SpaceX will launch 60 satellites into orbit around the Earth tonight, as the aerospace company owned by billionaire Elon Musk starts to build its Starlink internet service.
The purpose of Starlink is to provide cheap and reliable internet access worldwide – including in places that struggle with current infrastructure.
The Starlink network will eventually consist of a "super-constellation" of close to 12,000 satellites, providing global internet coverage, according to Musk.
SpaceX got the green light from the US Federal Communications Commission to start launching satellites last month, and was due to send the first 60 into orbit on Wednesday.
However, excessive winds over the Cape Canaveral Air Force Station in Florida meant the Falcon 9 rocket carrying the satellites was unable to take off.
The launch has been rescheduled for 22:30 EST on Thursday (02:30 GMT Friday).
Each satellite in the first Starlink launch weighs 227 kg, making this the heaviest SpaceX payload to date.
It will take 6 more launches of 60 satellites to achieve "minor coverage", and at least 12 more launches to achieve "moderate coverage", Musk said.
The company is required to put half of its constellation's satellites into operation by 2024.
Internet access for everyone
There's nothing new about using satellites for internet access, but the problem traditionally has been that these services don't offer a way to upload data quickly.
Their distance from Earth also means that the time it takes a signal to travel from you to the satellite and then to its destination is longer than normal earthbound communications.
For normal broadband you might see delays of 20 milliseconds (ms) while geostationary satellites have 550ms of delay. As a result, satellite broadband is usually only used when there is no other option.
However SpaceX's Starlink satellites will be placed in a much lower orbit – some of them just 340 miles above the surface of the Earth.
This will significantly reduce the latency – with SpaceX claiming the delay will be only 15ms.
The downside is that the satellites will not be in a geosynchronous orbit, so far more of them are needed to provide blanket coverage. They will also only last a few years before burning up.
Starlink is currently only authorised for operations in the United States.
First step to Mars?
If successful, Starlink could be a valuable investment for SpaceX, as demand for internet access is huge and there are lots of places on Earth where fixed-line broadband isn't practical.
Musk said he expects revenues from rocket launch services provided by SpaceX to top out at about $3 billion per year.
That makes Starlink key to generating the cash that SpaceX needs to fund Musk's larger dream of developing new spacecraft capable of flying paying customers to the moon and eventually trying to colonise Mars.
"We think this is a key stepping stone on the way towards establishing a self-sustaining city on Mars and a base on the moon," said Musk.
Space junk WARNING
Some space scientists warn that Elon Musk's plans – along with those of rival companies working on their own low-Earth-orbit constellations – raises the risk of creating dangerous debris.
"The worst case is: You launch all your satellites, you go bankrupt, and they all stay there," European Space Agency scientist Dr Stijn Lemmens told Scientific American.
"Then you have thousands of new satellites without a plan of getting them out of there. And you would have a Kessler-type of syndrome."
The Kessler syndrome is a scenario in which the density of objects in low Earth orbit is high enough that collisions between objects could cause a cascade, where each collision generates space debris that increases the likelihood of further collisions.
One implication is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges impractical for many generations.
SpaceX claims that, because all its satellites have their own propulsion systems, they can be manoeuvred to prevent collisions.
However, Glenn Peterson, a senior engineering specialist at the Aerospace Corporation, claims that if all the planned mega-constellations launch, current tracking technologies would generate over 67,000 "collision alerts" a year.
Operators would then have to choose whether to make hundreds of precautionary satellite manoeuvres a day, or risk the small chance of a collision.
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