SpaceX set to send Iridium-6/GRACE-FO missions spaceward
LOMPOC, Calif. — SpaceX is gearing up to launch another Falcon 9 rocket, this time with another set of Iridium NEXT communications satellites as well as NASA’s two Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) spacecraft. The mission is set to fly out of Space Launch Complex 4E at Vandenberg Air Force Base.
This will be the sixth Falcon 9 launch with Iridium NEXT satellites encapsulated on top of the vehicle. Only instead of the usual 10 spacecraft, Iridium Communications is only sending five for this particular flight. Additionally as part of a ride-share, NASA’s two GRACE-FO spacecraft are perched above the five Iridium satellites inside the rocket’s protective payload fairing.
After a successful static fire on May 18, 2018, SpaceX announced it is targeting 12:47 p.m. PDT (3:47 p.m. EDT / 19:47 GMT) May 22, 2018. A backup opportunity is scheduled for the following day, May 23, should it be needed.
“Just arrived in California for Tuesday’s launch of Iridium-6/GRACE-FO,” tweeted Iridium CEO Matt Desch. “Weather is looking very good for Tuesday, and everything else is on schedule.”
Indeed the weather is predicted to be 90 percent favorable for the May 22 launch attempt. Should a delay occur, weather is expected to improve to a 100 percent chance of favorable conditions.
Sending these payloads on their way to orbit will be a previously-flown Block 4 Falcon 9 first stage. That booster first sent the secretive Zuma payload into orbit on behalf of a non-disclosed U.S. government agency. SpaceX is not planning to recover the stage after launch.
Studying Earth with GRACE-FO
Once in an initial orbit of about 305 miles (490 kilometers), the first spacecraft to be deployed will be NASA’s GRACE-FO satellites. That is expected to occur around 11-12 minutes after liftoff.
According to NASA, GRACE-FO is a collaborative mission with the U.S. space agency and the German Research Centre for Geosciences (GFZ). They are designed to fly in tandem some 137 miles (220 kilometers) apart and monitor changes in Earth’s water cycle and surface mass.
As its name suggests, the mission is a follow-on to the GRACE mission, which operated between 2002 and 2017 to measure gravity anomalies to understand Earth’s ocean, geology and climate. The GRACE-FO design is similar to the original mission and features laser ranging technology in addition to the microwave ranging system used on the original.
SpaceX’s press kit states that as the twin GRACE-FO satellites fly over areas of higher and lower mass, the distance between the two spacecraft will chance ever-so-slightly.
“By precisely measuring these changes, the distribution of Earth’s mass can be mapped monthly and tracked over time,” the press kit reads. “This data can be used to monitor changes in ice sheets and glaciers, underground water storage, water in large lakes and rivers, and sea level, providing a unique view of Earth’s evolving climate and its water and energy cycles, with far-reaching societal benefits.”
According to NASA, the spacecraft are expected to operate for at least five years and map gravity changes, track variations in ice mass, towatal water shortage on land, sea level and ocean circulation and some solid earth processes like postglacial rebound and major earthquakes.
In fact, NASA says GRACE-FO is expected to be the first satellite system to directly measure global changes in water stored in the world’s largest underground aquifers.
“There really are no remote sensing products that are equivalent to GRACE data in giving a snapshot of conditions in deep aquifers,” Brian Wardlow, director of the Center for Advanced Land Management Information Technologies at the University of Nebraska, Lincoln, said in a NASA news release.
Video courtesy of NASA
Once they are deployed, the second stage with the five Iridium NEXT satellites should continue to coast around Earth for an additional 45 minutes before the lone Merlin Vacuum engine ignites for a second time to change its orbit. The burn is expected to last for about eight seconds.
The Iridium NEXT satellites are expected to begin deployment about eight minutes later and last for another seven. These five satellites are going to be the 50th-55th satellites orbited as part of Iridium Communication’s next-generation constellation. The company has contracted a total of eight launches with SpaceX to send 75 satellites into space.
According to Iridium Communications, a total of 81 Iridium NEXT satellites have been built by Thales Alenia Space to replace its existing constellation. Six of those will remain on the ground as spares should they be needed in the future. Additionally, only 66 satellites are required for the operational constellation. Nine are designed to serve as on-orbit spares.
Iridium Communications is well into the process of replacing its entire constellation of legacy satellites, some of which were orbited in 1997. The company has invested $3 billion on the next-generation satellites, which are being placed into six polar-orbiting planes, each containing 11 operational cross-linked satellites, the company said.
Since January 2017, Iridium Communications has been methodically replacing each of its legacy spacecraft with a next-generation satellite. This “slot swap” has been described as the largest of its kind.
Once this mission is concluded, Iridium Communications will begin focusing on its next contracted flight with SpaceX. The Iridium-7 flight, which will send 10 Iridium NEXT satellites into space, is expected to fly no earlier than July 2018. In a tweet in April, Iridium CEO Desch confirmed that mission will utilize a new Block 5 Falcon 9. Additionally, he said he wasn’t sure if the final flight, Iridium-8, will use a new or used Falcon 9.
Moreover, in a May 14 media conference call, Iridium CEO Desch said he expects the remaining launches (consisting of this flight and two additional dedicated Falcon 9 launches) should be completed by the third quarter of 2018 with the new satellites fully in place within 30 days of the final flight.
Should everything go as planned, the May 21 launch will be the 10th flight conducted by SpaceX in 2018, nine of which have been performed by a Falcon 9—five of those have used previously-flown first stage boosters. Altogether this is expected to be the 55th Falcon 9 flight since debuting in 2010.
Video courtesy of Iridium Communications
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a blog about the International Space Station, called Orbital Velocity.