On April 22, SpaceX’s Falcon 9 rocket carried 60 satellites into orbit, marking the company’s sixth operational launch of its Starlink satellites. With a total of 417 satellites now in operation, Elon Musk is closing in on his vision to deliver broadband internet access across the globe. Upon completion of its first phase, the Starlink network will consist of 1,584 small satellites that will work together as a constellation 340 miles above Earth’s atmosphere to provide affordable internet coverage to residents in the northern United States and Canada.
Musk’s endeavor underscores the lack of coverage around the planet – more than 3 billion people don’t have internet access, predominantly in remote areas. Satellite constellations, like Musk’s Starlink, aim to change that.
Location, location, location
To better understand the scope – and the challenges – of Starlink and other satellite constellations, it’s helpful to look back at the history of satellite telecommunications and the differences between satellites that are closer or further away from Earth.
Original satellite communications systems, circa the 1970s and 1980s, were based on satellites placed far above the Earth’s equator. The specific orbit is referred to as the geosynchronous Earth orbit or GEO. The GEO orbit is a circular orbit at a height of 22,300 miles above the equator. At that distance, the satellite velocity is such that the satellite completes an orbit every 24 hours and, therefore, to an observer on Earth, the satellite seems to be stationary, always hovering above at the same place in the sky. The approach was based on an October 1945 original publication, “Extra-Terrestrial Relays,” by Sir Arthur C. Clarke.
Since GEO satellites appear to be stationary in the sky, it is possible to point simple antenna dishes, without any tracking mechanisms, toward them. Theoretically, if the satellite retransmits the received signal back to Earth, any antenna that can see the satellite and points to it will be able to receive the transmitted signal. Clarke showed that each GEO satellite can cover almost half of the Earth and that implementing three GEO satellite systems could provide worldwide coverage.
Although we can cover the whole Earth with three GEO satellites – one every 120 degrees – the approach is not practical for numerous reasons:
- Business/markets reasons: Not all GEO orbital locations are valuable. A large percentage of Earth is covered by water/oceans with no permanent inhabitants so transmission of typical content over these areas will be a waste. An orbital location above Denver, in the middle of the United States, however, can be considered a prime location since it can provide access to millions of potential customers. An orbital location above the middle of the Atlantic Ocean covers limited direct customers, but can provide connectivity between Europe, the Americas and Africa.
- National interests: National interests drive the availability of orbital slots, which are controlled by the International Telecommunications Union.
- Available frequency spectrum: The limited available frequency bands and potential interference between operating satellites drove the allocation of orbital slots and frequencies.
- Earth curvature does not enable coverage of areas that are far North or far South from the equator. To use a GEO satellite located over the equator, antennas in those areas will have to be pointed very low toward the horizon and will not be able to establish a reliable communication path.
- Latency/propagation delay: The round-trip delay for a signal to travel to a GEO satellite and then transmitted back to Earth is greater than 500 msec. For typical heritage satellite communications uses, such as for TV programing, printed material and file transfers, this delay did not present an issue. However, with the advance of Internet usage, gaming, remote medicine, etc., latency became an issue.
In response to the GEO shortcomings, the concept of low-Earth orbit satellites systems (LEOs), constellations were developed.
Unlike the GEOs, which are synchronized to the Earth’s orbit, LEOs are closer and travel around the globe at a faster pace. If just one LEO were employed, the satellite would not always be directly above its coverage area, meaning internet connections would be spotty at best. To use a LEO satellite, a customer/user would need an antenna that can track the satellite fly-by and would have had only a limited period when the satellite is visible – when communication is possible. A constellation of LEOs, however, overcomes that issue.
Because a constellation is comprised of numerous satellites that are flying one after the other in the same orbit, as a satellite flies away and the link may be interrupted, the constellation software moves the connection to the “next” satellite so that the channel/link is not disconnected. In principle, to be able to provide consistent coverage, hundreds if not thousands of LEOs must be deployed as a system, also known as a constellation, to ensure that at least one satellite is always overhead.
In addition, since the LEO system does not need the GEO orbit, the satellites can be placed in orbits that are not restricted to the equator, they can be inclined to the equator and provide communication connections to the whole Earth, including North and South pole areas.
The result is many lower-cost large constellations of satellites that provide widespread coverage. The shift will have a huge impact on underserved communities, but as a relatively new concept, a learning curve still persists.
Musk’s constellation is not the first, but, so far, it is the biggest planned. There are several in operation, including Iridium, OneWeb, Globalstar and O3b, which stands for the “other 3 billion” that do not have access to broadband internet. And other companies like Amazon also have plans to get into the game. These ambitious efforts don’t come without risk, however. A few startups have gone bankrupt while others have struggled financially.
A major disadvantage of launching a constellation is the cost. Compared to a GEO, which costs around $200 million to manufacture, it has been estimated that one Starlink satellite costs $500,000 to manufacture. Musk has said that the number of satellites in his constellation could at some point rise as high as nearly 12,000, meaning his manufacturing expenses alone could exceed $6 billion. This cost comparison addresses only the satellite manufacturing; launch and insurance costs are additional expenses to consider. It should be noted, however, that not all constellations are slated to be as big as Starlink. Some have as few as a couple dozen satellites.
Regardless, anyone in the business of manufacturing satellites is undoubtedly working to bring costs down. Airbus, Boeing, Lockheed Martin and the dozens of other players in the satellite manufacturing space are streamlining their operations and looking to new technologies to reduce costs and time to market. 3-D printing is looking to be a solid process for achieving both.
In years past, 3-D printing was too slow and too expensive, and printable materials were still being developed. Today, however, companies like Lockheed have been ramping up its use in a range of satellite components. In an article published in Via Satellite magazine, Brian Kaplun, Lockheed’s additive manufacturing manager, said that the company is building entire bus structures for smaller satellites and with much shorter lead times.
“What in the past could have taken years to make can be manufactured within months or weeks with 3-D printing,” he said. “The propellant tanks, for example, using the traditional forging technology, would have had lead times anywhere from a year and a half to two years. With additive manufacturing we have produced an equivalent for the forgings in two weeks.”
Testing, testing, 1, 2, 3
The inherent differences between GEOs and LEOs inevitably dictate the way in which they are produced and maintained. At 22,000 miles from Earth, GEOs must be incredibly reliable. Understandably, a technician can’t be sent up to one to make repairs.
In addition, each of these satellites are unique and different, designed specifically for a specific mission from a specific orbital location to cover a specific part of the world. Therefore, a GEO must include significant redundancy (backup units and switching complexities) and undergo stringent and repeated testing throughout the manufacturing process and launch campaign, to ensure its long-term success. GEOs are tested in all kinds of operational configurations and extreme environments (thermal and vacuum) on the ground before they’re launched to make sure they last the mission life. Due to design, qualification, redundancy, and test levels the expected mission life of GEO satellites increased through the years from about seven years to at least 15 or 20.
Conversely, the large number of satellites in a LEO constellation and their relative low cost changed the overall design and testing approach. LEOs do not necessarily require the same level of testing. Testing can be random. Instead of performing QA checks on every single satellite produced, one in seven could be tested, for example. This, of course, is the nature of higher manufacturing levels. In addition, LEO satellites do not need internal high redundancy levels. Instead each of the LEO orbits include additional spare satellites that can be activated as necessary if an operational satellite fails. This philosophy simplifies the satellite design and significantly reduces the manufacturing, testing, production schedules and costs
In terms of functionality, GEOs are fairly simple compared to LEOs, generally speaking. Because they are in a synchronous orbit, no tracking hardware and software is required. LEOs, on the other hand, must have sophisticated software built in to move the communication link from satellite to satellite to establish and maintain communication connections with millions of handheld and other devices.
Currently, there are about 2,200 satellites in low-Earth orbit with thousands more on the horizon. This in itself adds an extra layer of manufacturing that must be performed. Astronomers, among others, are concerned that the reflectiveness of the satellites will interfere with their ability to observe the night sky using ground-based telescopes. In the case of Starlink, darkening treatments are being added as a coating to the satellites’ exteriors.
In the upcoming months and years, satellite constellations will mature and most likely become the preferred method for distributing the internet around the world. In turn, the manufacturing of these satellite systems will also mature and speed up in nature. In any other context, the sky would be the limit.