Space cannon could fire payloads to orbit in 10 minutes at Mach 20

Green Launch is one of a small handful of firms developing alternative launch methods that are more sustainable. As Green Launch co-founder Eric Robinson told Interesting Engineering (IE) in an interview, the company's method allows for "the least environmental impact per kilogram" of any orbital launch system. And it's arguably the most dramatic.

That's because Green Launch is firing small payloads into the sky using a massive space cannon.

Massive space cannon to drastically reduce costs and carbon emissions

Green Launch's explosive method has the potential to massively reduce the carbon footprint as well as the cost of small satellite launches, while also improving overall efficiency, Robinson told IE. 

In 2021, the company successfully tested its prototype cannon, a 54-foot (16.5-meter) launch tube called the hydrogen impulse launcher, by firing a payload into the stratosphere at a velocity exceeding Mach 3 — three times the speed of sound. 

It has the potential to open access to space for a whole host of new researchers who previously wouldn't have dreamed they could afford the costs of sending experiments to orbit.

"Due to air friction and subtleties of the rocket equation, launching small payloads with rockets is very difficult to do economically," Robinson explained. "Fortunately, this niche is accessible with impulse launch. The Green Launch model decreases small payload launch costs to the customer by at least a factor of two."

This is partly down to the increased payload fraction — the mass of the payload compared to the overall mass of the launch system — that Green Launch's system allows. 

Robinson points out that "traditional rockets are limited to a 1-4 percent payload fraction. In the case of Green Launch, however, the velocity achieved from the traditional first/second stage is imparted from the reusable ground-based Stage 0 launcher. The Green Launch vehicle payload fraction, therefore, may be [roughly] 10-20 percent."

In other words, Green Launch's system doesn't require the massive amount of fuel a traditional rocket would require to send payloads to orbit. That means that some of the weight of the launch system that would otherwise be assigned to fuel can instead be used for more scientific equipment and payloads.

What's more, the firm's current launcher "produces no CO2 or hydrocarbons, only water," Robinson explained, "[though] our eventual orbital system requires a solid rocket booster to circularize the orbit after the vehicle is in space." That system, however, would only require a fraction of the fuel used to send a traditional rocket to orbit, as the impulse launcher would do the majority of the heavy lifting.

"The ultimate, sustainable light-gas launch system would employ pure, compressed hydrogen heated by solar or nuclear power where the hydrogen is 99 percent captured and reused," said Robinson.

"Methane and RP-1 rocket fuel, meanwhile, produce at least 19 tons of CO2 for each payload ton put in orbit."

Space artillery experiments date back to the 1960s

Like most space companies, Green Launch builds upon a strong foundation of scientific experiments that have come before. The U.S.-based firm, in particular, owes a debt to U.S. Army experiments conducted in the 1960s.

That's because the concept of an artillery gun used as a low-cost orbital payload launch system dates back to the U.S. Army's High Altitude Research Project (HARP) in the 60s. HARP set a still-standing record in 1966 by firing a projectile past the 60-mile (100-km) Kármán Line — considered by many to be the boundary between Earth and space — to an altitude of 111 miles (180 km).

In the 90s, another one of Green Launch's eventual co-founders, current COO and Chief Science Officer Dr. John W. Hunter, worked on an offshoot of the HARP program at the Lawrence Livermore National Laboratory (LLNL) called SHARP — the 'S' was added to represent "super" high altitudes. During his time with the SHARP program, Hunter led the development of the world's largest "hydrogen impulse launcher."

As Robinson points out, "the concept for the SHARP system at LLNL was conceived by Dr. Hunter in a cocktail party during a discussion about systems that could launch faster than electric or magnetic launchers.

Green Launch, meanwhile, was formed six years ago with a plan to put payloads into orbit, something that HARP or SHARP never achieved."

To achieve that goal, Green Launch is building its own iteration of SHARP's hydrogen impulse launcher, which features a thin 400-foot-long (122 m) barrel filled with hydrogen mixed with helium and oxygen. Once these gases expand at massive speeds, they are capable of launching a projectile at velocities several times the speed of sound. SHARP broke records during the 90s by launching payloads at Mach 9 — nine times the speed of sound.

Dr. Hunter has previously stated that Green Launch will leverage his learnings from SHARP and that the company could eventually fire payloads to orbit in as little as 10 minutes, traveling at Mach 20.

Green Launch is developing a next-generation hydrogen impulse launcher

Green Launch aims to develop a new, larger system to match and then exceed the achievements of the HARP and SHARP programs.

"In December 2021, on our first vertical launch, we achieved a velocity of Mach 3.6 and, based on this velocity, an altitude of approximately 30 km," said Robinson. "We plan to sample the mesosphere 37 km this spring and will be designing and building our next larger system in the next two years."

The ultimate goal would be to surpass the U.S. Army's Kármán Line record, allowing small payloads to be regularly inserted into orbit with almost no carbon emissions when compared to traditional launch systems.

"From a physics standpoint, the Green Launch approach is scalable, limited only by your imagination or budget," Robinson continued, adding that the world record for projectile launch velocity stands at 11.2 km/sec using a light gas gun.

"We plan to limit our velocity to 6 km/sec (Mach 17) to reduce wear on the barrel," he said. "With advances in material science for liners and immaculate barrel preparation, we may be able to eventually reach higher velocities."

Green Launch's system draws comparisons to the work of another alternative launch firm called SpinLaunch, which recently launched an experimental NASA payload into the sky.

SpinLaunch is building a catapult-like system that will fire payloads into space at up to 5,000 mph using a spinning arm and a vacuum chamber. It also claims its low-emissions method will provide a much more affordable alternative to rocket launches. 

These alternatives will prove to be crucial as the world aims to turn the tide on the worst effects of climate change. Last year, a study published in the Journal of Geophysical Research: Atmospheres highlighted how rockets release tons of black carbon molecules into the stratosphere. An accumulation of this black carbon could result in a warmer stratosphere and a thinner ozone layer, according to the study. Black carbon particles can stay in the atmosphere for up to four years, leading some scientists to refer to this effect as the black umbrella.

Other than Green Launch, firms, such as U.K. rocket company Orbex are also aiming to make traditional rockets more sustainable by using biofuels for launch.

With firms like SpaceX looking to break launch cadence records year after year, and dominating the satellite launch market with more traditional rockets, sustainable alternatives like the ones developed by Green Launch, SpinLaunch, and others will become an increasing necessity.

Space exploration can bring a great many benefits to humans on Earth, but the environmental impact cannot be ignored in the face of an escalating climate crisis.