Warhead replacement program passes first key milestone

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A flight test of the '70s-era unarmed Minuteman III intercontinental ballistic missile lights up the night sky. Programs to sustain this leg of the U.S. nuclear deterrent are underway, including a replacement of the W78 nuclear warhead by Lawrence Livermore National Laboratory. Photo credit: U.S. Air Force.

Lawrence Livermore National Laboratory (LLNL) researchers passed their first program level key milestone in the W87-1 Modification Program (W87-1 Mod) on Sept. 24, keeping the program on schedule despite work stoppages due to the COVID-19 pandemic.

The W87-1 Mod will replace the W78 thermonuclear warhead with a modified design of the W87 warhead. The W78 is nearing the end of its functional lifespan after 37 years in service, perched atop the Air Force’s Minuteman III intercontinental ballistic missiles (ICBMs). The W87-1 will be paired with an updated Mark 21 reentry vehicle, called an Mk21A, and an ICBM system named the Ground-Based Strategic Deterrent (GBSD), both of which are being developed in parallel with the warhead. This new missile is slated to replace the ‘70s-era Minuteman III missiles, as well as the accompanying command and control systems. Upon completion, the U.S. ICBM force will consist of ICBMs with both the existing W87 warheads and W87-1 warheads. The W87-1 Program will require all new manufacturing of components, which has not been done since 1992.

The W87-1 milestone – called the Customer Requirements Review, or CRR – centered around the Department of Defense (DoD) and National Nuclear Security Administration (NNSA) concurring that the system requirements are complete, clear and consistently understood between stakeholders. This is a key step in ensuring the laboratories will develop a design that meets DoD requirements for weapon performance, safety, security and reliability.

As the lead nuclear design agency for the warhead, LLNL worked closely with a number of key partners to meet the milestone, including Sandia National Laboratory, NNSA, the U.S. Air Force and the DoD contractors responsible for developing the Mk21A and GBSD. In working toward completion of this milestone, the COVID-19 pandemic posed an unforeseen challenge to LLNL and their colleagues across the nuclear weapon enterprise.

“The pandemic has forced a lot of patience into our process, and a lot of creativity in how we communicate with stakeholders,” said Pritika Kumar, W87-1 requirements lead at LLNL. “Delays are never linear, but despite the shortened schedule, we have stuck to the original CRR timeline and scope. We’ve been making good use of virtual collaboration tools to get this milestone executed. We talk weekly with Sandia, NNSA and the DoD, and we’ve been able to resolve a lot of issues in those virtual meetings. It certainly has been a challenge, but we’ve been able to pivot and meet our milestone in spite of it all.”

The crucial role of the labs is to certify the safety, security and effectiveness of the nuclear warhead, and that it will function as expected when paired with its new delivery system. Key areas of focus in the certification plan are ensuring the functional integration of the whole system, and that that warhead can survive anticipated flight environments. To do this, LLNL experts will utilize the state of the art computational and experimental capabilities developed by the Stockpile Stewardship Program over the last 25 years.   

Experiments are already underway at LLNL’s National Ignition Facility, the High Explosives Applications Facility and the Contained Firing Facility to verify that material choices and component designs will function as designed, and that the integrated system is able to hold targets at risk well into the future. LLNL physicists and engineers are also working to develop novel experimental platforms that can help lend confidence in complex supercomputer models used to support the design of the warhead.

Modeling and simulation in support of this modernization program is underway using the Sierra high-performance computer, currently ranked the third fastest in the world. LLNL is concurrently working with industry to develop the first-ever “exascale” supercomputer. Dubbed El Capitan, the machine is scheduled to be up and running by 2023 – in time to make an impact on the modernization program – and is projected to be 50 times faster than Sierra. This speed up will enable LLNL to make regular use of high-resolution 3D simulations of the replacement warhead in operation.

To help ensure that the NNSA production capabilities are able to meet program needs, LLNL is working closely with colleagues at the production plants. One area of focus has been ensuring that there are enough “pits” for the warheads. Pits are the plutonium cores of a nuclear weapon that initiate the nuclear reactions that drive a nuclear weapon when they are compressed by the high explosives. The W87-1 will require newly manufactured pits certified by NNSA.

The W87-1 Mod is in Phase 6.2 of its development, the second phase of the warhead acquisition program, in which LLNL studies the feasibility of the design options. These options include the implementation of modern safety and security features in the warhead, like insensitive explosives and fire-resistant capabilities designed to prevent detonation in even the most extreme accident scenarios.

When the feasibility study phase of the design is complete in 2021, the program will enter into Phase 6.2a, which consists of developing cost estimates for the program. The program is scheduled to enter Phase 6.3 in 2022. During this phase, LLNL will enter the engineering development phase and working closely with NNSA production plants will ensure that the production processes deliver parts that meet requirements. The W87-1 is scheduled to produce its first production unit in 2030.

“We are on schedule, which is a real testament to the dedication and creativity of this team,” said Juliana Hsu, LLNL W87-1 Mod program manager. “This is a tremendously complex program with a lot of moving parts, even without work stoppages to protect our staff from the pandemic. Challenges occur, but we improvise, adapt, and overcome. I’m really proud of how the team has stepped up to keep us on track to ensure that the nation has the needed deterrent.”