Messages Through the Cosmos: A Review of Data Transfer in Space
Space data transfer has come a long way since those early calls to Houston. Here's a forward-looking glance at space communication technology.
Communication with astronauts and researchers in space is a multifaceted endeavor. Two-way communication relies on a combination of ground-based antennae spread across seven continents (in NASA’s case) and space relays. These networks are critical. Otherwise, spacecraft would need to hover directly aboveground stations to facilitate communication. Many mission-critical messages and data streams must be delivered more urgently—if not in real-time.
Future rover missions will continuously stream 4K video during a crawl. Additionally, traveling spacecraft will send telemetry data (including speed, positioning, and the like) to mission HQ on Earth. For now, though, monitoring data is compiled using a combination of Doppler, ranging, and Delta Differential One-Way Ranging (Delta DOR).
How might interstellar data be handled in the years ahead?
The Infrastructure of Space Communication
First, let's survey current space data transmission. The backbone of this infrastructure is a variety of antenna types. These variants range from miniature (higher frequency) to goliath, measuring 230 feet in diameter. The latter requires specialized components: namely cryogenically-cooled signal amplifiers, high-sensitivity receivers, and software-based error correction.
A family of cryogenic low-noise amplifiers. Image used courtesy of the National Radio Astronomy Observatory
This system must be able to reach deep spacecraft. For example, NASA’s Voyager 1 and Voyager 2 missions leverage this hardware to communicate from over 11 million miles away.
The Deep Space Network
NASA’s antennae generally grow larger as transmission distances increase. These antennae developments grow out of the Administration’s Deep Space Network (DSN), which is composed of specialized transmitter-receivers. The complete network is split between three primary base stations in Barstow, California; near Madrid, Spain; and in Canberra, Australia.
Specialized Data Links
There are also specialized data links for Mars missions. Rovers and other surface craft can connect to one another using ultra-high frequency (UHF) signals. Should an uplink with Earth be required, rovers like Perseverance can accomplish this in two ways. First, the rover can beam data to the Mars Relay Network—which then establishes communication with NASA operators. Alternatively, the rover may also use its high-gain antenna (HGA) to send messages directly to Earth. Beamforming helps this signal reach a precise location on our planet’s surface. Rover operators can steer this beam wherever they wish.
The “base station” situated atop Perseverance contains multiple components enabling communication both near and far. Accordingly, antennae affixed to companion craft like Ingenuity can receive direct transmissions from Perseverance. This eliminates the need for intermediary amplifiers.
Three Communication Bands
In terms of the Deep Space Network, radio waves across three different bands allow communication to the ground:
- The S-band (2 to 4 GHz)
- The X-band (8 to 12 GHz)
- The Ka-band (27 to 40 GHz)
Various satellite frequency bands. Image used courtesy of the European Space Agency
Both the X-band and Ka-band are commonly used today. They’re also particularly advantageous because their increased bandwidth allows spacecraft to transmit much more data simultaneously. What data rates are we seeing?
- 500 bits to 32,000 bits per second directly to Earth
- Variable rates reaching 2,000,000 bits per second to the Mars Reconnaissance Orbiter
- 128,000 to 256,000 bits per second to the Mars Odyssey Orbiter
Challenges—and Solutions—to Space Data Transmission
Despite this modern technology, data transfers to and from space remain complicated. While data transmission rates are impressive in many instances, it can take 20 hours to beam a 250-megabit data payload directly to Earth.
This latency can present issues for critical communications. When Mars is closest, messages can take roughly four minutes to reach Earth. Messages from planets residing over 250 million miles away can require a 48-minute round trip by comparison. Further, the radio waves behind these data transfers are vulnerable to interference, including radiation and physical obstructions. These transmissions are often riddled with “noise,” or data that’s corrupted, distorted, or otherwise meaningless.
Overall, how are NASA and other forces working to curb current shortcomings?
NASA Taps Optical Communication
Radio waves are limited in the amount of data they can transfer. NASA is already addressing this weakness by planning a move to infrared laser transmission. Also called optical communication, this method will unlock much higher data rates.
The Administration’s Laser Communications Relay Demonstration (LCRD) mission will test optical links between ground stations.
Rendering of the LCRD transmitting optical signals. Image used courtesy of NASA
These stations—located in California and Hawaii—will serve as testbeds for this new transmission method. Optical terminals in space can send data groundward.
Researchers Investigate AI-based Data Filtering and Compression
A group of West Virginia University engineers is also working to improve deep space communication. NASA’s Established Program to Stimulate Competitive Research has awarded researchers a $750,000 grant to investigate two primary avenues: AI-based data filtering and compression.
The former aims to eliminate noise and keep transfer payloads down (while ensuring they’re more valuable). The latter has benefits both for data at rest and data in transit. While some information is beamed constantly, other data must be stored prior to sending. Since data is getting richer and more plentiful, crews are seeing their storage devices fill up faster than ever. Compressing key data lessens its overall footprint.
New Rad-hard Ethernet SoCs
A company named TTTech has also unveiled a new series of space-ready network controllers to help supercharge data transmission. These new Ethernet SoCs are said to be "the world’s first radiation-hardened controllers" of their kind. Dubbed the Switch Controller HiRel and End System Controller HiRel, the devices are certified for space flight by STMicroelectronics.
TTTech's rad-hard SoC Ethernet network controllers. Image used courtesy of TTTech
Space is an inhospitable environment for many electronics. It’s also known that radiation can play a large role in signal degradation—which can prevent important data from reaching Earth. These chips are meant to solve this challenge on a localized, single-network scale. By hardening the pathways through which hard data can travel, and by delivering gigabit per second bandwidth, it’ll be much easier to send hi-res images and video.
Built for easy integration with existing systems, TTTech states that the chips are designed for robotics, satellites, and launch vehicles alike. All three of these are critical beneficiaries of the Deep Space Network. They must also communicate amongst themselves while active. Though onboard systems can vary widely in size and complexity, both controllers are made with wide compatibility in mind.
Swarm Offers Remote Data Access
Even Swarm—a recent SpaceX acquisition—has gotten in on the action. The Swarm Tile SMT module is a PCB surface-mount modem that facilitates remote data access. The technology has promise in today’s and tomorrow’s satellites—where it can boost data transfers when paired with a low-noise PSU.
Building Space Data Pathways
While not a laundry list of developments, these are some of the more promising approaches to improving space data transfers. NASA and commercial entities are taking the reins. As space missions become more ambitious and commercial interests swell, building better data pathways will soon become non-negotiable.