Humanity is set on the idea of visiting Mars in person, but there’s the pesky problem of hazardous radiation during long-duration spaceflights to get there. Scientists have raised concerns about brain damage, gastrointestinal issues and cancer on a journey to the red planet.
The two major players are NASA and SpaceX, which work together intimately on missions to the International Space Station but have competing ideas of what a crewed Mars mission would look like.
The biggest challenge (or constraint) is the mass of the payload (spacecraft, people, fuel, and supplies) needed to make the journey.
A Hohmann transfer between Earth and Mars takes around 259 days (between eight and nine months) and is only possible approximately every two years due to the different orbits around the Sun of Earth and Mars.
Reaching the ISS from Earth takes less than a day. A trip to Mars might take nearly a year, and a huge amount of fuel. The chemical engines used to launch a rocket into space with a fiery blast are not good at propelling a spacecraft to another planet.
With no gas stations between Earth and Mars, “You pretty much have to take all your fuel with you,” says Bill Emrich. He’s a nuclear engineer with NASA at the Marshall Space Flight Center in Huntsville, Ala. “If you’re going to do that, you want an engine that’s going to get a lot of miles per gallon.”
For example, the Saturn V rocket that launched Apollo 11 to the Moon weighed 3,000 tonnes. But it could launch only 140 tonnes (5% of its initial launch mass) to low Earth orbit, and 50 tonnes (less than 2% of its initial launch mass) to the Moon.
A spacecraft could reach Mars in a shorter time (SpaceX is claiming six months) but you guessed it. It would cost more fuel to do it that way.
Return to Earth
Apollo 11 entered Earth’s atmosphere at about 40,000km/h, which is just below the velocity required to escape Earth’s orbit.
A spacecraft entering Earth is able to use the drag generated by interaction with the atmosphere to slow down. This allows the craft to land safely on the Earth’s surface (provided it can survive the related heating).
But the atmosphere on Mars is about 100 times thinner than Earth’s. That means less potential for drag, so it isn’t possible to land safely without some kind of aid.
The gravity on Mars is 38% of Earth’s (so you’d feel lighter) but the air is principally carbon dioxide (CO₂) with several percent of nitrogen, so it’s completely unbreathable. We would need to build a climate-controlled place just to live there.
The thin atmosphere on Mars means it can’t retain heat as well as Earth does, so life on Mars is characterized by large extremes in temperature during the day/night cycle.
Mars has a maximum temperature of 30℃, which sounds quite pleasant, but its minimum temperature is -140℃, and its average temperature is -63℃. The average winter temperature at the Earth’s South Pole is about -49℃.
Spacecraft designers would need to focus on shielding astronauts from SEP, but there would be a reduced impact from damaging GCR during solar maximum. The team also recommends keeping a Mars round trip to less than four years in duration, though the study acknowledges this could change based on the development of new shielding materials.
The travel time to Mars can vary (it took NASA’s Perseverance mission about seven months to get there), but there are a couple of prime times coming up in the mid-2030s and 2050 when shorter Earth-to-Mars journeys will coincide with periods of solar maximum. Hopefully that will help with your Martian vacation planning.