Pad 39A tested to avoid STS-116 anomaly

by Chris Bergin

United Space Alliance and NASA engineers have successfully carried out a power outage test on Pad 39A, following a large scale power loss that occurred just as shuttle Discovery was leaving the Pad 39B on STS-116 last December.

The test – which was carried out at the weekend – was ordered in the wake of the 39B anomaly, which caused a cascade of power loss to elements of the pad and Mobile Launch Platform (MLP) at T-0, nearly causing loss of power to the Hardware Interface Modules (HIMs).

**Over 3000mb of STS-116 onwards related presentions and mission documentation available on L2 ** 

Source information and evaluations on the Pad 39B issue. NASA Daily Ops Report (Jan 23/Daily). NASA Launch Operations (Jan 23/Daily) – and more available on L2.

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The HIMs relay commands from the Firing Room at the Kennedy Space Center (KSC) to the ground support equipment at the pad. The loss of a HIM would not have endangered Discovery, due to fail safe/redundancy and the ability to scrub, added to the information pointing to the failure happened at the exact moment Discovery started to lift off the pad. However, it did lead to a long night for the ‘pad rats’ at KSC.

‘One of the power supplies on the MLP failed at T-0 and this made for a little bit of a long night for the people doing post-launch securing, which is plenty hazardous,’ noted one source. ‘It would’ve been a bad night indeed (for the facility, at least) had they been lost.’

Another source also noted it took several hours longer to safe the pad due to the power anomaly: ‘Some of the HIMs are new and utilized for first time for this launch. It was a longer night for the safing teams, approx. 4.5 hours before Engineering could get HIMs needed for ordnance safing powered up, and teams on pad for safing activities.’

Early information on what was the source of the fault points to an electrical fault in the Payload Changeout Room (PCR) at the pad, which caused a cascade throughout some of the pad and MLP systems.

‘The fault was power supply in the PCR (Payload Changeout Room), which took a dump, resulting in a cascade to racks in the MLP,’ noted source information. ‘The MLP is now fixed.’

The weekend of evaluations on Pad 39A, classed as ‘PAD A Power Outage Testing,’ was deemed a success. 39A will carry out the remaining shuttle launches, bar 39B’s final role as the pad that will host LON-326 – the rescue mission contingency for the launch of STS-125 to the Hubble Space Telescope in September 2008. The pad will then be officially handed over to Constellation for modification work ahead of the Ares I-1R test flight in 2009.

The test evaluated the pad’s Integrated Network Control System (INCS), which is a highly automated network system that sends data and commands between the Shuttle Launch Control Center (LCC) and the hardware end items, including connectivity with 40,000 end items located within 28 separate ground systems, all dispersed to 10 facilities over 16 square miles.

‘A complete power outage test was conducted at Pad A on Saturday morning,’ noted a NASA Ops report. ‘The primary purpose of this test is INCS validation. Call to stations was scheduled for 0600 hrs, with the outage occurring at daylight, approx. 0715 hrs, and lasted approx. 15 minutes. All three medium voltage power feeders (518, 612, and 606) were taken down, then restored sequentially.

‘After successful completion of the power out test, an outage was carried out on UPS 10 & 10A and 11 &11A for approximately 10 minutes on each UPS. The purpose of this test is to verify the output of the UPS power system in event of a loss of UPS power in support of the INCS modification.

‘The driver for this test is the power anomaly experienced directly after STS-116 launch at Pad B in December.’

The results of the tests proved there aren’t any outstanding issues with Pad 39A, as power was restored successfully, following the powerdowns.

‘Part 1: Power to feeders 518, 612, and 606 was brought down at 0718 hrs and restored in sequence by 0744 hrs with no major issues,’ added the Ops report. ‘Part 2: UPS 10/10A and 11/11A were brought down in sequence starting at 0804 hrs. All UPS were restored by 0838 hrs with no major issues.’

Pad 39A is set to host Atlantis from mid-February, ahead of the NET (No Earlier Than) March 15.


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