First Big Test for NASA's Lucy Satellite Wednesday Afternoon ET

Just over two years ago, October 16 of 2021, NASA's Lucy mission to the Trojan asteroids of Jupiter launched on its 12 year mission to the main asteroid belt before traveling to the L4 and L5 points; those gravitationally stable Lagrange points behind and ahead of Jupiter in its orbit where the Trojan asteroids are found. 

This plot, from the Southwest Research Institute shows a rather complicated looking mission trajectory for Lucy, but it oversimplifies the real path. Notice the text at the top that says, "Frame rotating with Jupiter?"  That means they created this view by fixing Jupiter's position, but during the 12 years of the mission, Jupiter and both groups of Trojan asteroids will complete a little more than one full orbit around the sun.  Assuming this is all rotating clockwise around a point near the sun (if not in the sun), in a fraction of those years, the L4 Trojans will be where the L5 are shown, the L5 Trojans will be in lower left hand side of the orbit, Earth will have completed a few complete orbits and everything else will also have rotated around that center point.

Not to get too distracted by the orbital mechanics, but on October 16 of '22, the one year anniversary of Lucy's launch, it completed a gravity assist maneuver, gaining speed in a flyby of Earth.  For just over a year, Lucy has been making a beeline for an intermediate target, and will be there Wednesday at 12:54 PM EDT, or 1654 UTC.  The mission will come to within 265 miles (425 km) of the small main belt asteroid Dinkinesh.

About an hour before the encounter, the spacecraft will begin attempting to lock on to the small asteroid so that its instruments are oriented toward it. This will allow for the best possible position to take data from Dinkinesh as Lucy speeds by at 10,000 mph (4,470 meters per second).

During this maneuver, Lucy's main antenna will be pointed away from Earth, so it will not be in communication with its operators at Goddard Space Flight Center in Greenbelt, Maryland. After the flyby, Lucy will reorient itself to reestablish communications with Earth through the Deep Space Network. Imagery and other data will be relayed back to Earth for several subsequent days.

On Oct. 28, the team sent the spacecraft what is known as the final knowledge update, a package of data with the most up to date information about the relative positions of the spacecraft and asteroid. This dataset is precise enough to guide the spacecraft for nearly all the half a million miles (800,000 km) that separated Lucy and Dinkinesh on Saturday the 28th

The ground team is quick to point out that when Lucy first tries to lock its terminal tracking system on the diminutive asteroid it may not be able to because of the asteroid's small size.  The system is not expected to “lock-on” to the asteroid until just a few minutes before closest approach. This system will autonomously reorient the spacecraft to keep the small asteroid within the field of view of the science instruments as the spacecraft zooms by at around 10,000 mph (4.5 m/s). This will be the first use of this terminal tracking system, and this flyby was designed to test the system in real spaceflight conditions.

Dinkinesh, which is nearly a kilometer across at its widest point, was discovered in 1999. It was unnamed when the Lucy mission targeted it for its first flyby as a test of the tracking system, en route to the Jovian trojan asteroids later this decade. So, Lucy mission scientists proposed the name Dinkinesh, the Ethiopian name for the Lucy fossils.

The name was approved earlier this year by the International Astronomical Union.

Before Lucy gets to either of the two swarms of Trojan asteroids, it will fly by another main belt asteroid in 2025 called Donaldjohanson for additional in-flight tests of the spacecraft systems and procedures.

Artist's concept rendering of Lucy flying by an asteroid.  Image credit NASA. 

You may recall that shortly after the mission began, they experienced a failure of those solar panels to deploy and latch open properly.  I had mentally filed away that the problem was solved, the arrays were properly deployed, latched and all that.  That's wrong.  The array they were having problems with never fully deployed properly, but was operating at about 90% of the planned power output.  While catching up on the mission to prepare this, I found that this January they said:

NASA’s Lucy mission team has decided to suspend further solar array deployment activities. The team determined that operating the mission with the solar array in the current unlatched state carries an acceptable level of risk and further deployment activities are unlikely to be beneficial at this time. The spacecraft continues to make progress along its planned trajectory.

UPDATE 11/1/2023 2145 EDT:  The word from NASA's Lucy mission blog is that "Lucy spacecraft has phoned home after its encounter with the small main belt asteroid, Dinkinesh. Based on the information received, the team has determined that the spacecraft is in good health and the team has commanded the spacecraft to start downlinking the data collected during the encounter."  They estimate it will take "up to a week" to download all the data.