When you put your hand out the window of a moving car, you feel a force pushing against you called drag. This force opposes a moving vehicle, and it’s part of the reason why your car naturally slows to a stop if you take your foot off the gas pedal. But drag doesn’t just slow down cars.

Aerospace engineers are working on using the drag force in space to develop more fuel-efficient spacecraft and missions, deorbit spacecraft without creating as much space junk, and even place probes in orbit around other planets.

Space is not a complete vacuum − at least not all of it. Earth’s atmosphere gets thinner with altitude, but it has enough air to impart a force of drag on orbiting spacecraft, even up to about 620 miles (1,000 kilometers).

As an aerospace engineering professor, I study how drag affects the movement of spacecraft in orbit. Aerobraking, as the name suggests, is a type of maneuver that uses the thin air in space to apply a drag force in the direction opposite to a spacecraft’s motion, much like braking in a car.

Changing an orbit

In space, aerobraking can change the orbit of a spacecraft while minimizing the use of its propulsion system and fuel.

Spacecraft that orbit around Earth do so in two types of orbits: circular and elliptical. In a circular orbit, the spacecraft is always at the same distance from the center of the Earth. As a result, it’s always moving at the same speed. An elliptical orbit is stretched, so the distance from Earth − and the speed the craft moves at − changes as the spacecraft travels along the orbit.

The closest point in an elliptical orbit around Earth, where the satellite or spacecraft is moving fastest, is called the perigee. The farthest point, where it’s moving slowest, is called the apogee.

The general idea behind aerobraking is to start in a large circular orbit and maneuver the spacecraft into a highly elliptical orbit, so that the lowest point in the orbit − the perigree − lies in the denser part of the upper atmosphere. For Earth, that’s between about 62 and 310 miles (100 and 500 kilometers), with the choice depending on time required to complete the orbit change.

As the spacecraft passes through this lowest point, the air exerts a drag force on it, which reduces the stretch of the orbit over time. This force pulls the craft toward a circular orbit smaller than the original orbit.

The first maneuver to put the spacecraft in an elliptical orbit so that drag can take effect does require using a propulsion system and some fuel. But once it’s in the elliptical orbit, drag from the atmosphere slows the craft, and it doesn’t need to use much, if any, fuel.

Aerobraking brings a craft from a large orbit to a small orbit and is not reversible − it can’t increase the size of an orbit. Increasing the size of an orbit or raising the spacecraft to a higher orbit requires propulsion and fuel.

Aerobraking uses

A common case where spacecraft controllers use aerobraking is when changing the craft’s orbit from a geostationary orbit − GEO − to a low Earth orbit, LEO. A GEO orbit is a circular orbit with an altitude of roughly 22,236 miles (35,786 km). In GEO, the spacecraft makes one orbit around Earth in 24 hours, so the spacecraft always stays above the same point on Earth’s surface.

Before aerobraking, the spacecraft’s onboard propulsion system thrusts in the opposite direction of the GEO orbit’s motion. This thrust puts it into an elliptical orbit. The craft passes through the atmosphere multiple times, which eventually circularizes the orbit.

Once it makes it to LEO, the spacecraft may need to use a little bit of fuel to propel itself up into its target orbit. Usually, the lowest point of the original elliptical orbit is lower than the final target circular orbit.

This process is conceptually similar to how the U.S. Space Force’s X-37B used aerobraking in early 2025.

The U.S. Space Force reported that its unmanned spaceplane, X-37B, used aerobraking. This test demonstrated the craft’s agility and maneuverability.

Another application for aerobraking is to make a spacecraft deorbit − or reenter the atmosphere − after it has stopped working. This way, the company or agency can dispose of the spacecraft and avoid creating space junk, since it will burn up in the lower atmosphere.

Aerobraking for interplanetary missions

A few Mars missions, including the Mars reconnaissance orbiter and the Mars Odyssey orbiter, have used aerobraking to reach their target orbits around the red planet.

For interplanetary missions like these, scientists use aerobraking in conjunction with the craft’s onboard propulsion system. When a spacecraft arrives at Mars, it does so in a hyperbolic orbit.

Unlike a circular or an elliptical orbit, the spacecraft’s path in hyperbolic orbit won’t keep it orbiting around Mars. Instead, it would fly through and depart Mars − unless it uses thrust from its propulsion system to get “captured” into a closed elliptical orbit.

As the spacecraft arrives at Mars, the onboard propulsion system fires to provide the force necessary to capture the spacecraft into a highly elliptical orbit around Mars. Once captured, scientists use aerobraking over several orbital passes through the atmosphere to achieve the final orbit, generally a circular one.

Aerobraking maneuvers can result in significant fuel savings. As humans get closer to landing on the surface of the red planet, the fuel savings enabled by aerobraking could save mass and allow each spacecraft headed to Mars to take more supplies.

In the grand arc of space exploration, aerobraking is not just a maneuver. It has a crucial role to play in the future of space operations and planetary missions and colonization.

Piyush Mehta, Associate Professor of Space Systems, West Virginia University

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

When Robert Francis Prevost appeared on the loggia of St Peter’s Basilica as Pope Leo XIV, he set three precedents.

He is the first pope from North America, the first Augustinian to occupy the throne of Peter, and the first native English-speaker to do so since Adrian IV in the 12th century.

Pope Leo XIV greeted Rome and the world with a simple benediction: “peace be with all of you”.

In choosing a blessing that stressed concord – and in issuing it in Italian and Spanish – he signalled both pastoral directness and cultural breadth.

A Chicago childhood and academic rigour

Prevost was born in Chicago in 1955.

Raised in the working-class suburb of Dolton, he served as an altar boy and attended St Augustine Seminary High School. He studied a bachelor of science at Villanova University, and earned a doctoral degree in canon law at the Angelicum in Rome.

Prevost entered the Augustinian order in 1977, professed solemn vows in 1981 and was ordained in 1982.

For Augustinians, virtue lies not in poverty for its own sake, but in the radical sharing of goods: community precedes individual achievement.

There are three pillars: interiority, the practical love of neighbour, and a relentless search for truth. This framework would guide Prevost’s missionary work, and his call for unity and peace.

Prevost has administered communities in more than 50 countries, but he first arrived as a missionary in northern Peru in 1985. Over the next decade he taught canon law, ran a seminary in Trujillo, judged marriage cases and led a fledgling parish on Lima’s urban fringe.

The experience sharpened his awareness of informal employment, extractive industries and migration – concerns that echo the Rerum novarum , an open letter issued by his namesake Leo XIII in 1891. They remain visible in Prevost’s social priorities today.

In 2015, he was appointed Bishop of Chiclayo, Peru, and, in 2023, prefect of the Dicastery for Bishops, effectively placing him in charge of vetting episcopal appointments world-wide.

What’s in a name?

Created cardinal in September 2023 and elevated to the rank of cardinal-bishop of Albano in February 2025, Prevost entered the conclave with a reputation for quiet competence, linguistic dexterity (he speaks five languages fluently) and unspectacular holiness.

The electors turned to him on the fourth ballot. An hour later he greeted the city and the world as Pope Leo XIV, first in Italian then in Spanish: a bilingual gesture honouring his Italian American Chicago roots and his Peruvian citizenship.

Leo XIV’s choice of name is a programmatic signal. By invoking examples of Rome’s protector Leo the Great (pope from 440–61) and the great social teacher Leo XIII (1878–1903), the new Pontiff intimates he will draw upon their precedent.

His substantive focus will remain squarely on the challenges of 2025: translating Augustinian communal spirituality into governance, extending the social teaching inaugurated by Leo XIII, and mediating polarised factions.

The memory of his Leo predecessors functions as a compass rather than a map, orienting a pontificate whose horizon is the digital, migratory and climatic upheavals of the 21st century.

We can expect where Leo the Great entered dialogue, Leo XIV will offer diplomacy. Where Leo XIII defended trade-union rights and attacked exploitative capitalism, Leo XIV must address labour, climate disruption and forced displacement.

If Leo XIII gave Catholicism its first systematic response to industrial modernity, Leo XIV may be tasked with articulating an Augustinian vision for the digital Anthropocene: a view of humanity as a pilgrim community, bound by shared love rather than algorithmic preference-profiling.

Of one heart

The opening sentence of the Rule of Saint Augustine is “be of one mind and heart on the way to God”.

The order’s stress on interior prayer rather than external activism complements Leo XIV’s preference for silent Eucharistic adoration over elaborate ceremony. The Augustinian tradition of learning aligns with his own scholarly instinct.

Consistent with Francis, Leo XIV has condemned abortion and euthanasia. He has criticised hard-line immigration policies in the United States. He holds the line only men can be deacons. In a 2012 address, he pointed to media normalisation of “alternative families comprised of same-sex partners”.

The combination marks him as a centrist prepared to defend doctrinal boundaries while pressing assertively on social justice, climate action and the governance transparency that Francis began but did not finish.

Challenges ahead

Leo XIV inherits a fragmented Church. Traditionalists fear doctrinal drift, while progressives want accelerated reform of governance, liturgy and the role of women.

His Augustinian commitment to shared discernment could provide a mediating structure. Meanwhile geopolitical crises demand renewed Holy See diplomacy and Vatican finances still run unsustainable deficits.

Ultimately, Leo XIV embodies a living dialogue between tradition and modernity.

Whether he succeeds will depend on his capacity to translate the Augustinian Order’s ancient ideal of one heart, one mind into structures that protect the vulnerable worker, the displaced migrant and the wounded planet.

Yet his formation, intellect and record of bridge-building suggest he understands the Church’s credibility now rests where it did in 1891 under Leo XIII: in that social charity and theological clarity are not rivals, but partners on the road to God.

Like Leo XIII, Leo XIV approaches the world not as an enemy to be refuted but as a moral terrain to be cultivated. His pontificate must confront the ecological, technological and migratory questions of our age.

His inaugural plea for peace hints at an integral vision in which social justice, ecological stewardship and human fraternity intersect.

Whether he can translate that vision into institutional reform and global moral leadership remains to be seen.

By invoking the heritage of Leo XIII, Leo XIV has set the compass of his papacy. It points toward a Church intellectually serious, socially committed and pastorally close: one speaking anew to workers in Amazon warehouses, migrants in detention camps, students in schools, refugees in the Sahel and young people navigating the gig economy.

If he succeeds, the name he chose will read as prophetic promise, linking 1891’s clarion call for justice with the uncharted demands of 2025 and beyond.

Darius von Guttner Sporzynski, Historian, Australian Catholic University

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