Today (Friday 30 March), SpaceX marks one year since it became the first launch provider to deliver a payload to orbit on a flight-proven booster. The triumphant success of the SES-10 mission in 2017 was further strengthened by the fact that its scorched first-stage hardware returned a second time to a smooth oceanic landing on the Autonomous Spaceport Drone Ship (ASDS) and an intact splashdown of the bulbous payload fairing was achieved. Each of these steps forms part of SpaceX’s overall plan to enhance the reusability characteristics of its Upgraded Falcon 9 fleet in an effort to bring launch costs down.
Since then, several other boosters have completed repeat missions and at 7:13 a.m. PST today marks the tenth occasion in a single year that a “used” booster has been blasted back into orbit on a second occasion. In doing so, this morning’s mission from Space Launch Complex (SLC)-4E at Vandenberg Air Force Base, Calif., delivered the Iridium NEXT-5 batch of ten spacecraft aloft, bringing to 50 the total number of these global mobile communications satellites currently in orbit. With an expectation that SpaceX will launch 75 Iridium NEXT birds by August 2018, its delivery rate now stands at almost 67 percent of the full constellation already in space.
Last October, Iridium announced that the NEXT-5 mission would ride a previously flown booster and the company is the first in history to re-use rockets to launch its own spacecraft. The NEXT-4 group of Iridiums, launched in December 2017, were lofted by an Upgraded Falcon 9 which had also delivered the NEXT-2 group the previous June. Similarly, today’s NEXT-5 booster had seen previous service on the NEXT-3 mission in October 2017. As a result, today’s booster retained its chacteristically sooty look, which prompted an opportunity for a spot of fun for Iridium CEO Matt Desch and his piece of chalk. “A few weeks ago, @IridiumBoss made a special visit to our old friend from #Iridium3, in the midst of preparations for #Iridium5,” Iridium Corp. tweeted. “In the soot of the #Iridium3 booster, the most eloquent, compelling and Shakespeare-esque message was written, destined for space!” The message? Iridium Rocks…Matt.
Liftoff of the 230-foot-tall (70-meter) Upgraded Falcon 9 occurred on time from Space Launch Complex (SLC)-4E at Vandenberg Air Force Base, Calif., at 7:13 a.m. PDT, less than a half-hour after local sunrise. The lighting conditions provided a spectacular backdrop for skywatchers, based along the California coastline and inland, as the tenth reused first stage began its mission. Since SES-10, SpaceX has used flight-proven boosters for BulgariaSat-1 in June 2017, SES-11 in October, the most recent previous batch of Iridium NEXT birds, just before Christmas, and more recently January’s GovSat-1, last month’s Paz and the twin side-mounted boosters for the long-awaited maiden voyage of the Falcon Heavy. With this morning’s flight bringing the reused tally up to ten boosters, SpaceX anticipates using two more proven first stages during its scheduled five-mission run of launches in April, beginning with the International Space Station (ISS)-bound CRS-14 Dragon cargo vehicle, next Tuesday.
Contracts between SpaceX and Iridium for this ambitious campaign were inked way back in June 2010 and, at the time, represented the largest single launch deal ever signed, worth an estimated $492 million. Over the coming months, Iridium NEXT will completely replace its aging network of first-generation satellites, whose earliest members were launched two decades ago. Iridium NEXT is being overseen by prime contractor Thales Alenia Space, with its subcontractor Orbital ATK selected to build the operational satellites, together with on-orbit and ground-based spares.
Each Iridium NEXT bird is based upon the Extended LifeTime Bus (EliTeBus)-1000, which previously saw service for the low-orbiting GlobalStar communications satellites. Weighing around 1,760 pounds (800 kg), they are powered by twin solar arrays and operate at a mean altitude of 485 miles (780 km), inclined 86.4 degrees to the equator, having the capability of a decade-long lifespan. Their solar arrays, when fully unfurled on-orbit, span 31 feet (9.4 meters) and generate two kilowatts of electricity, a 50-percent uplift over the power-producing potential of the first-generation Iridiums.
Under the original contract, SpaceX was expected to deliver 70 Iridium NEXT satellites into orbit, over seven missions, but in January 2017 it was announced that it would benefit from a “rideshare” arrangement, flying an additional five “spares” on an eighth Upgraded Falcon 9. This additional mission, presently targeted to launch in late April or early May 2018, will also carry the joint U.S./German Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. Two other Iridium NEXT satellites are expected to fly atop a silo-launched Dnepr rocket, courtesy of Moscow-based International Space Company (ISC) Kosmotras, although this mission is expected to occur further downstream.
According to Mr. Desch, the NEXT constellation is already supporting the on-orbit testing of the new Iridium Certus broadband service, which provides safety and critical L-band communications connectivity and promises speeds as high as 1.4 Mbps. Iridium expects Certus to be active on all of its NEXT satellites by the late summer of 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,” explained 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.”
The first ten Iridium NEXT birds were launched out of Vandenberg on 14 January 2017, followed by a second batch on 25 June, a third on 9 October and a fourth on 22 December. “Now that we are more than halfway deployed, we can really focus on the impact our next-generation of services will make on the industry,” said Iridium CEO Matt Desch. “Testing of our exciting new L-band broadband service, Iridium Certus, has been performing well and with every successful launch we are closer to bringing our full suite of Iridium NEXT solutions to life.” The fifth group of satellites were delivered to the mountain-ringed Californian launch complex, two by two, in motion- and temperature-controlled containers, with all ten confirmed to be on-site at Vandenberg by 12 March. They were mated to their payload dispenser, fueled and finally encapsulated within the fairing of the Upgraded Falcon 9 booster itself.
Following a customary Static Fire Test of the nine Merlin 1D+ engines on the rocket’s first stage on Sunday, 25 March, the pieces were set for Thursday’s launch of the sixth SpaceX mission of 2018. “Everything is currently looking green for launch on Thursday morning,” tweeted Mr. Desch. “Satellites are all happy and buttoned up and ready to go. An early view of the weather is very positive too…Beginning my pre-launch rituals and happy thoughts.” In the aftermath of the test, the booster was returned to a horizontal configuration and taken back to the assembly building, where the bullet-like payload fairing was installed.
However, on Tuesday, 27 March, the first technical issue came to light. “We are having an issue with one of the ten satellites in prep for #Iridium5,” tweeted Mr. Desch at 12:05 p.m. PDT Tuesday. “Our supplier and launch team is resetting for NET 31 March, with potential to shift into next week, if not resolved quickly. Launch success is priority #1.” However, within hours, the situation brightened. At 5:45 p.m. PST that same day came a follow-up tweet from Mr. Desch: “Positive update to our satellite and launch delay. Just been apprised there has been a technical resolution: satellites and F9 are in great shape and ready to go! Was ground harness test cable issue—now fixed. Launch now pulled back to Friday 30 March.”
The 230-foot-tall (70-meter) Upgraded Falcon 9 was confirmed vertical on SLC-4E on Thursday for the following morning’s “instantaneous” launch window. “Weather forecast looks excellent for our launch tomorrow morning,” tweeted Mr. Desch. “Light northeasterly winds should hopefully hold the marine layer offshore for a takeoff about 15 minutes after dawn.” Loading of the booster with liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1”, got underway in the small hours of Friday morning. At 7:03 a.m. PDT, as the countdown passed T-10 minutes, the terminal autosequencer was initiated and the nine first-stage engines were chilled down, ahead of the ignition sequence. At T-2 minutes, the Air Force Range Safety Officer verified that all ground-side assets were “Go for Launch” and the vehicle transitioned to Internal Power and assumed primary command of all critical functions, entering “Startup” at T-1 minute. At this point, the Niagara deluge system began flooding the surface of SLC-4E with 30,000 gallons (113,500 liters) of water, per minute, to suppress the acoustic energy at liftoff.
At T-3 seconds, the nine Merlins thundered to life, ramping up to a combined thrust of 1.5 million pounds (680,000 kg). Liftoff occurred precisely on time at 7:13 a.m. PDT and the vehicle followed a perfect ascent trajectory, its first stage providing the muscle for the first 2.5 minutes, before separating. In the meantime, with the first stage gone, the Merlin 1D+ Vacuum engine of the second stage ignited for the first of two “burns” to inject the ten Iridium NEXT satellites into their proscribed orbits. Generating 210,000 pounds (95,250 kg) of thrust, the engine performed with perfection. Its first burn lasted 6.5 minutes, with the engine shutting down a little over nine minutes after departing Vandenberg. At this point, the vehicle entered a prolonged period of “coasting”, lasting 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 leaving SLC-4E, the second stage fell silent, as planned, allowing the 15-minute deployment to proceed. A little over an hour into the mission, all ten Iridium NEXT-5 birds had been released from their dispenser and SpaceX has now transported almost 67 percent of its 75-strong tally of satellites to orbit. “What a sight!” tweeted Iridium Corp. “All ten SVs have successfully rolled off the dispenser.” Current plans call for further batches of ten to fly in June and August, with the rideshare mission of five Iridium NEXT satellites and GRACE-FO targeted for launch in late April.