Creating a high-speed backbone for the Interplanetary Internet
Earlier this year, we were truly amazed watching the high-quality videos coming from the Mars’ Perseverance mission descend on Mars. NASA’s Deep Space Network (DSN) is the current interplanetary communications backbone that made watching these videos possible. The DSN relies on radio frequency signals and a global ground network to provide communications from Earth to the upmost distant spacecrafts (Voyager twins), in addition to the many missions being carried out across our solar system. The Deep Space Network is completed by NASA’s Near Earth Network, a series of ground stations providing support to spacecrafts closer to Earth (all the way to the Moon) and the NASA Space network, a satellite relay service that provides up to 24×7 coverage of spacecrafts near Earth such as the International Space Station (ISS), and supporting mission launches as they transit the low Earth orbit. The European Space Agency’s Estrack network also provides for deep space and near Earth capabilities, Russia, China, Japan and India also have space networks with at least certain coverage of near and deep space.
Surprisingly, the DSN was formally created in the 70’s, much before Earth’s network of networks, the Internet. At the time, data communications were not part of the day to day communications paradigms so networks were very much focused on physical (radio) and link layer (e.g. error correction and link establishment/maintenance). Because of it, the DSN as well as the space and near Earth networks have gone through major upgrades to enhance communications to adapt to digital/data communications as well as improving link and physical layer capabilities. The DSN, being a limited resource (e.g. there is only one 70 m Antenna per coverage area), is slowly becoming a bottleneck as the number of missions (and data transmission requirements) increase. It has also come to a point in which these systems have stressed out the physical characteristics of the microwave links (and coding schemes) to get the highest throughput, i.e. several Megabit per second (106 bit/sec) at Mars. This is just enough to transmit one stream of video at high definition. Now, compare this to having Gigabit (109 bit/sec) at home, and you get an idea of the data rate requirements for a settlement on the Moon or Mars. A new high-speed backbone is needed for the Interplanetary Internet!
Figure. Downlink data rate evolution, from JPL/DESCANSO Deep Space Communications Book. NASA, other space agencies and the private sector have been working on the next steps in high-speed space communications. A major change that requires moving up from radio frequencies (with wavelengths in the centimeter order) to optical frequencies (tens to hundreds of nanometer). This would allow for higher throughput, in the order of hundreds of megabit per seconds to Mars. Many experiments and demonstrations are being built to elevate the technical readiness of the high-speed space optical network. • In 2013, NASA successfully launched the Lunar Laser Communications Demonstration (LLCD) which was capable of achieving 622 Megabit per second (Mbps) from the Moon. • Later this year (2021), NASA will launch the Laser Communications Relay Demonstration (LCRD), a demonstration of a two way laser relay system, critical in creating a near-Earth space optical network. This is the first stepping stone in augmenting the existing radio-based TDRS (Tracking Data Relay System). The LCRD will also make use of the new Optical Ground Stations (OGS-1 in California and OGS-2 in Hawaii). Note the European Space Agency (ESA) have already made 1-way optical relay possible with their European Data Relay System (EDRS) and the Japan Aerospace Exploration Agency (JAXA) have completed direct link checkout with optical ground systems in preparation to provide 2-way optical inter-satellite relay services using the Japanese Data Relay System (JDRS). • Also in 2021, NASA will launch the Terabyte Infrared Delivery (TBIRD) demonstration in low-Earth orbit that plans, via an optical link on a CubeSat, to achieve burst download speeds of 200 Gigabit per second, allowing for downloading large amount of data per day (Terabytes, hence the name). • In 2022, NASA plans to deliver the Integrated LCRD Low Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) aboard the International Space Station (ISS), becoming the first experimental space user of the LCRD, with the goal of achieving bit rates up to 1.2 Gigabit per second to Earth, increasing the bandwidth for research and development experiments’ data. • Launched in 2022, JPL’s Deep Space Optical Communications (DSOC) payload will travel onboard the Psyche mission spacecraft. Starting its first year of travel (the spacecraft is expected to reach the 16 Psyche asteroid in 2026), the experiment will test optical communications over extreme distances, obtaining valuable information about pointing challenges, among others. For the ground segment, two existing telescopes are enhanced including a new Ground Laser transmitter and a receiver respectively. The goal is to achieve 10 to 100 more throughput than conventional (RF) systems using comparable size and power. These experiments and demonstrations will lead to the use of the Orion Optical Communications System (known as O2O or Optical to Orion) in the Artemis II mission aimed for 2023. The goal of the optical communications system is to be able to support throughput over 600 Megabit per second, enough to livestream ultra high-definition (also known as 4k) video from the Moon. As the above lines indicate, there is great research, development, experimentation and plans going on for creating a high-speed space communications backbone. And there is more to it. Enabling a high-speed network also requires better performance at the networking level. Existing Delay Tolerant Networking (DTN) implementations may not be fast-enough in processing and routing/forwarding bundles (the data), potentially becoming a bottleneck. There are already signs of this issue in the DTN implementation on the International Space Station (ISS). Researchers at NASA Glenn Research Center are working on a High-speed DTN architecture to optimize spacecraft hardware design to better accommodate for high-speed (DTN) networking. From our group, the InterPlanetary Networking Special Interest Group (IPNSIG), we encourage you to continue gaining interest in space networking, and to contribute to our mission of realizing a functional and scalable system of interplanetary data communications: The High-Speed Interplanetary Internet! Dr. Alberto Montilla IPNSIG Board Member Spatiam Corporation Founding Board Member