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Raumfahrt - SpaceXs Crew Dragon fire sent hazardous chemical compounds into the environment

26.04.2019

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When a test fire of SpaceX's Crew Dragon capsule went up in smoke Saturday, the incident at Cape Canaveral Air Force Station puffed up a reddish plume that was seen for miles.

What few likely knew was just how toxic and potentially deadly that distant cloud could have been if winds had shifted onshore.

The special propellants for the Crew Dragon capsule – designed to carefully supply engine firings during liftoff anomalies and navigate the craft in space – are far more dangerous than those used for the typical launch. The hydrazine and nitrogen tetroxide used Saturday are called hypergolic fluids, meaning they react violently when they come in contact with one another. They have been used in rockets and spacecraft for decades because they can be stored over a long period of time and still be reliable.

But they are dangerous to handle.

To prevent any potential exposures to the public, tests like Saturday's are conducted when prevailing winds point away from population centers. 

SpaceX, NASA and the U.S. Air Force have remained tight-lipped on the April 20 incident, offering few details about the fire, which lofted reddish nitrogen tetroxide – sometimes referred to as fuming red nitric acid – into the sky as hundreds spectated a surfing festival at Cocoa Beach. 

There were no injuries. On Thursday, independent safety advisors said that NASA and the company had followed proper test procedures.

“The test site was fully cleared, and all safety protocol was followed,” Patricia Sanders, chair of NASA’s independent Aerospace Safety Advisory Panel, said Thursday during a quarterly meeting. “Both NASA and SpaceX immediately executed mishap plans per the agency and the company guidelines.”

Saturday's test failure cast a shadow of uncertainty over Elon Musk's $1 billion project to get humans back to orbit, launching from American soil. The last time that happened was July 2011, when space shuttle Atlantis made its swan song mission. Since then, NASA has been buying seats on Russian-made Soyuz rockets to get astronauts to the International Space Station.

SpaceX had said a pair of astronaut test pilots were on track to fly a Crew Dragon to the ISS as soon as July, but Saturday's test failure has clouded timelines.

SpaceX confirmed the capsule involved in Saturday's incident was the same one retrieved from a March 8 splashdown off the Florida coast, a wrap-up of its first successful automated flight to the ISS. Teams were preparing it for an in-flight abort test, which would see the capsule rapidly fly away from a failing rocket.

FLORIDA TODAY photographer Craig Bailey, covering Saturday's surfing festival in Cocoa Beach, captured an image of orange plume rising from SpaceX facilities at the Cape around 3:30 p.m. Teams were testing the capsule's SuperDraco engines at the time, which are the powerful pieces of hardware that propel the spacecraft away in the event of an emergency.

Notifying Space Coast authorities

SpaceX is required as part of their permit with the Florida Department of Environmental Protection to have a response plan in place in the event of an incident, which the company implemented, DEP officials said.  

"The fire department and base personnel responded accordingly," DEP officials said in a prepared statement. "The facility indicated they were able to fully contain the fire and material to the landing pad area and no other building or areas were affected. At this time, SpaceX is still conducting their investigation into the cause of the incident."

The company must submit a discovery report to DEP within 15 days with details about the incident, the state agency said.

"The Department will review that report and conduct a site visit, and then determine the next steps in the investigation and what further assessment or cleanup activities may be necessary," DEP officials said.

SpaceX could not be reached for comment Thursday.

Brevard County Emergency Management works with Cape Canaveral Air Force Station Emergency Management and Kennedy Space Center Emergency Management to respond to launch hazards or concerns, said Don Walker, spokesman for Brevard County.

Emergency Management is activated for every launch and is notified of static fire testing on the Air Force station, Walker said.

"In the case of SpaceX’s anomaly last weekend, there was no public safety threat, both due to wind direction and due to the distance of the incident from public areas," Walker added.

"If space launches, landings or other on-base activity results in an anomaly that is a public safety threat, Brevard County Emergency Management would use a variety of methods to alert the public to shelter indoors (go inside and stay inside)," Walker said. "These tools include social media, text messaging, AlertBrevard automated call/text/email notifications, and even wireless emergency alerts if appropriate. Information would also be shared immediately with all public safety agencies and 911 centers within the county."

The history of nitrogen tetroxide

Mishaps with hydrazine and nitrogen tetroxide have happened before, each offering lessons. Rocket accidents in decades past have evacuated entire towns. And if Saturday's toxic cloud had reached people, it would have potentially caused severe burns on contact. 

When space shuttle Columbia broke apart over Texas on Feb. 1, 2003, most of the hydrazine and nitrogen tetroxide propellants were thought to have likely burned up before reaching the ground, officials said at the time.

Nitrogen tetroxide is potentially more dangerous than liquid hydrogen and can produce toxic clouds of gas if one of the trucks that delivers it should ever have an accident. The chemical, which was used to ignite hydrazine fuel on the shuttle and Delta and Titan rockets, can eat through metal or skin.

In January 1997, when a Delta rocket blew up after liftoff, debris from the explosion fell into the Atlantic Ocean and at the Air Force station. Some landed around the launch pad, and a small fire flared up and a few dozen nearby parked cars were destroyed. Nearby residents were advised to stay inside, close windows and turn off their air conditioning systems to prevent vapors from entering homes. 

The worst accidental spill of nitrogen tetroxide in American history came in August of 1978 from a Titan rocket at McConnell Air Force Base in Wichita, Kansas, according to a study by a NASA scientist at KSC.

A total of 13,450 gallons of liquid nitrogen tetroxide spilled into the underground missile silo. Two members of the 381st Strategic Missile Wing were killed, and 25 more were injured from the toxic liquid and vapor exposure, according to the study, and the silo suffered extensive damage.

One supervisor died from exposure within minutes after his safety suit failed.

An estimated 100 people had to evacuate the nearby town of Rock, Kansas, to avoid the fumes pouring out of the silo.

Quelle: Florida Today

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