To say that the final voyage of Discovery has been anything but unbelievably remarkable and awe-inspiring would be to lessen the spirit of STS-133. Now, as she spends her final day in orbit of Earth, Discovery is preparing for reentry. Paraphrasing the Admiral (Bill Adama) himself: “Discovery has not failed us. She will not fail us, because we have not failed her. She’s seen a lot of history. She’s flown a lot of missions. Make no mistake: this will be her last.”
End of Mission -1 day:
With final clearance of Discovery’s extremely clean Thermal Protection System (TPS) for reentry, Discovery’s STS-133 Flight Crew is spending the day preparing Discovery for her last hurrah in Earth’s atmosphere.
After converting their good ship into an orbital craft following launch on 24 February, Discovery’s crew is repeating the procedures in reverse order, leaving only a few tasks to perform in the hours between wake-up and the Deorbit Burn tomorrow.
For today, Discovery’s crew conducted a pre-programmed series of tests on the vehicle’s Flight Control Surfaces (FCSs) to ensure that they can attain the necessary positions for a nominal reentry profile tomorrow.
Additionally, the crew conducted a “hot fire” test of Discovery’s RCS (Reaction Control System) thrusters. These thrusters will be used during the initial periods of Discovery’s reentry profile to maintain proper vehicle attitude until enough atmospheric pressure will allow the FCSs to take control of Discovery’s attitude commanding.
Following these events, Discovery’s crew will participate in the final on-orbit tribute for the flagship of NASA’s Space Shuttle fleet.
With that, the crew will power down Discovery’s Ku-Band antenna and stow it for reentry.
STS-133 News Articles (over 110 articles): http://www.nasaspaceflight.com/tag/sts-133/
Discovery and STS-133 – A clean ascent ahead of a clean landing:
With such a phenomenal performance on-orbit, a direct link to Discovery’s mission mangers’ ability to extend the mission by two flight days was the launch with as much cryo consumables as possible.
Following PRSD (Power Reactant Storage Distribution) system load on L-2 (Launch -2days), a full quantity of LH2 (Liquid Hydrogen) and LO2 (Liquid Oxygen) was registered in Discovery’s 4 PRSD tank sets.
In all, Discovery launched with 98.8% (90.9lbs) of LH2 in tank 1, 97.9% (90.1lbs) of LH2 in tank 2, 98.8% (90.9lbs) of LH2 in tank 3, and 98.8% (90.9lbs) of LH2 in tank 4. For LO2 quantities, Discovery launched with 95.7% (747lbs) of LO2 in tank 1, 95.2% (744lbs) of LO2 in tank 2, 96.1% and (751lbs) of LO2 in tank 3, and 95.2% (744lbs) of LO2 in tank 4.
According to the Ascent Summary Report, available for download on L2, “The average prelaunch boiloff rates were 0.068 lbm/hr-tank for LH2 and 0.23 lbm/hr-tank for LO2. The PRSD tank boiloff rates were nominal, indicating that the vacuum of each tank annulus is good.”
For the Fuel Cells themselves, which are fed by the PRSD, “Fuel Cell 3, ‘pin sharing’ was observed on cells 41/42 and 95/96 during pre-launch. Pin sharing was observed on these same 2 cell pairs during the Tanking Test and is of negligible impact.”
Likewise, Fuel Cell 2’s hydrogen meter was observed to be “biased high.” However, this condition was also previously seen during the Tanking Test and was also of no consequence for countdown and launch.
Furthermore, an ADTA 2 total temperature bias (on the low end of the scale) was observed during the countdown. In this case, the issue was a known and pre-existing condition, and the measurement in question was not used.
“At approximately MET 22:00, IDP 1’s status word 1 had a one bit toggle for one second. This appears to be a telemetry issue rather than a real error.”
Moreover at 17:15:41 EST, “MIAMI showed a ‘Non Critical Error Logged to MSU.’ The MEDS (Multifunctional Electronic Display System) Status Words show the error condition in Status Words (SW)1-3 = 00F0 0000 0000; nominal status is SW1-3 = 0070 0000 0000. This indicates a 1-bit change for one second. The changed bit indicates the Non Critical Error Present bit is set.”
The reason why this issue appears to be solely telemetry-based is because of a lack of change in the other status words at the time as well as the lack of display issues in Discovery’s crew cabin.
The situation could have resulted in a class D error, which is defined in the Ascent Summary Report as an error “where crew action is not required and the correctness of the display is not suspect but warrants archiving for post mission analysis. Note that an indication will be provided to the ground to initiate analysis of the MSU/VM.”
However, this type error can only occur if 20 DAS status changes have been experienced by the IDP when those changes could not be communicated to the GPC (General Purpose Computers).
“If the IDP-to-GPC communication is lost, the MDU (in this case CRT1) would show a Big-X/Poll Fail indication and a GPC I/O Error would be annunciated. Crew reported no such (glaring) anomaly and there was no Downlist indication of a GPC I/O (input/output) Error; therefore, this Category D error can be discounted as the cause for the ‘Non Critical Error Present’ scenario in this preliminary analysis” – further leading preliminary thought to the idea of a telemetry-noise error.
Shifting gears to the GPS (Global Positioning System) navigation aids, “OV-103 GPS receiver (MAGRS-3S) #2 was powered up at @ GMT 055\16:52:58 and was able to obtain valid key shortly afterward. As expected, for the next 2+ hours, GPS #2 remained in PVA (unaided mode) due to erroneous Shuttle Onboard time which still [had] I-Loads with values corresponding to last year’s launch attempt.”
An uplink was performed prior to T0 to correct the onboard time. This resulted in a correction of the disparity between the GPS time and the onboard time to only a 242-millisecond difference and the transition of GPS #2 to INS (valid aiding) mode.
Nonetheless, GPS#2 experienced issues during ascent in terms of maintaining a 4-satellite navigation lock due to blockages from the SRBs and External Tank – an issue that corrected itself following the roll heads-up maneuver at ~T+5mins 45secs.
All in all, Discovery performed a nominal ascent despite the later-than-planned launch time. T0 was registered at 16:53:24 EST with MECO (Main Engine Cutoff) following at 17:02:15 EST.
At liftoff, “Peak to peak lateral acceleration … was about 0.11 g which is less then the value of 0.19 g’s that could indicate a stud hang-up at liftoff. Final evaluation of hold down bolt performance depends on strain gauge analysis and launch pad and booster skirt inspection but there is no early indication of any issues.”
During SRB-powered flight, all SRB performance indications were right down the center line. As noted by the Ascent Summary Report, “SRB performance is indicated to be nominal as shown by a value of +0.092 seconds for TDEL_ADJUST which is within the dead band for Adaptive Guidance and Throttling of +/-0.21 seconds.”
Likewise the first stage throttle bucket was a nominal bucket of 104/104/72/104%. Maximum dynamic pressure was approximately 714 psi based on the L-4hr 50min balloon.
The RCS window protect firing for SRB separation occurred nominally at 16:55:30.1 EST. The total duration of the burn was 2.08 seconds utilizing thrusters F1U, F2U, and F3U.
Likewise, the dual OMS engine assist burn was nominal. Ignition of the OMS engines occurred at 16:55:41.4 EST; shutdown was registered at 16:58:13.6 EST.
Following MECO, a nominal ET separation was observed with all 10 down-firing PRCS (Primary RCS) jets firing.
The ET sep maneuver was a nominal 10 thruster translation that lasted for 7 seconds. The +X maneuver was then performed to specifications at 17:02:17.9 EST. This was a 10 second, 4 thruster translation.
Orbiter pitch-over for ET photography occurred at 17:03:00 EST. OMS-1 was not required and OMS-2 was performed nominally at 17:31:54.2 EST for a duration of 63.4 seconds resulting in a delta-V of 96.5 fps.
With that, Discovery’s ascent was, for all intents and purposes, flawless. A repeat, flawless performance is expected tomorrow as she gracefully descends into Earth’s atmosphere and glides to a landing at her home at the Kennedy Space Center.
(Further articles will follow. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers – for full and extensive live Flight Day coverage during the mission. Images used: Lead and within the article via L2’s large collection of unpublished STS-133 mission photos. Also photos via MaxQ/NASASpaceflight.com and Jacques van Oene, Spacepatches.nl).