Less than a month since it successfully delivered the fifth dedicated Dragon cargo craft into orbit, headed for the International Space Station (ISS), SpaceX—the Hawthorne, Calif.-based launch services provider, headed by entrepreneur Elon Musk—is primed to fly its second Falcon 9 v1.1 booster of the year on Sunday, 8 February. Liftoff of the mission is scheduled to occur during an “instantaneous” window at 6:10 p.m. EST, two minutes after local sunset, with Eastern Range approval having been granted for a backup opportunity at 6:07 p.m. Monday, if required. Although the Falcon has delivered payloads into low-Earth orbit and geostationary transfer orbit on its 14 previous missions, this flight will mark the first occasion that SpaceX has boosted a spacecraft onto a trajectory to the Sun-Earth L1 Lagrange Point, some 930,000 miles (1.5 million km) beyond the Home Planet.
As outlined in yesterday’s AmericaSpace article, the mission will carry the 1,250-pound (570-kg) Deep Space Climate Observatory (DSCOVR), destined for at least two years of operations to perform solar wind measurements in support of space weather requirements, to provide three-dimensional distribution analyses of the components of the solar wind, and to observe the entire sunlit face of Earth from the unique perspective afforded by the L1 location. Initially developed as the Triana imaging satellite, the program was canceled and mothballed in 2001, but was later revived and rejuvenated in 2008, chiefly under the initiative of the National Oceanic and Atmospheric Administration (NOAA).
For the Falcon 9 v1.1, the forthcoming launch also provides an opportunity to execute a second landing test of its first-stage hardware on the Autonomous Spaceport Drone Ship (ASDS) in the Atlantic Ocean. This vast, steel-hulled platform is a Marmac 300 Freight Barge, recommissioned and specially modified for use by SpaceX, and measures 288 feet (87.8 meters) in length, 100 feet (30.5 meters) in diameter and 19.8 feet (6 meters) deep, and has a gross mass in excess of 8.8 million pounds (3.9 million kg). Despite being unanchored during Falcon 9 v1.1 recovery operations, the ASDS is reportedly capable of holding its oceanic position to within 10 feet (3 meters), “even in a storm,” and utilizes Differential Global Positioning System (GPS) hardware and four diesel-powered azimuth thrusters, repurposed from oil rigs.
Azimuth thrusters can be rotated through a full 360 degrees to any horizontal angle (or “azimuth”), thereby rendering a rudder unnecessary, and offering increased maneuverability over a fixed propeller and rudder system. Each thruster aboard the ASDS is capable of producing 300 horsepower, with a 40-inch (101.6 cm) nozzle, and the system is of the mechanically-powered “L-drive” configuration, so named because the rotary motion describes an L-shaped right-angle turn. They form part of the Portable Dynamic Positioning System (PDPS), provided by Houston-based Thrustmaster of Texas, Inc., one of the world’s leading manufacturers of marine thruster systems.
As described by Thrustmaster, the PDPS consists of modular thrusters, containerized diesel-hydraulic power units and a Dynamic Positioning (DP) and Navigation Control Room, with hydraulic hose interfaces and control cables, and is suitable for vessels between 100 feet (30 meters) and 600 feet (180 meters) in length. According to Thrustmaster, the conversion of an ordinary barge into “a highly sophisticated dynamically-positioned vessel, all without the need for a dry dock” with the PDPS hardware can be performed “dockside, in the water, in less than a week.” These systems have seen worldwide use for applications ranging from the laying of undersea pipelines and cables to oil exploration.
The remarkably bold attempt to land a Falcon 9 v1.1 first stage on the ASDS—which SpaceX admitted carried only a 50-50 chance of success—experienced mixed fortunes during last month’s inaugural test, successfully returning from the edge of space and reaching the deck of the barge, but impacting at a 45-degree angle and exploding. “Close, but no cigar” was Mr. Musk’s tweeted summary, whilst AmericaSpace also understands from SpaceX that the ASDS was “in very good shape”, structurally, with limited hull damage and minor attention required in areas of the deck and railings. Certainly, images of the ASDS returning to port a few days after the landing attempt showed some bruising to the barge, together with elements of Falcon 9 v1.1 first stage debris, covered with tarpaulin.
During typical operations, the ASDS is stationed 186-250 miles (300-400 km) to the northeast of the launch facilities at Cape Canaveral Air Force Station. “Depending on where we port,” SpaceX told AmericaSpace recently, “the drive takes half a week or so to get to the landing location.” Supporting the emplacement of the ASDS for Sunday evening’s launch are the same two vessels as last time: the 82-foot-long (25-meter) Elsbeth III tug and the 164-foot-long (50-meter) Go Quest support boat. With a maximum speed of around 5.6 knots, the Elsbeth III is responsible for bringing the ASDS to its oceanic position, whilst the faster Go Quest—capable of up to 12.1 knots—takes up a support position, laden with communications and tracking equipment.
In the aftermath of last month’s test, both vessels returned to Port of Jacksonville and their positions were described as stationary by midday on 11 January, where they remained for the next few weeks. As of yesterday (Thursday, 5 February), both vessels were recorded as having departed the Port of Jacksonville, with the Elsbeth III having put to sea at 11:14 p.m. EST Wednesday and been followed by the Go Quest at 1:07 a.m. Thursday.
Both launch opportunities on Sunday and Monday are timed to occur a matter of minutes after local sunset, making this second ASDS landing attempt also the second time that the highly experimental feat will have been attempted in darkness. Current estimates from the 45th Space Wing at Patrick Air Force Base predict cloudy skies, with no probability of lightning or precipitation, although there is a less than 10-percent likelihood of a violation of the Cumulus Cloud Rule forcing a 24-hour scrub. Should Sunday’s launch attempt be postponed, the prospects slightly worsen from 90 percent favorable to 80-percent favorable on Monday, due to the possibility of violating the Thick Cloud Rule.
“A high-pressure area drops south into Florida on Saturday and Sunday, allowing for plenty of sunshine and temperatures near 21 degrees Celsius (70 degrees Fahrenheit) along the Space Coast,” the 45th reported on Thursday morning. “There is very little threat of launch weather rule violations.” However, it was highlighted that on Monday the high-pressure area will migrate into southern Florida, allowing a weak cold front to make its way northwards. “This will increase cloud cover over the northern half of the peninsula,” it was noted, “and create a risk for thick clouds over the Spaceport.”
Following a well-trodden processing regime, the Falcon 9 v1.1 moved smoothly through a Static Fire Test of its nine Merlin 1D first-stage engines on Saturday, 31 January, after which it was removed from SLC-40 for the installation of its DSCOVR payload. It then headed into the Launch Readiness Review (LRR) and Flight Readiness Review (FRR) milestones and is expected to return to SLC-40 and be raised to the vertical tomorrow (Saturday). As with Dragon cargo missions to the ISS, the DSCOVR launch window is an instantaneous one, with no margin to accommodate last-minute technical issues or poor weather. If the vehicle cannot launch at the prescribed time on Sunday, the attempt will be scrubbed and the countdown clock recycled to support the backup opportunity on Monday.
After rollout, the Falcon 9 v1.1 will be fueled with liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1.” The cryogenic nature of the oxygen—whose liquid state exists within a temperature range from -221.54 degrees Celsius (-368.77 degrees Fahrenheit) to -182.96 degrees Celsius (-297.33 degrees Fahrenheit)—requires the fuel lines of the engines to be chilled, in order to avoid thermally shocking or fracturing them. All propellants should be fully loaded within one hour and at 5:57 p.m. Sunday, assuming no technical constraints, the countdown will pass its final “Go/No-Go” polling point of all stations at T-13 minutes.
The Terminal Countdown will get underway at T-10 minutes, during which time the Merlin 1D engines will be chilled, ahead of their ignition sequence. All external power utilities from the Ground Support Equipment (GSE) will be disconnected and at 6:05 p.m. the roughly 90-second process of retracting the “strongback” from the vehicle will occur. The Flight Termination System (FTS)—which is tasked with destroying the Falcon 9 v1.1 in the event of a major accident during ascent—will be placed onto internal power and armed. By T-2 minutes and 15 seconds, the first stage propellant tanks will attain flight pressure, after which the engines will be purged with gaseous nitrogen and at T-60 seconds the SLC-40 complex’s “Niagara” deluge system of 53 nozzles will come to life, flooding the pad surface and flame trench with 30,000 gallons (113,500 liters) of water, per minute, to suppress acoustic energy radiating from the engine exhausts.
At T-3 seconds, the Merlins will roar to life, ramping up to a combined thrust of 1.3 million pounds (590,000 kg). Following computer-commanded health checks, the stack will be released from SLC-40 to begin SpaceX’s second mission of 2015. Immediately after clearing the tower, the booster will execute a combined pitch, roll, and yaw program maneuver to establish itself onto the proper flight azimuth to deliver DSCOVR into space. Eighty seconds into the climb uphill, the vehicle will exceed the speed of sound and experience a period of maximum aerodynamic duress—colloquially dubbed “Max Q”—on its airframe. At about this time, the Merlin 1D Vacuum engine of the second stage will undergo a chill-down protocol, ahead of its own ignition later in the ascent. At 6:12 p.m., 130 seconds after liftoff, two of the first-stage engines will throttle back, in order to reduce the rate of acceleration at the point of Main Engine Cutoff (MECO).
Finally at T+2 minutes and 58 seconds, the seven remaining engines will shut down, and, a few seconds later, the first stage will separate from the rapidly ascending stack. It will then attempt the second ASDS landing in the Atlantic Ocean. Traveling at a velocity of 2,900 mph (4,670 km/h), the stabilization of the 150-foot-tall (46-meter) first stage has been likened to someone balancing a rubber broomstick on their hand, in the midst of a fierce windstorm. Three Merlin firings will be performed to steadily reduce this velocity and stabilize the first stage: an initial “boost-back” burn will adjust the vehicle’s impact point, after which a “supersonic retro-propulsion” burn will slow it to about 560 mph (900 km/h) and a final “landing” burn will bring this down still further to just 4.5 mph (7.2 km/h).
During the final burn, the first stage will deploy its four extendable landing legs and a quartet of lattice-like hypersonic grid fins—configured in an “X-wing” layout—will be unfurled to control the lift vector and, together with engine gimbaling, will enable a precise touchdown on the ASDS. “Grid fins perform well in all velocity ranges, including supersonic and subsonic speeds, with the exception of the transonic regime, due to the shockwave enveloping the grid,” Spaceflight101 noted in June 2014. “These properties make them ideally suitable for the Falcon 9 first stage that starts out at supersonic speeds and returns to subsonic velocity as it travels through the atmosphere, en-route to the landing site.” With two degrees of freedom, the fins have the capacity to rotate and tilt, thereby enabling them to eliminate roll rates and maintaining control during flight. Unfortunately, it would appear that the failure of the fins to operate correctly—having run out of sufficient hydraulic fluid during atmospheric flight—was a contributory factor in last month’s failure. That shortfall is expected to be resolved for this second attempt.
With the first stage gone, the turn will then come for the Falcon 9 v1.1’s restartable second stage, whose Merlin 1D Vacuum engine—with a maximum thrust of 180,000 pounds (81,600 kg)—will come to life to support two discrete “burns,” then set DSCOVR free about a half-hour after leaving the Cape. The small spacecraft will then be on its own to complete the 110-day journey to reach the L1 Lagrange Point and should be on-station by the end of May.
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