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Comment by turtletontine | Hacker News Reader

Someone please answer my obvious question. We sent successful missions to the moon sixty years ago. What heat shield material was used for the Apollo capsules, and why would we need something different now? Are the Artemis mission parameters totally different in a way that requires a new design? Or was Apollo incredibly dangerous and we got lucky they didn’t all fail catastrophically? The article mentions Orion is much heavier than the Apollo capsules, does that really require a totally novel heat shield that takes $billions to develop?

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The Apollo command module used Avcoat, the same material as Orion. But there are two key differences:

1. The application method is different. Apollo applied it to a metal honeycomb structure with very small cells, while Orion uses blocks of the material. (NASA tried the honeycomb approach for Orion, but it was too labor-intensive).

2. Orion is much bigger and heavier than the Apollo command module. The informal consensus is that Apollo may have been at the upper size limit for using Avcoat.

> NASA tried the honeycomb approach for Orion, but it was too labor-intensive

So cost cutting, as always.

Engineering is done in the context of constraints, cost is one constraint - and its a relatively conserved constraint. Saving labor in one area allows for more care in other areas. Especially given that labor is often not cost constrained, but skill constrained, which is less elastic.

You would be the first person to ever accuse the Orion program of cutting costs.

There's different kinds of costs: cost to the government, and cost to actually build the thing.

The contractor has no trouble inflating the first one whenever they can, but they want to strip the second one to the bone to maximize profits.

More precise would be:

NASA is an organization that is dysfunctional and way too expensive for what it does. It then decided to use agressive cost cutting to cover up these problems.

The fix for not doing that by hand is to get a robot to do it, given the applicator is human-held, a human-strength Kuka with enough reach to cover the area it can handle before the applicator needs refurbishment of some sort which would give a good opportunity to move the robot to a new section of the heat shield.

For the Apollo spacecrafts:

> The paste-like material was gunned into each of the 330,000 cells of the fiberglass honeycomb individually, a process taking about six months. [1]

[1] https://en.wikipedia.org/wiki/AVCOAT#Apollo_Command_Module

Labor intensive methods aren't automatically better: you have more manual steps which must be done perfectly and validated etc.

Thats what engineering is. If you dont have to consider cost or labor, a lot of engineering becomes much easier.

Apollo was ridiculously expensive. it was a proof of concept, but not sustainable for long term exploration

How expensive in comparison to the nuclear submarines or nuclear carriers?

The Apollo program cost about as much as 22 Gerald Ford class nuclear carriers.

Amortized over the whole program, each launch cost the same as building 2 Gerald Ford class nuclear carriers, or $26 billion USD.

> How expensive in comparison to the nuclear submarines or nuclear carriers?

SLS already costs about as much as a nuclear submarine. Per launch.

At its peak the Apollo program was about 6% of US GDP.

About 4% of the federal budget and 6% of discretionary spending at its peak, not of GDP.

Still a very high number, but nowhere near the military-budget-levels you're talking about.

How reliable is this information?

Just out of curiosity, do we know if the honeycomb method worked before it was deemed too labor intensive? Because I'm told that using this block method results in chunks blowing out.

I'm also having a problem with this set-up: Apollo is at the upper size limit for avcoat; Orion is way bigger; use avcoat.

Reading a real front-fell-off aura from this project. It makes me wonder if spending 6% of GDP to develop and run a crewed lunar program 60 years ago and then immediately destroying the evidence, r&d artifacts, and materials fab capabilities was a good idea.

Apparently, it worked too well in Lockheed Martin opinion.

>Temperatures on re-entry “were lower than we expected” on EFT-1, Hawes told reporters here during Lockheed Martin’s annual media day.

>That data supports a Lockheed Martin proposal to scrap the current heat-shield design, which features a 5-meter-diameter honeycombed frame, in favor of an alternative composed of rectangular heat-resistant tiles glued together with a silicone-based adhesive, Hawes said.

https://spacenews.com/lockheed-martin-pressing-to-simplify-o...

too labor intensive - each launch already costs like $1bn, how bad can it be

As explained in the article, it’s typical margin cutting.

In this document (thats also linked in the main article) you find a great explanation to your question.

The original design used a honeycomb structure, because problems with cracking and gas permeability had been known (in the 1960s).

On the other hand it would be more labor intensive to build it in that way.

https://docs.google.com/document/d/1ddi792xdfNXcBwF8qpDUxmZz...

The very first Apollo attempt killed three astronauts. We would need something different now because the cold-war-crazy days are behind us, and we don't push ahead with missions that might end up in casualties.

We do push ahead with missions that might end up in casualties. It's just a matter of risk tolerance.

It's impossible to say a space flight mission has 0% chance of casualty. It might be impossible to say that for virtually any activity involving humans.

Arguably, the goal isnt to go to the moon. Thats the mission, but the goal is to improve our capabilities of space travel. Improving our understanding and engineering of heat shields is one such case

Related - what does SpaceX Dragon use for heat shield material and can it be used on Orion?

PICA-3, per https://caseyhandmer.wordpress.com/2025/10/31/nasas-orion-sp...

> All this would be inexplicable enough if, indeed, AVCOAT was the only known material from which heat shields could be built. But while Lockheed continues to soak the US taxpayer and play chicken with the lives of NASA’s astronauts with this “flight proven” (but completely different) design, Lockheed happily built a PICA heat shield for JPL’s large Mars rovers Curiosity and Perseverance, and SpaceX’s Dragon capsule also uses PICA-3.

Or Apollo development was a massive boondoggle that would never work and a small subset of those involved faked it to avoid being fired or going to prison. I know that directors of multibillion dollar projects lying to save their own skin is unheard of, but hear me out.

Artemis, launching on April Fools Day, seems like a joke waiting to happen.

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