Joel S. Levine, William & Mary

NASA plans to send humans on a scientific round trip to Mars potentially as early as 2035. The trip will take about six to seven months each way and will cover up to 250 million miles (402 million kilometers) each way. The astronauts may spend as many as 500 days on the planet’s surface before returning to Earth.

NASA’s Artemis program plans to return humans to the Moon this decade to practice and prepare for a Mars mission as early as the 2030s. While NASA has several reasons for pursuing such an ambitious mission, the biggest is scientific exploration and discovery.

I’m an atmospheric scientist and former NASA researcher involved in establishing the scientific questions a Mars mission would investigate. There are lots of mysteries to investigate on the red planet, including why Mars looks the way it does today, and whether it has ever hosted life, past or present.

Mars geology

Mars is an intriguing planet from a geological and atmospheric perspective. It formed with the rest of the solar system about 4.6 billion years ago. Around 3.8 billion years ago, the same time that life formed on Earth, early Mars was very Earth-like. It had abundant liquid water on its surface in the form of oceans, lakes and rivers and possessed a denser atmosphere.

While Mars’ surface is totally devoid of liquid water today, scientists have spotted evidence of those past lakes, rivers and even an ocean coastline on its surface. Its north and south poles are covered in frozen water, with a thin veneer of frozen carbon dioxide. At the south pole during the summer, the carbon dioxide veneer disappears, leaving the frozen water exposed.

Today, Mars’ atmosphere is very thin and about 95% carbon dioxide. It’s filled with atmospheric dust from the surface, which gives the atmosphere of Mars its characteristic reddish color.

Scientists know quite a bit about the planet’s surface from sending robotic missions, but there are still many interesting geologic features to investigate more closely. These features could tell researchers more about the solar system’s formation.

The northern and southern hemispheres of Mars look very different. About one-third of the surface of Mars – mostly in its northern hemisphere – is 2 to 4 miles (3.2-6.4 kilometers) lower in elevation, called the northern lowlands. The northern lowlands have a few large craters but are relatively smooth. The southern two-thirds of the planet, called the southern highlands, has lots of very old craters.

Mars also has the largest volcanoes that scientists have observed in the solar system. Its surface is peppered with deep craters from asteroid and meteor impacts that occurred during the early history of Mars. Sending astronauts to study these features can help researchers understand how and when major events happened during the early history of Mars.

Asking the right questions

NASA formed a panel called the Human Exploration of Mars Science Analysis Group to plan the future mission. I co-chaired the panel, with NASA scientist James B. Garvin, to develop and assess the key scientific questions about Mars. We wanted to figure out which research questions required a human mission to address, rather than cheaper robotic missions.

The panel came up with recommendations for several important scientific questions for human investigation on Mars.

One question asks whether there’s life on the planet today. Remember, life on Earth formed about 3.8 billion years ago, when Earth and Mars were similar-looking planets that both had abundant liquid water and Mars had a denser atmosphere.

Another question asks what sort of environmental changes led Mars to lose the widespread, plentiful liquid water on its surface, as well as some of its atmosphere.

These questions, alongside other recommendations from the panel, made it into NASA’s architectural plan for sending humans to Mars.

How do you get to Mars?

To send people to Mars and return them safely to Earth, NASA has developed a new, very powerful launch vehicle called the Space Launch System and a new human carrier spacecraft called Orion.

To prepare and train astronauts for living on and exploring Mars, NASA established a new program to return humans to the Moon, called the Artemis program.

In mythology, Artemis was Apollo’s twin sister. The Artemis astronauts will live and work on the Moon for months at a time to prepare for living and working on Mars.

The Space Launch System and Orion successfully launched on Nov. 16, 2022, as part of the Artemis I mission. It made the Artemis program’s first uncrewed flight to the Moon, and once there, Orion orbited the Moon for six days, getting as close as 80 miles (129 kilometers) above the surface.

Artemis I splashed back down to Earth on Dec. 11, 2022, after its 1.4 million-mile (2.2 million-kilometer) maiden journey.

Artemis III, the first mission to return humans to the lunar surface, is scheduled for 2026. The Artemis astronauts will land at the Moon’s south pole, where scientists believe there may be large deposits of subsurface water in the form of ice that astronauts could mine, melt, purify and drink. The Artemis astronauts will set up habitats on the surface of the Moon and spend several months exploring the lunar surface.

Since the Moon is a mere 240,000 miles (386,000 km) from Earth, it will act as a training ground for the future human exploration of Mars. While a Mars mission is still many years out, the Artemis program will help NASA develop the capabilities it needs to explore the red planet.

Joel S. Levine, Research Professor, Department of Applied Science, William & Mary

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Kabindra Shakya, Villanova University and Aimee Eggler, Villanova University

The air quality in the City Hall subway station in downtown Philadelphia is much worse than on the sidewalks directly above the station. That is a key finding of our new study published in the Journal of Exposure Science & Environmental Epidemiology.

We are an environmental scientist and a biochemist who assessed the air quality at the 15th Street-City Hall station in Philadelphia. We focused on this station because our previous study found it to have the highest levels of particulate matter among 12 Philly subway stations we measured on the busy Market-Frankford or Broad Street lines.

Most concerning, we found that there was about 10 times more black carbon inside the station than at street level. Black carbon, which is commonly called soot, is a major component of fine particulate air pollution. It is emitted from incomplete combustion of fossil fuels and biomass burning, and inhaling it is associated with adverse health effects such as asthma, heart attacks and lung cancer.

Our findings suggest that the black carbon is being generated by the subway system itself. Graphite used on brake pads is one potential source.

We also found that levels of ultrafine particles, or UFP, were about 1.7 times higher underground than above ground. While fine particles are up to 2.5 microns in diameter – about 35 times smaller than a grain of fine beach sand – ultrafine particles are 0.1 microns or smaller. These particles are concerning, as they penetrate deep into people’s lungs.

Limited access to outside air, the frequency of trains, a large number of passengers and its location in the heart of Center City may be some of the reasons for the high concentrations of particulate matter at the 15th Street station.

Subway air quality has previously been investigated in Philadelphia and several other U.S. cities, including Boston, New York City and Washington, D.C. A study of 71 subway stations in those metro areas found PATH stations in New York and New Jersey to have the highest concentration of fine particles. That study also found a similar concentration of fine particles, mainly iron and carbon, in Philadelphia as we found.

Our study, however, measured more types and sizes of particulate matter.

Why it matters

Our study highlights the need for Philadelphia to monitor the air quality in its subways and to reduce air pollution exposure for commuters and subway workers.

Several major factors contribute to subway air pollution. These include the subway system’s age, how worn the wheels and rails are, the frequency of trains, the use of a graphite lubricant on the brake pads, poor ventilation, station depth and the limits of access to outdoor air and outdoor traffic.

Having better ventilation, using platform screen doors and cleaning more often to minimize dust are a few ways to improve air quality.

While we believe air quality in the subway needs to be improved, our findings do not suggest that commuters should avoid taking the subway. Air pollution levels are highly variable across stations and over time, and commuters spend relatively short periods of time inside subway stations.

People with any health concerns, especially a lung condition, can get excellent protection by wearing an N95 mask or even a surgical mask. Subway workers can use air purifiers to reduce their exposure to particle pollution.

How we do our work

We simultaneously measured the particle pollution in the underground subway platform and the pedestrian pathway above ground using three types of monitors. We took measurements for six hours a day, from about 9 a.m. to 3 p.m., on five weekdays during the summer of 2022.

What’s next

The next step in this project is to expose lung cells in the lab to the air pollution particles from the 15th Street Station and measure the oxidative stress caused by the particles. This stress contributes to chronic diseases, including asthma, chronic obstructive pulmonary disease and lung cancers.

We will also examine the types of air particles, and the levels of various metals in them, to determine what about these particles from the subway causes stress to lung cells.

The Research Brief is a short take on interesting academic work.

Kabindra Shakya, Associate Professor of Environmental Science, Villanova University and Aimee Eggler, Associate Professor of Biochemistry, Villanova University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Dan Kotlyar, Georgia Institute of Technology

NASA plans to send crewed missions to Mars over the next decade – but the 140 million-mile (225 million-kilometer) journey to the red planet could take several months to years round trip.

This relatively long transit time is a result of the use of traditional chemical rocket fuel. An alternative technology to the chemically propelled rockets the agency develops now is called nuclear thermal propulsion, which uses nuclear fission and could one day power a rocket that makes the trip in just half the time.

Nuclear fission involves harvesting the incredible amount of energy released when an atom is split by a neutron. This reaction is known as a fission reaction. Fission technology is well established in power generation and nuclear-powered submarines, and its application to drive or power a rocket could one day give NASA a faster, more powerful alternative to chemically driven rockets.

NASA and the Defense Advanced Research Projects Agency are jointly developing NTP technology. They plan to deploy and demonstrate the capabilities of a prototype system in space in 2027 – potentially making it one of the first of its kind to be built and operated by the U.S.

Nuclear thermal propulsion could also one day power maneuverable space platforms that would protect American satellites in and beyond Earth’s orbit. But the technology is still in development.

I am an associate professor of nuclear engineering at the Georgia Institute of Technology whose research group builds models and simulations to improve and optimize designs for nuclear thermal propulsion systems. My hope and passion is to assist in designing the nuclear thermal propulsion engine that will take a crewed mission to Mars.

Nuclear versus chemical propulsion

Conventional chemical propulsion systems use a chemical reaction involving a light propellant, such as hydrogen, and an oxidizer. When mixed together, these two ignite, which results in propellant exiting the nozzle very quickly to propel the rocket.

These systems do not require any sort of ignition system, so they’re reliable. But these rockets must carry oxygen with them into space, which can weigh them down. Unlike chemical propulsion systems, nuclear thermal propulsion systems rely on nuclear fission reactions to heat the propellant that is then expelled from the nozzle to create the driving force or thrust.

In many fission reactions, researchers send a neutron toward a lighter isotope of uranium, uranium-235. The uranium absorbs the neutron, creating uranium-236. The uranium-236 then splits into two fragments – the fission products – and the reaction emits some assorted particles.

More than 400 nuclear power reactors in operation around the world currently use nuclear fission technology. The majority of these nuclear power reactors in operation are light water reactors. These fission reactors use water to slow down the neutrons and to absorb and transfer heat. The water can create steam directly in the core or in a steam generator, which drives a turbine to produce electricity.

Nuclear thermal propulsion systems operate in a similar way, but they use a different nuclear fuel that has more uranium-235. They also operate at a much higher temperature, which makes them extremely powerful and compact. Nuclear thermal propulsion systems have about 10 times more power density than a traditional light water reactor.

Nuclear propulsion could have a leg up on chemical propulsion for a few reasons.

Nuclear propulsion would expel propellant from the engine’s nozzle very quickly, generating high thrust. This high thrust allows the rocket to accelerate faster.

These systems also have a high specific impulse. Specific impulse measures how efficiently the propellant is used to generate thrust. Nuclear thermal propulsion systems have roughly twice the specific impulse of chemical rockets, which means they could cut the travel time by a factor of 2.

Nuclear thermal propulsion history

For decades, the U.S. government has funded the development of nuclear thermal propulsion technology. Between 1955 and 1973, programs at NASA, General Electric and Argonne National Laboratories produced and ground-tested 20 nuclear thermal propulsion engines.

But these pre-1973 designs relied on highly enriched uranium fuel. This fuel is no longer used because of its proliferation dangers, or dangers that have to do with the spread of nuclear material and technology.

The Global Threat Reduction Initiative, launched by the Department of Energy and National Nuclear Security Administration, aims to convert many of the research reactors employing highly enriched uranium fuel to high-assay, low-enriched uranium, or HALEU, fuel.

High-assay, low- enriched uranium fuel has less material capable of undergoing a fission reaction, compared with highly enriched uranium fuel. So, the rockets needs to have more HALEU fuel loaded on, which makes the engine heavier. To solve this issue, researchers are looking into special materials that would use fuel more efficiently in these reactors.

NASA and the DARPA’s Demonstration Rocket for Agile Cislunar Operations, or DRACO, program intends to use this high-assay, low-enriched uranium fuel in its nuclear thermal propulsion engine. The program plans to launch its rocket in 2027.

As part of the DRACO program, the aerospace company Lockheed Martin has partnered with BWX Technologies to develop the reactor and fuel designs.

The nuclear thermal propulsion engines in development by these groups will need to comply with specific performance and safety standards. They’ll need to have a core that can operate for the duration of the mission and perform the necessary maneuvers for a fast trip to Mars.

Ideally, the engine should be able to produce high specific impulse, while also satisfying the high thrust and low engine mass requirements.

Ongoing research

Before engineers can design an engine that satisfies all these standards, they need to start with models and simulations. These models help researchers, such as those in my group, understand how the engine would handle starting up and shutting down. These are operations that require quick, massive temperature and pressure changes.

The nuclear thermal propulsion engine will differ from all existing fission power systems, so engineers will need to build software tools that work with this new engine.

My group designs and analyzes nuclear thermal propulsion reactors using models. We model these complex reactor systems to see how things such as temperature changes may affect the reactor and the rocket’s safety. But simulating these effects can take a lot of expensive computing power.

We’ve been working to develop new computational tools that model how these reactors act while they’re starting up and operated without using as much computing power.

My colleagues and I hope this research can one day help develop models that could autonomously control the rocket.

Dan Kotlyar, Associate Professor of Nuclear and Radiological Engineering, Georgia Institute of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.