Is it possible that SpaceX has succeeded in making orbital launches boring? Increasingly, the answer to this question appears to be yes.

On Friday the California-based company launched two Falcon 9 rockets within the span of just a little more than four hours. At 12:26 pm local time, a Falcon 9 rocket carried 52 of SpaceX’s own Starlink satellites into low-Earth orbit from a launch pad at Vandenberg Space Force Base in California. A mere 4 hours and 12 minutes later, another Falcon 9 rocket delivered two large communications satellites into geostationary transfer orbit for the Luxembourg-based satellite company SES from Kennedy Space Center.

This broke SpaceX’s own record for the shortest time duration between two launches. However, the overall record for the lowest time between two launches of the same rocket still belongs to the Russian-built Soyuz vehicle. In June 2013, Roscosmos launched a Soyuz booster from Kazakhstan, and Arianespace launched a Soyuz from French Guiana within two hours. Those launches were conducted by two separate space agencies, on separate continents, however.

Accelerating cadence

Friday’s launch of the two SES satellites was, overall, SpaceX’s 19th orbital mission for the calendar year. As of today, the company is launching a Falcon rocket every 4.1 days and remains on pace to launch approximately 90 rockets before the end of 2023.

To put this into perspective, a decade ago, the United States launched an average of 15 to 20 orbital rockets a year, total. In 2022, the United States recorded its most launches in any calendar year, ever, with 78 orbital flights. This year, barring a catastrophic accident with the Falcon 9 booster, that number will easily get into triple digits. The all-time record for orbital launches in a single year is held by the Soviet Union, with 101, in 1982.

A decade ago, SpaceX was still an upstart in the global launch industry. In the year 2013, it launched the Falcon 9 rocket a grand total of three times in a single year for the first time. This was actually a pretty monumental achievement for the company, as it introduced both its second launch pad at Vandenberg Air Force Base and a substantially upgraded variant, 1.1, of the Falcon 9 rocket. It also flew commercial missions for the first time and began experimenting with ocean-based landings.

In that competitive environment a decade ago, SpaceX still lagged far behind its main competitors, including Roscosmos, Europe-based Arianespace, and US-based United Launch Alliance. This year those numbers have swung massively around. Through today, Russia has launched three rockets, two Soyuz and one Proton, in 2023. Arianespace has yet to launch a single mission, and nor has United Launch Alliance.

No longer a competition

Put another way, SpaceX’s main competitors over the last decade have launched three rockets this year. SpaceX, by comparison, just launched three rockets in three days, including the CRS-27 mission flown for NASA on the evening of March 14. Increasingly, only the combined efforts of China’s government and its nascent commercial launch sector can pose a challenge to SpaceX’s launch dominance. That nation has a total of 11 orbital launches this year.

SpaceX founder Elon Musk has said he would like the launch industry to achieve airline-like operations with rockets one day. His company is not there yet, as it takes a couple of weeks to land, refurbish, and relaunch a Falcon 9 first stage. Each mission still requires a brand-new second stage. And the fastest turnaround time at its three launch pads, Cape Canaveral and Kennedy Space Center in Florida, and Vandenberg in California, is still about a week for each facility.

But they sure have come a long way in a decade.

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The people of Chelyabinsk in Russia got the surprise of their lives on the morning of February 15, 2013. That’s when a small asteroid exploded overhead. The resulting shockwave damaged buildings, injured people, and sent a sonic boom thundering across the region.

The Chelyabinsk impactor was about 20 meters across. It broke up in the atmosphere in an airburst and sent a shower of debris across the landscape. The event awakened people to the dangers of incoming space debris. Since we experience frequent warnings about near-Earth objects, scientists want to understand what a piece of space rock can do.

These days, there are many observation programs across the planet. For example, NASA operates its Sentry System and ESA sponsors the NEODyS project. They and others track incoming space rock. The observation data help predict the impacts of all but the very smallest asteroid chunks that come our way. Despite those programs, it’s inevitable that something like the Chelyabinsk asteroid chunk will slip through. So, it’s important to understand what happens during such an impact.

Modeling the Chelyabinsk Meteor

Scientists around the world began studying the event almost as soon as it happened. They collected bits of the debris and studied images of the entire event. Researchers with the Planetary Defense program at the Lawrence Livermore National Laboratory recently released a highly detailed 3D animation of a simulated chunk of space rock modeled after the Chelyabinsk impactor. They based the materials of the object in their animation on meteorites recovered from the ground.

Because people recorded the event with cell phones and security cameras, the team compared their model to what everybody witnessed. It turned out to be very close to what actually happened.

“This is something that can really only be captured with 3D simulation,” said Jason Pearl, lead researcher on the project. “When you combine LLNL’s specialized expertise in impact physics and hydrocodes with the Lab’s state-of-the-art High Performance Computing capabilities, we were uniquely positioned to model and simulate the meteor in full 3D. Our research underlines the importance of using these types of high-fidelity models to understand asteroid airburst events. A lot of smaller asteroids are rubble piles or loosely bound collections of space gravel, so the possibility of a monolith is really interesting.”

So, How Did the Chelyabinsk Object Shatter?

The most often-asked question about the rock that smacked into Earth over Russia was: was it a single chunk of debris? Or was it a flying rubble pile? If it was a monolithic chunk of rock, that would imply specific details about the strength of the rock and how it broke up. If it was a flying rubble pile, it might have broken up earlier and higher in the atmosphere. The LLNL experiment implies strongly that the impact was a single monolithic rock. It broke up under the heat and pressure of atmospheric entry.

To model the impactor and its behavior, the research team used a computational method called “smoothed particle hydrodynamics (SPH).” It models an object in a fluidic flow. In this case, it treats the atmosphere as a fluid. The model also simulates what happens as a Chelyabinsk-sized hunk of rock moves through the simulated air.

In their simulation, the team found that the incoming object started to break up from the rear and the cracks moved from back to front. The timescale of crack propagation toward the front of the asteroid controls the time at which the asteroid splits into smaller fragments while entering Earth’s atmosphere. A collection of fragments lies near the shock front and that shields the rest of the fragmenting rock. Finally, when the impactor reaches about 30 kilometers above Earth’s surface, intact fragments separate. That’s when the debris is exposed to the free stream. Eventually, the debris cloud decelerates very quickly and the remaining fragments continue to break up as they fly through the air toward the ground.

The Physics of the Breakup

The disintegration of the Chelyabinsk object provided scientists with a “physics-rich” event to study. According to LLNL physicist Mike Owen, the coupling of the asteroid to the atmosphere depends on how much surface area it has. The greater the surface area, the more exposure it has to heat, stress and pressure. Those all combine to break it up.

“As the asteroid enters the atmosphere, you start to have sort of a catastrophic failure,” Owen said. “And it tends to compress in the direction of travel. It was like the asteroid was being squeezed in the direction of travel, breaking into distinct pieces that started to separate and break perpendicular to the direction of travel. All of a sudden, you’ve got a lot more material being exposed to the hypersonic interaction with the air, a lot more heat being dumped in, a lot more stress on it, which makes it break faster and you get sort of a cascading runaway process.”

Using Chelyabinsk To Understand Future Impacts

Models of impactors like this one provide insight into future events when chunks of space rock will hit Earth. One long-term goal would be to use such models to assess what will happen to a target region during an impact. Meteoric impacts are natural disasters that affect our planet just as fires and floods do. As such, there’s a need to predict and understand them so that people can be more prepared.

Researcher Cody Raskin points to our increased ability to detect such incoming impactors. “If we can see a small asteroid approaching Earth in time, we could run our model and inform authorities of the potential risk, similar to a hurricane map,” said Raskin. “They could then take appropriate protective actions, such as evacuating residents or issuing shelter-in-place orders, ultimately saving lives.”

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