Elon Musk is already dreaming of a gargantuan 'next-generation' Starship. If built, the rocket's body would be wider than an NBA basketball court.

• SpaceX is working on building a fully reusable rocket-and-spaceship system called Starship.
• Based on a presentation given by company founder Elon Musk in September 2018, the finished rocket may stand about 387 feet (118 meters) tall and 30 feet (9 meters) wide.
• But Musk tweeted on Wednesday that he's already envisioning a "next gen" Starship that'd be 60 feet (18 meters) in diameter. That's wider than an NBA basketball court.
• That doubled diameter could give the "next gen" Starship about eight times as much volume as the first version, enabling ambitious trips to Mars - but either vehicle has yet to be built.
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A day after SpaceX's final flight of Starhopper - a stubby prototype of an enormous planned launch system, called Starship - company founder Elon Musk dropped a clue about his super-size plans for the future.

Musk tweeted on Wednesday that he'll present SpaceX's latest thinking about the Starship system on September 28. The date marks the 11th anniversary of the company reaching orbit for the first time with its Falcon 1 rocket.

Until then, most of what we know about Starship comes from Musk's latest presentation from September 2018. At that time, the vehicle was still called the "Big Falcon Rocket" and was supposed to be made out of carbon-fiber composites. SpaceX is now using stainless steel but appears to be keeping similar dimensions, based on several renderings posted by Musk (including one of a Starship spaceship on the moon's surface).

Read more: Elon Musk says SpaceX could land on the moon in 2 years. A NASA executive says 'we'll partner with them, and we'll get there faster' if the company can pull it off.

Those dimensions suggest the first operational version of Starship would be a vehicle about 30 feet (9 meters) wide and 387 feet (118 meters) tall. Yet Musk is already dreaming up an even bigger version of Starship.

He revealed part of his grand plan when a Twitter user asked about a 39-foot-wide (12 meters) version of Starship. Musk replied that a "next-gen" version of Starship would probably be double that diameter: a width of 18 meters, or nearly 60 feet.

That's wider than an NBA basketball court.

The following graphic shows about how big the first Starship system would be compared to its prototypes, such as Starhopper and Starship Mark 1. The Apollo-era Saturn V rocket and NASA's upcoming Space Launch System moon rocket are also included for scale.

However, performing some basic math helps reveal the scale of what Musk is proposing to do with SpaceX in the far-flung future.

A 'next gen' Starship may have 8 times the volume of the first operational Starship

Simplifying the dimensions of the first-generation Starship into a cylinder (and ignoring its aerodynamic nosecone) gives a finished volume of about 7.5 million liters. The same calculation on the next-generation Starship - assuming its height also doubles, to about 775 feet (236 meters) - gives an approximate volume of 60 million liters.

So in effect, doubling the width and height leads to a launch vehicle about eight times as voluminous. Even if the next-generation Starship wasn't taller than many skyscrapers, it'd still presumably be several times bigger in size than its still-hypothetical predecessor.

Potentially octupling the volume says little about how much payload or people a next-generation Starship could haul into orbit, or how deep into space such a gigantic spacecraft could go. But it's hard not to imagine the answers are "more, bigger, faster, and farther" since it could tote that much more fuel and carry many times more Raptor rocket engines.

Read more: SpaceX test-fired a giant rocket engine with 'insane power' for moon and Mars missions. The future of Elon Musk's company may ride on its unrivaled performance.

Certainly, a nosecone with a diameter as wide as a basketball court's width is larger than that of any other planned rocket, and it would accommodate space telescopes that astronomers could only dream of right now. For example, NASA's upcoming James Webb Space Telescope (JWST) will fold up into a 15-foot-wide (4.57 meter) fairing of an Ariane 5 rocket in 2021. If a next-gen Starship is ever realized, though, it could fit six or more of the $10-billion space observatories into its fairing at once.

However, Musk envisions building a city on Mars that will be self-sustaining by the 2050s (and eventually has pizza joints). If he hopes to see that mission accomplished before his time on Earth is done, SpaceX may need the biggest rocket its leader can dream up.