Boldly go

Since the last moon landing, NASA built the Space Shuttle, partnered with other countries to build and staff the International Space Station, and wasted more than a $100 billion on nonreusable large rockets, currently called Space Launch System. NASA has also led in planetary science with probes that have outperformed and produced great scientific data at relatively low costs.

Then there was Elon Musk. Not having gotten the memo that you must throw away the biggest and most expensive part of your rocket, the first stage, Musk, a South African-American entrepreneur, built a reusable booster, Falcon 9, which transformed the economics of spaceflight. The more powerful Falcon Heavy first flew six years ago. Every few months another SpaceX Starship launches from the Texas coast on the world’s largest booster, Super Heavy, designed to take more than 100 tons into Earth orbit, with Starship intended to eventually voyage to the Moon and Mars.

Musk’s SpaceX, Jeff Bezos’s Blue Origin, and other private innovators are the future of human space flight and space settlement. To understand that future, we need to understand a few things: Delta-V, the rocket equation, distances, what it takes to live in space, space resources, and space economics.

In space travel, the fundamental measure of the difficulty of getting from one place to another is Delta-V, the change in velocity required. Earth’s gravity is the most formidable obstacle, like being in a deep well, requiring a Delta-V of more than 9 kilometers per second to get to LEO, low Earth orbit, when atmospheric drag and gravitational drag during ascent are factored in. In Delta-V terms, it is easier to reach the Moon’s surface from LEO than it is to travel the few hundred vertical kilometers to orbit.

The rocket equation describes the diminishing returns inherent for chemical rockets. Each added kilo of rocket fuel must push upwards not only the rocket body and any upper stages, but also the other fuel already on the rocket. As the needed Delta-V is greater than the best specific impulse (effective exhaust velocity) of the burning fuel, the mass that can be pushed into orbit is a small fraction of total mass at launch.

Distances in space are daunting, 384,000 kilometers to the Moon, 55 million kilometers to Mars at closest approach, and hundreds of millions of kilometers to the asteroids. Other star systems, 40 trillion kilometers or farther, are out of reach. Delta-Vs for planetary journeys are attainable, but travel times are long, nine months to Mars in an efficient Hohmann transfer orbit.

Space voyaging and living is nothing like when Europeans traveled to the New World of the Americas, which was still a hospitable environment. We only survive in space when we have a functioning small bit of Earth around us: regulated temperatures rather than boiling or freezing, breathable air rather than deadly vacuum, and either a small ecosystem to regenerate air, food, and water or constant resupply from an external source. For longer-term survival, humans require significant gravity or artificial gravity in spinning habitats and significant shielding from deadly radiation. All of this must be highly reliable or humans in space will die.

For such an arduous and expensive endeavor there should be worthwhile reasons. The space equivalent of the ancient Spice Trade may be the asteroid 16 Psyche, 222 kilometers wide and mostly metal, perhaps including huge quantities of gold, platinum, and other metals scarce and expensive on Earth. Closer to home, space company Interlune is developing Helium-3 mining systems for the Lunar south pole.

We will settle the Moon before Mars, as it is three days away rather than many months away. Luxury space tourism creates sufficient demand for initial settlements in orbiting space stations and on the Moon. Some specialized manufacturing may benefit from zero-gravity in space. Space solar power beamed to Earth is probably uneconomical but is being tested. Space-based shielding of sunlight at the Lagrange One point appears too expensive in initial designs, but is worth studying as a way to reduce global warming.

Space economics is like yacht economics: “If you have to ask, you can’t afford it.” It costs more than a $1 billion per year per person on the International Space Station. The good news is that launch costs have dropped from around $20,000 per kilo to $1,500 per kilo with Falcon Heavy and may be less than $300 per kilo when Starship is operational. A 70-times reduction in launch costs is very good news for space travel, space business, and space settlement. The economies of scale that result when a hundred Starships are flying, along with competing ships from other companies, will reduce costs further.

Space is the hardest thing that humanity has ever attempted, but it can be done. In the next century we will settle in space, on the Moon, on Mars, and among the asteroids. Let’s boldly go!