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Elon Musk’s SpaceX AMA: Living on Mars, Spaceship Info, Timeline
SpaceX CEO Elon Musk hosted a Reddit AMA (Ask Me Anything) earlier this afternoon and spent several hours drinking whiskey, trolling the audience, answering some great questions, and generally having a blast. He revealed a vast array of fascinating new details about SpaceX’s giant new rocket (BFR), its upper stage spaceship (BFS), and much more.
All of Musk’s answers from the AMA have been collated and organized by category below. You’ll want to shy away from the AMA page itself, currently clocking in at more 10,000 comments.
When useful, particularly dense and technical responses have been summarized in italics for a broader audience.
Living on Mars
Q: Obviously there will be an extreme amount of care put into what is sent on the first missions, and the obvious answer of “Solar Panels” and “Fuel Production Equipment” is included, but what else?
A (Elon): Our goal is get you there and ensure the basic infrastructure for propellant production and survival is in place. 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.
Q: Does your Mars city feature permanently anchored BFS spaceships?
A (Elon): Wouldn’t read too much into that illustration
The aforementioned Martian city. Spaceships can be seen near the center. (SpaceX)
Q: Have any candidate landing sites for the Mars base been identified?
A (Elon): Landing site needs to be low altitude to maximize aero braking, be close to ice for propellant production and not have giant boulders. Closer to the equator is better too for solar power production and not freezing your ass off.
Q: Who will design and build the ISRU system for the propellant depot, and how far along is it?
A (Elon): SpaceX. Design is pretty far along. It’s a key part of the whole system.
Without ISRU (In-Situ Resource Utilization), BFS is unlikely to ever be able to take humans to Mars affordably enough to enable large colonies. This news is thus of huge importance, and suggests that SpaceX will be able to focus on developing BFR and BFS near-term.
Another hypothetical SpaceX city on Mars. Bases will need to be located near water resources. (SpaceX)
SpaceX Big F** Spaceship (BFS)
Q: Will the BFS landing propellants have to be actively cooled on the long trip to Mars?
A (Elon): The main tanks will be vented to vacuum, the outside of the ship is well insulated (primarily for reentry heating) and the nose of the ship will be pointed mostly towards the sun, so very little heat is expected to reach the header tanks. That said, the propellant can be cooled either with a small amount of evaporation. Down the road, we might add a cryocooler.
A (Elon): exactly (while methane could be kept in its liquid form solely through high pressure storage, the pressures required are immense and would require tanks that would be far too heavy for a rocket’s second stage.
Cold liquid oxygen and methane will unavoidably warm up over time, eventually returning to their gaseous forms if allowed. SpaceX’s solution for BFS, which will spend several months between Earth and Mars, is to rely on the Ship’s already great insulation, as well as minimal evaporative cooling (similar to how swamp coolers work).
Q: Will the BFS heat shield be mounted on the skin, or embedded?
A (Elon): The heat shield plates will be mounted directly to the primary tank wall. That’s the most mass efficient way to go. Don’t want to build a box in box.
Dragon 2’s PICA-X heat shield can be seen on the right. BFS’s heat shield will be made of the same material, albeit on a much larger scale. (SpaceX)
Q: Can the BFS delta wings and heat shield be removed for deep space missions?
A (Elon): Wouldn’t call what BFS has a delta wing. It is quite small (and light) relative to the rest of the vehicle and is never actually used to generate lift in the way that an aircraft wing is used.
Its true purpose is to “balance out” the ship, ensuring that it doesn’t enter engines first from orbit (that would be really bad), and provide pitch and yaw control during reentry.
Q: Why is the 2017 BFS spaceship largely cylindrical?
A (Elon): Best mass ratio is achieved by not building a box in a box. The propellant tanks need to be cylindrical to be remotely mass efficient and they have to carry ascent load, so lowest mass solution is just to mount the heat shield plates directly to the tank wall.
For a rocket, mass ratio refers to its weight with a full load of propellant divided by its weight while completely empty. The lighter a rocket’s structure, the more mass it can lift into a given orbit.
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- SpaceX’s conceptual Interplanetary Transport System from 2016 was considerably larger and more structurally complex than 2017’s BFR. (SpaceX)
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- The relatively cylindrical BFS reduces complexity and lowers weight. (SpaceX)
Q: How does the BFS achieve vertical stabilization, without a tail?
A (Elon): Tails are lame
A (Elon): +1 (The space shuttle’s vertical stabilizer was completely useless for most of the reentry profile, as it was in complete aerodynamic shadow. I think it’s clear a craft doesn’t need one for reentry, only for subsonic gliding, which BFS doesn’t really do.)
BFS doesn’t need a tail because tails add weight, are of little use during orbital reentry, and BFS is not intended to glide.
Q: Why was the number of BFS landing legs increased from 3 to 4?
A (Elon): Because 4
A (Elon): Improves stability in rough terrain
Q: How is the radiation shielding in the ITS?
A (Elon): Ambient radiation damage is not significant for our transit times. Just need a solar storm shelter, which is a small part of the ship. Buzz Aldrin is 87.
While radiation fearmongers may balk at this statement, it is to some extent true. The risks from radiation (PDF) for a six month journey in deep space are approximately similar to several dozen CT scans, while two years spent on the surface of Mars with little to no shielding would result in about the same amount of exposure. Underground habitats could alleviate a considerable amount of the risk from living on Mars’ surface.
The issues and dangers posed by radiation ought not be trivialized but they can be dealt with, particularly if BFR can deliver massive payloads to the planet.
Q: Why was the location and shape of the BFS header/landing tanks changed?
A (Elon): The aspiration by the change was to avoid/minimize plumbing hell, but we don’t super love the current header tank/plumbing design. Further refinement is likely.
Header tanks refer to smaller tanks contained within the main propellant tanks that are used to ignite engines in microgravity. It’s easier to pressurize or simply fill the smaller tanks than it is to do so with the massive main tanks.
BFS’ header tanks circled in red. (SpaceX)
BFS Tanker
Q: Will the BFS tanker’s payload section be empty, or include extra propellant tanks?
A (Elon): At first, the tanker will just be a ship with no payload. Down the road, we will build a dedicated tanker that will have an extremely high full to empty mass ratio (warning: it will look kinda weird).
Using one version of the BFS as both a tanker and ship will streamline the initial development process for the rocket.
Two Spaceships docked for refuelling. (SpaceX)
Q: Will the BFS tanker ships (have to) do a hoverslam landing?
A (Elon): Landing will not be a hoverslam, depending on what you mean by the “slam” part. Thrust to weight of 1.3 will feel quite gentle. The tanker will only feel the 0.3 part, as gravity cancels out the 1. Launch is also around 1.3 T/W, so it will look pretty much like a launch in reverse….
BFS will land relatively gently, and BFR’s liftoff will also be gentle.
Development schedule
Q: With the first two cargo missions scheduled to land on Mars in 2022, what kind of development progress can we expect to see from SpaceX in the next 5 or so years leading up to the maiden flight?
Will we see BFS hops or smaller test vehicles similar to Grasshopper/F9R-Dev? Facilities being built? Propellant plant testing? etc. etc.
A (Elon): A lot. Yes, yes, and yes.
A (Elon): Will be starting with a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance. 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.
Next step will be doing orbital velocity Ship flights, which will need all of the above. 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. Earth is the wrong planet for single stage to orbit. No problemo on Mars.
The first real tests of the BFR will be done by hopping a full-scale BFS “several hundred kilometers”. BFS is capable of launching itself and a tiny payload into orbit, but the utility is limited on Earth. On Mars, BFS will be far more capable as a single stage to orbit (SSTO) launch vehicle.
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- F9R-dev, used to test vertical take off and landing for Falcon 9. BFR will go through a similar program with its spaceship upper stage prior to orbital missions. (Steve Jurvetson)
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- F9R sadly suffered a software bug and self-destructed in 2014, but SpaceX had already learned most of what it needed to begin Falcon 9 recoveries. (Steve Jurvetson)
Raptor and rocket propulsion
Q: Why was Raptor thrust reduced from ~300 tons-force to ~170 tons-force?
A (Elon): We chickened out. 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.
The Raptor engine’s maximum thrust has been decreased mainly because the size of the rocket decreased, from 12m to 9m in diameter. For redundancy’s sake, SpaceX has added a third central engine to the spaceship, versus the two engines mentioned at the 2017 IAC.
BFS’ delta “wings” from the rear of the ship. Also shown are the Raptors, with the two in the center now reportedly expanded to three engines. (SpaceX)
Q: Will the BFR autogenous pressurization system be heat exchanger based?
A (Elon): We plan to use the Incendio spell from Harry Potter
A (Elon): But, yes and probably
Autogenous pressurization refers to the method of propellant tank pressurization used. In microgravity conditions, tanks must be pressurized to keep fuel flowing to the engines and to improve the density of the fuel. While Falcon 9 currently uses high-pressure helium, ITS and now BFR have been designed to use the actual propellant in their tanks (methane and oxygen) for pressurization. This reduces the number of failure modes on BFR and improves the spaceship’s payload capabilities.
Q: Will the BFS methalox control thrusters be derived from Raptor or from SuperDraco engines?
A (Elon): The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
Like Falcon 9, BFR will need gas thrusters (RCS, reaction control system) to control its orientation (and refuel) while in microgravity conditions. While Falcon uses cold nitrogen gas thrusters, BFR will utilize the propellant it is already carrying for Raptor, methane and oxygen. Again, the goal of this is to reduce complexity.
Q: Could you update us on the status of scaling up the Raptor prototype to the final size?
A (Elon): Thrust scaling is the easy part. Very simple to scale the dev Raptor to 170 tons.
The flight engine design is much lighter and tighter, and is extremely focused on reliability. The objective is to meet or exceed passenger airline levels of safety. If our engine is even close to a jet engine in reliability, has a flak shield to protect against a rapid unscheduled disassembly and we have more engines than the typical two of most airliners, then exceeding airline safety should be possible.
That will be especially important for point to point journeys on Earth. The advantage of getting somewhere in 30 mins by rocket instead of 15 hours by plane will be negatively affected if “but also, you might die” is on the ticket.
SpaceX’s subscale Raptor, the one seen in videos and photos of it firing, is understood to be a bit more than half the size of the operational engine described at IAC 2017. Increasing the scale of the engine is not the difficult aspect of development. Rather, optimization, weight reduction, and extreme reusability are the main sources of difficulty needed before Raptor is flight-ready. This reusability is central to the goal of reliable and rapid reuse of orbital-class rockets.
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- SpaceX revealed this stunning photo of Raptor’s first (partial) hot-fire test the night before Musk’s talk at Guadalajara. (SpaceX)
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- SpaceX’s subscale Raptor engine has completed more than 1200 seconds of testing in less than two years. (SpaceX)
Q: Can BFS vacuum-Raptors be fired at sea level pressure?
A: The “vacuum” or high area ratio Raptors can operate at full thrust at sea level. Not recommended.
Put simply, vacuum nozzles do not like to operate in an atmosphere.
Mars communications
Q: Does SpaceX have any interest in putting more satellites in orbit around Mars (or even rockets) for internet/communications before we get feet on the ground? Or are the current 5-6 active ones we have there sufficient?
A (Elon): Yes
Q: Also will there be some form of an internet or communications link with Earth? Is SpaceX going to be in charge of putting this in or are you contracting some other companies?
A (Elon): If anyone wants to build a high bandwidth comm link to Mars, please do.
Taken side by side, this likely indicates that SpaceX will develop a high-bandwidth Mars-Earth communications link if nobody else does, but that they would logical prefer that someone else builds that infrastructure beforehand.
Q: The concept of an internet connection on Mars is kinda awesome. You could theoretically make an internet protocol that would mirror a subset of the internet near Mars. A user would need to queue up the parts of the internet they wanted available and the servers would sync the relevant data.
A (Elon): Nerd
A (Elon): 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. Something like that. Earth to Mars is over 22 light-minutes at max distance.
A (Elon): 3 light-minutes at closest distance. So you could Snapchat, I suppose. If that’s a thing in the future.
The communication delay between Earth and Mars (at least several minutes one-way) will prevent any Martian habitats from simply integrating with Earth’s Internet. The delay will require some sort of mediation. As an example, a user on Mars could select the websites they want to browse or videos they want to watch beforehand, and they would be available between several minutes and an hour later.
SpaceX’s Starlink satellite constellation efforts could provide the company with valuable experience that can be applied around Mars. (unofficial logo by Eric Ralph)
Boring!
Q: Boring question about Mars:
A (Elon): More boring!
Miscellaneous silliness
Q: This is one bizarre AMA so far…
A (Elon): Just wait…
Q: i feel like thats a threat. “just wait. it will get way more bizarre than that. let me finish my whiskey”
A (Elon): How did you know? I am actually drinking whiskey right now. Really.
…No comment…
All things considered, this was a wildly successful AMA. Elon clearly had a whole lot of fun, the audience got lightheartedly trolled, and SpaceX fans will undoubtedly be chewing over the technical details he elucidated for weeks to come. Special thanks are owed to the subreddit /r/SpaceX and user /u/_Rocket_, who together managed to flood the AMA with an array of intelligent, pointed, and reasonable questions, at least ten of which were answered by Musk.
News
Tesla’s Cybercab battery design could make robotaxis even cheaper
Tesla built the Cybercab’s battery pack with spare room for a future switch to LFP.
Tesla built the Cybercab’s battery pack with empty space inside it on purpose, and the reason points to a cheaper robotaxi down the road.
Robert Sumpf, Tesla’s director of mechanical design engineering for battery modules and packs, said the extra room beside and beneath the Cybercab’s modules was left there so the company can move to lithium iron phosphate cells later. “So, we protected this pack to go to an even lower energy dense chemistry as we scale and need to bring LFP into the platform,” Sumpf said in a Cybercab deep dive with Munro Live.
The Cybercab runs on Tesla’s own 4680 cells with a nickel chemistry today. LFP cells store less energy for their size, so a straight swap would cut range. The reserved space lets Tesla add more LFP cells to make up the difference. In return, Tesla would get cells that cost less, run cooler and survive more charge cycles. LFP became the most used EV battery chemistry in the world last year.
Not all of that room was planned for a chemistry change. Lars Moravy, Tesla’s Vice President of Vehicle Engineering, said part of it exists because “we didn’t need as many batteries as we thought we did.” Tesla told Sandy Munro in early 2025 that it was targeting a Cybercab pack under 50 kWh with close to 300 miles of range.
The pack also breaks from the structural design Tesla used in some Model Y and Cybertruck builds. Instead of potting hundreds of cells into one block, the Cybercab uses four separate, individually sealed modules, so a bad module can be replaced without scrapping the whole pack. Sumpf was blunt about the older approach, giving the Model Y structural battery “a grade D” because it was hard to build and nearly impossible to repair. He estimated a fully structural pack gains about 10% more cell volume, but said “the issue is the service cost.”
That cost matters more for a car that rarely sits parked. Cybercab chief engineer Eric Earley said replacing an entire pack “before half a million miles is a killer on cost,” which is why remanufacturing and serviceability were built into the design from the start.
The same Munro Live tour produced Moravy’s admission that the Cybercab line at Giga Texas is now outpacing Robotaxi deployments, along with a look at the robotaxi’s unorthodox paint process. Tesla is aiming to deliver the first Cybercabs to outside customers by the end of 2026, though Elon Musk has said the vast majority will stay owned by Tesla and run as a transport service.
Sumpf did not give a date for an LFP version, name a cell supplier or say how a chemistry change would affect range. For now, the 4680 cars keep piling up: Texas DMV records from Tuesday list 544 Cybercabs authorized for Tesla’s Robotaxi fleet, more than the 507 Model Ys on the same roster for the first time.
United Airlines CEO Scott Kirby said that SpaceX’s Starlink satellite internet is its leading competitive advantage in the U.S. airline industry. However, in recent comments, while he described the service as “the biggest competitive advantage” the carrier currently holds, he also acknowledged that the edge is temporary.
“…everybody eventually is going to have high-speed low earth orbit internet connectivity. It’s going to be a must-have. We are going to have a few years of being the only airline that has it at scale, and that’s our mission,” Kirby said. Until everyone has it, United aims to capitalize on its head start by converting trial users into long-term loyal customers.
🚨 United CEO Scott Kirby calls Starlink “the biggest competitive advantage,” but says it’s temporary.
“I think it’s the biggest competitive advantage. And it’s temporary. Like it’s not, everybody eventually is going to have high speed low earth orbit internet connectivity. It’s going to be a must-have. But we are going to have a few years of being the only airline that has it at scale, and that’s our mission.”
“I think we’re going to convince customers that United is the best airline and we’re going to get customers to switch their loyalty, to get our credit card, switch their loyalty to United. Not because of Starlink. They’re going to try us for Starlink and they’re going to stay with all the other technology, and everything else is better, and the technology in particular is so much better than technology other, and it’s accelerating because we’ve got the right tech stack, and because we’re like, our gap is getting wider and wider with our technology every day.”
Next: LAX becomes United’s first 100% Starlink hub in the first half of next year, and the United app will show your Starlink odds for each flight. https://t.co/hToyFWaWj7
— TESLARATI (@Teslarati) October 27, 2026
United has moved faster than its rivals on Starlink installations. As of mid-to-late October 2026, the system was on roughly 43 percent of its fleet, with plans to reach 61 percent by year-end, 87 percent by June 2027, and full fleet coverage by the end of next year.
The airline already operates more Starlink-equipped flights than the rest of the U.S. industry combined. Los Angeles International Airport is scheduled to become United’s first 100 percent Starlink hub in the first half of 2027, and the carrier’s app will display the likelihood that any given flight has the service.
Kirby has pointed to early evidence that the offering influences booking decisions. Some passengers loyal to other airlines are already switching flights for Starlink connectivity, something the airline, along with American Airlines, has tried to leverage against competing airlines. Both companies used status-match programs, and some of those customers are pursuing company-specific credit cards, which signals an intent to stay.
Once onboard, these customers encounter the airline’s broader investments in aircraft, larger seat-back screens, oversized bins, connection tools, and a mobile app that Kirby says outperforms competitors. Wi-Fi satisfaction scores on Starlink-equipped planes have been reported to be nearly double those on aircraft with other systems.
Competitors are moving slowly to do the same. Southwest Airlines began installations in 2025 and expects to complete them soon. Delta is pursuing Amazon’s Leo system, while American expects to start Starlink work in early 2027 and has not yet detailed regional-fleet plans. This timeline gap gives United a multi-year window in which it remains the only major U.S. carrier offering Starlink at scale.
Kirby has framed the strategy as pressing that advantage while simultaneously widening gaps in other technology areas so that customers who try United for the Wi-Fi remain for the overall experience.
The approach reflects a calculated bet that superior in-flight connectivity can accelerate share gains and support longer-term financial targets, including a 10 percent pre-tax margin goal.
High-speed internet is particularly valued by premium and business travelers who can work or stream reliably. As low-Earth-orbit service becomes ubiquitous, the temporary nature of the pure connectivity edge means United’s retention will depend on whether its other product and operational improvements keep pace.
Tesla Cybercab skips the traditional paint shop entirely, marking an unorthodox process for coloring the fully autonomous vehicle. However, the decision was a smart one, as it slashed factory costs, floor space utilization, and complexity, since Tesla relied on specialized alloys and in-mold coloring.
Munro Live was given the opportunity to do a factory walkthrough with Tesla Vice President of Vehicle Engineering Lars Moravy, who explained and detailed how Cybercab production at Giga Texas eliminates one of the automotive manufacturing industry’s most expensive and space-hungry elements.
A conventional paint line can cost hundreds of millions of dollars and require a million man-hours to build. Moravy framed the choice around Tesla’s core rule: “Question the requirements: why do you need paint?”
🚨 Super cool quote from the Cybercab breakdown on the decision to avoid traditional paint:
“One of the most expensive parts of the factory is a paint line… a few hundred million dollars, a million man hours to build one… rule number one at Tesla, question the requirements. Why do you need paint?… the alloys we use in the castings… don’t oxidize and reduce strength over time.” -@larsmoravy
Model Y and Cybertruck bodies are fully coated and painted. On Cybercab, only the side pieces get the anti-corrosion dip coat, and there’s no paint shop at all, which helps cut factory floor space per car by about 50%.
— TESLARATI (@Teslarati) October 26, 2026
The structural answer lies in material selection. The aluminum alloys used in Cybercab’s front and rear castings do not oxidize and lose strength over time, the way many common automotive aluminum alloys do. Only the side modules, built around hot-stamped boron-steel door rings, receive an anti-corrosion e-coat, or dip coat. Front and rear modules skip coating altogether.
Model Y and Model 3 bodies, by contrast, are fully coated and painted.
Exterior colors come from the plastics shop, which Tesla engineers described as “our paint shop” for the Cybercab. Body panels are produced via reaction injection molding, referred to as RIM. Color is then mixed into a polyurethane resin at the mix head immediately before injection, so the panel emerges already colored with a Class-A surface.
Robots trim overflow to control sink marks and flow lines. The process avoids conventional spray-paint defects like orange peel and paint bleed. Scratches can still be repaired with compatible coatings that behave “basically like paint.” Because color is integral rather than a surface layer, shallow scratches do not expose a contrasting undercoat.
The secret behind Tesla’s Cybercab Gold goes well beyond just the color
Tesla has also explored related approaches, including in-mold lamination and painted films on stamped panels.
The manufacturing payoff is substantial because removing the paint shop, combined with the “unboxed” modular process that builds and tests front, rear, side, and center modules in parallel before a short final assembly, cuts factory floor space per vehicle by about 50 percent.
Final assembly itself uses only about 25 automated stations, far fewer than the typical Model Y line, and the overall line runs at about 78 percent automation, Moravy said. The approach also eliminates volatile organic compound emissions associated with traditional spray painting for these panels and shortens the coloring cycle from hours to minutes.
Cybercab’s paint strategy is clearly less about aesthetics than about systematically deleting capital-intensive, energy-heavy, and space-consuming steps once material science and process design make them unnecessary. It is a concrete example of Tesla applying first-principles questioning to one of the auto industry’s most entrenched factory requirements.
Tesla’s Cybercab battery design could make robotaxis even cheaper
Starlink is ‘biggest competitive advantage,’ but it’s temporary, United CEO says
