Elon Musk drops by Reddit to answer people’s burning Mars questions

Alan Martin October 16, 2017

PayPal, Tesla and – most importantly for this – SpaceX founder Elon Musk took to Reddit last night to answer questions on his recent IAC 2017 talk about moon bases and Mars colonies. Perhaps wary of being asked whether or not he’d favour fighting a horse-sized duck or a small army of duck-sized horses, Musk eschewed /r/iama for the most classy and focused backdrop of /r/space.

Here are some of the highlights from Musk’s Reddit pop-in.

SpaceX won’t do it alone

We know that getting to Mars is a huge problem – and the commute is only part of the puzzle. When foxyjim99 asked how you’d calculate the food needed for a successful mission, Musk suggested that this wasn’t SpaceX’s burden alone. “Our goal is get you there and ensure the basic infrastructure for propellant production and survival is in place,” he explained, suggesting it’s “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,” he added.

Plans for Mars to Earth communications are currently a little fuzzy

An interesting follow up to this came when asked about how people would communicate with Earth, and whether there were plans for some kind of space internet. “If anyone wants to build a high bandwidth comm link to Mars, please do,” came Musk’s reply.

When someone came up with a blueprint for such a system, Musk’s response was quite entertaining: elon_musk_calls_reddit_user_a_nerd

…fortunately, that wasn’t all the user got for his trouble. “But, yes, it would make sense to strip the headers out and do a UDP-style feed with extreme compression and a CRC check to confirm the packet is good, then do a batch resend of the CRC-failed packets,” Musk eventually responded, revealing himself to be just as nerdy, if not moreso. “Something like that. Earth to Mars is over 22 light-minutes at max distance.”

“3 light-minutes at closest distance. So you could Snapchat, I suppose. If that’s a thing in the future,” he added.

SpaceX “chickened out” on original Raptor thrust

Originally, the engines on the Raptor were claimed to have 300 tonnes of thrust force, but that was later revised to “just” 170 tonnes. Why? “We chickened out,” Musk replied, elaborating a little later on.

“The engine thrust dropped roughly in proportion to the vehicle mass reduction from the first IAC talk,” he explained. “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.”

Some parts of Raptor will be 3D-printed

“Is it practical to 3D-print the Raptor’s main combustion chamber, or is casting+machining still a better technique,” asked the appropriately named __Rocket__.

“Some parts of Raptor will be printed, but most of it will be machined forgings,” Musk responded. “We developed a new metal alloy for the oxygen pump that has both high strength at temperature and won’t burn. Pretty much anything will burn in high pressure, hot, almost pure oxygen.”

Musk doesn’t take himself too seriously

When __Rocket__ returned to ask more questions about the autogenous pressurisation system (specifically whether it would be heat exchanged based), Musk gave away SpaceX’s big secret. “We plan to use the Incendio spell from Harry Potter,” he replied.

And when music_nuho impertinently told the SpaceX CEO “you can’t land on moon using 3MN engine,” Musk quoted a great philosopher and motivational speaker. “Yes, you can. – Bob, the Builder,” he said.

You can read the full AMA on Reddit.

Image: Steve Jurvetson used under Creative Commons