On November 1st, 2023,
NASA's Lucy spacecraft will fly by a small Main Belt asteroid named Dinkinesh.
This flyby was added to Lucy's list of targets in January 2023.
There will now be ten asteroids that the Lucy mission
will explore on its record breaking tour.
Dinkinesh will be the smallest Main Belt asteroid
to have ever been well-imaged by a spacecraft,
registering at only about a half-mile in size.
The primary purpose of this encounter
is to test the spacecraft's Terminal Tracking System, which will keep Lucy's instruments
pointing at the asteroid as it flies by at 10,000 miles per hour.
This test may prove crucial to the overall success of the mission.
Even with the best Earth-based observations of these distant objects,
there will still be some uncertainty about precisely where each target
will be as Lucy approaches it. During its journey,
Lucy will utilize its L’LORRI instrument for optical navigation to improve that knowledge;
but uncertainties as large as a hundred miles may still remain.
If nothing was done, the science instruments
could completely miss the asteroid during the closest approach.
It's for this reason
that Lucy uses the Terminal Tracking System
to image the Trojan targets in the final hours of an approach,
and to autonomously update the spacecraft's onboard
knowledge of the location of the asteroid in space.
This in turn, allows the instruments to aim with precision,
which will facilitate better imaging and measurement of these small bodies.
The Dinkinesh asteroid presents
the perfect opportunity to test this system.
The geometry of this encounter,
particularly the angle that the spacecraft approaches the asteroid relative to the Sun,
is very similar to the mission's planned Trojan asteroid encounters.
This allows NASA to essentially carry out a dress rehearsal under similar conditions
well in advance of the spacecraft's main scientific targets.
It's also a full year and a half earlier than the already planned Donaldjohanson asteroid encounter,
which will serve as a more intricate and complex test of the spacecraft's systems and instruments.
And since Dinkinesh is much smaller
than any of the Trojan asteroids that Lucy will be collecting data on,
this test is meant to challenge the Terminal Tracking System’s capabilities.
It's likely that the system will lock on to Dinkinesh
for only a few minutes before closest approach,
compared to the hour or more it will have for the Trojan targets.
So, no matter the end result,
this flyby will provide Lucy's science team and flight engineers
with important insights into how the tracking system can function.
After the encounter with Dinkinesh, Lucy's orbit around the Sun will bring it back
towards Earth for its second gravity assist in December 2024.
That assist will send the spacecraft off to meet its main objectives among the Trojan asteroids.
While the primary purpose of the Dinkinesh encounter
is an engineering test,
the data collected may also provide insight on the relationship between the Main Belt asteroids
and near-Earth asteroids.
It's an exciting addition to Lucy's groundbreaking mission.