NASA comment on SpaceX Dragon heat shield [Update]

heat shield wear on Dragon Capsule

NASA has since responded, contradicting our reporting. NASA’s full comment below.

SpaceX’s Dragon capsule has been very successful since its first crewed launch on Demo-2. While reuse is paramount to SpaceX’s mission, the Dragon capsule heat shield has started to cause issues once again that could put astronauts at risk. 

Update

The information in this story was provided to Space Explored independently by sources at NASA and SpaceX. Space Explored reached out to multiple NASA centers, which deferred the questions back to SpaceX, and SpaceX declined to comment on the record to Space Explored.

Following the publication of the story, NASA provided the following statement to Space Explored.

The data associated with Dragon’s recent crew reentries was normal – the system performed as designed without dispute. There has not been a hypergol leak during the return of a crewed Dragon mission nor any contamination with the heat shield causing excessive wear. SpaceX and NASA perform a full engineering review of the heat shield’s thermal protection system following each return, including prior to the launch of the Crew-4 mission currently at the International Space Station. The heat shield composite structure (structure below the tile) was re-flown per normal planning and refurbishment processes. The thermal protection system on the primary heat shield for Crew-4 was new, as it has been for all human spaceflight missions. SpaceX has only demonstrated reuse of selected PICA (Phenolic-Impregnated Carbon Ablator) tiles, which is a lightweight material designed to withstand high temperatures, as part of the heat shield on cargo flights.

NASA and SpaceX are currently in the process of determining hardware allocation for the agency’s upcoming SpaceX Crew-5 mission, including the Dragon heat shield. SpaceX has a rigorous testing process to put every component and system through its paces to ensure safety and reliability. In early May, a new heat shield composite structure intended for flight on Crew-5 did not pass an acceptance test. The test did its job and found a manufacturing defect. NASA and SpaceX will use another heat shield for the flight that will undergo the same rigorous testing prior to flight.

Crew safety remains the top priority for both NASA and SpaceX and we continue to target September 2022 for launch of Crew-5.

SpaceX’s Dragon capsule hasn’t been totally free of issues up to this point, but the issues have been comparably minor. With the Inspiration 4 mission in September, issues with the capsule’s toilet became widely publicized. While clearly not ideal for the astronauts, the toilet posed no major threat to the safety of the crew.

Slightly more concerning, on Crew-2’s return last year, one of the four main parachutes was slow to fully deploy. SpaceX’s capsule is designed to be able to safely land even with only three parachutes. Crew-2’s deceleration was still nominal, and that parachute behavior was seen in tests, so SpaceX and NASA could continue operating as normal. Crew-3 launched in a brand new Crew capsule – Dragon capsule Endurance – just a few days after Crew-2’s splashdown.

Heat shields

One of the most important parts of any spacecraft is the thermal protection system (often abbreviated as TPS), with the heat shield being the primary component. The heat shield protects spacecraft from the immense destructive power of atmospheric reentry – and there are multiple ways spacecraft can go about doing that.

There are two main sections to SpaceX’s Dragon capsule thermal protection system: the back shell and the primary heat shield. The primary heat shield uses a proprietary material called PICA-X, an iteration of NASA’s PICA. PICA stands for Phenolic-Impregnated Carbon Ablator, and that “Ablator” is the key part of it. Dragon also uses a version of SPAM (SpaceX proprietary ablative material).

An ablative heat shield, as SpaceX uses on Dragon’s primary heat shield, works by heating part of the material itself into gas and burning away, thus moving the heat buildup away from the capsule. By comparison, a thermal soak heat shield – as was used on the Space Shuttle – is designed to absorb the heat and radiate it, without the material burning away. There are also other heat shield types, such as active cooling, which SpaceX had planned to use on its Starship rocket at one point. The thickness of the Dragon capsule’s heat shield allows it to act partially as a thermal soak, but the outer layer will still ablate, reducing the heat shield thickness.

Heat shield issue on Demo 2

After the return of Bob Behnken and Doug Hurley in Demo-2, some unexpected wear was found on the capsule’s heat shield. There was deep erosion on parts of the capsule’s heat shield when SpaceX inspected it after its flight. While the company claimed there was no risk to the astronauts, they still decided to update the heat shield ahead of the operational flight of Crew-1. The additional wear appeared around locations where bolts connected to the capsule’s trunk, so those specific locations were improved. The reason given for this wear was unexpected air patterns around the four bolt locations.

Axiom-1 heat shield issues

Axiom-1 was the first fully private astronaut crew to go to the International Space Station. Led by former NASA Astronaut Michael López-Alegría, the four-person crew had a somewhat extended stay on the station after weather delayed their return. They flew on Crew Dragon Endeavour for the third flight of the spacecraft, which previously carried Demo-2 and Crew-2.

While those watching the flight would have been unaware of any complications during the launch, Space Explored has been made aware of a cascade of issues. The most serious affected the spacecraft during its return to Earth. Hypergolic propellant made its way into the Crew Dragon Endeavour’s heat shield, according to sources at SpaceX and NASA who spoke with Space Explored. This hypergolic propellant is used by the Crew Dragon in its Draco engines – hypergolic means that the two parts spontaneously combust upon contact. It is believed that this hypergolic propellant impacted the integrity of the heatshield, causing dangerously excessive wear upon reentry.

SpaceX memo & NESC investigation

Space Explored has also been made aware of an internal memo at SpaceX addressing other issues during the flight of the Axiom private astronauts. Further, SpaceX made NASA aware of the issues with Axiom’s Crew Dragon heat shield, which has led to an NESC inquiry taking place in relation to the excessive wear. NESC is NASA’s Engineering and Safety Center, which was created in the wake of the Columbia disaster on the recommendation of the Columbia Accident Investigation Board. NESC’s mission is to “perform value-added independent testing, analysis, and assessments of NASA’s high-risk projects to ensure safety and mission success,” which works “proactively to help NASA avoid future problems.”

Space Explored has reached out to NASA and SpaceX regarding these issues. NASA quickly deferred the questions to SpaceX, as it is their vehicle, and SpaceX did not immediately respond to our request for comment.

SpaceX keeping heat shield quiet while raising funds

Space Explored was made aware of these issues with the Crew Dragon spacecraft multiple days before a CNBC report noted that the company was looking to raise another $1.7 billion. It’s unclear what risks have been disclosed to investors.

TPS reuse

Last year, it became known that SpaceX was planning to reuse its thermal protection system for Dragon between launches – both the backshell and the primary heat shield. Heat shield reuse requires in-depth inspection, though the possibilities with inspection are limited, and the number of times an ablative heat shield can be reused is limited.

Crew-4 heat shield reuse could pose potential threat

Crew-4’s launch had a number of “firsts.” The mission was the first commercial crew launch on a fourth flight booster. That all went off without a hitch, and SpaceX’s reuse of Falcon 9 Block 5 boosters has been very successful to this point. More concerning, SpaceX also reused the composite heat shield structure for the first time (despite the capsule being new).

 We will have a first time reuse on the composite heat shield structure on the Dragon vehicle for this flight. And then in particular we are reusing four Draco thrusters on this flight.

Steve Stich, Program Manager NASA’s Commercial Crew Program

This has some at NASA who spoke with Space Explored worried about the crew’s return, in light of the excessive wear that occurred previously. The launch occurred on April 27, just two days after Axiom’s April 25 return, and it is not clear if SpaceX and NASA were fully aware of the situation with Axiom-1’s heat shield before launch.

Space Explored’s take

The positive is that the astronauts thus far have made it back safely. Reuse is core to SpaceX’s plans as a company, and reusing Dragon capsules is a key part of that – especially since SpaceX ended production of the Dragon capsule after Crew 4’s Crew Dragon Freedom (though this could be restarted). While SpaceX would like to reuse the thermal protection system, the safety of astronauts must always be a top priority. If that means spending the extra expense and time between missions to replace the entire heat shield rather than relying on a potentially sub-par inspection, it is always worth it. While Crew Dragon may be SpaceX’s product, and SpaceX may be willing to take some risks, NASA is responsible for ensuring its astronauts have a safe journey to and from the space station as part of its Commercial Crew Program. NASA must act conservatively and minimize all risks possible during the inherently dangerous activity of human spaceflight. Taking shortcuts does not pay off.

Space Explored is continuing to look into the situation. If you are familiar with the situation and have information to share, you can reach out to me at derek@spaceexplored.com or reach me privately on Signal at (321) 317-7615.

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