Orbit is a marvel of modern tech, dotted with satellites, each the product of humanity’s most advanced engineering, producing imagery, doing science and much more, then communicating back to Earth with the 2020s equivalent of dialup.
That’s slow and intermittent, with the pipeline from space – particularly the increasingly populated Low Earth Orbit (LEO) – severely constrained.
With orbits around 90 minutes for the typical LEO satellite, there’s very little time, often minutes, to download data to a ground station.
Even at the highest download speeds, there’s often far more data than can be delivered in the time available. Some may have to be dumped, while what does arrive could be hours old.
And LEO is crowded, with more than 4500 active satellites and more arriving all the time, all relying for communications back to Earth on increasingly limited Radio Frequency (RF) spectrum.
“Regrettably for the folks with satellite in LEO, it’s largely still the dialup age, while we take ubiquitous connectivity for granted everywhere else,” says Glen Tindall, Chief Executive Officer for space systems with Australian defence and space technology company Electro Optic Systems (EOS).
So what’s to be done?
EOS has come up with an innovative plan to place a small constellation of communications relay satellites in Medium Earth Orbit (MEO), able to communicate by laser with satellites in LEO, then relay their data to a ground stations.
This has been named SpaceLink, with planned launch of the first satellite in 2024.
“SpaceLink is a business that EOS owns. It’s actually domiciled in the US and we have done that for a few different reasons,” Tindall told the recent MiLCIS conference in Canberra.
“The largest body of users will be perhaps indirectly government users. Although our customer base is commercial organisations, at the end of the value chain, most of the imagery that is generated from LEO satellites ends up on the desk of a government user somewhere.
“We took the view that given that most of the customers are out there in government land in the US, we needed to have something that was very acceptable to the US government in order to maximise uptake in that customer base.”
SpaceLink will place one of its four ground stations in Australia, with the others in the continental US, Hawaii and the Middle East.
There’s another issue for satellite operators acquiring sensitive information. Tindall said many satellite businesses would not care if their data landed in Japan and travelled back to the US by way of India.
“But government organisations generally do care very much about how their data transits from the sensor into their data centre,” he said.
“We have the ability to take data directly from a customer’s asset in space without passing through anyone else’s territory direct to home turf. This is a highly valued capability by government agencies.
“We provide continuous connectivity. Anyone who has had continuous connectivity doesn’t want intermittent any more.”
EOS calls this a communications superhighway for the growing space economy.
Tindall said one query routinely put to him was along the lines: If this is such a great idea, why isn’t Elon Musk doing it with his ever expanding LEO Starlink constellation?
The answer is that the high closing and passing speeds of LEO satellites make it technologically challenging for optical communications. Plus the RF spectrum for communication from LEO satellites to ground – mostly S and X-Band – is already crowded.
“There is no more spectrum to be had. Everybody is using the same spectrum. Everybody is trying to operate into a relatively small number of gateway stations,” Tindall says.
“There is one in Norway which is very well known. There are some in Australia. Essentially there are more LEO customers wanting to use the same spectrum over the same gateway sites and it is becoming congested.
“That spectrum isn’t getting any wider. The amount of data you can jam through those pipes is really constrained.”
Which makes operating their satellites from MEO appealing.
For those not familiar with orbit definitions, LEO extends out to 2000 kilometres from the Earth surface, though most satellites are much lower. The International Space Station (ISS) is around 400 kilometres.
MEO extends from 2000 kilometres to just below geosynchronous (GEO) orbit which is at precisely 35,786 kilometres.
LEO, being closest to Earth, is especially useful for imaging and internet connectivity satellites. It’s the easiest and cheapest to reach and also the most congested.
By comparison MEO is vast and almost empty. The best known users are constellations of positioning and navigation satellites such as the US GPS, European Galileo, Chinese BeiDou and Russian GLONASS.
Fortuitously, SpaceLink managed to acquire a 21 gigahertz allocation of MEO RF spectrum in the Q and V Bands from the US Federal Communications Commission.
That came courtesy a defunct US company whose assets EOS acquired. This was the most spectrum ever allocated by the FCC to any satellite constellation.
As a foreign-owned company EOS had to go through the US version of Australia’s Foreign Investment Review Board (FIRB).
“We were granted that in record time, within a month. The reason we were told we were granted that spectrum right was because it’s a big piece of spectrum and the next countries in line might not be so friendly to the US as Australia,” he said.
“Secondly EOS is a known quantity in the US so they felt we were a safe pair of hands. We have a FCC licence requirement to bring that spectrum into use in 2024.”
The plan is for LEO satellites to communicate with SpaceLink by two-way laser links, though they will be backwards compatible with legacy RF users such as some NASA satellites.
Communications with the ground terminals will be by RF.
Tindall says free space optical communications is pretty much a solved problem. A number of companies produce the optical heads which will need to go on new LEO satellites to communicate with SpaceLink.
“A problem still needing solving is passing through the earth’s atmosphere. There’s this 10 kilometre stretch near the bottom that’s full of turbulence, eddies, clouds and moisture that light doesn’t like,” he said.
“It’s not at 99.5 per cent or better so it’s not at an operational level of capability at the moment. We think we will get there and we have a pathway but we are not betting the bank on this for the first constellation.”
Operating satellites in MEO does present challenges which don’t exist in LEO. Satellites experience far high levels of radiation and must be appropriately hardened in order to achieve the anticipated 15 year lifespan.
Last year EOS announced it had contracted OHB of Bremen, Germany, to manufacture four satellites in a deal worth US$300 million. OHB manufactured 34 satellites for Europe’s Galileo navigation constellation.
The EOS birds are big satellites, each massing 700 kilograms, with significant power requirements and substantial expansion capabilities.
For example, optical modulation is by basic on-off keying which can still achieve speeds up to 10 gigabits. More advanced modulation technologies could deliver vastly greater speeds.
Tindall says they need three satellites to be operational but have opted for four for redundancy.
He says their challenge now is to sign up the clients, with a list of 200 potential customers, of which the top 50 are regarded as serious contenders.
Customer number one is the Committee for the Advancement of Science in Space, the part of NASA which runs the ISS. A pair of optical terminals will be flown to the ISS to allow communication with SpaceLink.
The obvious first takers will be companies supplying imagery to US government agencies.
Tindall says EOS would love for the US National Reconnaissance Office to write them a cheque.
“We don’t think they are going to be a first mover,” he said.
“However there are a lot of private organisation that build and fly their own satellites, they take pictures of stuff and sell those pictures to the government. That is our initial target market.”
The expectation is that once one such company is on board, others will have to follow, on the basis that the customer simply won’t be interested in anything other than near real time imagery.
As the project has progressed, other potential customers have emerged. Anyone doing human spaceflight will want real time communications, as will emerging operators of private scientific research space stations and in-orbit servicing.
SpaceLink has already been selected by NASA as contender to replace its ageing constellation of data relay satellites.
There are also unanticipated military applications. The US Army is most interested in capabilities for real time observation delivered by SpaceLink to support precision long range fires.
This would appear most relevant to the US Prompt Global Strike program which aspires to be able to deliver a conventional warhead, by way of hypersonic missile, anywhere on Earth within an hour.
“We are actually getting more traction than I would have imagined in those markets than in the LEO side which is where I thought it would all happen,” Tindall said.