SpaceX launches five Iridium satellites and twin science spacecraft

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WASHINGTON — A SpaceX Falcon 9 still sporting soot from its last mission successfully launched May 22 with five Iridium Next satellites and two science satellites for NASA and the German Research Center for Geosciences.

The rocket, reusing a first stage booster that successfully launched Northrop Grumman’s failed Zuma mission in January, took off from Vandenberg Air Force Base, California, at 3:48 p.m. Eastern.

The twin Gravity Recovery and Climate Experiment Follow On (GRACE-FO) satellites separated from the rocket’s upper stage approximately 11 minutes later. Iridium’s five spacecraft separated one by one around 65 minutes into the mission.

SpaceX did not attempt to recover the Falcon 9’s first stage. The rocket was a Block 4 version, designed for two to three reflights of the same first stage. SpaceX’s Block 5 Falcon 9, which had its first flight 11 days ago carrying the Bangabandhu-1 telecom satellite, is designed for 10 reflights with the same booster and no refurbishment.

The company did try to recover the payload fairings, used to protect the satellites as the rocket exited the atmosphere, but was unsuccessful.

The fairings landing in the Pacific Ocean after deploying parachutes to slow their descent. SpaceX’s launch narrator said a recovery vessel named Mr. Steven “came very close” to catching them using a giant upward facing net. Mr. Steven is so far 0 for 3 trying to catch the fairings.

Iridium and the GRACE-FO team originally planned to launch today’s satellites on separate Dnepr missions, but had to find another ride when Russia halted missions on the converted intercontinental ballistic missile. Iridium’s Dnepr launch of two satellites was supposed to occur in 2015; GRACE-FO was to launch in 2017.

Without access to Dnepr, Iridium and the German Research Center for Geosciences (GFZ) joined forces to book a single Falcon 9, splitting the cost between them.

Iridium used the extra lift capacity to launch three more Iridium Next satellites than it would have using the Dnepr vehicle. The May 22 launch grows the constellation to 55 Iridium Next satellites in orbit.

Iridium anticipates completing the Iridium Next constellation by this fall. The full constellation is to consist of 66 operational satellites, nine in-orbit spares and six ground spares. Iridium spent around $3 billion on Iridium Next, purchasing the satellites from Thales Alenia Space in Europe. Orbital ATK integrated the satellites at its Gilbert, Arizona, factory.

The GRACE-FO mission is a joint effort of NASA and GFZ. It is a successor to the original GRACE mission, also a U.S.-German partnership, that operated from 2002 until late last year.

The twin GRACE-FO spacecraft will fly in the same orbit, separated by 220 kilometers. A microwave ranging system will measure minute changes in that distance created by variations in the Earth’s gravitational field. Scientists will use those variations, which change over time, to measure the movement of masses of water created by effects like the loss of ice in Antarctica and Greenland.

“GRACE was really a revolutionary mission for us understanding the water cycle and how the climate behaves,” said Frank Webb, GRACE-FO project scientist at the Jet Propulsion Laboratory, during a pre-launch briefing May 21. “This is the science that we will be continuing with GRACE Follow On.”

In addition to the microwave ranging system also used by the original GRACE satellite, the GRACE-FO satellites will use a laser rangefinder to measure their separation. That promises at least an order of magnitude accuracy improvement, said Frank Flechtner, GRACE-FO project manager at GFZ.

The GRACE-FO spacecraft are equipped with laser retroreflectors that allow ground stations to accurately measure their orbits, further improving the accuracy of the data. Sensors on the spacecraft will be able to collect GPS radio occultation data for atmospheric sounding, similar to that provided by the U.S.-Taiwan COSMIC constellation and commercial satellites operated by Spire.

NASA’s share of the GRACE-FO mission cost is $430 million. GFZ spent about $91 million on its contribution to the mission.

Today’s launch was the tenth SpaceX mission conducted this year.