Modern rocketry turns 100—and NASA says the best is yet to come

We are in the space age. Rockets are launched into space almost every day. Orbital space stations have now hosted humans continuously for decades. The sky is teeming with satellites and space telescopes. Humans have been to the Moon and are returning. And the robots are scattered across the solar system and roaming the surface of Mars.

All this incredible innovation owes its debt to a modest experiment that took place 100 years ago: on March 16, 1926, an American physicist and engineer (and occasionally Scientific American contributor) Robert H. Goddard launched an 11-foot-tall, 10-pound prototype rocket nicknamed “Nell” from a cabbage field in Auburn, Massachusetts. Nell was in the air for only a few seconds, but her flight marked a milestone: the first-ever liftoff of a liquid-fueled rocket.

Before this time, among other things, solid fuel had been used in all previous rockets, dating back to the gunpowder-filled “fire arrows” that were used to fight Mongol invaders in 13th-century China. Liquid fuels give rockets more powerful thrust and, thanks to their variable flow, also provide more control, precisely what would be needed for any serious attempt at spaceflight. Other early visionaries—Russian Konstantin Tsiolkovsky and German Hermann Oberth—had also realized the transformative potential of liquid-fueled rockets, but Goddard was the first to prove it.

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The rest, as they say, is history. To commemorate the centennial of Goddard’s flight and understand what the future holds for rockets, Scientific American spoke with two NASA experts: Kurt Polzin, chief engineer of the space nuclear propulsion project at NASA’s Marshall Space Flight Center, and David Manzella, senior space propulsion technologist at NASA’s Glenn Research Center.

[An edited transcript of the interview follows.]

Given how modest Goddard’s “Nell” prototype is compared to today’s rockets, do you think it’s really accurate to say that Nell’s flight a century ago marks the beginning of “modern rockets”?

KURT POLZIN: Robert Goddard was a pioneering figure who pushed rockets beyond their early roots in solid propellant systems, such as canisters filled with gunpowder. His scientific and analytical approach established a framework for the systematic engineering and improvement of rocket components, a methodology still followed today.

Goddard’s landmark flight laid the foundation for the development of various space propulsion systems, including chemical rockets, thermal nuclear rockets, and solar and nuclear electric propulsion. Despite their differences, these systems share a common principle: converting an energy source (whether chemical bonds, nuclear reactions, or solar energy) into a high-speed flow of gas or particles that produces thrust.

Notably, Goddard’s insight extended to electric propulsion. In his notes, he recognized the potential of accelerating charged particles, such as electrons, for propulsion, a concept that anticipated the ion thrusters today used in modern spacecraft.

Space launches are now so common that they are barely considered newsworthy. It might seem like we’ve reached the limit of what Goddard-inspired chemical rockets can do. What do you think are the remaining boundaries?

POLZIN: Chemical rockets, often associated with Goddard’s pioneering work but now encompassing a century of collective innovation, constitute the backbone of space exploration. Traditional propellant combinations such as liquid oxygen – liquid hydrogen, liquid oxygen – kerosene and various solid propellants for rocket engines have been greatly improved. Recent developments by “new space” companies have introduced alternatives such as methane and hybrid propellants, which could offer additional benefits in terms of reliability, cost and operational flexibility.

Innovative approaches such as propulsive landings (used by SpaceX’s Falcon 9 and Blue Origin’s New Glenn rockets, for example) have reduced launch costs and increased launch frequency, making space more accessible than ever. Chemical rockets will likely remain the primary means of reaching orbit for the foreseeable future, but it is important to remember that no “ultimate” rocket can actually exist: different missions require different solutions, and no single rocket design can meet all objectives.

Looking ahead, several frontiers remain for chemical rockets. Advances in cryogenic fluid management could enable long-duration missions using chemical propellants by preventing evaporation, while continued work on nuclear propulsion and the proliferation of miniature propulsion systems for “CubeSats” and “SmallSats” promise to further expand the landscape. And we haven’t even begun to scratch the surface of use cases like flying rockets to other planets, whether to change locations or to launch payloads or astronauts from the surface.

David, this question is for you. Propulsion systems in space are quite different from rockets used to launch payloads from planets. What excites you about where rockets are going?

DAVID MANZELLA: That’s right, so I personally work on space propulsion systems, which are the technologies used to propel spacecraft once they reach orbit. For these systems, the fundamental challenge is not to have a thrust/mass ratio greater than 1; that is, they generally produce less thrust than would be required to put a payload into orbit. But you need propulsion in space because objects placed in orbit are valuable and you generally want to keep them going for many years.

Currently, that means that when you launch something, right from the start, you have to take all the fuel you’re going to need and use it for the life of that spacecraft. The technologies we work on attempt to solve this problem by making extremely fuel-efficient rocket engines – what we generally call thrusters – and one of the best ways to do this is to augment your propellant by adding electrical power. And this energy is generated in space.

Today, this is done using photovoltaic solar panels. Keep in mind, however, that the more powerful these electrical systems are, the more punch these electrically powered thrusters can pack and the bigger the things we can push into space.

My favorite model is NASA’s Power and Propulsion Element under development, which has a 60-kilowatt power system that its onboard propulsion system could use to push an 18,000-kilogram spacecraft to the moon using less than 3,000 kilograms of propellant. This is quite the opposite of launchers, where 90% of the mass is made up of propellant, isn’t it?

It’s impressive. And I know that the power and propulsion element has not yet flown into space – you and your colleagues I turned it on for the very first timein fact, during a test last year. What excites you about the future?

MANZELLA: What’s exciting about the future is that even more powerful systems can be developed and photovoltaic solar panels could one day be replaced by nuclear systems generating orders of magnitude more electricity. NASA is currently developing the technology needed to enable this, including for human exploration of Mars. This is what excites me!

POLZIN: Let me chime in on that as well. What excites me most about the future of rockets is the expanded horizon of performance and applications. Rockets, at their core, are essential tools to enable the exploration and use of space, but not the instruments of discovery themselves. Their true value lies in their ability to provide the technologies and payloads that drive scientific research, exploration, and, increasingly, the establishment of a sustainable human presence beyond Earth.

When it comes to performance, innovation continues to push the boundaries. Advances in propulsion systems promise greater efficiency, reliability and range. This is achieved through incremental improvements in chemical rockets, experimentation with new propellant combinations such as methane or hybrids or research into systems such as solar, electric and nuclear propulsion. These developments are crucial for tackling ambitious missions, such as crewed trips to Mars or sample return missions in deep space. And a diverse range of propulsion systems is essential to achieving a wide range of scientific, commercial and exploratory objectives.

From an application perspective, the most interesting developments involve moving beyond exploration to expansion and use. We are beginning to think boldly about questions like: How can we safely deliver and return humans from Mars? How can we collect and return samples from distant bodies in the solar system? What infrastructure is needed to move from initial exploration to establishing a permanent presence in space? The vision goes further and involves leveraging the resources and capabilities gained through expansion into space through NASA’s Artemis program, enabling sustainable operations and new opportunities for science, industry and even daily life beyond our planet.

Ultimately, the future of rocketry is about delivering new possibilities. As end users gain access to an increasing range of launch options, they are better equipped to pursue diverse missions: advancing scientific knowledge, developing commercial enterprises, or laying the foundation for a permanent space civilization. This field thrives on bold thinking and inventive solutions, and I am very excited to see how these will shape the next era of space exploration and development.

MANZELLA: We are indeed entering a new era in the history of humanity where each of us could be impacted on a daily basis by space systems. I think this trend will only accelerate in the future. It’s clear that space is becoming an increasingly important part of our way of life as technology advances. And yes, much of this progress dates back to Robert Goddard’s first flight a century ago.