With Sunday’s spectacular launch-and-landing of an Upgraded Falcon 9 from Vandenberg Air Force Base, Calif., almost a quarter of all of SpaceX’s missions have flown in 2017 alone. Nine launches in the first six months of the calendar year establishes a new “personal best” for the Hawthorne, Calif.-headquartered organization, which previously achieved eight flights in 2016 and six fully successful missions in 2015 and 2014 apiece. SpaceX has long insisted that it aims to launch its Upgraded Falcon 9s at intervals of around two weeks—a boast which, by and large, it has accomplished in 2017—but this weekend also offered a unique “double-header” for CEO Elon Musk, coming a mere 48 hours after Friday’s successful BulgariaSat-1 launch. It also secured another record for SpaceX, which has now launched three missions in the span of a single calendar month.
“We are once again proud to support another successful launch of Iridium NEXT,” said Air Force Col. Michael S. Hough, who witnessed his first launch since taking over as 30th Space Wing Commander at Vandenberg, earlier this month. “This launch is a perfect demonstration of the high level of teamwork and precision that exists between Team Vandenberg and SpaceX.”
Today’s flight—which left Earth at the start (and end) of an “instantaneous” launch window at 1:25:18 p.m. PDT—represented only the fourth outing by a SpaceX vehicle from Space Launch Complex (SLC)-4E at mountain-ringed Vandenberg on the United States’ west coast. Eight minutes later, its first stage plunged back to Earth and alighted smoothly on the deck of the Autonomous Spaceport Drone Ship (ASDS), nicknamed “Just Read the Instructions”, positioned offshore in the Pacific Ocean. The mission was tasked with delivering a second set of ten Iridium NEXT communications satellites into low-Earth orbit, following on the heels of lofting an inaugural “batch” in January 2017. In doing so, SpaceX would fulfil the second segment of a seven-year-old contract which should see it deliver 75 Iridium NEXT birds into orbit by mid-2018.
When the details for this mammoth contract were agreed between SpaceX and Iridium, back in June 2010, it marked the largest single launch deal ever signed, worth an estimated $492 million. Over the next few months, Iridium NEXT will completely replace an aging network of its first-generation satellites, whose earliest members were launched two decades ago. In June 2010, the second-generation Iridium NEXT system was unveiled, with Thales Alenia Space and its subcontractor Orbital Sciences Corp. (later Orbital ATK) selected to build dozens of operational satellites and on-orbit and ground-based spares.
Iridium NEXT is based upon the Extended LifeTime Bus (ELiTeBus)-1000 spacecraft design, previously employed for low-orbiting GlobalStar communications satellites. Weighing around 1,760 pounds (800 kg), they are powered by twin solar arrays and capable of supporting a decade-long lifespan. The solar arrays—spanning 31 feet (9.4 meters) when fully unfurled and capable of generating 2 kilowatts of electricity—would offer a 50-percent uplift over the power-producing potential of the first-generation Iridiums.
SpaceX was originally expected to deliver 70 Iridium NEXT satellites into orbit, spread across seven missions by its Upgraded Falcon 9. The first flight occurred in January and successfully placed ten satellites into low-Earth orbit, with an expectation that the next mission would occur in April, followed by the remainder at roughly two-month intervals. However, on 31 January Iridium announced that it would benefit from a “rideshare” arrangement, flying another five spare satellites on another Upgraded Falcon 9, carrying NASA’s Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission in early 2018. All told, it is expected that SpaceX vehicles will transport no fewer than 75 Iridium NEXT satellites into space. Launch of the second batch was initially targeted for mid-April 2017, but in February a delay of two months was announced.
By the beginning of May, the initial ten satellites completed a rigorous testing and validation process and had been fully integrated into the Iridium on-orbit constellation. “We are deploying the largest satellite constellation and the world and it works,” exulted Bertrand Maureau, executive vice president of telecommunications at Thales Alenia Space. “We met challenges that were unprecedented in the space sector, in terms of end-to-end system performance and production rate.”
As SpaceX’s launch cadence improved during the first few months of 2017, an initial target date of 29 June was announced for the second Iridium NEXT batch. By the third week of May, Iridium CEO Matt Desch revealed that the first pair of satellites for the launch—as well as the first stage of the Upgraded Falcon 9 itself—were en-route to Vandenberg. On the 25th, Mr. Desch noted that the second stage of the rocket had arrived at the West Coast launch site and that four of the Iridium NEXT satellites were deep into processing. At the same time, he revealed that the “instantaneous” launch was being brought forward to 1:25:18 p.m. PDT on 25 June, due to the opening of Western Range availability.
With SpaceX’s launch of the CRS-11 Dragon cargo mission correspondingly moved into the first week of June, and the high-energy BulgariaSat-1 also slated for June, this promised the tantalizing possibility that (for the first time) as many as three Falcons might fly in a single calendar month.
“We’re excited for this next launch,” said Mr. Desch in an Iridium press release. “Satellites have already started to arrive at the launch site and are undergoing pre-launchg preparations, so we’ll be ready to go. An earlier launch date is all the better for our constellation deployment plans.” By 6 June, all ten satellites were on-site at Vandenberg, mated to their specialized dispenser, with fueling about to commence. A week later, fueling was complete and the Iridium batch was encapsulated inside the bulbous payload fairing of the Upgraded Falcon 9. However, following last September’s on-the-pad explosion of Amos-6, customers’ payloads are now installed after the customary Static Fire Test of the nine Merlin 1D+ engines of the first stage.
This firing took place on Tuesday, 20 June, after which the booster was returned to a horizontal configuration and the Iridium NEXT batch was installed. “Static fire a success,” tweeted Mr. Desch. “Weekend VAFB weather looks benign so far as well, so we’re on track for a Sunday launch.” That same day, Iridium Corp. itself tweeted that all ten of its satellites were “locked and loaded” for launch. Late on Saturday, SpaceX released an image of the 230-foot-tall (70-meter) Falcon 9, only hours away from its fourth flight out of Vandenberg Air Force Base. The west coast site was previously used for the launch of Canada’s CASSIOPE science mission in September 2013, followed by NASA’s Jason-3 ocean altimetry spacecraft in January 2016 and most recently the first batch of Iridium NEXT satellites in January 2017.
Weather conditions at Vandenberg were predicted to be 100-percent favorable, with the 30th Space Wing anticipating the presence of low shallow stratus clouds and fog during the final phase of Sunday’s countdown. “By T-0, the marine layer will have broken out, the stratus will be clearing out and visibility restrictions lifted,” it was noted in an L-2 weather briefing on Friday. “The overall POV [Probability of Violation] will be 0% with no constraints of concern.” This was expected to remain favorable in the event of a 24-hour slip to the backup launch opportunity on Monday.
Due to the requirements of the Iridium NEXT payload, Sunday’s launch window was an “instantaneous” one, timed for 1:25:18 p.m. PDT, with no margin to accommodate last-minute technical issues. Any slip would almost certainly trigger a scrub and a minimum 24-hour recycle of the countdown.
Aiming for the bullseye, the SpaceX team pressed into Sunday with the effort to gets its personal-best-beating ninth Upgraded Falcon 9 of the year off the pad. Fueling of the booster with a highly refined form of rocket-grade kerosene (known as “RP-1”) got underway about one hour before T-0. Shortly thereafter, at 35 minutes before launch, liquid oxygen began flowing into the tanks. Unfortunately, hopes that Vandenberg’s fog would lift proved unfounded and the booster remained virtually shrouded in the gloom.
At 1:15 p.m. PDT, with ten minutes remaining before T-0, the terminal countdown autosequencer was initiated. The nine Merlin 1D+ first-stage engines, arranged in a circle of eight, with a ninth at the centre, were chilled, ahead of ignition, and the Flight Termination System (FTS) was placed onto internal power and armed. In the final minutes, the Upgraded Falcon 9 transitioned to internal power and the Iridium NEXT payload was powered-up, with the vehicle assuming primary command of all critical functions—entering “Startup”—at T-60 seconds. At the same time, the pad deluge system began to flood the SLC-4E surface with water to reduce the reflected energy at liftoff.
Three seconds before launch, the nine Merlin 1D+ engines roared to life, kicking out a combined thrust of 1.5 million pounds (680,000 kg). The vehicle departed SLC-4E precisely on the opening (and closure) of Sunday’s launch window, on the stroke of 1:25 p.m. PDT. Climbing smoothly into the fog, the booster performed with characteristic perfection, passing maximum aerodynamic turbulence (“Max Q”) at 70 seconds. Two-and-a-half minutes into ascent, the first stage was jettisoned, beginning a complex sequence of maneuvers to bring it back through the “sensible” atmosphere to alight on the deck of SpaceX’s West Coast-based drone ship, “Just Read the Instructions”.
The drone ship had been drawn out to sea from Port of Los Angeles by the NRC Quest cargo vessel on Saturday morning, bound for a position about 186 miles (300 km) off the California coastline. Shortly after the separation, the first stage deployed its four hypersonic grid fins, configured in an “X-wing” layout, which for this mission are of a noticeably modified design.
“Flying with larger & significantly upgraded hypersonic grid fins,” explained SpaceX CEO Elon Musk in a recent tweet. “Single-piece cast & cut titanium. Can take re-entry heat with no shielding.” In a subsequent tweet, Mr. Musk noted that the fins are unpainted, since they would glow red-hot during their hypersonic re-entry. “Trying these things out for the first time today,” added former NASA astronaut Garrett Reisman, who now serves as SpaceX’s head of crew operations.
To accomplish a precise touchdown on the drone ship, the Upgraded Falcon 9’s first stage “flipped” itself, assisted by on-board nitrogen-fed thrusters, and executed Entry and Landing burns to incrementally slow it down, initially to about 560 mph (900 km/h) and finally to a touchdown velocity of 4.5 mph (7.2. km/h). However, conditions were anticipated to be less than optimum, due to weather conditions near the ASDS. “Drone ship repositioned due to extreme weather,” Mr. Musk tweeted, shortly before launch. “Will be tight.” Tightness aside, the first stage headed smoothly back through the “sensible” atmosphere and alighted on the deck at 1:32 p.m., a mere seven minutes and 45 seconds after leaving SLC-4E. “New titanium grid fins worked even better than expected,” tweeted Mr. Musk. “Should be capable of an indefinite number of flights with no service.”
In the meantime, the primary goal of today’s mission continued. Following the departure of the Upgraded Falcon 9’s first stage, the Merlin 1D+ Vacuum engine of the second stage ignited and burned for more than 5.5 minutes, shutting down a little over nine minutes after launch. At this point, the vehicle entered a prolonged period of “coasting”, lasting almost three-quarters of an hour, until the Merlin 1D+ Vacuum was lit a second time to position the Iridium NEXT group of satellites for deployment into an orbit about 390 miles (625 km) above Earth. By this point, the vehicle was moving in excess of 16,700 mph (27,100 km/h).
Fifty-two minutes after leaving Vandenberg, the second stage fell silent for the last time, allowing for the 15-minute deployment process to get underway, with each satellite departing at 100-second intervals. The tenth Iridium departed the second stage approximately 71 minutes after leaving Vandenberg Air Force Base. SpaceX has now successfully transported more than a quarter of its 75-strong Iridium NEXT tally to orbit. Current plans envisage the next load of ten satellites to fly in August and the remainder to follow at approximately two-month intervals thereafter.