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SpaceX's entire Environmental Assessment is based on old data that understates true impact
An ESGH Exclusive
"The Fruit of the Poisonous Tree" is one of my favorite legal metaphors. Generally the phrase is used for collection of evidence obtained by illegal means. If a warrant isn't granted for a wiretap on a suspect, any evidence from this surveillance is inadmissible in court. And any subsequent evidence obtained as a result of the wiretap is similarly poisoned.
Today we're not talking about poisoned fruit in the exact same manner but it’s helpful construct.
If you’re new here, read this section for some background:
To catch up, SpaceX is trying to get approval to test launch some Big Honkin’ Rockets from their facility in South Texas, and needs the Federal Aviation Administration (FAA) to sign off on the project. The FAA needs to make sure they follow environmental laws to the extent that they don’t get sued into the ground. Everyone with an interest in Aerospace has been watching developments in Boca Chica for months.
When SpaceX submitted the draft Programmatic Environmental Assessment (PEA) for the company's Starship program in Texas, it did so under the National Environmental Policy Act (NEPA). NEPA is grandaddy of all environmental laws and incorporates rules and regulations from a wide variety of agencies. As a reminder the PEA is the minor permitting and approval process through NEPA.
In choosing to go the PEA route, instead of the more cumbersome and time consuming Environmental Impact Statement (EIS) process, SpaceX had to describe an operation that would not create a "Significant" impact to the environment. I've written thousands of words on the topic; about how the idea that a spaceport on a tiny patch of land in the middle of a wildlife refuge used to test the largest rocket in human history, complete with a natural gas processing and utility sized power facilities could be "insignificant" to the environment is plainly absurd.
All that said, the delineation between "significant" and "not significant" is at times a matter of debate, often with blurred lines dependent on experts' opinions and political expediency .
NEPA explicitly requires disclosure of all impacts. This isn't just describing the impacts themselves; rocket heat plumes and explosions will kill wildlife and annoy the locals. We all accept that. But the extent of impacts is critical. Applicants must use commonly accepted techniques, based on science and law, to try to estimate how many Endangered species will be killed, how much habitat will be lost, how many buildings may be damaged due to sonic booms and anomalies, how many tons of air and water emissions are likely to be generated and so on.
Back in December, I posted about SpaceX’s constantly moving target on the Raptor engines and total thrust of the “Super Heavy” booster, the first stage rocket that lifts Starship into the upper atmosphere.
Musk intends to proceed with Engines at 245 tons of thrust going forward, a 30% increase over the 187.5 tons (375 klbf) represented in the noise study in the Environmental Assessment.
Why does that matter?
Setting aside all of the nuances of sound attenuation and modeling (an extraordinarily complex field of study), a simple framework from NASA is that the sound (in dB) correlates to engine thrust on a log-log basis.
A 30% increase in thrust is a 3-4 point increase in decibel level at the reference frequency. That 3-4 point increase means the power of the sound wave itself is ~2x more powerful than the 1.x Raptor engines. The impact on the entire booster’s sound output is unclear, but it’s not likely to be less powerful.
My focus at the time was on the individual engines and not the total size of the Super Heavy Booster.
The PEA and every related document describes in words a Super Heavy booster that generates 74 mega-newtons (MN) of energy. This energy comes out of the rocket in the form of heat, sound and most importantly: Thrust, the energy that will allow Starship to escape the confines of Earth’s gravity.
Modeling a rocket's heat plume, estimating air emissions and mapping out sound contours is about as settled of a science that exists. No model is perfect, of course, but it's pretty basic "rocket science," as such things go. These model outputs are then plugged into every impact determination, from property damage to wildlife and habitats. This week CNBC reported on the Draft Final Biological Opinion from the Fish and Wildlife service (FWS), which is required to satisfy Section 7 review under the Endangered Species Act, and was seen as a critical step in order for FAA to certify the PEA as legally viable. The document was acquired by a FOIA request by CNBC and available here.
The Document obtained by CNBC offered a ton of new insights; the resulting analysis was a good headline outcome for SpaceX as FWS didn’t throw a wrench in the project by determining that it was unlikely to “Significantly Modify” Endangered Species Habitat. We’ll put most of it aside and focus on one part of the timeline included by FWS:
Service asked if there was new information to consider in the project description and effects for the recent version 2.0 of the Raptor rocket engines that are reported to have 30% increased thrust. SpaceX response: As the efficiency of the Raptor engine increases, the total number of engines needed to achieve the maximum thrust (74 MN) decreases. So, we can use fewer Raptor 2.0 engines to achieve the same maximum thrust of 74 MN. Even with the use of the Raptor 2.0 engine, the maximum thrust will not exceed 74 MN, which is the maximum thrust identified in the BA and PEA. Accordingly, the information noted below does not prompt any changes in the project description or effects.
Similar questions to those I brought up about the ever-changing Raptor size made their way to FWS and they, in turn, asked SpaceX about it. On the surface, SpaceX’s answer tracks logically, but they re-iterate 74 MN of energy, which is 16.8 million pounds of thrust. I then remembered that The Noise Assessment in Appendix B of the PEA, which I discussed in December states:
The Super Heavy Booster would use thirty-seven Raptor engines that each provide sea-level thrust of about 375 Klbf
37 * 375,000 lb = 13.9 million pounds = 61.8 Mega-Newtons
74 Mega-newtons is 20% larger than the Super Heavy Described in the noise assessment. Because of the log-log relationship between engine power and noise output, this represents a ~50% or greater increase to sound impacts to the surrounding habitats. And indeed, if we zoom in, we can see that the sound model for orbital launches was completed in September of 2019.
Likewise, the Plume Exhaust Model in Appendix E of the PEA, which was completed in June of 2019, tells a similar story. The total thrust isn’t given, but they do give us Specific Impulse of the Engines as modeled (349. 6 lbf-s/lbm). This model states there will be 31 Raptor Engines. It also provides a detail about mass flow rate:
The PERCORP modelling of the Raptor thrust chamber included 1.2% of the total engine flow (13.89 lb/s) as film coolant
It follows then that the total mass flow rate is 13.89/0.012 or 1,157 lb/sec. The Rocket Equation can be used to solve for Thrust
Thrust(F) = Specific Impulse (Isp) * Mass flow rate (m-dot) * Gravitational constant
Thrust = 13 million pounds = 57 Mega-newtons
74 Mega-newtons as stated in the PEA represents a 30% increase from the values in this model!
And indeed, In January of 2019, that is what Musk was tweeting.
SpaceX updated their website for Starship in late September 2019, which formalized a long rumored plan to increase Super Heavy thrust, this time to 72 Mega-newtons. This change does not appear to be reflected in the 2019 models, however. These 2019 models were given to FWS to determine ecological effects on endangered species and were used throughout the PEA to describe impacts empirically. They seem to be deficient on their face. But, that’s not all!
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Did SpaceX just copy/paste?
In August of 2019, SpaceX submitted an Environmental Assessment to Launch Starship from Kennedy Space Center in Florida. The EA describes the project as:
The booster would be powered by 31 Raptor engines and Starship would be powered by seven Raptor engines. The Raptor engine was recently developed and is currently in Texas undergoing tests. Starship/Super Heavy maximum lift-off mass is approximately 5,000 metric tons (MT), with a lift-off thrust of up to 62 meganewtons (MN) (13.9 million lbs)
Note the 13.9 million pound thrust value. Now, here’s where it gets really interesting.
Here’s the Weighted dBA sound contour for Starship Super Heavy (62 MN variety)
The sound attenuation is 110 dB at ~4 miles and 100 dB at ~6 miles. Now take a look at the 74 MN variety (20% bigger) in Boca Chica
That’s right! 6 miles to 100 dBA on land and 4 miles to 110 dBA over water.
Now for comparison, here's the Weighted 100 dBA contour for SLS Block 2 (the other Moon rocket!). Starship is 35% larger by thrust and the sound curve difference is huge. Remembering that decibels are a logarithmic scale, the 100 dBA curve is 3 miles away for SLS as compared to 6 miles away for Starship.
Wrapping it all up
Now, in fairness, sound attenuation models do depend on ambient air conditions, ground albedo and moisture and vegetation. But given that
The supporting documents and models for Boca Chica were developed in 2019
The Starship EA for launch approval SpaceX was pursuing at Kennedy Space Center, also in late 2019, explicitly notes a 20% smaller first stage booster than the current 74 Mega-newtons
The sound contours are nearly identical from the two rockets that are over 3 million pounds of thrust separated
SpaceX has cut corners every single step of the way on this PEA
Unless there are some documents that aren’t public record, I’m going to say that it looks like SpaceX messed up. Big time. Again. And maybe wasted a ton of FAA’s time.
If this all proves out, that SpaceX indeed submitted years old models for sound contours, heat plumes and rocket emissions, then the Biological Opinion that we saw this week is out of date before they even finished. The Endangered Species Act consultation is null and void from the get go. Additionally, any impacts in the PEA that rely on this potentially massive error are “fruits of the poisonous tree” and run massively afoul of the law. There’s no way FAA could grant approval if what I’m seeing is true. And SpaceX would have no one to blame but themselves for this embarrassing oversight.