STS-131: Discovery undocks – STORRM and TriDAR highlighted

by Chris Bergin

Following a highly successful docked mission, the STS-131 crew have undock from the International Space Station (ISS) – on schedule at 7:52am Central. Discovery is due to land at the Kennedy Space Center (KSC) on Monday – weather permitting. The crew have completed tasks associated with STS-134’s STORRM test objective, while a root cause has been found for TriDAR’s issues during Flight Day 3.

STS-131 Latest:

Flight Day 13 marked the final middeck transfers between the Station and Discovery, which were 100 percent completed well ahead of the crew’s farewell ceremony.

High praise for the STS-131 crew was provided by ISS commander Oleg Kotov, who thanked the crew for their excellent work during the docked phase of the mission.

“This is the time when we have to say goodbye. Excellent crew. Discovery 19A did excellent job, enjoyed working with them, really sad to let them go, but it’s time,” noted the Russian commander. “Thank you very much for your help and the job you did for us.”

“Wonderful stay for the shuttle Discovery crew. Thanks for the preparation and prepack you did,” noted STS-131 commander Alan ‘Dex’ Poindexter in returning the compliment. “You treated us with the utmost hospitality. Three outstanding EVAs and great robotics. Thanks for the help with transfers.

“We’re sorry to go, we’d all like to stay much longer. With that we’d like to say thanks and see you back home.”

Hatches on the Shuttle and Station side were then closed – prior to depressurization of the Pressurized Mating Adaptor (PMA), as Discovery’s crew started Rendezvous tool checkouts on the orbiter. A one and a half lap flyaround of the Station followed shortly after undocking, providing a stunning survey of the orbital complex.

STS-131 Specific Articles:


The crew were requested to take close-out photographs of docking target after hatch closure, as part of a Detailed/Development Test Objective (DTO) known as STORRM (Sensor Test for Orion RelNav Risk Mitigation), which would have provided help for Orion’s docking to the ISS, prior to its demotion to the role of an ISS lifeboat.

However, it will aid future commercial spacecraft that are set to visit the station in future years.

“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). STS-132/ULF4 team is aware of the docking target changes.

“Sensor Test for Orion Rel-Nav Risk Mitigation (STORRM) DTO. Advanced relative navigation system test similar to DragonEye and TriDAR. Baseline system for Orion.

“STS-131 (Launch – April 5): Install reflective elements IVA. STS-134 (Launch ~ July 29). Primary DTO tasks. Laser system in TCS slot, recorder on sidewall. Data collection during docking, undocking, and re-rendezvous. STS-133 (Launch ~ Sept 16). Remove reflective elements IVA.”

The final simulation run using the GNS simulator at the Johnson Space Center (JSC) was carried out on Friday, which related to data recording session for STORRM’s role on STS-134.

“Starting this Friday, the GNS will no longer be scheduled for training events,” pre-empted an associated memo (L2) about the end of GNS’ operation lifetime. “It will not be dismantled yet since the future of Human Space flight is still very dynamic.”

TriDAR Status: 

An interference on a cable caused issues with the latest test of the TriDAR system, which debuted during the Approach Rendezvous and Docking (AR&D) phase of STS-128, when Discovery helped verify the performance of Neptec’s vision system for unmanned AR&D via a DTO.

“TriDAR System Overview: Guidance sensor for Rendezvous and docking. Bearing and range up to >3km. 6-DOF relative pose, rates from 3D data up to 200m. Uses target geometry, no cooperative targets,” noted a system overview presentation (L2).

“Combines the sensor with embedded tracking software. Sensor includes triangulation and LIDAR 3D imaging in a single optical path. Optimal performance at both short and long range. Thermal imager added for long range bearing. Largely based on OBSS Laser Camera System (LCS).”

While the system worked well on STS-128, the problems during STS-131 were noted in a MMT (Mission Management Team) presentation on the TriDAR’s issues during Flight Day 3.

“Summary of Events: Initial powerup issues with CB labeling. TriDAR procedures show correct SW PWR 3 labeling. CB was closed during TriDAR activation to correct config. Successful TriDAR activation following CB reconfig,” the presentation (L2) outlined.

“TriDAR communications issue: A/G call informed TriDAR that comms status indicator was yellow indicating loss of comms between PGSC and TriDAR unit. Signature indicates RJ45 cable may not have been seated correctly. Cable was reseated and PGSC TriDAR SW was restarted successfully. Aft Main B power telemetry indicated that TriDAR operated normally for approximately 2 hours following restart.

“Following RPM (R-bar Pitch Maneuver), ground telemetry indicated that nominal operations ceased (confirmed by A/G call post dock). Cause undetermined at this point (waiting for TriDAR PGSC log data).”

Despite the cable issue, TriDAR did provide useful data during Flight Day 3’s Rendezvous with the ISS. As part of the investigation, focus was placed on bringing the system back to full operation for undocking and flyaround.

“Focusing on ensuring undock and flyaround activities. Working to streamline troubleshooting procedure,” added the presentation. “Ground telemetry indicates that TriDAR collected required data until RPM. Undock should cover the ranges missed during rendezvous.”

With the root cause confirmed as cable interference, the plan for undock involved obtaining the backup LCS cable and using it in place of the prerouted TriDAR cable, as they are identical.

The crew’s activation and deactivation procedures were modified accordingly, hopefully resulting in a nominal performance of the TriDAR system.

Related Articles