Schedules are showing the External Tank camera – which will ride with Atlantis’ ET-138 – is to be modified – allowing it to beam back video of the tank’s disintegration after parting ways with the orbiter at MECO (Main Engine Cut Off). Meanwhile, STS-135′s pad flow now includes the replacement of the left outboard Window Contamination Control (WCCS) desiccant tubing.
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Riding with the final ET on the final Shuttle mission, the camera is hoped to provide a star role during both Atlantis’ ascent and ET-138′s demise, after engineers noted a modification on the flow schedule (L2 information).
The modification will involve the rewiring of the camera’s battery pack – believed to be specific to the G-Switch timer activation – allowing it to film from lift off, through ascent to MECO, but then allowed to continue operating through until the ET breaks up – depending on how long the camera survives as the tank re-enters.
“The camera system provides the capability to RF downlink the ET camera video signal to ground stations from RF activation until G-switch timer activation at MET 15 minutes, which effectively turns off the transmitter (a G-switch is a mechanical device that senses acceleration in order to close its contacts),” the INCO handbook explains.
“However, the most critical portion of image gathering is prior to SRB separation, for debris transport analysis purposes, while imagery after SRB separation is only highly desirable (thus the reason for the switch’s shutdown task).”
Now, per schedule, a small team from the Michoud Assembly Facility (MAF) will carry out the modification during NDE (Non Destructive Evaluation) testing after the tanking test. The mod is in the flow for June 25.
However, no notes – at this time – have confirmed how the footage will be beamed back, given the ground station set up loses the ability for the camera to transmit to Wallops after MECO due to LOS (Loss Of Signal). It is likely a P3 Orion aircraft – or a ship in the required vicinity – will be utilized.
The video signal – which is frequency modulated on a 2272.5 MHz carrier and downlinked to ground stations – would need to be picked up as far as in an area near the Cook Islands, which is the disposal area for the tank after it re-enters.
As is usual, most of the tank is destroyed during entry, with only the chance of a few smaller pieces – such as attach points and aft orbiter connections – managing to make it down to the ocean surface.
Previously, only footage a few minutes after MECO has been seen – via handheld video taken by the orbiter’s crew on the flight deck. A video was also taken during STS-29, when ET-36′s re-entry over Indian Ocean was viewed by a US Navy Aircraft.
The prospect of footage from the tank itself – as it vents and starts to disintegrate – on the final ever shuttle mission, may not be up to the high standards of the Soyuz “Flyabout” footage of Endeavour and the ISS, but it would provide a potentially stunning viewpoint of the final Shuttle ET, prior to its demise.
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