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NASA tested a new SLS booster that may never fly, and the end of it blew off

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NASA didn’t want to say much about one of the tests, and the other one lost its nozzle.

An uncontained plume of exhaust appeared near the nozzle of an SLS solid rocket booster moments before its nozzle was destroyed during a test-firing Thursday. Credit: NASA

NASA’s Space Launch System appears to have a finite shelf life. The Trump administration wants to cancel it after just three launches, while the preliminary text of a bill making its way through Congress would extend it to five flights.

But chances are low the Space Launch System will make it to nine flights, and if it does, it’s questionable that it would reach that point before 2040. The SLS rocket is a core piece of NASA’s plan to return US astronauts to the Moon under the Artemis program, but the White House seeks to cancel the program in favor of cheaper commercial alternatives.

For the second time in less than a week, NASA test-fired new propulsion hardware Thursday that the agency would need to keep SLS alive. Last Friday, a new liquid-fueled RS-25 engine ignited on a test stand at NASA’s Stennis Space Center in Mississippi. The hydrogen-fueled engine is the first of its kind to be manufactured since the end of the Space Shuttle program. This particular RS-25 engine is assigned to power the fifth flight of the SLS rocket, a mission known as Artemis V.

Then, on Thursday of this week, NASA and Northrop Grumman test-fired a new solid rocket booster in Utah. This booster features a new design that NASA would use to power SLS rockets beginning with the ninth mission, or Artemis IX. The motor tested on Thursday isn’t flight-worthy. It’s a test unit that engineers will use to gather data on the rocket’s performance.

While the engine test in Mississippi apparently went according to plan, the ground firing of the new solid rocket booster didn’t go quite as smoothly. Less than two minutes into the burn, the motor’s exhaust nozzle violently shattered into countless shards of debris. You can watch the moment in the YouTube video below.

At the start of the program nearly 15 years ago, NASA and its backers in Congress pitched the SLS rocket as the powerhouse behind a new era of deep space exploration. The Space Launch System, they said, would have the advantage of recycling old space shuttle engines and boosters, fast-tracking the new rocket’s path to the launch pad for less money than the cost of an all-new vehicle.

That didn’t pan out. Each Artemis mission costs $4.2 billion per flight, and that’s with shuttle-era engines and boosters that NASA and its contractors already have in their inventories. NASA’s 16 leftover shuttle main engines are enough for the first four SLS flights. NASA has leftover parts for eight pairs of solid rocket boosters.

It has been 10 years

Recognizing that shuttle-era parts will eventually run out, NASA signed a contract with Aerojet Rocketdyne to set the stage for the production of new RS-25 engines in 2015. NASA later ordered an initial batch of six RS-25 engines from Aerojet, then added 18 more to the order in 2020, at a price of about $100 million per engine. NASA and its contractor aim to reduce the cost to $70 million per engine, but even that figure is many times the cost of engines of comparable size and power: Blue Origin’s BE-4 and SpaceX’s Raptor.

Finally, NASA test-fired a new flight-rated RS-25 engine for the first time last week at Stennis Space Center. The agency has often provided a livestream of its engine tests at Stennis, but it didn’t offer the public any live video. And this particular test was a pretty big deal. L3Harris, which acquired Aerojet Rocketdyne in 2023, has finally reactivated the RS-25 production line after a decade and billions of dollars of funding.

In fact, NASA made no public statement about the RS-25 test until Monday, and the agency didn’t mention its assignment to fly on the Artemis V mission. If the Trump administration gets its way, the engine will never fly. Maybe that’s fine, but after so long with so much taxpayer investment, this is a milestone worth publicizing, if not celebrating.

L3Harris issued a press release Tuesday confirming the engine’s planned use on the fifth SLS mission. The engine completed a 500-second acceptance test, throttling up to 111 percent of rated thrust, demonstrating more power than engines that flew on the space shuttle or on the first SLS launch in 2022.

A new RS-25 engine, No. 20001, was installed on its test stand in Mississippi earlier this year. Credit: NASA

“This successful acceptance test shows that we’ve been able to replicate the RS-25’s performance and reliability, while incorporating modern manufacturing techniques and upgraded components such as the main combustion chamber, nozzle, and pogo accumulator assembly,” said Kristin Houston, president of space propulsion and power systems at Aerojet Rocketdyne, L3Harris. “Our propulsion technology is key to ensuring the United States leads in lunar exploration, creates a sustained presence on the Moon and does not cede this strategic frontier to other nations.”

The test-firing last Friday came a few days before the 50th anniversary of the first space shuttle main engine test at Stennis on June 24, 1975. That engine carried the serial number 0001. The new RS-25 engine is designated No. 20001.

Watch out

NASA followed last week’s low-key engine test with the test-firing of a solid-fueled booster at Northrop Grumman’s rocket test site in Promontory, Utah, on Thursday. Held in place on its side, the booster produced 3.9 million pounds of thrust, outclassing the power output of the existing boosters assigned to the first eight SLS missions.

Unlike the RS-25 firing at Stennis, NASA chose to broadcast the booster test. Everything appeared to go well until 1 minute and 40 seconds into the burn, when a fiery plume of super-hot exhaust appeared to burn through part of the booster’s structure just above the nozzle. Moments later, the nozzle disintegrated.

Solid rocket boosters can’t be turned off after ignition, and for better or worse, the motor continued firing until it ran out of propellant about 30 seconds later. The rocket sparked a fire in the hills overlooking the test stand.

This was the first test-firing of the Booster Obsolescence and Life Extension (BOLE) program, which aims to develop a higher-performance solid rocket booster for SLS missions. NASA awarded Northrop Grumman a $3.2 billion contract in 2021 to produce boosters with existing shuttle parts for five SLS missions (Artemis IV-VIII), and design, develop, and test a new booster design for Artemis IX.

The boosters produce more than 75 percent of the thrust required to propel the SLS rocket off the launch pad with NASA’s crewed Orion spacecraft on top. Four RS-25 engines power the core stage, collectively generating more than 2 million pounds of thrust.

Northrop Grumman calls the new booster “the largest and most powerful segmented solid rocket motor ever built for human spaceflight.”

One of the most significant changes with the BOLE booster design is that it replaces shuttle-era steel cases with carbon-fiber composite cases. Northrop says the new cases are lighter and stronger. It also replaces the booster’s hydraulic thrust vector control steering system with an electronic system. The propellant packed inside the booster is also different, using a mix that Northrop packs inside its commercial rocket motors instead of the recipe used for the space shuttle.

Northrop Grumman has had a tough time with rocket nozzles in recent years. In 2019, a test motor for the company’s now-canceled Omega rocket lost its nozzle during a test-firing in Utah. Then, last year, a smaller Northrop-made booster flying on United Launch Alliance’s Vulcan rocket lost its nozzle in flight. Vulcan’s guidance system and main engines corrected for the problem, and the rocket still achieved its planned orbit.

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Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.

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SpaceX launches military satellites tuned to track hypersonic missiles

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Trackers —

These satellites will participate in joint missile tracking exercises later this year.

–

SpaceX launched a Falcon 9 rocket Wednesday with six missile-tracking satellites for the US military.

Enlarge / SpaceX launched a Falcon 9 rocket Wednesday with six missile-tracking satellites for the US military.

Two prototype satellites for the Missile Defense Agency and four missile tracking satellites for the US Space Force rode a SpaceX Falcon 9 rocket into orbit Wednesday from Florida’s Space Coast.

These satellites are part of a new generation of spacecraft designed to track hypersonic missiles launched by China or Russia and perhaps emerging missile threats from Iran or North Korea, which are developing their own hypersonic weapons.

Hypersonic missiles are smaller and more maneuverable than conventional ballistic missiles, which the US military’s legacy missile defense satellites can detect when they launch. Infrared sensors on the military’s older-generation missile tracking satellites are tuned to pick out bright thermal signatures from missile exhaust.

The new threat paradigm

Hypersonic missiles represent a new challenge for the Space Force and the Missile Defense Agency (MDA). For one thing, ballistic missiles follow a predictable parabolic trajectory that takes them into space. Hypersonic missiles are smaller and comparatively dim, and they spend more time flying in Earth’s atmosphere. Their maneuverability makes them difficult to track.

A nearly 5-year-old military organization called the Space Development Agency (SDA) has launched 27 prototype satellites over the last year to prove the Pentagon’s concept for a constellation of hundreds of small, relatively low-cost spacecraft in low-Earth orbit. This new fleet of satellites, which the SDA calls the Proliferated Warfighter Space Architecture (PWSA), will eventually number hundreds of spacecraft to track missiles and relay data about their flight paths down to the ground. The tracking data will provide an early warning to those targeted by hypersonic missiles and help generate a firing solution for interceptors to shoot them down.

The SDA constellation combines conventional tactical radio links, laser inter-satellite communications, and wide-view infrared sensors. The agency, now part of the Space Force, plans to launch successive generations, or tranches, of small satellites, each introducing new technology. The SDA’s approach relies on commercially available spacecraft and sensor technology and will be more resilient to attack from an adversary than the military’s conventional space assets. Those legacy military satellites often cost hundreds of millions or billions of dollars apiece, with architectures that rely on small numbers of large satellites that might appear like a sitting duck to an adversary determined to inflict damage.

Four of the small SDA satellites and two larger spacecraft for the Missile Defense Agency were aboard a SpaceX Falcon 9 rocket when it lifted off from Cape Canaveral Space Force Station at 5: 30 pm EST (2230 UTC) Wednesday.

The rocket headed northeast from Cape Canaveral to place the six payloads into low-Earth orbit. Officials from the Space Force declared the launch a success later Wednesday evening.

The SDA’s four tracking satellites, built by L3Harris, are the last spacecraft the agency will launch in its prototype constellation, called Tranche 0. Beginning later this year, the SDA plans to kick off a rapid-fire launch campaign with SpaceX and United Launch Alliance to quickly build out its operational Tranche 1 constellation, with launches set to occur at one-month intervals to deploy approximately 150 satellites. Then, there will be a Tranche 2 constellation with more advanced sensor technologies.

The primary payloads aboard Wednesday’s launch were for the MDA. These two Hypersonic and Ballistic Tracking Space Sensor (HBTSS) satellites, one supplied by L3Harris and the other by Northrop Grumman, will demonstrate medium field-of-view sensors. Those sensors can’t cover as much territory as the SDA satellites but will provide more sensitive and detailed missile tracking data.

This illustration shows how the HBTSS satellites can track hypersonic missiles as they glide and maneuver through the atmosphere, evading detection by conventional missile tracking spacecraft, such as the Space Force's DSP and SBIRS satellites.

This illustration shows how the HBTSS satellites can track hypersonic missiles as they glide and maneuver through the atmosphere, evading detection by conventional missile tracking spacecraft, such as the Space Force’s DSP and SBIRS satellites.

“Our advanced satellites on orbit will bring the integrated and resilient missile warning and defense capabilities the US requires against adversaries developing more advanced maneuverable missiles,” said Christopher Kubasik, chairman and CEO of L3Harris. “L3Harris delivered this advanced missile tracking capability on behalf of MDA and SDA on orbit in just over three years after work was authorized to proceed. We are proud to be a critical part of the new space sensing architecture.”

The HBTSS satellites, valued at more than $300 million, and the SDA’s tracking prototypes will participate in joint military exercises in the coming months, where the wide-view SDA satellites will provide “cueing data” to the MDA’s HBTSS spacecraft. The narrower field of view of the HBTSS satellites can provide more specific, target-quality data to a ground-based interceptor, according to a report last year published by the Congressional Research Service. Future tranches, or generations, of SDA satellites will incorporate the medium field-of-view sensing capability flying on the MDA’s HBTSS satellites.

With SDA taking over the responsibility for making this technology operational, that will leave the MDA, which has historically flown its own missile tracking satellites, focused on next-generation sensor development, an MDA spokesperson told Ars.

Military officials decided only last year to place the four SDA satellites on the same launch as the MDA’s HBTSS mission. With all six satellites flying in the same orbital plane, there will be opportunities to see the same targets with both types of spacecraft and sensors. These targets may include scheduled US military missile tests or foreign launches.

“The intent to be able to work with cooperative and noncooperative targets to be able to do our demonstrations,” a senior SDA official said during a background briefing.

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