After capturing images of Vega, one of the brightest stars in Earth’s night sky, the Double Asteroid Redirection Test’s (DART) camera recently focused on another stunning spectacle: Jupiter and its four largest moons.
NASA’s DART spacecraft is currently cruising toward its highly-anticipated September 26 encounter with the binary asteroid Didymos. Meanwhile, during the journey, the spacecraft’s imager — the Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO — has snapped thousands of pictures of stars. The pictures provide the data necessary for the Johns Hopkins Applied Physics Laboratory (APL) team leading the mission for NASA to support ongoing spacecraft testing and rehearsals in preparation for the spacecraft’s kinetic impact into Dimorphos, the moon of Didymos.
DRACO is the only instrument on DART. As such, not only will it capture images of Didymos and Dimorphos, but it will also support the Small-body Maneuvering Autonomous Real Time Navigation (SMART Nav). This is the spacecraft’s autonomous guidance system, which will guide DART to impact.
To test the SMART Nav system, the mission operations team pointed the DRACO imager to Jupiter on July 1 and August 2. The team used it to detect and target Jupiter’s moon Europa as it emerged from behind Jupiter. This is similar to how Dimorphos will visually separate from the larger asteroid Didymos in the hours leading up to impact. While the test obviously didn’t involve DART colliding with Jupiter or its moons, it did give the APL-led SMART Nav team the chance to assess how well the SMART Nav system performs in flight. Before this Jupiter test, SMART Nav testing was done via simulations on the ground.
The test provided valuable experience for the SMART Nav team, including knowledge of how the SMART Nav team views data from the spacecraft. “Every time we do one of these tests, we tweak the displays, make them a little bit better and a little bit more responsive to what we will actually be looking for during the real terminal event,” said Peter Ericksen SMART Nav software engineer at APL.
Although the DART spacecraft is designed to operate fully autonomously during the terminal approach, the SMART Nav team will still be monitoring how objects are tracked in the scene. This includes their intensities, the number of pixels, and how consistently they’re being identified. Corrective action using preplanned contingencies will be taken only if there are significant and mission-threatening deviations from expectations. With Jupiter and its moons, the team had a chance to better understand how the intensities and number of pixels of objects might vary as the targets move across the detector.
The image above is a cropped composite of a DRACO image centered on Jupiter taken during one of these SMART Nav tests. It was taken when DART was approximately 16 million miles (26 million km) from Earth with Jupiter approximately 435 million miles (700 million km) away from the spacecraft. Two brightness and contrast stretches, made to optimize Jupiter and its moons, respectively, were combined to form this view. From left to right are Ganymede, Jupiter, Europa, Io, and Callisto.
“The Jupiter tests gave us the opportunity for DRACO to image something in our own solar system,” said Carolyn Ernst, DRACO instrument scientist at APL. “The images look fantastic, and we are excited for what DRACO will reveal about Didymos and Dimorphos in the hours and minutes leading up to impact!”
DART was developed and is managed by the Johns Hopkins Applied Physics Laboratory (APL) for NASA’s Planetary Defense Coordination Office. DART is the world’s first planetary defense test mission, and will intentionally execute a kinetic impact into Dimorphos to slightly change its motion in space. Although no known asteroid poses a threat to Earth currently, the DART mission will demonstrate that a spacecraft can autonomously navigate to a kinetic impact on a relatively small target asteroid, and that this is a viable technique to deflect a genuinely dangerous asteroid, if one were ever discovered. DART will reach its target on September 26, 2022.