Going into the Artemis II mission last spring, probably the biggest concern
we'd hear about was the heat shield issues that were seen on the
unmanned Artemis I mission back in late 2022. Probably the best set of
pictures I've got
were posted in January of this year. The heat shield on an Orion capsule uses the ablative technique that has been used since
the early days of spaceflight; the base of the capsule is coated with an
ablative material called Avcoat that's supposed to essentially disintegrate slowly and in a
controlled way. Instead, large chunks were missing. Lots of chunks. Back when
the capsule was recovered, a single picture taken by a recovery diver was released. The heat shield was obviously much, much better than Artemis I's shield.
The Artemis 2 Orion heat shield underwater after splashdown on April 10, 2026.
(Image credit: U.S. Navy) Some image processing by me to bring up the overall
brightness of the image and get more of the shield to show up.
A report on the detailed examination performed on the Artemis II heat
shield was released and reported on today.
After the Artemis I mission in 2022, there were more than 100 char loss
sites observed across the dish-shaped heat shield at the base of Orion, some
of which were more than an inch deep. On the Artemis II heat shield, he
said, there were approximately nine char loss sites observed. “So it was a
big improvement,” said Hill, former director of Mission Operations at
NASA.
...
At the base of Orion are 186 blocks of a material called Avcoat; they are
individually attached to provide a protective layer that allows the
spacecraft to survive the heating of atmospheric reentry. Analysis after the
Artemis I mission found that this Avcoat material was “impermeable,”
essentially meaning it could not breathe. During reentry, gases became
trapped in the heat shield, leading to cracking.
After considering several options, including swapping the heat shield out
for a newer one with more permeable Avcoat, NASA decided instead to change
Orion’s reentry profile. For Artemis II, it would return through Earth’s
atmosphere at a steeper angle, spending fewer minutes in the environment
where this outgassing occurred during Artemis I.
A quote about engineering I was told while I was still in school, and
that I've stated here before, is that "engineering is the art of compromise" -
it's practically always the case that when you improve the performance of
something that you're struggling to improve, you make something else worse.
The final design you end with is better at the one characteristic that you
worked to change but something you weren't trying to improve got worse. In
this case, the performance of the heat shield was remarkably better but "the
new reentry profile reduced the vehicle’s “downrange” capability from 4,800
nautical miles to 1,775 miles. Downrange capability is the distance a
spacecraft can travel, relative to the Earth’s surface, from the point of
atmospheric reentry."
Does reducing the downrange capability to less than 40% of what it
started out as matter? It's not as good as it was, so that has to be
considered differently for every mission. The trade is that reduction in downrange capability reduced the
number of missing chunks from 100 to 9.
An interesting side note here is that this was talked about at a meeting
of NASA’s
Aerospace Safety Advisory Panel and let's just say they haven't exactly always been fanboys of
NASA management.
Toward the end of the safety panel’s meeting on Monday, a few members made
some striking comments about their experiences working with NASA this year.
For long-time listeners to meetings of the Aerospace Safety Advisory Panel,
which is distinctly independent from NASA and tasked with identifying safety
issues, these were eye-opening statements.
In describing the
panel’s deliberations during its quarterly meeting, Hill said, “Words like
impressive, stunning, and shocking were all brought up about the progress
that the agency has made in the last year, and even more rapidly just in the
last four months.”
The bottom line here is that Panel's members and the other people they
interviewed seem convinced the improvement is all due to Jared Isaacman, and
they praise him for it.
“In an empowering or enabling way, the changes that we are hearing in the
leadership voice at the very top of the agency, and then down into the
agency, are aligning the team on a coherent strategy and then taking the
steps to execute on that strategy,” Hill said. “Again, it’s nothing short of
impressive, and it’s directly related to recommendations we’ve had open for
a number of years.”