By Kai Farrimond
SpaceX launched the third batch of Iridium NEXT Satellites on Monday, marking the start of a hectic week for the company.
The Iridium NEXT Constellation, expected to be completed during 2018, consists of 66 operational satellites, 6 on-orbit spares and 9 on-ground spares in case of an on-orbit failure. The constellation, when complete will provide L-band data speeds up to 128 kbit/s to mobile terminals, up to 1.5 Mbit/s to Iridium OpenPort class terminals and high-speed Ka band service of up to 8 Mbit/s to fixed/transportable terminals.
The contract to launch the 75 satellites was signed in June 2010, making it the largest commercial rocket launch deal ever at the time, costing Iridium $492 million.
The first Iridium NEXT launch, on January 14, was SpaceX’s return to flight following the AMOS-6 mishap in September 2016 which destroyed Falcon and it’s passenger.
On October 5th, Falcon 9 without the 10 Iridium Satellites, rolled out and went vertical on SLC-4E at Vandenberg Air Force Base. The vehicle then went through its launch procedures and fired up its engines for just a few seconds.
The vehicle was then de-tanked of it’s RP-1 and LOX and rolled back into the Horizontal Integration Facility.
Over the next few days, engineers secured the payload fairing, holding the satellites, to the top of the second stage. The vehicle was then rolled out and taken into the vertical position again.
On the day of the launch, the SpaceX teams began loading of Rocket Propellant-1 at T-70 Minutes, followed by Liquid Oxygen loading at T-35.
At T-7 Minutes, the first stage engines began a process called “chill down”. This is where the Super-chilled LOX is passed through the turbo pump on the engines, getting them ready for ignition.
At T-5 Minutes, Falcon 9 was pressurised in preparation for strongback retract. This was followed by the opening of the cradle arms and retraction of the strongback at T-4 Minutes.
T-60 Seconds: The flight computer entered startup and the propellant tanks were pressurised for flight.
T-3 Seconds: The 9 Merlin engines ignited and a series of checks were initiated.
T-0 Seconds: The clamps holding Falcon to the ground released and the vehicle launched.
At T+70 Seconds, the Falcon 9 passed through the area of Maximum Aerodynamic Pressure (Max-Q) and the vehicle saw it’s highest stresses of the flight.
At T+1 Minute, 35 Seconds, the Second Stage engine began to chill down in preparation for its upcoming ignition.
MECO (Main Engine Cutoff) occured at T+2 Minutes, 28 Seconds. Followed 2 seconds later by First Stage separation and Second Stage ignition.
During all this, the First Stage was performing its flip manoeuvre and ignited three of its 9 Merlin Engines to begin heading towards ‘Just Read The Instructions’.
The fairing separated at T+3 Minutes, 17 Seconds and the Boostback Burn on Stage 1 Shutdown shortly after.
Just over 2 minutes later, those same three engines re-lit to slow the First Stage down as it hit Earth’s atmosphere. This burn lasted around 10 seconds.
At T+6 Minutes, 55 Seconds, A single Merlin Engine ignited on the First Stage for the Landing Burn and the Falcon successfully landed on the ‘Just Read The Instructions’ Droneship.
Second Engine Cutoff – 1 (SECO-1) occurred at T+9 Minutes, 2 Seconds, placing the Second Stage and its payloads into a preliminary orbit. The stage then entered a 43-minute coast phase and the engine re-lit for just 3-seconds, circularising the orbit of the Upper Stage to 625km.
The deployment of the first Iridium Satellite occurred at T+57:13 followed by the next 9, 90 seconds apart from each other.
The final Iridium NEXT Satellite deployed at T+1hr, 12 Minutes and 12 Seconds. The Second Stage will now perform some avoidance manoeuvres from the satellites followed by a de-orbit burn to reduce the amount of space junk in LEO.
Next up for SpaceX is the SES-11 Launch in just 2 days from now. This launch will reuse the booster previously used on the CRS-10 Mission and will launch from LC-39A.