Immediately after the Trinity test—the detonation of the world’s first atomic bomb on July 16, 1945—scientists realized the immense destructive power of nuclear weapons.
In fact, exactly 15 months after the Trinity test, physicist J. Robert Oppenheimer addressed the American Philosophical Society:
“It is a practical thing to avert atomic war. It is a practical thing to recognize the fraternity of the peoples of the world. It is a practical thing to recognize as a common responsibility, wholly incapable of unilateral solution, the completely common peril that atomic weapons constitutes for the world. To recognize that only by community of responsibility is there any hope of meeting that peril.”
Over the years, largely motivated by the expansive Soviet and U.S. nuclear testing programs, the global “community of responsibility” has enacted several treaties to limit the sizes and locations of nuclear detonations. In 1963, the Limited Test Ban Treaty prohibited nuclear detonations in the Earth’s atmosphere, underwater, and in outer space. In 1976, the Threshold Test-Ban Treaty limited the size of underground nuclear detonations to 150 kilotons. Most recently, the Comprehensive Nuclear-Test-Ban Treaty (CTBT) prohibits all nuclear detonations, period.
President Bill Clinton signed the CTBT in 1996, and although the United States has not ratified the treaty, it has maintained a unilateral moratorium on nuclear testing since 1992. But what about other countries? How do we know if they’re playing by the rules? “A treaty by itself without the means to verify it is just a piece of paper,” says Marc Kippen, a scientist and program manager in the Global Security associate directorate at Los Alamos National Laboratory. “So, when we go into a treaty, we’re big on making sure we have the methods and means to verify that no one is breaking it.”
In other words, the United States has the tools—many of them developed at Los Alamos in conjunction with Sandia National Laboratories and other organizations—to detect nuclear explosions anywhere in, on, or above the world, at any time.
“The deterrent is not so much that we use these tools” to monitor nuclear events, Kippen says, “but that the tools are there, and other countries know they are there.” Other countries realize they’ll be caught if they detonate a nuclear weapon.
About 300 Laboratory employees (most of whom are in the Lab’s Intelligence and Space Research division) focus specifically on developing satellite instruments to detect and measure aboveground nuclear explosions in the atmosphere and outer space. This type of work has a long history at Los Alamos and Sandia, whose nuclear-detonation-detecting sensors were first launched on Vela satellites in the 1960s as a way to verify the Limited Test Ban Treaty.
The Velas (there were 12 of them) and their modern‑day descendants operate in more or less the same way: specialized sensing instruments on satellites detect and measure the products of a nuclear explosion. At high altitudes and in outer space, the most easily detected products are x-rays, gamma rays, and neutrons. At lower altitudes, these products interact with the atmosphere and produce detectable optical and radio signatures. If certain levels of products are detected in the right proportions, the ground systems analyzing the sensor data can definitively identify a nuclear blast, estimate where and when it occurred, and gauge how big it was.
“Vela was the kitchen sink satellite that included neutron, gamma, particle, optical, and radio sensors,” explains scientist Brian Dougherty, of the Lab’s Space Science and Applications group. “A lot of the instruments we fly now are more or less the same design, conceptually, because it works.”
But how do we know it works? This is where Los Alamos being a weapons lab—a place that specializes in the design, maintenance, and effects of nuclear weapons—comes in handy. Using data from recent nonnuclear experiments and legacy nuclear testing data, Los Alamos weapons experts use complex supercomputer models to simulate how nuclear weapons detonate—including the products they release. What happens next is what the space‑based detection researchers care about. “The weapon has done something, has created signals, and so that’s where we pick it up,” explains Charlie Light, an engineer and program manager in the Lab’s Intelligence and Space Research division. “We leverage the weapons models.”
And they also leverage weapons scientists. “At Los Alamos, subject matter experts on outer space and nuclear explosion byproducts collaborate,” says Ben Norman, a scientist in the Lab’s Space Science and Applications group. “Having access to weapons experts is really important because there is variability in weapons output.”
Armed with information from the Lab’s weapons programs, space scientists use computer models, such as Distributed Infrastructure Offering Real-time Access for Modeling and Analysis (DIORAMA) to simulate outer space, complete with orbiting satellites and various types of natural and human-caused (that is, nuclear) products. Such models allow scientists to virtually test their sensors in various scenarios to ensure they meet the mission needs.
As computer modeling and simulation has improved, so has sensing instrumentation and satellite technology. A satellite can soar through space in several ways. A satellite in geostationary earth orbit (GEO) circles with the Earth, above the same location at all times. Starting in the 1970s, updated sensing payloads—successors of those on the Velas—from Los Alamos and Sandia started to be flown in GEO aboard the U.S. Air Force’s Defense Support Program (DSP) satellites. The DSP satellites formed the first incarnation of the U.S. Nuclear Detonation Detection System (USNDS)—a combination of sensing payloads, satellites, communications, and ground computer systems that constantly monitor and report nuclear detonations. The USNDS umbrella continues to this day, although the components have changed over time.
In the late 1970s, researchers at the U.S. Naval Research Laboratory were developing the Global Positioning System (GPS). The system, which is operated today by the U.S. Space Force, uses a constellation of about 30 satellites to transmit position, navigation, and timing data to users on the ground. These satellites fly in medium Earth orbit and circle the Earth twice a day. Nuclear detonation detection sensors from the national laboratories were first flown on GPS satellites in April 1980, and they’ve been on board ever since. Each GPS satellite hosts a collection of sensors called a global burst detector (GBD) payload.
Animation: Los Alamos National Laboratory, Visible Team
A variety of sensors, on a variety of satellites, in a variety of orbits provide comprehensive coverage of the Earth and space at all times. “Having sensors in different orbits, persistently over time, gives us the ability to monitor all the time, everywhere, without fail,” Kippen says.
Like all technology, nuclear detonation detection sensors don’t last forever. Aging due to the wear and tear from orbital temperature cycling and harsh space weather radiation mean that sensors must be replaced every so often.
In 2005, for example, some Los Alamos–designed sensors on geostationary satellites had neared the end of their useful lives, and the opportunity to replace them with upgraded sensors resulted in the Space and Atmospheric Burst Reporting System (SABRS)—a newer sensing payload developed at Los Alamos. SABRS-1, -2, and -3 are currently in orbit on host GEO satellites; SABRS-4 is under construction; and SABRS-Prime (the updated follow‑on to the original SABRS series) is in early design phases.
Each iteration of SABRS is more advanced than its predecessor, but they all specialize in detecting high-altitude and space nuclear detonations. SABRS instruments are able to detect two types of gamma rays: prompt gamma rays, which are the initial burst of gamma rays in a nuclear explosion, and delayed gamma rays, which are found in radioactive decay after the initial burst. SABRS instruments can also detect high- and low-energy charged particles, as well as neutrons.
All SABRS payload development and fabrication work takes place at Los Alamos, and each SABRS payload takes about four and a half years to build, test, and deliver for integration with its host satellite.
The SABRS-4 unit is in the midst of this process and should be ready for integration with a satellite in the next couple years.
Even though SABRS-4 is still being constructed, its technology and parts are already considered dated. “For the longer-term future, it is no longer possible to build more SABRS payloads because many of the specialized electronic components are obsolete and no longer available,” Kippen says. “Hence, the Los Alamos team has started to design a new payload— SABRS-Prime—based on modern components.”
SABRS-Prime is also an opportunity to consider new payload configurations. Unlike previous SABRS models, which are essentially one large and three small boxes of instruments placed onto a satellite, SABRS-Prime instruments can be split up and distributed on the satellite wherever it makes the most sense to house them. “We’re designing something a little less aggregated,” Dougherty says. “This might ease our accommodation onto host satellites because the satellite developers can choose to put the different sensors and processors in different places to balance their thermal loads, mass loads, and such.”
SABRS-Prime is just one of several new sensing payloads in development. Because sensing payloads are crucial to national— and global—security, scientists and engineers are always planning far in advance, innovating new sensing techniques and technology that will one day go into space. But the design and development process for this technology—which must be able to survive in space for decades—is onerous and lengthy. For example, the modernized GBD payloads slated to begin space deployment on new GPS satellites later this decade started their development process at Los Alamos and Sandia more than 10 years ago. That process included development of two new Los Alamos GBD components: the x-ray, gamma-ray, and particle sensing hard radiation (HRS) sensor and the radio-frequency sensing electromagnetic pulse (EMP) sensor. Each component includes a full suite of modern technologies that were proven based on decades of prior research and development (R&D).
An essential part of this ongoing R&D process is fielding space experiments to demonstrate and validate new technology in the space environment before it is used for USNDS payloads. For example, the Space and Endo-Atmospheric NuDet (Nuclear Detonation) Surveillance Experimentation and Risk-Reduction, or SENSER, project (again, a collaboration between Los Alamos and Sandia) is flying a suite of newer technologies that may one day contribute to future USNDS payloads. SENSER instruments employ newer technologies to collect information across the electromagnetic spectrum, including radio frequency, optical, x-ray, and high-energy gamma-ray data. “SENSER is an experimental payload that allows us to do a lot of commanding and reconfiguration to truly dive into the performance of the technologies and perform a broad range of studies and unique data collections,” explains Alexei Klimenko, of the Lab’s Space and Stockpile Management group. “The technologies that SENSER is helping to advance will be considered for application to future space-based treaty monitoring payloads and other space missions.”
Another experimental technology demonstration and validation project at Los Alamos is the Experiment for Space Radiation Analysis (ESRA). ESRA researchers are developing a new generation of plasma and energetic particle sensors. The data collected by these sensors will allow researchers to better understand how instruments are affected by space weather and evaluate if the sensing technology is suitable for future USNDS use.
Unlike SENSER, which flies on a GEO satellite, ESRA will orbit on an elliptical path known as geosynchronous transfer orbit (GTO). Instead of maintaining a constant distance from the Earth, GTO satellites are sometimes closer and sometimes farther away. This variation in environment provides a range of conditions for sensors to collect data. “Designing and operating satellite systems in GTO provides the perfect scenario to demonstrate and validate space systems across many space environments,” says Carlos Maldonado, the ESRA project leader of the Lab’s Space Science and Applications group.
ESRA is scheduled to launch in 2024. It will ride on its own dedicated small satellite, known as a CubeSat. ESRA will also be the first Los Alamos space experiment to fly on a commercially produced satellite (as opposed to a satellite produced by a defense contractor or by Los Alamos) and the first to use commercial ground stations to communicate with the satellite. Developers hope that by partnering with these companies, ESRA and other emerging technologies can be launched more often and at a lower cost than historically was possible.
Currently, data collected by USNDS satellite-borne sensing equipment is transmitted down to Earth, where it is collected and processed in ground-based computing systems operated by the U.S. Air Force. These systems, assisted by human operators, examine data from all the USNDS sensors, all the time, searching for the telltale signs of a nuclear explosion. If data points to a nuclear explosion, the operators report it to national command authorities, including the White House.
Although the Laboratory is not involved in initial analysis of whether a nuclear event has occurred, scientists and engineers at Los Alamos do support that analysis as necessary.
Los Alamos researchers also use the data for other purposes, including tracking the performance of the sensors over time, developing long-term maintenance plans, and advancing technologies for future satellites. Each generation of sensors provides data that helps with the creation of the next generation. “We’ve been doing this for nearly 65 years,” Kippen says. “It makes sense to have the Lab involved in this very unique mission.” ★