SpaceX Falcon 9 Block 4 - CRS-12 - Launching August 14, 2017
Screenshot of CRS-12 ready to launch from Pad 39A by SpaceX
Mission Rundown: SpaceX Falcon 9 Block 4 - CRS-12
Written: January 23, 2021
We got better engines on Block 4
On August 14, 2017, SpaceX launched its twelfth Commercial Resupply Services mission (CRS-12) from Launch Complex 39A - LC-39A at NASA’s Kennedy Space Center, Florida. Liftoff occurred at 12:31 p.m. EDT, or 16:31 UTC and was followed approximately two and a half minutes later by separation of the first and second stages. The first stage of Falcon 9 then successfully landed back at SpaceX’s Landing Zone 1 - LZ-1 at Cape Canaveral Air Force Station, Florida.
The Dragon Payload
NASA has contracted for the CRS-12 mission from SpaceX and therefore determines the primary payload, date/time of launch, and orbital parameters for the Dragon space capsule C113-1. CRS-12 carried a total of 2 910 kg (6 415 lb) of material into orbit. It included 1 652 kg (3 642 lb) of pressurized cargo with packaging bound for the International Space Station, and 1 258 kg (2 773 lb) of unpressurised cargo composed of the CREAM instrument, to be mounted externally to the ISS.
CRS-12 is the last of the original order of twelve missions awarded to SpaceX under the CRS contract. Originally scheduled for December 2016, the flight was delayed multiple times to August 2017. Launch occurred on 14 August 2017 at 16:31:37 UTC from Kennedy Space Center's Launch Complex 39A aboard a SpaceX Falcon 9 rocket.
After Dragon rendezvoused with the ISS on 16 August 2017, the station's Canadarm2 grappled the spacecraft at 10:52 UTC. It berthed to Harmony at 13:07 UTC.
Having been at the ISS for a month, the CRS-12 Dragon capsule was unberthed in the late hours of 16 September 2017 and was released by Canadarm2 on 17 September at 08:40 UTC. After performing separation burns to take it out of the vicinity of the ISS, the Dragon performed a deorbit burn to enable atmospheric reentry. The spacecraft successfully landed in the Pacific Ocean at 14:14 UTC, returning approximately 1 700 kilograms (3 800 lb) of experiments and equipment to Earth.
What is a Falcon 9 Block 4
The Block 4 version is a crossover between Falcon 9 Full Thrust and Falcon 9 Block 5. First change was mounting Block 4 second stages on three regular V1.2 boosters to give an extra kick to deliver 6 tons payloads into Super Synchronous Geostationary Transfer Orbits and expending the boosters for a few hundred kilos of extra payload. These three missions were NROL-76 and Inmarsat-5 F5 in May 2017, and Intelsat 35e in July 2017.
The second stage uses extra chilled cryogenic LOX in an optimized Merlin 1D# vacuum engine with throttle down capacity from 934 kN to 360 kN, so the Thrust to Weight ratio never exceeds 5 times Gravity during orbit insertion. The payloads are usually not built for more than 5 G. Word of warning though. The Merlin engine thrust values are all over the place having found 4-5 different sources on the Web. This is what I know to be true.
The next development was the throttling of the Falcon 9 first stage Merlin 1D# engines, which in the Full Thrust version couldn't be throttled down, but they could be choked by throttling down the fuel flow just before stage separation and during Max Q.
Experiments with the basic Merlin 1D fuel/oxidizer mixture ratio is controlled by the sizing of the propellant supply tubes to each engine, with only a small amount of the total flow trimmed out by a "servo-motor-controlled butterfly valve" to provide fine control of the mixture ratio. Thus the first stage 1D engines could be throttled down to about 70% of its maximum performance.
Further thrust control was being made with pintle injectors in the combustion chamber, and reducing the throttle down to 40%. An increase of thrust and burn time using super chilled cryogenic LOX and chilled RP-1 with an increase in the propellant density was already achieved in the order of 17% on Falcon 9 Full Thrust aka. V1.2.
The experiments with the Merlin 1D showed, that throttling the fuel flow to the engine and specifically the turbopump, increasing the propellant density, throttling the combustion chamber to create a constant pressure and thereby constant thrust had the Merlin Engine go through three versions 1D, 1D+ and 1D# before the Block 5 version.
- 1D sea level thrust 654 kN. Falcon 9 V1.1. Regular propellant. Fuel flow control.
- 1D+ sea level thrust 756 kN. Falcon 9 Full Thrust using super chilled propellant.
- 1D# sea level thrust 783 kN. Falcon 9 Block 4. Constant thrust and chamber control.
The final iteration of Merlin 1D# is a change of the turbo pump construction with a sea level “maximum thrust” of 845 kN, which is used in Falcon 9 Block 5.
I think that the Block iterations 1-5 are just engine block versions and the rest of the changes to the rockets propellant tanks, COPV tanks, grid fins, landing legs, use of fire suppression materials, interstages, payload adaptor fitting rings, fairing versions and dragon capsule versions of cargo and crew are just a general tweaking of Falcon 9.
- 1C sea level thrust 4940 kN. Falcon 9 V1.0. Regular propellant. No fuel flow control.
- 1D sea level thrust 5885 kN. Falcon 9 V1.1. Regular propellant. Fuel flow control.
- 1D+ sea level thrust 6885 kN. Falcon 9 Full Thrust using super chilled propellant.
- 1D# sea level thrust 7047 kN. Falcon 9 Block 4. Constant thrust and chamber control.
- 1D# sea level thrust 7607 kN. Falcon 9 Block 5. New turbopump shaft 7% more thrust.
I found this figure by chance looking for Block 4 on Google photos, which compares a Block 4 with a Block 5 during a similar flight profile with Iridium NEXT payloads. The 7% more powerful Block 5 is able to gain height more easily than Block 4, who by the looks of it is using more propellant with a MECO 2 seconds later. The Block 5 glides longer though using its titanium grid fins, so they reach the same landing burn place.
The only thing wrong in this flight profile comparison is the boost back or boost down burn effect on the two trajectories. They should bend downwards or change direction midair in the Boostback section. There are two other ways of naming these changes in flight directions.
The boost brake burn which is a partly boost back burn but not a boost down burn. There is no need to get down too fast. And the boost turn burn where the rocket changes flight direction midair up to 90 degrees right or left further out to sea or to shore in order to land on a prepared Landing Zone - LZ-5 - in South Carolina, if such a need should arise. Fx. Falcon Heavy with an ISS expansion 20 ton payload.
Flight Profile comparison found on Google photo search
And I haven't even gone into the fray of the nozzle expansion ratio, chamber pressure and regenerative cooling of the rocket engine, which all contribute to increasing the thrust and controllability of a Merlin engine. So I kept it relatively simple.
After diving into this topic, I know, I’m no rocket scientist. My head hurts so much now. Damn Corona self isolation. If you are bored out of your mind, find another hobby, like how they build Pyramids or Stonehenge. I already did that. Not that hard. The ancient people were smarter than you think. Aliens? Bah Humbug.
Just imagine me as Ebenezer Scrooge.
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