On the Benefits of Small-sized LEO Mega-constellations from the Positioning Perspective




Figure 1. Constellation layout for Kuiper (a), OneWeb (b), Starlink (c), and Telesat (d).


Nowadays, launching satellite constellations is becoming more and more affordable. Thanks to the last technological advances, the cost related to developing and launching satellites into space is considerably reducing. Two of the most important factors leading to the emergence of a new “low-cost” space segment are the fully (or partial) reusable launching systems and satellite miniaturization.


The satellite launching is one of the most expensive parts of the definition phase of a satellite constellation. Fully-reusable launching systems, as of 2022, are still under development. But once ready, a fully reusable launcher would drastically reduce the satellite launch costs, even compared with the current partial reusable systems. For example, current prices for a single launching (which may contain one or several satellites) are about 2M$, compared with more than 100M$ of traditional satellite launching systems.

The miniaturization of satellites is redefining the usage of space. Small satellites are considerably cheaper to design and build, whose cost can be about 500k€, compared to the 100-300M$ cost for a regular-size satellite. The typical mass for a small satellite is below 100 kg, while regular-size satellites are heavier than 500 kg. The mass and satellite volume also influence the final launching price. Less satellites will be able to be put in orbit at the same time if satellites have bigger masses, and then the full constellation will need a higher number of independent launchings.


LEO altitudes are ranging from 200 km to 2000 km around the Earth. Some of the most promising mega-constellations (i.e., satellite constellations with thousands of satellites) partially already in the sky, or planned to be launched in the coming years, are Amazon Kuiper, OneWeb, SpaceX Starlink, and Telesat. These constellations could, in theory, provide Positioning Navigation and Timing (PNT) services by means of a dedicated payload, which would be added or a modified existing payload of these constellations. The concept of using such LEO mega-constellations for additional services, for which they were not initially designed, is called Signals of Opportunity (SoO). SoO thus consists of reutilizing wireless transmissions for a different purpose (e.g., PNT service) than the initialOneWeb thought one (e.g., broadband communications, Earth Observation, etc.).


Table 1. Summary of the main orbital parameters for the most promising LEO mega-constellations.

Name

Country

Topology

Satellite Mass (kg)

Altitude (Km)

Total Satellites

Orbital Planes

Inclination (deg)

Frequency Band

Kuiper

USA

Walker Star

250

590-650

7774

1173

33-80

Ku/Ka

Oneweb

UK

Walker Star

380

1200

7808

100

54 and 97.7

Ku/Ka

Starlink

USA

Walker Star

145

340-614

34404

478

33-148

Ku/Ka

Telesat

Canada

Walker Star

≈700

1015 and 1325

1671

67

98.98 and 50.88

Ku/Ka



Table 1 summarizes the main orbital parameters for Amazon Kuiper, OneWeb, SpaceX Starlink, and Telesat constellations. All four mega-constellations share a similar constellation topology (Walker star topology) and similar planned frequency bands (Ku/Ka frequency bands). Some of these constellations plan to use frequency bands as high as the V-band for some of the links. The satellite mass among various mega constellations is very different. The most lightweight system is the Starlink system, with approximately 145 kg per satellite, followed quite close by Kuiper (250 kg), and OneWeb (380 kg). Telesat satellites’ weight is planned to be about 700 kg, having a similar size to GNSS Galileo satellites. Kuiper and Starlink will use similar orbit altitudes, namely between 600-650 km. Starlink will include satellites orbiting at altitudes as low as 340 km. Starlink, with more than 34k satellites, is planned to be the densest satellite constellation ever, followed (by far) by OneWeb and Kuiper, with 7808 and 7774 satellites, respectively. The orbital planes, namely the independent orbits of a group of satellites in the same satellite constellation, are also quite diverse among various LEO mega-constellations. This roughly means that the total number of satellites will be split into the total number of orbital planes. The Kuiper constellation will be the most diverse in terms of satellite splitting, having 1173 orbital planes. Next, there will be Starlink with 478 orbital planes, and finally OneWeb and Telesat, with 100 and 67 orbital planes, respectively. Finally, the constellation inclination will vary among the different orbital planes. Some of these planes will share the same inclination, but at different altitudes. The inclination affects the coverage at high or low latitudes. Higher inclinations are given more coverage to polar regions, while lower inclinations offer higher coverage to the equatorial region. Kuiper and Starlink will have similar inclinations, especially for the equatorial region, while OneWeb and Telesat will have only two different inclinations at about 50° and 98-99°.


As we have seen, the Telesat constellation will be the one with the lowest complexity in terms of orbital parameters, while Starlink will be the most complex. Telesat is not using small-size satellites; in fact, the Telesat satellite mass will be almost 7 times bigger with respect to Starlink. There remains still to analyze deeply which are the benefits (if any) of more complex constellations from the point of view of PNT compared to less complex constellations.


As a summary, in this blog post, we have provided a quick overview of the benefits of small-sized mega-constellations from the positioning perspective. We have analyzed which are the main advantages of the constellations, and the factors are making these solutions a good candidate for the future of satellite navigation

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