Last-Minute Scrub Stalls Dragon Mission; Next Attempt NET Friday

Bearing the CRS-5 Dragon cargo craft within its nose, the Falcon 9 v1.1 stands patiently to execute the United States' first mission of 2015. Photo Credit: AmericaSpace

Bearing the CRS-5 Dragon cargo craft within its nose, the Falcon 9 v1.1 stands patiently to execute the United States’ first mission of 2015. Photo Credit: Mike Killian/AmericaSpace

SpaceX must wait until Friday, at the earliest, to despatch its fifth dedicated Dragon cargo mission (CRS-5) to the International Space Station (ISS), following today’s scrubbed launch attempt. In spite of an apparently smooth countdown, and near-perfect weather conditions at Cape Canaveral Air Force Station, Fla., the mission—which is being conducted under the language of SpaceX’s $1.6 billion Commercial Resupply Services contract with NASA—succumbed to a “Hold, Hold, Hold” call about 85 seconds before T-0 and the clock was halted. Since the ISS rendezvous commitment dictated an “instantaneous” launch window, lasting just one second, at 6:20:29 a.m. EST, it was obvious that no further attempt to get the Falcon 9 v1.1 booster airborne could be made, and steps were immediately taken to begin draining propellants and safing the vehicle for the backup opportunity at 5:09 a.m. on Friday, 9 January. Initially described as having been triggered by “an issue with the second stage,” early indications suggest that actuator drift on the thrust vector control system is the root cause.

This was a pity, for the countdown to today’s launch attempt had proceeded with remarkable smoothness. The Falcon 9 v1.1 was transferred to Space Launch Complex (SLC)-40 at the Cape late Sunday evening, and after the final loading of critical payloads, the vehicle was erected to a vertical configuration by means of the “strongback” arm on Monday. In yesterday’s press conference at the Kennedy Space Center (KSC)—featuring ISS Program Manager Mike Suffredini of NASA, together with SpaceX Vice President of Mission Assurance Dr. Hans Koenigsmann and Launch Weather Officer Major Perry Sweat of the 45th Weather Squadron at Patrick Air Force Base—it was noted that weather conditions had steadily improved from an initial 60 percent favorable to about 80 percent favorable. However, Major Sweat did point out that weather forecasting does become “dicey” when dealing with instantaneous launch windows.

The CRS-5 mission is expected to make the first attempt to land on an ocean-based barge, using its landing legs. Photo Credit: Mike Killian/AmericaSpace

The CRS-5 mission is expected to make the first attempt to land on an ocean-based barge, using its landing legs. Photo Credit: Mike Killian/AmericaSpace

By the small hours of Tuesday morning, the outlook appeared to have improved yet further, to 90 percent favorable, with the only minor issue centering upon a possible violation of the Thick Cloud Rule. “The temperature is at 20 degrees Celsius (69 degrees Fahrenheit) and winds have diminished over the last few hours,” AmericaSpace’s Launch Tracker noted at 5:24 a.m., “and there are currently no Launch Commit Criteria (LCC) violations.” As this encouraging news emerged, the fueling of the Falcon 9 v1.1 was concluded and liquid oxygen tanking transitioned from “fast-fill” into “replenishment” mode, in order to replace any cryogens boiled off in the remaining interval before T-0.

At 5:53 a.m., with just 27 minutes remaining before the scheduled liftoff, the ISS itself passed directly over the Cape. Doubtless, the incumbent Expedition 42 crew—commanded by NASA astronaut Barry “Butch” Wilmore—were waiting anxiously at the space station’s windows to witness the blazing launch, which was timed to occur 56 minutes before local sunrise in Florida.

In the meantime, at 6:07 a.m. the countdown reached its final “Go-No Go” polling point of all stations at T-13 minutes. Passing smoothly through the polls set up the proper conditions for the onset of the Terminal Countdown at T-10 minutes. “The Terminal Countdown is completely automated and although it is possible for a manual hold to be cold, any delay in the countdown is normally computerized,” explained the Launch Tracker. “The countdown can even be aborted after the main engines have been ignited.” After Autosequence Start at 6:10 a.m., the nine Merlin 1D engines of the first stage were chilled down, ahead of ignition, and all external power utilities from the Ground Support Equipment (GSE) were disconnected. The vehicle transitioned to internal power at 6:14 a.m., and the automated retraction of the strongback got underway a couple of minutes later. The Flight Termination System (FTS)—which would destroy the Falcon 9 v1.1 in the event of a major accident during ascent—was placed onto internal power and armed at 6:17 a.m.

Hissing and whining like a real dragon, about the break the shackles of Earth, the vehicle moaned through its final stages of tanking and pressurization. The Merlin 1D engines were purged with gaseous nitrogen and the Launch Director issued a “Go for Launch.” This was followed by a clipped “Range Green” from the Range Operations Co-ordinator (ROC), but at T-85 seconds a “Hold, Hold, Hold” call was heard over the loop. The call was immediately actioned, and the countdown clock stopped at T-81 seconds.

NASA astronaut Terry Virts packing stuff that will return to Earth on the SpaceX CRS-5 Dragon, which is scheduled to fly to ISS this week. Photo Credit: Terry Virts / NASA (@AstroTerry via Twitter)

NASA astronaut Terry Virts packing stuff that will return to Earth on the SpaceX CRS-5 Dragon, which is scheduled to fly to ISS this week. Photo Credit: Terry Virts / NASA (@AstroTerry via Twitter)

Since the mission had to launch at precisely 6:20:29 a.m., it was clear that no contingency time existed within today’s window and an automatic scrub was unavoidable. In the seconds after the hold call, effects to secure the FTS, restore the strongback and drain propellants from the Falcon 9 v1.1 got underway, as SpaceX’s safing procedures kicked into action. “Had the launch team not called the hold, then an automatic hold would have been called later in the countdown,” the Launch Tracker explained, “as this was outside the acceptable Launch Commit Criteria (LCC).”

In terms of the cause of today’s scrub, initial suspicion centered on “an issue with the second stage,” which was swiftly narrowed to actuator drift on the thrust vector control system. This was subsequently confirmed by a SpaceX statement: “During the terminal count, engineers observed drift on one of the two thrust vector actuators on the second stage that would likely have caused an automatic abort. Engineers called a hold in order to take a closer look.” Looking ahead to Friday’s launch attempt—timed to occur at 5:09 a.m., a full two hours before local sunrise—the weather forecast anticipates an 80 percent probability of acceptable conditions, with Flight Through Precipitation described as the principal violating factor.

 

Want to keep up-to-date with all things space? Be sure to “Like” AmericaSpace on Facebook and follow us on Twitter: @AmericaSpace

Missions » ISS » COTS » CRS-5 »

3 comments to Last-Minute Scrub Stalls Dragon Mission; Next Attempt NET Friday