Concluding a highly successful docked mission for STS-134, Endeavour and her crew undocked at 22:55 Central on Sunday, ahead of a busy and prolonged farewell to the Station which she was heavily involved in building. It involves nearly five hours of work until Endeavour’s final separation burn, as she performed a debut manuever specific to the STORRM Development Test Objective (DTO).
STS-134 Undocking:
Following a pre-departure reconfiguration of one of the EMU (Spacesuits) to be left on Station for use at a later date by Expedition 28 flight engineer Ron Garan, work on the Carbon Dioxide Removal Assembly (CDRA), and the final transfers of equipment and supplies between Endeavour and the ISS, the STS-134 crew bid farewell to the ISS crew on Flight Day 14.
“We’ve had a very successful mission, a really good 10 days or so,” noted STS-134 commander Mark Kelly. “Looking forward to getting home and giving the ISS crew some peace and quiet.”
Commander Kelly’s best wishes were responded to by Russian Commander Andrei Borisenko, who wished the crew a “soft landing”, a possible internal joke to how the orbiters are much easier on the crews when compared to the Soyuz during re-entry and landing.
In the end, hatches between the two spacecraft were open for joint crew operations for a total of 10 days, 23 hours, 45 minutes. Hatches closed between Endeavour and the space station at 6:23am Central – 12 days, 22 hours, 27 minutes into the mission.
Following leak checks and the checkout of systems to be used for the Flight Day 15’s undocking, Endeavour’s crew went into their final sleep period whilst still being attached to the orbital outpost.
STS-134 Specific Articles: http://www.nasaspaceflight.com/tag/sts-134/
In preparation for 22:55 Central undocking, the ISS’ Solar Alpha Rotary Joints (SARJ) were locked, and the four giant arrays were feathered, so as to protect the arrays from plume impingement as Endeavour pulsed her Reaction Control System (RCS) jets to move gently away from the Station.
The arrays on both the European ATV-2 (Automated Transfer Vehicle) and those on the Russian segment, were also be feathered for the same reason.
Easing away from the Station for a period of nearly 30 minutes, Endeavour was commanded through a stunning flyaround of the ISS, taking over one hour, prior to the debut of the STORRM (Sensor Test for Orion Relative Navigation Risk Mitigation) DTO.
STORRM Overview:
The STORRM flight test on STS-134 is demonstrating the first US-developed, highly-reliable navigation sensor – the Vision Navigation Sensor (VNS) – designed expressly for rendezvous and docking for future American spacecraft.
Utilizing state-of-the-art laser-based sensor technology necessary for accurate, robust, and safe navigation between the docking vehicles, the system incorporates advanced LiDAR (Light Detection And Ranging) technology that can determine shapes, intensity and distance to objects from as far away as three miles or as close as five feet.
Its applications are wide-ranging, providing the required hazard avoidance data required for safe landing on asteroids, the moon, and Mars. The sensing technology may also improve a variety of Earth-bound applications such as climate and environmental observations, robotic maneuvering, topographical surveillance, and hazard avoidance systems for cars or aircraft.
Lockheed Martin and Ball Aerospace independently invested several million dollars in developing and building the space-qualified VNS being flown on STORRM, originally designed with the Orion crew exploration vehicle in mind.
While Orion continues to be developed, amid much fanfare for a name-change to the Multi Purpose Crew Vehicle (MPCV), its main launch vehicle companion – the Space Launch System (SLS) – is potentially just days away from transitioning from study to development.
It is hoped specific missions will also be named soon, which will likely utilize the STORRM technologies under investigation during Endeavour’s DTO.
Preparations for this full-up test began in April of last year, when Orion retro-reflectors were installed on the ISS visual docking target during STS-131.
“STORRM DTO #703 Docking Target Installation: Background: Relative Navigation sensors for Orion vehicle require special ‘reflectors’ on the PMA-2 docking target,” explained STS-131 Flight Readiness Review (FRR) documentation on L2.
“DTO #703 (post-undocking re-rendezvous) slated to fly on STS-134/ULF6. STS-131/19A will fly and transfer STORRM DTO docking target reflectors to ISS. ISS crew will install reflectors and STS-131 crew will take close-out photographs of docking target after hatch closure (prior to undock).”
Opening STORRM’s role with STS-134, a large amount of data was gathered during Flight Day 3’s rendezvous and docking with the ISS.
“Sensor Test for Orion Relative-Navigation Risk Mitigation (STORRM) Development Test Objective (DTO) performance during rendezvous and docking was excellent. STORRM collected 232 GB of Docking Camera data and 108 GB of Vision Navigation Sensor (VNS) data,” noted an overview (L2) to the Mission Management Team (MMT).
“The key technology for STORRM, the VNS, performed as expected in terms of moding, laser firing, and imaging the ISS. The team was able to see images from the docking camera in real-time as well.”
During the downloading of the VNS data via the Ku band system, a problem relating to the STORRM Local Area Network (LAN) connection at the access point of the hardware was noted. However, this only caused a slight delay to the data reaching the ground.
“STORRM DTO exhibited an Ethernet problem during the VNS data retrieval from Data Recorder Unit (DRU) 1 which may be caused by connections; the STORRM ground controllers did not receive all of the files to be down linked,” added a later MMT overview.
“The data transmission halted several times with duration of half hour to an hour each. There (was a need) for some reconfiguration to retrieve the rest of the files, prior to power down DRU1.”
Ready for action after undocking, a series of presentations and videos (L2) overviewed the role of the STORRM hardware.
“Undock: Sensors are powered on 30 minutes prior to physical separation. As Orbiter “backs away”, sensor settings are applied as a function of range to ISS. Orbiter remains in “Target Track” when not performing translational burns,” noted one presentation.
For undocking, TV Monitors – the displays on the Payload General Support Computer (PGSC) – showed Range Bin Transitions and VNS and Docking Camera (DC) images – however, the latter was noted to be out of action for the undocking per the Mission Status Briefing on Sunday.
“TV Monitors will show STORRM Software Application sending commands to sensors as a function of range to ISS,” the presentation noted. “TV Monitors will also show VNS and DC images of STORRM reflectors and the ISS docking target.”
To accomplish the STORRM DTO, just after undocking from the ISS, Endeavour’s Commander and Pilot performed the standard back out and ISS Flyaround maneuvers through the Sep 1 burn.
However, in terms of nominal Shuttle/ISS undockings, Flyarounds, and separations, this is where the similarity for STS-134 ended.
Endeavour’s Sep burns 2 and 3 (including all the mandatory STORRM burns) were redesigned to facilitate a mini re-rendezvous with the ISS to “accomplish the STORRM re-rendezvous objectives” before completing the flyout of Endeavour to a point “in front” of the ISS in terms of the vehicles’ orbital trajectories and relative positions.
The additional time taken to perform the STORRM DTO was built into the mission time, aided by the lack of Late Inspections – which normally take up to five hours of the flight day. The inspections were completed late into the docked mission, due to the requirement to leave the Orbiter Boom Sensor System (OBSS) on Station to become the Integrated Boom Assembly (IBA).
Once Endeavour is back in her Orbiter Processing Facility (OPF) during post flight deserving, the entire raw data will be collated for evaluation.
“VNS: Perform calculations on raw data (range and intensity measurements) to determine geometric centroids to reflective elements, range and bearing to target, and pose,” added another presentation on the forward plan.
“Compare VNS measurements with Orbiter sensors and relative best estimated trajectories. Investigate any anomalous data collected. Characterize measurements. Update ground models as appropriate. Incorporate data into Orion simulations to assess filter performance.
“DC: Convert raw data to images (if any are available, per failure). Perform assessments of images for piloting cues. Exposure/gain control algorithm performance. Perform assessments of images for use in star tracking. Perform Natural Feature Image Recognition analysis. Investigate any anomalous data collected. Update ground models as appropriate.”
As with a number of DTOs being carried out by the orbiters, NASA managers have ensured their legacy is not just historical, but one where future spacecraft will directly benefit from their vast experience.
(Images via L2 presentations, videos and images – plus nasa.gov images stitched by Ron Smith III). Extensive coverage is being provided on the news site, forum and L2 special sections – the latter of which is the world’s best front row seat to Shuttle missions. With specific and extensive flight day coverage, from interactive “one stop” FD live coverage in the open forum, to internal documentation, photos, videos and content in the specific L2 FD areas).