STS-119: Discovery enters launch countdown – crew arrives at KSC

by Chris Gebhardt

Following the Flight Readiness Review (FRR) approval for launch, and the arrival of the STS-119 crew,  Discovery has entered the launch countdown (S0007) at 7pm local time Sunday evening. The three day countdown is targeting a 9:20pm launch of Discovery on Wednesday evening.

While the Flow Control Valve (FCV) issue dominated much of the discussion surrounding Discovery’s launch, engineers around the United States have compiled their final reports on various aspects of the long anticipated flight, making sure that all aspects of the mission are thoroughly understood.

Click here for articles on the FCV issue since STS-126.

One of the first alterations to the STS-119 mission was a change in the External Tank (ET) and Solid Rocket Booster (SRB) stack that veteran Orbiter Discovery would use to reach orbit.

The stack that Discovery will use was originally set to fly with Space Shuttle Atlantis on STS-125 last year; however, Discovery gained the stack in an agency-wide effort to, among other things, curtail delays in the hand-over of a Mobile Launch Platform (MLP) to the Constellation Program for the Ares I-X test flight this coming summer.

After Atlantis was de-stacked from her ET and SRBs, technicians performed a variety of tests and checkout procedures to verify that all the equipment was working properly.

“All items associated with stack swap are ready to support mission,” notes a Flight Readiness Review (FRR) document available for download on L2. The ET camera as well as the various engineering cameras on the SRBs all checked out and have been cleared to support STS-119.

Furthermore, Discovery’s umbilical well ET camera and flash system have passed all inspections.

Given the short nature of Discovery’s launch window – March 11 through March 16 – a chart of Discovery’s launch times shows that all launch attempts through March 15 would be classified as night launches, meaning that Discovery’s ET umbilical well camera will be photographing the ET in relative darkness once Discovery separates from the tank after reaching her initial orbit.

While a launch attempt on March 16 would technically be classified as a day launch, lighting conditions in orbit will prevent the use of hand-held photography of the tank. Similarly, a launch on March 16 would still be classified as ‘dark’ for umbilical well photography of the tank.

The technical definition of a night launch by NASA is any launch occurring between sunset +15 minutes and sunrise -15 minutes and has nothing to do with relative lighting for ET photography on orbit.

a33Further items reviewed by mission planners relate to the flame trench damage observed after Discovery’s last flight, STS-124 on May 31st of last year. Following the liberation of thousands of bricks from the flame trench, technicians installed a series of pressure sensors throughout the trench to monitor the pressure environment during lift-off.

According to the FRR document for STS-119, ‘ten static pressure sensors (six on the west side and four on the east side) were installed on Pad A to measure the SRB flame trench environment during launch.”

The instrumentation showed that the maximum and minimum static pressures during the launch of STS-126 did not violate the design environment of the trench.

In addition to the pressure sensors, three new Infrared cameras were installed around Pad-A to monitor debris items during lift-off. The cameras performed extremely well during STS-126 and are ready to support STS-119.

One further issue observed during STS-126 last year revolved around the radar tracking system. According to the System Engineering and Integration Office, two radar anomalies were detected during STS-126.

The first problem related to interference which precluded the NASA Debris Radar (NDR-C1 radar) from supporting Endeavour’s launch. After a careful review of the interference, the Eastern Range and NDR developed a five step process to ensure that this type of interference does not prevent the radar from supporting future missions.

The plan mandates the following actions: phasing checks for all radars that support launch operations, an updated phasing location to be more flight-like, an update to the ‘phasing slot assignment table,’ a jointly developed troubleshooting procedure to be used if future interference is encountered, and finally a jointly agreed upon pre-mission test to ensure ‘confidence’ in the outlined plan.

a27The second radar issue pertained to a low system sensitivity on the NDR X-3 Radar. Resolution of this issue for STS-119 will involve comparing the sensitivities between the X3 and X4 radars and a resolution of the ‘pedestal differences’ since no issues were encountered with the X4 radar.

Further changes to the radar tracking systems for STS-119 will involve the C-band and X-band radar systems.

C-band radar operation enhancements include a revised Range PRD for new phasing angles and requirements, the protection of a 20 v/m for on-orbit debris tracking, the removal of EVA debris tracking constraints, and an advanced sensitivity for orbital debris tracking.

X-band radar operation enhancements include improvements to the RTP software for X3 and X4, X4 tracking of the SRBs from T+2mins 30secs through T+5mins 10secs followed by X3 SRB tracking from T+5mins 10secs through T+7minutes, and improvements in cross-network performance of acquisition assets in the event of loss of voice communication from NDROC and ship operators.

Furthermore, another item of interest for launch operations is the pad hold time available for Discovery’s consumables. The FRR documents indicate Discovery will have approximately 161 hours (just under seven days) of pad hold time available, with oxygen being the limiting commodity.

This pad hold time analysis was based on the assumption that two Station-Shuttle-Power-Transfer-System (SSPTS) converters would be powered up for the entirety of the docked mission.

Moreover, while the 161 hours of pad hold time is encouraging given the unique nature of Discovery’s launch window, the finality of preserving three launch attempts in a row at the beginning of the launch window (March 11-13) has not yet been finalized.

Given the fact that there is the option of shortening Discovery’s mission in the event of a launch between March 14 and 16, the option of trying for three launch attempts in a row at the beginning of the window would preserve the complete duration of the mission.

However, there are several factors to consider when trying for three launch attempts in a row, not the least of which is launch team fatigue. Another contributing factor – and related issue – is the possibility of an on-pad abort.

“The thing we try to protect with three in a row, from a launch team perspective, is the on-pad abort,” said Launch Director Mike Leinbach during the post-FRR presser. “That’s the most critical thing we do on the launch team. If the team is fatigued I wouldn’t want to go into that.

“Going into this launch countdown three attempts in a row may well be an option for us and so they’re working their manning schedule accordingly.”

As such, the launch team is taking the necessary steps to preserve the option of three launch attempts in a row if, for some reason, Discovery is still on the launch pad after March 12.

L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

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