SpaceX is the final stages of preparing for a launch attempt on Tuesday, May 22, to deliver the next five Iridium NEXT global mobile communications satellites to orbit, along with a pair of formation-flying, gravity-measuring NASA spacecraft. Liftoff atop an already flight-proven Falcon 9 rocket, used previously to launch the classified ZUMA mission earlier this year, is scheduled for precisely 12:47:58 pm PDT (19:47:58 UTC) from Vandenberg AFB, California.
“Weather is looking very good for Tuesday, and everything else is on schedule“, said Matt Desch, CEO of Iridium Corp., looking ahead at SpaceX’s tenth commercial flight out of the mountain-ringed launch site.
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Five batches of the Iridium NEXT constellation have been launched atop Falcons from Vandenberg already, and up to six more flights are planned from there for 2018.
Tuesday’s mission will bring to 55 the total number launched by SpaceX since January 2017—into low-Earth orbit, together with the joint U.S./NASA – German Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) payload.
Over the course of the last year, Iridium NEXT has become a regular feature of the SpaceX launch campaign. Contracts were inked 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 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 satellite 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, span 31 feet (9.4 meters) and generate two kilowatts of electricity, a 50-percent uplift over the power-producing potential of earlier 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. It was noted that this additional mission would be co-manifested with the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) payload.
Two more missions, tentatively scheduled for June and August 2018, will deliver another 20 Iridium NEXT birds to orbit, bringing SpaceX’s total tally to 75.
According to 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.”
Alongside the five Iridium NEXT satellites for the mission is GRACE-FO, a “follow-on” program to the highly successful 2002-2017 Gravity Recovery and Climate Experiment, conducted between NASA and the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, or DLR). Launched from Russia’s Plesetsk cosmodrome in March 2002, GRACE consisted of two low-orbiting satellites, which undertook detailed measurements of gravity-field anomalies in support of oceanography, geology and climate research. Flying 137 miles (220 km) apart, the satellites used microwave ranging, Global Positioning System (GPS) timing, star-trackers and an accelerometer to precisely measure the distance between themselves to within a fraction of the diameter of a human hair, in order to better understand Earth’s ever-changing gravitational dynamics.
Throughout their long mission, the GRACE duo returned monthly gravity anomaly maps which were a thousand times more accurate than earlier measurements. This contributed significantly to scientists’ understanding of long-range physical processes on Earth, ranging from ice-sheet thinning and mass-loss in Greenland and Antarctica to magma movement within the planet’s interior. GRACE enabled determinations of planet-wide changes in water distribution, including sea-level rises caused by glacial melting, and has provided new insights into global ocean circulation, weather and climate processes, earthquakes, geodetic modelling and even the impact of human interactions, such as from the depletion of large aquifers. All told, by the end of its life, the mission’s data was utilized in more than 4,300 research publications spanning multiple Earth sciences fields.
“GRACE has provided paradigm-shifting insights into the interactions of our planet’s ocean, atmosphere and solid Earth components,” said Principal Investigator Byron Tapley of the University of Texas at Austin. “It has advanced our understanding of the contribution of polar ice melt to global sea level rise and the amount of atmospheric heat absorbed by the ocean. Recent applications include monitoring and managing global water resources used for consumption, agriculture and industry; and assessing flood and earthquake hazards.”
However, in order to function, both satellites had to be fully functional. Last September, an age-related battery issue cropped up in the GRACE-2 satellite and by mid-October it became clear that the problem could not be rectified. This prompted a decision to wind the mission to a conclusion. GRACE-2 re-entered the atmosphere in December, followed by GRACE-1 in mid-March 2018. Originally baselined to operate for just five years, the twins had returned an unprecedented 15 years of advanced science. “GRACE was an excellent example of a research satellite mission that advanced science and also provided near-term societal benefits,” said Michael Freilich, director of the Earth Science Division at NASA Headquarters in Washington, D.C. “Using cutting-edge technology to make exquisitely precise distance measurements, GRACE improved our scientific understanding of our complex home planet, while at the same time providing information that was used in the U.S. and internationally to improve the accuracy of environmental monitoring and forecasts.”
Yet the demise of GRACE by no means marked the end of their mission. A “follow-on” program, dubbed GRACE-FO, had been in work for several years, with contracts to build another pair of spacecraft having been signed in November 2012 between NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., and Ottobrunn, Germany-headquartered EADS Astrium (now part of Airbus Defence and Space). The GRACE-FO twins would be virtually identical to their predecessors, trapezoidal in cross-section, and each measuring 10 feet (3 meters) x 6.6 feet (2 meters) x 2.6 feet (0.8 meters) and some 1,280 pounds (580 kg) in weight. Also like their predecessors, they would operate in a 310-mile-high (500 km) Sun-synchronous orbit, at a near-polar inclination of 89.9 degrees to the equator, and flying about 137 miles (220 km) apart. Built on the framework of Airbus’ flight-proven Flexbus platform, the spacecraft saw previous service not only for the original GRACE twins, but also for Germany’s 2000-launched Challenging Mini-Satellite Payload (CHAMP), an Earth resources and gravity-mapping mission.
In May 2015, Airbus announced that the structures for the two GRACE-FO satellites had been delivered and the development and design phase of the mission had been completed at its Defence and Space facility in Friedrichshafen, Germany. This allowed the start of building of the mission itself. By late 2016, the first GRACE-FO satellite was completed and despatched to the Industrieanlagen-Betriebsgesellschaft (IABG) analysis and test engineering center in Ottobrunn, near Munich, followed by its twin a few weeks later. At Ottobrunn, they underwent extensive testing—including acoustic runs in IABG’s 50,000-cubic-foot (1,400-cubic-meter) echo chamber in May 2017—and last November Airbus announced that the year-long test campaign had been successfully completed. On 11 December, the twins were loaded aboard an air freighter at Munich airport for delivery to Vandenberg. Counting the satellites and their support and test equipment, a total of more than 100,700 pounds (45,700 kg) of hardware arrived at the West Coast launch site on 12 December in support of the GRACE-FO mission.
As a “rideshare” mission with the five Iridium NEXT birds, the payload configuration for this flight is a notably bespoke one. SpaceX provided a single, five-satellite dispenser for Iridium, sitting at the “bottom” of the payload stack, whilst Airbus provided its own dispenser for the GRACE-FO twins, mounted above it. “This structure was developed in classical configuration,” Airbus explained in an August 2017 news release, “with a central carbon-fiber cylinder, with the satellites held in place by four hold-down and release mechanisms, which each have springs, connectors and necessary harnesses.”
The processing campaign at Vandenberg proceeded with characteristic quietness, as the satellites were installed into their respective dispenser and encapsulated within the payload fairing. A customary Static Fire Test of the nine Merlin 1D+ engines on the Upgraded Falcon 9’s first stage was conducted on Friday, 18 May, allowing SpaceX to declare its readiness to support an opening launch attempt on Tuesday, 22 May. 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.
Once launched, the GRACE-FO satellites will be deployed first, followed by restart of the Falcon’s second stage to go to a separate orbit, where it will then deploy the five Iridium Next satellites (GRACE-FO in an 89 degree orbit, Iridium-NEXT to 86.4 degree orbit).
SpaceX does not intend to land and recover the rocket’s first stage, as the company is transitioning to a dedicated fleet of their new ‘Block 5’ Falcon 9s, which will eventually be capable of flying more than one launch within 24 hours, conducting 10 flights before needing refurbishment and 100 flights before retirement.
SpaceX will, however, attempt to recover the payload fairings with their ‘Catcher’s Mitt’ boat named Mr Steven, something they have attempted a few times prior with limited success. The idea being the fairings parachute down where a waiting Mr Steven catches them in a giant net.
You can even follow Mr Steven online HERE.
– Written by Ben Evans and Mike Killian
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