Spaceflight Insider

Elon Musk shows off Interplanetary Transport System

Interplanetary Transport System on 39A

A rendering of what SpaceX expects the Interplanetary Transport System to look like. The rocket will launch from historic Launch Complex 39A, which sent the first humans to the Moon in 1969. Image Credit: SpaceX

In a presentation akin to something out of science fiction, Elon Musk, founder and CEO of SpaceX, announced the Interplanetary Transport System (ITS). The two-stage rocket would be bigger and send more payloads to orbit (and beyond) than anything in the history of spaceflight.

At the 67th International Astronautical Congress held in Guadalajara, Mexico, Musk detailed the components of ITS – a giant booster stage with an equally giant spaceship totaling 400 feet (122 meters) tall. The NewSpace entrepreneur’s discussion was titled “Making humans a Multiplanetary Species”.

The booster stage would be 254 feet (77.5 meters) tall and 39 feet (12 meters) wide. It would sport 42 raptor engines at the bottom – coincidentally, the same number as the “Answer to the Ultimate Question of Life, the Universe, and Everything” in one of Musk’s favorite books, The Hitchhiker’s Guide to the Galaxy.

The spaceship, which doubles as an upper stage, would be 162 feet (49.5 meters) long and 56 feet (17 meters) wide. It would have a total of 9 engines (3 sea-level and 6 vacuum versions).

The expendable version of the rocket would be able to take 550 metric tons to low-Earth orbit (LEO), while the fully reusable version would take 300 metric tons. After being refueled on orbit, it could take up to 450 metric tons to the surface of Mars.

“It’s quite big,” Musk said after showing off the basic numbers. “In the long term, the ship’s will be even bigger than this. It needs to be about this size because in order to fit about 100 people in the pressurized section plus carry the luggage and all the unpressurized cargo to build propellant plants and build everything from iron foundries to pizza joints.”

Musk said that while he won’t be on the first ship, he hopes to name it Heart of Gold – after the ship with the Infinite Improbability Drive from The Hitchhiker’s Guide to the Galaxy.

“I like that it is driven by the Infinite Improbability Drive because our ship is also improbably,” Musk said.

The Interplanetary Transport System

A flight profile for the Interplanetary Transportation System. Image Credit: SpaceX

A flight profile for the Interplanetary Transport System. Image Credit: SpaceX

The whole system would launch from Kennedy Space Center’s Launch Pad 39A. The rocket’s first stage would have a similar launch profile as the Falcon 9. It would launch, and at stage separation, turn around and fly back to the launch site.

Then the upper stage, which is also the spaceship, would continue burning for orbit. Once in orbit, it would be refueled by a “tanker” version of the spaceship. After it is fully fueled, it makes the burn for Mars.

According to Musk, depending on what planetary alignment you use, you could get to Mars in as little as 80 days with the ITS.

After landing on the Red Planet, it would refuel using in-situ propellant production to create the liquid oxygen and methane fuel. It would then launch directly back to Earth and land.

Once back on Earth, it would be prepared again for another journey to the Red Planet.

Both the rocket booster and spaceship would be powered by Raptor engines that the company is currently developing.

Musk said SpaceX is targeting reusing the booster up to 1,000 times, the tanker 100 times and the Mars spaceship 12 times.

The Raptor Engine


The Raptor engine. Click to enlarge. Image Credit: SpaceX

SpaceX has been testing their successor to the Merlin engine for a couple of years now. Only recently did the company ship the engine to the test stand at McGregor, Texas. On Sept. 26, the engine was fired for the first time, albeit briefly.

Musk thanked his team for working seven days a week to get the first test firing done before the IAC announcement.

The engine is a full-flow staged combustion engine – one of only three that have ever developed to the point of testing. It has a chamber pressure of 300 bars – three times that of the Merlin 1D. This allows the engine to be powerful, but still small. In fact, Musk said the engine will be about the same size as the Merlin engines.

The engines will consume subcooled liquid oxygen and subcooled liquid methane, similar to what the company’s current rocket, the Falcon 9, does with liquid oxygen and rocket-grade kerosene.

The engine will be able to throttle between 20 percent and 100 percent of rated thrust. At sea level, its thrust will be 685,700 pound-force (3,050 kilonewtons) with a specific impulse (Isp) of 334 seconds. In vacuum, the engine will have 786,800 pound-force (3,500 kilonewtons) of thrust with a 382 second Isp.

The Rocket Booster

ITS booster

The rocket booster. Image Credit: SpaceX

Using 42 of these engines, the boost stage, which does not yet have a name, will accelerate the whole stack – including the spaceship on top – to a velocity of 5,375 mph (8,650 km/h) at stage separation.

The booster will then return to the launch site using only 7 percent of the total booster propellant load. Grid fins will guide the giant rocket back for a precise landing – on the launch mount.

The ITS engine cluster. Click to enlarge. Image Credit: SpaceX

The ITS engine cluster. Click to enlarge. Image Credit: SpaceX

“We’re getting quite comfortable with the accuracy of the landing,” Musk said. “With the addition of some maneuvering thrusters, we can actually put the booster right back on the launch stand. Those fins at the base [of the rocket] are essentially centering features to take out any minor position mismatch at the launch site.”

The base of this booster will have a central cluster of seven Raptor engines that can gimbal and steer the rocket. The rest of the engines will be clustered in two rings around the center. The inner ring will have 14 engines, while the outer ring will have 21. These rings of engines will be fixed in place as they will not be needed for steering.

The tank that would hold the densified fuel would be made of carbon-fiber, as opposed to the aluminum-lithium alloy the Falcon 9 uses. Additionally, these tanks would not be pressurized by helium but by the gaseous version of the methane and oxygen. These gasses would also be used as thrusters for both the booster and spaceship.

On takeoff, the total thrust of the vehicle will be 28.8 million pound-force (128 million newtons).

“It’ll be quite tectonic when it takes off,” Musk said. “They sort of over-sized the pad in doing Saturn V. As a result, we can actually do a much larger vehicle on that same launch pad.”

The Interplanetary Spaceship

ITS spaceship

The ITS spaceship. Image Credit: SpaceX

As for the spaceship, it also doubles as an upper stage. It would reach orbit with its tanks nearly empty. On top of the tanks would be a cargo and living compartment with space for up to 100 people for a journey to the Red Planet.

“This vehicle [system] is intended to carry huge numbers of people, possibly millions of tons of cargo to Mars,” Musk said. “So, you really need something quite large in order to do that.”

Once it gets into orbit, it would need to be refueled. That would be done by launching a similar version modified to only carry propellant. It could take up to three to five of these “tankers” to refuel the spaceship.

Once fully fueled, and the planets align – occurring once every 26 months – the burn for Mars can occur.

With its nine engines, it would have a total vacuum thrust of 6.97 million pound-force (31 million newtons). This would allow it to take the 450 metric tons of humans or supplies to Mars.

Once on its cruise to the Red Planet, the spaceship would deploy two massive solar arrays to generate a total of 200 kilowatts of electricity. Musk also believes this is enough power to refuel the ship after it lands on Mars.


Interplanetary Transport Timeline

A rough timeline for Interplanetary Transport System development. Image Credit: SpaceX

Musk has a history of being overly optimistic on timelines. Some have deemed this “Elon Time”. However, he left the timeline for developing the Interplanetary Transport System intentionally fuzzy.

The SpaceX CEO wants the first development spaceship built in four years to start doing suborbital flights with it – similar to the Grasshopper program that lead to reusable Falcon 9 first stages.

The booster rocket, Musk believes, is pretty straight forward. He said it involves scaling up the technology from Falcon 9.

“Not a lot of showstoppers there,” Musk said.

However, he pointed out testing the system together will take a lot longer.

“If things go well, it’ll be in the 10-year timeframe,” Musk said.

But Musk won’t wait for that. SpaceX plans on sending a modified unpiloted Crew Dragon, called Red Dragon, to Mars in 2018.

After that, SpaceX plans to send at least one capsule to Mars during every Mars rendezvous opportunity to deliver up to 3 metric tons of usable cargo or science equipment on the surface.

Additionally, the company has started testing the Raptor engine as well as a developmental carbon fiber cryogenic oxygen tank for the spaceship. In fact, Musk said that tank was finished.

“This is really the hardest part of the spaceship,” Musk said. “The other pieces, we have a pretty good handle on, so we wanted to tackle it first.”

Musk said by putting supercooled liquid oxygen and methane inside the tank, it could crack and leak. However, preliminary tests on the development tank have shown neither problem. He said the sheer scale of building these tanks is also challenging as you have to lay out the material the right way on a huge mold, cure the mold at temperature, etc.

“It’s just really hard to make large carbon fiber structures that can do all of those things and carry incredible loads,” Musk said.

The Long Game

ITS at Mars

A rendering of the Interplanetary Transportation System spaceship nearing Mars. Image Credit: SpaceX

Musk believes Mars is the best candidate in the Solar System to begin building a self-sustaining multi-planetary species. He said that early Mars was a lot like Earth and if humans could warm the planet up, it would once again have a thick atmosphere.

In order for enough people to make the trip through interplanetary space, the cost needs to be low enough. Musk believes that cost needs to be around $200,000.

To do that, Musk believes four technologies must be developed and perfected: Full reusability, refueling in orbit, propellant production on Mars, and the right propellant.

Without refueling in orbit, Musk said, the cost would be at least five times higher. Additionally, not refueling would require a three-stage booster. If the system were three stages, then it would need to be five to ten times the size and cost on top of that.

As far as fuel, the company chose methane because it is readily available to produce on Mars and is much easier to handle. While hydrogen is more efficient, it is harder to handle.

“Methane is better almost across the board,” Musk said.

Musk said whatever system is designed, whether it is by SpaceX or someone else, these are the four areas that need to be solved.

As for ITS, he said it would look almost exactly like what was shown today. The simulation was made by the SpaceX engineering computer aided design models.

“This is not what it might look like,” Musk said, “It is what we plan to make it look like.”

Musk said that in the future, the ships would need to be even bigger than this. It is already this big because it needs to fit about 100 people inside.

Using ITS, Musk said that to get a million people on Mars, you’d need 10,000 trips. Once the first one goes to the Red Planet, he estimates it would only take 40–100 years to get a fully self-sustaining civilization on Mars.

ITS vs Saturn V

ITS compared to the Saturn V. Image Credit: SpaceX

Beyond Mars

Additionally, Musk said that the system can open up the entire Solar System to people. If fuel depots based on this design were put on asteroids or other areas around the Solar System, people could go anywhere they wanted just by planet or moon hopping.

“The goal of SpaceX is to build the transport system,” Musk said. “Once that transport system is built, then there is a tremendous opportunity for anyone that wants to go to Mars to create something new or build a new planet.”

Musk and Mars

Image Credit: SpaceX

In a bid to make spaceflight cheaper, Musk started SpaceX. It took the company four tries to get into orbit. The first successful launch was flight 4 of the Falcon 1. Image Credit: SpaceX

Musk’s Mars ambitions go back even before SpaceX was founded. Before he knew much about rocketry, he met with members of the Mars Society at a fundraiser mid-2001 – a $500 per plate event at one of the members’ homes.

Musk invited himself and paid $5,000. Robert Zubrin, the head of the Mars Society, took note and invited him to coffee prior to the dinner to tell him about the society’s accomplishments and goals, including a plan to send a capsule into orbit carrying a crew of mice. The mice capsule would spin to give it one-third gravity – the gravity on Mars. The mice would live and procreate.

After the talk, Zubrin placed Musk at the VIP table next to himself as well as James Cameron and Carol Stoker – planetary scientists for NASA.

After joining the society’s board of directors, Musk donated another $100,000 for the Mars Desert Research Station in Utah.

This was around the time PayPal was being sold to Ebay for $1.5 billion. Musk was the largest shareholder.

Soon, Musk started thinking beyond the Mars Society’s goals. He wondered about the possibility of sending the mice to Mars.

Not long into the mice-to-Mars discussion, the goal took on a new form – sending a robotic greenhouse to Mars to grow plants. It seemed doable and bold. The idea was to have a live video feed to people could watch the plants grow – the first life on Mars.

Too Expensive

However, as he and his small team of engineers started digging into the idea more, they found it more complicated than first imagined. Additionally, Musk’s trips to Russia to acquire an intercontinental ballistic missile were a waste of his time as the Russians either didn’t take him seriously or were wanting to take as much of his money as they could – possibly both.

Musk came out of 2001 and early 2002 realizing the cost of sending a payload into space was too much. So, in June 2002, he founded Space Exploration Technologies to radically change the way the space industry thinks about rockets.

At a minimum, Musk has done that. And now with today’s Interplanetary Transportation System announcement, he is poised to go farther and bolder than any successful aerospace company to date.

But who will pay for this plan?

Show Me the Money

SpaceX has done a lot in its more than 14 years as a NewSpace company. All of the Falcon 1 was privately funded, much of it through Musk’s own checkbook. However, in 2006, SpaceX started receiving Space Act Agreements from NASA to help them with their Dragon capsule. In 2008, they would be one of two companies to get a Commercial Resupply Services contract to send cargo to the International Space Station.

That money, in addition to other investors and Musk, helped accelerate both Dragon and the Falcon 9 v1.0 rocket. Musk has repeatedly stated that without NASA money, it would have taken longer than it actually did.

Dragon and Falcon 9 both flew in 2010. Regardless of where the money came from, SpaceX estimated in 2011 that the total developmental cost of the rocket to be around $300 million. NASA estimated that with traditional cost-plus contracts, it would have been $3.6 billion.

Between Dragon and Falcon 9 v1.0, NASA provided $396 million and SpaceX provided more than $450 million.

Commercial Revenue

Today, SpaceX gets its revenue from more than just NASA, although the U.S. space agency remains the company’s largest customer. Much of the Falcon 9 first stage reusability efforts have been financed from the profits the NewSpace firm has made from these missions.

It also helps that for each mission, after the first stage detaches, it is essentially a free test.

The company has also upgraded Falcon 9 to a new Full Thrust variant and boosted the Merlin 1D engine’s performance to make it one of the most efficient American-made hydrocarbon engines. None of that could have been done up front. It took many years from the Falcon 1 to today.

Paying for the Interplanetary Transport System

SpaceX Raptor with mach diamonds

Elon Musk tweeted this picture of SpaceX’s Raptor engine during its first test firing. Photo Credit: SpaceX

So who will pay for Musk’s next chapter of SpaceX history? No doubt Musk and SpaceX will go it alone if they have to, but they would likely not achieve the already ambitious timeline without some funding help – likely from NASA.

Right now, however, NASA isn’t interested in funding a commercial alternative to the Space Launch System or Orion.

As things stand now, SpaceX is allocating less than 5 percent of the company on ITS and spending only a few tens of millions.

Musk expects to spend more resources on the project as SpaceX finishes development of the final version of the Falcon 9 and Dragon 2 and get reusability of the Falcon 9 first stage and Dragon 2 sorted out.

“Within a year-and-a-half to two years, most of SpaceX will be on the system,” Musk said later in a question-and-answer session.

After that, Musk hopes the company will devote about $300 million a year to the project. Overall, he estimates the total developmental cost to be around $10 billion.

For the production vehicles, Musk estimates it would cost $230 million to build the booster, $130 million to build the tanker, and $200 million to build the spaceship. That means if the company just built one of each, it would be over a half-billion dollars.

Musk estimates that one flight to Mars using ITS could cost around $62 million, about the same as one Falcon 9 today.

To pay for the trip, after everything is developed and tested, Musk expects people to hand over less than $200,000 per person – a price he expects to lower as the system optimizes.

Funding Sources

However, as far as development funding goes, Musk wasn’t shy to say that there wasn’t much at the moment. In a slide, he showed funding sources ranging from launching satellites, sending cargo and astronauts to the International Space Station, Kickstarter to even stealing underpants.

The last option was a reference to an episode of Comedy Central’s South Park in which the main characters do a presentation on gnomes who steal underpants to make a profit – a three phase business plan with no visible path to success.

Musk said a lot of people in the private sector are interested in funding Mars bases, but he insisted that this would have to be a huge public-private partnership.

“That’s how the United States was established,” Musk said.

He said SpaceX is trying to make as much progress as it can with the limited resources it has available.

“I think as we show this is possible, that this dream is real, I think the support will snowball over time,” Musk said. “The main reason why I’m personally accumulating assets is in order to fund this.”

Video courtesy of SpaceX


Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a blog about the International Space Station, called Orbital Velocity. He met with members of the SpaceFlight Insider team during the flight of a United Launch Alliance Atlas V 551 rocket with the MUOS-4 satellite. Richardson joined our team shortly thereafter. His passion for space ignited when he watched Space Shuttle Discovery launch into space Oct. 29, 1998. Today, this fervor has accelerated toward orbit and shows no signs of slowing down. After dabbling in math and engineering courses in college, he soon realized his true calling was communicating to others about space. Since joining SpaceFlight Insider in 2015, Richardson has worked to increase the quality of our content, eventually becoming our managing editor.

Reader Comments

Great post! The best and more complete about this event I found on the net!

Too big to not fail…?

What a time to be alive.

I have no idea if ITS will be a success or not, and you know what? I don’t care. Success would be amazing, but even a failed ITS project is going to be a huge boon to human spaceflight in terms of new technologies and techniques. If my underpants will help in this venture, then send in the gnomes, Mr. Musk.

This was well received by the audience. Very impressive and extremely ambitious.

Kinda sad that the average person is walking around today w/ little, if any, care about what was quite possibly one of the biggest life-altering announcements in the history of human evolution.
Oh well… I guess that just leaves more legroom for the rest of us.
I already live near Boca Raton, FL, so it’s just nice to know that I’ll have a different retirement destination available when the time comes. 😉 Thanx Elon!

Maybe I’m being pedantic, but when I looked at some older plans for Mars colonies and after I watched the video for SpaceX’s ITS I did not see a hatch large enough or an alternative means for offloading big equipment or habitation modules, maybe like Bigelow’s.

Maybe I missed it during my casual viewing, there are probably more detailed plans or schematics somewehere..

As massive as this system appears, it doesn’t look like a lot of room for 100 colonists and supplies. But then, I’m the kind of guy that likes a lot of elbo room. I wish SpaceX much success in the years to come. It is indeed a great time to be alive. Now, if only others could get inspired by this as well. Time will tell.

I am very curious. I understand the “engine out” redundancy factor, but why so many small engines as opposed to fewer larger engines like the Saturn V. 42 engines seems like an awful lot of start-up requirements, with corresponding potential failure to start issues. But it would make for quite the impressive “dance floor”.

I am generally appalled though not surprised at the vitriol attacks on Elon Musk’s SpaceX business. Most of the criticism is unjustified and easily shown to be false. Mister Musk has done an enormous service to humanity in general by at the minimum shaking up the rocket launch services industry that is grossly overpriced, none innovative and displaying very little “rocket science”.
Even the SLS is nothing more than a bunch of old technology parts thrown together in a very expensive and slow manner giving an overpriced Saturn / Apollo capability.
Mister Musk have time and again done what was said to be impossible. Every brain on the planet said hypersonic retrograde thrusting was technically impossible as was landing on a platform at sea on a reusable first stage orbital launch vehicle.
Now SpaceX gives us at an unheard of low development cost the Raptor Rocket engine that performance is nothing less than extraordinary. The Merlin engine has the thrust to weight ratio higher than any rocket every made. The Raptor engine has three times the thrust as the Merlin at generally the same size. It must have a thrust to weight ratio that is astonishing.
Moreover a full flow staged combustion engine has never been made before. The chamber pressure is the highest of any rocket before it at 4371 psig and its reusable! Compare that with the chamber pressure champ up to this point, the RD-180 of 3,870 psig.
It was said the United States could not make a single staged combustion rocket engine of that performance because of the exotic metallurgy that only the Russian knew.
The Raptor 382 ISP compared with the vacuum ISP of the highly lauded RD-180 of 338 is also exceptional.
One should not forget that giant carbon composite fuel tank. It is important to remember that the Venture Star project was supposed to be the single stage to orbit replacement spacecraft for the shuttle. It was canceled after $1.5 billion because they couldn’t make the cryogenic carbon composite fuel tank work. Apparently SpaceX at a shoestring budget has made one much larger successfully.
I watch in awe Elon Musk and his team and expect truly great things.

Couldn’t have said it better.
Every governamental plan of human exploration now seems obsolete and primitive.
The world does not know the giant that is walking among us.
We are on the verge of an unprecedent transformation in our civilization.

NASA has launched more than 150 crewed missions while SpaceX hasn’t launched a single person anywhere. The comments fanboys have made about others, show an appalling lack of respect, especially considering SpaceX’s history over the past 14 months.
The company has lost 2 payloads in that period. This means the company and its fans have exactly zero right disrespecting others. You can talk trash after the Falcon 9 stops blowing itself and its customer’s payload up.
While fancy computer-generated graphics might spur you to make snarky comments, it ain’t launching nobody nowhere. SpaceX has accomplished great things, including landing its first stage on a ASDS out in the Atlantic and back at CCAFS. However, that doesn’t mitigate the fact that it has demonstrated it can only conduct a rate of launch of about 4 times per year. ULA trounces that at about 12 launches per year (and without blowing stuff up).
So before you bad mouth the work of others and talk about how giants are walking among us, you might want to work on launching something other than uncrewed cargo spacecraft and commsats. A giant might indeed be walking among us – but he’s fallen flat on his face twice in a little over a year.
I mean come on, at least have SpaceX launch one person to LEO before all of this talk about “transforming civilizations.”
You come across as either ill-informed or dishonest when your company suffered a massive setback just a month ago, and then try to talk down to others about how much better you think you are. Musk can show all the fancy CGI and PowerPoints he wants, but in the end all that imagery doesn’t resurrect the CRS-7 Dragon that’s sitting at the bottom of the Atlantic – or erase the scorch marks at SLC 40.

I think there is no need to be so upset about a simple comment. No one is being disrespectful about what has been done by anyone, but the new concepts of things that are being shown are way to inovative to not be exalted. Even though the fails that have happened, we cannot minimize the importance of the reusability that is proven to be feasible that no one ever tried and neither the giant feat that is the raptor configurations. What NASA has done to the human knowledge is something that will last forever in the history and every single effort that has been done by them has an enormous value. They can not be blamed by the lack of innovation since the government badly gives them money.
We must take Elon Musk as an example of courage and innovation because he is the one in the frontline when it comes to fails, fancy cg’s and dreams. I mean, come on, how many billionaires gives it’s face to say things like he…

No one is being disrespectful? What about Commander Bill’s comment: “Even the SLS is nothing more than a bunch of old technology parts thrown together in a very expensive and slow manner giving an overpriced Saturn / Apollo capability.” Typical SpaceX fan, rewriting reality and spinning lies out of truth.
Since the government “badly” gives them money? You must be referring to the fact SpaceX wouldn’t have accomplished any of what it has without all the funds NASA has paid SpaceX? Yeah, considering the attitudes of its fans, I think this is an honest assessment. Why should NASA fund the dreams of those who hate and bash them?
What the establishment has noted is SpaceX fans are ungrateful/disrespectful, even after their rockets blow themselves and their payloads to pieces. When you guys bad mouth NASA? You’re disrespecting the folks who’ve enabled SpaceX to accomplish all it has. When most groups encounter a spectacular failure like SpaceX has recently (twice) they don’t unveil plans to send people to Mars, Jupiter and Saturn and they certainly don’t talk smack like Commander Bill and others have.

the ITS can’t bring us to Mars but it’s good for a sci-fi movie 🙂

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