Monday, December 11, 2023

It's the latency, FCC

Section 706 of the Telecommunications Act of 1996 orders the FCC to “encourage the deployment on a reasonable and timely basis of advanced telecommunications capability to all Americans.” On October 25, The FCC issued a notice of inquiry (NOI) into how well we are doing and invited comments.

The NOI points out that COVID and the concomitant increase in the use of interactive applications has “made it clear that broadband is no longer a luxury but a necessity that will only become more important with time" and proposes “an increase from the existing fixed broadband speed benchmark of 25 Mbps download and 3 Mbps upload (25/3 Mbps) to 100/20 Mbps." They also seek comment on a long-term speed goal of 1,000/500 Mbps.

The focus is clearly on speed. They mention latency on page 12 and jitter and packet loss on page 15, but the FCC made no metrics recommendations on those metrics and requested comments.

Dave Taht, Chief Science Officer of LibreQOS and an embedded Linux developer and consultant since 1998, drafted a comment arguing that the FCC should “balance its near-term efforts on achieving Internet resilience and minimizing latency, instead of only increasing speed.” Taht invited experts to suggest edits to and sign his draft and the submitted comment has 63 signatures, many of which would be familiar to CircleID readers. 

Taht says “Calls for further bandwidth increases are analogous to calling for cars to have top speeds of 100, 500, or 1000 miles per hour” and the "only way to improve responsiveness is to robustly and reliably reduce the latency, and especially the 'latency under load'.” He points out that low latency, not speed, is critical for today’s interactive applications and high latency reduces aggregate network efficiency and increases variability in the user experience. 

Much Internet latency is caused by bufferbloat – packets working their way through queues that build up in routers and other network equipment. Taht has spent years developing tools to measure latency and reduce bufferbloat and he documents his work and that of others in his 27-page NOI comment.

How much speed does one need? 

That depends on the applications you use, which is a moving target. My first home Internet terminal was a 10-character per-second (CPS) ASR-33 Teletype with an acoustic coupler. I used it for email, FTP, Telnet, and network news and I was able to collaborate with distant colleagues. I loved it and 100 CPS would not have made a big difference because 10 CPS was about as fast as I could read and faster than I could type. My first connected computer used a 300-bps modem, and modem speeds increased to 56 Kbps driven by applications like Web, and voice over IP.

Today, Poa Internet in Kenya offers uncapped 4 Mbps service which is sufficient for downloading software, articles, books, movies, etc., shopping, making voice-over-IP calls, listening to podcasts, reading newspapers, etc., and, importantly, creating content and inventing and developing applications and services that are relevant to Africa.  

Netflix speed recommendations (source)
Streaming video is the most speed-intensive application I use today and Netflix recommends 15 Mbps for viewing UHD 4k movies. Poa Internet customers might be able to view 720p video.

Spectrum, my ISP today,  offers three plans – up to 300, 500, and 1,000 Mb/s.  I have a 300 Mbps cable connection which is more than I need. M-Lab's Internet performance test service, which measures speed and latency unloaded and while simulating background activity reported that my latency increased from 16 to 53 ms when downloading was active and 41 ms when uploading was active. Speeds were 355.3 Mbps download and 11.2 Mbps upload. Considering Netflix’s recommendation, it is unsurprising that streaming two movies on my home WiFi network while running the M-Lab test did not make much difference.

As long as I only watch one movie at a time, I suspect I would not notice much difference if Spectrum only provided me with the current FCC benchmark of 25/3 Mbps. This raises the question of opportunity cost. How much capital and operating cost could Spectrum have saved if they had only provisioned, say, a choice between 25/3 and 50/6 Mbps? Would the savings be sufficient to fill in white spaces in their national broadband map

Spectrum dismisses latency, writing:

Latency is typically measured in milliseconds, and generally has no significant impact on typical everyday internet usage. As latency varies based on any number of factors, most importantly the distance between a customer's internet connected device and the ultimate internet destination (as well as the number, variety, and quality of networks your packets cross), it is not possible to provide customers with a single figure that will define latency as part of a user experience.

Page load time as a function of latency (source)
If we could come up with a "single figure" to define and measure latency, ISPs would have an incentive to improve it, and the FCC could adopt benchmarks. While a single figure may be impossible, could tests isolate the latency in an ISP network and the customer premises equipment (CPE) they supply? Could we use imperfect surrogates for latency like page-load times? Could we benchmark components like the CPE an ISP provides?

While the FCC and ISP marketing are focused on speed today, attention to latency and its measurement is growing within the technical community. To learn more and get involved, check Dave's Bufferbloat.net site and LibreQOS and watch Dave's talk here. You can also give the FCC feedback by commenting on Proceeding 22-270 on the FCC Express Comments Page.

Update 1/18/2024

Elon Musk summarized SpaceX's 2023 accomplishments in a recent talk at Starbase in Texas, He covered many topics including Starlink. He stated that their biggest single technical goal for the year was to get mean latency under 20 ms. (He estimated that 10 ms was the theoretical minimum given the speed of light). Doing so will require a combination of steps including launching satellites with inter-satellite laser links, adding ground stations, and heeding the advice Dave Taht has been offering for years.

Update 7/15/2014

SpaceX Starlink has begun delivering on Elon Musks commitment to reduce latency and they are letting users know by including latency values and distribution in the Starlink app. (The 100 ms latency spike at the end of the distribution must reflect handoffs between satellites).

All ISPs should report and advertise latency as well as throughput, which is less important than latency in many applications. 


Wednesday, November 01, 2023

Space-ground optical (laser) communication

 

Inter-satellite laser links are in use now, but the technology for optical links to the ground is still being developed and tested. 


Optical frequency laser communication links have many advantages over radio frequency (RF) links:
  • Optical transmission is much faster than RF communication.
  • Optical terminals are smaller and cheaper than RF terminals and use less power.
  •  It's harder to intercept or jam optical signals so they are more secure and, conversely, better for clandestine use.
  • Multiple optical beams can be transmitted simultaneously to multiply speed.
  • Optical transmission is license-free. (There isn't enough RF spectrum to accommodate all of the currently proposed satellites).
SpaceX is equipping its new satellites with inter-satellite laser links (ISLLs). They now have over 8,000 optical terminals in orbit (3 per satellite) and they communicate at up to 100 Gbps. The other low-Earth orbit Internet service providers will follow SpaceX's lead.

Optical communication works well between satellites in the vacuum of space, but optical signals are weakened and distorted by clouds, rain, water vapor, dust, heat gradients, pollen, etc. in the atmosphere so today SpaceX and others use RF frequencies for communication between space and the ground.

Optical space-ground projects

Given the long list of optical advantages, many organizations are working on technology to adjust for atmospheric interference and use optical communication between space and the ground. The following are a few examples of optical communication research and development by NASA, universities, the military, private industry, and the Chinese. 

Ten years ago, NASA demonstrated optical communication between a satellite orbiting the moon and Earth, and they are updating that now. They have a data relay satellite in geosynchronous orbit for relaying data from other satellites to the ground and they are working on transmission from deep space beyond the Moon so we will be able to see video from Mars when we land there. They have also transmitted data between a cubesat with a 2.3 kg payload and the ground at a rate of 200 Gbps. 

ETH Zurich test site
Researchers at ETH Zürich have transmitted data from a mountaintop to their lab 53 kilometers away at up to 0.94 Tbit/s/channel. (Note that the top of the stratosphere is only 50 km from the ground). They adjust for atmospheric variance using sophisticated algorithms and terminals with adaptive optics that can correct the wave phase 1,500 times per second. Their technology can scale up to 40 channels and they are working on more efficient modulation schemes.

The ETH Zürich transmission was from a fixed point on top of a mountain to their lab – how about from a moving satellite? LEO satellites move across the sky at an angular tracking rate of ∼1 deg/s and researchers at the University of Western Australia have demonstrated that they can maintain contact with a drone moving back and forth at that rate. 

In Ukraine, SpaceX Starlink has demonstrated both the military value of satellite Internet and the drawback of being dependent on a private company.

SDA Tracking Layer constellation (source)
The Space Development Agency (SDA) of the Space Force is developing two constellations, a Tracking Layer constellation for warning of, tracking, and targeting advanced missile threats and a Transport Layer constellation providing connectivity to the full range of warfighter platforms. 

There will be ISLLs, using SDA standard optical communication terminals, within and between the early constellations. The early satellites will use RF links to the ground, but optical links are planned.

Tracking plus transport to intercept missiles with planned
optical links to the ground (source)
Space Force policy is to scale up its use of commercial capabilities and Mynaric has been awarded Tracking and Transport Layer contracts for their CONDOR Mk3 optical terminal. CACI International and Tesat terminals have also been certified and will be used -- standards enable competition.

Mynaric has also been selected to participate in a demonstration of links between various space-based optical terminals and an optical ground station they will design. 

The SDA is also working with Aalyria, a startup with two products, Tightbeam and Spacetime, that are based on intellectual property acquired from Google. 

Tightbeam is an optical communication technology that sounds similar to that of ETH Zürich. Using adaptive mirrors and proprietary algorithms, they have transferred data to and from a local mountain at 400 Gbps per channel, (They can use four channels simultaneously). They recently signed a maritime contract for connectivity "starting at" 100 Gbps. 

Tightbeam is only available through Spacetime, an extremely ambitious network operating system for controlling fixed and mobile assets and the links between them on Earth, in the air, and in space. Spacetime runs a simulation of the network and if an upcoming problem is predicted -- for example a weather event or an airplane banking -- Spacetime will reconfigure the network to route around it in 200 ms

(Spacetime is open source with open APIs and Spacetime networks can “federate,” accessing each other’s assets to create a “network of networks.” Sound familiar? APIs are open and they hope to establish standards -- reminiscent of Ethernet vs early proprietary LAN technology. I recommend watching this Spcetime presentation).

Intelsat has provided geostationary satellite communication since the 1960s and is also working with Aalyria on multi-orbit service and space-to-ground optical communication. (They are also considering a medium Earth orbit constellation -- could federating with SES's mPower constellation be an alternative to creating their own)?

I searched for and found two Chinese optical space-ground experiments, one by Beidou in 2021 and a recent test by The Chinese Academy of Sciences with a 10 Gbps transmission rate. I checked with Blaine Curcio, an expert on Chinese space, and he does not know of other tests.

Ground infrastructure

If projects like the above succeed in developing cost-effective space-ground optical communication technology, we will need significant investment in well-designed ground infrastructure. Optical antennas can be added to existing RF ground stations or new optical ground stations can be built.

World cloud cover map (source)
Augmenting existing ground stations makes sense if they are in suitable locations because they already have real estate, power, and Internet connectivity. For example, SpaceX has 75 gateways in North America, several of which are in arid regions of northern Mexico and the US southwest.

New ground stations with optical gateways will also be needed. They should be in relatively cloud-free places and, if possible, near centers of demand and locations with access to high-speed terrestrial Internet connections and power. The current locations of astronomical observatories might be considered.

African gateways
One of the United Nations Sustainable Development Goals is "to build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" -- to reduce the digital divide. The needs of underserved areas should also be considered in locating ground stations. Today, SpaceX has only two RF ground stations in Africa, and there are arid regions in the north and south that might be suitable locations for optical ground stations.

ISLL path between arid areas in Mexico and Africa (source).
Such opportunities will increase as ISLLs proliferate.
Even if locations are carefully selected, routing around unfavorable weather or other atmospheric problems will occur at times. That will be facilitated by the proliferation of ISLLs. Furthermore, the addition of ISLLs to sharply inclined orbits will facilitate routing around winter in the northern and southern hemispheres.

Addendum

This post is based on a presentation at a recent UN Internet Governance Forum panel but it has been significantly revised and extended. You can get a copy of the revised PowerPoint presentation here.

The presentation includes a Frequency terminology cheat sheet.

For an excellent tutorial on the properties of laser light, click here.

Thanks to Brian Barrit of Aalyria and Shane Walsh of The University of Western Australia for their input.

Update 11/3/2023

NASA's ILLUMA-T optical terminal will be delivered to the International Space Station in a SpaceX Cargo Dragon launch scheduled for no earlier than November 5. Once installed on the exterior of the space station it will enable two-way communication through the data relay satellite mentioned above to and from optical ground stations in Hawaii and California at 1.2 Gbps.

Monday, September 18, 2023

Will Telesat survive?

In 2017, Telesat, an established Canadian geostationary satellite operator, announced a planned low-Earth orbit Internet service constellation. The plan called for 117 satellites with inter-satellite laser links in a mix of inclined and polar orbits, enabling global coverage. They planned to ignore the consumer market and designed for the enterprise, government, mobile backhaul, mobility, and rural community markets. The mass of their production satellites would be roughly four times that of SpaceX's first-generation satellites. Telesat orbited their first test satellite a month before SpaceX. 

Today, there are over 5,000 Starlink satellites in orbit and Telesat plans to begin launching production satellites in 2026 and won't begin service until 2027. How did Telesat fall so far behind?

Unlike SpaceX, which is fully integrated, Telesat sought vendors for satellite manufacturing, antennas, and launch service, and spent time and money on collaborative design with potential contractors and soliciting and evaluating bids. In February 2021, Telesat selected Thales Alenia Space as the prime contractor for an initial constellation of 298 satellites. (Musk's integrated approach to manufacturing cars or rockets is reminiscent of Henry Ford)

In 2022, Covid, supply chain shortages, inflation, and financing difficulties, led Telesat to cut the constellation to 198 satellites. The schedule slippage raised concerns over Telesat's spectrum licenses (they will have to apply for an extension), and they needed additional capital while their geostationary satellite revenue was declining slightly. Telesat stock, which was offered at $40 per share was trading for a fourth of its initial price and bonds were trading well below par. 

The stock price doubled with the Hail Mary announcements. 
Telesat recently announced two decisions that Tim Farrar, President of TMF Associates, characterizes as a Hail Mary play. 

Last month, MDA, which had been selected to provide Telesat antennas last year, replaced Thales Alenia Space as the prime contractor and manufacturer of the satellites. Telesat expects the new satellites to be about 750 kg -- around the mass of SpaceX's second-generation "Mini" satellites. With these changes, Telesat has funding for the first 156 satellites with the remainder to be paid for from revenue once 156 are in service. 

This month, Telesat announced that they had contracted with SpaceX for fourteen launches starting in 2026. (Note that SpaceX is also launching satellites for competitor OneWeb and Amazon is being sued by shareholders for not considering SpaceX to launch their competing Project Kuiper satellites).

Telesat has lost valuable time. The delay has given SpaceX time to sign over 1.5 million customers, enter the non-consumer markets Telesat is focusing on, and begin launching their second-generation satellites equipped with inter-satellite laser links in both polar and inclined orbits. OneWeb will also be in service and competing with Telesat by 2026. Telesat also says that, despite having geostationary satellites, they will not provide multi-orbit service, while others will

I was on a podcast panel a while back with a Canadian colleague, and he believes the Canadian government will keep Telesat going if needed. I hope Telesat completes its Hail Mary pass -- we need all the competition we can get and the government and military need alternatives to Starlink.

Update 10/19/2023

Telesat explains the benefits of its Lightspeed constellation over rival LEO broadband constellations.

  • Lightspeed satellites orbit at higher altitudes than the others therefore each satellite can serve a larger area with fewer gateways, handoffs are less frequent, and collision risk is lower.
  • Each satellite has four inter-satellite antennas, creating a fixed mesh in space (SpaceX satellites have three).
  • There are only 198 satellites, but Lightspeed antennas can provide nearly 300,000 beams and aggregate up to 15 Gbps within a hot spot like an airport.
  • They will offer service-level agreements including committed information rates.
  • They will work with existing service providers and equipment manufacturers. 

These points are intended to differentiate Telesat from SpaceX, which has a head start in consumer and non-consumer markets, but the stock market is not impressed.

Update 2/26/2024

Avanti Communication, a geostationary satellite operator (GSO) serving government and enterprises in Africa and Europe and Telesat have signed a memorandum of understanding to provide multi-orbit Internet service. Avanti will be marketing Lightspeed service, but the two constellations will operate independently and will not be federating using Aalyria Spacetime. 

GSOs are diversifying by launching non-GSO constellations (SES and Telesat) or buying a low--Earth orbit (LEO) company (Eutelsat-OneWeb). Avanti had decided to market Lightspeed, giving them a LEO product and giving Telesat a customer. Still, Telesat stock continues to fall.

Thursday, July 20, 2023

Google Bard fails to answer satellite Internet questions

Bard made false, inconsistent statements, overlooked pertinent evidence, and overlooked expertise.

In an earlier post, I asked whether electronically steered antennas (ESAs) would replace parabolic antennas in satellite ground stations. I did some research and concluded that it is likely that they will. Next, I discussed the same question with ChatGPT and, while it made several false statements, it made a relevant point that I had overlooked. The relevant addition was positive, but the errors were troublesome, so I decided to try ChatGPT's competitor Google Bard.

Since the P in Chat GPT stands for "pre-trained," I began by asking Bard if it was more up-to-date than ChatGPT and it replied, "Bard is able to access the internet in real-time, while ChatGPT-4 is limited to a dataset that only goes up to late 2021." It added that it had last been updated on June 7, 2023.

That was encouraging since antenna technology has improved since late 2021 and at least two new products incorporating ESAs have been announced since that time, BlueHalo's mobile ground station and Thinkom's gateway array.

But my optimism faded when I began by asking Bard to "list the advantages of electronically steered antennas over parabolic antennas in ground stations for LEO Internet service constellations" and then asked it to "list the advantages of parabolic antennas over electronically steered antennas." The results of the two queries are shown here.

The replies are less complete and specific than those given by ChatGPT, and they are inconsistent -- Bard credits both ESAs and parabolic antennas as being cheaper. Furthermore, there was no indication that Bard was aware of the BlueHalo or Thinkom products, so I asked three leading questions:

  • Have there been recent satellite ground station innovations?
  • Any new hardware?
  • Any innovative new products?
It did not mention either BlueHalo or Thinkom, but after the third try it suggested that I try a Google search for "Innovative new products for satellite ground station" and that returned many links, including one to the Thinkom array of antennas.
My next query demonstrated an extreme lack of awareness. I asked if China's Long March 5B rocket would be used to launch their GuoWang satellite constellation. Bard answered that it would and added that it "will be the first time that a country has launched such a large constellation of satellites." 
Evidently, GuoWang is more frequently associated with Chinese propaganda than the SpaceX Starlink constellation in the Bard training set. (Garbage in, garbage out).
Red and blue text indicates errors (source)

A final example illustrates Bard's inability to recognize expertise. I asked Bard "Who is Larry Press", and it answered with the error-ridden professional biography shown here. The red text highlights statements that are false and the blue highlights work done in collaboration with others, not by me alone.

One can understand some of the errors. For example, I got my Ph.D. from UCLA, not USC, but I did teach at USC for a while and that may be more frequently mentioned in the training set. Similarly, I have been on several editorial boards, but I no longer am. I am an expert on my own biography and a simple Google Search would have found a somewhat dated, but accurate short biography on the Web. 
I was also disappointed in the promise that Bard would provide links to references. It only cites references when it "directly quotes at length from a webpage". I only saw one reference during my experimentation, and it was irrelevant.
"Artificial intelligence" programs have succeeded over the years in many specific tasks. As an undergraduate, I had the privilege of taking a course from Herbert Simon and learned about his chess-playing and theorem-proving programs. Arthur Samuel's checker playing program learned to beat him, and expert systems assist doctors in making some diagnoses. I even wrote an interactive program based on concept acquisition models that assisted researchers in multivariate data analysis. (It could be an Internet service today).
Artificial neural nets have also had success in specific tasks from recognizing zip codes on envelopes to playing Go and Chess and helping robots do back flips and they will succeed at other tasks like helping Microsoft Windows users or writing poetry. (I submitted haikus written by Bard and ChatGPT to the AI detector GPTZero and it reported that they were "likely to have been written entirely by a human").
But none of these programs are generally intelligent.
The illusion of intelligence results from the ability to generate responsive grammatical sentences in a conversation, but that is a low bar. Many years ago, I placed Teletype terminals in a public library and people conversed, sometimes for hours, with ELIZA, a simple simulation of a non-directive therapist. You can try ELIZA for yourself here.
The common practice of referring to errors as "hallucinations" furthers the illusion of intelligence.

Update 9/27/2023
I could not recall the verb "scrub" for navigating through a timeline, so I asked ChatGPT and Bard for help. ChatGPT got it;

Update 10/25/2023

A colleague told me that Bard had cited him as the author of a journal article. I searched for it using Google and could not find it so I asked him about it. It turned out that he had never written an article with the cited title and that the journal it cited had gone out of print two years before the cited publication date.


Friday, June 16, 2023

Will Electronically Steered Antennas Replace Parabolic Antennas in Satellite Ground Stations? (ChatGPT-Assisted Version)

In a previous post, I asked whether electronically steered antennas (ESAs) would replace parabolic antennas in satellite ground stations. I read a few articles suggested by others and by Google search, used some common sense, produced a list of advantages of ESAs, and concluded that it was likely they would eventually replace parabolic antennas for many applications. 

Many of the articles I found were written by companies selling products or services and I'm not an antenna expert -- more a curious journalist. ChatGPT has access to the entire Internet, and I wondered if it could have helped me improve what I wrote or convinced me to reach a different conclusion, so I queried it three times

Since I had listed the advantages of ESAs over parabolic antennas, I began by asking ChatGPT to list the advantages of electronically steered antennas over parabolic antennas for satellite ground stations.

In my post, I listed twelve bullet-point advantages. The ChatGPT answer was more verbose, beginning with a restatement of the question and listing and elaborating on seven advantages. The elaborated replies included all but one of my bullet points, spectral efficiency, and it included an advantage that I had overlooked, interference mitigation, and explained why that was so.

In spite of these glitches, ChatGPT reached nearly the same conclusion as I had, saying "It's worth noting that while electronically steered antennas offer numerous advantages, they also have some limitations, such as higher cost and complexity compared to parabolic antennas. However, ongoing advancements in technology are continuously addressing these challenges, making electronically steered antennas increasingly attractive for satellite ground station applications."

Since it had failed to mention spectral efficiency, I asked, "What about spectral efficiency?" and it replied with an apology for missing the point and went on to list and elaborate on five ways in which ESA made more efficient use of bandwidth.

You can see the dialog here

Since ChatGPT generally agreed with me, I asked it to play devil's advocate and list the advantages of parabolic antennas over electronically steered antennas for satellite ground stations. 

Perhaps I was biased by the experience of having written my earlier post, but I found myself questioning some of its cited advantages. For example, one was "wide coverage" but that would not apply to Thinkom's array of arrays. Another was "simplicity ... making them easier to manufacture, install and maintain." ChatGPT was contradicting its previous response in which it said ESAs were more reliable and required because parabolic antennas "have mechanical parts that can be subject to wear and require regular maintenance."

I also realized that my question was a bit off -- it focused on the antenna rather than the entire ground station -- so I asked it to "list the advantages of satellite ground stations that use parabolic antennas over satellite ground stations that use electronically steered antennas". One of the advantages it listed was suitability for high-frequency Ka and Ku bands, but both Thinkom and BlueHalo use those bands and Thinkom is targeting even higher frequencies. It also repeated the simplicity advantage.

You can see the dialog here.

Finally, I asked the title question from my previous post -- will electronically steered antennas replace parabolic antennas in satellite ground stations?

It listed points under three headings -- advantages of ESAs, limitations of ESAs, and application-specific considerations and concluded that:

"While there is potential for Electronically Steered Antennas to replace parabolic antennas in certain satellite ground station applications, it is not a straightforward or immediate transition. The adoption of ESAs will depend on factors such as technology advancements, cost reductions, performance improvements, and specific application requirements."

It reversed itself once more by listing improved reliability as an advantage of ESAs, but the conclusion was similar to the conclusion in my original post. It also revealed a shortcoming in my formulation of the question. Since I have been writing a lot about Internet service constellations, I overlooked other applications in my previous post and did not specify that I was interested in broadband Internet service. (A human editor would have known that I was writing for an Internet-related publication, would have been aware of my previous writing, and assumed I was focused on Internet applications).

It pointed out that parabolic antennas had an advantage for deep space communication, so I asked a more fully qualified question -- Will electronically steered antennas replace parabolic antennas in ground stations for LEO, MEO, and GEO Internet service constellations?

The reply seemed vaguer and non-committal this time, but was also similar to mine:

"Considering these factors, it is likely that a combination of ESAs and parabolic antennas will be employed in future ground stations for LEO, MEO, and GEO internet service constellations. The specific configuration and utilization of each technology will depend on various factors, including cost, performance requirements, deployment scenarios, and network architectures." 

You can see the dialog here.

Conclusion

So, what is the role of ChatGPT in this sort of journalism? It served me as an editor or referee reviewing what I had written. I would have made two changes after getting feedback from ChatGPT -- I would have mentioned that I was focused on LEO, MEO, and GEO Internet service applications, and I would have included interference mitigation as one of the advantages of ESAs.

ChatGPT made a couple of misstatements and did not "know" about the possibility of an array of antennas like that of Thinkom with its wide elevation angle range. To its credit, I liked the way it apologized for overlooking spectral efficiency as an advantage for ESAs and it was an indefatigable and patient interviewee. It was also free (for the time being).

I consulted ChatGPT after drafting my article, but I could have used it as a research tool before writing. Had I done so, I might have been misled by some of its mistakes and I wouldn't have discovered Thinkom's innovation. Furthermore, its prose was not clear and concise -- I don't think it could pass a Turing Test on writing style. In this case, an old-fashioned Internet search engine was a far better pre-writing tool.

ChatGPT would be improved if it gave links to the sources of its assertions. Like autocomplete, it generates sentences by repeatedly appending the most probable next word in text documents found on the Internet, so the final string is novel. (That's not the way I generate sentences -- they follow from an idea). Might a list of the documents providing the most words be useful? (Google Bard adds citations, but I've not tried it out yet).

While ChatGPT helped me, I don't believe a ground station expert would have learned anything new by interacting with it and a beginner like a student writing a term paper would have been misled. The curious journalist was the sweet spot in this case, but this is version 3.5 of ChatGPT, which had a data-cutoff date before BlueHalo and Thinkom announced the products I've mentioned. I'll revisit it when I get access to ChatGPT4.

PS -- Let me know if you read the dialogs I linked to and notice something I missed,

Thursday, June 08, 2023

Will electronically steered antennas replace parabolic antennas in satellite ground stations?

ThinKom gateway -- an array of electronically steered arrays

Might ChatGPT, which has access to the entire Internet, have come to a different conclusion than me? Stay tuned.

Three recent developments make me wonder whether we are on the cusp of a shift in satellite ground station technology from parabolic to electronically steered antennas (ESAs). 
The Space Force Satellite Control Network (source)

The U.S. Space Force operates the Satellite Control Network, with 19 parabolic antennas at seven locations around the world. The network was established in 1959 and a report by the Government Accountability Office found that it should be updated to help the Space Force better manage future efforts. Last year, The Space Force awarded BlueHalo a $1.4 billion contract to modernize space operations using their software-defined ESAs and the OpenSpace software-defined satellite ground system from Kratos. This article says they will upgrade 12 "ground stations" starting in 2025, which I assume means they will install 12 ESAs at the seven locations shown here.

In March, the Air Force Research Lab selected ThinKom for its next-generation gateway solution -- an integrated array of ESAs. The following month, ground station operator Kongsberg Satellite Services (KSAT) and ThinKom announced a partnership to bring ThinKom’s gateway array to the commercial ground station market. The Air Force contract will help fund the development of the gateway and the partnership plans to have a fully operational system in 2024.

ThinKom antenna design (source video)
ThinKom and KSAT are a good match. KSAT has experience operating ground stations with 270 antennas at 26 locations and ThinKom has a hybrid mechanical/phased array antenna design utilizing three rotating platters. Rotating the feed and aperture platters together steers the beam in azimuth; rotating them relative to each other steers beam elevation; and rotating the polarizer platter selects between left and right polarization. The partnership's first commercial "customer" will likely be KSAT itself.

Finally, OneWeb will soon be online globally. Arctic Space Technologies is building a 27-antenna ground station for them, and it will be operational in the third quarter of this year. Given the short timeline, the antennas will probably be parabolic, but OneWeb is committed to and has signed a contract for multi-orbit service. I asked about the possibility of ESAs and got no reply.

I wrote the following list of advantages of ESAs in ground stations after visiting the sites and reading the articles I've linked to above and using a little common sense:
  • Reliability (though ThinKom's hybrid antenna may be less reliable than a pure ESA)
  • Wide elevation angle range (in a ThinKom array)
  • Wideband (Thinkom is targeting Q and Vbands -- what about atmospheric interference)?
  • Multiple beams
  • Instant switching between frequency bands
  • Spectral efficiency
  • Instant switching between LEO, MEO, and GEO orbits (a "selling point" for OneWeb)
  • Fast handoffs between satellites
  • Compact and small footprint (especially with ThinKom gateway)
  • Reduced power requirement
  • Lower installation cost
  • Portability
Prices may be high today and standards not solidified, but with technical progress and increased production quantities, parabolic ground station antennas seem likely to go the way of vacuum tubes, mag tape, and core memories. 
 
But the articles I read were about ESA projects so the advantages may have been overstated. Might ChatGPT, which has access to the entire Internet, have done better or come to a different conclusion than me? Stay tuned.

Sunday, April 23, 2023

China and Taiwan recognize Starlink's military value

Starlink has a conflict of interest.

Ukrainian Starlink traffic March 6-May 22, 2022 (source)
When Russia invaded Ukraine, SpaceX had around 2,000 satellites in orbit. It was clear from the first day of the war that a low-Earth orbit (LEO) constellation of around 2,000 satellites would be a valuable military and civilian asset. The first truckload of Starlink terminals arrived in Ukraine on February 28, 2022, four days after the invasion. By March 19, there were 5,000 terminals in Ukraine and 150,000 active daily users by May 2nd.
China and Taiwan have both seen the strategic value of 2,000 Starlink satellites.

Initially, China planned two LEO Internet service constellations, but they were abandoned in favor of a single constellation, GuoWang, which would be operated by a state-owned company called China SatNet. Since satellite Internet had been deemed critical infrastructure China SatNet was not placed under The China Aerospace Science and Technology Corporation (CASC), China's main state-owned space conglomerate, but was made an independent entity at the same level as CASC, empowered to select its own government and privately-owned launch providers, satellite producers and other vendors. 

China space consultant Jean Deville thinks it is likely that the GuoWang satellite constellation will start to deploy this year on a Long March 5B rocket. The mass of Starlink Gen 2 v 9-1 satellites is 303 kg and the mass to LEO of a Long March 5 is 25,000 kg. If GwoWang's satellites had the same mass, it would take 83 fully packed launches to orbit 2,000 satellites, and doing that in five years would require developing reusability.

China sees Starlink as a weapon (source
The Chinese assessment of Starlink as a military threat is found in articles like:

The Taiwan Ministry of Digital Affairs has noted that since the Russian invasion, Ukraine "has depended on Starlink satellite communications to connect to the world" and they have an $18 million plan to place satellite receivers in 700 places at home and abroad, to maintain government communications "during emergencies such as natural disasters or wars." The ministry said it was "willing to cooperate with any qualified satellite service provider" and that is wise because Elon Musk would have a conflict of interest in the case of a war between China and Taiwan and we may have already seen evidence of that conflict.

Taiwan's vulnerable undersea cables (source)
In February 2023, SpaceX’s chief operating officer Gwynne Shotwell said "We know the military is using [Starlink satellites] for comms, and that's ok ... But our intent was never to have them use it for offensive purposes" and they began geofencing satellites when they were above water or Russian-occupied territory inside Ukraine. 

In March 2022 I wrote that the Ukrainian army was using drones to spot targets and relay their coordinates over Starlink to "the artillery guy and create target acquisition” and they were also using drones equipped with bombs. 

That sounds "offensive" to me, but more likely Shotwell was going along with the peace plan Elon Musk tweeted calling for Ukraine to cede Crimea and holding UN-supervised elections by the people who remained and were still alive in the "annexed regions."

More cynically, there may have been pressure from Russia's ally China. Tesla plans a large battery factory in China and makes and sells a lot of cars there, and Shotwell knew that the Chinese government had stalled Tesla's plan to expand auto production there because of concerns about Starlink in January. (I wonder if Ukraine was discussed during Musk's recent trip to China).

The above is speculative and indirect, but the threat to Tesla would be direct if Starlink were to aid Taiwan in the event of a Chinese invasion. (Tesla would be in jeopardy in the case of a Chinese invasion regardless Starlink). Taiwan should be talking with OneWeb, Telesat, Amazon Project Kuiper, and the European Union's recently approved IRIS² project and consult the technicians and military people working with Starlink in Ukraine.