By Gary Deel, Ph.D., JD
Faculty Director, School of Business, American Military University
Last year, Elon Musk’s company SpaceX announced a grand vision to provide intra-planetary transportation services via daily commercial rocket launches around the world, just like airlines.
SpaceX is already in the testing phases for their newest — and largest — rocket, Starship (formerly Big Falcon Rocket or BFR). It is enormous, to say the least; the rocket weighs almost 10 million pounds and is 118 meters in height.
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SpaceX Intends Intra-Planetary Journeys to Moon and Various Planets
The original vision of Starship was to provide a new vehicle for a manned return to the Moon, and eventual voyages to other planets such as Mars. SpaceX is still planning to accomplish those goals, too.
However, Musk and SpaceX Chief Operating Officer Gwynne Shotwell revealed in September 2017 that they also plan to use the giant rocket for intra-planetary parabolic flights here on Earth. The idea would be to construct launch pads in major cities around the world, and Starship would then be used to make jump flights between them.
The rocket would launch vertically and land vertically. It would be designed to use retrorocket propulsion in the same way that SpaceX’s current Falcon 9 rockets return to Earth after launches.
Intra-Planetary Rocket Flights Would Slash Travel Time between Cities
The appeal of this business idea is obvious once you see the specs. Starship could make trips in minutes that would otherwise take passengers hours and hours by airplane flight.
For example, a trip from New York City to Shanghai takes more than 15 hours by plane. But with Starship, the same flight could (theoretically) be accomplished in 39 minutes — from liftoff to touchdown.
Musk and Shotwell have claimed that rocket flights on Starship could be priced competitively with conventional air travel. This idea has been met with skepticism by some people, but it is at least plausible with mass-market penetration.
How Long Would It Take for Rocket Trips to Be Affordable?
SpaceX estimates that Starship will be capable of carrying 100 or so passengers per trip, but it hasn’t commented specifically on what it thinks about how much initial fares will run. We can only speculate on how long it might take for prices to be reasonably affordable.
As a space enthusiast who actively roots for the advent of commercial spaceflight, I honestly think that cost concerns won’t be the biggest challenges this new industry will face. When SpaceX developed the first-ever reusable, first-stage boosters for their unmanned logistics contracts, this product completely revolutionized the cost floors on rocket launches.
Instead of discarding their rockets and spending $60M USD building new ones after each flight, SpaceX can now refurbish a recovered booster and re-fly it within mere days of a prior launch, and at a fraction of the replacement cost. I have confidence that this type of innovation will eventually bring affordability to commercial manned spaceflight.
Designing a Comfortable Flying Experience Would Be Challenging
However, the bigger challenge is probably designing a flight experience such that gravitational forces (G-forces) would not require passengers to undergo significant flight training before launch or avoid flying altogether. This problem could cripple the burgeoning industry before it ever gets moving.
One G is the normal gravitational pull we feel from Earth’s gravity every day (this is the normal baseline for living things on our planet). The amount of gravity to which we are exposed partially determines our weight. Suppose you weigh 150 pounds here at 1 G on Earth’s surface; you would obviously weigh less on the Moon where the gravity is weaker.
However, another factor that determines the G-force you feel is acceleration. We’re reminded of this force whenever we go up in an elevator.
The gravity of the Earth is obviously the same in an elevator as it is elsewhere. But when the elevator pulls us away from the Earth we feel a slightly stronger G-force for a brief instant, until the elevator finishes accelerating to its top speed.
Likewise, the opposite is also true when we go down in an elevator. There is a momentary acceleration toward the Earth as the elevator falls, and we feel a small reduction in G-force (that slight feeling of being lighter for a second or two).
This acceleration is really important. While elevators pose no significant concern for us, with greater accelerations come much greater problems.
The Saturn V rocket, the most powerful rocket mankind has ever developed, pulled as much as 4 Gs on launch. This means that astronauts felt as much as four times the normal pressure on their bodies during the ascension.
To put that another way, Neil Armstrong weighed approximately 165 pounds here on Earth at 1 G. But during the launch of Apollo 11, he felt as if he weighed 660 pounds. Imagine how uncomfortable that must have been.
Now, it’s not likely that commercial space rockets like Starship will be pulling 4 Gs. But even SpaceX’s workhorse Falcon 9 rocket routinely pulls between 2 and 3 Gs on average.
Gravitational Forces Exerted on Humans Have Their Hazards
The G-force needed for acceleration is a problem for several reasons. First, many people have medical conditions that would make exposure to these kinds of G-forces dangerous or even fatal. Weak hearts, blood pressure irregularities or pregnancies, for example, would all be major deal breakers for the kind of rocket-based travel that requires extreme acceleration changes.
Even for otherwise healthy people who would be medically cleared to participate in such flights, the extreme acceleration, deceleration, and feelings of weightlessness can commonly cause nausea, motion sickness, and even a loss of consciousness. People occasionally get sick or lightheaded on ordinary airplane flights where G-forces are minimal. One can only imagine what this effect would be like for passengers exposed to more violent flight dynamics.
Space tourists might look forward to the thrill of a powerful rocket ride or the feeling of weightlessness as part of the experience. However, a businessperson hopping aboard a rocket in Los Angeles because of the need to get to Berlin in an hour for a meeting probably wouldn’t feel the same way.
Professional astronauts train for months to prepare for space flight in order to condition themselves to overcome physical issues like motion sickness. But that kind of training is just not practicable for the average space traveler.
Imagine that you called Delta Airlines to book a flight today, and the agent advised you that you would first need to undergo flight training several hours a day for the next two to three months before you could make the trip. How likely would you be to buy the ticket then?
The interesting thing is that rockets do not have to pull extreme G-forces. One could, in theory, develop a rocket that accelerated much more slowly…for instance, no more aggressively than the airplanes we already ride in every day (which pull 1.2 to 1.3 Gs on average).
However, there are two drawbacks to this idea. First and foremost, such a rocket would take longer to achieve a lower maximum speed, and as a result, would not be able to get where it was going nearly as quickly. This delay would be a major disadvantage when the biggest appeal is obviously time savings.
Second, because such a rocket would take much longer to make the same flight, it would burn more fuel in the process. Due to its slower speed, the rocket may not be able to reach as high an altitude in its parabolic arc, which means more air resistance and more power (i.e. fuel) needed to overcome that resistance. This raises costs for travelers in an industry that already struggles to compete with the economies of traditional air travel.
These challenges are not insurmountable. However, they will require a thoughtful design of rockets and rocket engines to allow for accelerations that are tolerable for the average person (1.5-2 Gs or so) without the need for specialized skills, training, or medical screening.
Throttleable engines using liquid propellants could be programmed by computer to minimize G-forces in acceleration as dynamic atmospheric pressures change outside a rocket on ascent. A descent must be equally well-controlled so that feelings of weightlessness don’t lead to nausea and lightheadedness.
SpaceX’s Starship design is exciting, but they will need to work out how the giant Raptor engines that propel the craft will do so in a way that maximizes fuel efficiency without creating an uncomfortable ride. If Starship is to take off and land in the same orientation (i.e. engines facing down), then the rocket will inevitably have to ‘flip’ and re-orient itself at some point in the trajectory of its flights.
This transition — however brief — will inevitably be uncomfortable for a lot of passengers as they will experience some period of momentary weightlessness. Suffice it to say the ‘fasten seat belt’ sign will be illuminated, and passengers will not be free to move about the cabin.
SpaceX’s idea for intra-planetary rocket transit is exciting and worth pursuing. But if it is to be a viable competitor with traditional air travel, the passenger experience will have to be extremely well thought out in order to avoid alienating large demographics of travelers who would otherwise jump at the chance to ride rockets around the planet.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a JD in Law and a Ph.D. in Hospitality/Business Management. He teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.
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