CAPE CANAVERAL, AFS – After overcoming a nerve-wracking crisis after successfully launching their fifth Falcon 9 rocket, SpaceX appears to have salvaged the latest commercial International Space Station resupply mission. Liftoff of the Falcon 9 occurred on time at 10:10 a.m. EST, during an instantaneous launch window, under cloudy skies but otherwise perfect weather. The 157 foot tall vehicle’s nine Merlin-1C engines, producing a total of 855,000 lbs thrust, powered Falcon through the lower atmosphere before shutting down three minutes after launch.
At that point, the second stage and its single Merlin engine ignited for the remaining six minutes of powered flight to complete the trip to orbit. With pinpoint accuracy, the vehicle delivered Dragon and 2,300 pounds of supplies and hardware into a preliminary orbit 199 km by 323 km high and an inclination of 51.6 degrees and released the spacecraft to begin its rendezvous with the space station. That’s when unexpected trouble threatened the entire mission.
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Unlike the last mission in December, the first stage performed flawlessly, bolstering confidence that SpaceX successfully addressed a problem which caused one of the first stage engines to shutdown approximately 80 seconds after launch. Nobody expected problems with Dragon, which has proven to be a reliable and capable spacecraft.
After separation, the Dragon spacecraft’s onboard computers began a pre-programmed sequence to power up its propulsion system, deploy the solar arrays and open the GNC door to expose the grapple fixture the station’s arm will grab during berthing. However, almost immediately, the computers aborted the post-insertion sequence when three of the four thruster pods failed to pressurize. This also prevented Dragon from deploying its two solar arrays, leaving the spacecraft in free-drift and lacking full power.
“Issue with Dragon thruster pods. System inhibiting three of four from initializing. About to command inhibit override,” SpaceX founder and Chief Engineer Elon Musk tweeted from SpaceX Mission Control shortly after it became apparent that Dragon had experienced a serious failure that threatened the $133 million mission.
Dragon is equipped with four pods, two containing 4 Draco thrusters and two with 5. The bell-shaped capsule uses the twenty thrusters to maintain attitude control, perform rendezvous burns and they also fire to decelerate Dragon and drop it from orbit at the end of the mission. NASA’s mission rules prohibit berthing Dragon unless at least three of the pods are operational.
Over the course of the next four hours, mission operators worked diligently to initialize the thruster pods as well as deploy the solar arrays, without which the mission would be all but certainly doomed. Compounding the urgency, without the thrusters, Dragon could possibly drop from orbit within two days and potentially burn up on re-entry.
All in all, Musk accurately summed up the atmosphere in Mission Control, telling reporters at a postlaunch teleconference that it was “a little frightening”.
When the thruster recovery took longer than expected, controllers decided to command the solar array deployment about 2 hours after launch. It is preferred to have full thruster control when the arrays spring out like wings and impart additional side forces on the spacecraft. However, temperatures were falling rapidly in the spacecraft and it was necessary to deploy the arrays to give Dragon full electrical power. It also helped stabilize the spacecraft’s spin in much the same way as a spinning figure skater will slow down by extending their arms.
Finally, about four hours after launch, Musk relayed the information everyone had been waiting to hear, “Thruster pods one through four are now operating nominally. Preparing to raise orbit. All systems green.”
With Dragon fully back in action, engineers quickly performed an orbit-raising maneuver to ensure Dragon would stay in orbit and put the spacecraft on track to rendezvous with the space station.
Near real-time analysis determined that there was possibly a problem with the oxidizer feed mechanism for the thruster pods that prevented three of them from pressurizing and shutting down the spacecraft’s on-orbit deployment sequence. Mission controllers used a technique called a “pressure hammer” in an attempt to clear the blockage or balky regulator. This required repeatedly cycling valves to dislodge the blockage and allow the super-cold liquid helium to pressurize Dragon’s oxidizer tanks. Eventually, the effort paid off and SpaceX was able to initialize all four pods.
“We noticed after separation that only one of the four thruster pods engaged or was ready to engage,” said Musk after launch. “And then we saw that the oxidizer pressure in three of the four tanks was low.”
“We think there may have been a blockage of some kind or stuck check valve going from the helium pressurant tank to the oxidizer tank,” Musk said. “Whatever that blockage is seems to have alleviated.”
Although it is pure speculation at this point, the blockage, if it existed, could have been either debris or more likely a small crystal of frozen oxidizer in the line.
While Dragon appears to have weathered the storm no worse for the wear, at this point, the trouble experienced today has already resulted in a delay for Saturday’s planned berthing of the spacecraft. SpaceX officials expressed confidence that NASA will still allow the craft to rendezvous with ISS, although a thorough checkout of Dragon’s systems is required to build confidence that the same problem won’t return during the spacecraft’s final approach to the station.
NASA and SpaceX are looking at early Sunday morning for the next possible opportunity to berth Dragon to the station. That, of course, will only happen if all the spacecraft’s systems check out okay and ISS mission managers give the go-ahead for the supply craft’s delayed arrival.
Despite Dragon’s difficulty after launch, NASA managers expressed confidence in the SpaceX team and its handling of the crisis in particular.
“They did everything exactly right with the vehicle,” said NASA Associate Administrator for Space Operations Bill Gerstenmaier. “The team in Hawthorne was awesome. They prioritized immediately what things they needed to do.”
Obviously, both SpaceX and NASA will have to conduct a thorough analysis of the spacecraft to ensure that a problem like this doesn’t recur. That is likely to happen before SpaceX makes its next ISS resupply mission. But for now, the focus is on the coming days with the rendezvous and berthing of the third commercial spacecraft to visit the space station.
Dragon is carrying about 2,300 pounds of cargo, of which 1,268 pounds are supplies, including critical materials to support the 160 investigations – 50 of which are new – planned for the station’s Expedition 34 crew.
Several studies involve a small flowering plant called thale cress, or Arabidopsis thaliana. The Plant Signaling investigation and Biological Research in Canisters (BRIC) 17-1 both study how the plants’ gene expressions change in microgravity. Scientists think plant cells living in space do not behave the same way as cells in plants on Earth, and the experiments will examine these changes on a molecular level. Cell cultures derived from thale cress plants are grown in Petri dishes and later examined to determine which genes are involved in certain cellular changes. A related experiment, BRIC 17-2, exposes thale cress seedlings to low oxygen levels to examine its effects on the health of their roots.
Another study making a round trip with Dragon will look at how metal mixtures solidify. Coarsening in Solid Liquid Mixtures-3 (CSLM-3) examines the growth and solidification of lead-based liquids that contain small amounts of tin. When the liquid solidifies, the tin forms small branch-like structures called dendrites. By using tiny amounts of tin, scientists can observe single dendrites at a time, which would be impossible on the ground because of gravity’s effects. By understanding how temperatures and time control the growth of these dendrites, materials scientists may find new ways to produce materials from molten metals.
Dragon is delivering the Advanced Colloids Experiment-M-1 (ACE-M-1) investigation on behalf of Procter & Gamble, which owns several brands of personal care products. ACE-M-1 testing will take advantage of the microgravity environment of station to study how microscopic particles spread out and clump together in gels and creams.
Along with scientists from NASA centers and private industry, plenty of students are excited for the deployment of their own experiments, facilitated by the NanoRacks system. Students from several California schools developed investigations to study bacteria, iron corrosion, battery performance and carbon dioxide levels aboard station, all of which will be delivered by Dragon.
Finally, the Wet Lab Kit will provide crew members with frequently-used tools and supplies needed to perform in-orbit experiment sample manipulation and analysis. Wetlab will increase experiments’ science return while decreasing the time between investigations.
After about three weeks on orbit, Dragon will return with about 2,668 pounds of cargo, which includes crew supplies, scientific materials (including results from human research), biotechnology, materials and education experiments, as well as space station hardware. Return to Earth is currently scheduled for March 25, but may slip accordingly with the slip in the craft’s arrival at the station.
(Matthew Travis / Zero-G News)
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