We are firmly in the space age, with rockets launching into space nearly every day. Humans have lived continuously on orbital space stations for decades, and the sky is filled with satellites and space telescopes. Humans have already traveled to the moon and are planning to return. Meanwhile, robots are spread throughout the solar system and exploring Mars.
This remarkable progress traces back to a humble experiment conducted 100 years ago. On March 16, 1926, Robert H. Goddard, an American physicist and engineer who occasionally contributed to Scientific American, launched a prototype rocket named “Nell” from a cabbage patch in Auburn, Massachusetts. Though it was only airborne for a few seconds, this 11-foot-tall, 10-pound rocket was significant as the first liquid-fueled rocket to lift off.
Before Goddard’s launch, rockets relied on solid fuels, a practice dating back to the gunpowder-filled “fire arrows” used in 13th-century China against Mongol invaders. Liquid fuels provided rockets with more powerful thrust and greater control due to their adjustable flow, which was essential for spaceflight. Although other visionaries like Russia’s Konstantin Tsiolkovsky and Germany’s Hermann Oberth had also recognized the potential of liquid-fueled rockets, Goddard was the first to demonstrate it.
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The rest is history. To celebrate the 100th anniversary of Goddard’s launch and explore the future of rocketry, Scientific American consulted with two NASA experts—Kurt Polzin, the chief engineer of the Space Nuclear Propulsion Project at NASA’s Marshall Space Flight Center, and David Manzella, a senior technologist for in-space propulsion at NASA’s Glenn Research Center.
[An edited transcript of the interview follows.]
Considering the simplicity of Goddard’s “Nell” compared to today’s rockets, is it accurate to consider Nell’s flight a century ago the start of “modern rocketry?”
KURT POLZIN: Robert Goddard was a trailblazer who advanced rocketry beyond its early reliance on solid propellant systems, like gunpowder-filled canisters. His scientific and analytical approach set a precedent for systematically engineering and enhancing rocket components, a practice still used today.
Goddard’s groundbreaking flight laid the foundation for developing various space propulsion systems, including chemical, nuclear-thermal, and both solar- and nuclear-electric propulsion. Despite their differences, these systems share a common principle: converting energy sources—be it chemical bonds, nuclear reactions, or solar power—into a high-speed stream of gas or particles that generates thrust.
Significantly, Goddard also foresaw the potential of electric propulsion. His notes highlighted the possibility of using charged particles, like electrons, for propulsion—a concept that anticipated the ion thrusters used in modern spacecraft.
With space launches now so frequent they’re hardly newsworthy, have we reached the limits of what Goddard-inspired chemical rockets can achieve? What are the future frontiers?
POLZIN: Chemical rockets, which trace their lineage to Goddard’s pioneering efforts, have underpinned space exploration for a century. Traditional propellant combinations, such as liquid oxygen–liquid hydrogen and liquid oxygen–kerosene, along with various solid rocket motor propellants, have been refined over the years. New developments by “new space” companies have introduced alternatives like methane and hybrid propellants, offering potential benefits in reliability, cost, and operational flexibility.
Innovative techniques like propulsive boost-stage landings, as seen with SpaceX’s Falcon 9 and Blue Origin’s New Glenn rockets, have lowered launch costs and increased launch frequency, making space more accessible. Chemical rockets are likely to remain the primary method for reaching orbit for the foreseeable future; however, no single rocket design can fulfill all mission needs.
Looking forward, chemical rocketry still has many frontiers to explore. Advances in cryogenic fluid management could enable long-duration missions using chemical propellants by preventing boil-off. Simultaneously, ongoing work in nuclear propulsion and the growth of miniature propulsion systems for “CubeSats” and “SmallSats” will further expand possibilities. Additionally, we are only beginning to explore the potential of using rockets to navigate other planets, whether for relocation or launching payloads or astronauts from their surfaces.
David, since in-space propulsion systems differ from rockets launching from planets, what excites you about rocketry’s future?
DAVID MANZELLA: I specialize in in-space propulsion systems, which propel spacecraft once they’re in orbit. The main challenge for these systems is their thrust-to-mass ratio, which is typically less than 1, meaning they produce less thrust than needed to lift a payload into orbit. However, in-space propulsion is crucial because orbiting objects are valuable and usually meant for long-term operation.
Currently, when launching a spacecraft, it must carry all the fuel required for its operational lifespan. Our work focuses on creating highly fuel-efficient rocket engines, known as thrusters, by enhancing propellants with electrical energy generated in space.
We currently achieve this using photovoltaic solar arrays. The more powerful these electrical systems become, the greater the thrust these electric propulsion thrusters can provide, allowing us to move larger objects in space.
A prime example is NASA’s developing Power and Propulsion Element, which features a 60-kilowatt power system that can propel an 18,000-kilogram spacecraft to the moon with less than 3,000 kg of propellant. This contrasts with launch vehicles, where propellant makes up 90 percent of the mass.
That’s impressive. The Power and Propulsion Element hasn’t flown in space yet, but you and your team powered it up for the first time last year. What about the future excites you?
MANZELLA: The future holds promise with the development of even more powerful systems, and photovoltaic solar arrays could eventually be replaced by nuclear systems yielding significantly more electricity. NASA is currently working on this technology, including for human exploration of Mars, and that’s what excites me!
POLZIN: I’d like to add that what excites me most about rocketry’s future is the expanding potential for both performance and application. Rockets are crucial tools for exploring and utilizing space, delivering the technologies and payloads that enable scientific research, exploration, and the growing human presence beyond Earth.
Innovations in propulsion systems continue to push the limits of efficiency, reliability, and range. This progress is evident in the incremental improvements in chemical rockets, experiments with new propellant combinations like methane or hybrids, and the pursuit of solar electric and nuclear propulsion systems. These advancements are vital for ambitious missions, such as crewed Mars journeys or deep-space sample return missions, and a diverse range of propulsion systems is necessary to meet varied scientific, commercial, and exploratory goals.
In terms of application, the most exciting developments involve transitioning from exploration to expansion and utilization. We are starting to address bold questions like how to safely deliver and return humans from Mars, how to collect and return samples from distant solar system bodies, and what infrastructure is needed to move from initial exploration to a permanent space presence. This vision extends to leveraging resources and capabilities from NASA’s Artemis program, facilitating sustainable operations, and creating new opportunities for science, industry, and even daily life beyond our planet.
Ultimately, the future of rocketry is about unlocking new possibilities. As more launch options become available, users can pursue a wider range of missions, from advancing scientific knowledge to developing commercial ventures or establishing a permanent spacefaring society. The field thrives on bold thinking and innovative solutions, and I am eager to see how these will shape the next era of space exploration and development.
MANZELLA: We are indeed entering a new era where space-based systems could impact us all daily. This trend is likely to accelerate as technology advances. Much of this progress can be traced back to Robert Goddard’s first flight a century ago.
