SpaceX Falcon 9 Block 5 - SAOCOM 1A - Launching October 7/8, 2018
Screenshot of SAOCOM 1A on SLC-4E and LZ-4W with Everyday Astronaut Tim Dodd as host
Mission Rundown: SpaceX Falcon 9 - SAOCOM 1A
Written: January 11, 2021
Don’t fly for me Argentina
SpaceX is being commissioned by CONAE, the Argentine space agency, to send the SAOCOM 1A satellite into a low Earth sun synchronous orbit. SpaceX will be launching the satellite on top of one of their Falcon 9 rockets.
Two things are extra exciting about this launch: For the first time on the west coast, SpaceX will be attempting a Return to Launch Site (RTLS) landing for the Falcon 9 booster at the former Space Launch Complex 4 west - SLC-4W now LZ-4.
The booster B1048-2 previously supported the Iridium-7 NEXT launched in July 2018 from the 4 East launchpad placed on Vandenberg Air Force Base (SLC 4E).
This is the second time SpaceX will be reflying a Block 5 booster, making it the second time this rocket flies twice. This marks an important milestone as SpaceX takes another mighty step towards full, rapid reusability.
The Payload
Screenshot: The SAOCOM 1A getting ready for shipment to SpaceX
Satélite Argentino de Observación Con Microondas, or SAOCOM, is a constellation of radar-imaging satellites that is being established by Argentina 's national space agency, Comisión Nacional de Actividades Espaciales (CONAE).
The constellation, whose name means Argentine satellite for microwave observation, will consist of two satellites, which will be interoperated with Italy’s COSMO-SkyMed system. COSMO-SkyMed is a four-satellite constellation that was deployed between 2007 and 2010, with a new generation of satellites slated to begin launching next year.
CONAE was an early customer for the Falcon 9, signing a contract for SpaceX to launch both of the SAOCOM satellites in April 2009: over a year before the rocket made its maiden flight and still three months before the smaller Falcon 1 made SpaceX’s first successful launch with a functional payload. At the time, the two launches were scheduled to take place between 2012 and 2013.
SAOCOM 1A is a 3 000-kilogram satellite. Built by INVAP, it is based around the same platform used for the SAC-C remote sensing satellite which launched aboard a Delta II rocket in November 2000. SAOCOM 1A is designed to operate for five years.
SAOCOM 1A and 1B are both identical Earth observation satellites which have L-Band microwave radar and infrared cameras. Both with the ability to image the Earth in any weather or lighting conditions, see through clouds and at night, and be used to monitor for disasters. SAOCOM 1A will be in orbit next year 2019.
They will join a joint Italia-Argentina SIASGE (Sistema Italo Argentino de Satélites para la Gestión de Emergencias) constellation with 4 Italian COSMO SkyMed Satellites, that carry complentamery S-Band radars.
First Stage Burn Times, Speeds and Propellant Mass
This time SpaceX delivered the telemetry on the first stage giving me a rare opportunity to analyze the performance of the first stage during ascent, boost back burn, reentry burn and finally the landing burn. Rocket thrust time equals burn time but not thrust levels.
9 Merlin 1D# engines produce a maximum thrust of 7 607 kN with an available burntime of 162 seconds, which is used to lift the Falcon 9 rocket weighing 549 metric ton into a parabolic trajectory, from which the second stage continues to orbit after 144 second burntime on the first stage. Gravity on the first stage is 5 391 kN and therefore the thrust to weight ratio is 1,44. Rocket thrust divided by rocket mass in Earth's gravity.
All 9 Merlin 1D# engines from ignition to Main Engines Cut Off - MECO were burning for a period of 147 seconds almost at full throttle except at Mach One, MaxQ and just before stage separation. The Boost Back Burn, the Re-entry Burn and the Landing Burn were all equivalent to 21 seconds of full burn time giving a total of 168 second burn time. This is 6 second too much in burntime according to Falcon 9 engine specifications.
The down throttling of the 9 Merlin 1D# engines increases the burn time durations, so it is logical to assume that the 6 second extra burn time plus whatever propellant reserve in the fuel tanks have been gained by throttling the 9 Merlin 1D# engines during assent, and by throttling the main 3 Merlin 1D# engines during the Boost Back Burn, the Reentry Burn and especially the Landing Burn.
Given that the ratio of LOX to RP-1 is 2,327 part LOX to 1,0 part RP-1 it can be assumed that LOX density of 1.255 g/cm3 in super chilled condition and with RP-1 chilled density of 0.842 g/cm3, that 2,920 kg LOX + 0,842 kg RP-1 is consumed per second per engine.
3,762 kg propellant x 9 Merlin 1D# engines x 162 second burntime = 5 485 kg propellant.
That doesn't fit with the fact that the 9 Merlin 1D# engines have 410,9 ton of propellant in the first stage fuel tanks. We can now estimate the size of the parts of propellant in the LOX/RP-1 ratio by dividing the 410,9 ton with the 5,485 ton which gives 74,91 as the number of portions of propellant that 9 Merlin 1D# engines consume.
The 74,91 could be the nozzle throat area in square centimeters or the ratio 1:74,91 of the nozzle throat compared to the Merlin 1D# rocket engine nozzle rim.
74,91 x 3,762 kg propellant x 9 Merlin 1D# x 162 second = 410 900 kg propellant.
The ratio of LOX to RP-1 is 2,327 part LOX to 1,0 part RP-1 must be multiplied by the part factor 74,91, which is 218,73 kg or 174,29 liter LOX and 63,07 kg or 74,91 liter RP-1 “which is the 1,0 part” consumed per second per Merlin 1D# engine at full thrust.
It is now possible to calculate the minimum tank volume of both types of propellants by multiplying with the number of engines and the total burn time. 174,29 liter x 9 Merlin 1D# engines x 162 seconds burn time = 254 118 liter equivalent to 254,12 m3 of LOX tank space in the first stage. 74,91 liter x 9 Merlin 1D# engines x 162 seconds burn time = 109 219 liter equivalent to 109,22 m3 of RP-1 tank space in the first stage.
Wikipedia states that the first stage has a 287 400 kg LOX tank capacity and a 123 500 kg RP-1 tank capacity which is not quite equivalent to the calculated propellant mass in kilo. 218,73 kg x 9 Merlin 1D# engines x 162 seconds burn time = 318 908,34 kilo LOX. 63,07 kilo x 9 Merlin 1D# engines x 162 seconds burn time = 91 956,06 kg RP-1.
If you add the two numbers you get 410 864,4 kilo calculated propellant capacity and if you also add wikipedia's numbers you get almost the same tank capacity number of 410 900 kg propellant. I have therefore found a flaw in the wikipedia numbers.
With 2 242,8 liters of propellant is consumed by the 9 Merlin 1D# engines every second of full thrust during liftoff. This is equivalent to 592,5 gallons of propellants to those metric impared. At some point during a SpaceX webcast Jessica Anderson stated that Falcon 9 during liftoff consumed 700 gallon of propellant every second. This is proven incorrect by the calculations above this paragraph.
The schedule below is used for calculating burn times and velocity on the first stage.
The given LOX/RP-1 data is found on Wikipedia along with weight data on Falcon 9.
Liquid oxygen has a density of 1.141 g/cm3 (1.141 kg/L or 1141 kg/m3) when subcooled it gets a density of 1.255 g/cm3 (1.255 kg/L or 1255 kg/m3)
The capability of sub-cooling the RP-1 fuel to −7 °C is giving a 2.5–4% density increase from 0.81 g/cm3 (0.81 kg/L or 810 kg/m3) to 0.842 g/cm3 (0.842 kg/L or 842 kg/m3) given a 4% increase in density of 32 kg pr. m3.
The precise amount of propellant and tank volume wasn’t known, so I’m calculating the minimum volume and mass numbers from data I believe to be true.
The excess amount of LOX used to superchill the second stage Merlin vacuum engines, bleed the pipes empty after Second Engine Cut Off and rechill the Merlin vacuum engine were likewise not known. It’s a balancing act with unknown LOX pipe volumes, so I’ll add a little more LOX.
Anyway, I'm just playing around with the given numbers. Don’t mind me.
