“Starship is now more than twice as powerful as the Saturn V Moon rocket and, in a year or so, it will be three times as powerful at 10,000 metric tons of thrust. More importantly, it is designed to be fully reusable, burning ~80% liquid oxygen and ~20% liquid methane (very low cost propellant). This enables cost per ton to orbital space to be ~10,000% lower than Saturn V. Starship is the difference between being a multiplanet or single planet civilization. Building a new world on Mars is now possible.” ~@elonmusk

A nuclear engine would be very beneficial when available.  Presumably, it would add the capability of continuous power output for many years enabling continuous acceleration when in space and thereby shortening the trip time and trip cost compared to CH4+O2, and then power for deceleration to enter Mars orbit.  In contrast, CH4 and O2 fuel would need to be used more conservatively to achieve an optimal Mars orbital velocity but no more than that.  Once that velocity was achieved, then the main CH4+O2 engines would need to shut down and the Starship would essentially coast with only internal power for life support and guidance correction power operating during the much longer trip between the Earth launch window and the Mars orbit to conserve precious CH4+O2.  Taking the nuclear power plant to Mars surface, the powerplant’s energy could be used to produce oxygen, methane and other needed chemicals from the abundant CO2 in Martian atmosphere, soil, as well as the crew’s waste, especially waste and recycled water.   Given Elon’s time frame, it would appear that he must be planning already for small fission reactors, not on yet to be proven small fusion reactors.   

Elon Musk, many other people and I would answer the question “why go there?” by saying that the human race must become multiplanetary.  It’s one of those destiny questions like, “To be, or not to be?”  “Not to be” is fatalistic, deterministic. Not acceptable or even realistic to me. Freedom is our God-given destiny.  “To be” means free and self-determined.  Some are free and will want to be free while residing on Earth, some will want to be free and explore.  Secondly, it assuages the intrinsically human need to explore to know more, like Magellan, Columbus, etc.  

SpaceX is exploring the use of nuclear power for future Mars missions. In 2019, NASA awarded SpaceX a contract to develop a nuclear power source for the Artemis program, which aimed to return humans to the Moon by 2024 and establish a sustainable presence on the lunar surface.

Nuclear Power Options: 

SpaceX is reportedly considering several nuclear power options, including:

• Small Modular Reactors (SMRs): Compact, lightweight reactors that can provide a reliable and efficient source of power.  Seems to me to be a good area to explore for Earth bound transportation, EV’s etc too; better than lithium. 
• Radioisotope Thermoelectric Generators (RTGs): Similar to those used in NASA’s Curiosity Rover, these convert the heat generated by radioactive decay into electricity.

Benefits:

• Long-term power: Nuclear power can provide a reliable and long-lasting source of energy for Mars missions.in space
• Reduced reliance on solar panels: Nuclear power can operate during periods of low sunlight or dust storms on Mars.

SpaceX is exploring the use of solar sails, also known as solar photon sails or light sails, for its Mars missions. Solar sails use the pressure of solar photons to propel a spacecraft, providing a lightweight and efficient means of propulsion.  Like a nuclear powered engine, solar sails could also provide continuous power for continuous acceleration and shorter trip times. 

Solar Sail Concepts:

SpaceX is investigating several solar sail concepts, including:

• Starship’s Solar Sails: The Starship spacecraft, designed for lunar and Mars missions, may incorporate solar sails to provide additional propulsion.

Benefits:

• Increased efficiency: Solar sails can provide a significant increase in propulsion efficiency, especially for long-duration missions.
• Reduced mass: Solar sails are lightweight, reducing the mass of the spacecraft and enabling more efficient transportation, compared to carrying fuel for similar acceleration.

Challenges:

• Solar sail size and deployment: Large solar sails require complex deployment mechanisms and may be vulnerable to damage during launch and operation.  A difficult to sense swarm of tiny meteorites could destroy it.  Back propulsion needed.
• Solar sail material: The material used for the solar sail must be lightweight, durable, and resistant to radiation, extreme temperatures, and high speed particles.

With the addition of nuclear power at the Martian surface, there is already sufficient material, gravity and incoming solar energy on Mars for terraforming, which is not the case on Earth’s moon so far as we know today.  Mars atmosphere is much more concentrated in CO2 that Earth’s.  The CO2 atmospheric concentration on Mars is approximately 95% by volume; this is very useful for many things as a chemical precursor but of course is not breathable even with the addition of sufficient oxygen.  CO2 + hydrogen + nitrogen and abundant energy gives you ammonia for fertilizer and all sorts of plastics.  Already H2O has been discovered on Mars. The NASA Perseverance rover found evidence of past water on Mars, including signs of ancient rivers, lakes, and even an ocean.  If those oceans resembled Earths, there could be relative abundant uranium dust.  The rover has also detected water ice at the Martian poles and mid-latitudes.  Nitrogen gas has been detected, making up about 2.7% of the Martian atmosphere by volume.  The essential elements of life are there, but in very different abundances than earth.

Surface gravity on Mars is approximately 38% of the surface gravity on Earth, with an average gravitational acceleration of 3.72076 m/s^2. This means that if you weigh 100 pounds on Earth, you would weigh only about 38 pounds on Mars; this becomes a critical factor.  Weight has advantages and disadvantages for life on Mars with regard to terraforming and humans and animals living on the surface.  Most likely a dome or a sealed cave would be needed to create atmospheric conditions for humans, as well as space suits for sufficient air pressure, breathable air, radiation protection and temperature control.  Mars’ atmosphere is thinner (I.e., shorter distance between surface and space) than Earth’s because it has a weaker magnetic field, which allows solar winds to strip away Mars’ atmospheric gases.  Somewhat counterintuitively, Mars has higher atmospheric concentrations of Ar, He, H2 than Earth because Mars’ atmosphere is thinner and less of these gases have been stripped away by the constant cosmic ray flux at the outer edges of Mars’ atmosphere.  He could be useful for nuclear applications and transportation, Argon as an thermal insulator, and H2 as a reactant gas.

According to an Insolation – Energy Education article, the average solar insolation on Earth is around 4-5 kWh/m^2 per day.  But, comparing solar insolation of Earth versus Mars is a more complex calculation than it may seem at first look.  The average solar insolation on Earth’s surface is approximately 343 W/m², which is equivalent to the solar constant (1370 W/m² or 1 AU) spread out over the entire planet semi-sphere due to the Earth’s rotation and reduced by the angle of incidence; but this averaged calculation is not very useful for a man or growing a plant at a specific point on Mars’s smaller surface area.  The comparison is not as simple as reducing insolation at Earth’s surface by the inverse square law and the Mars’ increased distance from the sun and reducing the area and angle of incidence.  Near the equators of both planets, insolation is more concentrated and less concentrated at the poles.  Earth’s atmosphere is much thicker and contains much more clouds than Mars’ atmosphere, and those high Earth clouds especially reflect more solar radiation.  The thinner Mars atmosphere allows relatively more radiation at all wavelengths to reach the surface, including the more dangerous ionizing radiation; Earth’s atmosphere absorbs and scatters more before it reaches the surface.  This could be a life-saving difference in the case of solar flares and non-solar cosmic rays.  I would rather find and rely on measurement from the Mars Rover. 

Cosmic rays are high-energy particles that originate from outside the Earth’s atmosphere, primarily from solar flares, supernovae, and other astrophysical sources. They can include a variety of particles, such as protons, electrons, and heavy ions, as well as gamma rays and neutrinos.  Cosmic rays are a significant concern for astronauts on the International Space Station and presumably will be during deep space missions or planetary surfaces. The radiation levels can be high and cancer-causing levels especially during flares and coronal mass ejections, supernovae, etc.  (Presumably, flights from Earth to Mars would always be designed to travel farther away from the sun, and never be a secant curve route inside Earth’s orbit around the sun.)  Is there a way to capture cosmic rays and convert them into an energy source in space or on the surface of a planet with thin or no atmosphere?   

Assuming fission energy will eventually be available on Mars, and trace uranium is recoverable there as it is from soil and ocean here, then the more practical problem for living on Mars may well be due to its lower gravity.  Since humans would weigh much less on Mars, lengthy stays with no artificial gravity on the surface will drastically and eventually permanently change human, animal and plant body structures, especially muscle and bone density and strength.  Humans and animals who stay long may not be able to return.  Oops!  There may be reproduction issues.  Oops. 

That’s enough Martian dreaming for today.  Perhaps you enjoyed the ride as much as I did.

Bud