SpaceX’s CRS-3 Dragon contamination concern cleared
A sewing machine, used to stitch the cloth shields that are used to protect payloads in Dragon’s trunk, is understood to have been a potential cause of the oil contamination that played a part in a postponement to the CRS-3/SpX-3 mission to the International Space Station (ISS). However, on Friday, SpaceX noted they had cleared the potential of the stains outgassing in a vacuum – which could have been a threat to the optics on two of Dragon’s payloads.
SpaceX delayed their next mission to the ISS to a NET (No Earlier Than) launch target of March 30, citing “open items” that require additional time to remedy, so as “to ensure the highest possible level of mission assurance.”
Falcon 9 and Dragon had already passed the Flight Readiness Review (FRR) stage, before successfully completing a Static Fire test at SpaceX’s SLC-40 launch complex. The duo then returned to the hanger for final pre-launch processing and a Launch Readiness Review (LRR).
With just three days to launch, SpaceX officials noted the slip, without citing any specifics surrounding the delay. However, CBS’ Bill Harwood revealed the issue was related to contamination being found inside the Dragon’s trunk section.
Since then, NASA officials have publicly noted the contamination is specific to the beta cloth shields that protect the trunk payloads from the corrosive effects of atomic oxygen when the spacecraft is in space.
Multiple L2 sources have noted the contamination is understood to be oil from a sewing machine that was used to stitch the beta cloth shields during their manufacture. These “machine oil stains” have been found in the threads on the cloth.
The stains were found during final processing, with SpaceX usually loading their payloads very close to the scheduled launch date. The fact that it was found will be a feather in the cap of their quality assurance process.
SpaceX, asked by NASASpaceFlight.com for a status update at the beginning of this week, had not yet responded at the time of publication. However, Gwynne Shotwell, President and Chief Operating Officer of SpaceX, addressed the postponement on The Space Show on Friday.
Firstly, it was noted that four issues were still being worked when SpaceX opted the delay the launch, with the oil stains being just one of the issues of note.
“We were working four issues,” noted Ms. Shotwell. “We were struggling on some data transfer buffering with Houston. We wanted a little more time to work with the Range on trajectory (relating to re-entry and landing of the first stage). My operations crew was in a time crunch for Dragon, which is a very new Dragon.
“Finally, we did notice stains on the impact shielding – which looks like a blanket – inside the Dragon trunk. So it was the combination of those four things that resulted in our thinking we need to step back and that we do everything we can to make this mission successful and go work these issues.”
The payloads that were evaluated against such outgassing includes the High Definition Earth Viewing (HDEV) package, that is comprised of four high-definition cameras to be placed on the Station’s exterior for use in streaming live video of Earth for online viewing.
The HDEV visible HD video cameras are a fixed payload camera system that requires no zoom, no pan or tilt mechanisms. One camera will be pointed forwards, into the ISS’ velocity vector, with two cameras aft (wake), and the other one camera pointing nadir.
The OPALS payload aims to demonstrate free-space optical communications technology. The hardware employs a package that will be capable of receiving a laser beacon that will be transmitted from a ground telescope.
While maintaining lock on the uplink beacon using a closed loop control system and a two-axis gimbal, the OPALS flight system will downlink a modulated laser beam with a formatted video.
The payload consists of a gimbal-mounted optical head, and a sealed container to hold the electronics, laser and motor drivers. The optical head houses a camera to track the beacon and a lens collimator system to transmit the data laser
Outgassing of the oil could – it had earlier been suggested – contaminate the delicate optics of the HDEV cameras and the OPALS equipment. At worst, the contamination could coat and fog the optics.
Notably, this type of concern ranges back into the Space Shuttle days, where several lessons were learned about the potential of material/substance outgassing and impacts on payload optics, specifically on the Hubble Space Telescope’s highly sensitive cameras.
Even the EMU gloves that were used during HST servicing mission spacewalks were “baked out” before each HST flight to remove potential contamination from the silicone of the gloves.
While it was initially thought SpaceX engineers would either coat the cloths with protective material, or completely replacing the cloth shields in the Dragon’s trunk, Ms. Shotwell noted they had since cleared the concern and will fly the shields as-is.
“With respect to the contamination, it was oil from the manufacturing process,” added Ms. Shotwell. “It was in very regular pattens and it didn’t show up right away when they were manufactured. So luckily, our pre-encapsulation checks caught it and then a really hard working team – SpaceX, NASA, Boeing – took a really hard look at what was the contamination – which was oil.
“In the end we decided to use it as-is. It did not add substantial risk to the optical payloads that are located in the trunk. (However,) it’s worth saying the trunk never had any contamination control requirements on it, so taking on these optical payloads, we were all leaning forward to make this work. So that’s probably why you see some of the jitter on the contamination issues.
The latest launch date of March 30 – which has since been approved by the Eastern Range – was partly dictated by a Russian Soyuz that is heading to the ISS on March 25, while an Atlas V is also set for launch on the 25th and will hold the Range around that date.
A March 30 launch target calls for a 22:50pm Eastern T-0, with a backup date available on April 2, at 21:39pm Eastern.
Ms. Shotwell noted March 30 is currently “looking good”.
(Images: SpaceX and NASA)
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