NASA leaves its Artemis I rocket exposed to winds above design limits

NASA leaves its Artemis I rocket exposed to winds above design limits

The top of the Space Launch System rocket and the Orion spacecraft probably faced the strongest gusts of wind on Thursday morning.
Enlarge / The top of the Space Launch System rocket and the Orion spacecraft probably faced the strongest gusts of wind on Thursday morning.

Trevor Mahlman

Early Thursday morning, Hurricane Nicole made landfall near Vero Beach on the east coast of Florida. Because Nicole had a very large eye, nearly 60 miles in diameter, her strongest winds were located well north of this landing position.

As a result, Kennedy Space Center experienced some of Nicole’s most intense gusts of wind late Wednesday night and Thursday morning. While such winds from a Category 1 hurricane are unlikely to damage facilities, they are of concern as the space agency left its Artemis I mission – comprised of the Space Launch System rocket and the Orion spacecraft – displayed on a platform at Launch Complex-39B. The pad is a stone’s throw from the Atlantic Ocean.

How strong were the winds? The National Weather Service hosts data from NASA sensors attached to this launch pad’s three light towers on a public website. It can be a bit difficult to interpret the readings as there are sensors at altitudes ranging from 132 feet to 457 feet. However, most of the publicly available data appears to be from an altitude of around 230 feet, which would represent the area of ​​the Space Launch System rocket where the middle 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. Additionally, the agency said in a blog post on Tuesday, “Current forecasts predict that the greatest risks to the pad are high winds that are not expected to exceed the SLS design.”

Based on publicly available data, however, it appears the rocket was exposed to near gusts of wind at or above 74.4 knots for several hours Thursday morning. A peak gust of 87 knots was reported on the National Weather Service site, with several gusts above NASA design levels. It is possible that the design limit of 74.4 nodes has some headroom.

The space agency is wrong to suggest that forecasters have not predicted such winds since Nicole. The reality is that the wind speed probability forecasts from the National Hurricane Center predicted the possibility of such strong winds, even though they were not the most likely scenario. On Tuesday, shortly before NASA released its blog update downplaying the risks to Nicole’s Artemis I, the National Hurricane Center predicted a 15% chance of hurricane-force winds near Kennedy Space Center, which would have produced gusts similar to those measured Thursday morning at the launch site.

And after

What shall we do now? Nominally, the space agency is still targeting a launch attempt at 1:04 a.m. ET (06:04 UTC) on Wednesday, November 16. Theoretically this is still 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 rocket’s structural integrity after being exposed to prolonged periods of high winds. A rocket is designed to climb, so although its structure can withstand intense pressure and winds in the vertical direction, it is not designed to withstand similar winds in the horizontal direction.

In a series of tweets, Metzger predicted that structural engineers will have a busy two weeks to assess the risk of storm damage and possibly request waivers to fly the vehicle after it was exposed to those loads. It will be a difficult task. It is not possible to X-ray the structures inside the rocket, so this process will involve running and re-running structural calculations. At some point, program management will have to decide if the risk — which includes the potential for the rocket to break during launch — is too high to fly without further inspections or corrective work.

So why didn’t NASA just back up for cover? Timing here is key. It takes about three days to prepare and bring the rocket from the launch pad to the Kennedy Space Center Assembly Vehicle Protection Building. So NASA probably should have made the rollback decision on 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 haven’t been made available to the public to talk about their decision-making process, but NASA’s blog posted on Tuesday suggests that a final call did indeed go out on Sunday evening: Based on predicted weather conditions and options for backtracking before the storm hits, the agency determined late Sunday that the safest option for launch hardware was to keep the Space Launch System rocket and spacecraft. spacecraft secured on the platform.”

From the space agency’s perspective on Sunday, there was clearly a non-zero risk of damaging winds to the rocket, but it was low, probably less than 5%. Rolling the rocket back at the time would have eliminated several launch attempts, and possibly even wiped out the entire November launch window, for the long-awaited Artemis I mission. Had the launch been delayed to December, it would have opened up a a host of other issues for the agency, perhaps the most critical being that its certification of the service life of solid rocket propellant — those massive powder-based propellants that have been stacked for almost two years — was on the verge to expire.

NASA therefore had many good reasons for wanting to pull the Artemis I mission off the launch pad this month. As a result, they played around with the weather a bit. They may have lost.

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