KENNEDY SPACE CENTER, Fla. — A SpaceX Falcon 9 rocket is ready to launch a Dragon cargo spacecraft to the International Space Station July 18, although a risk assessment for a Dragon abort scenario has led NASA to decide to evacuate part of the center during the launch.

SpaceX performed a static fire test of the upgraded Falcon 9 on the pad at Launch Complex 40 at Cape Canaveral Air Force Station at around 8:30 a.m. Eastern July 16. That test, part of the company’s standard pre-launch preparations, appeared to go well.

“Everything looks very good right now,” said Hans Koenigsmann, vice president of flight reliability for SpaceX, at a NASA pre-launch briefing here several hours after the test. A final decision to proceed with the launch awaited a launch readiness review scheduled for later in the day. “I don’t expect anything at this time other than a go” for the launch, scheduled for 12:45 a.m. Eastern July 18, he said.

The launch is not affected by a last-minute hiccup in plans created by a risk assessment completed July 17 by the U.S. Air Force 45th Space Wing, which operates Cape Canaveral Air Force Station. NASA informed media late that day that “multiple NASA facilities including the Vehicle Assembly Building and the Press Site will be closed at least 60 minutes prior to launch.”

Cody Chambers of KSC’s range safety office said at the briefing that NASA made the decision because of concerns that the Dragon spacecraft could, in the event of a launch abort, land on center property. The hazard area does not extend outside of KSC property, he said.

“What we’re looking at is, in the event of a Dragon abort scenario, the predominant winds would carry the spacecraft back towards KSC property,” he said. “The spacecraft, on impacting the ground, could see a risk of releasing some toxic commodities” such as the nitrogen tetroxide and hydrazine propellants for its thrusters.

This scenario has not occurred before because Dragon did not have an abort capability prior to the loss of a Dragon spacecraft on a Falcon 9 launch failure in June 2015. SpaceX updated the spacecraft’s software after that accident to give it the ability to deploy its parachutes in the event of a similar launch failure in the future. The first Dragon with that capability launched in April, but winds for that launch were blowing in a different direction and thus no evacuation of KSC property was required.

The decision took many by surprise and forced NASA and others to scramble to make backup plans for issues ranging from alternative view sites for guests of the launch to television coverage. “We are driven by uncertainty,” Chambers said when asked about the timing of the risk analysis and decision to close part of KSC for the launch. He added NASA may make “adjustments as necessary” for those closure plans based on updated analyses closer to launch.

Landing plans

What is not a factor in the risk assessment, he said, is SpaceX’s plan to attempt to land the Falcon 9 first stage on a pad at the former Launch Complex 13 at Cape Canaveral, now called Landing Zone 1 by SpaceX. That will be only the second time the company has attempted to bring the first stage back to land, after the successful landing of the first stage on an Orbcomm satellite launch in December 2015.

Koenigsmann said the difficulty of this landing will be “on par” with that earlier landing. While a return to land requires more propellant than a landing at sea, the trajectory of this flight will be more benign that previous landings of stages on missions to carry satellite into geostationary orbit.

“I’m pretty optimistic at this point in time that we’ll land it, but I will always knock on wood,” he said.

SpaceX has successfully landed four stages to date, one on land and three on a ship at sea. The stage from the December Orbcomm mission, the first successful landing of any kind, will be put on display outside of SpaceX’s headquarters. Koenigsmann said the stage from an April Dragon launch will likely to be the first to be reflown, some time this fall. SpaceX “is in talks” with a potential, unnamed customer for that mission, he said.

Dragon cargo

The primary purpose for the launch, though, is to send a Dragon cargo spacecraft on to the ISS, the ninth such mission under SpaceX’s Commercial Resupply Services (CRS) contract with NASA. The Dragon is carrying more than 2,250 kilograms of supplies, experiments and hardware to the station.

The Dragon’s payload includes the second International Docking Adapter (IDA), which will be installed on the station to allow commercial crew vehicles under development by Boeing and SpaceX to dock with the station. The first (IDA) was lost with the rest of the Dragon spacecraft in the June 2015 Falcon 9 launch failure.

NASA is developing a third IDA to replace the one lost in last year’s launch failure. That third adapter is tentatively scheduled to launch on SpaceX’s CRS-16 cargo mission in 2018, said Kirk Shireman, NASA ISS program manager, during a July 13 briefing at the ISS Research and Development Conference in San Diego. That launch could be moved up, he said, but the IDA can only fly on Dragon missions to the station since it’s carried as external cargo.

At least one IDA needs to be installed on the station to support commercial crew flights, starting with test flights by SpaceX in 2017 and Boeing in early 2018. Shireman added that some future cargo vehicles may also use the ports to dock with the station, rather than be berthed by the station’s robotic arm as they are today.

He added, though, that commercial crew missions require only one, and not two, IDAs in place. “There is no requirement to have both IDAs on orbit prior to the launch of the first commercial crew test flight,” he said. Having two, though, does provide some flexibility in crew handovers by allowing two vehicles to be docked simultaneously.

Among the research payloads flying on this mission is a handheld device that will perform the first DNA sequencing experiments in space. Sarah Wallace, a microbiologist at NASA’s Johnson Space Center, said at the July 13 briefing the experiment will sequence the genomes of several organisms, including a mouse, and compare them to identical tests done on the ground.

Wallace said Kate Rubins, a biologist and NASA astronaut who arrived at the station earlier this month, helped with the experiment design, although the equipment is designed to be simple enough that any trained astronaut can use it. “We believe it’s going to be a game-changer to have this capability on the ISS,” Wallace said.