The Orion Heat Shield Saga - Everything You Need To Know

0:04 Hello, it's Scott Manley here.

0:06 Orion is on its way home.

0:08 As I speak, it's about 8 hours from reentering over the Pacific.

0:12 It's been a fantastic mission, but of course,

0:14 now we are waiting to see whether the questions

0:17 over the heat shield performance will be answered.

0:19 And I'm going to say it's probably going to be fine, but I can't guarantee that.

0:24 The Orion spacecraft traces its development back to 2005.

0:28 Back then, it was the Crew Exploration

0:30 Vehicle as part of the Constellation Program.

0:33 Now, while the Constellation Program was canceled,

0:36 the Orion spacecraft continued development.

0:39 The Space Shuttle Program was considered a long one

0:41 when it took 12 years before humans flew on it.

0:44 Orion has taken 20.

0:47 And of course, one of the most important questions that had

0:49 to be answered was what kind of heat shield would be used.

0:52 And back in 2005, the the Space Shuttle

0:55 Program had been going for a really long time.

0:57 There was a lot of skill in the heat shields, a lot of understanding,

1:01 and those materials would be fine for the low Earth orbit version of Orion,

1:06 but they wouldn't be useful for lunar return.

1:08 And it turns out that a lot of the skills and knowledge that had been

1:11 developed in ablative heat shields for the Apollo

1:14 program had sort of waned and withered.

1:18 So, NASA set up the Crew

1:20 Exploration Thermal Protection System Advanced Development Project,

1:24 and they looked at about half a dozen different types of ablative material.

1:29 They also looked at the shuttle material,

1:30 but very quickly found that it wouldn't handle the heating

1:34 that was it would be endured from a lunar return.

1:37 Now, the two leading ones that came out of this were the Avcoat material,

1:41 which was used on the Apollo missions,

1:44 and something newer called PICA, phenolic impregnated carbon ablator.

1:49 Both of these are very similar in principle.

1:52 They have this phenolic resin, which is a type of resin that sets

1:55 into a plastic a thermal plastic material with strong molecular interlinks.

2:00 And as it heats up, it starts to off-gas and creates you know,

2:05 nitrogen and other gases, which carry the heat away.

2:09 So, this helps keep it cool and helps create an insulating layer.

2:12 The main difference is that PICA is has like a carbon fiber matrix, right?

2:17 So, that's carbon ablator.

2:19 Uh whereas Avcoat has a silica-based matrix to give it force.

2:23 So, it's more like fiberglass.

2:26 So, while PICA had all the advantages of modern technology,

2:29 Avcoat had the advantages of Apollo heritage.

2:33 But it also had Apollo-era manufacturing and environmental rules.

2:38 So, it included a lot of asbestos,

2:40 which is great for lots of things except for human lungs.

2:44 So, they had to modify the formulation,

2:47 and then they had to figure out how to manufacture

2:49 the stuff again because nobody had made it in a long time.

2:52 And this is video or film of manufacturing

2:55 the heat shield for the Apollo spacecraft.

2:57 As you can see, they've got this like you know,

3:00 honeycomb matrix over the surface,

3:02 and they're using these caulk guns to inject the material into each cell.

3:06 This is an enormous an enormously laborious process,

3:09 even if you do get to say your day job is caulk rocket.

3:13 And so, they had to set up a production facility using this technique.

3:17 And while they definitely considered the possibility

3:19 of automating this using like robots,

3:22 for the early samples that were used for testing

3:24 and for the very first heat shield that was built, they did this all by hand.

3:29 So, all of the candidate materials went through

3:31 extensive testing particularly at NASA Ames Arc Jet facility,

3:36 where it's essentially a wind tunnel with the air

3:39 heated by a lightning bolt in a bottle.

3:42 It's generating something like 60 MW of heating,

3:45 and that isn't even enough sometimes for some conditions.

3:47 So, they actually have big lasers in another room,

3:50 which will shine on the surface to make it even hotter.

3:53 This another test eliminated many of the candidate materials from contention,

3:57 leaving basically PICA and Avcoat.

3:59 And the decision was to go with Avcoat

4:01 because the Avcoat had the Apollo heritage,

4:05 and it had a large monolithic you know, heat shield rather than the PICA,

4:10 which was built in blocks, which meant that they had like ridges and gaps,

4:13 and there was some concern that it didn't handle those quite as well.

4:17 But PICA didn't lose out entirely.

4:19 It turned out that all the skills that had been developed in ablative

4:22 material were really useful when they started landing large rovers on Mars.

4:26 And the Mars Science Laboratory used PICA as its heat shield material.

4:30 Also, SpaceX created their own version, PICA X,

4:33 which is used on the Dragon spacecraft.

4:36 And so, development of Orion continued.

4:38 There was the Orion Exploration Flight Test EFT-1,

4:42 where the spacecraft was flown on a Delta IV Heavy,

4:45 which kind of makes sense because the Delta IV upper

4:48 stage was adapted into the Interim Cryogenic Propulsion Stage or ICPS,

4:53 which is used as upper stage for the early SLS launches.

4:57 So, that's what flew on the Artemis II flight.

5:00 But this flight on the Delta IV was the first

5:02 real flight of the Orion spacecraft of the Artemis program,

5:06 even if you think about it.

5:08 What this was going to do was you know, a number of in-flight tests,

5:11 but it was very specifically going to test the heat shield.

5:14 They were going to use the great power of the Delta

5:17 IV Heavy to boost the Orion spacecraft into a highly eccentric orbit,

5:22 so that the spacecraft would come back at very high orbital speeds and test

5:26 that heat heat heat heat shield to show that it could handle the loads,

5:30 to show that it was capable before they started putting on top

5:33 of larger rockets and having the spacecraft return from the moon.

5:37 They wanted to make sure the heat shield was going to work.

5:39 So, the spacecraft it did its mission, it came back, it landed,

5:43 it was recovered, and that heat shield was went over with a fine-tooth comb.

5:47 They applied all the science they could to make

5:50 sure that this thing had performed exactly as required.

5:53 And the spacecraft that actually flew this mission

5:55 is in the Kennedy Space Center Visitor Center.

5:58 You can actually go and check it out, and you can see the backshell off it.

6:02 You can't see the heat shield because that has been removed for testing.

6:06 So, anyway, the test was a success,

6:08 but the experience of building this heat shield led to some discussion

6:12 about whether they could really trust trust the quality of a heat shield,

6:15 which was built by such a laborious process.

6:17 It took a very long time.

6:19 Uh and because it was built up as this sort of like you know,

6:23 monolithic process, if there was a problem,

6:26 it might mean that they have to actually

6:28 go back and throw away the entire heat shield.

6:31 And so, they said, "Well, look, we have modern technology here.

6:35 Here's a new way we could build it." They They came up with a new design,

6:39 which involved essentially casting really nice

6:42 perfect blocks of the heat shield material.

6:45 So, they would say essentially set it,

6:47 and then they would machine it to the exact shape,

6:50 creating tiles that fit together almost perfectly on underlying structure.

6:56 And look, that seems like a perfectly good decision.

6:58 It's supposed to save money.

7:00 It guarantees that you know,

7:01 every single piece is perfect because you've analyzed it beforehand.

7:05 I mean, the big thing I would say against it is this was

7:08 one of the reasons why you rejected the more modern PICA material,

7:14 but you know, hey, you you've already got the contract,

7:17 so now you can change things to be cheaper, right?

7:20 So, anyway, this new improved process is used to build

7:22 heat shield for the first flight around the moon.

7:25 And once that's finished,

7:26 it's shipped off to the Cape to get integrated into the spacecraft.

7:30 Then they start working on the heat shield for Artemis II.

7:33 And in 2019, that gets shipped off.

7:36 That gets shipped off before Artemis I flies.

7:40 And so, in late 2022, Artemis I takes to the skies.

7:45 It heads up, it flies past the moon,

7:47 it swings around the moon for about a month,

7:49 and eventually comes back in December.

7:52 And it performs a skip reentry.

7:54 Now, skip reentry is something that's been well understood.

7:57 It was potentially part of the Apollo program,

8:00 and in the end they didn't use it.

8:01 But one of the advantages of the skip reentry is in theory,

8:04 it lets the heat shield cool down.

8:07 But also, skip reentry allows you to increase

8:10 or improve like the downrange capability for precision landings.

8:14 And that means that Orion can return to waters close

8:18 to the United States for a much larger part of the lunar month.

8:22 It improves the survivability from many more like return trajectories.

8:28 But as you probably know by now,

8:30 this reentry did not go exactly as they had planned or anticipated.

8:35 When the spacecraft was recovered,

8:37 they found that there were chunks that had broken off the heat shield, right?

8:41 A spallation process where the material's getting kicked out.

8:45 And initially, it wasn't clear why this happened.

8:49 Also, it wasn't clear how big a danger this was to the spacecraft itself,

8:53 whether a large enough chunk could break off

8:56 and potentially leave a hole in the heat shield,

8:58 which would result in the loss of the vehicle.

9:01 And so, there's been a lot of work done the last few years to decide whether it

9:05 was safe to fly the heat shield as is

9:07 or whether they needed an entirely new heat shield.

9:10 So, this is a photo showing some of the damage to the heat shield,

9:13 and if you zoom in, you can see these big gouges that have been you know,

9:17 broken out of the heat shield during the entry process.

9:21 And so, after a lot of work,

9:22 NASA's conclusion was that these things were broken off

9:26 or pushed out by the formation of gas underneath the surface.

9:30 And so, what happens is that the gas forms

9:33 underneath the surface inside the material, and as it expands,

9:37 it has got nowhere to go, and eventually it finds a flaw and causes a crack,

9:41 and the crack causes a chunk to pop off.

9:43 And they were able to replicate this behavior inside NASA Ames Arc Jet facility.

9:50 And so, based on these results,

9:51 the mission designers think that they could just modify

9:54 the trajectory of Artemis II so that the spallation doesn't happen.

9:59 So, how does that actually work?

10:00 How can you change the trajectory?

10:01 So, we're going to go back a little

10:04 and explain again how ablative heat shields work.

10:06 What the deal with ablative heat shields is

10:09 that they get burned up over time intentionally.

10:12 There's a made of a material a chemical that as it's

10:15 heated it absorbs the heat and undergoes a chemical

10:18 reaction which evolves gas and the gas leaks

10:21 to the surface and it provides and forms a protective layer.

10:25 And as the gas evaporates it leaves behind the heavier materials.

10:28 It leaves behind the silicon dioxide right the quartz

10:32 and that forms what's called a char layer right?

10:35 So, it's just like charred material but there's voids in this char

10:39 through which the gas can escape and the heat can

10:41 come in cause more stuff to paralyze is the technical term

10:45 it's burning without oxygen and it leaks out through this right?

10:48 But the scientists who studied the process

10:51 believe that what happened is that during

10:53 the skip re-entry they eject themselves back up into space for a bit of time.

10:58 Now, the heat shield is still hot and cooling down and it's cooling down by heat

11:02 you know radiating that heat into space but also

11:05 that heat is conducting into the heat shield

11:08 and it's not hot enough to generate that char

11:11 layer anymore the the layer with the holes

11:13 but it is hot enough to cause the stuff

11:16 to break down and begin generating those gases.

11:19 And so the heat layer would go deep enough down it would generate enough gas

11:24 pressure and then a piece would spall off and leave a hole in the heat shield.

11:30 So, there is a regime where you are not heating

11:33 the heat shield quickly enough for it to work properly.

11:36 What's really important here is that during that skip

11:39 there's a portion of the flight where you're not

11:41 generating that porous char layer on the surface and there's

11:46 still heat and the heat is generating the gas.

11:48 So, the way to fix this they think is by not skipping so far

11:53 out of the atmosphere you spend a long time with the heat building up.

11:56 You perhaps stay lower down that you continue

11:58 to generate that char layer on the surface.

12:01 And so if we look at the trajectory which was used in Artemis 1 from guidance

12:06 paper you can see that they reached an altitude of almost you know 290,000 ft.

12:13 Whereas the plans for Artemis 2 don't have it skipping nearly as high.

12:18 This means that it never really leaves

12:19 the atmosphere although the skip does allow larger down

12:22 range so that they can have more opportunities

12:25 for return that meant more launch windows really.

12:28 And so everyone is hoping that this will

12:30 actually address the problem and there seems to be

12:32 a decent amount of science to back it

12:34 up but there's certainly detractors who claim otherwise.

12:38 So, now why wasn't this spallation problem found on the original flight?

12:43 Well, I mean the main reason is again they had all this like

12:46 these cells this matrix of material where they had to fill everything together.

12:50 Well, that acted as a structure that held everything.

12:53 So, if a crack happened inside one of these due

12:56 to gas pressure the crack would not propagate sideways beyond each cell.

13:00 So, now if you've got this far in the video I'm sure there's a bunch of you

13:03 out there who said aha like the cut

13:05 costs in the heat shield that was the problem.

13:08 And there's a bunch of you out there who

13:08 said aha they changed the formula because of environmental laws.

13:12 That's the problem.

13:14 And the truth is if you come into one

13:17 of these engineering problems where you're trying to solve a safety

13:20 critical situation and you have preconceived notions of what you

13:24 want to blame that is a terrible way to approach engineering.

13:29 I'm sure if you'd used the classic 1960s Avcoat formula and made

13:33 big blocks off it would have had exactly the same problem and there

13:37 are reasons beyond cost to switch over to a tile based solution

13:42 where you're able to you accurately test and analyze every single section.

13:46 It makes a lot more sense and of course now that we understand

13:50 the problem we have a solution and that solution will fly on Artemis 3.

13:55 Remember this image the spallation being generated inside the arc jet tunnel?

14:00 Well, the section in the middle is where the spallation is happening.

14:03 The section at the top it's not happening and that's

14:06 because they created two slightly different versions of the material.

14:10 They figured out how to create a slightly more porous version

14:15 of the Avcoat so that if there is gas underneath it

14:18 will percolate all the way to the surface and release the pressure

14:21 and that is what they will be using for Artemis 3.

14:25 But then Artemis 3 now isn't going to the moon.

14:29 It may not even go beyond low Earth orbit

14:31 although it would be nice if they could do that.

14:33 That means they won't be able to test this heat shield for Artemis 4.

14:37 So, there's no guarantee there won't be any

14:39 further problems with the heat shield in this vehicle.

14:42 Regardless I hope the people have been working in the labs have

14:45 got it all right and I hope the crew comes home safely.

14:48 Godspeed.

14:49 See you on the ground.

14:50 I'm Scott Manley.

14:51 Fly safe.

15:05 [music]