As work continues on Discovery’s External Tank’s (ET) Intertank stringers, Space Shuttle Program (SSP) managers are refining Discovery’s (STS-133’s) December launch opportunities – which include the extension of the primary and thus far only confirmed launch window and the potential of both a mid- and late-December launch window should the International Space Station Program choose to sacrifice 600 lbs upmass cargo.
Launch Window Planning for November 30 – December 7 Window:
Following the November 5 scrub of STS-133’s first launch attempt due to a “severe” gaseous hydrogen leak from the Ground Umbilical Carrier Panel (GUCP), and the subsequent discovery of the foam crack on the ET Intertank region on the side of the ET that faces the Orbiter, NASA managers agreed to delay the launch of Discovery and STS-133 to NET (No Earlier Than) November 30 – the opening day of the next available launch window.
This move, however, took the launch date out of step with the baselined and approved launch date of November 1, 2010 as defined in the Flight Definition Requirements Document (FDRD).
“Program direction to change the STS-133 Launch Date from November 1, 2010 to November 30, 2010,” notes a Launch Windows Change presentation – available for download on L2. “BACKGROUND: STS-133/ULF5 mission is currently baselined in the FDRD for a launch on November 1, 2010.”
As such, a Change Request has been put forth to officially move the STS-133 launch date to NET Nov. 30.
Initially, this early December window opened on November 30th and closed on Dec 5th due to the Soyuz 23S undocking in late-November and the Soyuz 25S launch/docking in mid-December.
However, refinement of the Soyuz dates led to a two day slip of the Soyuz 25S launch, moving from December 13 to December 15. This delay, in turn, has added two additional launch days to the end of the primary December window for Discovery, making the launch window November 30 – December 7.
“Next available launch window November 30 thru December 7, 2010 based on manifest constraints. Window closes Dec. 7 due to 25S docking on Dec 17.”
However, a Program Requirements Control Board (PRCD) meeting yesterday took the necessary step of slipping the earliest possible launch date for Discovery to December 3rd at 0252 EST to allow teams the time they need to gather and analyze data on the ET Intertank Stringer crack issue – emphasizing safety over schedule.
In practical terms, this now means that Discovery – should the primary December window be an actual possibility from a flight rationale standpoint – would have five days to launch (Dec. 3-7). This would translate to four launch attempts in five days, the standard practice for Shuttle launch operations.
For the duration of this window, the complete, full-up mission timeline would be accomplished, with Discovery and NASA executing the planned 11+1+2 day flight for a launch between Dec. 3 thru 6 and an 11+0+2 day mission for a launch on December 7.
The elimination of the +1 mission day (which would only be used for on orbit contingencies to either dock to the ISS on FD-4 (Flight Day 4) or to ensure that all CAT I mission objectives are accomplished) would ensure that Discovery has safely undocked from the ISS prior to the docking of the Soyuz 25S rocket and ISS crew on Dec. 17.
Nonetheless, the accomplishment of all mission objectives, mainly the CAT III objectives, is still being discussed since there will be, during this launch window, only three people on the ISS. STS-133 was originally planned to utilize a six person ISS crew.
Initial assessments show that all CAT I and CAT II objectives can be accomplished under the standard mission timeline, culminating in an ascending node reentry and landing over the Pacific and Central America on FD-12 (Flight Day 12).
However, a get well in the schedule/mission timeline to allow for completion of the CAT III objectives may be possible by changing Discovery’s mission timeline to align with a descending node reentry over the heartland of the United States on FD-12.
A descending node reentry has been selected for two previous post-Columbia flights: STS-120 (November 2007) and STS-131 (April 2010). Both of these missions, coincidentally, were flown by Orbiter Discovery.
“Ascending vs. Descending landings still being assessed,” notes the PRCB presentation. “Descending landing opportunities buy additional docked time and more time to complete CAT 3 objectives.”
While this move would buy roughly 24 hours of additional crew work time in the mission schedule, it would come at the cost of 45 lbs of additional O2 (oxygen) for Discovery’s Fuel Cells and extra propellant for her FRCS (Forward Reaction Control System), ARCS (Aft RCS), and OMS (Orbital Maneuvering System) engines. This extra propellant weight would have a direct effect on the amount of cargo Discovery could carry to with her at launch.
However, the consideration of upmass capability v. ascending/descending node reentries might end up being a moot point since initial estimates show an increase in Ascent Performance Margin (APM) for STS-133 for the Nov. 30 – Dec. 7 launch window.
“APM Impacts for the November 30 – December 7 launch period: Special Flight Design cycle was requested to increase the OMS Assist Timer (duration of the OMS assist burn during ascent). Some APM gain is expected.”
Moreover, the slip to the November 30 – December 7 window will necessitate a change to the ascent I-load design season.
“Nov. 30 causes a change in the ascent I-load design season (transition to winter),” notes the PRCB launch windows presentation. “I-load changes based on Mass properties updates and a change to the Ascent OMS Assist Timer (adding 7 seconds to increase performance) has been requested by the Flight Director.
“This redesign of I-loads will be done outside the standard process timeline. Time allowed for USA Flight Operations (FO) to design I-Loads and the independent verification by Boeing PI/Flight software will be significantly reduced.”
In all, every department concurred with the launch windows update presentation, with the ET Project stating that “Resolution of the repair of the GUCP leak and the repair of the Intertank stringer are underway and proceeding according to schedule. Both schedules are success oriented and based on the information known at the time of this submittal.”
Additionally, the SRB RSS (Range Safety System) batteries will “wet life expire” on 12/3/10. The batteries will be R&Red (Removed and Replaced) and the necessary OMRSD retests performed.
Potential Mid-/Late-December Launch Window:
With the critical path to Dec. 3 for STS-133 resting on the successful R&R and doubler installation for the cracked ET Intertank Stringers, reapplication of TPS (Thermal Protection System) foam to the ET, and the development of flight rationale for this issue, the possibility exists that either flight rationale will not be created in time to make the early December window or that SSP management will opt to take additional time to understand the stringer crack issue before approving flight rationale.
In theory, this could eliminate the early December window from launch consideration. OFFICIALLY, that would mean a multi-month delay to STS-133 and a resultant launch date of No Earlier Than (NET) Sunday, February 27, 2011 based on a month-long Solar Beta Angle Cutout (January 1, 2011 – February 1), the launch and month-long mission of Japan’s second HTV to the ISS (mid-January thru mid-February), and the planned February 15 launch of ESA’s (European Space Agency’s) Automated Transfer Vehicle (ATV) and subsequent late-February docking of ATV-2 to the ISS.
Nonetheless, upon review of the December ISS traffic schedule following the realigned ATV-2 launch date, the Space Shuttle Program has identified a potential (and slightly complicated) launch window in the mid-/late-December 2010 period.
As noted by NASA personnel, there is a potential launch window under discussion that opens on December 17.
“Starting to look at some opportunities after the 25S docking in December and early January, before the beta cutout, just to be strategic,” notes the November 18 Standup Integration Report.
While this is a purely strategic move, it would, nonetheless, be up to the International Space Station Program to decide whether or not to take advantage of this potential launch window because it would require the ISS Program to remove ~600 lbs of payload from Discovery to meet the mid-/late-December APM requirements for launch of STS-133.
Moreover, the exact duration of the this potential window is uncertain due to the Year End Rollover (YERO) consideration of potentially having Discovery on-orbit and docked the ISS during her computer transition from Dec. 31, 2010 to January 1, 2011 – a computer transition that has to be performed manually at the GMT (Greenwich Mean Time) midnight year end transition.
Based on the original design of the Shuttle orbiter’s computers, it was never intended that a Shuttle mission would fly over the YERO. Therefore, all YERO computer resets could be performed on the ground and any minor glitches as a result of this manual reset accounted for on the ground.
However, as first highlighted by Discovery’s STS-116 mission in December 2006, the potential need in the final years of the Shuttle Program to execute a Shuttle/ISS mission over the YERO became a serious consideration, so much so that a patch to allow for the on-orbit reset of the computer timers was devised.
Moreover, this patch came with the stipulation that the Orbiter must be docked to the ISS at the GMT midnight YERO so as to mitigate any minor glitches that might occur during the manual reset.
Since this patch was developed, however, no Shuttle mission has fallen into consideration for flight over the YERO – not out of hesitation or an unwillingness to execute a mission over the YERO, but because STS-116 has been the only mission in the post-Columbia era to launch in the month of December. All other missions toward the end of the calendar years have either launched in November as scheduled (STS-126 and STS-129) or incurred multi-month delays (STS-122) that eliminated December from launch consideration.
Nonetheless, should this potential window become a reality, and the SSP and ISSP agree to execute the mission over the YERO if necessary, the launch window would potentially shape up as follows: Dec. 17-19: launch and execute a full-up mission with return of Discovery to Earth by No Later Than (NLT) Dec. 30, 2010 – the last day to get down on the ground before the GMT YERO occurs on Dec. 31 in the Eastern and Central time zones in the United States.
This December 17-19 window would thus preclude the need to fly the mission over the YERO as the mission could be accomplished in full prior to or by December 30.
Furthermore, a launch on Dec. 17 would protect both of the landing contingency days built into the mission and still ensure a landing by NLT Dec. 30. However, for a full up mission, a launch on Dec. 18 would protect only one landing contingency day, and a launch on Dec. 19 would protect neither contingency day and would force a landing on the nominal EOM (End of Mission) day at any available landing site.
Therefore, in order to protect the landing contingency days, launching on Dec. 18 would involve eliminating one flight day and one EVA from the mission timeline. Likewise, launching on Dec. 19 and preserving both landing contingency days would involve eliminating two flight days and both EVAs from the mission timeline.
Continually, for a launch on December 20-21, the full-up STS-133 mission could neither be completed prior to the YERO nor allow Discovery to be docked to the ISS at the YERO based on consumables and mission duration.
Thus, December 20-21 could be completely eliminated from launch consideration or a truncated version of the STS-133 mission executed instead.
In this manner, if December 20 was selected as a launch option, the elimination of one flight day and one EVA (Spacewalk) from the mission would be required to ensure that Discovery was back on the ground NLT Dec. 30. This version of the mission timeline would not protect either of the two landing contingency days and would force a landing on the nominal EOM day. To protect one landing contingency day, two flight days and both EVAs would have to be eliminated from the timeline.
Likewise, a launch on December 21 (if selected) would involve the elimination of two flight days and both of the mission’s EVAs from the timeline to ensure a landing NLT Dec. 30. To accomplish CAT I and CAT II objectives, this version of the mission timeline would not protect either landing contingency day, nor could additional days be removed from the mission while still accomplishing the CAT I and CAT II objectives.
Furthermore, based on CAT I and CAT II mission objectives and YERO considerations, there would be no launch opportunities for Discovery/STS-133 on December 22 and 23 as the Orbiter would be in post-undock free orbit at the YERO based on a full-up or truncated mission timeline.
STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-133/
Launch opportunities for a full-up mission could then, potentially, resume on December 24 and would involve Discovery being docked to the ISS at the YERO. This launch period would extend from Dec. 24 thru Dec. 29 – which would ensure a docking of Discovery to the ISS before the YERO (and with time to spare).
This potential window would then close on Dec. 29 as a launch on Dec. 30 or Dec. 31 would result in Discovery being in pre-dock orbital free flight at the YERO.
According to recent documents, the next Solar Beta Angle Cutout begins on January 1, 2011 and extends thru February 1. However, this will be evaluated, as Solar Beta Angles always are, to determine if there are launch opportunities available in early January.
However, one thing is, and always has been certain. Discovery will not launch until NASA and the SSP are ready to safely execute the mission.
As Deputy Space Shuttle Program Manager Leroy Cain noted in the latest Standup Integration Report, “If there is a way to make [Dec. 3-7] at the end of all of our work where we have a very thoughtful and complete assessment of where we think we are as it relates to the risk associated with these anomalies, and we can do something within this launch period, then we will.
“If we can’t – then we won’t, and we are not going to do anything until we are ready to go fly safely. We have other launch periods, as we always do.
“The team is doing an outstanding job. And as usual, if we just get out of the way and let them tell us when they are ready to come talk to us and give us a status and updates, we always do better. That is our intent here and is what we are trying to put into practice.”
(Images via NASA.gov and L2 resources)