SpaceX Falcon 9 Block 4 - Iridium-3 NEXT - Launching October 9, 2017
Screenshot from SpaceX of Falcon 9 B4 - Iridium-3 NEXT hosted by Tim Dodd
Mission Rundown: SpaceX B4 - Iridium-3 NEXT
Written: January 23, 2021
Last one in orbit loses his place
SpaceX will launch a Falcon 9 block 4 booster to put 10 Iridium communication satellites into a low earth polar orbit. The instantaneous launch opportunity is at 07:13:51 p.m. PDT, or 12:37:01 UTC. The deployment of the 10 Iridium® NEXT satellites will begin about an hour after launch.
Falcon 9’s first stage booster B1041-1 is launching the Iridium-3 mission from Space Launch Complex 4 East (SLC-4E) at Vandenberg Air Force Station on October 9, 2017. After stage separation, SpaceX will be attempting a first stage landing on the west coast drone ship, Just Read The Instructions.
Iridium-3 NEXT
Iridium-3 NEXT, the third flight, will launch its 10 Iridium NEXT satellites into orbit plane 4 which is completed except for one spare satellite vehicle. The 10 spacecraft aboard Monday’s October 9, 2017 launch are Satellite Vehicles (SV) 107, 119, 122, 125, 127, 129, 132, 133, 136 and 139. SV-127 was originally built as SV-100, but was later redesignated.
By November 7, 2017 Matt Desch CEO of Iridium Communications announced that the last pair of twenty year old Satellite Vehicles (SV5 and SV6) are being deorbited after being relieved of their data relay duties. By the end of the year 2017 a further 6 old SV satellite vehicles will be relieved and deorbited thus completing orbit plane 4.
Iridium’s first-generation LM-700 satellites were originally designed to operate for seven years. However, some of the oldest spacecraft have been in operation for over twenty years, and the youngest satellites have been in orbit for over fifteen.
With 95 first generation satellites launched, 60 were deployed in groups of five by 12 Delta II rockets flying from Vandenberg Air Force Base, 21 were carried in three groups of seven aboard 3 Proton-K/Blok-DM2 rockets flying from the Baikonur Cosmodrome, six pairs were launched by 6 Chang Zheng 2C/SD vehicles flying from China’s Taiyuan Satellite Launch Centre, a last pair was launched aboard 1 Rokot/Briz-KM from the Plesetsk Cosmodrome. The Rokot launch, in June 2002, was the final replenishment of the original constellation.
The second-generation Iridium-NEXT ELiTe-1000 satellites began to be deployed into the existing constellation in January 2017. Iridium Communications, the successor company to Iridium SSC, has ordered a total of 81 new satellites being built by Thales Alenia Space and Orbital ATK: 66 operational units, nine on-orbit spares, and six on ground spares yet to be put into orbit.
The first ten Iridium NEXT satellites are stacked and encapsulated in the Falcon 9 fairing for launch from Vandenberg Air Force Base, CA, in early 2017 (image credit: Iridium)
In August 2008, Iridium selected two companies — Lockheed Martin and Thales Alenia Space — to participate in the final phase of the procurement of the next-generation satellite constellation.
In June 2010, the winner of the contract was announced as Thales Alenia Space, in a $2.1 billion deal underwritten by Compagnie Française d'Assurance pour le Commerce Extérieur. Iridium additionally stated that it expected to spend about $800 million to launch the satellites and upgrade some ground facilities.
The constellation provides L band data speeds of up to 128 kbit/s to mobile terminals, up to 1.5 Mbit/s to Iridium Pilot marine terminals, and high-speed Ka-band service of up to 8 Mbit/s to fixed/transportable terminals. The NEXT satellites incorporate a secondary payload for Aireon, a space-qualified ADS-B data receiver for use by air traffic control and, via FlightAware, by airlines. A tertiary payload on 58 satellites is a marine AIS ship-tracker receiver for Canadian company ExactEarth
The design phase was completed by 2010, and Iridium stated that the old constellation of satellites would remain operational until Iridium NEXT is fully operational, with many satellites expected to remain in service until the 2020s, while the NEXT satellites would have improved bandwidth.
The new system was to be backward-compatible with the current system, which means the transmissions between old and new satellites were with reduced data streams in crossover operations. Between the new satellites nothing was reduced in the data relays.
SpaceX was contracted to launch all the Iridium NEXT satellites. All the Iridium NEXT launches have taken place using a Falcon 9 rocket launch from Vandenberg Air Force Base in California. Deployment of the constellation began in January 2017, with the launch of the first ten Iridium NEXT satellites.
The Orbit Shuffle
Circular polar orbit, altitude = 780 km, inclination = 86.4°, period = 104 minutes - The 75 SV - Satellite Vehicles in the constellation will be positioned in 6 orbital planes. Each satellite will take turns passing overhead within sight of any given point on Earth, and will be accessible for uploads/downloads every seven minutes with a quarter second delay in handover to the next one of the 11 satellites in the orbit plane.
Of the six orbit planes, the northbound satellites appear to be on the dayside of Earth, while the southbound satellites are on the nightside of Earth. The figure below shows orbit plane 1-6 on the northbound dayside starting with the Pacific/Alaska orbit plane 1 and going East to the Balkan/Finland orbit plane 6. At least on this date: May 23, 2021 at 18:16.
The inclination of 86.4° secures a full coverage of Earth as it spins eastwards underneath with 15° each hour. However, the Iridium NEXT six orbits are not Sun-synchronous orbits which would require a larger inclination of at least 96.4° during launch from Vandenberg Air Force Base to be Sun-synchronous. I suspect that by November the northbound orbits are on the nightside of Earth and in fact reversed.
However, the first 10 Iridium NEXT satellites were delivered to a 625 km temporary parking orbit where they will be tested and exercised by Iridium over the coming weeks. Upon meeting testing and validation requirements, the satellites will then be moved into their 780 km operational orbit and begin providing service to Iridium’s customers.
The 66 satellite main constellation (+9 in-orbit spares), configured in 6 orbital planes with 11 evenly spaced slots per plane, provides continuous global coverage as demonstrated by the RF footprints in Figure 6. This is achieved through cross-linked satellites operating as a fully meshed network that is supported by multiple in-orbit spares to provide real-time data downlink to the Iridium operated ground station network.
The Iridium constellation has a design lifetime greater than 10 years in a polar orbit at 780 km with an inclination of 86.4°.
Because SpaceX can’t launch the 75 Iridium NEXT satellites with just 6 rockets and will be launching them in 8 Falcon 9’s into the 6 planes “polar orbits”. It basically means that a fair deal of satellite shuffling will go on in those 6 orbit planes. 60 satellites can be delivered directly to their intended orbit plane, but 11 satellites must change their orbit planes.
Each orbit crosses the five other orbits at both poles in a “dance” at the intersection, but if you look closely the Orbit Planes 3 & 4, 2 & 5 and the last “Norwegian” 1 & 6 intersections which are furthest away from the North Pole in three different angles and therefore distances.
Imagine 6 satellites flying North crossing each other and passing 3.6° from the North Pole and flying South on the other side. It yields twelve slices with six cuts aka. orbit planes.
Vandenberg Air Force Base is placed at 34,633o north, 120,613o west, so it’s given that a change in time from 12 o’clock high noon will give a different orbit relative to the Sun, if the orbit is Sun Synchronous. A 12 o’clock noon UTC launch towards south has a 120,613o west orbit, while a 10 o’clock UTC launch is a 150,613o west orbit, because the earth shifts 15 degrees eastward per hour. Vandenberg Air Force Base is 8:02:27,12 behind Greenwich Median Time or UTC time.
I thought that the Falcon 9 launches from Vandenberg Air Force Base was staggered with 2 hours between them, but they are launched in a uneven sekvens with as little as 57 minutes or 2 hours 23 minutes at the longest between them, so I conclude there is something about rocket launch mechanics, I don’t get.
All Falcon 9’s with Iridium NEXT satellites launched from Vandenberg Air Force Base flying south. All launched in a lower, faster parking orbit of 625 km altitude. And there are uneven insertions into orbit planes 1-6 in the wrong order.
The UTC launch dates/times are as follows:
So why does Iridium Next need a 1 second launch window in a Polar LEO?
Apparently the Iridium NEXT launch orbit plane precesses at a rate of about 5.5 min/day earlier compared to the launch site SLC-4E at Vandenberg Air Force Base, California. This means that the southbound launch orbit comes 330 seconds earlier each day depending on the daily chosen orbit plane or every 23 hours, 54 minutes and 30 seconds.
I haven’t found a source explaining orbit mechanics yet. Sorry.
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