Questions tagged [falcon-9]

Questions regarding the Falcon launch vehicle developed by SpaceX for medium payloads (15,000 lbs) to LEO and GEO (via GTO, second stage cannot inject into GEO direct)

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2answers
169 views

Falcon 9 vs Apollo Landing: Key Differences?

So I'm struggling to model a Falcon 9 vertical landing. And because Falcon 9 info is scarce, I'm looking for more public info sources---like the apollo missions. The Apollos did basically vertical ...
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0answers
43 views

Falcon 9: transonic attitude control on reentry

Attitude control on the falcon 9 is done with engine thrust vectoring, cold gas thrusters, and grid fins. After the reentry burn, when the rocket stage is in the atmosphere, there is a short period ...
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Falcon 9 cold gas thrusters: why in line with grid fins?

The cold gas thrusters of the Falcon 9 are right in line with the grid fins. The grid fins deploy immediately after MECO and stay deployed while the cold gas thrusters fire. And it seems the expelled ...
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Falcon 9 flipover duration

This launch video shows a very gradual stage-1 flipover. The flipover starts right after MECO, before the 3:00 mark, and it continues slowly until just after the 6:00 mark. Or that's the impression I ...
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Why do Falcon 9 grid fins open in piecemeal fashion?

The grid fins on Falcon 9 seem to open in piecemeal fashion: extending a few degrees, pausing, extending a few degrees, pausing, etc. Any reason why this happens? The rocket stage is around 80 km high,...
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1answer
96 views

How do grid fins actually work? Which aerodynamic mechanism(s) produce the torque on the spacecraft?

I’m trying to model the steering force that grid fins exert on a falcon 9. I know these things are not just grid-shaped fins but actually grids of fins. And each of those fins will experience drag and ...
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1answer
83 views

State vector update on reentry

The integration errors from IMU state measurements would seem very problematic when you're coming in for a landing, where error tolerances would probably be as small as they could get. This must mean ...
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2answers
431 views

Ullage control with single engine stage?

How does a single-engine upper stage, like that of Falcon 9, do ullage control before starting the engine? Does it fire its cold gas thrusters? Does it fire the engine at minimum throttle for a second ...
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1answer
29 views

Ullage control on stage shutdown?

Is ullage control a thing only engine startup? Would a rocket like the Saturn V or Falcon 9 leave an engine running for a second or two longer just for ullage control?
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27 views

3g Throttling: Does Falcon 9 kill engines if acceleration over 3G?

I'm simulating a launch and I often hit minimum throttle before I hit MECO (triggered at 15% fuel mass---my reserve for stage-1 reentry). Acceleration then begins to rise to maybe 3.3 g by the time ...
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33 views

Falcon 9 landing speed estimate?

How fast is a Falcon 9 stage 1 going when it touches ground? Rough estimates are OK. An upper limit would be helpful too. I'm getting 5.5 m/s (12 mph) in simulation and wondering how reasonable this ...
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33 views

Falcon 9 Reentry Burn Duration?

The videos and simulations I've seen suggest the reentry burn lasts 30 seconds. This is followed by the final landing burn and it may be preceded by a boostback burn. I'm interested only in the ...
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18 views

Falcon 9 Stage-1 Helium Capacity

Is it known roughly how much helium a Falcon 9 stage 1 carries for leg deployment? Any educated guesses as to what the volume or mass might be? I don't imagine there are pictures of the stage-1 helium ...
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90 views

Vertical Landing: Calculating start altitude for hoverslam landing burn

So I've been thinking about hover slam landings. I want to simulate one. This is the best I've come up with so far. It's all high school physics. Am I far off? Scenario Say you're landing a rocket ...
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0answers
26 views

Falcon 9 Legs: helium just for pushers or also for telescopic cylinders?

For the longest time I assumed the Falcon 9 legs use pressurized helium to extend. But gravity by itself would cause them to extend---so long as you first kick them out from their stowed position. For ...
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25 views

Falcon 9: Landing leg helium pressure?

So it seems the Falcon 9 landing legs are powered by a helium precharge. Does anyone know the pressure of that precharge? If no numbers for Falcon 9, is there at least a reasonable range of what the ...
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1answer
358 views

How did the SpaceX come up with such a disruptive design in the Falcon 9?

Because of the answers to Why has a rocket system like Starship never been proposed before? , now I need to ask something I'd always taken for granted. If Falcon 9 wasn't revolutionary for technical ...
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48 views

Falcon 9 Flipover Direction?

Consider a Falcon 9 at MECO. The rocket's close to 30 deg relative to the local horizon, down from the 90 deg it had at launch. Stage 1 separates and flips more or less 180 degrees for the return ...
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1answer
29 views

Falcon 9: How many engines on first burn in two-burn reentry?

Consider a Falcon 9 two-burn reentry maneuver. My understanding is that the second, final, burn is always single-engine. And I think the first burn can be either single-engine or three-engine. But I'm ...
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42 views

Falcon 9 legs: precharged helium?

I've read the Falcon 9 uses helium pneumatics to extend its legs. The separation pushers are also helium pneumatics and I believe those are precharged so no pumps required. Are the leg cylinders ...
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1answer
94 views

Hover Slam Landing: How is it Done?

I want to simulate a hover slam landing. Is there an overview of the maneuver anywhere? I'm especially interested in the control algorithm used to bring the rocket stage to a halt at just the right ...
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2answers
103 views

Falcon 9 Max Q on reentry?

Max Q for a Falcon 9 is on the order of 30-40 kPa during launch. What would the number be on descent? Do they allow for greater dynamic pressures in that portion of the flight? Or is the rocket still ...
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2answers
3k views

What is this line, what is it called, what is the reason behind it?

I started following SpaceX recently. I used to read the updates but now I am diving deeper to learn new things. SpaceX is fascinating and I really like everything about it. But I have question, I don'...
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1answer
104 views

Can Falcon 9's engines be ignited more than 4 times if there is enough TEA-TEB?

SpaceX's Falcon 9 uses TEA-TEB as a ignitor for its Merlin engines. My question is if the rocket has more TEA-TEB, can the engine be shut down and restarted more than 4 times?
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1answer
119 views

If a company/agency has already developed a kerolox/hydrolox rocket, is it wise for them to switch to an all-methalox rocket? (to lower costs)

Multiple rockets, such as the Atlas V or Saturn V, have used the combination of a kerosene/liquid oxygen (kerolox) lower stage for higher density and thrust within the atmosphere and a liquid hydrogen/...
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0answers
38 views

Falcon 9: Stable platform or strapdown IMU?

What type of IMU does the Falcon 9 use? Is it a stable platform aligned with a global frame by gimbals? Or is it a strapdown system fixed to the body of the rocket and therefore aligned not with a ...
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1answer
107 views

How long is Falcon 9 suicide burn?

My question is How long is a Falcon 9 suicide burn? I assume the answer might vary between rides, depending on the payload lifted and its destination orbit so the time might not be the same for a ...
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0answers
29 views

What is the inlet and outlet pressure of Merlin LOX/RP-1 turbopump?

I got the inlet and outlet pressure of Saturn V engines turbopumps here, but I couldn't find the turbopump pressure of the Merlin engine of Falcon 9.
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1answer
93 views

Does Falcon 9 perform static fires before every launch?

Before launching every Falcon 9 rocket, is SpaceX performing a Wet Dress Rehearshal (WDR) and a static fire? If not before every launch then is it doing it before every first launch of a new booster? ...
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43 views

How long to flip over stage 1 of Falcon 9?

Curious how fast stage 1 flips over. 180 degrees is a lot of turning. At a rate of 5 deg/s, it would take 36 seconds to flip. This seems very long for the maneuver. A more modest duration of 10 s ...
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1answer
101 views

Falcon 9 altitude and speed during reentry burn?

After MECO, stage 1 of Falcon 9 does up to three engine burns: a boostback burn followed by a reentry burn followed by a final landing burn. I'm interested here in the reentry burn. How high and how ...
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0answers
51 views

How much lower is max q if launching from high altitude (i.e. mountain top)?

I looked at very simple max q formula: q=1/2 ρv^2 (https://en.wikipedia.org/wiki/Max_q). As air density is lower with altitude, the max q should be lower as well, and also should occur at higher ...
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36 views

Falcon 9 Angle of attack on return flight?

Do they control for angle of attack on the return flight of stage 1 of Falcon 9? Once it reenters thick atmosphere, aerodynamic stresses would be a concern as during launch, maybe more so because you ...
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0answers
28 views

Falcon 9 Stage-1 Reentry Burn: Throttle Setting, Duration?

How long does stage 1 of Falcon 9 fire its engines during its reentry burn, and what throttle setting do they use? Also, is it known how much fuel is left at MECO? Thanks if you know and can share!
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Does the Falcon 9 stage 1 have cold gas thrusters near the bottom?

I've seen the cold gas thruster pods on the interstage of Falcon 9, and I know that stage 2 has them too, even if there seem to be zero pictures of them on the web (they're the only means of roll ...
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18 views

Falcon 9 Stage 1 Guidance After Separation?

Does anyone know how stage 1 of Falcon 9 is guided immediately after stage separation? I'm not interested at this point in getting it to a precise landing spot, nor am I interested in the landing ...
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42 views

Pressure level inside Falcon 9 tanks?

What is the pressure level inside the Falcon 9 liquid oxygen tanks, RP-1 tanks, and helium tanks - at launch? The question is for both stages Related question: Pressure inside a launch fairing - ...
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1answer
129 views

How powerful do cold gas thrusters normally get?

Modern rockets like the Falcon 9 use cold gas thrusters for steering on landing approach when the engines are dead. Cold gas thrusters are common in smaller satellites and spacecraft, which way a ...
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0answers
24 views

Falcon 9 CGT Force?

Curious how much force the Falcon 9 cold gas thrusters produce for steering? I've seen numbers in the range of 25--100 lbf, but not sure where in this range (or outside it) the Falcon 9 falls. If you ...
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1answer
77 views

Does the SpaceX Falcon 9 first stage fleet, fly in order?

SpaceX by the end of 2020, made it very clear that they have solved the first stage reflight problem. Two cores have flown 7 times. Several are over 4 flights. At the beginning of 2021 they have about ...
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61 views

Why does Falcon 9 launch with Crew Dragon solar panels facing down?

I noticed in video of the first crewed mission in August that Falcon 9 pitches down with the Dragon solar panels facing down. I'd been expecting the solar panels to be facing up, because sun. Does ...
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2answers
722 views

How do they determine dynamic pressure has hit a max?

Max-Q is a key event during launch, and dynamic pressure is closely monitored so they know when a max is hit. But how exactly do they know when Q hits a max? If you track the rate at which Q is ...
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36 views

Coordinate axes of Falcon 9 on launchpad 39A

Can someone please correct me on the orientation of the Falcon 9 rocket as it sits on launchpad 39A at Kennedy? Looking at the image below, which way should X (red), Y (green), and Z (blue) face? I ...
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33 views

Orbital Insertion Altitude for Rendevous with ISS

When SpaceX launches a CRS mission to the ISS, what altitude do they target at orbital insertion? If the ISS is 400 km above ground, do they target 400 km at SECO? Or do they target a lower number---...
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1answer
106 views

Rocket dashboard: separation/pyro indicators

I'm curious about rocket dashboards. Separation events are big things and they depend on pyro bolts detonating and linear charges or pneumatic pushers firing immediately afterward. There must be ...
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1answer
134 views

Gimbal Check: Before or After Engine Ignition?

Is the engine gimbal check done before or after ignition? Also curious: How many seconds does the check take? What does it consist of? Do they gimbal each engine separately, or do they gimbal all ...
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0answers
25 views

Falcon 9: SECO target altitude/speed?

Is there a typical target altitude and speed for SECO on a Falcon 9 CRS launch? SECO precedes orbital insertion but there are multiple orbital adjustments afterward, so I also wonder: does Dragon have ...
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1answer
445 views

Is there an acronym for secondary engine startup? SESU?

We have acronyms for main engine cutoff (MECO) and secondary engine cutoff (SECO). Do we have an acronym for secondary engine startup---SESU maybe?
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2answers
571 views

Falcon 9 TVC: Which engines participate in roll control?

Stage 1 of Falcon 9 uses its gimballed engines during launch to control roll, pitch, and yaw. Only the eight peripheral engines can be used for roll control since the center engine couldn't possibly ...
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4answers
3k views

Are SpaceX Falcon rocket boosters significantly cheaper to operate than traditional expendable boosters?

The title pretty much sums it all up. I remember somebody once remarked about the space shuttle program that “the space shuttle was originally designed to be a space truck. But the shuttle is to ...

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