This website is dedicated to studies of Mars and Moon technology and mission analysis. I am open to add work of others as well – Donald Rapp
KEY WORDS: Mars, Moon, space mission, propulsion, ISRU, system engineering
My credentials can be viewed here
Click on any link to see papers
Editorial:
Human missions to Mars - a topic that was studied 1,000 times (actually) and remains a chimera in PowerPoint. In the past, planetary missions were severely limited in mass and missions were planned to minimize mass sent to LEO. The advent of the SpaceX Starship that is reputed to be able to affordably land 100 metric tons on Mars will change all the rules. Instead of minimizing mass, the game is now to use mass to reduce complexity and risk, or to contemplate far more ambitious missions. SpaceX is making bold claims about sending a human crew to Mars via the Starship in the next few years but I have argued they can't do it, the main problem (among several) is producing 1,200 metric tons of propellant for the return trip from indigenous Mars water and CO2. I have proposed instead, a slimmed down mission using the Starship that does not require indigenous Mars water - a tremendous reduction in challenge, complexity and risk. My papers with links are listed at: https://www.drdrapp.com
2015 to 2018 was the tail end of an era when high costs to launch materiel into space made the central theme of space mission engineering reducing mass launched from Earth. The question of “take it or make it” then seemed to favor “make it”. That is, utilizing extraterrestrial resources to produce needed products (where possible) rather than bringing resources from Earth. Under the title “in situ resource utilization” (ISRU)” many engineers analyzed and developed processes and implementation procedures for utilizing Martian or lunar resources.
Starting around a decade ago, SpaceX brought down the cost of launching materiel into space with new launch vehicles, particularly the Falcon 9. This significantly changed the equation for “take it or make it”, raising the bar for potential use of ISRU. Meanwhile, insular ISRU enthusiasts continued to ignore this dramatic change and pursued ISRU approaches that were no longer competitive in the short run, although possibly useful in the longer run for very large missions.
Today, SpaceX is in the final stages of testing the huge “Starship” claimed to be capable of landing 100 metric tons on Mars at an extraordinarily low cost. When the Starship becomes operational, the entire field of ISRU will undergo a seismic shift, as competition from bringing resources from Earth turns out to be “faster, cheaper, better”. Some ISRU processes will remain worthwhile; others will fall by the wayside.
The advent of the Starship will change fundamental Mars and lunar mission design. Instead of minimizing mission mass, the guiding principle will be to use large amounts of mass to reduce risk, provide better crew support, improve efficiency, and allow more ambitious missions.
For lunar ISRU, the bar will be raised so high that no form of lunar ISRU is likely to be competitive with bringing resources from Earth. Current NASA plans for lunar ISRU, developed ten years ago, are no longer viable, and probably never were viable even when launch cost was higher.
The situation is more complicated for Mars ISRU. Over the period 2022-2023, the Mars “MOXIE” Project (of which I was one of five co-investigators) demonstrated conversion of Martian CO2 to O2 on Mars by electrolysis. This remains a viable form of Martian ISRU and I will report on that. Other, even more ambitious forms of Martian ISRU depend on use of accessible H2O on Mars. For some large Mars missions, finding and exploiting H2O on Mars is a necessity. In the last ten years, many new observations of H2O on Mars were made from orbit. I recently wrote a 70-page review of water on Mars that is now undergoing journal review. (link) However, finding accessible H2O on Mars at an acceptably low latitude remains a challenge. The entire field of ISRU is now undergoing massive change.
Get to the Moon and do what?
The plan to send a crew to the Moon was originated when it was believed that sending a crew to Mars was too ambitious and too costly to contemplate. NASA had to do something with astronauts so why not the Moon? In that same era, SpaceX was developing the Starship which could totally change the economics of sending huge loads to very interesting Mars, and they are pursuing that goal while NASA is engaged on a seemingly fruitless effort to land on the blah Moon.
Any plan to send a human crew to explore Moon or Mars requires (among many other things) tons of propellant to blast off from Moon or Mars for return to Earth. The highest energy propellants are stored cryogenically. Two propellants are needed: (1) a fuel, either methane or hydrogen, and (2) oxygen. Oxygen represents the greatest mass of propellant.
Martian ISPP has a much greater mission impact than lunar ISPP because it has much greater leverage. If ISPP were to replace all the oxygen ascent propellants on one liftoff from each planet, the mass saving in LEO per liftoff form the Moon would be about 10 to 13 tons, and about 240 to 300 tons per liftoff from Mars. The inherent value of Martian ISPP per liftoff far exceeds that for the lunar ISPP. Therefore, use of ISPP has a much greater impact on reducing mass on a Mars mission than it does on a lunar mission.
In addition to leverage, there is a great disparity between the challenges and complexity of lunar ISPP vs. Mars ISPP. Mars ISPP based on atmosphere only is relatively simple with high payoff. However, lunar ISPP is so challenging it might not even be technically feasible, and if it can be made feasible, the cost will be so high that the payoff may be nil compared to the cost, and the risk is high.
NASA is now embarked on a major initiative to return humans to the Moon whereas a human expedition to Mars is likely to be relegated to at least several decades in the future. As a result, NASA is heavily focused on unattractive lunar ISPP and has diminished interest in attractive Martian ISPP despite an extremely successful demonstration on Mars by MOXIE. Since the NASA Administrator outvoted the NASA system engineers and selected a "short stay" (without ISPP) concept as the current baseline for a human mission to Mars, Martian ISPP is not regarded as important by NASA. Yet, the short stay concept (aka "plant the flag and run") has almost all the risks of a long stay mission but almost none of the accomplishments. The short stay mission depends on nuclear propulsion which introduces a number of problems, some technical and some political. link
The NASA Administrator is a giant fan that blows a strong wind. The NASA system engineers are like weather vanes that align with the prevailing wind, despite their private doubts.
NASA also has some misconceptions about what they call the "Gateway" – a concept to use lunar produced propellants to send spacecraft throughout the solar system. But when the numbers are crunched, it doesn't work.
A great foundation was laid for Mars ISPP by the MOXIE Project. The field of solid-oxide electrolysis is active and burgeoning for terrestrial applications to climate control. NASA can leverage technology advances in that field at relatively moderate investment levels to further advance Mars ISPP. Yet NASA does not seem to have the intellect to appreciate this and continues to pursue a seriously problematic lunar ISPP program.
Editorial: The ultimate tautology
Why is NASA returning to the Moon?
To produce propellants
Why is NASA producing propellants on the Moon?
So it can return to the Moon
General Papers on Mars and Lunar ISRU
Papers related to the MOXIE Mars Project
Recent papers pertaining to Moon and Mars
Lunar-Derived Propellants for Fueling Mars-Bound Spacecraft in Cis-Lunar Space by Donald Rapp
Mars Ascent Propellants and Life Support Resources - Take it or Make it? by Donald Rapp
The Value of Utilization of Extraterrestrial Resources for Propellant Production for Space Exploration - A Perspective
by Donald Rapp