Wednesday, August 3, 2022

NASA's Lucy Mission to Jupiter's Trojan Asteroids is Back on Track

Last October 16, NASA's Lucy spacecraft started its multiyear mission to Jupiter's Trojan asteroids.  Within two days, it was reported that one of the solar power arrays had not unfolded and latched properly.  In an update today, August 3rd, NASA Goddard Space Flight Center announced that the efforts to repair the satellite have succeeded and the mission will proceed as planned

NASA Goddard released this rendering of the satellite before work was done and it's easy to see the solar array on the right isn't fully opened.  They explained that even in this position, it was producing about 90% of its rated power, so the mission didn't seem to be in lots of trouble.  

Although not in lots of trouble, it was imperative to understand what had really happened so they could be sure it wouldn't degrade even farther on its own.

In situations like this, the standard response is to call together a "Tiger Team" or (less flashy named) anomaly response team of scientists and engineers from all the contractors involved: spacecraft builder Lockheed Martin, solar array designer Northrop Grumman, science mission leader Southwest Research Institute (SwRI); and mission operations leader NASA’s Goddard Space Flight Center.  From the description at NASA's Goddard SFC:

To evaluate Lucy’s solar array configuration in real time, the team fired thrusters on the spacecraft and gathered data on how those forces made the solar array vibrate. Next, they fed the data into a detailed model of the array’s motor assembly to infer how rigid Lucy’s array was – which helped uncover the source of the issue.

At last, they closed in on the root cause: a lanyard designed to pull Lucy’s massive solar array open was likely snarled on its bobbin-like spool. 

After months of further brainstorming and testing, Lucy’s team settled on two potential paths forward.

In one, they would pull harder on the lanyard by running the array’s back-up deployment motor at the same time as its primary motor. The power from two motors should allow the jammed lanyard to wind in further and engage array’s latching mechanism. While both motors were never originally intended to operate at the same time, the team used models to ensure the concept would work.

The second option was simply to use it as it was.  Since they were getting 90% of the expected power out of that panel and designing a critical system like that without lots of design margin Just Isn't Done, there was no reason to think they absolutely needed to open the array completely.  But they went ahead and tried.  

After months of simulations and testing, NASA decided to move forward with the first option – a multi-step attempt to fully redeploy the solar array. On seven occasions in May and June, the team commanded the spacecraft to simultaneously run the primary and backup solar array deployment motors. The effort succeeded, pulling in the lanyard, and further opening and tensioning the array.

The mission now estimates that Lucy’s solar array is between 353 degrees and 357 degrees open (out of 360 total degrees for a fully deployed array). While the array is not fully latched, it is under substantially more tension, making it stable enough for the spacecraft to operate as needed for mission operations.

The next mission milestone for Lucy is a gravity assist flyby of Earth this October.  Lucy is not scheduled to reach the first asteroid on its mission until April of  '25.  Here, I'm going to fill in some background from the piece I wrote on this mission in October '21.

Lucy is an interesting mission that seems totally academic.  The mission is to the Trojan asteroids, orbiting at the LaGrange points of Jupiter, ahead of and behind Jupiter itself in its orbit around the sun.  

The $981 million mission will fly an extremely complex trajectory over the span of a dozen years. The spacecraft will swing by Earth a total of three times for gravitational assists as it visits a main-belt asteroid, 52246 Donaldjohanson, and subsequently flies by eight Trojan asteroids that share Jupiter's orbit around the Sun.
Lucy will fly by its first asteroid target in April 2025, a main-belt asteroid named after Donald Johanson, the American anthropologist who co-discovered the famed "Lucy" fossil in 1974. The fossil, of a female hominin species that lived about 3.2 million years ago, supported the evolutionary idea that bipedalism preceded an increase in brain size.

The mission itself is named after that fossil Lucy as well.  It's a fanciful name, but these asteroids themselves are considered to be old fossils from the formation of the solar system. 

This is Lucy's trajectory over the next 12 years.  It looks complex but it's even more complex than this shows.  This perspective is created by fixing Jupiter's position, so during the 12 years of the mission that this is showing, Jupiter and both groups of Trojan asteroids will complete a little more than one full orbit around the sun, making this a more complex plot.  Plot from the Southwest Research Institute, the scientists behind the mission.  

I'll leave you with this mind-blower.

Somewhat ironically, although Lucy is visiting the "Jupiter trojans," it will never be closer to Jupiter than when it is on Earth. This is because the Trojans trail Jupiter at a greater distance than the distance that lies between Earth and the Solar System's largest planet.




  1. These guys and gals that run the missions are unsung heros, able to troubleshoot and possibly fix things that are too far away from a Service Call...
    Actually, anything above LEO is unavailable for service, let's face it. For now, anyway - there's already talk of servicing JWST!

    My admiration for the designers, engineers, techs, programmers, orbital planners, etc. that do Real. Deep. Science. And. Engineering, that spend countless sleepless hours trying to unscrew the unscrewable, keeping things on track and running as smoothly as they can with limited time, budget, and many constraints. These people don't seek the limelight, they ARE the Real Scientists, they keep their heads down and Just Do It.

    Good On Ya, Mates!!
    (As one Engineer to another!)

  2. I wish that they'd just fly plutonium generators on these missions. Far fewer moving parts, much greater reliability and cost is not an issue.

    1. That's a sore spot for me. This is the first mission going that far out using solar arrays instead of an RTG (Radioisotope Thermal Generator). It's going to get 3% of the power we get on Earth. Voyager is still running on RTGs - 40 years into a four year mission and so far out that no solar array could work (well, maybe if it's planet-sized).

      I don't remember what the probe was (maybe Galileo?), but in the late '80s there were big protests up on the Cape. They could literally show videos of trains crashing into an RTG with no radiation leakage and the moron greenies still climbed fences to go obstruct the launch.

  3. A quick search found four anti-nuke protests at the Cape. Interestingly three of them occurred during the month of October:
    - Oct 1989: Atlantis launch of Galileo
    - Oct 1990: Discovery launch of Ulysses
    - Oct 1997: Titan IV/Centaur launch of Cassini
    - Jan 2006: Atlas V/Centaur launch of New Horizons mission to Pluto

    According to the NYT, only 30 showed up to protest the New Horizons launch. Apparently they couldn't endure the chilly Florida January climate!

    1. I meant to answer this yesterday, but thanks for looking that up. My gut is that the one I'm thinking of was in the late 80s, but 89 and 90 are too close to sort out. It was probably one of those two.

      A totally different memory is that I remember my wife and I riding our bikes over to the beach the morning of the New Horizons launch and pulling off the road to watch it.