The growth of mega-constellations is rapidly increasing the number of rocket
launches required to place new satellites in space. While Low Earth Orbit (LEO)
broadband satellites help to connect unconnected communities and achieve the
Sustainable Development Goals, there are also a range of negative environmental
externalities, from the burning of rocket fuels and resulting environmental
emissions. We present sustainability analytics for phase 1 of the three main
LEO constellations including Amazon Kuiper (3,236 satellites), OneWeb (648
satellites), and SpaceX Starlink (4,425 satellites). In baseline scenarios over
five years, we find a per subscriber carbon dioxide equivalent (CO2​eq) of
0.70±0.34 tonnes for Kuiper, 1.41±0.71 tonnes for OneWeb and
0.47±0.15 tonnes CO2​eq/subscriber for Starlink. However, in the
worst-case emissions scenario these values increase to 3.02±1.48 tonnes for
Kuiper, 1.7±0.71 tonnes for OneWeb and 1.04±0.33 tonnes
CO2​eq/subscriber for Starlink, more than 31-91 times higher than equivalent
terrestrial mobile broadband. Importantly, phase 2 constellations propose to
increase the number of satellites by an order-of-magnitude higher, highlighting
the pressing need to mitigate negative environmental impacts. Strategic choices
in rocket design and fuel options can help to substantially mitigate negative
sustainability impacts