A century ago, Robert Hutchings Goddard – a physics professor branded ‘Moon Man’ by the public and ridiculed by the press – launched the world’s first liquid-fuelled rocket.
On 16 March 1926 it ascended 12.5 metres (41ft) into the air, reached 97 km/h (60mph) then bellyflopped into a cabbage patch.
But this odd apparatus was the progenitor of every future rocket. Goddard had realised liquid propellants were more efficient and controllable than solids. He patented designs for multi-stage rockets and liquid-fuelled rockets – both essential for later conquering space.
However, the conventional wisdom of the day regarded rockets not as serious science but glorified fireworks, and space travel as pure fantasy.
Goddard was roundly mocked, with one newspaper calling him, “a severe strain on credulity”. Goddard hit back. “Every vision is a joke,” he retorted, “until the first man accomplishes it.”
Goddard’s accomplishment proved as momentous to spaceflight as the Wright Brothers were to aviation. But only after his death did rocket engineers realise the immense debt they owed him. Today, Goddard is revered as a founding father of space rockets.
More advanced rocket tech
However, now the way we travel through space needs to change. Since the dawn of the Space Age, exploration of the cosmos has relied upon these chemical rockets which demand vast quantities of propellants to achieve sufficient velocities to escape our planet’s gravity.
The fastest object launched from Earth was NASA’s New Horizons spacecraft, which attained a departure velocity of 58,580 km/h (36,400 mph) on 19 January 2006. New Horizons then took 9.5 years to travel 4.7 billion km (2.9 billion miles) to reach Pluto.
The Moon can be reached in a few days, Mars in a few months and Jupiter in a few years. But to depart the Solar System and traverse interstellar space is a totally different proposition – the closest star, Proxima Centauri, would take 75,000 years and a prohibitively enormous amount of propellant to reach with current tech.
One hundred years on, new and evolving technologies stand ready to enable our next steps into space. Some, like Goddard’s first rocket, may strain credulity but could still happen in our lifetimes. Here are eight new propulsion methods that could transform the ways we explore the cosmos.
1. Electrodynamic tethers
Electrodynamic tethers – long, conducting cables that generate electricity as they trawl through planetary magnetic fields – may help power future spacecraft, braking or accelerating them, raising or lowering orbits and cutting costs. In 1996, a tethered satellite deployed from the Space Shuttle tested the concept, generating a potential of 3,500 volts.
Tethers could help maintain satellites’ orbits, eliminating costly reboost missions. They may also be able to remove space debris from orbit.
Further ahead, tethers might utilise interstellar magnetic fields to power starships beyond our Solar System. Built from light, durable Kevlar, carbon nanotubes or high-strength M5 synthetic fibres, they could enable the first ‘space elevators’, lifting and lowering payloads to and from Earth orbit at a fraction of today’s costs.
2. Beam powered ‘sails’
Ultra-thin solar ‘sails’ are already an economical, low-mass and fuel-free propulsion system, their lack of moving parts making them highly reliable. In 2010, Japan’s IKONOS mission to Venus tested a solar sail in interplanetary space for the first time.
Future plans envisage sails pushed through space by lasers or microwaves beamed from Earth. This would demand huge, interconnected ‘farms’ of beam-steerable lasers with combined outputs of 100 gigawatts – enough to power millions of homes – but if realised, its impact on space exploration would be profound.
Sail-borne spacecraft ‘beamed’ into space could conceivably reach the nearest star system, Alpha Centauri, about 4.35 lightyears from us, within 30–40 years – a far cry from the tens of millennia it would take today’s chemical rockets.
Notably, the Breakthrough Starshot concept proposed sending a flotilla of tiny ‘nanoprobes’ to Alpha Centauri using beamed lasers.
3. Quantum sail propulsion
Quantum solar sails are a more advanced sail design that use quantum mechanics principles.
They would be built from ultra-thin sheets capable of manipulating light at photonic levels, which would give increased control and efficiency compared to standard methods.
4. Quantum-dot and perovskite solar arrays
Solar arrays have powered spacecraft for decades, but they tend to be ineffective at distances beyond Jupiter due to the weakness of sunlight falling on them so far from the Sun. Historically, solar arrays employed materials like silicon, cadmium telluride and gallium arsenide, although their weight and complexity spurred newer designs.
Technologies are now being created which can gather solar power in far more efficient ways. ‘Quantum-dot’ cells, using semiconducting particles a few nanometres wide, can be specifically ‘tuned’ to push their power-producing efficiency as high as 65% – far greater than current solar arrays, with power efficiencies around the 30% mark.
More power equals more capability for future missions. The quantum-dot market is projected to grow from £700 million ($0.91 billion) in 2024 to £2.5 billion ($3.17 billion) by 2033.
Another alternative, perovskite solar cells, which can attain efficiencies 35 per cent greater than current cells, are cheap, defect-tolerant and simple to manufacture.
But they are also sensitive to moisture, which limits their durability, and their lead content adds toxicity problems – particularly for crewed missions. In 2015, the largest perovskite cell was the size of a fingernail, so scalability will be a tough nut to crack.
5. Plasma propulsion using advanced ion drives
Plasma propulsion is another exciting technology on the horizon. Former NASA astronaut Franklin Chang-Diaz’s Variable Specific Impulse Magnetoplasma Rocket (VASIMR) – a variable-thrust plasma engine fuelled by xenon or argon – could reach Mars in 39 days, much sooner than the current six to nine months.
Plasma engines might also haul cargo cheaply to lunar orbit and cut travel times to Jupiter or Saturn from six years to 14 months.
6. Direct fusion propulsion
Direct fusion propulsion uses the energy from a fusion reaction to generate thrust directly, doing away with heavy power conversion equipment. Using non-radioactive deuterium and helium-3 instead of plutonium-238 (as used on missions like Voyager, Cassini, Galileo, and Perseverance), it also reduces radiation risks to astronauts and limits the mass of radiation shielding.
Direct fusion drives could enable crewed voyages to Mars in four months and send a 9,979 kg (22,000 lb) payload to Saturn’s moon Titan in 2.6 years.
One “credible and exciting” 2017 proposal for direct fusion developed for NASA at the Princeton Plasma Physics Laboratory envisaged reaching Pluto in 3.7 years, compared to the 9.5 years that New Horizons took to get there.
Direct fusion would furnish an extra 2 megawatts of power for science upon arrival, with laser communications beaming 30-50 megawatts of power from an orbiter to a Pluto lander with enormous data-collecting potential.
7. Antimatter-catalysed microfusion
Antimatter-catalysed microfusion is a conceptual technology where small quantities of antimatter are injected into pellets of deuterium, tritium and uranium to produce energy.
Studies have found that a spacecraft powered this way could fly a Jupiter round-trip in 18 months, a one-way visit to Pluto in three years or place a 122-metre (400ft) radio telescope at the edge of the Solar System in 18 years to study the centre of the Milky Way.
But the science remains in its infancy. Worldwide, antimatter production is low, some 1-10 nanograms per year. Storage is also a difficult challenge – the record for storage of antihydrogen atoms to date is just 1,000 seconds – as well as being hugely expensive.
8. Nuclear thermal propulsion
Nuclear thermal propulsion, which draws energy from atomic fission reactions instead of traditional chemical reactions, could provide comparatively unlimited energy to help us explore the cosmos. If fully realised, it could double or even triple payload capability, halve mission times to Mars and lessen radiation loads on astronauts.
In 2019, Congress awarded NASA £93m ($125m) to build a prototype nuclear thermal propulsion rocket by 2027. But the Trump administration’s sweeping 2025 budget cuts hastened the research programme’s cancellation.
All these emerging technologies carry great promise: from near-term achievables like tethers, sails and advanced solar cells to more exotic direct fusion propulsion, antimatter-catalysed microfusion and nuclear thermal propulsion. Some may happen soon; others might take decades or more.
But we are reminded by Robert H Goddard himself about another missing piece to this equation – the quiet dreamer, their work ridiculed as “a severe strain on credulity”. In a mere four decades, Goddard’s genius saw rockets metamorphose from glorified fireworks to delivering the first human landing on the Moon. The coming decades promise to be no less exciting.
