WASHINGTON — SpaceX Chief Executive Elon Musk provided some additional details Oct. 23 about a Mars transportation system he unveiled last month, including plans to test in the near future one of its key technologies.

In an “Ask Me Anything” discussion on the website Reddit, organized on short notice, Musk answered more than a dozen questions posed by users about the Interplanetary Transport System he announced in a Sept. 27 speech at the International Astronautical Congress in Mexico.

That system consists of a large reusable booster that will use 42 of the company’s Raptor engines currently under development, along with a reusable spacecraft designed to carry 100 people to the surface of Mars and return to Earth. Development of the Raptor engine, which completed its first test firing shortly before his speech, was one of the key technologies for the system that he announced.

Another was a large propellant tank made of carbon composite materials, far larger than any tank of those materials produced to date. “This is really the hardest part of the spaceship. The other pieces we have a pretty good handle on, but this is the trickiest one, so we wanted to tackle it first,” he said in that speech, showing a full-sized tank the company had just completed.

“Yeah, for those that know their stuff, that was really the big news,” Musk said in response to a question about the tank on Reddit. “In theory, it should hold cryogenic propellant without leaking and without a sealing linker. Early tests are promising.”

Musk said that SpaceX will continue tests of that tank in the near future. “Will take it up to 2/3 of burst pressure on an ocean barge in the coming weeks,” he wrote.

Most of the other questions that Musk answered in the session, of many hundreds submitted, dealt with specific technical aspects of the architecture. He did, though, offer in one response a rough outline of how the system would be implemented, noting that SpaceX was “still far from figuring this out in detail.”

That approach starts with previously-announced plans to send Dragon spacecraft to Mars, starting as soon as 2018. These “Red Dragon” missions would initially demonstrate landing technologies to “make sure we know how to land without adding a crater,” he said. They would later test the ability access water needed for the later crewed missions, both for life support and to produce methane and liquid oxygen propellants needed for return trips.

The first spaceship of the Interplanetary Transport System, which Musk has dubbed “Heart of Gold” after a fiction spaceship from the novel The Hitchhiker’s Guide to the Galaxy, would fly to Mars without a crew. Instead, Musk wrote, the spaceship would carry equipment to build a propellant plant needed to fuel later spaceships.

SpaceX large booster launch
Illustration of SpaceX’s Mars booster and spacecraft taking off. Credit: SpaceX Credit: SpaceX
Illustration of SpaceX’s Mars booster and spacecraft taking off. Credit: SpaceX Credit: SpaceX

That would be followed by a single crewed spacecraft to set up a “rudimentary” base and complete the propellant plant. After that, he said, he would try to “double the number of flights with each Earth-Mars orbital rendezvous, which is every 26 months, until the city can grow by itself.”

Some non-technical elements of the system remain challenging, Musk said. “I think we need a new name. ITS just isn’t working,” he said. The rocket and spaceship are known internally by the acronyms BFR and BFS respectively, but he suggested those might not be suitable for public use.

Musk did not answer any questions submitted about the status of the company’s Falcon 9 rocket, grounded since a Sept. 1 explosion during preparations for a static-fire test destroyed a Falcon 9 and its Amos-6 satellite payload. He did, though, briefly address an upcoming, and “final,” version of the rocket, which he called Block 5, that is designed for frequent reusability.

“Falcon 9 Block 5 — the final version in the series — is the one that has the most performance and is designed for easy reuse, so it just makes sense to focus on that long term and retire the earlier versions,” he wrote. That version includes many “minor refinements” but also increased thrust and improved landing legs, he said.

The first of the Block 5 Falcon 9 vehicles will begin production in three months, with an initial flight in six to eight months. With its entry into service, he said he doesn’t expect recovered first stages from the older Block 3 and Block 4 versions of the rocket to be reused more than a few times.

In a speech earlier this month, SpaceX President Gwynne Shotwell said she believed the updated version of the Falcon 9 could be reused up to 10 times. Musk, though, was more optimistic. “I think the F9 boosters could be used almost indefinitely, so long as there is scheduled maintenance and careful inspections,” he said.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...