Let’s unpack some questions about Russia’s role in North Korea’s rocket program

Russian President Vladimir Putin will reportedly visit North Korea later this month, and you can bet collaboration on missiles and space programs will be on the agenda.

The bilateral summit in Pyongyang will follow a mysterious North Korean rocket launch on May 27, which ended in a fireball over the Yellow Sea. The fact that this launch fell short of orbit is not unusual—two of the country's three previous satellite launch attempts failed. But North Korea's official state news agency dropped some big news in the last paragraph of its report on the May 27 launch.

The Korean Central News Agency called the launch vehicle a "new-type satellite carrier rocket" and attributed the likely cause of the failure to "the reliability of operation of the newly developed liquid oxygen + petroleum engine" on the first stage booster. A small North Korean military spy satellite was destroyed. The fiery demise of the North Korean rocket was captured in a video recorded by the Japanese news broadcaster NHK.

Petroleum almost certainly means kerosene, a refined petroleum fuel used on a range of rockets, including SpaceX's Falcon 9, United Launch Alliance's Atlas V, and Russia's Soyuz and Angara.

“The North Koreans are clearly toying with us," said Jeffrey Lewis, a nonproliferation expert at the Middlebury Institute of International Studies. "They went out of their way to tell us what the propellant was, which is very deliberate because it’s a short statement and they don’t normally do that. They made a point of doing that, so I suspect they want us to be wondering what’s going on."

Surprise from Sohae

Veteran observers of North Korea's rocket program anticipated the country's next satellite launch would use the same Chollima-1 rocket it used on three flights last year. But North Korea's official statement suggests this was something different, and entirely unexpected, at least by anyone without access to classified information.

Ahead of the launch, North Korea released warning notices outlining the drop zones downrange where sections of the rocket would fall into the sea after lifting off from Sohae Satellite Launching Station on the country's northwestern coast.

A day before the May 27 launch, South Korea's Yonhap news agency reported a "large number of Russian experts" entered North Korea to support the launch effort. A senior South Korean defense official told Yonhap that North Korea staged more rocket engine tests than expected during the run-up to the May 27 flight.

Then, North Korea announced that this wasn't just another flight of the Chollima-1 rocket but something new. The Chollima 1 used the same mix of hydrazine and nitrogen tetroxide propellants as North Korea's ballistic missiles. This combination of toxic propellants has the benefit of simplicity—these liquids are hypergolic, meaning they combust upon contact with one another. No ignition source is needed.

A television monitor at a train station in South Korea shows an image of the launch of North Korea's Chollima-1 rocket last year.

Credit: Kim Jae-Hwan/SOPA Images/LightRocket via Getty Images

Kerosene and liquid oxygen are nontoxic and more fuel-efficient. But liquid oxygen has to be kept at super-cold temperatures, requiring special handling and insulation to prevent boil-off as it is loaded into the rocket.

Complicated rocket science

Putin's upcoming trip to North Korea, first reported by Russia's Vedomosti newspaper, will reciprocate North Korean leader Kim Jong Un's trip to the Vostochny Cosmodrome in Russia's Far East last September. At Vostochny, Russia's newest space launch site, Kim saw hardware and infrastructure for the Russian Angara rocket and discussed cooperation on military matters. When asked whether Russia would help North Korea launch a satellite, Putin replied: "That's why we're here."

Since then, US officials have released evidence Russia has used ballistic missiles produced in North Korea in its war against Ukraine. In exchange for missiles and other military munitions, Russia has shipped oil, corn, wheat, and other food products to North Korea. But Russia's support doesn't end there. A White House spokesperson said earlier this year that North Korea is seeking military assistance from Russia in violation of international sanctions, "including fighter aircraft, surface-to-air missiles, armored vehicles, ballistic missile production equipment or materials, and other advanced technologies."

Diplomats engaged in a back-and-forth debate on Russia's cooperation with North Korea during a May 31 meeting of the United Nations Security Council.

Hwang Joon-kook, South Korea's ambassador to the UN, said it's natural to suspect Russia assisted in the failed rocket launch last month, and such technical cooperation would violate multiple Security Council resolutions. He raised questions about North Korea's use of new propellants.

"There simply cannot be such a quantum leap in highly complicated rocket science in such a short period of time, and therefore, it is natural that we suspect possible technology transfer," he said.

Lewis agrees. “It seems very likely to me that the shift in propellant type is a function of the access to Russia and Russian technology," he told Ars. "It’s hard to otherwise explain why they would have given up on a space launcher design that they just tested a year ago," he said, referring to the Chollima-1, which failed on its first two flights but then successfully put a North Korean satellite into orbit last November.

Hwang Joon-kook, the South Korean ambassador to the United Nations, speaks during a meeting of the UN Security Council in January.

Credit: Selcuk Acar/Anadolu via Getty Images

Russia's deputy permanent representative to the UN, Anna Evstigneeva, said her country's cooperation with North Korea is "exclusively constructive and lawful in nature. It does not threaten or violate anyone, and it will continue." Her statement in the UN Security Council is inconsistent with the evidence of Russia's use of North Korean weapons in Ukraine.

North Korea launched its first satellite in 2012 with a modified ballistic missile after several failed tries, then repeated the feat in 2016 and with the new Chollima-1 rocket in 2023.

So far, though, there's no proof of exactly what, if any, assistance Russia has offered North Korea's space program. Until now, all of North Korea's satellite launch attempts have used rockets derived from the country's missile program, using the same boosters and engines that could power nuclear warheads to distant targets in the United States.

This path toward spaceflight mirrors the way the US, the Soviet Union, and China developed their first satellite launch vehicles. The Soviets modified the R-7, the world's first intercontinental ballistic missile, to launch the Sputnik satellite in 1957. The first US satellite, Explorer I, was launched on a rocket derived from the Jupiter medium-range missile.

Some early ballistic missiles used the same kerosene and liquid oxygen, or kerolox, propellants as North Korea's new launcher, then second-generation Cold War-era missiles transitioned to use hypergolic fuel. Most modern long-range ballistic missiles use solid propellant, which is generally more reliable and has the advantage of being available for use at a moment's notice.

North Korea is in the process of making the switchover from hypergolic to solid fuel in its military's missile program, a change that could add to the country's ability to mount an attack. However, the introduction of a new kerolox engine would not necessarily be applicable to North Korean missiles.

“You could make a terrible missile out of it, but why would you do that when you already have a much better propellant combination in a perfectly serviceable engine," Lewis said.

Ultimately, though, a reliable kerolox rocket could improve North Korea's ability to put larger satellites into orbit that can spy from space. So far, US and South Korean officials have said North Korea's satellites have shown little military utility.

Double-dipping on the Korean peninsula?

The extent of Russia's supposed collaboration on North Korea's new rocket remains a mystery, but it wouldn't be the first time Russia has exported rocket technology to the region.

In the nascent days of South Korea's space launch program, Russia supplied liquid-fueled boosters for three flights of the Naro-1 rocket, a stepping stone to South Korea's all-domestic Nuri launcher. The Naro-1 launched three times, and finally succeeded to become the first rocket launched from South Korea to reach orbit in 2013.

Khrunichev, one of Russia's oldest aerospace contractors, manufactured the entire first stage for each Naro-1 rocket, complete with a kerosene-fueled engine. The boosters are similar to those used on Russia's Angara rocket, which uses the same kerolox propellant mix as the new North Korean rocket.

It just so happens that Kim Jong Un saw parts for the Angara rocket, including its RD-191 engine, when he visited the Vostochny Cosmodrome with Putin last year. Because there have been no signs that North Korea was developing its own kerolox engine, there is widespread speculation that Russia either exported an engine or, perhaps less likely, sent engineers to help the North Koreans build their own.

In either case, swapping one type of engine for another on a rocket is no simple task, particularly if they're using different propellants. The booster stage that North Korea launched last month with the new kerolox engine probably has a different design than the hypergolic Chollima-1. This would surely take longer than the eight-and-a-half months since Kim's trip to Russia.

The Naro-1 rocket, made with a Russian booster and South Korean upper stage, lifts off on a 2010 mission.

Credit: Photo by Kim Ki-Nam-pool/Getty Images

"It could have been that the Russians exported a whole booster and it just didn't work because it's rocket science, and sometimes that happens," Lewis said. “If I were the Russians and I wanted to troll, I would export exactly the same thing [to North Korea that] I exported to South Korea.

"It could be that the Russians gave them an engine, or gave them some help, and it was a crash program and it failed," he said. "It could be that this program has existed for a long time, and we just never knew about it, and the Russians helped them get over the finish line.

"I think all of those things are possible," Lewis said. "It is just very notable that they have switched propellant types.”

Jonathan McDowell, an astrophysicist and renowned tracker of spaceflight activities, suggested North Korea may have covertly developed a new rocket engine, with or without Russian help. "I agree this isn't something they just started to work on a few months ago," he told Ars.

North Korea has rushed rockets to the launch pad before, sometimes catching US intelligence officials by surprise. On many of these occasions, the rockets failed on their first test flights. "When a country is willing to take significant technical risk, then the timelines get compressed," Lewis said.

In recent years, North Korea has been more forthcoming about its launch failures than in the early years of its launch program. Last year, the country's state news agency published photos of the Chollima-1 rocket, even while admitting it failed in flight. However, North Korea released no images of its new rocket after its May 27 launch.

Perhaps North Korean officials are withholding photos until the new rocket has a successful launch, or maybe Putin and Kim will discuss the launch during their meeting later this month. If North Korea clams up about the new rocket, US officials might disclose more about what they know.

"Then we’ll be able to work out how North Korean it is and how Russian it is," Lewis said.