STS-135 Special Topics, Mission Timeline Get-wells Reviewed

by Chris Gebhardt

As the flight crew and engineers close in on the targeted July 8 launch of Space Shuttle orbiter Atlantis and the STS-135/ULF7 mission to the International Space Station, mission managers are continuing their Flight Readiness Review process with a thorough review of the new operations, special topics, items of interest, and mission timeline get-wells from both a Space Shuttle and Space Station point of view.

Ascent/Entry Topics:

The latest review – the Space Shuttle Program (SSP) Flight Readiness Review (FRR) was completed at the Johnson Space Center (JSC) on Tuesday (29 presentations available on L2). This followed numerous departmental FRRs and the recent large scale MOD FRR.

As with all Space Shuttle missions, the STS-135 flight of OV-104 Atlantis will be filled with special topics and operations that the flight crew, mission controllers, and NASA managers must be aware of prior the vehicle’s launch next month.

The first of these special topics pertains to an odd occurrence during Atlantis’s launch window on Tuesday, July 12. On this day, the actual preferred in-plane launch time – the time when the Earth’s rotation will bring Launch Pad 39A into direct alignment with the International Space Station’s orbital ground track – is 09:50:16 EDT… a full 10secs before the opening of the planar rendezvous launch window at 09:50:26 EDT.

A small phase angle on this day is the reason for this oddity and will also result in a truncated launch window of only 5mins for Flight Day 3 rendezvous. There is an additional 3mins 10secs of window available on July 12 for a FD-4 rendezvous of Atlantis with the ISS; however, given the timeline sensitive nature of STS-135 and the non-existence of a +1 on-orbit extension day, it is doubtful mission managers will approve the use of the available FD-4 rendezvous window for STS-135’s launch campaign.

STS-135 Specific Articles:

A similar small phase angle on July 15 will also result in a shortened launch window of only 8mins 18secs for the day, with the in-plane launch time falling 3mins 18secs after the opening of the window instead of the customary dead-center of the launch window.

Aside from rendezvous phasing constraints during the launch window, the only other Ascent/Entry topic discussed at the June 14 MOD FRR (Mission Operations Directorate Flight Readiness Review) that gained mention in the Flight Director’s presentation was the status of the TACtical Air Navigation (TACAN) and Microwave Scanning Beam Landing System (MSBLS) at the Transoceanic Abort Landing (TAL) site in Istres, France.

The TAL sites – Istres, France; Moron, Spain; and Zaragoza, Spain – are critical in-tact landing abort sites for the Space Shuttle orbiter during ascent should an Orbiter systems failure or SSME (Space Shuttle Main Engine) failure/premature shutdown force a diversion from the nominal ascent profile.

A TAL abort is one of five certified abort modes for the Space Shuttle during ascent. The other four are Return To Launch Site (RTLS), East Coast Abort Landing (ECAL), Abort Once Around (AOA), and Abort To Orbit (ATO). 

In the 134 flight history of the Space Shuttle Program, only once has a Space Shuttle crew had to make use of an in-tact abort mode. The STS-51F mission of the orbiter Challenger in July 1985 experienced an engine sensor anomaly that tripped a cutoff of the center SSME 5min 43secs after liftoff resulting in an ATO.

For STS-135’s ascent, if it occurs on time on July 8, the flight control team will not be tracking any potential issues with either the TACAN or MSBLS at Istres, France. As noted by the Flight Director’s presentation to the MOD FRR, “Istres TACAN recertified by the FAA (Federation Aviation Administration) on April 7, 2011 after antenna R&R (removal and replacement) and is available for STS-135.”

Despite the primary TACAN’s availability for STS-135, the Nimes, France TACAN will not be available following its planned decommissioning on June 1. Nimes was, until June 1, the only “flight-rule sanctioned backup for Istres TACAN.”

Currently, the TACAN certifications for the other two TAL sites in Spain are viable through July 18 (Moron) and July 19 (Zaragoza). If STS-135 launches on time, there will be no issue with the pending certification lapse of the Moron and Zaragoza TACANs; however, should launch slip either to or beyond these dates, a “Contingency certification plan” is in place to ensure that these assets are available for Atlantis when she launches on STS-135.

New Operations:

Debuting two New Operations for the final flight of the Atlantis is the dual ops and support of the PMM (Permanent Multipurpose Module) Leonardo – delivered to the ISS on STS-133/Discovery in February – and the MPLM (Multi-Purpose Logistics Module) Raffaello flying up to and back from Station on Atlantis.

Since the PMM Leonardo is, for all intents and purposes, an MPLM as far as Station software support is concerned, the MOD FRR Flight Director’s presentation notes that “ISS software has no accommodations for a second MPLM.”

To this end, the primary telemetry and command controls will be maintained to MPLM Raffaello during the joint Atlantis/Station mission. PMM Leonardo will, during STS-135, be activated each morning for a systems review. Fire detection within Leonardo during the Atlantis mission will be the responsibility of the joint Shuttle/Station crew.

Each evening, the PMM Leonardo will be deactivated and its hatch left open to remain compliant with Flight Rule B17-202 “Actions for Cabin Smoke Detection Loss.”

Additionally, ground commanding will be performed twice daily to “switch interface from MPLM to PMM to accomplish PMM reconfigurations. Swap back to MPLM when complete (i.e. no telemetry / command with PMM most of the joint mission).”

Both the Atlantis and ISS crews have been trained on these plans.

The second new operation for the STS-135 mission is the modified Shuttle Flyaround of the ISS complex following undocking.

“ISS Program requirement to obtain engineering-quality photos of portions of ISS not normally seen (±Y views),” notes the MOD FRR Flight Director’s presentation – available for download on L2.

To accommodate this requirement, a YVV half-lap flyaround technique was developed. This plan will involve a nominal undocking of orbiter Atlantis from the ISS with a flyout to 600ft on +V bar (Velocity vector, or direction of travel for the ISS).

The ISS will then perform a 90-degree yaw maneuver followed by the Atlantis crew performing a half-lap flyaround of the newly oriented orbital complex.

Once on the opposite side of the ISS (the -V bar) in relation to her undocking position, Atlantis will perform a separation maneuver to increase her rate of separation from the ISS.

This procedure required minimal changes to the shuttle undock/flyaround procedure checklist, and both Shuttle and Station crews practiced the new procedure in a joint-simulation on April 25, 2011.

Items of Interest:

As presented to the MOD FRR, there are three major items of interest for the STS-135 flight, the first being a corrupt data anomaly from TDRS-Z (Tracking and Data Relay Satellite).

“Guam Data Interface System/Internet Protocol Equipment (GDIS/IPE) replaced prior to STS-133. Multiple instances of corrupt data and voice observed during STS-133 and STS-134.”

The system itself performs data transmission/receipt services at Guam and White Sands, New Mexico.

For STS-133, an In-Flight Anomaly (IFA) was declared to characterize the issues seen on that flight. “IFA STS-133-G-003 Guam Data Interface System Replacement (GDIS-R) Return Service Anomaly documented issue. Issue limited only to Shuttle S-band and K-band services from TDRS-Z transmissions to Guam ground site-to-White Sands Complex.”

During Endeavour’s STS-134 flight in May, the issue reoccurred, leading to the development of a “fail-over” procedure that was successful in restoring all data and voice transmission during the flight.

To date, troubleshooting is continuing and root cause has not been identified.

Moreover, the second item of interest for STS-135 is the extremely small crew size.  “Smallest STS crew size flown on ISS assembly or logistics mission,” notes the MOD FRR.

To accommodate the reduced crew size and still ensure that all necessary on-orbit tasks are accomplished prior to rendezvous with the International Space Station on FD-3, the crew will wake up later on launch day than previous missions and stay up later than normal on FD-1.

Normally, a flight crew wakes up on launch day ~9.5hrs prior to liftoff and goes to bed 6.5hrs after liftoff (MET – Mission Elapsed Time – 6.5hrs).

For STS-135, the crew will wake up 7.5hrs before launch and go to bed 8.5hrs after reaching orbit.

As noted by the MOD, the “Waterfall effect allows completion of FD2 TPS inspection and FD3 Rndz” while not violating medical flight rules.

Joint Operations Panel assessments and crew training have indicated no issues with this rearrangement of standard wake/sleep times for ISS flights. In fact, only “Slight changes to crew tasking and middeck comm config to accommodate 4 crew for Ascent / Entry / Rendezvous” were required for STS-135.

Nonetheless, the biggest item of interest for STS-135 is the lack of a dedicated Launch On Need (LON) rescue mission that all Shuttle flights and crews have had since flight operations resumed in July 2005 with STS-114.

“Conceptual return plan agreed to at program manager level. Mixed ISS/shuttle crew return on 4 separate Soyuz vehicles (fly up two Soyuz w/ 1 empty seat; one w/ 2 empty seats).”

Under this plan, the last STS-135 crew member would be returned to Earth in June 2012 should a TPS/system contingency on Atlantis prevent her from returning her crew safely to Earth.

Should this become a reality (an unlikely event), the STS-135 crew would return to Earth in the following order: MS2 Rex Walheim on Soyuz 26S in September 2011; CDR Chris Ferguson on Soyuz 27S in November 2011; MS1 Sandy Magnus on Soyuz 29S in April 2012; and PLT Doug Hurly on Soyuz 30S in June 2012.

To accommodate this plan, the Shuttle crew has been fitted for Russian Soyuz Sokol suits and Soyuz seat liners and have received minimal training on ISS exercise, emergencies, routine ops, and Soyuz return procedures.

STS-135 Cargo Transfers and Timeline Get-wells:

As previously reported by, the STS-135 mission carries an extremely tight timeline given the amount of cargo transfers necessary for the fight and limited time Atlantis can remain on-orbit.

To this end, NASA began reviewing options for timeline get-wells when it became obvious that there was simply too much mission and not enough time to accomplish it all.

These timeline woes have since been alleviated thanks to the addition of 25hrs of Russian crew time for cargo transfer operations and a reduction in the return cargo in MPLM Raffaello.

“Timeline accommodates all planned cargo transfer activities. Plan includes 25 hrs Russian crew cargo transfer time and ISS Program reduction of MPLM cargo return target – key enabler for getting timeline ‘in the box.'”

However, the STS-135 mission timeline also had to take into account a MPLM disposition philosophy for on-orbit contingencies.

“Previously, if MPLM not loaded on-orbit to pre-flight certified config, leave MPLM on ISS if MPLM mass outside pre-flight Verification Loads Analysis (VLA) limits.  Next Shuttle could retrieve MPLM from ISS.”

The problem here is that there is no “next Shuttle” following STS-135, and the ISS’s systems cannot support two MPLMs for a prolonged period of time.

Thus, for STS-135, every effort will be made to certify the MPLM Raffaello’s weight “safe” for return even if it cannot be loaded to the VLA limit of 21,000 lbs – a milestone which will be nominally reached by FD-9.

If the MPLM cannot be certified safe for return before the crew can load it to 21,000 lbs, and a contingency is declared mandating Atlantis’s immediate return to Earth, a slightly more drastic option would have to be considered, albeit it, “a last resort.”

This last resort effort would see the MPLM removed from the ISS, stowed in Atlantis’s cargo bay, and then jettisoned from Atlantis following undocking and separation from the ISS – resulting in fiery death plunge of Raffaello into Earth’s atmosphere after Atlantis and her crew have safely returned to Earth.

(Images: Via L2 and Further articles on STS-135′s status will be provided as information arrives, driven by L2′s new and fast expanding STS-135 Special Section which is already into the FRR content and live flow coverage, plus more.)

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