Dragon safely en route to ISS as SpaceX review Falcon 9 ascent issues

by Chris Bergin

SpaceX’s Dragon is continuing its journey to the International Space Station (ISS) on its debut Commercial Resupply Mission (CRS-1/SpX-1). Meanwhile, evaluations are taking place into the failure of Engine 1 – possibly related to the failure of the Merlin 1C fuel dome – and the unsuccessful delivery of the first Orbcomm satellite to its preferred orbit.

Falcon 9 CRS-1 Launch:

SpaceX successfully launched their Falcon 9 rocket on Sunday, via an issue-free countdown, allowing for lift-off to occur at the first attempt.

Due to the near-instantaneous launch window, any issues during the terminal count would normally result in a scrub for the day.

“Successful” is the accurate way to portray the launch, given Falcon 9’s primary objective was to loft Dragon uphill to his orbital destination.

However, as was observed in video footage of the ascent, an incident occurred around 1:19 into the launch – initially causing internet speculation of an explosion on the aft of the vehicle.

The vehicle continued on its trajectory and successfully staged as advertised.

SpaceX have been quick to provide some level of clarification into the event, noting Engine 1 suddenly lost pressure, resulting in an engine shutdown command being issued.

We know the engine did not explode, because we continued to receive data from it,” noted SpaceX, before providing insight into the observed debris falling from the aft during the event.

“Our review indicates that the fairing that protects the engine from aerodynamic loads ruptured due to the engine pressure release, and that none of Falcon 9’s other eight engines were impacted by this event.”

While the full details of the ongoing evaluations are likely to remain restricted, as with most commercial companies, preliminary source information (L2 LINK to F9/Dragon CRS-1 Post Launch Updates) appears to be centering around the failure being related to a fracturing of the Merlin 1C engine’s fuel dome.

The failure is understood to be localized in that area on Engine 1, explaining why the engine continued to send data after the event.

Falcon 9 is designed to be able to cope with two engines out during ascent, and regardless of the outcome of SpaceX’s evaluations into the Engine 1 issue, the fact the vehicle continued on its primary mission of lofting Dragon to orbit will provide additional confidence in Falcon 9’s ability to deal with a loss of engine.

“We will continue to review all flight data in order to understand the cause of the anomaly, and will devote the resources necessary to identify the problem and apply those lessons to future flights,” added SpaceX. “We will provide additional information as it becomes available.”

The flight computer compensated for the loss of engine and created a new ascent profile in real time to ensure Dragon’s entry into orbit for subsequent rendezvous and berthing with the ISS. SpaceX note orbit was achieved, and there was no effect on Dragon or the cargo resupply mission.

Some impacts to the mission have been noted, albeit without confirmed relation to the Falcon 9 Engine 1 incident, such as the planned coelliptic burn, which was classed as requiring more fuel than calculated prior to launch.

Also, the first Orbcomm satellite to ride with the Falcon 9 faces a very bleak future after it was deployed into an unworkable orbit.

The plan called for Falcon 9’s second stage to make a short second burn to raise its orbit ahead of deploying the Orbcomm satellite, around 45 minutes after Dragon had been separated. The burn of the second stage was, however, contingent on the stage being deemed healthy enough to make the burn.

Source information (L2 LINK) noted the health checks were specific to the stage’s pneumatic pressure, tank pressures, propellant mass, attitude and orbital radius, with some of the checks being carried out at SECO-1 during the mission, with another check scheduled at SES-2 (Second Engine Start 2).

Unfortunately, the propellant mass check at SECO-1 failed to pass the requirements to ensure safe insertion of Orbcomm and the second stage in an orbit away from Station, resulting in no second burn commanded.

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The requirements were put in place after NASA teams evaluated the potential collision risk of Falcon 9 deployed Orbcomm satellites with the ISS. As such, NASA engineers had to use their experienced Monte Carlo analysis methods to set the safety parameters.

The backup plan was used to deploy the satellite into the upper stage’s parking orbit. The satellite is alive, in an elliptical orbit, but is likely not to survive for very long. The current plan is understood to revolve around using the small amount of remaining fuel to circular orbit, to provide it with a little more time on orbit before it eventually re-enters.

Per current reports, the Dragon began its early on-orbit operations nominally, with the first major milestone being deployment of its solar arrays 119 seconds after spacecraft separation.

Two and a quarter hours later, the spacecraft’s guidance, navigation and control (GNC) bay door opened.

Following the burn to circularise its orbit, Dragon will prepare for rendezvous with the ISS. Arrival at the space station is scheduled for Flight Day 3, on October 11, via a Radial Bar Approach manuever.

The Dragon spacecraft is carrying 905 kilograms (1995 lb) of cargo to the space station, consisting of 461.5 kilograms (1015 lb) of usable items, and the rest packaging.

(Images: via SpaceX, Orbcomm and L2’s SpaceX Dragon Mission Special Section – Containing presentations, videos, images (Over 800mb of unreleased hi res images from the C2+ mission alone), space industry member discussion and more).

(Click here: http://www.nasaspaceflight.com/l2/ – to view how you can support NSF and access the best space flight content on the entire internet).

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