Iridium & SpaceX: trust remains present

Iridium Next Cover

Three days after Elon Musk’s magnificent teaser (photos of the Falcon Heavy in the hangar) and one minute after the launch of a Japanese H-IIA rocket, a Falcon 9 took off. On board? Satellites 31 to 40 of the Iridium NEXT constellation. This rocket departed from California, specifically from the Vandenberg military base (launch pad SLC-4E) at 2:27 a.m.

Satellite coverage of Iridium (identical to the news). In yellow: 1 satellite visible, in orange: 2 satellites visible, in red: more than 2 satellites.

The Iridium NEXT satellites are replacing the old Iridium constellation. They provide worldwide telecommunication services. Iridium decided to replace the old satellites because they were becoming outdated: in addition to potential age-related failures, newer and more efficient technologies had been developed. To enable global telecommunications, the Iridium NEXT satellites are placed in circular orbits at an altitude of 780km, distributed across six planes to ensure that there is always at least one satellite above each person. These orbits are nearly polar: they are inclined at 86.4°.

Satellite Iridium Next
Artist’s rendition of a NEXT satellite in orbit.

In the long run, this new constellation will contain 81 satellites: 75 in orbit (all launched by SpaceX) and 6 on the ground as reserves that can replace a defective satellite. The Iridium satellites will be deorbited after being placed in a storage orbit, with each Iridium Next satellite ensuring the continuity of the satellite it replaces: this is referred to as a “slot.” In June 2010, Iridium Corporation ordered this constellation from Thales Alenia Space for 2.1 billion euros. The satellites are expected to be fully deployed by mid-2018.

Each satellite weighs approximately 800kg at liftoff, but a dispenser holds the ten satellites as a single unit. This dispenser weighs about 300kg, bringing the total payload of this flight to around 8.3 tons. This mass remains well below the launcher’s maximum capacity. Indeed, a Falcon 9 rocket can send up to 22.8 tons into equatorial low Earth orbit.

All units feature two solar panels, manufactured by RUAG Space, capable of rotating on an axis to remain facing the Sun to ensure the electrical supply of the systems. On board an Iridium NEXT satellite, there are precisely 4 Li-ion batteries of 5.6 Ah qualified for space use to store energy and be able to release it during shadow phases. Thus, we achieve a total capacity of 22.4 Ah thanks to these batteries designed in a Saft factory in Poitiers, which are engineered to last for at least 12 years.

There are also a large number of antennas on the satellite: the first is a complex active antenna that allows the satellite to communicate with ground stations to monitor and monitor the unit’s activities.

The second is an active L-band antenna that delivers 1.5 Mb/s over a radius of 4,500 km on the ground thanks to its 48 beams. It is this antenna that allows for worldwide telephone communication, but other Ka-band antennas are also used for inter-satellite links as well as supplementary communication with the ground.

Thanks to these satellites, third-party companies have a new opportunity that was not present on the old Iridium satellites: the ability to implant their own payload onto the units. This payload must not exceed 50kg per satellite and benefits from an electrical power supply of 50 to 200W. To deploy this commercial addition, one must pay Iridium 7 million euros and an annual operating cost of 1.5 million euros. These additional payloads, limited to one per satellite, could have been built by CNES or Thales Alenia Space, but Iridium has entered into a permanent contract with Aireon.

So it is Aireon that wins the exclusivity and secures the right to deploy an ADS-B payload on each Iridium NEXT satellite. This payload is an air traffic surveillance system that provides ground stations with the position (based on the same principles as GPS or Galileo) of each appropriately equipped aircraft, along with other data.

The first launch of Iridium NEXT satellites took place on January 14, 2017. This new launch, the fourth, orbited satellites 31 to 40 and reused a stage that had already flown during the Iridium NEXT II mission. Since the first launch of Iridium NEXT satellites on January 14, 2017, SpaceX has thus sent half of the satellites of the constellation into space. SpaceX started and ended the year 2017 with launches of Iridium NEXT satellites, making it a great year for the private company!

Between these two Falcon 9 flights, 15 other launches of these rockets have taken off, bringing the total number of Falcon 9 launches this year to 17. The next launch that we are eagerly awaiting is the Falcon Heavy. According to the latest information and photos of the launcher, as well as the payload (Elon Musk’s personal Tesla Roadster, their latest announced and presented model), the launch is expected to take place next January. Let’s hope the flight goes well, although it’s not a sure thing, according to the big boss himself!

Intégration des 10 satellites dans la coiffe
Intégration des 10 satellites dans la coiffe

The booster thus experienced its second launch but did not undergo a new landing. Nothing is certain regarding the reason for this “abandonment,” but it was planned in advance as indicated by some elements. It could be assumed that SpaceX wanted to test a new reentry angle and/or internal software, taking advantage of the fact that this stage version is outdated. Indeed, it is a Block 3 while SpaceX is preparing to complete the Block 5 version. This booster would have therefore taken up space unnecessarily, introducing heterogeneity into the company’s fleet of first stages. The booster likely landed smoothly in the Pacific Ocean, as if to simulate a real landing: indeed, the booster had aluminum grid fins (the grids seen deploying after separation, allowing for guidance during reentry) but was devoid of its legs. Without the legs, the booster cannot land, but the presence of these fins suggests that the stage was not abandoned after separation: SpaceX typically removes some recovery tools from its launchers if they are not used.

To conclude this article, let’s revisit the launch timeline. A few days before the flight, the booster had undergone its static fire test. This test, now customary, allows SpaceX to verify that the first stage operates smoothly. Here is the sequence of events before and during the launch, along with some images of the flight.

The launch was a total success and marks a very successful end to the year 2017 for SpaceX. There were no failures, whether in the launch or landing. The only downside is that SpaceX had aimed to launch 20 Falcon 9 rockets this year, but ‘only’ 17 were launched.

Sources : SpaceX, Iridium Corporation, Thales Alenia Space, Wikipedia