Musk provides more insight on SpaceX’s Mars ambitions
Less than a month after Elon Musk revealed SpaceX’s updated Mars mission architecture at the 2017 International Astronautical Congress, the billionaire CEO made himself available to the public to answer further questions about the company’s ambitious undertaking. In a surprise tweet on Oct. 14, 2017, the SpaceX founder gave short notice to taking part in an “Ask Me Anything” (AMA) on the popular website, Reddit.
Engines, shields, and quips… oh, my!
Taking to the /r/space subreddit, Musk answered curated questions from the Reddit community on topics ranging from propulsion to thermal and radiation protection, and he occasionally took the opportunity to inject a bit of humor along the way.
Many of the questions centered around the changes to the company’s Big F—ing Rocket (BFR) and Big F—ing Ship (BFS) in the year following 2016’s unveiling.
When questioned about the modifications to the vehicle’s design – losing many of the curves and control surfaces that were seen last year – Musk indicated the necessities of mass conservation and function led to many of the updates.
“Best mass ratio is achieved by not building a box in a box,” Musk said. “The propellant tanks need to be cylindrical to be remotely mass efficient and they have to carry ascent load, so [the] lowest mass solution is just to mount the heat shield plates directly to the tank wall.”
Similar questions about changes to the BFS’s outer mold line and interior structure were attributed to needing to save mass, or in the case of a particular aerodynamic surface, finding there is no need.
“Tails are lame,” Musk said when asked about the lack of a vertical stabilizer.
However, while a tail was found to be superfluous, the addition of a fourth landing leg was required for greater stability on uneven terrain.
Less is more
Of particular interest to one questioner was the significant reduction in thrust from the planned Raptor engines, which are now rated at nearly half of what was initially announced. The engine’s planned output was reduced from approximately 300 tons (3,000 kilonewtons) of thrust at sea level to 170 tons (1,700 kilonewtons).
In a departure from his tendency to provide short responses, Musk went into a fair amount of detail regarding the reduction in engine power:
The engine thrust dropped roughly in proportion to the vehicle mass reduction from the first IAC talk. In order to be able to land the BF Ship with an engine failure at the worst possible moment, you have to have multiple engines. The difficulty of deep throttling an engine increases in a non-linear way, so 2:1 is fairly easy, but a deep 5:1 is very hard. Granularity is also a big factor. If you just have two engines that do everything, the engine complexity is much higher and, if one fails, you’ve lost half your power. Btw, we modified the BFS design since IAC to add a third medium area ratio Raptor engine partly for that reason (lose only 1/3 thrust in engine out) and allow landings with higher payload mass for the Earth to Earth transport function.
Musk also said the Raptor engines will be a mixture of additive manufacturing and traditional machining.
One of the key hurdles in developing an engine that can be re-used with little-to-no refurbishment is the construction of an oxygen pump that can resist degradation in a high-temperature, pure oxygen environment. Musk said SpaceX has developed a new alloy that remains stable under such harsh conditions while maintaining its strength, greatly improving the engine’s longevity, reliability, and performance.
While many of the questions focused on the particulars of the rocket and ship, there was also interest in how SpaceX will equip those who plan to live – and survive – on the Red Planet.
Not unlike the pioneers who embarked on the trip westward across North America in the 1800s, Martian settlers will have to bring what they can with them or learn to live off the land. It has been known that Mars holds the resources necessary to produce oxygen, water, and even methane for refueling rockets. What is less clear is what conditions would greet those early travelers on Mars.
“Our goal is [to] get you there and ensure the basic infrastructure for propellant production and survival is in place,” Musk said. “A rough analogy is that we are trying to build the equivalent of the transcontinental railway. A vast amount of industry will need to be built on Mars by many other companies and millions of people.”
Some of the infrastructure, like in situ resource utilization (ISRU) machinery, will be developed and supplied by SpaceX. Musk also insinuated one of his other ventures, The Boring Company, may provide beneficial services on Mars.
However, none of that matters if one is exposed to lethal radiation en route to the Red Planet. Musk, however, seems to believe dedicated radiation shielding on the ship is unnecessary for the transit, holding Buzz Aldrin as proof, having reached 87 years (and counting) and having survived a Lunar transit. Nevertheless, there will be shelters on the ship in which occupants can ride out any severe space weather.
As for where the potential colonists may settle, the SpaceX CEO noted that the Martian equatorial regions would be perfect for solar power generation and comparatively moderate temperatures, though one would also need to be situated near a low-altitude ice source.
Lots to get done before 2022
In order to meet Musk’s ambitious target of a cargo mission to Mars in 2022, SpaceX has quite a bit of work to do, not the least of which is testing out the vehicle’s propulsion, ascent/descent avionics, and thermal protection systems.
“[SpaceX will] be starting with a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance,” Musk said. “Those are fairly easy on the vehicle, as no heat shield is needed, we can have a large amount of reserve propellant and don’t need the high area ratio, deep space Raptor engines.”
Musk said the next step would be to do orbital velocity flights with the BFS, which will need heat shields, reserve propellant, and deep space Raptor engines.
“Worth noting that BFS is capable of reaching orbit by itself with low payload, but having the BF Booster increases payload by more than an order of magnitude,” Musk said. “Earth is the wrong planet for single stage to orbit. No problemo on Mars.”
SpaceX CEO Elon Musk unveils the company’s updated Mars plans at the 2017 IAC.
Video courtesy of SpaceX
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.