Early Thursday morning, SpaceX launched its Paz mission, using its workhorse Falcon-9 rocket. It might have been a routine launch, except it wasn’t. Hours before its earlier scheduled launch on Wednesday — before bad weather forced postponement — CEO Elon Musk had spoken of Starlink, a constellation of satellites that would provide a cheap, high speed, global Internet connection.
“Today’s Falcon launch carries 2 SpaceX test satellites for global broadband. If successful, (the) Starlink constellation will serve (the) least served,” he tweeted. The UN Broadband Commission for Sustainable Development estimated in 2016 that 57% of the world’s population was offline.
So, what is the Starlink constellation?
Starlink will likely have 12,000 small satellites in two layers — low earth orbit (LEO) and very low earth orbit (VLEO).
The LEO constellation will have 4,425 satellites at altitude between 1,110 km and 1,325 km, and will operate in the Ku, Ka and V band (in increasing order of frequency). The VLEO constellation will have 7,518 satellites at altitude between 335 km and 346 km, and will operate in V band frequencies.
The LEO constellation will provide high-speed broadband services around the world; the VLEO constellation will enhance capacity.
Being at a higher altitude, LEO constellation satellites will have a larger spot beam, i.e. the area on Earth covered by a satellite’s transmission antenna. LEO satellites will travel at high speeds, and VLEO satellites are expected to compensate for possible losses of satellite-device connection, and signal attenuation.
Was Thursday’s launch about Starlink?
Only partly. Space-based Internet is largely unproven, and the two identical 400 kg satellites, Tintin A and Tintin B, are test satellites. SpaceX has written to the US Federal Communications Commission that the “experimental engineering verification vehicles… will enable (it) to assess… technologies”. The designed lifetime of each satellite is only six months. To defy gravity and atmospheric drag and stay in comparatively permanent orbit, a satellite must be at an altitude of at least 36,000 km — unless proper propulsion is used to keep them up.
What can go wrong?
12,000 satellites is more than the total number ever launched, and will be a challenge to build and maintain. Also, as Joseph W Gangestad of the nonprofit Aerospace Corporation has written, “This unprecedented proliferation of satellites, particularly in LEO, will bring with it dramatic jumps in the risk of collision, debris generation and its cascading effects for future collisions, and the number of close-approach warnings for active satellites.”
Who else is trying something like this?
Facebook had plans to launch a satellite, the Amos-6, to cover parts of Africa in 2016, but it was destroyed after its ride, SpaceX’s Falcon-9 rocket, exploded before launch. Since then, the company has been developing light-based wireless communication. US-based OneWeb is reportedly planning to send 900 satellites next year. Telesat Canada is expected to have two constellations of 117 satellites each.
Okay, what was the main payload of the Paz mission?
Paz, the Spanish radar imaging satellite. According to Hisdesat, the company that developed it, its applications include military use (border control, intelligence, military operations, enforcement of international treaties), as well as civilian use (environmental monitoring, protection of natural resources, surface monitoring, city and infrastructure planning, monitoring of natural catastrophes and high-resolution mapping). Its camera has ultra high resolution of up to 25 cm.