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Many Voices, One Freedom: United in the 1st Amendment

March 29, 2024

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With Monday’s Falcon 9 launch of 46 Starlink satellites designed to provide internet access to most of the Earth, SpaceX CEO Elon Musk demonstrates yet again that he really knows his stuff when it comes to operations in Low Earth Orbit (LEO). His perfection of the once-only-dreamed-of vertical landing rocket booster is also a demonstration of his genius. It is no exaggeration to say that billionaire Musk is invariably the smartest man in the room wherever he goes. 

But even brilliant people can sometimes be misled by their own enthusiasm. As we explained in “Will Humans Get to Mars Anytime Soon?,” part 1 of our America Out Loud Mars series, SpaceX’s plans to send the first humans to the red planet sometime in the 2020s is hopelessly impractical. Yes, we could send humans to Mars before the end of the decade, but they would all be dead by the time they got there. It is simply too far away to make such a trip until we have far more experience operating on the Moon and in other regions of space much closer than Mars.

And when we eventually do go, and we undoubtedly will at some point in the future, it would almost certainly not be following the simple mission architecture envisioned by Musk. SpaceX promotes a direct flight from LEO to the surface of Mars and then directly back to Earth (see figure below). While its simplicity is appealing, Texas-based mathematician Don Pauly has computed a far more energy-efficient way to get to Mars, one that requires much less fuel. According to Pauly’s calculations, Elon’s Starship mission architecture can only carry four tonnes of cargo to Mars and return to Earth. The method Pauly proposes promises 200 tonnes instead.

ITS System Architecture – Image: SpaceX

 

Pauly’s plan is to divide the Mars landing project into several sections to address the fuel and freight issues. SpaceX’s Starship will bring fuel, freight and parts up to LEO, where a freighter version of Starship will be assembled. As the freighter will be designed to travel in a vacuum, it will require only three engines (instead of six in Starships), may be made of thinner materials (as it will not require rapid acceleration or deceleration) and need not be streamlined. This will greatly reduce the propellant requirement and allow it to carry about 5 tonnes more freight. 

Starship will then return to Earth and serve as a shuttle for several more flights to deliver more of the same. After the freighter is constructed and fully fueled, it will be sent to L2, the Lagrange point in space on the far side of the Moon. The L2 area is a region where the gravity of the Sun, Moon and Earth combine to allow objects left there to remain in place. Eighteenth-century mathematicians Leonhard Euler and Joseph-Louis Lagrange discovered that there are five special points in space in a three-body system where a gravitational equilibrium could be maintained. L2, about 40,000 miles from the center of the Moon, as well as the four other Lagrange points, L1, L3, L4 and L5, in the Earth/Moon system, are demonstrated in the figure below.  

Location of Lagrange points in the Earth/Moon system (Sun to the left)

 

While the Lagrange points L4 and L5 are stable equilibrium points, in that an object placed in those places would stay there (with respect to the Earth and Moon), L2 is an “unstable equilibrium point.” This means that, similar to balancing a pencil on its point, keeping a spacecraft at L2 is theoretically possible, but any perturbing force will cause it to move away. Pauly explains, however, that only a very small amount of thrust, using only about 0.25% of the propellant load of a fully-fueled Starship, would be required to keep the spacecraft at L2 for a month. He believes that the ion drive for Musk’s Starlink satellites would also supply sufficient thrust.

The freighter will be left at L2 behind the Moon as a fuel and supply dump and will in turn be refueled. Other freighters will follow which will have been assembled and refueled in LEO by Starship and also moved to L2. Enough fuel will always be retained on L2 freighters to return to LEO.

When the first freighter at L2 is full of propellant, cargo and crew, it will be launched toward Mars at its first favorable orbital alignment with Earth. That occurs once every 778 days, or about 26 months and has a launch window of about one month. Besides Earth and Mars having to be in the right positions for launch, launching from L2 at about the time of Full Moon, when the Moon is directly opposite the Sun in the sky, has the advantage that the velocity of L2 in its orbit around Earth gives the spacecraft a “free” 1,163 meters per second boost on its way to Mars. Then, only an additional 1,805 m/s is needed to “climb” to Mars. It will take 238 days, or about 8 months, to reach Mars, following a trajectory such as in the animated gif below.

Typical 238-days Earth-Mars trajectory

 

Arriving in the vicinity of Mars, the spacecraft will land on Phobos, the closest satellite to the planet. As we explained in part one of this article, Phobos has a tiny gravity that will be useful for unloading freight, making it an ideal supply dump. The freighter must remain on Phobos for 540 days until Mars and Earth reach proper alignment for the return trip. During that 18-months, the crew will do construction work and grow food. Phobos will be turned into a propellant and food factory for visiting spacecraft. Future spacecraft can leave Earth with a one-way supply of propellant and food in order to carry more freight. 

When Earth’s and Mars’ orbits align, the crew will load samples of Phobos into their ship and return to L2 to exchange crews. Total round trip time will be 1,016 days or 34 months, during which time the supply dump at L2 will be replenished and the next Phobos shuttle prepared. 

Phobos regolith is expected to contain organic material from meteorites and will need to be examined by scientists on earth. Equipment will be designed that can turn these samples into methane and oxygen for spacecraft propellant. That equipment will be prepared for delivery on the next available freighter to Phobos. Phobos will then be turned into a fuel factory for visiting spacecraft. In fact, propellant can then be sent back to L2 in returning freighters which will reduce the amount of fuel that needs to be brought to L2 from Earth. This is important since, when bringing propellant up from the deep gravitational well of the Earth, most of the propellant is lost in this process.

With Phobos fully established as a supply depot, a manned Starship can then be sent from Earth to L2, refueled there and then launched to Phobos where it will be refueled and filled with food before going on to Mars. Its heat shields will protect it during atmospheric entry on Mars. The atmosphere of Mars is thick enough to burn up unprotected spacecraft but too thin for everything else, including parachutes.

The Mars astronauts should land in an area where ice is likely to be found and a nuclear power plant then is offloaded on the planet for use in propellant manufacturing. After gathering samples of the terrain, the crew can launch back to Phobos for refueling before flying back to the Earth. It is likely that water and carbon dioxide can be made into propellant more easily on Mars than by processing the organic material on Phobos. As we explained in part 1 of this article, plans to use solar panels to generate the huge amount of electrical power necessary to manufacture propellant on Mars is infeasible. To make enough liquid methane and oxygen on Mars in a year’s time requires 22,000 solar panels, weighing 220 tonnes, and about 100 tons of lithium batteries to provide power at night. A nuclear reactor weighing the same amount will make nearly 100 times the power. A practical nuclear reactor designed for spacecraft will weigh about 30 tonnes and put out 1 Megawatt of power. This will allow the manufacture of enough propellant to fill the tanks of a Starship in about five months. Nuclear power will also be required on the flight home for many purposes, not the least of which is a low-temperature cryocooler to keep the methane and oxygen below their boiling point to prevent the huge loss that would otherwise occur due to boil off.

There is no question that eventually traveling to and settling Mars offers huge benefits to the long-term survival of humanity. But it can only happen after we have established the necessary space infrastructure and have accumulated the many man-years of experience operating in deep space needed to carry out the mission safely. That said, there are plenty of exciting manned space missions that we can accomplish in the coming decades—living on the Moon, establishing a space station at the Lagrange points and even intercepting and landing on an asteroid during a close flyby of Earth—to keep the next generation of space travelers motivated to continue to go “when no one has gone before.”

MANY VOICES, ONE FREEDOM: UNITED IN THE 1ST AMENDMENT

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