SpaceX Falcon 9 Block 5 - RadarSat - Launching June 12, 2019
Screenshot of Tim Dodd: SpaceX launch Falcon 9 through the fog with RadarSat - WOW
Mission Rundown: SpaceX Falcon 9 B5 - RadarSat
Written: January 5, 2021
: Screenshot from Tim Dodd: SpaceX RadarSat Overview by Geoff Barrett
Three brothers left to see the World
SpaceX will be launching the RADARSAT constellation of 3 satellite vehicles for the Canadian Space Agency (CSA) on a Falcon 9 rocket from Space Launch Complex 4E - SLC-4E at the Vandenberg Air Force Base (VAFB).
The three satellites were launched on 12 June 2019 at 14:17 UTC on board a Falcon 9 rocket, who’s regular Payload Adaptor Fitting was equipped with a three clover adaptor, on which the three RadarSats were mounted on release clamps.
This booster, B1051, is flying for the second time. It previously boosted the DM-1 Crew Dragon capsule to orbit in March 2019. No recovery of the type 1 fairings.
The Three Clover Payload
The constellation consists of three identical satellites built by MacDonald, Dettwiler and Associates ltd. (MDA). Each satellite weighs 1 430 kg (3 153 pounds). The instruments onboard are a C-Band synthetic aperture radar and an Automatic Identification System. The objectives of the satellites are to perform maritime surveillance, with ship detection, ice monitoring, oil pollution monitoring and maritime wind measurement, as well as disaster management and environmental monitoring.
The satellites will fly in a Sun synchronous low Earth orbit at an altitude of approximately 600 km (373 miles), at an inclination of 97.74 degrees and an orbit taking ~ 96 minutes.
Screenshot of the RadarSat satellite. Credit: Canadian Space Agency.
This is the third RadarSat mission for CSA. RadarSat-1 was launched on a Delta II on November 4, 1995 ending its mission on March 29, 2013. RadarSat-2 was launched on a Soyuz-FG Fregat rocket on December 14, 2007 and is still active.
Originally booster B1050 was planned to be used for this mission. However, after the failed landing of B1050, booster B1051 was moved up to be used in this mission.
Three Merlins? That’s a good question
Liquid Chris: Why does SpaceX use three Merlin 1D# rocket engines during reentry?
When you fall, you accelerate by 1 g aka. 9,82 m/s2. Multiplied by your weight “mass”, you get the Force -1 N pr. kilo weight. To stop that you need +1 N pr. kilo weight just to hover or maintain your current falling speed, but you need to break. If you don’t, Earth will stop you dead in an instant. Just ask SN8 and SN9.
A descending Falcon 9 booster weighing 20-25 ton dry + x tons of propellant traveling 4-5 times faster than a bullet needs a lot of thrust to break midair without crumbling itself like an empty Beer Can. So the +G force must not exceed 3,5 G.
This booster B1051-2 had an entry burn at 40:57 by 3 Merlin 1D# for 23 seconds, and they lit up in a one - three - one sekvens, each sekvens taking 4 seconds, 19 seconds and 2 seconds. How they were throttled on the entry burn is unknown, but each Merlin 1D# rocket engine has a 845 kN - 482 kN thrust range.
They have a max. thrust of + 2 535 kN to counter a - 400 kN (I’m guessing double dry weight) speeding down towards earth, but that's a thrust to weight ratio of 6,3, which is too much. A rocket hull is like a beer can, it will crumble and disintegrate. At minimum thrust of 1 446 kN reduces the thrust to weight ratio to 3,6, which is structurally survivable.
B1051-2 had an available burn time of 9 x 162 seconds and used 9 x 140 seconds on the accent burn, 1-3-1 x 40 seconds on boost back burn, 1-3-1 x 23 seconds on entry burn and 1 x 34 seconds on the landing burn. 162 - 140 = 22 second burntime left, or 66 seconds burntime for 3 Merlin 1D#, so 66 - 40 = 26 second burntime left. The entry burn used 23 seconds so there is now only 3 seconds left, or 9 seconds by one engine, even that's not enough for the 34 second landing burn.
Now here's the throttle to the rescue. A low “idle” thrust burn takes longer than a full thrust burn, because it has a lesser fuel consumption. 482 kN is 57% of 845 kN and must use 57% less propellant, so 23 seconds at 57% thrust is equivalent to a 13,1 second 100% burn time. Now there is 10 plus 9 second full thrust burn time left for the landing burn.
19 seconds full thrust landing burn or with 57% “idle” thrust in 33,33 seconds which is almost enough to make the 34 second landing burn.
Now the throttle has been used several times during the flight before the entry burn, and the throttle hasn't been either full up or only at “idle” at 57%. That means, the fuel consumption has been less during throttle down periods, so the remaining burn time increases by the throttle down usages and throttle percentages.
Now a genuine rocket scientist can tweak these thrust numbers to such a degree, that the booster lands on fumes or at least 100 kilo propellant left in the tanks.
That should “sort of” answer the 3 engine reentry burn question. - Rocket Mechanic -
This needs more work... Decent speed km/h? Delta V? Energy content m x V2 ? The variable propellant weight? Oh Man… My head hurts… Doctor… DOCTOR... WHO
Now some three months later I found a minor nugget. This will help with this question. The green throttle curve is slowly building up G-forces. Each spike down is a throttling down with less and less propellant intake and usage in the Merlin 1D# engines. There is data for both stages during ascent.
‘There’s Gold in them there Hills.’ John Houston. Movie actor.
