Mining and Refueling in Space

Introduction

Fig. 1: - Asteroid Mining Concept from the 1970s. (Source: Wikimedia Commons. Courtesy of NASA)

As interest in space exploration grows more and moreover the years, and the exciting new age of space race among the privatized corporations, humans are undoubtedly going to explore more and more of the final frontier. To both explore and habitat space and other planets, conventional rocket launch from Earth seems less and less economically feasible for longer space missions. There are significant interests about and reasonings behind manufacturing propellant and refueling in space. This concept has been brought up and studied as early asin the 1970s as shown in Fig.1. In this article, I want to show why this concept makes sense economically, and what the current state of the arts are, and where we are headed.

Launching Things into Space is Very Expensive

The most expensive part of any rocket launch is the initial portion where the rocket goes through the atmosphere of the Earth. For example, the most iconic and powerful rocket that humans ever build to this date is the Saturn V, which is used for all the NASA Apollo missions. The Saturn V has a total mass of 2,970,000 kg but is only capable of delivering 140,000 kg of payload to the Low Earth Orbit (LEO). There is a total of three stages of the rocket. The first and Second stage was used purely to accelerate the rocket close to the escape velocity of the Earth. The third stage was used to finish the boosting and fly to and back from the Moon. In this calculation, we are only going to calculate the amount of fuel spent in the first two stages, as the best-case scenario. The first stage carries 770,000 liters of kerosene fuel and 1,200,000 liters of liquid oxygen. The second stage carries 984,000 liters of liquid hydrogen fuel and 303,000 liters of liquid oxygen. [1] Kerosene has a density of 0.8201 kg/liter, liquid oxygen has a density of 1.141 kg/liter, liquid hydrogen has a density of 0.071 kg/liter:

This gives a fuel mass fraction of

Thus about 78 percent of the total mass of Saturn V was used to escape the Earth's atmosphere.

Alternative

To solve this issue, refueling in space is a promising concept for future space travel. Other celestial bodies often have an abundant source of water-ice. Water can be decomposed into hydrogen and oxygen via electrolysis. And both ingredients can be combusted for rocket propulsion. Recently a lot of proposals and studies have been done on using the Moon as a fuel station, to manufacture rocket fuel with the ice thats in the polar region of the Moon. This will act as an intermediate gas station between the Earth and the Moon, and more lunar related human exploration and habitant are being planned and proposed. One study found that processing lunar water into rocket propellant could be generating $2.4 billion in revenue annually. [2] This concept could be easily expanded to other celestial bodies such as Mars, or even asteroids to create a network of gas station in space for interplanetary travel.

Current Technology

Here is a review of current proposed ways and technology that could achieve the goal of turning ice into rocket fuel. The main difficulty is the mining portion of the operation as the processing mainly relies on electrolysis which is a well-understood process. Giner Labs currently has a very lightweight, high-pressure water electrolyzer technology that can produce dry oxygen and hydrogen at a pressure of up to 80 bars. [3]

There are various proposed means of mining ice. They are usually divided into two subcategory, active mining, and passive mining. Active mining methods includes drills mounted on rovers and subsurface heating and extraction. [4,5] Passive mining methods include thermal mining, where the heat is applied directly on the surface via concentrated sunlight to sublimate ice into vapor, then captured in ice form through cold traps. [6]

Conclusion

In order to keep expanding human exploration in space, the ability to manufacture propellent in-situ is necessary. A good experimental test ground for these technology developments is the moon, as NASA is eyeing the return of humans to the closest celestial body to us. In the future, these technologies will be used not only on the moon, on the planets we are trying to expand to and inhabit, but also on smaller celestial bodies such as asteroids, to form a network of "gas station" in space, acting as the cornerstone of interplanetary travel.

© Tony Chen. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] "Technical Information Summary AS-501 - Apollo Saturn V Flight Vehicle," U.S. National Aeronautics and Space Administration, A-ASTR-S-67-65, September 1967.

[2] D. Kornuta et al., "Commerical Lunar Propellant Architecture: A Collaborative Study of Lunar Propellant Production," Reach 13, 100026 (2019).

[3] S. Li et al., "Direct Evidence of Surface Exposed Water Ice in the Lunar Polar Regions," Proc. Natl. Acad. Sci. (USA) 115, 8907 (2018).

[4] K, Zacny et al., "Volatile Extractor (PVX) For In-Situ Resource Ultilization (ISRU)," Planetary Science Vision Workshop, 2017.

[5] A, Colaprete et al., "An Overview of the Lunar Crater Observation and Sensing Satellite (LCROSS)," Space Sci. Rev. 167, 3 (2012).

[6] G. F. Sowers and C. B. Dreyer, "Ice Mining in Lunar Permanently Shadowed Regions," New Space 7, 235 (2019).