After a multi-month hiatus, SpaceX stands ready to resume cargo delivery flights to the International Space Station (ISS), under the terms of its Commercial Resupply Services (CRS) commitment to NASA. The CRS-10 mission of its Dragon spacecraft—laden with 5,489 pounds (2,490 kg) of pressurized and unpressurized payloads, supplies and experiments for the outpost—will launch atop an Upgraded Falcon 9 booster, no sooner than 10:01 a.m. EST Saturday, 18 February. The “instantaneous” window may be shifted slightly sooner, with Patrick Air Force Base noting a slightly earlier T-0 of 9:58 a.m. This will be the first launch from Pad 39A at the Kennedy Space Center (KSC) in Florida since the end of the Space Shuttle era in July 2011. The complex is currently under a 20-year lease to SpaceX, supporting its Upgraded Falcon 9 and forthcoming Falcon Heavy operations.
As outlined in a previous AmericaSpace article, CRS-10 was originally targeted to fly last fall, but was one of several missions which fell victim to significant delay, after the 1 September 2016 explosion of an Upgraded Falcon 9 on Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla. Following last month’s return-to-flight mission, carrying the first ten Iridium NEXT satellites from Vandenberg Air Force Base, Calif., it was anticipated that the EchoStar-XXIII communications satellite would be first to fly from Pad 39A under a SpaceX banner. However, in late January, the Hawthorne, Calif.-based launch services provider announced the need for “additional testing of ground systems” at the complex and the decision to fly CRS-10 first in the mid-February timeframe.
Built in the early 1960s for Project Apollo, Pad 39A has seen 94 of the most historic missions ever conducted in the annals of human space exploration. Its first launch—albeit uncrewed—came on 9 November 1967, with the maiden voyage of the mammoth Saturn V, and it was subsequently used for the historic Apollo 8 circumlunar voyage in December 1968, as well as Apollo 9 and all but one of the eight Moon-bound missions which followed, through December 1972. Closing out Project Apollo, Pad 39A hosted the final Saturn V launch, carrying America’s Skylab space station, in May 1973, before the complex was deactivated and reconfigured for Space Shuttle operations.
Between April 1981 and July 2011, the newly rejuvenated pad supported no less than 82 shuttle launches, including the maiden flights of all of the operational orbiters, except Endeavour. The first American woman astronaut flew from Pad 39A, as did the first African-American spacefarer and the largest crew ever launched on a single vehicle in October 1985. Other accolades included the first mission of Spacelab, the first shuttle-Mir docking, the first ISS assembly flight and the first piloted launch of the 21st century.
In addition to American nationals, the first Canadian man and woman, the first Dutchman, the first Saudi, the first Mexican and the first Belgian were launched from Pad 39A. Tragically, so too was STS-107, the final voyage of Columbia, on 16 January 2003. Last used for Atlantis’ and the shuttle program’s swansong mission in July 2011, the complex is a Site on the U.S. National Register of Historic Places (NRHP) and in April 2014 was transferred to SpaceX on a 20-year lease for Falcon 9 and Falcon Heavy missions.
The pad’s new look was exhibited to the world in the fall of 2015, when the massive Transporter-Erector (TE) for future missions was rolled out along the former Crawlerway and raised into position for several days of initial tests. A large Horizontal Integration Facility (HIF)—not dissimilar to the one at SLC-40 at neighboring Cape Canaveral Air Force Station—was fabricated and much of the former Pad 39A infrastructure, including the Rotating Service Structure (RSS), was dismantled.
Last Friday, SpaceX CEO Elon Musk noted that the 230-foot-tall (70-meter) Upgraded Falcon 9 for the CRS-10 mission was in a vertical configuration at the pad. The event was welcomed on Twitter, with former astronaut Wendy Lawrence—who launched from Pad 39A on three of her four shuttle missions—tweeting: “Sooooo good to see a rocket on this launch pad again”. Two days later, on Sunday the customary Static Fire Test of the booster’s nine Merlin 1D+ first-stage engines was conducted. New rules implemented in after last September’s accident—which destroyed the $195 million Amos-6 communications satellite—require the customer’s payload to be installed after the completion of the Static Fire Test. As such, the CRS-10 Dragon was installed atop the booster
Saturday’s mission will be the 30th launch of a Falcon 9, since June 2010, as well as the tenth flight by the Upgraded version of the vehicle, which benefits from an enhanced suite of Merlin 1D+ engines on its first and second stages. First flown in December 2015, it can transport up to 50,300 pounds (22,800 kg) into low-Earth orbit and up to 18,300 pounds (8,300 kg) to Geostationary Transfer Orbit (GTO). This represents an approximately 72-percent hike over its predecessor, the Falcon 9 v1.1, which completed 15 missions between September 2013 and January 2016. And prior to that were five flights by the first-generation Falcon 9 v1.0 from June 2010 through March 2013.
The Upgraded Falcon 9 benefits from “densified” cryogenic propellants, chilled much closer to their freezing point and loaded much later in the countdown, normally from around T-35 minutes. This densification affords the vehicle a greater performance flexibility. However, in readiness for last month’s return-to-flight mission, the loading of rocket-grade kerosene (known as “RP-1”) and liquid oxygen actually got underway more than an hour before T-0, thereby eliminating the rush to get the rocket fully fueled. It remains to be seen if a similar protocol will be adopted for the CRS-10 pre-launch campaign.
Weather conditions for Saturday’s opening launch attempt look iffy, with only a 50-percent chance that Mother Nature will co-operate. In its L-3 weather briefing, issued yesterday (Wednesday), the 45th Space Wing at Patrick Air Force Base highlighted “significant winds with thunderstorms” across Central Florida, followed by a brief break in the likelihood of rain by Thursday, tempered by a strengthening upper-level trough over the Gulf of Mexico on Friday. This is expected to generate widespread clouds and rain, migrating eastwards over the Florida peninsula by Saturday morning. “The clouds and rain will gradually increase through the countdown and be entrenched over the Spaceport by midday,” the 45th Space Wing explained. “The primary weather concern for launch Saturday is the thick cloud cover and rain showers associated with the upper-level trough.”
If Saturday’s attempt is missed, SpaceX has Eastern Range approval for a backup attempt at 9:38 a.m. EST Sunday, with conditions expected to improve to 70-percent-favorable. “On Sunday, the cloudiness and rain associated with the upper-level trough will continue to slowly move east, diminishing through the countdown,” it was noted. “The main weather concern will be cumulus clouds, associated with lingering instability.”
In spite of this gloomy outlook, if the launch occurs on-time Saturday, the Upgraded Falcon 9 will deliver Dragon into low-Earth orbit, under the combined impulse of its nine Merlin 1D+ first-stage engines and the restartable Merlin 1D+ Vacuum second-stage engine. After Dragon separates from the Falcon’s second stage, a little under ten minutes into the flight, it will deploy its electricity-generating solar arrays. Later, the Guidance and Navigation Control (GNC) Bay Door will open to expose the rendezvous sensors, which are critical in guiding Dragon towards the ISS.
As with previous missions, CRS-10 will approach the space station along the “R-Bar” (or “Earth Radius Vector”), which provides an imaginary line from Earth’s center towards the ISS, effectively approaching its quarry from “below”. In so doing, Dragon will take advantage of natural gravitational forces to brake its final approach and reduce the need to perform excessive numbers of thruster burns. By Monday morning, it will reach a “Hold Point” about 1.5 miles (2.4 km) from the station, whereupon it must pass a “Go/No-Go” poll of flight controllers in order to draw nearer.
Further polls and holds will be made at distances of 3,700 feet (1,130 meters) and 820 feet (250 meters), after which Dragon will creep toward its target at less than 3 inches (7.6 cm) per second. Critically, at 650 feet (200 meters), it will enter the “Keep-Out Sphere” (KOS), which provides a collision avoidance exclusion zone, and its rate of closure will be slowed yet further to just under 2 inches (5 cm) per second. After clearance has been granted for the robotic visitor to advance to the 30-foot (10-meter) “Capture Point,” the final stage of the rendezvous will get underway, bringing Dragon within range of Canadarm2 and capture by Expedition 50 Flight Engineer Thomas Pesquet, backed-up by Commander Shane Kimbrough. Both men will be based in the station’s multi-windowed cupola. Last week, Pesquet participated in robotics training, ahead of his first Visiting Vehicle (VV) capture in the lead role. “One joystick to control rotations, one for translations,” tweeted the former Air France Airbus A320 pilot. “Like flying a plane, but more tri-dimensional.”
The Robotics Officer (ROBO) in the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, will then command the physical berthing of the cargo ship to the Earth-facing (or “nadir”) Common Berthing Mechanism (CBM) of the Harmony node. Berthing will occur in two stages, with the Expedition 50 crew overseeing “First Stage Capture”, in which hooks from the node’s nadir CBM will extend ensnare the cargo ship and pull their respective CBMs into a tight mechanized embrace. “Second Stage Capture” will then rigidize the two connected vehicles, driving 16 bolts and establishing Dragon as part of the ISS for the next month. Shortly afterwards, the crew will be given a “Go” to pressurize the vestibule leading from the Harmony nadir hatch into the cargo ship.
Last week, representatives from NASA and academia, as well as students, gathered to present details of the many science payloads which will ride uphill aboard CRS-10. Although the exact manifest remained in flux until quite late, the mission will deliver a total of 5,489 pounds (2,490 kg) in Dragon’s pressurized cargo module and also aboard its external “trunk”. The pressurized payload, totaling 3,373 pounds (1,530 kg), includes 1,614 pounds (732 kg) of scientific investigations, 653 pounds (296 kg) of crew supplies, 842 pounds (382 kg) of vehicle hardware, 22 pounds (10 kg) of Extravehicular Activity (EVA) equipment, together with smaller quantities of computer resources and equipment for the station’s Russian Orbital Segment (ROS).
Meanwhile, inside Dragon’s trunk—and totaling 2,116 pounds (960 kg)—will be the 1,146-pound (520 kg) Stratospheric Aerosol and Gas Experiment (SAGE)-III and the 970-pound (440 kg) Space Test Program (STP)-H5, which includes the Lightning Imaging Sensor (LIS). Assuming an on-time berthing at the station on Monday morning, it is planned for ROBO to extract STP-H5 from the trunk on Wednesday and installed onto ExPRESS Logistics Carrier (ELC)-1 on the station’s port-side P-3 truss on Friday, 24 February. It is expected that the LIS instrument will remain operational for about two years, conducting global lightning observations in tandem with the recently-launched Geostationary Operational Environmental Satellite (GOES)-16.
The second CRS-10 external payload, SAGE-III, will be robotically detached from the trunk on Sunday, 26 February, and installed on Friday, 3 March. Destined to take long-term measurements of ozone, aerosols, water vapor and associated gases, SAGE-III requires a continuous and unobstructed view of Earth’s atmospheric “limb” and has been assigned a payload site on ELC-4, situated on the station’s starboard-side S-3 truss. Due to the restricted envelope at the payload site, SAGE-III is equipped with an Instrument Payload (IP) and Nadir Viewing Platform (NVP), allowing it to translate the ELC-4 interface by 90 degrees. SAGE-III will be removed from Dragon and “temp-stowed” on the Enhanced Orbital Replacement Unit (ORU) Temporary Platform (EOTP) on the Dextre robotic manipulator. The NVP will then be installed directly onto ELC-4 and the IP will be installed onto the NVP.
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