"SpaceX and OneWeb, a communications firm, plan to launch satellites in their thousands, not hundreds." What does it mean by "in their thousands"?
There are two ways to describe multitudes - in their hundreds/thousands/millions or by the hundreds/thousands/millions.
I can't find a precise distinction between the two idioms, but some examples are:
Londoners came out on the streets in their thousands https://www.macmillandictionary.com/dictionary/british/in-their-hundreds-thousands-millions
When the potato famine hit Ireland, the Irish began emigrating by the thousand https://idioms.thefreedictionary.com/by+the+thousand
UPDATE: One user pointed out that in the thousands is also acceptable and widely used.
"In their thousands" means simply that the quantity is several thousands, not specifying exactly how many.
in their hundreds/thousands/millions
used for saying how many people or things do something, without being exact
Londoners came out on the streets in their thousands.
— Macmillan Dictionary
Some examples from Google Books:
When, therefore, hundreds of thousands of the dead were restored to life, and flocked to the city in their thousands, how could the Jews have let go such an opportunity?
It was therefore resolved, as the only alternative, to arouse the people, Essex fondly imagining that his voice, if he called upon them, would bring them in their thousands and tens of thousands to support his cause.
This was the time when action should have been taken: a military operation was needed to protect the Tutsi, sheltering in their thousands in well identified places such as churches, hospitals and stadia.
The breadth of their appeal lay in their ability to reflect the aspirations of their time, as much as of their own people, and to speak in their own terms, both to the Urdu readers in their thousands and to educated elites of the cities
I assume they mean they will launch a lot more.
I would have said, "... by the thousands.."
Edit about "in": I think they are mixing the numerical range form in the -quantity- with the more literary groupings form by the -quantity-
The temperature was in the hundreds.
They sold by the hundreds.
That form usually is applied to a person's range of age: "The couple was married in their fifties." So maybe they mean they will only launch very old objects? That seems unlikely.
Sometimes the in their form is used in a poetic sense: "It was a clear night, the stars were out in their thousands." At that point the numerical meaning of thousands becomes some relative term like a whole lot.
That's why I said I think they mean a lot more.
This is a question about the future age of the company (They are in their 100s/1000s). It is similar to the sentences about human age: 'He is his 30s. She is her 30s. They are in their 30s.'