How can I boost production late in the game to get a Science victory?

I've found that leading in science at King level isn't too hard in Civ 6, but there's a huge amount of production required in order to complete the 5 Spaceport projects

What can I do to boost my late-game production?

Edit: This should be less of an issue since the Winter 2016 patch reduced the cost of all Space Race projects by 40%

City:

• Obvious one first: focus your city on production!
• Aim to build other cities' Industrial Zones within 6 tiles of your main production city's city center, to benefit from their Power Plant bonus

Note that since the Winter 2016 patch, factories no longer stack:

Cities can no longer receive yields from more than one regional building per type; they take the highest (ex. production from multiple Factories)

Wonders:

• Ruhr Valley (+30% production, and +1 Production for each Mine and Quarry in this city. Must be built along a River adjacent to an Industrial Zone district with a Factory).

Trade:

• Base trade routes from this city, prioritizing production
• Until you get Ecommerce (see below), domestic trade will probably generate more production than international

Great People:

• Sergei Korolev (Great Engineer) grants 1,500 production towards Space Race project construction
• Carl Sagan (Great Scientist) grants 3,000 production towards Space Race project construction - enough to one-shot a Mars component

Builders:

• Chop woods belonging to your production city to grant 200 production (or jungle for 100 production/100 food). Then replant woods and create Lumber Mills (note that you can't chop rebuilt woods).
  • Chopping woods for production can be done more than 3 tiles from your city, providing the production city is the closest of your cities to the wood.
• Build mines on any unoccupied hills, especially next to the Industrial Zone
  • Remember that mines will still provide an adjacency bonus to your Industrial Zone even if the mine itself is 4 tiles from your city.

Government:

• Consider switching to Communism for the 10% production bonus

Policies:

• Integrated Space Cell (+15% production towards Space Race Projects if a city has either a Military Academy or a Seaport).
• Ecommerce (+5 production and +10 gold from international Trade Routes)
• Arsenal of Democracy (Your Trade Routes to an Ally's city provide +2 Food and +2 Production for both cities)
• Five-Year Plan (+100% Campus and Industrial Zone district adjacency bonuses)

City States:

• Prioritize getting suzerainty of Industrial cities