STS-116 launch window may be reduced

by Chris Bergin

Discovery’s second flight of the year, STS-116, may only have three days of opportunity to launch, due to concerns over how the orbiter’s software will cope when 2006 turns to 2007 whilst in orbit.

Fuelled by a “wish” to keep overtime costs down during the Christmas and New Year holidays, the NET (No Earlier Than) December 14 could postpone the International Space Station assembly flight to next year if Discovery fails to launch within the window.

**The 170 page STS-116 Flight Plan is available in full on L2**

**Discovery STS-116 Live Update Pages**

STS-116 will be the 117th Shuttle mission and twentieth station flight (12A.1), carrying the P5 Truss and SPACEHAB to the outpost. The mission was set to have a short window – around seven days, but three days will be restrictive to getting Discovery off the pad.

A note, acquired by sources, claims: ‘Year End Roll-Over (YERO) STS-116 Evaluation – JSC’s (Johnson Space Center) YERO team has been recalled to investigate the possibility of flying STS-116 over the year end this December.

‘If it is determined that a YERO event cannot be supported in flight, then the launch window will be limited to December 14-16. The first YERO team meeting in support of this task was held on June 27. DV is heading the effort.’

This is understood to relate to time management in the PASS/BFS, which are integral elements of the avionics software for the orbiter’s GPCs (General Purpose Computers), with evaluations on-going how the software would cope with a change in the year whilst on orbit.

PASS (Primary Avionics System Software) consists of application software, which performs the actual functions that are required to fly and operate the vehicle, and operating system software, which controls the computer operations and provides the facilities to ensure that the application software can execute.

The Backup Flight Software (BFS) provides backup capability for the critical phases of a mission in case of a failure of PASS. It can, at a turn of a switch, complete ascent or entry safely, maintain vehicle control on orbit, and perform the systems management function during ascent and entry (when there is no PASS systems management).

As noted in the Flight Rules document, ‘The onboard GPC’s do not roll over (reset to GMT day 1) at year-end; the MTU (Master Timing Unit) does. For the GPC’s to accept the MTU time, they must be taken to standby and reinitialized.

‘This results in a period of no vehicle control, no navigation updates, and no payload support. Since this is unacceptable, the MTU is forced to accept GPC time. When this is done, the orbiter no longer reflects true GMT as reflected by WWV.’

This period of transition with the orbiter’s software – and ultimately the period of no control – may be the reasoning engineers are looking at ensuring the 12 day mission returns to Earth before the turn of the year.

Also noted by sources is the ‘convenient’ side effect of reducing costs associated with this mission. Overtime costs of running a mission through the holidays, inclusive of New Year, has been estimated by sources to be ‘in the millions of dollars.’

A decision is likely to be taken in the next month or two.

**FREE STS-121 VIDEOS** – Re-Entry and Landing. SRB Cam, Docking, Hatch Opening. Rbar (RPM) Video (8x). Flight Deck ascent video. Five videos of the debris events. Full T-30 mins to T+60 mins STS-121 launch video and all views of launch, plus more.
(Video section is FREE, but you need to sign up as a member of the forum to enter the video section of the site. We only use your e-mail to send you your password. It will not be used for spam etc.)

** Job Opportunities** If you are awaiting a response, please re-send due to e-mail failure.

              LIVE UPDATE PAGES

Related Articles