After a year of records and “personal bests”, SpaceX aims to launch a pair of Upgraded Falcon 9 boosters within two days of each other this week, delivering a ten-strong batch of Iridium NEXT communications satellites to Low-Earth Orbit (LEO) on Monday, 9 October, followed by the heavyweight SES-11 payload to Geostationary Transfer Orbit (GTO) on Wednesday, 11 October. Already, 2017 has seen the long-awaited inauguration of Pad 39A for SpaceX operations, as well as its first classified payload on behalf of the National Reconnaissance Office (NRO), its first reused Upgraded Falcon 9 first stage and its first reused Dragon cargo vehicle.
Monday’s Iridium NEXT launch occurred during an “instantaneous” window, which opened at 5:37 a.m. PDT (8:37 a.m. EDT) from Space Launch Complex (SLC)-4E at Vandenberg Air Force Base, Calif., and represented SpaceX’s 14th mission of the year. It also brings to more than 40 the total number of major payloads launched into orbit by SpaceX in 2017. Less than eight minutes later, the Upgraded Falcon 9’s returning first stage alighted smoothly on the Autonomous Spaceport Drone Ship (ASDS), “Just Read the Instructions”, situated a couple hundred miles off the California coastline.
Following a customary Static Fire Test of the nine Merlin 1D+ engines on the rocket’s first stage, last Thursday, all seemed set for SpaceX’s second “double-header” weekend of 2017, following the flight of BulgariaSat and a previous batch of Iridium NEXT satellites in June. However, with SES-11 targeted to fly from historic Pad 39A at the Kennedy Space Center (KSC) in Florida on Saturday evening, and Iridium NEXT from Vandenberg early Monday, the possibility arose that two Upgraded Falcon 9s could fly within 38 hours of one another. This would soundly eclipse SpaceX’s previous personal-best of 49 hours between its flights in June. However, it was not to be. Later on Thursday, in an unexpected announcement, SpaceX revealed a switch of the launching order, with SES-11 moving to Wednesday, 11 October, and Iridium NEXT retaining its original spot on Monday morning.
The surprise appears to have been shared not only by outside observers, but also by Iridium CEO Matt Desch, who tweeted his enthusiasm for the upcoming launches early Thursday. “Getting real!” wrote Mr. Desch. “Weather currently looks good for Monday morning, and all else is on track. Busy @SpaceX weekend—rooting for SES-11 on Sat!” In the wake of Thursday’s Static Fire Test, the booster was returned to a horizontal orientation and transferred back to its assembly building, where the bullet-like payload fairing, which housed the ten Iridium NEXT satellites, was installed. The 230-foot-tall (70-meter) Upgraded Falcon 9 was declared vertical on SLC-4E on Sunday afternoon, with a 90-percent likelihood of acceptable weather conditions for Monday’s “instantaneous” launch window.
As well as being an important mission for SpaceX and Iridium, it was an important mission for the 30th Space Wing at Vandenberg. “Our mission is to provide assured access to space and to do it safely and securely,” explained Col. Michael S. Hough, 30th Space Wing Commander. “SpaceX’s and 30 SW’s ever-present “can-do” attitude and job pride will be on display for the Iridium-3 launch.”
In readiness for today’s flight, SpaceX engineers began loading the Upgraded Falcon 9 with liquid oxygen and a highly-refined form of rocket-grade kerosene, known as “RP-1”. Passing T-10 minutes, the terminal autosequencer was initiated and the nine Merlin 1D+ engines were chilled down, preparatory to ignition. At T-2 minutes, the Air Force Range Safety Officer declared all ground assets to be “Go for Launch” and the booster transferred to Internal Power and assumed primary control of all critical functions, going into “Startup” at T-1 minute. At this point, the Niagara deluge system began flooding the surface of Pad 39A with 30,000 gallons (113,500 liters) of water, per minute, to suppress the acoustic energy.
Three seconds before liftoff, the nine Merlins roared to life, ramping up to a combined thrust of 1.5 million pounds (680,000 kg). Liftoff occurred precisely on time at 5:37 a.m. PDT (8:37 a.m. EDT) and the vehicle followed a perfect ascent trajectory, its first stage providing the muscle for the first 2.5 minutes, before separating. It then commenced a six-minute descent back to Earth, guided by a set of hypersonic grid-fins and engine burns, to alight smoothly on the Autonomous Spaceport Drone Ship (ASDS), “Just Read the Instructions”, situated in the Pacific Ocean, off the California coastline. Today’s landing was the tenth successful touchdown of a Falcon 9 first stage on the drone ship, since April 2016.
In the meantime, with the first stage gone, the turn came for the second stage, whose Merlin 1D+ Vacuum engine ignited for the first of two “burns” to deliver the ten Iridium NEXT satellites into orbit. Generating 210,000 pounds (95,250 kg) of thrust, the engine performed admirably. Its first burn lasted 6.5 minutes, with the engine shutting down a little over nine minutes into ascent. At this stage, the vehicle entered a prolonged period of “coasting”, lasting almost three-quarters of an hour, until the Merlin 1D+ Vacuum was re-lit for a few seconds to position the satellite group for deployment.
Fifty-two minutes after departing SLC-4E, the second stage fell silent for the final time, allowing the 15-minute deployment to be executed. A little over an hour into the mission, all ten Iridium NEXT satellites were released from their dispenser and SpaceX has now successfully transported 40 percent of its 75-strong tally into orbit. “Iridium has acquired healthy signals from all ten satellites,” SpaceX tweeted at 6:50 a.m. PDT (9:50 a.m. EDT). Current plans envisage the next load of ten satellites to follow as soon as late November, with others at roughly two-month intervals thereafter.
Today’s success follows hard on the heels of the first ten Iridium NEXT satellites, launched in January, and the second set, which flew in June. The contract between SpaceX and Iridium, inked way back in June 2010, marked the largest single launch deal ever signed, worth an estimate $492 million. Over the coming months, Iridium NEXT will completely replace an aging network of 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. (now 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, previously employed for low-orbiting GlobalStar communications satellites. Weighing around 1,760 pounds (800 kg), they are powered by twin solar arrays and operate at an altitude of 485 miles (780 km), inclined 86.4 degrees to the equator 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. However, on 31 January 2017, 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.
And their contribution is expected to be significant, for Iridium CEO Matt Desch noted that the newly-launched birds will add to the on-orbit testing of the new Iridium Certus broadband service. Marketed as Iridium’s truly global broadband service, providing safety and critical L-band communications connectivity via Iridium NEXT, Certus promises speeds of up to 1.4 Mbps. Testing is already underway on previously-launched satellites and Iridium expects Certus to be active on all of the NEXT satellites by mid-2018.
“Iridium Certus is going to fundamentally change the status quo in satellite connectivity for aviation, maritime, land-mobile, Internet of Things (IoT) and government users,” said Mr. Desch in an Iridium news release. “Achieving this major milestone continues our momentum for our mission to introduce world-changing broadband services and applications designed to help our partners provide critical connectivity solutions, both standalone and in support of other broadband technologies.”