A manned mission to Mars wouldn’t be like the Apollo mission to the Moon. It would require many more steps along the way to prepare crews plus develop and test the necessary technologies. After all, Mars is about 140 million miles (225 million km) from Earth (depending on where each planet is in its orbit) compared to the Moon, which is an average of 238,855 miles (384,400 km) from Earth. Mars is on the order of 500 times more distant. A round trip would take several years.

There would likely be missions to intermediate destinations, including Earth’s moon and the Martian moons. Each step would teach us and prepare us for the next, helping us meet challenges incrementally.

The satellite Rosetta snapped this photo of Mars from about 149,000 miles (240,000 km) away. Credit

Credit: ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA, CC BY-SA 3.0 IGO .

There are many but three stand out:

1. how to propel and power a mission on the way to and from Mars;
2. the protection of astronauts against radiation; and
3. the entry into orbit, descent, and landing on Mars.

Getting a spaceship to Mars doesn’t just mean using a bigger rocket than the one used to go to the Moon. Sophisticated, advanced propulsion systems will be needed to get spacecraft to Mars, land humans on the planet, get them back off Mars, and return them to Earth.

Powering that kind of system (without carrying too much weight on board) could draw on chemical, nuclear, or solar power, but all three options pose severe challenges. For example, nuclear reactors could both propel astronauts to Mars and power their spaceships. But there’s likely to be some opposition to launching nuclear reactors into space.

The Earth’s magnetic field protects people on the ground and in low Earth orbit from excessive radiation, but astronauts going to and from Mars would face much higher radiation levels. Shielding could protect them from charged particles given off by the Sun, but protecting astronauts from powerful cosmic rays would be much harder.

A human mission to Mars would probably require precisely landing a ship weighing many tons very close to food, fuel, and other materials sent to the planet in advance. The technology needed to do this doesn’t exist today, though experts are studying various concepts. If humans are to land on Mars before the middle of this century, development of such systems needs to begin soon.

Returning to the Moon and landing humans on the moons of Mars would demonstrate capabilities and improve technologies needed for the ultimate goal of sending humans to Mars.

In December of 1972, Apollo 17 astronauts Eugene Cernan (pictured) and Harrison Schmitt (barely visible in the reflection on Cernan’s helmet) were the last men to walk on the Moon. Credit

NASA / Harrison H. Schmitt

New missions to the surface of the Moon could develop many of the technologies needed to land people on Mars. It also would allow for scientific exploration that couldn’t be done during the Apollo program and would provide many opportunities for international and commercial cooperation.

Traveling to the moons of Mars would incorporate many of the features of a Mars mission without the challenge of descending to and ascending from the planet’s surface. For example, human health issues could be investigated to see if missions to Mars’ surface are possible.

Moving humans beyond low Earth orbit will almost certainly require partnerships among countries, given the resources required. Even then, national budgets for human space exploration would need to grow considerably faster than inflation. Most of all, success will depend on focus and commitment.

An artist’s concept of astronauts and human habitats on Mars. Credit

NASA

The United States has had a publicly funded human spaceflight program for more than half a century. But the program’s goals and mission plans have changed frequently, and there’s no national consensus on where the program should go.

A human mission to Mars would require a strong commitment among partner countries over a long period of time. Even so, there are likely to be shifts in national priorities and cooperative agreements over the decades. Thus, partners would also need to see value in achieving shorter-term goals in faster timeframes to stay interested and committed.