Launch preparations '' moved to
LC-39A on September 30, 2007. mated to the
Solid Rocket Boosters. Following STS-118 in August 2007, NASA managers decided to make modifications to the
external tank to be used on STS-120, and modify the
liquid oxygen feed-line brackets. The change involved a new low-density foam application, and thinner gaskets. Shuttle Program Managers decided to do this to reduce the foam loss from the area that had been noted since
STS-114's "Return to Flight" mission in 2005. STS-118 had a small gouge on the belly of the orbiter due to a chunk of foam that impacted during launch in August 2007. The week of September 17, 2007, NASA managers decided to delay ''Discovery's
rollover to the Vehicle Assembly Building (VAB), due to a hydraulic fluid leak from the right main landing gear strut. The strut repair was successfully completed on September 19, 2007. Discovery
then moved to the VAB, and was mated to the External Tank and Solid Rocket Boosters. Perched atop the mobile launcher platform, Discovery'' arrived at Launch complex 39A on September 30, 2007. The crew of STS-120 arrived at Kennedy Space Center on October 7, 2007, and began final preparations, including the
terminal countdown demonstration test, or "Dress Rehearsal", scheduled for October 7, 2007, through October 10, 2007. On October 9, 2007, NASA's Engineering and Safety Center, an independent review group set up after the 2003
Columbia disaster, advised replacement of three of ''Discovery's
reinforced carbon-carbon (RCC) panels on the leading wing edge, due to a loss of small amounts of the protective silicon-carbide coating. NASA reviewed the issue of oxidation of the panels for several months, using a variety of specialized testing methods, including thermography. These tests showed that the panels had not worsened over the course of the past two flights of Discovery
, and the orbiter project engineers concluded in August that Discovery
was safe to launch as is. Had a decision been made to repair the panels, the orbiter would have been rolled back to the VAB, delaying the launch. The issue of the RCC panels raised by NESC was found to be of little immediate concern, because the NESC took pre-flight thermography data from Endeavour
and compared it with Discovery
, but there was no commonality in flight history between the two vehicles. The research showed no significant difference between the panels prior to STS-114, and the panels today, which indicates the coating has not worsened during the previous flights, adding confidence that Discovery's'' RCC panels have had no deterioration in the flights since.
October 23 (Flight Day 1, Launch) Discovery launched on time at 11:38
EDT (15:38
UTC). In the countdown's final minutes, a piece of ice, measuring x was seen on the hydrogen umbilical between the orbiter and the external tank. The inspection team was called back to the pad (a contingency that has been practiced, and used before), to get a closer look at the ice build-up. NASA flight controllers deemed it too small to pose a threat to the thermal protection system. The ice was attached to a
Kapton purge barrier near the LH2 umbilical
pyrotechnic canister closeout. Had it been on other metal surfaces around the liner, this may have posed a threat of staying on and breaking off at a critical part of launch. Despite these issues, the launch continued as planned. The forecast for launch initially was a 60% chance of weather prohibiting launch, and although the launch team weather officers were tracking an incoming storm, the weather remained favorable for launch. Present for the launch was
George Lucas, to see off the Star Wars lightsaber. In a press briefing following launch, NASA managers noted a few "events" involving debris, but they occurred later in ascent, after the period of maximum aerodynamic
velocity and speed, and were not concerning.
October 24 (Flight day 2) The crew of STS-120 spent their first full day in space by performing the RCC survey, using the
Shuttle Remote Manipulator System (SRMS), and the
Orbiter Boom Sensor System (OBSS). The crew also worked on various tasks such as inspecting the
Extravehicular Mobility Units (EMUs, or spacesuits) that will be used on the EVAs, and doing some preliminary work to get ready for docking with the International Space Station on Thursday. Deputy Shuttle Program Manager and Mission Management Team (MMT) chairman John Shannon noted during the status briefing that the preliminary data the team had reviewed showed no items of concern, and the ascent imagery showed no significant losses prior to SRB separation. Shannon said there were several items the team was waiting for higher resolution imagery to assess, including a possible protruding gap filler, and some external tank foam losses, but there was nothing to indicate any problems. Shannon also noted that a vapor trail was seen coming off the external tank for several seconds during launch, but noted that this was a condition seen during both STS-114, and
STS-121, and was found to be condensate coming off the back side of the tank. Due to the temperature and humidity, combined with the angle of the Sun for ''Discovery's'' launch, the plume appeared more dramatic in some of the imagery. This was considered an "expected condition", and Shannon confirmed it was of no concern. Following docking, the joint crews conducted a station safety review, and Tani's custom Soyuz seatliner was transferred from
Discovery to the
Soyuz TMA-11, with Anderson's seat liner taken into
Discovery. This marked the official end of Expedition 16 for Anderson, and the start of Tani's increment. Just before the two crews signed off to sleep, they were informed that after preliminary review of the RPM photography, focused inspection of the orbiter's heat shield would not be required. During the MMT briefing, Shannon confirmed that initial evaluation of the available data showed
Discovery to be a "pretty clean vehicle". He also confirmed they were not working any issues or items of interest. Shannon said the piece of ice that was looked at prior to launch dislodged during main engine ignition, and as it fell, the ice appeared to graze the underside of the orbiter at the beginning of ascent, but the area around the impact site was in good condition, and the ice did not appear to have caused any damage.
October 26 (Flight day 4) The two crews started the day by preparing for the mission's first spacewalk, which began at 10:02 UTC, and ended at 16:16 UTC. Parazynski and Wheelock successfully completed all EVA activities, including preparing
Harmony for removal from the payload bay. Wilson, Tani, and Anderson controlled the station's robotic arm, moving
Harmony out of the bay and onto the port side of the
Unity node. At 15:38 UTC,
Harmony was officially mated to the space station. The station's new addition adds to the station's living volume, an increase of almost 20%, from to . At the Mission Management Team meeting, managers cleared ''Discovery's'' heat shield for reentry, and verified that focused inspection was not required, but noted that late inspection will still be performed on flight day 13 following undocking. John Shannon mentioned that managers have decided to add a task to the second EVA, asking the astronauts to visually inspect the Solar Alpha Rotary Joint (SARJ) on the starboard side, as the joint has registered some vibration for the past month and a half. While the friction is not constant or severe, managers will have Tani remove the insulation covers from the joint to photograph the swing bolts on the joint since Tani would be near the area during the EVA. Whitson, Malenchenko, and Nespoli entered first, wearing masks, and installed a temporary air duct to the node, to allow the air inside to circulate through the station's filters.
October 28 (Flight day 6) The two crews awoke at 05:08 UTC, and began preparing for the second EVA. Parazynski and Tani began the spacewalk at 09:32 UTC, a half-hour ahead of the planned timeline. The pair started with the P6 truss, removing the attachments to the Z1 truss, which allowed Wilson and Wheelock to use the station's robotic arm to move the truss to a position where it was "parked" for the night. Joking to Wilson "Don't drop it!", Parazynski then moved on and installed handrails onto
Harmony, while Tani went to inspect some items requested by the managers, including handrails on a Crew and Equipment Translation Aid (CETA) cart, that was considered as a possible cause of
Rick Mastracchio's glove tear on STS-118. "It's like the result that you get with the metal, iron filings and you put a magnet under it and they stand straight up."
October 29 (Flight day 7) The two crews used the morning to move the P6 truss from its overnight position on the station's robotic arm, over to the shuttle's robotic arm. The crew then moved the station's arm along the
mobile transporter to an outboard work site that allows attachment of the P6 truss to its new location on the
P5 truss on Tuesday. Managers on the ground had Whitson perform an experiment on the shavings Tani collected from the SARJ on Sunday's EVA, putting a magnet under a slip of paper, and testing to see if the shavings collected on the paper, to ascertain if they were metal. The test confirmed the particles collected by Tani were
ferrous. This information allowed the managers on the ground to rule out some possibilities of the origin of the particles, such as the thermal covers, which are made of aluminized mylar. The Mission Management Team discussed the SARJ issues with the ISS team, and decided to add an extra docked day to the mission, between flight days 11 and 12. The new plan changed the objectives of EVA four from the heat shield repair materials testing, to a more thorough inspection of the starboard SARJ. The EVA completed the installation of the P6 solar arrays onto the P5 truss, and the rest of the EVA activities were accomplished successfully, with the EVA ending at 15:53 UTC. Once the P6 solar array was attached, the process of deploying the arrays began. The first set of arrays, 2B, was successfully deployed with no issues, but during the deployment of the 4B array, the crew halted when they noticed an abnormality. During a press briefing, ISS Program Manager Mike Suffredini said the crew took high resolution images of the solar array, and the managers would analyze the images overnight to determine a course of action. Sufredini mentioned that with the array in the 90% unfurled position, it was still generating 97% of the expected power to the station, only slightly less than a fully unfurled array.
October 31 (Flight day 9) and the former
First Lady talk to the STS-120 astronauts and the Expedition 16 crewmembers during a visit to the
Mission Control Center, at
Johnson Space Center in
Houston. The crew began the day working through a variety of tasks, including preparing for the fourth EVA, installing a Zero Gravity Stowage Rack in
Harmony, and working with some of the experiments on board. Nespoli and Melroy participated in a Public Affairs event (PAO), and received a call from the President of Italy,
Giorgio Napolitano. The entire crew took part in a second PAO event, fielding calls from news agencies from the United States, Europe, and Russia. Around 15:00 UTC, mission control informed the crew that Thursday's planned EVA would be postponed to either Friday, or perhaps Saturday, to allow for a new EVA plan to be worked out, which would include troubleshooting of the P6 solar arrays.
November 1 (Flight day 10) Shortly after awakening in the morning, the crew was informed that the managers had chosen to take an extra day to evaluate and plan the fourth EVA. Managers initially planned for the EVA to be done on flight day 11, but would use an extra day to conduct further analysis and allow the crew to have extra time to make the tools and equipment needed, and to review and practice the procedures. The crew took some time out to gather in the
Harmony module to speak with former president
George H. W. Bush and his wife, Barbara, who were visiting Johnson Space Center. The rest of the day was devoted to assembling and configuring the new equipment and tools that would be required for the solar array repair, including a tool termed a "cufflink". The tear in the array is located at one of the hinges, which carries the load of the array, so the cufflink will be a load-bearing strap to relieve the pressure from the snagged area, transferring the load from the hinge, to the cufflink. The cufflink is made up of two wires, with two tabs at the end, that are threaded through existing reinforced aluminum holes in the solar array panels. The EVA plans call for the space station's robotic arm to grapple the shuttle's orbital inspection boom, with an extension on the end, to allow Parazynski to reach the solar array while positioned on a foot restraint at the end of the system. The spacewalk began at 10:03 UTC. After translating out to the robotic arm, Parazynski attached himself to the adjustable portable foot restraint (APFR), and was taken to the solar array worksite. Working slowly, with direction from Wheelock and the ground team, Parazynski secured the five cufflinks to the array, and then backed away to observe the deploy action. Inside the station, the crew deployed the array a half a "bay" at a time, and the array was fully deployed at 15:23 UTC. After performing additional inspections of both the 2B, and 4B arrays, Parazynski and Wheelock finished the EVA at 17:22 UTC. With the mission's final spacewalk completed, Parazynski has completed seven EVAs, for a total time of 47 hours, 05 minutes, placing him 5th overall for total EVA duration. Wheelock completed three EVAs, for a total time of 20 hours, 41 minutes, and the total EVA time for STS-120 was 27 hours, 14 minutes.
November 4 (Flight day 13) The Shuttle and station crews spent the day transferring cargo, and resting in preparation for Monday's departure of
Discovery. Nespoli and Melroy spent some time in the morning speaking to the Italian media, and later in the day the crew had some off-duty time. Following the traditional farewell ceremony, the hatches were closed at 20:03 UTC. During the emotional ceremony, Anderson spoke to the ground crew, expressing his gratitude for their support during his 137 days as an Expedition crewmember.
November 5 (Flight day 14) The two crews spent the morning preparing for ''Discovery's
undocking from the International Space Station. At 10:32 UTC, the orbiter successfully backed away from the Pressurized Mating Adapter on the Destiny'' Laboratory, and pilot Zamka began the fly-around to allow the shuttle crew to photograph the new configuration of the station. After performing the final separation burn, focused inspection began, to scan the wing leading edges and nose cap, the final analysis that allows the ground team to clear the orbiter for re-entry on Wednesday.
November 6 (Flight day 15) The crew of
Discovery spent the day preparing Wednesday's landing. In addition to doing final packing and stowing activities, Melroy and Zamka did a check of the orbiter's systems, including the flight control systems, and the reaction control system jets. The crew took some time out in the morning to speak to the media, and then had a deorbit preparation briefing with the ground team. Melroy performed a burn of the orbiter's engines in the afternoon, an orbit adjustment burn done to refine the orbiter's trajectory for the two Wednesday landing opportunities at Kennedy Space Center. NASA managers officially cleared
Discovery's heat shield for landing after reviewing the data sent down by the final inspection on Monday.
November 7 (Flight day 16, Landing) The crew of
Discovery got to work preparing for landing following their wake up call. NASA did not activate either
Edwards Air Force Base, or
White Sands, as the weather looked favorable for both
landing opportunities at Kennedy. The weather forecast at the
Shuttle Landing Facility called for good visibility, with mostly sunny skies, although the headwinds would be evaluated, as they had been peaking at . Due to the sleep shifting done by the crew earlier in the mission to schedule the extra mission days, the landing was done on what is called a "descending" node entry. Unlike ascending node entries, this entry trajectory brought the shuttle diagonally across the United States for the first time since
STS-107. The shuttle passed over Vancouver,
British Columbia, Canada, and angled down towards Florida. Once the orbiter reached Florida, Melroy performed a 195-degree right overhead turn along the heading alignment cone (HAC) in order to line up for a landing on Runway 33. ''Discovery's
payload bay doors were closed at 14:13 UTC, and the crew began fluid loading at 16:00 UTC. Fluid loading is a procedure that involves drinking high salt content fluids, which allows the astronauts to adjust to the return to gravity, and reduces the chance of hypotension upon returning to Earth. Shortly after 16:00 UTC, the crew began to get into their launch and entry suits, and ingress into their respective seats for landing. Discovery
began to feel the effects of gravity around , as it traveled above the North Pacific Ocean at 17:30 UTC. Total mission time was 15 days, 2 hours, 23 minutes, 55 seconds, for a distance of 6.25 million miles in 238 orbits. The completion of STS-120 marks the longest duration mission for Discovery''. == Extra-vehicular activity ==