Trevor Mahlmann
Early on Thursday morning, Hurricane Nicole made landfall near Vero Beach, on Florida’s eastern coast. Because Nicole had a very large eye, nearly 60 miles in diameter, its strongest winds were located well to the north of this landfalling position.
As a result of this, Kennedy Space Center took some of the most intense wind gusts from Nicole late on Wednesday night and Thursday morning. While such winds from a Category 1 hurricane are unlikely to damage facilities, they are of concern because the space agency left its Artemis I mission—consisting of the Space Launch System rocket and Orion spacecraft—exposed on a pad at Launch Complex-39B. The pad is a stone’s throw from the Atlantic Ocean.
How intense were the winds? The National Weather Service hosts data from NASA sensors attached to this launch pad’s three lighting towers on a public website. It can be a little difficult to interpret the readings because there are sensors at altitudes varying from 132 feet to 457 feet. Most of the publicly available data appears to come from an altitude of about 230 feet, however, which would represent the area of the Space Launch System rocket where the core stage is attached to the upper stage. The entire stack reaches a height of about 370 feet above the ground.
Prior to Nicole’s arrival, NASA said its SLS rocket was designed to withstand wind gusts of 74.4 knots. Moreover, the agency stated on Tuesday in a blog post, “Current forecasts predict the greatest risks at the pad are high winds that are not expected to exceed the SLS design.”
From the publicly available data, however, it appears that the rocket was exposed to wind gusts near, at, or above 74.4 knots for several hours on Thursday morning. A peak gust of 87 knots was reported on the National Weather Service site, with multiple gusts above NASA’s design levels. It is possible that the 74.4-knot design limit has some margin built into it.
The space agency is incorrect to suggest that forecasters did not predict such winds from Nicole. The reality is that wind speed probability forecasts from the National Hurricane Center allowed for the possibility of winds that high, even if they were not the most likely scenario. On Tuesday, shortly before NASA issued its blog post update downplaying the risks to Artemis I from Nicole, the National Hurricane Center predicted a 15 percent chance of hurricane-force winds near Kennedy Space Center, which would have produced gusts similar to those measured Thursday morning at the launch site.
What’s next
So what happens now? Nominally, the space agency is still targeting a launch attempt at 1:04 am ET (06:04 UTC) on Wednesday, November 16. Theoretically that remains possible, but in reality it seems unlikely. When it is safe for NASA employees and contractors to return to Kennedy Space Center, perhaps later today or Friday, they will begin inspections of the vehicle.
According to Phil Metzger, an engineer who worked on the space shuttle program for NASA, the most likely concern will be the structural integrity of the rocket after being exposed to prolonged periods of high winds. A rocket is designed to go upward, so although its structure can endure intense pressure and winds in a vertical direction, it is not designed to withstand similar winds in the horizontal direction.
In a series of tweets, Metzger predicted that it will be a busy couple of weeks for structural engineers to assess the risks of damage from the storm and potentially seek waivers to fly the vehicle after its exposure to these loads. This will be a difficult task. There is no ability to X-ray the structures inside the rocket, so this process will involve running, and re-running, structural calculations. At some point the program’s leadership will have to decide whether the risk—which includes the potential for the rocket to break apart during launch—is too high to fly without further inspections or remedial work.
So why did NASA not just roll back for cover? The timing here is key. It takes about three days to prepare and roll the rocket back from the launch pad to the protective Vehicle Assembly Building at Kennedy Space Center. NASA, therefore, probably would have had to make the rollback decision Sunday. At the time, the most likely outcome, predicted by forecasters, was that the rocket would have been exposed to 40-knot winds.
Space agency officials have not been made publicly available to talk about their decision-making process, but NASA’s blog post on Tuesday suggests that a final call was indeed made on Sunday night: “Based on expected weather conditions and options to roll back ahead of the storm, the agency determined Sunday evening the safest option for the launch hardware was to keep the Space Launch System rocket and Orion spacecraft secured at the pad.”
From the space agency’s vantage point on Sunday, there was clearly a non-zero risk of damaging winds to the rocket, but it was low, probably less than 5 percent. Rolling the rocket back at the time would have taken away several launch attempts, and perhaps even wiped out the entire November launch period, for the long-awaited Artemis I mission. If the launch was delayed into December, that would have opened up a host of other problems for the agency, perhaps most critically that its certification of the solid rocket booster lifetime—these massive powder-based boosters have been stacked for nearly two years—was about to expire.
So NASA had a lot of good reasons to want to get the Artemis I mission off the launch pad this month. Accordingly, they gambled a bit with the weather. They may have lost.
