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Is the Defense Innovation Unit’s Hybrid Space Architecture the “ARPANET” of Space and Will It Run on Aalyria Spacetime?

Spacetime’s user interface shows changing links and topology over time (source)

The goal of the Defense Innovation Unit (DIU) of the Department of Defense is to strengthen our national security by accelerating the adoption of commercial technology throughout the military and strengthening our allied and national security innovation bases. Space is one of its areas of focus and two of the space “lines of effort” are multi-orbit operations and logistics and hardware-to-software transformation modernization.

The DIU’s Hybrid Space Architecture (HSA) program seeks to provide global, ubiquitous, and secure Internet connectivity throughout the space domain for commercial, civil, and military users, including international allies and partners. Several companies are developing multi-orbit Internet service between the low-Earth orbit (LEO) and geostationary (GEO) satellites and medium-Earth orbit (MEO) satellites and GEO satellites, but the HSA is more ambitious, calling for a “robust, secure software-defined network which integrates diverse telecom systems across LEO, MEO, GEO orbits, and cislunar space.” The DIU recently awarded contracts to four companies to begin work on the HSA. They expect to award more contracts and plan on-orbit demonstrations within 24 months.

One of the awards went to Aalyria, a startup that is marketing Spacetime. Spacetime is a multi-layer, multi-orbit, operating system for a temporospatial network that “captures the potential for software-defined controllers to utilize knowledge of physics to make predictions about the future state of the lower-level network” for end-to-end path optimization. Those predictions require simulation of both the network stack and astronomical physics that began with the integration of space and network simulators at NASA.

The practical application of Spacetime grew out of Google’s early efforts at connecting rural areas and developing nations. In a recent podcast interview, Brian Barritt, Aalyria CTO, and Executive VP said Spacetime exceeds the HSA requirements since it can integrate and optimize paths across terrestrial, air, LEO, MEO, GEO, cislunar, and eventually deep-space networks. (Vint Cerf, an early proponent of delay-tolerant networking for use in a Solar-System Internet is on the Aalyria Advisory Board and considers Spacetime to be applicable to NASA’s next-generation space communications architecture).

Barritt says Spacetime was used by hundreds of thousands of users of Project Loon and is ready for adoption today. He added that Spacetime networks can interoperate, optimizing paths and potentially sharing assets across a federated network of networks of up to a combined size of fifteen million possible links (for now).

Several LEO broadband constellations are working on LEO, GEO and air integrations—OneWeb seems to be farthest along—but these efforts are of limited scope compared to Spacetime. Furthermore, they are proprietary solutions, and Barritt says Spacetime APIs are open and available now, and they hope to make them an open standard. (Years ago, I worked on a project benchmarking Apple’s local area network technology, AppleTalk, against IBM’s Token-ring and Ethernet. The benchmark results were irrelevant because Ethernet was an open standard).

A multi-orbit network requires optical communication links between satellites. SpaceX has begun deploying satellites with optical inter-satellite links in their Starlink constellation and many vendors are working on space-space optical communication. DARPA is also pursuing a space-space standard that may become the “Ethernet” of inter-satellite links. Barritt says Spacetime drivers can be written to incorporate any optical terminal.

SpaceX recently moved to affordable pricing as performance faltered in some locations due to oversubscription given limited spectrum availability and gateway capacity. They will add capacity by improving technology and launching more satellites, but growing traffic volume will require optical (and v-band RF) links between satellites and the ground, and those are problematic due to atmospheric signal distortion.

Barritt says Aalyria’s Tightbeam optical terminals can adapt to adverse atmospheric conditions under program control, for example, cutting transmission speed to increase signal power to maintain signal integrity. Spacetime can adjust Tightbeam power, route around inclement weather, or find an RF link if that yields the optimal path. Tesat, Mynaric, Skyloom, the Space Development Agency, and Chinese companies are also working on optical space-ground communication and Spacetime drivers should be able to accommodate their terminals if they are superior to Tightbeam.

Barritt ended the interview by stating that despite the failure of Loon, high altitude platforms are not dead and spoke of the hypothetical case of a LEO broadband constellation that was over capacity in a region. He suggested that if it were running Spacetime, it could federate with lighter-than-air vehicles to add capacity.


Lest you run out and invest in Aalyria after reading this, I must add a disclaimer or two. Most of what I have said is based on statements from Aalyria and Brian Barrett’s interview, which I encourage you to listen to.

While Project Loon logged over two million Spacetime-user hours, there have been no other adoptions as far as I know. Telesat initially planned to use Spacetime but that was canceled in favor of a network operating system from Thales Alenia Space. I don’t know why that change was made, but it may have been because Telesat had been contemplating the integration of their LEO and GEO constellations and decided to keep them independent.

Tightbeam has been tested over long, challenging terrestrial links like from the ground to a mountaintop in the San Francisco Bay area and from aircraft to the ground, but not yet from space.

The commitments of today’s LEO companies, particularly SpaceX and OneWeb, to proprietary operating systems might be Spacetime’s biggest problem. SpaceX has around 500,000 residential subscribers, and OneWeb and Eutelsat have merged and are committed to and working on LEO-GEO integration for OneWeb’s version 2 satellites, which they hope to begin launching in mid-2025.

We will know a lot more about Spacetime and Tightbeam when we see the on-orbit HSA demonstration in 24 months.


Rather than end on a disclaimer, I’ll offer some utopian science fiction. The current version of Spacetime can handle up to fifteen million links, which must require massive, parallel computation, but Barritt envisions federations of Spacetime networks if they can increase the link limit. That could enable the sharing of common resources like Amazon’s ground-station service or federation of future broadband network generations. (Has Amazon settled on control software for the Project Kuiper constellation)?

LeoLabs offers satellite and debris tracking and collision avoidance as a service that, like Spacetime, requires powerful simulation. Would there be a meaningful way for the two companies to collaborate on collision avoidance?

Last and least likely, how about a Spacetime federation that includes China’s Satnet constellation? That is politically inconceivable today, but it will be many years before Satnet is ready to launch satellites and global challenges will be more pressing by the time they are.

Update Nov 23, 2022:

DIU has awarded four contracts in the second phase of HSA to companies collectively pursuing the goals of an agile and resilient communications architecture that will move data across commercial, military, and allied assets while integrating multi-domain cloud-based storage and analytics. The organizations joining the DIU effort include SpiderOak Mission Systems, Amazon Web Services, and Project Kuiper, and Microsoft Azure Space.

Note that Amazon and Microsoft will be competing on cloud access and ground station service and Project Kuiper, not SpaceX Starlink, will be working on connecting the unconnected. The others are focused on battlefield status, security, and privacy.

Update Mar 13, 2023:

Aalyria has a commercial contract in addition to its DIU contract.

Rivada Space Networks will use Spacetime, in its planned low-Earth orbit communications constellation. The constellation will provide secure satellite networks with pole-to-pole reach, offering end-to-end latencies similar or better than terrestrial fiber. It “will operate like an optical backbone in space using lasers to interconnect satellites to deliver an ultra-secure and highly reliable global data network for business operations in the telecom, enterprise, maritime, energy and government services markets.”

Update Feb 15, 2024:

Aalyria demonstrated a satellite mesh network for the Defense Innovation Unit. The network included about 630 satellites from three commercial satellite operators: OneWeb, Viasat, and Intelsat. They used terminals from OneWeb, Kymeta, Viasat, and Comtech. Fixed and mobile ground terminals were placed in four sites on two continents. The demonstration was at the Naval Research Lab, which is also evaluating Aalyria’s Tightbeam optical communication technology.

By Larry Press, Professor of Information Systems at California State University

He has been on the faculties of the University of Lund, Sweden and the University of Southern California, and worked for IBM and the System Development Corporation. Larry maintains a blog on Internet applications and implications at cis471.blogspot.com and follows Cuban Internet development at laredcubana.blogspot.com.

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