[NSF] The Evolution of the Big Falcon Rocket

[Orionid]

The Evolution of the Big Falcon Rocket (1)
written by Phillip Gaynor August 9, 2018


 
On September 29th, 2017, SpaceX CEO Elon Musk unveiled detailed plans of the Big Falcon Rocket at the 68th International Astronautical Congress in Adelaide, Australia.  It was a follow-up speech to the prior year’s presentation when he first discussed the architecture of what was then called the Interplanetary Transport System.  In his highly anticipated speech, Musk laid out the detailed plans for a two stage rocket to enable the colonization of Mars, a moon base, and hypersonic long-distance travel on Earth.

The design featured an enormous Booster that would be powered by 31 Raptor engines, planned to be the world’s most advanced and highest pressure chemical rocket engine. Following stage separation, the booster would return to Earth and land near or on the launch pad.

There were three variants of the rocket’s second stage planned: a Spaceship, Tanker and Cargo Lifter.  The primary of which, the BFR Spaceship, was also the colonization vehicle and that could carry up to 100 passengers and a hundred tonnes of cargo.  One possible use of the Spaceship was as the world’s first hypersonic passenger transport vehicle, which would enable travel between any two points on Earth in under an hour.  Its primary envisioned mission, however, was to be a colonization vehicle for the Moon, Mars and beyond.

The Spaceship would be propelled by four vacuum optimized Raptor engines, feature a heat shield for atmospheric reentry, and land on the Earth and Mars via two Raptor booster engines and four extendable landing legs.

To enable the BFR Spaceship to make it to Mars, it would be refueled in orbit by multiple flights of a similarly sized Tanker, which would be an alternate second stage for the booster.

Once fully refueled, the Spaceship would make the burn for Mars and sustain the crew over the multi-month journey. At Mars it would enter the atmosphere, slowing down via a combination of drag and retro propulsion so as to safely land.

Once unloaded, the Spaceship would be refueled using local resources, specialized equipment and the Sabatier reaction. It would then launch back to Earth, where it would touch down upon land not far from its launch pad.


BFR and BFS mission sequence – via SpaceX

A Cargo Lifter version of the Spaceship would also be designed to launch satellites into orbit and resupply manned space stations around the Earth.  This would allow the BFR to entirely replace the SpaceX Falcon 9 and Falcon Heavy rocket family, albeit with vehicles of a much greater scale.

Musk believed that the system’s fully reusable nature would ultimately improve the economics of colonizing Mars by five million percent (i.e., be 50,000 times cheaper than using expendable rockets for the same purpose).

, which was understandable given the ambition of the proposed plans. It was also the first plan to be proposed by the owner of a private rocket company, lending the vision more credibility, since the plan could be done much cheaper than traditional methods. It was a plan that owed its existence to and reflected the decades of prior work done on how best to get humans to Mars.


Von Braun Mars Base – via AIAA Horizons magazine.

The first person to lay the groundwork for Musk’s speech was the former head of Nazi Germany’s V-2 rocket program, Dr. Wernher von Braun. In 1948, while working for the US Army, he began writing a detailed book called “The Mars Project” in which he laid out how the exploration of Mars might be accomplished. In the plan, von Braun envisioned a fleet of 10 spaceships lifted into orbit by reusable shuttles and powered by engines burning a hypergolic mix of nitric acid and hydrazine propellant.

Many other projects for Mars exploration were worked out in the intervening years since then, all of them floundering on the issue of cost. However, in 1990, a new plan by Martin Marietta engineers Robert Zubrin and David Baker took shape. Called “Mars Direct”, it attempted to show that a trip to Mars with current technology would not only be feasible but also cost-effective, a pressing concern given that high cost is what caused Congress to cancel President George H. W. Bush’s Space Exploration Initiative that same year. Zubrin’s 12 man team at Martin Marietta envisioned a simple and stripped down strategy for getting to Mars.


Painting by Robert Murray shows a Mars Direct camp

It envisioned first launching an Earth Return Vehicle (ERV) to Mars via the Ares launch vehicle. The ERV would come equipped with a small nuclear reactor and specialized equipment to produce methane and oxygen propellant on Mars.

Once another ERV and Mars Habitat Unit (MHU) were launched to Mars, the original ERV would be refueled. 18 months after landing, it would lift off and return to Earth. The plan called for launching an MHU and ERV to Mars for future missions every 26 months, similar to Musk’s plan.

Elon Musk had once fantasized about colonizing other planets as a boy growing up in Pretoria, South Africa. In June 2001 however, he finally had the means and the time to pursue his passion. He had survived a harrowing year. He had been ousted from his position as PayPal CEO on a flight to Australia in October 2000.


PayPal Chief Executive Officer Peter Thiel, left, and founder Elon Musk, right, pose with the PayPal logo at corporate headquarters in Palo Alto, Calif., Oct. 20, 2000. Paul Sakuma—AP

In late December 2000 and early January 2001, Musk contracted a rare form of Malaria, which he narrowly survived. Perhaps tired of life in Silicon Valley, he moved to Los Angeles and turned to his old interest in space.

Musk did not originally know what he wanted to do in space, but he soon purchased an old Soviet flight manual and began talking about space travel and changing the world. Not long afterward, the non-profit Mars Society group, which was dedicated to exploring and settling the Red Planet, sent out invitations for a $500 a plate fundraiser to its usual attendees.

Robert Zubrin, head of the Mars Society, was floored when someone named Musk responded, whom no one remembered inviting, sending them a check for $5,000. At the fundraiser, Zubrin sat Musk at the VIP table with himself, Director James Cameron and NASA scientist Carol Stoker. Zubrin pitched Musk on the Translife Mission, which would carry mice in Earth orbit and spin fast enough to replicate Martian gravity as they lived and reproduced.

Musk was enthused about the Translife Mission but soon envisioned an even more ambitious version: sending the mice to Mars. The first seeds of the BFR had been laid.

His desire at the time was not to colonize Mars but to reinvigorate enthusiasm for science, space exploration, and technology to inspire the public. His determination to change the inertia of space policy was reinforced by visiting NASA’s website, which to Musk’s disappointment featured neither a plan nor a schedule for the human exploration of Mars.

Musk’s ambitions of doing one grand gesture in space along with his burgeoning contacts in the space industry resulted in his resignation from the Mars Society and the founding of the “Life to Mars Foundation” later that year. The foundation soon set up working sessions featuring engineers from the Jet Propulsion Laboratory, scientists, Director James Cameron and Orbital Sciences Corporation’s Chief Technical Officer, Michael Griffin.

The experts soon settled on a new mission called “Mars Oasis”, which could be done for Musk’s budget of $20 to $30 million. The plan called for buying a sizable but cheap rocket and using it to land a robotic greenhouse on Mars. It upset Robert Zubrin and the Mars Society, since not only would it be a purely symbolic effort, but would also endanger NASA’s contamination protocols.


Reusable spinach Greenhouse for Mars designed in 2013 by Greek students

Musk pressed on regardless, intending to buy a Russian intercontinental ballistic missile (ICBM) and use it as the Mars Oasis’ launch vehicle. By late October 2001 Musk had recruited his friend from college, Adeo Ressi, as well as former international intelligence agent and space enthusiast Jim Cantrell, to fly to Moscow with him as he attempted to buy a huge R-36 (SS-18 Satan) ICBM. Michael Griffin would join the team once there.

They met with members of NPO Lavochkin, a robotic probe manufacturer, and Kosmotras, the launch service company for the Dnepr rocket, the commercial version of the R-36.  They were met with much derision, with some Russian chief designers so contemptuous they even spat upon them. Eventually, things came to a head at a Moscow meeting, when Musk asked how much a missile would cost.

The Russians demanded $8 million per rocket, which Musk countered with an offer of that amount for two. The Russians scoffed and insulted Musk, after which Musk determined they were either not being serious with him or wanted to extract as much of his money as possible. He stormed out and the small team took a cab trip back to the airport.

It was on the flight back to the US that Musk showed Cantrell and Griffin a spreadsheet with rocket performance and fabrication cost calculations he had been working on, saying, “I think we can build this rocket ourselves”. The Russians’ disrespect of Musk had backfired completely.

By April 2002 Musk abandoned his idea for a publicity stunt and instead turned towards founding a rocket launch company. This dismayed Robert Zubrin and many others, as they expected that Musk, like rocket entrepreneur Andrew Beal, would fail utterly.

Space Exploration Technologies, or SpaceX, was founded in June 2002 with the goal to drastically cut the cost of access to space. With eBay buying out PayPal for $1.5 billion, Musk suddenly had $180 million to fund SpaceX and any other venture.

It took until March 24, 2006 for SpaceX to finally launch its first rocket, the small Falcon 1, which failed soon after launch.


Maiden launch of Falcon 1 – Credit Thom Rogers/SpaceX

The same year SpaceX was given seed money by NASA to fund a much larger ten-engined rocket – nine engines on the first stage, one on the second stage – called the Falcon 9, canceling plans for the smaller Falcon 5 rocket.

Before the decision was made to go ahead with the Falcon 9 though, Musk made plans to eventually build something called the BFR, or “Big Falcon Rocket”, which at that time was planned to have the biggest engine in history according to Musk biographer Ashlee Vance.

After the second Falcon 1 failed on March 21, 2007, defense consultant Pete Worden talked to Musk, who despite the recent failure struck up a conversation about settling Mars. Musk’s Mars ambitions had finally eclipsed Robert Zubrin’s.

However, with SpaceX’s failures and both SpaceX and Musk’s car firm, Tesla, losing money, Musk had to prioritize getting the Falcon 1 into orbit and earning money. A third failure followed on August 3, 2008, after which Musk only had enough money for one more attempt.

Luckily the fourth launch on September 28, 2008 was successful.




While the success alleviated immediate concerns about SpaceX, Musk was going through personal issues while his finances were becoming ever more perilous. His firms were bleeding cash in the midst of the Great Recession even as Musk’s personal wealth dropped ever lower. In the end, he was saved by two events. One was the sale of software startup Everdream, which together with other funds helped Musk raise $20 million, which was then matched by other Tesla investors and ended up saving Tesla.

SpaceX, however, still needed help, which arrived unexpectedly on December 23, 2008, when NASA awarded SpaceX $1.6 billion in a COTS contract to deliver supplies to the International Space Station. His dreams of settling Mars and revolutionizing the car industry had been saved.

On June 18, 2009, the first public mention of the Raptor rocket engine was made by SpaceX’s Max Vozoff at the American Institute of Aeronautics and Astronautics (AIAA) Innovations in Orbit: An Exploration of Commercial Crew and Cargo Transportation event.




More details of the Raptor engine were given in July 2010 at the 46th Joint Propulsion Conference.  It was to have a vacuum thrust of 667 kN (150,000 lbf), produce an ISP of 470.1 seconds, and be capable of throttling from 50 to 100%. It was supposed to have been a hydrogen/oxygen upper stage engine to power an upgraded version of SpaceX’s Falcon 9 medium lift launch vehicle then under development.

Conceptual ideas for the massive Falcon X, Falcon X Heavy and Falcon XX super heavy lift launch vehicles were also presented at the 2010 Joint Propulsion Conference. These were to be powered by very large Merlin 2 engines producing 7,565 kN (1,700,766 lbf) of thrust, with an ISP of 285.0 seconds at sea level and 321.4 seconds in a vacuum. These vehicles were to be essentially larger cousins of SpaceX’s Merlin 1 engine, which were kerosene/liquid oxygen burners that used the simple gas generator cycle. Shortly after the presentation, Musk disavowed that the ideas shown were firm plans for future rockets.

SpaceX’s future Mars rocket designs would be most heavily influenced by the firm’s Falcon 9 medium lift launch vehicle. When it debuted on June 4th, 2010, the 318 tonne rocket was a mixture of design elements old and new.

The Falcon 9 boasted first stage engine out capability, an ability last seen on the US Saturn IB rocket in 1975. It also featured common bulkheads to save mass and trim the rocket’s height, a feature used in 1960s era Saturn rockets, all versions of the Centaur stage, and the Ariane 5 launch vehicle.

New features in the design included friction stir welding of parts and lightweight aluminum-lithium alloy construction, both of which trimmed dry mass and upped the payload mass. Fabrication costs were lowered by using a single set of tooling to build both common diameter stages and by incorporating off the shelf redundant electronics. As a result, the Falcon 9 v1.0 was amongst the cheapest performers when it debuted. Musk, however, knew that in order to enable the colonization of Mars, he needed reusable rockets.

To enable this, Musk had SpaceX employ a two-track development strategy.  The first track would focus on reusable rocket testing, while the second would focus on upgrading the Falcon 9 launch vehicle to provide enough margin for reuse.  In 2011 development started on a Falcon 9 core stage with metal legs attached called the Grasshopper.


Grasshopper test – credit SpaceX

This vehicle was flown eight times in increasingly long “hops” in order to improve SpaceX’s experience with vertical rocket landings.

Eventually, the original Grasshopper was retired in 2013 and an even larger Grasshopper 2, based on the core stage of a Falcon 9 v1.1, was pressed into service.

Grasshopper 2 would eventually make four successful flights before it was lost during its fifth flight.

The Falcon 9 v1.0 was successfully flown five times between 2010 and 2013 before being replaced by the higher lift capacity Falcon 9 v1.1, which essentially was a new launch vehicle.  Although it had the same diameter as its predecessor, v1.1 featured a new octaweb thrust structure, enlarged propellant tanks and 19% higher thrust and more efficient Merlin 1D engines.  Later versions were even equipped with legs and fins for landing attempts.  The first flew on September 29th, 2013, with a total of 14 successful launches out of 15 attempts.  SpaceX’s initial landing attempts were onto barges positioned out at sea, however all three landing attempts with the v1.1 failed.

The design rapidly evolved further into the Falcon 9 v1.2, the first launch of which saw a Falcon 9 core stage safely landed near its launch pad on December 22nd, 2015. To enable the landing, the Falcon 9 v1.2 had added extendable landing legs onto its core stage, upgraded cold gas thrusters, improved guidance programming for retro propulsion, and accuracy improving grid fins.

[Orionid]

The Evolution of the Big Falcon Rocket (2)


First Falcon 9 landing – Credit SpaceX

The rocket also set a record as the most efficient launch vehicle ever launched to Low Earth Orbit (LEO), which provided the performance margin necessary for reuse. Although the rocket featured typical upgrades like higher thrust engines, enlarged propellant tanks and a strengthened structure, it also featured a new design element. It used chilled propellant to increase its propellant density, which improved performance by allowing the Falcon 9 to carry more propellant at almost no cost in dry mass. Almost all of the Falcon 9’s design architecture would later be used in the design of the BFR.

SpaceX’s Raptor engine went almost entirely unmentioned from August 2010 until June 2011, when engineer Jeff Thornburg was placed in charge of development and given a small team to work on the engine. Its development proceeded slowly due to its low level of priority.

By October 2012, with SpaceX’s engine expertise growing and finances improving, the Raptor had transformed into an engine several times as powerful as the Merlin 1 engine. Multiple Raptor engines were to power a future rocket capable of lifting 150-200 tonnes to LEO.

The next month, Musk announced that the Raptor was to be a methane fueled engine, which was the preferred fuel for SpaceX’s Mars colonization ambitions. The engine’s cycle was changed from gas generator to a staged combustion cycle, which was more complicated but allowed higher efficiency and thrust.

Methane was chosen over kerosene due to it being cleaner, being possible to synthesize on Mars, and being easier to use in a multi-start engine. Additionally, Methane won out over hydrogen, which can also be produced on Mars, because liquid methane is much more energy dense, which allowed for a lighter and cheaper BFR. Lastly, methane does not cause metal embrittlement and has higher melting and boiling points, allowing it to be stored for much longer periods without heavy propellant boil off. The Raptor’s first thrust figure of at least 2,942 kN (661,400 lbf) was announced in October 2013.

Nasaspaceflight.com (NSF) member experts became intrigued with the possibilities suggested by these early revelations.  Within months, NSF member expert Dmitry Vorontsov created the very first images, mass estimates and launch simulations of the SpaceX Mars launch vehicle in a dedicated L2 evaluation section.  Vorontsov’s intuition was that that the initial design would resemble an enlarged Falcon 9 with 9 Raptor engines on the first stage and a single Raptor engine on the upper stage.  He also evaluated a triple core version of the design, which SpaceX was understood to be evaluating at that time.

NSF’s early work showed that a single 9.8 meter core version of this rocket was only capable of lifting 120 tonnes, less than the 150-200 tonnes SpaceX claimed. A triple core version massing 5,440 tonnes and powered by twenty eight Raptor engines would have been capable of lifting more than 286 tonnes to LEO.

In March 2014, SpaceX Vice President of Propulsion Tom Mueller confirmed Vorontsov’s choice of a Falcon 9 style engine configuration of nine Raptor engines on the core stage and one on the upper stage.


Early BFR conceptions – rendered by Dmitry Vorontsov for NSF/L2

Mueller also announced an increase in the Raptor engine’s thrust to 4,448 kN (1,000,000 lbf), and the choice of a 10 meter diameter for the rocket. Also, the Raptor engine would be employing a rarely used but highly efficient combustion cycle called full flow staged combustion.

New NSF evaluations showed this would improve the lift capability of the single core version to 174 tonnes to LEO. Although record-breaking, such a rocket by itself was not capable enough to allow the colonization of Mars, let alone a return journey.

NSF’s experts at the time believed the likely course was to employ a “dual launch” approach, with the Mars colonization spacecraft being launched with crew into orbit and then refueled by a tanker spacecraft.  A similar approach but with multiple tanker launches would later be confirmed in October 2015 as SpaceX’s preferred launch architecture.

In this approach, following the final refueling the tanker would return to Earth while the spaceship would make the burn for Mars. Once on Mars, the spaceship would be refueled with specialized equipment and local resources, much like was envisioned in Robert Zubrin’s Mars Direct project.

In May 2014, further details of the Raptor engine were given at the Space Propulsion conference in Cologne, Germany. Raptor’s sea level thrust had increased to 6,914 kN (1,554,300 lbf). The vacuum version of Raptor had a thrust of 8,238 kN (1,851,900 lbf) and an ISP of 380 seconds.

The result was the vehicle’s thrust had jumped to 66,223 kN (13,988,300 lbf). In June 2014, as SpaceX started Raptor component testing, Mueller revised the Raptor engine’s thrust to 7,414 kN (1,666,700 lbf), which rivaled the most powerful rocket engines ever built. The vehicle’s total thrust as a result increased a further 7.23% to 66,723 kN (15,000,000 lbf).

Furthermore, details emerged that SpaceX was moving away from considering a multi core design and was instead concentrating on a single large core, with diameters ranging from 10 to 15 meters under consideration.

The major reason for this shift likely was due to the much smaller performance penalty for reuse allowed by a single core rocket versus a multi core rocket. Following the upgrade in thrust, NSF evaluations showed that any of the single core variants under consideration would have been capable of lifting more than 300 tonnes to LEO.

Further NSF evaluations also showed that due to its sheer size and the high ISP of its engines, barge landing reuse would only cost about 4% of the rocket’s maximum capability.

In January 2015 SpaceX reversed course and suddenly revised the Raptor engine’s thrust down to 2,256 kN (507,100 lbf), though no mention was made of changes in the rocket’s overall thrust or design, other than there would be a lot of engines.

With the design’s future direction now clouded in uncertainty, a fellow team member of Vorontsov’s suggested that SpaceX was taking a radically different approach. To save on engine development costs, they believed SpaceX had simply tripled the number of Raptor engines on its launch vehicle to compensate for the drastic reduction in engine thrust.  This would later be confirmed to NSF in October 2015.

NSF experts’ evaluations showed that the new engine parameters would likely result in a 5,200 tonne launch vehicle powered by 27 Raptor engines on a 12.5 meter diameter core stage and three Raptor Vacuum engines on a 12.5 meter diameter second stage. Although the resulting rocket suffered a minor hit to performance from the increased number of engines, it would still be capable of lifting 280 tonnes to LEO.


Envisioning of Raptor Engines on BFR booster – rendered by NSF member Doesitfloat

In 2016 NSF learned that a large number of possible designs had been under consideration in the prior year for the Mars Colonial Transporter (MCT), as it was then known. There were two basic possible design choices.

The first was to make the MCT spaceship as a sort of super-sized capsule complete with its own engines for getting off Mars, a design which NSF learned SpaceX had actively considered. The second possibility was a lifting body design, also with its own engines for getting off Mars. The capsule design was more proven and conservative but offered less mass and space for cargo, crew and propellant, while the lifting body would offer greater mass and space but was less proven.

A consensus was reached amongst NSF’s experts that regardless of the design choice the MCT spaceship would enter the atmosphere on its side to maximize surface area.  It was uncertain however whether the MCT would land vertically upon its tail or land horizontally on Mars.  While a horizontal lander would enable easy off-loading and safer landings, it would also be more complicated to engineer.

One major design choice for SpaceX was whether the spaceship would be incorporated into the rocket’s second stage to save on design costs and mission complexity, or whether it would be its own dedicated stage in order to maximize performance.  Given the plethora of design variations possible, by July 2015 NSF experts had identified more than twenty possible designs for the Mars Colonial Transporter spaceship.

SpaceX meanwhile had suffered a launch failure of its Falcon 9 rocket on June 28th, 2015, that led to a 260 million dollar loss for the firm due to the inability to launch while the failure was investigated. NSF learned that as a result, the announcement of SpaceX’s Mars plans were to be pushed back until after the firm had returned to flight.


CRS-7’s launch failure – via SpaceX webcast screenshot.

The firm continued to make progress on the Raptor engine’s development however, with its oxygen pre-burner component undergoing a full power test that same month. By August 2015 Musk announced that the Raptor would feature an oxygen to methane ratio of 3.8:1.

NSF gained further insights in October 2015 about Musk’s plan. The MCT was to be 180 meters tall single stick design of 12 meters in diameter, launch off the pad with 62,239 kN (13,992,041 lbf) of thrust, and be capable of reusably lifting 236 tonnes to LEO.

It would then make a three to five month journey to Mars while carrying a full load of cargo, 100 colonists and crew. Once there, it would enter the atmosphere and slow down via a combination of atmospheric drag and retro propulsion. Early plans called for an initial Mars base to be created by landing ten spaceships in close proximity and using cranes and robots to start up preliminary propellant production.

Energy for both the base and its propellant factory would be provided by a mixture of small nuclear reactors and deployed solar panel arrays. Once up and running, plans called for sending at least ten colonists and crew on the initial manned mission to Mars to get the colony properly started. The spaceships, however, would return to Earth each synodic period so that they could be refurbished back on Earth and readied for the next launch window.

While the plan resembled Zubrin’s, it featured Earth orbit refueling of the colonization spaceships, which Zubrin’s plan did not, as SpaceX counted on fully reusing all parts of their rockets.

The plans centered on a common BFR core stage used to launch both the spaceship and the tankers used to refuel them in orbit. The booster’s listed thrust figures revealed it would have 27 Raptor engines, just as Vorontsov’s team had predicted, matching the number on SpaceX’s upcoming Falcon Heavy lifter.

It would be the greatest number of engines on any rocket stage since 30 NK-15 engines were used to propel the Soviet Union’s failed moon rocket, the N-1. The stage’s propellant mass alone would be several hundred tonnes more than the entire Saturn V or N-1 launch vehicle’s liftoff mass.


The engines on the base of the Soviet N1 rocket.

NSF learned the core stage would also have a significantly higher ideal staging velocity than the expendable version of the Falcon 9 thanks to its more efficient Raptor engines.

The plan’s summary outlined intentions to reuse both the core stage and its upper stages, with the core stage being capable of launching more than 15 times. When reusing both stages, payload to LEO would only drop to 200 tonnes.  NSF experts quickly realized this would only be accomplished if the firm attempted to land the enormous stage on either an island or autonomous drone ship downrange. This gives a far smaller hit to payload to orbit (estimates range from 4-12.5%) than the nearly 50% hit to payload caused by returning the core stage to the launch site.

Fewer details were available about the spaceship and tanker, though both were 60 meters long, vertical landing lifting body designs and would be capable of docking and transferring propellant. The thrust ratio of the core stage to the spaceship/tanker stages was a low 5:1, while most rockets have thrust ratios of 8:1 or more.

NSF experts realized this ratio meant that there would be five Raptor Vacuum engines on the spaceship. It was thought this lower thrust ratio was due to SpaceX attempting to trim the delta-V of the core stage so that it could be more easily reused. NSF later learned that three central atmosphere optimized Raptor engines would also be present for landings. The engine layout added engine redundancy in flight but had the drawback of adding more dry mass.

The spaceship itself would feature a large habitat section complete with suites of crew cabins mounted on top. To carry cargo, the spaceship would feature a lower cargo bay mounted above the Raptor engines, with the engines fed via a pair of central tubes that would cut through the cargo bay. This layout would allow the easy offloading of heavy cargo like vehicles or nuclear reactors.

The spaceship and its tanker counterpart would be supported by five extendable landing legs that would not fold down like the Falcon 9’s legs. There were no plans for a launch abort system (LAS) on the spaceship, which surprised many of the NSF experts, as the vehicle would be transporting 100 colonists at a time. A LAS is required for NASA’s Commercial Crew Program’s vehicles in contrast.

Although the launch vehicle would emulate the Falcon 9 v1.2’s design in its use of chilled propellant and multiple versions of one engine to power everything, there were a number of key design differences. Its propellant tanks would be made out of carbon fiber, a radical design change in the industry that would allow for a more efficient rocket.




They would also not be pressurized by gaseous helium, as is done with many US rockets and which was involved in the disintegration of two Falcon 9 upper stages. Instead, SpaceX would use gaseous forms of both propellants to autogenously pressurize the tanks, eliminating a major failure point at an approximate mass penalty of just less than 1% of payload.

NSF learned that other fuel and oxidizer combinations were under consideration, with perhaps the most plausible alternative being C2H4/O2 (Ethylene/Oxygen).

Regardless of the chosen diameter, the enormous BFR mentioned in the plans would be the most efficient launch vehicle to LEO ever, besting the latest record holder, the expendable version of the Falcon Heavy launch vehicle (4.49% of launch mass), by over half a percent. On a relative percentage basis, the payload as a percentage of launch mass would be some 11% greater than the next most efficient rocket. The rocket would, however, have a thrust to weight ratio of 1.36 to 1, which meant the launch vehicle could potentially lift even more with larger propellant tanks.



NSF assembled a design team of top experts, who would be advised by rocket designers Dmitry Vorontsov and Chuck Longton (co-founder of the DIRECT Project), to make sense of the figures and design elements (more workings in this L2 Evaluation Thread).

The NSF design team quickly settled on the most likely design being a 105 meter tall, 15 meter diameter two stage launch vehicle massing some 5,500 tonnes. As they ran the figures and filled in various holes in the documentation, they came to several realizations.

The plan’s summary mentioned a height of 180 meters was likely outdated, as the rocket’s thrust dictated a much shorter vehicle. It was also likely that the performance figures were extremely conservative, as simulations showed the vehicle with the given diameter lifting more than 280 tonnes to LEO with Falcon 9 style mass optimization.

NSF experts also noted that the design would need to produce approximately 100 kW of power from its solar arrays at Mars to support 100 colonists and crew. Given Mars receives 37-51% of the sunlight Earth receives depending on its distance, the spaceship’s solar panel arrays would need to produce 270 kW near Earth in order to meet minimum Mars power requirements.

The nuclear reactor type thought most likely by NSF experts to power the colony would be a Thorium fueled molten salt reactor, which would be able to take advantage of Mars’ extensive thorium reserves.

The NSF design team also noted some areas of concern that SpaceX would need to work on, including the lack of a mentioned launch abort system and possible debris strikes on the engines or spacecraft at Mars landing and liftoff. Simulations showed the spaceship’s Raptor engines would unleash a force equivalent to that of a Category 5 hurricane underneath the vehicle at Mars liftoff, which would increase the risk of a debris strike.

NSF confirmed new details about the design’s evolution in February 2016. The firm had selected an 81 m tall, 12 m diameter design with around two times the thrust of a Saturn V. A larger 88 m tall, 14 m diameter design with three times the Saturn V’s thrust lost out.

One possible reason for this was that evaluations showed that the 12 m design would require a smaller exclusion area of approximately 8 km (5 miles) in the event of a vehicle failure on the pad.  SpaceX had evaluated this area by looking at over-pressurization, which would fall to safe levels at this distance.  Any design more than twice as large as a Saturn V would face restrictions on launch site selection due to an enlarged exclusion area.

The Raptor engine’s thrust was shrunk 13% to 1,961 kN (440,850 lbf), forcing a change in design architecture. The booster would feature 42 Raptor engines, giving the rocket 82,362 kN (18,515,700 lbf) of thrust, 23.4% more than it had before. It carried 3,650 tonnes of propellant at a 3.58 Oxygen/Fuel ratio. It was to land near the launch pad instead of at sea via a combination of thrusters powered by hot ullage gas and grid fins. This change would give SpaceX easier launch operations at a very significant cost in payload capacity.

The Mars Ship saw an even more drastic change, shrinking from 60 m in length to 41 m while all cargo and crew was now positioned on top. This layout won out over two others. The first featured the propellant tanks in the nose, above the pressurized crew compartment, with the unpressurized cargo bay sandwiched between the crew and the engines.

[Orionid]

The Evolution of the Big Falcon Rocket (3)


Elon 2017 IAC, showing crane in operation on the moon

This layout offered easy cargo and crew off loading and improved stability after landing due to being bottom heavy. Unfortunately, due to the propellant feedlines cutting through the manned areas and the cargo bay, it had the worst crew environment, less cargo space and the highest dry mass. The prior default layout resolved the crew environment issue by moving the crew on top, placing the propellant tanks in the middle, and leaving the cargo bay on the bottom.

This layout afforded greater stability during landing at the cost of less easy crew offloading, but was ultimately rejected in favor of the crew and cargo sections being placed on top together. This layout was 9% and 8% lighter than the prior two layouts, a huge advantage for the high delta-v return from Mars. It also offered more commonality with its Tanker stablemate, which would trim manufacturing and design expenses. These advantages were considered worth the cost of inferior landing stability and reduced ease of offloading.

SpaceX would compensate for this layout’s inferior offloading characteristics by adding a gantry crane for moving heavy cargo down to Mars. The crew would be able to get down to Mars via an egress raceway from the 1100 cubic meter pressurized compartment. In addition to these changes, the engine configuration saw the addition of a sixth vacuum engine, bringing the total number of engines on the Mars Ship to nine.

The vacuum version of the engines were to be 5.5 m long and 3.8 m in diameter, while the landing engines would be considerably smaller. All nine of the engines would fire after stage separation to minimize gravity losses of the 1,750 tonne vehicle, with the landing engines shutting down when no longer of benefit. The engines would be fed from propellant tanks containing 1,450 tonnes of propellant. They would be protected in turn by a unique interstage aero shell, which covered the engines but not the rear. This arrangement offered protection with minimal mass.

The Ship and its Tanker stablemate would both enter the atmosphere on their sides. SpaceX had considered capsule entry, but nixed the idea after finding that it made protecting the engines very difficult. Side entry, in contrast, protected the engines, spread the heating over a wider area, and was lower mass thanks to the benefit of integrating the structure with the heat shield.

In a development anticipated by NSF expert Dmitry Vorontsov, SpaceX modified the Tanker to use enlarged tanks that could hold 1,650 tonnes of propellant. This change would allow the design to carry substantially more propellant into orbit. At 27 meters, however, it would be much shorter than the Mars Ship.

In order to swing the vehicles around from side entry to engines first for final landing, NSF learned that SpaceX considered using aerodynamic surfaces, engine gimbaling, differential throttle or a combination. The Ship and the Tanker would both feature a docking port on their backs with automatic couplers. Three options for refueling were considered, including capillary action, diaphragm tanks and settling the tanks via rotation and pressure assist. The latter was selected due to the prior schemes not being practical for such a large design.


BRS refuelling render by Michel Lamontagne for NSF/L2

The firm anticipated that one Tanker would be refueled by several others first before transferring all of the propellant at once to the Mars Ship. This would minimize exposure of the passengers and crew to microgravity and radiation while cutting consumption of food supplies.

NSF learned that other design elements for both the Ship and Tanker had also been decided upon. One element was the use of spherical header tanks inside the propellant tanks to hold propellant used for landings. This would be done to prevent the sloshing of propellant from causing a critical engine flame out during atmospheric entry.

The Ship would feature water, brine and solid waste storage around the upper edges of its oxygen tank. Above this storage, the unpressurized cargo hold would be located. It would feature two 3 meter tall decks supported by a central column. This area would contain power systems, thermal systems, un-deployed solar arrays, radiators, life support, air handling, storage and avionics.

Cargo would be transferred out of a large cargo door via an extending gantry crane and lowered to the surface.

The pressurized section above could be entered into via an airlock attached to a docking port. It would feature the same central support column as the cargo bay. There were to be four levels, with three 2.5 m tall floors for crew, food and crew accommodation, and a much larger top level.

This level contained the crew mess and launch/landing seats. The vehicle’s nose contained control thrusters to control its fine movement. One element in flux was the extendable landing legs of the Tanker and Ship, of which there were five but which they were going to be heavily upgraded in size and durability.

SpaceX decided that instead of just using carbon fiber for the propellant tanks, the booster’s structure would be entirely made of carbon fiber, as would the Tanker and Ship.


Photo of the tank, via Elon Musk’s 2017 IAC speech.

SpaceX made this decision due to carbon fiber benefitting reusability via its higher fatigue limits, as well as its greater geometric stiffness. This was vital, as it would no longer be possible to efficiently prevent propellant tank buckling via ullage gas pressure due to the vehicle’s size and use of autogenous pressurization.

SpaceX planned on reusing the Booster, Tanker and Ship 1000, 100 and 12 times respectively, with the Ship’s reuse heavily limited by the massive heating it would endure during its aero capture into Earth Orbit. NSF learned that two launch sites were being considered: KSC/Cape Canaveral, Florida and Brownsville, Texas, with the former having more than twice as many launch opportunities as the latter. This was due to its superior geographic location for Mars launches.

The design continued to evolve behind the scenes between February 2016 and the time of . It was announced the day before Musk’s address that SpaceX had conducted the first test firing of a sub-scale Raptor engine.


Raptor test firing at McGregor – Credit SpaceX

The following presentation by Musk first noted the very aggressive goal of improving the cost of transport to Mars by five million percent to around the median cost of an American house. To enable this, Musk said, orbital refueling was necessary, as it would spread development costs over more launches, compress the schedule, make performance shortfalls less problematic, and allow for a launcher 10-20% as costly as the alternative.

Refueling on Mars, much like in Zubrin’s plan, was also included to allow reuse of the ship and leverage the resources of Mars. According to Musk, Methane was selected as the fuel because it allowed a smaller vehicle size than hydrogen, had the lowest costs, allowed easy reuse, could be produced on Mars, and was just as transferable in orbit as kerosene.

The system architecture showed the system would have a common booster stage and two upper stage versions. The first upper stage would be the ITS (Interplanetary Transport System) Spaceship itself, while the second would be the ITS Tanker. The reuse goals were the same as in February, with the Booster, Tanker and Spaceship being rated for 1000, 100 and 12 reuses (over 12 Mars synods totaling 26 years). The system would also use autogenous pressurization of propellant tanks and a carbon fiber primary structure as expected.

SpaceX’s grand ambitions finally became fully apparent when the launch vehicle’s expendable payload capacity of 550 tonnes was announced. The rocket would be 133% more capable than the version SpaceX had planned just the year before.

This incredible performance was enabled by the Raptor engine. Its sea level thrust had increased by 55.5% from 1,961 kN (440,850 lbf) to 3,050 kN (685,667 lbf), its sea level ISP was up 3.9% (334 seconds versus 321.4 seconds prior), it was now capable of throttling 20-100%, and its 300 bar chamber pressure was the highest in rocket engine history.


The Raptor Engine via the 2016 IAC presentation

Its vacuum version would feature an even higher thrust of 3,500 kN (786,831 lbf) and an ISP of 382 seconds, the highest hydrocarbon ISP engine on record, thanks to a very large 200 to one expansion ratio nozzle. The Booster’s engine count of 42 Raptor engines remained the same.

Thanks to the engine’s large increase in thrust, the Booster developed an astounding 128.1 MN (28,798,026 lbf) of thrust, which allowed the 6,700 tonne, 77.5 meter (254.27 ft) tall, 12 meter (39.37 ft) diameter stage to more than double the Saturn V’s entire mass. Similar to the Falcon 9, it would use a combination of rocket retro-propulsion and grid fins to guide itself back to Earth. Despite featuring an even higher separation velocity than the Falcon 9, it would require just 7% of its propellant to return to its launch pad for reuse.

The ITS Spaceship’s height of 49.5 meters (162.4 ft) was 21% longer than the previously planned 41 meters (134.51 ft). However, it had the same long term goal of carrying more than 100 crew and passengers, although the vehicle massed more and had a wider diameter of 17 meters (55.77 ft) while using the same engine configuration. Its 31 MN (6,969,077 lbf) of thrust would boost the 2,100 tonne vehicle and up to 300 tonnes of cargo into LEO, where it would unfurl its solar panel arrays.


Comparison to the Saturn V graphic – via SpaceX

It would land vertically on Earth and Mars via three centrally located Raptor engines, and could deliver up to 450 tonnes of cargo to Mars. Unlike the plans detailed in February however, it would use three massive landing legs rather than five smaller legs. It maintained enlarged versions of the crew and cargo compartments on top from the February 2016 design.

Its Tanker stablemate differed from its February design by being the same length and shape as the Spaceship. However, it used enlarged tanks and swapped functionality for 40% less dry mass, which allowed it to carry 27% more propellant to orbit. Altogether, this system would allow Mars journeys averaging 115 days, with the ITS Spaceship either aerocapturing into orbit or proceeding directly to landing upon arrival at Mars.

One curious omission in the speech concerned SpaceX’s prior interest in an all-in-one island facility, which had been assumed in the run-up to the speech.

This plan called for the ITS to be built in a factory within the island facility. Once a rocket was built it would be sent to a nearby test stand, where it would have been fired. After testing finished it would be moved a short distance to the launch pad, and then launched and landed there. Nearby hangars would allow SpaceX personnel to maintain and fix the vehicles as needed.

Such a site would have allowed SpaceX to build, test, launch and land the ITS away from population centers and maintain a rapid launch rate without drawing as much complaint from locals.

Experts at NSF and elsewhere raised questions about the sheer size of the vehicle as proposed at the time, ranging from the event of an anomaly during launch – which may have required a much larger Blast Danger Area (BDA), through to the issue that the design produced so much thrust that it could not be handled by either the 39A or 39B launch pads at Cape Canaveral.

Built in the early 1960s for the Apollo program, the pads were designed to handle up to 53,379 kN (12,000,000 lb) of thrust.  While they could be upgraded at a substantial cost in time and money, this would also lose SpaceX, NASA and others all use of the pads during the construction work.


BFR launching from 39A – notional – from SpaceX

Another concern with the vehicle’s thrust was the sheer acoustic vibration would complicate its engineering and draw more opposition to launches.  In addition, the core stage was still large enough that had it had an accident while attempting to land on the launch mounts, an explosion large enough to substantially damage the pad would result.

Other concerns centered around the ITS Spaceship.  The primary concern was its complete lack of a Launch Abort System (LAS), a feature NASA was notably required for SpaceX’s Dragon capsule.  Should there have been an explosive failure, it was not clear that the crew could be gotten to safety.  With up to 100 people on board, the potential for loss of life multiple times worse than any Shuttle disaster was dangerously high.

The use of three landing legs entailed lessened stability versus four or more leg designs and unlike five or six-leg designs, had no redundancy if a leg failed.  The speech also did not heavily cover the design’s radiation protection.  Given the radiation levels astronauts and colonists would encounter on the way to Mars, the relative dearth of details on the Spaceship’s radiation protection was surprising.

The most pressing issue with the design was the lack of details on how to make money with it apart from Mars.  Development would likely take years and cost in the order of 10 billion dollars, but its uneconomical size and lack of satellite launch capability drastically hurt its business case.  The issue was even referenced in the speech by Musk.

Following the speech NSF learned in February 2017 that the design was evolving in a smaller direction. One design of the ITS under consideration featured a diameter of 10 meters (32.81 ft) and as few as 16 Raptor engines on its booster. Within months, however, SpaceX decided to go with an even smaller 9 meter (29.53 ft) diameter design in order to avoid building an all-new factory. This would ease production at a cost of more complicated and expensive logistics for stage transportation and testing.

In the run-up to the next speech in September 2017, Raptor engine testing continued at a vigorous pace. The sub-scale test engine possessed a chamber pressure of 200 Bar and a thrust of 1 MN (224,808 lbf). According to Musk, it also used a new alloy to help its oxygen-rich turbopump resist oxidization. By the time of Musk’s September International Astronautical Congress speech in Adelaide, Australia, the sub-scale prototype had completed 1200 seconds of firings across 42 tests.

revealed the Raptor engine’s designed sea level thrust had been shrunk by 44.3% from 3,050 kN (685,700 lbf) to 1,700 kN (382,200 lbf).  Its initial version would have a lower chamber pressure of 250 Bar, which was 50 Bar, or 16.7% less than the final planned version.  With a nozzle diameter of 1.3 meters (4 ft 3 in) this allowed it to develop an Isp of 330 seconds at sea level.  The vacuum version was to have 1,900 kN (427,100 lbf) of thrust produced from a 2.4 m (7 ft 10.5 in) nozzle and had an Isp of 375 seconds.

Only 31 Raptor engines would be attached to the updated BFR’s 9 m diameter, 58 m long booster stage, which would allow it to produce a still impressive 52.7 MN (11,847,400 lbf) of thrust at sea level.


BFR flow at 39A as envisioned by Jdeshetler for NSF/L2

This was a 58.9% drop compared with the prior design and coincidentally was just low enough for SpaceX’s 39A launch pad to handle with minimal modifications.

The rocket would still produce 55.7% more thrust than the Saturn V moon rocket, the current world record holder for most capable and successful carrier rocket. Other benefits of the size change included a much smaller exclusion zone, lower development costs and a lower risk of engine failure during launch.

Attached to the booster stage could be any of three different upper stages, all sharing the same outer mold line and powered by a mixture of four Raptor vacuum engines and two Raptor booster engines. The six engines would produce 11,268 kN (2,533,100 lbf) of thrust after stage separation.

[Orionid]

The Evolution of the Big Falcon Rocket (4)


BFS cross section – via SpaceX

Once the stage’s thrust to weight ratio had improved, the landing engines would shut down. Each stage would boast a modest delta wing and four landing legs, allowing the stage to de-orbit and land vertically.

The updated Spaceship stage would mass up to 1,335 tonnes at launch, carry up to 1,100 tonnes of propellant, and have a modest dry mass of 85 tonnes. Its design featured a side-mounted docking station along with two large windows in place of the ITS Spaceship’s massive main window.

Although much smaller than before, it still boasted 825 cubic meters (29,134.6 cubic feet) of pressurized space, only 9.9% less than the International Space Station (915.6 cubic meters/32,334.1 cubic feet) but not in fact more than the 2,100 cubic meters (74,160.8 cubic feet) of an Airbus A380 as SpaceX claimed.

Internally, it would have 40 cabins housing up to 100 passengers, space toilets, a galley, large common spaces and even a solar storm shelter to address radiation concerns.


BFS docked to the ISS – SpaceX

It would be refueled in orbit by an equally large BFR Tanker via milli-gravity acceleration achieved via control thrusters and propellant tank rotation.

The third version of the upper stage was a modified carrier rocket stage which would enable the design to launch commercial satellites.  It housed a massive payload bay, which would open and close via a hinged door.

This would be mounted on only one side of the vehicle, with the ventral side protected by the integrated heat shield.


Deploy render – via SpaceX

All three variants would mass up to 4,400 tonnes and stand 106 meters (347.8 feet) tall on the pad. The BFR would have a payload capacity of up to 250 tonnes for an expendable launch and 150 tonnes for a fully reusable launch. This capacity would make the BFR system the world’s most efficient LEO launch system ever built, with over 5.68% of launch mass making it to orbit if figures are accurate. That would make the BFR some 26.5% more efficient at launching its mass into Low Earth Orbit than the current record-holder, SpaceX’s Falcon Heavy (4.49%).

The three upper stage variants would enable the BFR system to support commercial Earth orbit satellite launches, Earth and beyond Earth orbit spaceflight, and missions to the Moon, Mars and beyond via refueling of the BFR Spaceship. In addition, Musk revealed SpaceX’s plans for using the BFR to enable traveling between any two cities on Earth in under an hour. Eventually, this enormous rocket system would even replace SpaceX’s Falcon 9 rocket family and potentially bring costs down radically thanks to full reusability.

Somewhat ironically, the trimming of the vehicle’s size from 10,500 tonnes to 4,400 tonnes was what enabled the BFR’s uses to expand so dramatically. It also alleviated the most pressing design concerns over development cost, exclusion zones, and launch pads.  In the months that have followed, SpaceX has updated the design to include a third sea level Raptor engine on the upper stage to enable “airline levels” of safety via an engine-out capability.  Whether this is possible in rocketry when 2-6% of orbital rocket flights fail every year remains to be seen.

At IAC 2017 in September, Musk also announced that the firm had already ordered the tooling for the BFR’s main tanks and begun construction on the factory, with production of the first BFR to nominally start in the second quarter of 2018. The first two cargo flights to Mars would nominally be in 2022 to prepare a long-term Martian base and eventually a colony. As always with Musk, he has set SpaceX an ambitious schedule of development and flights for the new BFR. It is unlikely Musk’s firm will achieve the schedule, but SpaceX does have a track record of accomplishing its goals eventually.

At a news conference for the first launch of SpaceX’s new Falcon Heavy rocket on February 6th, Musk mentioned tests the firm hoped to do with the BFR Spaceship. “If we get lucky, we’ll be able to do short hopper flights with the spaceship part of BFR maybe next year,” Musk said. These would follow those of the Grasshopper prototypes, and testing would take place either at its South Texas launch site, nearby, or from ship-to-ship. Further mentions of the BFR’s evolution were made the next month by Musk.

On March 8th, 2018, Elon Musk tweeted the first image of the tooling for the BFR’s main body, which dwarfed a Tesla Model 3 parked next to it.

Later on March 11th, 2018, while at South by Southwest, Musk noted that the design was “evolving rapidly” and the construction of the second stage Spaceship was proceeding.

He mentioned one goal of the BFR, the colonization of Mars, might enable humanity to survive a nuclear war on Earth. The BFR’s development would be paid for, in part, by SpaceX’s upcoming Starlink broadband internet satellite constellation, which would contain as many as 10,000 small satellites.

Later in March, documents emerged that a company called WW Marine Composites LLC had applied to repair a vacant lot at Berth 240 on Terminal Island, Los Angeles, which had been approved by the Board of Harbor Commission.


Teslarati photographer Pauline Acalin (@w00ki33) photo of the facility

Eric Berger of Ars Technica noted that the firm appeared to be a subsidiary of SpaceX, with an anonymous source confirming that the site was intended for the BFR’s manufacture. SpaceX Spokeswoman Eva Behrend confirmed some of this to the Los Angeles Times, saying that the company was in talks with the Port of Los Angeles regarding the “potential of leasing additional land for operations”, which other documents confirmed were rocket-related.

With the BFR’s factory shifting to the Port of Los Angeles, that would not only ease transportation issues for SpaceX, but also potentially allow it to build the BFR with a diameter greater than 9 meters, allowing further improvement of the rocket’s potentially record-breaking efficiency.

The ambitious plans presented by Musk represented the culmination of a lifelong passion. It was that passionate interest in space that brought him into contact with prior Mars visionary Robert Zubrin, whose Translife Mission ultimately inspired Musk towards an even grander vision.

When Russian engineers thwarted Musk’s early goals in space, he instead gambled his fortune on SpaceX. Thanks to finally achieving orbit with the Falcon 1 rocket, Musk’s dreams of Mars colonization was ultimately saved in December 2008. Since that time, Musk’s vision has matured and grown alongside SpaceX.

The firm’s development of the Falcon 9 into the world’s first partially reusable launch vehicle – past the Space Shuttle – and the most efficient rocket ever heavily shaped the Big Falcon Rocket.

Much like the Falcon 9, since it was first conceived the BFR has more than doubled in thrust and payload, while also becoming more efficient by adapting all carbon fiber construction. The result was nothing less than a fully reusable launch vehicle system that would be unprecedented in capabilities and technology.

Musk’s presentations showed that SpaceX would like to be the transportation company enabling the colonization of Mars, reducing the firm’s expenses and risk. This, however, will mean that it must rely upon third parties to figure out the difficult logistics of creating and growing a colony on Mars. However, this may change as Musk has been noted in the past to grow impatient with the slow progress of others, and to undertake the tasks he sees as required himself.


Elon’s envisioning of a Mars base – via SpaceX

Although these second sets of plans presented by Musk were extensive, and in some ways less ambitious than the 2016 designs, they were not comprehensive.

There remain concerns with the scope of ambitions, getting to Mars and back, the financing of the BFR, and even with the vehicle’s design. Left out are details like the design of the Mars propellant production system, the building of the first Mars base, and the nuclear reactors with which SpaceX originally hoped to power the colony. There even remain questions about the BFR design, from its lack of a launch abort system, its non-redundant landing leg setup, and how its life support system would work over a Martian round-trip.

Will SpaceX’s Starlink Constellation actually finance the BFR’s creation, or will it lead to financial problems, as Iridium, the world’s only global satellite phone constellation, did for Motorola? Success in creating Starlink, let alone the BFR, is far from guaranteed. Will the US government help fund a 100 passenger rocket design that doesn’t feature a launch abort system? Can the vehicle minimize the radiation exposure of its passengers to NASA acceptable levels on the multi-month trip to Mars? How will the colonists on Mars survive? If the current primary energy source of solar panels proves inadequate, does SpaceX plan on launching nuclear reactors to Mars to provide part of the colony’s power as it originally intended to?

As to when the next update is expected, it could be soon.

Chris B - NSF
@NASASpaceflight
 · Jul 14, 2018
Replying to @elonmusk
Let's have some updated BFR info please, Elon.

Got to give the people what they want. 😎🚀

Elon Musk
✔
@elonmusk
In a month or so

3:51 AM - Jul 14, 2018
2,124
187 people are talking about this

Based on the rapid evolution of the design, with an additional engine added just a few weeks after the 2017 presentation, we can expect the BFR to be further refined.

Musk and SpaceX have accustomed us to a continuous iterative design process, as seen with the evolution of the Falcon 9 rocket.

Even in its current unfinished state, the SpaceX plan is unquestionably the most ambitious Mars colonization vision ever presented.

(This feature article was the result of months of evaluations into public and envisioned information and community edited via a draft process in this L2 thread)

Source: The Evolution of the Big Falcon Rocket