the average distance between the Earth and the Sun. It's important to note that the transmitted beam-width is inversely proportional to the wavelength used. In simpler terms, shorter wavelengths allow for the creation of narrower and more focused laser beams.
The downlink bandwidth, on the other hand, hinges on the diameter of the ground telescope and is subject to variations, particularly in daytime conditions.
Three pivotal technologies have been developed for the DSOC project:
- A low-mass spacecraft disturbance isolation and pointing assembly, meticulously designed to operate effectively even in the presence of spacecraft-induced vibrations.
- A high-efficiency flight laser transmitter, ensuring the reliable transmission of laser signals across vast interstellar distances.
- A pair of high-efficiency photon counting detector arrays, strategically integrated into both the flight optical transceiver and the ground-based receiver, typically in the form of a telescope.
When considering the data rates required for forthcoming deep space missions, the flight laser transmitter boasts a laser power of 4 watts at a wavelength of 1.55 µm. On the ground systems side, the uplink relies on a telescope with a 1-meter aperture and 5 kW of power, operating at a wavelength of 1.064 µm.
Conversely, the downlink communication leverages a 5-meter telescope capable of functioning both day and night, with the flexibility to point within 12 degrees of the Sun.
In terms of physical specifications, the flight laser transmitter weighs less than 29 kilograms, and its power consumption is under 100 watts. These attributes make it highly suitable for the stringent demands of deep space exploration.
The DSOC technology takes a significant leap forward by accompanying NASA's Psyche mission, scheduled for launch in October 2023. This mission revolves around the exploration of the metal-rich asteroid 16 Psyche and is expected to reach the asteroid belt in 2029.
The inclusion of a Deep Space Optical Communication demonstration as part of the Psyche mission underscores the pioneering efforts to push the boundaries of optical communication technology beyond the confines of Earth.
Here are five key insights regarding this groundbreaking technology demonstration:
DSOC marks NASA's first attempt at exploring how lasers can enhance data transmission in deep space. Traditional radio waves have been the primary communication method for missions beyond the Moon.
The shift to optical communications could offer data rates 10 to 100 times higher than current systems, contributing to more effective human and robotic exploration missions and enabling advanced scientific instruments.
The DSOC technology demonstration involves components both in space and on Earth. The flight laser transceiver, integrated with NASA's Psyche spacecraft, employs a near-infrared laser transmitter for high-rate data transmission to Earth and a photon-counting camera to receive laser beams sent from Earth.
Due to the absence of dedicated deep space optical communication infrastructure on Earth, two ground telescopes have been upgraded for DSOC. Operations are managed by NASA's Jet Propulsion Laboratory in California, with a high-power near-infrared laser transmitter situated at the Optical Communications Telescope Laboratory at JPL's Table Mountain facility.
Data transmitted from the flight transceiver is collected by the 200-inch Hale Telescope at Caltech's Palomar Observatory, equipped with a specialized superconducting high-efficiency detector array.
DSOC is designed to demonstrate high-rate data transmission across distances of up to 240 million miles during the initial two years of Psyche's six-year voyage to the asteroid belt. As the spacecraft moves farther from Earth, decoding the data becomes increasingly challenging as laser photon signals become fainter.
Additionally, the time it takes for photons to travel increases, resulting in a 20-minute lag at the farthest point of the tech demo. The constantly changing positions of Earth and the spacecraft necessitate adjustments to ensure accurate transmission between the ground receiver and flight transceiver.
Achieving precise pointing of the flight laser transceiver and ground-based laser transmitter is crucial. This precision is comparable to hitting a dime from a mile away while the dime is in motion. The transceiver must be isolated from spacecraft vibrations that could misalign the laser beam.
Psyche initially aligns the flight transceiver towards Earth, and autonomous systems on the flight transceiver, assisted by the Table Mountain uplink beacon laser, control the downlink laser signal to Palomar Observatory. The Hale Telescope is equipped with a cryogenically cooled superconducting nanowire photon-counting array receiver, designed by JPL.
It utilizes high-speed electronics to record the arrival times of single photons for signal decoding. The DSOC team developed innovative signal-processing techniques to extract information from the faint laser signals transmitted over vast distances.
DSOC represents NASA's latest venture into optical communications. Prior projects, such as the Lunar Laser Communications Demonstration and Laser Communications Relay Demonstration, tested high-data-rate optical communications between Earth and the Moon, and from geostationary orbit.
DSOC pushes the boundaries by extending optical communications into deep space, making high-bandwidth communication feasible far beyond the Moon. Success in this endeavor could lead to high-data-rate communications supporting humanity's ambitious goals, including NASA's mission to send astronauts to Mars.
Visualization of NASA's Deep Space Optical Communications technology in space
NASA's upcoming mission to send astronauts to Mars is set to be supported by a near-infrared laser transceiver, known as DSOC. The transceiver will be launched on the Psyche mission in October, bound for a metal-rich asteroid.
During the initial two years of the journey, the transceiver will establish communication with two ground stations in Southern California. This stage involves rigorous testing of highly sensitive detectors, powerful laser transmitters, and innovative methods to decode signals transmitted from deep space.
The strategic shift toward laser (optical) communication is rooted in its remarkable bandwidth potential compared to the traditional use of radio waves, relied upon by NASA for over half a century.
Both radio and near-infrared laser communications utilize electromagnetic waves for data transmission, but near-infrared light can compress data into much tighter waves, enabling ground stations to receive significantly more data simultaneously.
DSOC was designed to demonstrate 10 to 100 times the data-return capacity of state-of-the-art radio systems used in space today. High-bandwidth laser communications for near-Earth orbit and moon-orbiting satellites have been proven, but deep space presents new challenges. Experiments like DSOC play a pivotal role in advancing technologies that will be regularly employed by spacecraft and ground systems in the future.
The DSOC transceiver aboard Psyche incorporates several innovative technologies, such as a never-before-flown photon-counting camera connected to an 8.6-inch aperture telescope. It autonomously scans for and locks onto the high-power near-infrared laser uplink transmitted by the Optical Communication Telescope Laboratory at JPL's Table Mountain Facility. Ground system upgrades will facilitate optical communications for future deep space missions.
Upon locking onto the uplink laser, the transceiver will locate the 200-inch Hale Telescope at Caltech's Palomar Observatory in San Diego County, California. Using its near-infrared laser, the transceiver will transmit high-rate data to Palomar.
The Hale Telescope has been equipped with a novel superconducting nanowire single photon detector assembly to receive the high-rate downlink laser from the DSOC transceiver.
The vast distances involved present another challenge for the tech demo, as the time taken for photons to reach their destination increases, resulting in a lag of up to tens of minutes.
Deep space optical communication involves the transmission of data using laser beams in the near-infrared region of the electromagnetic spectrum. A laser beacon is transmitted from Earth to assist in stabilizing and pointing the downlink laser beam. Highly efficient codes are used to ensure error-free communication.
This laser-based system allows for significantly higher data transmission rates compared to traditional radio wave communication. The technology compensates for challenges such as background noise from Earth's atmosphere and the Sun, and it operates by transmitting laser signals over vast interstellar distances to and from spacecraft.
Deep space communication refers to the exchange of data and information between spacecraft, probes, or rovers and their respective mission control centers on Earth when these space entities are located at great distances from our planet. It involves the use of advanced technologies such as deep space optical communication (DSOC), as well as traditional radio wave communication.
Deep space communication is vital for missions that extend far beyond Earth's immediate vicinity, including those exploring celestial bodies, the outer reaches of our solar system, and beyond. It plays a crucial role in sending commands, receiving scientific data, images, and telemetry, and ensuring the success of deep space missions.
The vast majority of spacecraft use radio waves to communicate with one another. Typically, their frequency range is between 300 MHz and 40 GHz, which corresponds to the radio bands established by the IEEE. Data is sent in a radio frequency (RF) system by use of electromagnetic waves between antennas.
Satellites designed to transfer data between spacecraft and Earth serve as intermediaries. They provide an option to transmissions directly to Earth. Data from the ISS is sent to ground stations in Mexico and Guam, for instance, by means of tracking and data relay satellites (TDRS).
NASA's Space Communications and Navigation (SCaN) program and its Technology Demonstration Missions (TDM) program have supported a string of optical communication experiments leading up to Deep Space Optical Communications (DSOC).
NASA's Space Technology Mission Directorate (TDM) and Space Operations Mission Directorate (SCaN) are both managed by the Jet Propulsion Laboratory (JPL) at Caltech in Pasadena, California.
Arizona State University serves as the mission's lead institution. Management, system engineering, integration and testing, and mission operations are all tasks that JPL is in charge of for this project.
NASA's Discovery Program, overseen by the Marshall Space Flight Center in Huntsville, Alabama, has chosen Psyche as its fourteenth mission.
Kennedy Space Center is home to NASA's Launch Services Program, which is in charge of the launch operation. The spaceship's chassis for its powerful solar electric propulsion system was built by Maxar Technologies in Palo Alto, California.