Feb 13, 2021 03:14 AM
https://arstechnica.com/science/2021/02/...ropulsion/
EXCERPTS: . . . That's a problem. NASA has a couple of baseline missions for sending four or more astronauts to Mars, but relying on chemical propulsion to venture beyond the Moon probably won't cut it. The main reason is that it takes a whole 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 humans-to-Mars mission still requires 1,000 to 4,000 metric tons of propellant.
[...] A new report from the National Academies of Sciences, Engineering, and Medicine offers some answers ... "One of the primary takeaways of the report is that if we want to send humans to Mars, and we want to do so repeatedly and in a sustainable way, nuclear space propulsion is on the path," said Bobby Braun, director for planetary science at the Jet Propulsion Laboratory and co-chair of the committee that wrote the report, in an interview.
[...] Nuclear propulsion requires significantly less fuel than chemical propulsion, often less than 500 metric tons. That would be helpful for a Mars mission that would include several advance missions to pre-stage cargo on the red planet. Nuclear propulsion's fuel consumption is also more consistent with the launch opportunities afforded by the orbits of Earth and Mars. During some conjunctions, which occur about every 26 months, the propellant required to complete a Mars mission with chemical propellants is so high that it simply is not feasible.
If NASA is to use nuclear propulsion in human missions during the 2030s, it must get started on technology development immediately, the report says. So far, the agency has been somewhat reticent to move quickly on nuclear propulsion. This may be partly due to the fact that the space agency is so heavily invested in the Space Launch System rocket and chemical propulsion needed for the Artemis Moon Program.
In recent years, therefore, NASA has not asked for nuclear propulsion funding. Congress has appropriated money for the effort anyway. In the fiscal year 2021 budget bill, NASA received $110 million for nuclear thermal propulsion development.
Braun said it would cost substantially 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.
[...] And what of the Starship concept that SpaceX is building to send humans to Mars? The project seeks to address the problem of needing a lot of chemical propellant by developing a low-cost, reusable launch system. SpaceX engineers know it will take a lot of fuel to reach Mars, but they believe the problem is solvable if Starship can be built to fly often and for relatively little money. The basic concept is to launch a Starship to orbit with empty tanks and transfer fuel launched by other Starships in low-Earth orbit before a single vehicle flies to Mars.
Braun said SpaceX is developing a plan to send humans to Mars with different assumptions than NASA. "I think there's a fundamental difference in the assumptions that NASA tends to make for what kind of infrastructure is needed at Mars," he said.
That's not to say Starship cannot work. However, it does illustrate the challenge of mounting a mission to Mars with chemical-only propulsion.... (MORE - details)
EXCERPTS: . . . That's a problem. NASA has a couple of baseline missions for sending four or more astronauts to Mars, but relying on chemical propulsion to venture beyond the Moon probably won't cut it. The main reason is that it takes a whole 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 humans-to-Mars mission still requires 1,000 to 4,000 metric tons of propellant.
[...] A new report from the National Academies of Sciences, Engineering, and Medicine offers some answers ... "One of the primary takeaways of the report is that if we want to send humans to Mars, and we want to do so repeatedly and in a sustainable way, nuclear space propulsion is on the path," said Bobby Braun, director for planetary science at the Jet Propulsion Laboratory and co-chair of the committee that wrote the report, in an interview.
[...] Nuclear propulsion requires significantly less fuel than chemical propulsion, often less than 500 metric tons. That would be helpful for a Mars mission that would include several advance missions to pre-stage cargo on the red planet. Nuclear propulsion's fuel consumption is also more consistent with the launch opportunities afforded by the orbits of Earth and Mars. During some conjunctions, which occur about every 26 months, the propellant required to complete a Mars mission with chemical propellants is so high that it simply is not feasible.
If NASA is to use nuclear propulsion in human missions during the 2030s, it must get started on technology development immediately, the report says. So far, the agency has been somewhat reticent to move quickly on nuclear propulsion. This may be partly due to the fact that the space agency is so heavily invested in the Space Launch System rocket and chemical propulsion needed for the Artemis Moon Program.
In recent years, therefore, NASA has not asked for nuclear propulsion funding. Congress has appropriated money for the effort anyway. In the fiscal year 2021 budget bill, NASA received $110 million for nuclear thermal propulsion development.
Braun said it would cost substantially 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.
[...] And what of the Starship concept that SpaceX is building to send humans to Mars? The project seeks to address the problem of needing a lot of chemical propellant by developing a low-cost, reusable launch system. SpaceX engineers know it will take a lot of fuel to reach Mars, but they believe the problem is solvable if Starship can be built to fly often and for relatively little money. The basic concept is to launch a Starship to orbit with empty tanks and transfer fuel launched by other Starships in low-Earth orbit before a single vehicle flies to Mars.
Braun said SpaceX is developing a plan to send humans to Mars with different assumptions than NASA. "I think there's a fundamental difference in the assumptions that NASA tends to make for what kind of infrastructure is needed at Mars," he said.
That's not to say Starship cannot work. However, it does illustrate the challenge of mounting a mission to Mars with chemical-only propulsion.... (MORE - details)