SpaceX Falcon 9 Full Thrust - Intelsat 35E - Launching July 5, 2017
Screenshot of SpaceX - Intelsat 35E - July 5, 2017 hosted by Tim Dodd
Mission Rundown: SpaceX Falcon 9 FT - Intelsat 35E
Written: January 26, 2021
Running on empty all the way up hill
SpaceX is targeting the launch of Intelsat 35e from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center in Florida. The 58-minute launch window opens on Monday, July 5, at 7:37 p.m. EDT, or 23:37 UTC. The satellite will be deployed approximately 32 minutes after launch.
This Falcon 9 is the third of the three precursors to the Block 4, because there is a Block 4 second stage on top with the payload Intelsat 35e inside the fairings.
The Falcon 9 is barely able to perform its mission when the satellites become too heavy, so the Falcon 9 Full Thrust Merlin 1D+ vacuum engines were upgraded to Block 4 status on the very next flight with a major engine tweak.
The payload Intelsat 35E
Intelsat 35E was designed and manufactured by Boeing on the Boeing 702MP satellite bus. It had a launch mass of 6 761 kg (14 905 lb), the largest Intelsat's currently active satellite, and has a design life of more than 15 years.
It is powered by two wings, with four panels each, of triple-junction GaAs solar cells. The 702MP platform was designed to generate between 6 and 12 kW.
Its payload was the fourth high-throughput EpicNG deployment. The EpicNG is characterized by the implementation of frequency reuse due to a mix of frequency and polarization in small-spot beams. Not only applied to the classical HTS Ka band, but also applied to the same technique in Ku band and C band. The EpicNG series also keeps the use of wide beams to offer high throughput and broadcast capabilities in the same satellite.
In the case of Intelsat 35e, the C-band side has EpicNG spot beams with a total downlink bandwidth of 4,356 MHz. The spot beams offer high bandwidth for Europe, Sub-Sahara Africa, and the Americas. The Ku band has 39 transponder equivalents for a total downlink bandwidth of 1,404 MHz. Of the Ku three wide beams, one cover the Caribbean, one covers Europe and the Mediterranean, and the third beam covers Europe and Northern Africa.
Launch history (It took awhile)
Following two aborted launch attempts earlier in July, Intelsat 35e was launched on 5 July 2017 from the SpaceX-leased launch pad 39A in Florida. No attempt to recover the first-stage booster was made on this launch, as the first stage was flown in expendable mode in order to maximize the orbital energy imparted to this high-mass commsat,
For planning purposes, the launch had been planned for as early as 1st Quarter 2017. During an interview with Intelsat's CEO Stephen Spengler in February 2016, it was disclosed that Intelsat 35e was expected to launch in 2017. In August 2016, it emerged that the launch was assigned to a Falcon 9 Full Thrust mission scheduled for the first quarter of 2017. Performance improvements of the Falcon 9 vehicle family enable the launch of this 6-tonne satellite without upgrading to a Falcon Heavy variant.
Intelsat 35e was initially prepared for launch on 2 July 2017 from launch pad 39A, with a 59-minute-duration launch window. The first launch attempt was aborted at T-9 seconds in the countdown for a GNC-criteria violation. With insufficient time to recycle, the launch was scrubbed and the next attempt was scheduled with a 24-hour delay.
This second launch attempt was made on 3 July, and it too was aborted by the onboard computers at the same T minus 9 seconds in the countdown. Having already been pushed to the end of the launch window with no time to recycle, this resulted in a scrub for the second consecutive day.
Intelsat 35e could have been rescheduled for a 4 July 2017 launch. However, in the event, the 4 July launch was postponed — per SpaceX, "out of an abundance of caution" — prior to loading propellants. A complete check of the systems both on the rocket and on the pad was performed. Intelsat 35e was finally launched and placed in orbit on July 5, 2017.
The Final Flight of Falcon 9 B1037
The flight data in the launch debriefing tells a story, about what an expendable rocket can do as a regular launch vehicle, if it wasn’t designed to land downrange. SpaceX could just make run of the mill rockets fast, reliable and efficient, but they are going above and beyond that with the return to launchsite capability they have.
Not since the days of Mercury, Gemini and Apollo have SpaceX with Falcon 9 captured the heart and soul of mankind, so we all think we can do anything and everything. If we just spend the money, let rocket engineers think long and hard and design a rocket that is built like nothing ever seen. Falcon 9.
At full throttle the 9 Merlin 1D+ on paper have 162 seconds burntime, and B1037 used a total of 167 second burn time since ignition 2 seconds prior to launch, those 5 seconds extra burn time was gained by throttling down during Max Q, or by overtopping the propellant tanks. Maybe a little of both.
I don’t know if the 162 seconds of burntime is calculated with throttling down during Max Q. If so, then the propellant tanks are really topped off to the brim.
The dataset - Velocity 0 - 9 483 km/h - Altitude 73,1 km - tells us what the 410,9 ton of superchilled propellant going through 9 Merlin 1D+ can do in 167 seconds when burning 2,5 ton propellant a second. B1037 did fairly early fly almost directly east in order to use the atmosphere as extra lift under the fuselage, while gaining height slowly.
At 55 km altitude the air is so thin and lacking oxygen, that the exhaust plume loses its colour and probably some of its lift capacity, but at those speeds who knows. B1037 lost its last propellant at T+00:02:45, did the stage separation 2 seconds later and then fell in a free fall up to its apogee and down into the Atlantic Ocean at a place known only to the SpaceX flight engineers.
This is the exclusion zone, in which ships and planes are prohibited during launch. The dot in the larger exclusion zone could probably be the booster B1037 resting place.
The final flight of second stage
Stage 2 however continued its flight plan from 73,1 km altitude at a speed of 9 483 km/h at T+00:02:55 at SES-1. And on SECO-1 at T+00:08:40 after 355 second burn time the second stage reached 164 km altitude at a speed of 26 865 km/h gaining through its burn 83,9 km altitude and 17 456 km/h in extra speed.
Stage 2 is a Block 4 iteration, meaning it can throttle down from 930 kN to 360 kN with its Merlin 1D+ vacuum engine, and that may affect the burn time table. The Merlin 1D+ vacuum engine with its 107,5 ton propellant has a designed burn time of 397 seconds and it's unknown how much throttle is used and for how long. But with 355 seconds used, there is 42 second burn time left.
SES-2 to SECO-2 took 60 seconds, so it must have throttled down to gain the missing 18 second burn time. The second stage was spent as well as the first stage, so the satellites weight of 6,7 ton plus the empty weight of the second stage 4 tons giving a total of 10,7 ton in a thrust to weight ratio must not exceed 5:1, because most satellites are not built for higher loads than that on it.
1 g on 10,7 ton is 104,9 kN and 5 g on it is 524,7 kN, which is within the throttle range on the Merlin 1D+ vacuum engine that is 930 kN to 360 kN. If you now calculate the fuel consumption of the engine at that thrust level, add the mass of the consumed fuel to the empty weight and recalculate the thrust to weight ratio, you will get an earlier thrust setting and you can backtrack the fuel consumption and throttle levels on stage 2. It’s the hard way of using the rocket equation, but use a spreadsheet to do it.
Okay. 107,5 ton of propellant disappear in 397 seconds leaving a fuel consumption of 270,78 kg per second at full thrust at 930 kN. 524,7 kN is 56,96% of that full thrust, so the fuel consumption is 56,96% of 270,78 kg equivalent to 154,3 kg (1,5 kN) which is added to the empty weight of stage 2 and Intelsat 35e. That is step One for 1 second burn time which is repeated 415 times until the second stage is full of propellant.
If you come up short or in too early, your fuel consumption of 56,96% is wrong. It’s possible to calculate every second of thrust levels, fuel consumption, velocity and performance of a Falcon 9 rocket, if one wants to do it. So ask yourself:
Do you want to be a rocket scientist?
Either way any scientist or engineer must at all times prove what they know, how they know it and why this solution is the best solution. On any given day we all must prove ourselves, especially on exams days.
Stage 2 fate is not mentioned anywhere but the transfer orbit is 248 km by 48 000 km with no propellant left, so it will take some time to deorbit on its own. Atmospheric drag in 240 km is very low, but it’s there. I wonder how long SpaceX has control over the RCS thrusters, and how much Nitrogen gas is left and can excess Helium gas be rerouted through the RCS thrusters or dumped directly through the Merlin engine.
If so, point stage 2 in a braking direction at apogee and let it rip, this will lower the perigee and thereby increase the atmospheric drag at a lower altitude. It ain't pretty but it will work a little faster than letting gravity and drag do its job.
