Researchers compared results of asteroid deflection simulations to experimental data.
Credit: Lawrence Livermore National Laboratory (LLNL)

Thwarting an incoming asteroid that has Earth in its crosshairs will mean deflecting or disrupting the hazardous object.

Already on the books is the Double Asteroid Redirection Test (DART) mission in 2021 – the first-ever kinetic impact deflection demonstration on a near-Earth asteroid.  

“We’re preparing for something that has a very low probability of happening in our lifetimes, but a very high consequence if it were to occur,” says Lawrence Livermore National Laboratory (LLNL) physicist Tané Remington. “Time will be the enemy if we see something headed our way one day. We may have a limited window to deflect it, and we will want to be certain that we know how to avert disaster.”

DART mission schematic shows the impact on the moonlet of asteroid (65803) Didymos. Post-impact observations from Earth-based optical telescopes and planetary radar would, in turn, measure the change in the moonlet’s orbit about the parent body.
Also shown is planned ride-along CubeSat, the Italian Space Agency’s Light Italian CubeSat for Imaging of Asteroid (LICIACube).
Credits: NASA/Johns Hopkins Applied Physics Lab

DART mission

The findings of a new study by Remington and colleagues is titled “Numerical Simulations of Laboratory‐Scale, Hypervelocity‐Impact Experiments for Asteroid‐Deflection Code Validation.” The work identified sensitivities in the code parameters that can help researchers working to design a modeling plan for the DART mission.

The DART mission is being developed and led for NASA by the Johns Hopkins University Applied Physics Laboratory. NASA’s Planetary Defense Coordination Office is the lead for planetary defense activities and is sponsoring the DART mission.

Illustration of the DART spacecraft with the Roll Out Solar Arrays (ROSA) extended.
Credit: NASA

The DART spacecraft will launch in late July of 2021. The target is a binary (two asteroids orbiting each other) near-Earth asteroid named Didymos that is being intensely observed using telescopes on Earth to precisely measure its properties before impact.

The DART spacecraft will deliberately crash into the smaller moonlet in the binary asteroid – dubbed Didymoon – in September of 2022 at a speed of approximately 6.6 km/s.

The collision will change the speed of the moonlet in its orbit around the main body by a fraction of one percent, but this will change the orbital period of the moonlet by several minutes – enough to be observed and measured using telescopes on Earth.

Code confidence

But understanding how multiple variables might affect a kinetic deflection attempt relies upon large-scale hydrodynamic simulations thoroughly vetted against relevant laboratory‐scale experiments.

However, do we know our codes are correct?

The new study investigated the accuracy of the codes by comparing simulation results to the data from a 1991 laboratory experiment conducted at Kyoto University in Japan where a hypervelocity projectile impacted a basalt sphere target.

“In an effort to gain confidence in our codes, this work compares our simulation results to data from a well‐known laboratory‐scale experiment to assess the accuracy of our models,” the LLNL planetary defense research team explains. “We find that our code can produce results that closely resemble the experimental findings, giving assurance to the planetary defense community that our code can correctly simulate asteroid or comet mitigation.”

Credit: NASA/Johns Hopkins APL

Momentum transfer

“This study suggests that the DART mission will impart a smaller momentum transfer than previously calculated,” said Mike Owen, LLNL physicist, coauthor on the paper and developer of the “Spheral” code – an adaptive smoothed-particle hydrodynamics code.

“If there were an Earthbound asteroid, underestimating momentum transfer could mean the difference between a successful deflection mission and an impact. It’s critical we get the right answer. Having real world data to compare to is like having the answer in the back of the book,” Owen says in a LLNL statement.

To read the full paper – “Numerical Simulations of Laboratory‐Scale, Hypervelocity‐Impact Experiments for Asteroid‐Deflection Code Validation” – slated for publication in the April issue of the American Geophysical Union journal Earth and Space Science, go to:

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