≡ Menu

Laser Communications: A Step at a Time to Deep Space

My last look at laser communications inside the NASA playbook was a year ago, and for a variety of reasons it’s time to catch up with the Laser Communications Relay Demonstration (LCRD), which launched in late 2021, and the projects that will follow. LCRD has now been certified for its mission of shaking out laser systems in terms of effectiveness and potential for relay operations. Ideally, we’d like to receive data from other missions and relay to the ground in a seamless optical network. How close are we to such a result?

Image: The Laser Communications Relay Demonstration payload. Credit: NASA Goddard Space Flight Center.

LCRD is now in geosynchronous orbit almost 36,000 kilometers above the equator, poised for its two year mission, but before we proceed, note this. The voice is that of Rick Butler, project lead for the LCRD experimenters program at NASA GSFC:

“We will start receiving some experiment results almost immediately, while others are long-term and will take time for trends to emerge during LCRD’s two-year experiment period. LCRD will answer the aerospace industry’s questions about laser communications as an operational option for high bandwidth applications.

“The program is still looking for new experiments, and anyone who is interested should reach out. We are tapping into the laser communications community and these experiments will show how optical will work for international organizations, industry, and academia.”

The Opportunities for Experiments page at GSFC offers the overview for anyone looking to join this effort with ideas for experiments to test optical communications links. Contact information for proposals is provided, and I also note that NASA intends to use LCRD to relay New Year’s resolutions submitted by the public through social media accounts as a demonstration of laser communications capabilities. Sure, it’s a bit of a stunt, but it makes optical communications visible to a general audience as we move into the era of laser networking for space missions near and far.

TeraByte InfraRed Delivery (TBIRD) is to follow, having launched on May 25 of this year. Here scientists are pushing the data downlink, going to 200 gigabits per second, which will represent the highest optical rate NASA has yet achieved. A single 7-minute pass of this CubeSat in low-Earth orbit will return terabytes of data. TBIRD, build by MIT, is integrated into the PTD-3 CubeSat as part of a technology demonstrator mission.

This is exciting stuff in its own right: The Pathfinder Technology Demonstrator program emphasizes using the same spacecraft bus and avionics platform designs across various missions, which moves toward modular spacecraft that are more efficient and easier to produce.

Image: Illustration of TBIRD downlinking data over lasers links to Optical Ground Station 1 in California (not drawn to scale). Credit: NASA/Dave Ryan.

The plan for TBIRD is to demonstrate the stability of laser pointing, with the spacecraft directed toward the ground station at Table Mountain, California. Without moving parts, the laser communications testing will rely on the pointing ability of the entire spacecraft. Beth Keer (NASA GSFC) is TBIRD project manager:

“In the past, we’ve designed our instruments and spacecraft around the constraint of how much data we can get down or back from space to Earth. With optical communications, we’re blowing that out of the water as far as the amount of data we can bring back. It is truly a game-changing capability.”

I’ll also mention a component of laser testing that will go to the International Space Station in the form of ILLUMA-T, which stands for Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal. Sending data at 1.2 gigabits per second, the device will communicate with LCRD, which will then relay data on ISS experiments and other information to ground stations at Haleakalā, Hawaii or Table Mountain.

Image: Illustration of LCRD relaying data from ILLUMA-T on the International Space Station to a ground station on Earth. Credit: NASA’s Goddard Space Flight Center/Dave Ryan

While NASA has been using communication relay satellites since 1983, the ability of LCRD to send and receive data from both missions and ground stations from its geosynchronous orbit means we will have achieved the agency’s first two-way, end-to-end optical relay. ILLUMA-T will shake out this system, demonstrating low-Earth orbit to geosynchronous orbit to ground station links in an end-to-end system.

SpaceX uses laser links to move Internet traffic from spacecraft to spacecraft in its Starlink system, and the European Space Agency does the same for its system of environmental monitoring satellites, but both of these use conventional radio to return data to Earth, and a direct link of optical data to Earth is the logical next step.

Extending further from the Earth, the Artemis II mission will carry its own Optical Communications System aboard the Orion spacecraft, making it the first crewed lunar flight demonstrating laser communications. With a downlink rate as high as 260 megabits per second, the system will be able to send high-resolution images and video.

While we wait to see when the Psyche mission will fly, I note that the Deep Space Optical Communications package is aboard, an attempt to increase communications performance by up to 100 times over conventional deep space missions. Now we take laser technologies outside the Earth-Moon system, with the Hale Telescope at Palomar receiving high-speed data from the transceiver aboard the spacecraft. The uplink will be from a laser transmitter at the JPL Table Mountain facility. This experimental effort is scheduled to begin not long after launch and will extend for at least a year and perhaps longer depending on results.

Can we look at laser communications from an interstellar perspective? Early work on this points to the potential as well as the difficulties. According to one JPL study, it would take an installation the size of the Hubble Space Telescope, beaming a 20-watt laser signal, to reach us from Alpha Centauri, so we have a long way to go before we can contemplate such methods between stars.

We can work wonders up to a point: The Deep Space Network can pick up Voyager’s 23-watt radio signal even though it is billions of times weaker than the power it would take to operate a digital wristwatch. But going interstellar will require moving to lasers to narrow beam diffraction (the Voyager signal is now over 1000 times Earth’s diameter). We know how to communicate if we can put the equipment where we need it, but getting payloads of any size – even a microchip – to another star continues to challenge our best scientists.

Exploring that gravitational lens communications relay described by Claudio Maccone may be one way around the problem. We already have a mission under study at JPL to reach 550 AU and beyond with the express purpose of imaging a planet around a nearby star. One step at a time, then, both for exoplanet observation using the Sun’s gravitational lens and, in some latter mission, possibly exploiting its magnification for communications. And one step at a time for lasers. Let’s get Psyche launched and see what DSOC can do.

tzf_img_post
{ 13 comments… add one }
  • ole burde August 16, 2022, 14:37

    This might remove constraints in unexpected places , such as volunteer based teleoperation of a few thousand micro-robots on the moon …

  • Alex Tolley August 16, 2022, 14:39

    To put this in some perspective, the Mars Reconnaissance Orbiter has a microwave communication system with Earth to deliver high resolution, compressed images of 5GB in size. The maximum data rate uses the Ka-band microwave transmitter.

    This IR laser system looks like it is capable of a minimum 10x performance increase, and potentially much more based on the IR wavelength used. As the atmosphere window centers around 10 uM and assuming the MRO microwave is around 1 cm, theoretical bandwidth performance is around 100x, all other things being equal.

    With a 250 Mbs downlink, it would not be able to deliver 5GB (~ 49 Gbit) hi-res images to the ground that fast. OTOH, a 600 MB MP4 1-hour movie with a 720p resolution could be downloaded in less than 30 seconds, which certainly allows pretty decent resolution video. A BluRay movie with 2160p resolution could be easily transmitted live within the downlink bandwidth.

    So, if my calculations are at least in the ballpark, the bandwidth should be able to support a large number of satellites and probes, as well as ensure the Artemis moon mission can send live video at a resolution that is far higher than the later Apollo video moon missions.

  • Thomas R Mazanec August 16, 2022, 18:08

    What are the laser wavelengths of these in Angstroms?

    • Alex Tolley August 16, 2022, 21:19

      I have been unable to find a document with the laser wavelength[s] given. Only that the bandwidth will increase 10-100x that of radio transmissions.

      If I am correct that the 10uM wavelength centers around the IR low-absorption window for the atmosphere to allow reliable transmission through any weather, the conversion to Angstroms is
      1 uM = 10,000 A, or 1 nM = 10 A.
      Red light is around 800 nM, (8000 A) to provide some context.

    • Robin Datta August 17, 2022, 0:20

      Angstrom 10,000
      micron 1
      millimeter 0.001
      Converter+ for IOS & IPadOS.

      Angstroms to millimeters conversion – Google Search

      Calculator in Windows 10 : options under Converter for converting units of measurement.

  • Robin Datta August 17, 2022, 0:37

    Perhaps beyond Sol’s gravitational focal point might be found relay stations that take advantage both of gravitational lensing and superior collimation techniques with minimal leakage of the carrier beams such that they have as yet remained undetected?

  • Jeff Wright August 17, 2022, 4:14

    Maybe combined with beam propulsion? A sail as sensor..

  • Antonio August 17, 2022, 17:33

    OT: Rocket Lab has announced that it will pay for the development and launch costs of the Venus life-searching spacecraft.

    https://arstechnica.com/science/2022/08/rocket-lab-will-self-fund-a-mission-to-search-for-life-in-the-clouds-of-venus/

    • Alex Tolley August 17, 2022, 20:18

      In a recent Zoom webinar, Sara Seager said she didn’t know what the cost of the mission would be, only that the VLF team is getting about $1m to fund the scientific instrument and pay the team.

      Elsewhere I have seen a suggestion of around $50m for the rocket and mission O/H, but I suspect that is just an informed guess, and I would hope lower, as that is not much less than a SpaceX F9 to orbit.

      Rocket Lab is hoping to do a number of interplanetary missions so this may well be an investment to prove the value of their Electron rocket and Photon interplanetary cruise vehicle. It should also increase confidence in their next, larger rocket.

  • James M. Essig August 18, 2022, 7:49

    It would be nice to extend laser communications with any other civilizations.

    I like the idea of humanity being accepted into a broader brotherhood network of rf and laser-light-based communications.

    The caveat here is that advanced extra-solar civilizations would actually exist.

  • Mike Serfas August 18, 2022, 18:29

    This certainly seems like a logical step forward, with many benefits for science. Nonetheless, I’m afraid my thoughts are turning more to the potential risks of such a network. According to https://ntrs.nasa.gov/api/citations/
    20210026049/downloads/Riesing-SPIE-2022-v5.pdf the total draw of the TBIRD system is approximately 105 watts, though I assume a much smaller fraction goes to the laser. It’s a small module in a cubesat, made with commercial transceivers. For now, I don’t think there can be a hazard, because the pointing accuracy is around 10 microradians, which I assume means a satellite at 1000 km will only be able to target to within 100 meters. And the power is delivered in a circle of 0.25 degrees, which is yet larger. There is certainly no basis for my fear at this time.

    Nonetheless, in concept, a well-designed network, one capable of doing good things like beaming heat at the Voyager spacecraft to keep them in operation, might eventually become so precise and/or so powerful that it could set a fire in dry terrain. If so, a single hacker, co-opting many transmitters of the network to his own ends, could set hundreds of thousands of fires in an afternoon and put an end to some nation. So while I wish this prototype good luck … I hope someone at NASA will remember to be wary when things are going best.

  • ljk August 29, 2022, 12:50

    Speaking of long-distance space communications…

    https://earthsky.org/space/seti-finds-sign-of-intelligence-our-own-voyager-1/

  • ljk August 29, 2022, 12:57

    Physicists Say They’ve Built an Atom Laser That Can Run ‘Forever’

    17 June 2022

    By MICHELLE STARR

    A new breakthrough has allowed physicists to create a beam of atoms that behaves the same way as a laser, and that can theoretically stay on “forever”.

    This might finally mean the technology is on its way to practical application, although significant limitations still apply.

    Nevertheless, this is a huge step forward for what is known as an “atom laser” – a beam made of atoms marching as a single wave that could one day be used for testing fundamental physical constants, and engineering precision technology.

    Atom lasers have been around for a minute. The first atom laser was created by a team of MIT physicists back in 1996. The concept sounds pretty simple: just as a traditional light-based laser consists of photons moving with their waves in sync, a laser made of atoms would require their own wave-like nature to align before being shuffled out as a beam.

    As with many things in science, however, it is easier to conceptualize than to realize. At the root of the atom laser is a state of matter called a Bose-Einstein condensate, or BEC.

    Full article here:

    https://www.sciencealert.com/physicists-have-built-an-atom-laser-they-say-can-stay-on-forever

Leave a Comment