NASA
Getting people to Mars and back is quite difficult. Incredibly difficult in fact. Many challenges are faced by NASA and other would-be Mars pioneers in planning missions to the red planet, but the most important of them is the amount of propellant required.
During the Apollo program, 50 years ago, people went to the moon using chemical propulsion, that is, rocket engines that burned liquid oxygen and hydrogen in a combustion chamber. This has its advantages, such as giving NASA the ability to quickly start and stop an engine, and the technology was the most mature for space travel at the time. Since then, a few new propulsion techniques have been devised in space. But none are better or faster for humans than chemical propulsion.
That is a problem. NASA has some basic missions to send four or more astronauts to Mars, but relying on chemical propulsion to go beyond the moon probably isn’t enough. The main reason is that it takes a lot of rocket fuel to send supplies and astronauts to Mars. Even in favorable scenarios where Earth and Mars line up every 26 months, a human-to-Mars mission still requires 1,000 to 4,000 tons of propellant.
Consider this if it is difficult to visualize. When upgraded to its Block 1B configuration, NASA’s Space Launch System rocket will have a deadweight of 105 tons to low Earth orbit. NASA expects to launch this missile once a year, and the cost is likely to be around $ 2 billion for flights. So getting enough fuel into orbit for a mission to Mars would require at least 10 launches of the SLS rocket, or about a decade and $ 20 billion. Just for the fuel.
The bottom line: If we’re going to Mars, we’ll probably have to think about other ways to do it.
Going nuclear
A new report from the National Academies of Sciences, Engineering, and Medicine offers some answers in two such ways. Conducted at the request of NASA, a broad committee of experts assessed the feasibility of two propellants – nuclear thermal and nuclear electric – for a human mission launched to Mars in 2039.
“One of the main takeaways from the report is that if we want to send humans to Mars, and we want to do it repeatedly and sustainably, nuclear space propulsion is underway,” said Bobby Braun, director of planetary science. at the Jet Propulsion Laboratory and co-chair of the committee that wrote the report, in an interview.
The committee was not asked to recommend a particular technology, each of which relies on nuclear reactions, but works differently. Nuclear thermal propulsion (NTP) involves a rocket engine in which a nuclear reactor replaces the combustion chamber and burns liquid hydrogen as fuel. Nuclear electric propulsion (NEP) converts heat from a nuclear fission reactor into electrical energy, such as a terrestrial power plant, and then uses this energy to produce thrust by accelerating an ionized propellant such as xenon.
“If you look at the committee’s recommendations for NTP, we thought an aggressive program, based on the fundamental work that has been done recently, could get us there,” Braun said of the Mars 2039 goal. “For NEP we felt it was unclear whether such a program could get us there, but we didn’t come to the conclusion that it couldn’t get us there. “
Nuclear propulsion requires significantly less fuel than chemical propulsion, often less than 500 tons. That would be useful for a Mars mission that would include several forward missions to prepare cargo for the red planet. The fuel economy of nuclear propulsion is also more in line with the launch capabilities offered by the orbits of the Earth and Mars. During some conjunctions, which occur approximately every 26 months, the propellant required to complete a Mars mission with chemical propellants is so high that it is simply not feasible.
A plan for NASA
In the 2030s, if NASA wants to use nuclear propulsion on human missions, it must immediately begin developing technology, the report said. So far, the agency has been somewhat reluctant to move quickly to nuclear propulsion. This may be due in part to the fact that the space agency has invested so heavily in the Space Launch System rocket and the chemical propulsion required for the Artemis Moon program.
Therefore, NASA has not solicited funding for nuclear propulsion in recent years. Regardless, Congress has allocated money for the effort. In fiscal year 2021, NASA received $ 110 million for the development of nuclear thermal propulsion.
Braun said it would cost significantly more – at least an order of magnitude – for NASA to work with the Department of Energy and other parts of the government to develop this technology and begin cargo flights to Mars in the mid-2030s. However, he said this is the kind of project that NASA would be well positioned to undertake.
“It’s the kind of technology challenge NASA was built for, and it’s the kind of technology challenge our country expects NASA to overcome,” Braun said. You know, all the way back to the Apollo program, this is the kind of thing that NASA was made for. So I think they could do it. ‘
Starship
And what about the spaceship concept SpaceX is building to send humans to Mars? The project seeks to address the issue of requiring a lot of chemical propellant by developing a low-cost, reusable launch system. SpaceX engineers know that it takes a lot of fuel to get to Mars, but they believe the problem can be solved if Starship can be built to fly often and for relatively little money. The basic concept is to orbit a spaceship with empty tanks and transfer fuel launched by other starships into low Earth orbit before a single vehicle flies to Mars.
Braun said SpaceX is developing a plan to send humans to Mars with assumptions different from NASA. “I think there is a fundamental difference in the assumptions NASA tends to make for the kind of infrastructure needed on Mars,” he said.
That’s not to say Starship can’t work. However, it illustrates the challenge of setting up a mission to Mars using only chemical propulsion. To use traditional propulsion, you need to push the limits of reuse and heavy lift rockets to the limit – which is exactly what SpaceX is trying to do with its fully reusable launch system.