“This Starship is designed to traverse our entire solar system and beyond to the cloud of objects surrounding us. A future Starship, much larger and more advanced, will travel to other star systems.” ~ Elon Musk
SpaceX want to make us a multiplanetary species through colonizing Mars and have a stretch goal of going interstellar. Recently they performed a successful orbital test of Starship, their first Mars capable vehicle, yet building an interstellar vehicle would be an inordinate challenge even for a company as successful as SpaceX. Certainly there are some big questions attached to such a groundbreaking project which they’ll need to address: -
1. How could they fund such an ambitious project?
2. What architecture would they use for the interstellar vehicle?
3. Where will they build it?
4. When could we reasonably expect to see this project completed?
OK, given what we know about the technical challenges, SpaceX plans and capabilities, let’s try to divine their intent.
Interstellar Finance
Historically Elon Musk has used the companies he controls to finance all the new products they need for Mars. SpaceX designs and builds launch vehicles and satellite systems, Tesla produces surface vehicles, solar energy systems and AI androids, The Boring Company manufactures tunneling equipment for mining subsurface ice and excavating radiation proof habitats, Neuralink should allow colonists to communicate directly with each other and the Internet of Things (IoT). No doubt the non-SpaceX companies could assist in supplying some of the equipment but financing interstellar would lie far beyond their means. In monetary terms, trillions of dollars would be required which is too much to ask of any small private company or even a large public corporation like Tesla.
Likely the onus would be on SpaceX to provide interstellar transport, no doubt based on the colony ships they intend to use for Mars. However, once colonization commences it could consume all of SpaceX’s cash for decades; they intend to create a self sustaining city on Mars, which will likely cost trillions. Fortunately SpaceX’s Starlink service could generate up to $1tn in revenue per annum at software margins, which should be enough to cover Mars colonization.
“The total addressable market for launch, with a conservative outlook on commercial human passengers, is probably about $6 billion. But the addressable market for global broadband is $1 trillion. If you want to help fund long term Mars development programs, you want to go into markets and sectors that are much bigger than the one you're in, especially if there's enough connective tissue between that giant market, and what you're doing now.” ~ SpaceX President Gwynne Shotwell/Via Satellite
Interestingly SpaceX want Mars to be independent from Earth, ideally governed by direct democracy, with its citizens voting on important issues, likely via Neuralink. Essentially Mars will become the latest and greatest Musk enterprise, and no doubt hold him in high regard as their main benefactor. As the Mars colony finds its feet they could make a significant contribution to interstellar development by way of their technical expertise. SpaceX finances should have significantly improved by this time due to increased space utilization. Mass transit will have become established between the Earth, Moon and Mars, supported by their Starlink system, likely pushing SpaceX revenue beyond the $1tn mark. To illustrate the potential, SpaceX were awarded development contracts worth $1.8bn for Starshield and $2.89bn for the Human Landing System (HLS), suggesting the longterm revenue derived from actually operating these systems could be far higher.
Likely too in the longterm, the Mars colony should be better able to support itself due to its burgeoning local economy. This would allow SpaceX to redirect their financial support of the colony to the interstellar project, assuming SpaceX continue their trajectory of exponential space development.
Interstellar Architecture
An interstellar craft could take many decades to reach the nearest star systems, so effectively they will become space colonies with their own ecosystems and cultures. Of necessity each craft must be huge to carry all the necessary colony equipment and support a sufficiently diverse crew, consisting of hundreds of people to ensure genetic viability once they arrive.
Given the scale of these interstellar vehicles, SpaceX would need to construct them in space, such as in orbit around Mars. This would allow personnel, AI systems and sophisticated components to be supplied from the surface, and provide easy access to the moons Phobos and Deimos to source raw materials. Fortunately SpaceX manufacturing is already highly automated, which suggests they could build any scale of vehicle if these techniques can be adapted for space construction. The design of any space vehicle is built around the capabilities of its engines, hence the design of their interstellar vehicle would rely on the type of drive available.
"We're actually trying to get hold of some nuclear material [for work on nuclear propulsion] - it's hard, by the way" ~ SpaceX President Gwynne Shotwell/MIT
SpaceX have a longstanding interest in nuclear technology both for propulsion and power generation. Unfortunately they encountered significant regulatory roadblocks pursuing this technology and currently rely on NASA to provide Small Modular Reactors (SMEs) through their Kilopower program. Fortunately no such regulations will apply on Mars, where there is a plentiful supply of nuclear materials.
Using a fission engine to drive an interstellar vehicle should be feasible, assuming they employ a more advanced design of reactor. However, it might take centuries to reach the closest habitable planets, which implies these voyages could take generations to complete. Given these constraints the vehicle scale would likely be measured in kilometers and millions of tons – something far from ideal. The vehicle’s habitable section would be located some distance from the nuclear engines and require heavy shielding to protect its crew from ionizing radiation, suggesting such large vehicle mass is unavoidable.
“Focus Fusion generates a beam of ions that accelerates rapidly away from the central anode, and by rapidly we mean at around a thousand kilometers per second! That works out to around one million seconds of specific impulse, a measure of rocket engine efficiency.” ~ LPP Fusion
One possible alternative is nuclear fusion, and while there have been many false dawns, a number of private fusion projects have achieved promising results over the past decades. Perhaps in a few decades more, one of these efforts might produce a viable fusion engine capable of delivering ten times the power of a fission engine. In addition, if it uses an aneutronic fusion reaction, the engine would emit negligible radiation, making it far safer for transporting people. Even so the vehicle size would still be considerable, with interstellar journeys lasting the better part of a lifetime.
“I think that if we were to do interstellar travel then the best way to do it would be with an anti-matter drive, that would give you the best mass efficiency would be antimatter. But even in a best case situation, that's a very long journey even to get to Proxima Centauri.” ~ Elon Musk/IAC 2016
Antimatter could provide exponentially more power than fusion, potentially making interstellar vehicles far more practical. Potentially it could reduce journey time to decades and require significantly less propellant carried onboard the vehicle. They might even employ a Bussard ramjet which extracts hydrogen propellant from the interstellar medium in transit, potentially reducing the vehicle’s propellant mass to virtually zero. While antimatter is relatively rare on Earth and difficult to synthesize, antimatter particles are known to collect in the magnetospheres of planets, such as Earth’s Van Allen belt. Hence it should be possible to harvest these anti-particles using a spacecraft equipped with an electromagnetic scoop, assuming some means is found to refine and store them. However, the main drawback to using an antimatter engine is radiation, by definition antimatter annihilation is highly energetic, hence releases significant quantities of ionizing radiation. Again this implies the vehicle’s mass and size would need to be considerable to limit the crew’s exposure.
Ideally an interstellar transport vehicle would be capable of faster than light travel, potentially reducing transit time to years or even months. This might be possible with something like an Alcubierre drive which generates a wave in the fabric of space that’s used to surf to other star systems. This space wave isn’t physical hence can travel faster than the speed of light, and because space itself is moving the vehicle suffers no time dilation effects. However, the technical challenge of creating such a vehicle would be extraordinary, due to the amount of energy consumed by the Alcubierre drive, plus manipulation of dark energy or use of exotic materials. Considering these technical challenges, this might be something they wish to pursue after establishing numerous interstellar colonies, given a century or two of scientific and technologic advances.
Interstellar Facilities
“So as soon as we've got a base on Mars, we can see a base on the moon but certainly one on Mars, which creates a very powerful forcing function for making space technology better every year and that is what will lead us to interstellar travel.” ~ Elon Musk/IAC 2016
Elon Musk’s mission is to make humanity a multiplanetary species in the shortest time possible. Hence he intends to relocate to Mars in the next ten years to assist the colony building process. Normally he works to overcome the biggest bottleneck to his mission, and these will mostly be found on Mars as the colony experiences its first growing pains. No doubt thousands of quality personnel and engineers will follow him there to assist with this process, similar to when he moved to Boca Chica Texas during the early years of Starship development. Such a concentration of talent per capita will no doubt supercharge the colonization effort, allowing it to progress by leaps and bounds.
Mars will likely become a hotbed for technologic development, in response to all the problems they must solve from living in this new environment. They say: “if you want something done, ask a busy person” and no one will be busier than Mars colonists. Their space technology in particular will be par excellence if Mars become the transport hub for the solar system, which seems likely given its strategic advantages such as low gravity, thin atmosphere and proximity to the main asteroid belt. No doubt their orbital construction yards could be repurposed for an interstellar transport, essentially there’s no limit to vehicle size when you build in space.
As previously discussed, SpaceX will likely reduce their financial support to the Mars colony when it becomes better able to support itself as the local economy grows. Hence selecting Mars for the interstellar construction effort would help to mitigate the effect of reduced direct funding through supplying these funds indirectly.
Interstellar Schedule
“People tell us we’re crazy every day, but we need to ignore that and push forward. We are trying to find a breakthrough in propulsion technology that allows us to go beyond the Moon, beyond Mars, beyond the entire Solar System. Certainly, within 50 years we’ll have a path that will allow us to fly to other worlds.” ~ Gwynne Shotwell/CTECH
Gwynne’s prediction of 50 years to project completion sounds aggressive until you compare it to their other achievements. It only took them 5 years to develop booster landing and 10 years to launch Starship, a Super Heavy Lift vehicle with twice the power of the Saturn V moon rocket. Important to note they are always improving their internal processes to become more efficient and accelerate the speed of development. Overall a 50 year project duration seems quite conservative given all they achieved so far.
“It’s possible to make a self-sustaining city on Mars by 2050, if we start in 5 years & take 10 orbital synchronizations.” ~ Elon Musk
Creating a self-sufficient Mars colony by 2050, sounds overambitious without some step advance in space technology. However, in 50 years time, when large tonnage can be transported to Mars on a commercial basis, this should allow SpaceX to shift focus to its interstellar project. Seems a long time to wait but no doubt there will be plenty of preparatory work to look forward to in the interim.
In Conclusion
SpaceX’s plan to develop Starship into an interstellar spacecraft is ambitious, but they are probably in the best position to attempt such work. Their revenue should exceed NASA’s budget by 2025, and likely become an order of magnitude greater in the decades to follow. This should allow them to establish a vibrant Mars colony with negligible bureaucracy, regulations and taxation, which seems the ideal place to pursue such an ambitious project. Certainly if this effort requires large quantities of nuclear materials, antimatter or warping spacetime...it would seem wise to perform this work somewhere far from Earth.
Hopefully Elon Musk will be on hand to assist this project, accompanied by his cadre of ace engineers. Doubtless some advanced AI would be used for the design and construction process plus manage the complex ship systems, significantly reducing the overall challenge. While it might seem strange to rely on a large corporation to pursue such work, no doubt SpaceX will have evolved into something far greater in the next 50 years given their current trajectory.