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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Does the Merlin vacuum engine on SpaceX's Falcon 9 gimbal?

SpaceX uses the Merlin Vacuum engine on the second stage of the Falcon 9 launch vehicle. Does the merlin vacuum engine gimbal or does the second stage uses only nitrogen cold gas thrusters for ...
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What is the purpose of having a planned hold during a countdown for a rocket launch? [duplicate]

NASA had many with the space shuttle, ULA always had a planned hold at T-4 minutes, and yet other launch providers like SpaceX don't. What is the purpose of a planned hold, and why do some launchers ...
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0 votes
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Why does the SpaceX Falcon 9 perform a entry burn? [duplicate]

Why should SpaceX perform 2 burns which increases the probability of failure? I understand the landing burn, but what is the purpose of the entry burn? On SpaceX webcasts it says "To slows our ...
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1 vote
0 answers
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Why can't the Falcon 9 first stage touch the water? [duplicate]

SpaceX is spending considerable effort to catch the Falcon 9 first stage onto a giant drone ship. I am aware that salt water ruins almost everything in the long run, but the first stage is a composite ...
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1 vote
1 answer
140 views

Could Falcon 9 be Caught by the Orbital Launch Tower?

Would it be possible to catch Falcon 9 with the orbital launch tower by its current grid fins or load points that could be added? If they can do this and then remove the landing legs, would mass ...
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1 answer
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What is the reliability of the Merlin engine?

I know that Merlin is extremely reliable, at least over 99%. I do know of one time when one failed, on Falcon 9's fourth launch. SpaceX had used hundreds, if not thousands, of them. I assume there is ...
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1 vote
0 answers
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What would happen if a rocket was shot? [duplicate]

After the pre-launch explosion in 2016 of their Falcon 9 rocket, SpaceX seriously considered sabotage, going as far as to see how easy it would be to shoot the Falcon 9 rocket from the ULA building. ...
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5 votes
1 answer
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What is the current turnaround time for Vandenberg SLC-4E?

Is there public knowledge for the turnaround time for this Falcon 9 B5 pad?
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2 votes
1 answer
107 views

How did this upper stage end up on a collision course with the moon?

The upper stage of the Falcon 9 rocket that launched the DSCOVR spacecraft is expected to accidentally crash into the moon soon. How did it get into this position? I found answers here that say it was,...
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5 votes
1 answer
129 views

Has Falcon 9 block 5's design stopped evolving?

Spacex famously iteratively improves the design when developing rockets, with each unit being slightly (or not-so-slightly) better than the previous. These days Spacex seems to be focusing most of ...
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3 votes
2 answers
129 views

Why not first stage rocket recovery at launching site after one orbit?

Rockets first stage recovery at launch site needs a significant amount of fuel for going back. This is why SpaceX most often uses sea platform and booster back burn for re-entry. As we see on Falcon9 ...
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3 votes
0 answers
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Is SpaceX on the way to a reliability record? [duplicate]

One of the most striking phenomena of Falcon 9 launches is how smoothly they go, at least for the outside spectator. SpaceX launches a lot. Apparently, they have now had 109 successful missions in a ...
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4 votes
1 answer
218 views

Has a single Falcon 9 ever launched twice in a day?

Musk says in this Tweet on Nov 9, 2019, "If we build as many Starships as Falcons, so ~100 vehicles & each does 100 tons to orbit, that’s a capacity of 10 million tons of payload to orbit ...
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4 votes
1 answer
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How does the Falcon 9 upper stage settle its propellants?

I understand the upper stage separates with the use of pneumatic pushers, but what settles the propellants in the upper stage tanks so that the propellant is pushed back to the intake? The pushers ...
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13 votes
1 answer
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Cost per launch to ISS: Starliner vs Crew Dragon

What is the cost to NASA per launch to ISS of Starliner vs Crew Dragon? The Crew Dragon flights uses the SpaceX Falcon 9-FT with the first stage reusable, along with the partially reusable Crew ...
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5 votes
0 answers
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Will the International Space Station be able to see the Falcon 9 (Inspiration4 launch)

Will astronauts aboard the International Space Station be able to see any part of the Inspiration4 flight of the Falcon 9 during launch and/or during orbit?
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1 answer
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How will the Inspiration 4 capsule deorbit?

Soon the Inspiration 4 mission will launch and the crew will orbit the Earth for three days. How will the crew capsule then deorbit? Will it use the super/regular Draco thrusters?
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7 votes
1 answer
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Would it be possible for a Falcon 9 booster stage to land after an in-flight launch failure?

We all know that the Falcon 9 is designed for reusability, but there still have been some hull losses. Though this hasn't happened yet, say a Falcon 9 experiences an in-flight failure where four core ...
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4 votes
0 answers
154 views

How does a returning Falcon first stage decide when to end its re-entry burn?

When a Falcon 9 first stage is returning to Earth to land, it performs a brief re-entry burn in order to slow down. My question is, what criteria does the first stage control software use to decide ...
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8 votes
1 answer
398 views

Why do recent launch vehicles like that of Space X and Rocket Lab have far fewer umbilicals than before? What has changed?

Launch vehicles using mobile launch pads have many umbilical connections, whereas the ones using TEL launch structure with strongback, don't. Why is that? As seen in the picture, Electron has just one ...
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4 votes
1 answer
625 views

Which Falcon-9 launches were of a Falcon-9R rocket?

I have heard about Falcon 9 1.1 and Falcon 9 FT, but what is a Falcon 9R? If I understand correctly R = "reusable" which seems to apply to a lot of them. Are the Falcon 9 FT rockets launched ...
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2 votes
1 answer
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Puzzler; what can we learn about the distance and direction of Earth from this cool SpaceX-tweeted image of Earth and a vacuum nozzle?

The 18-June-2021 Spacex-tweeted below says: View from Falcon 9's second stage Merlin Vacuum engine There is information out there about the approximate exit diameter and length of the nozzle and ...
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22 votes
2 answers
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Do Falcon 9s get a thorough wash or a fresh coat of paint (they look clean pre-reflight)?

Before/during reflight, the boosters look white and clean, but after, they don't. I'm not sure if that's soot and/or burned paint. I looked but it doesn't seem to have been asked before. RE Is Falcon ...
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1 vote
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Why does the signal get lost every single time a Falcon 9 booster or Falcon Heavy booster lands on a droneship? [duplicate]

SpaceX reuses the Falcon 9 boosters and they sometimes fly back from space and land on land or sometimes at sea. In the sea landings, they land the booster on a floating drone ship(mainly, Of Course, ...
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3 votes
1 answer
197 views

Moment of inertia data for rocket stage?

I'm modeling a rocket launch and would like to compare my calculated moments of inertia to actual real-world data from other rockets. Any rocket would do, though those similar in size to Falcon 9 ...
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6 votes
0 answers
217 views

Bumps/nodes on rocket skin: What are they?

I've wondered for a while now what the many bumps and nodes on a rocket's skin are. Picture below for example (red lines mark bumps). Can someone clarify?
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5 votes
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Crew Dragon: How thick is the skin?

Auto body panels are about 20-gauge, or just under 1 mm thick. This is fine for many reasons: thin panels are light for good fuel economy and crumple easily for shock absorption without unnecessary ...
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2 votes
1 answer
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Dragon Launch Escape: Attitude Control?

I've read the superdracos have a deep throttle range suited for attitude control during powered landings---an old requirement that's long been dropped. This has me wondering: are the superdracos ...
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4 votes
1 answer
177 views

Crew Dragon: Could launch escape thrust determine payload capacity?

The superdracos in Dragon's launch escape system each produce $\color{black}{\texttt{71.2 kN}}$ (16,000 lbf) of thrust. There are eight superdracos, giving a combined thrust of $\color{black}{\texttt{...
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1 vote
1 answer
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What is the semicircular puff coming from the Falcon 9 first stage in this picture?

When I was watching the Crew 2 launch this morning, I noticed that while the first stage was coasting up and back down, it kept giving off arc-shaped "puffs". I did not see any corresponding ...
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2 votes
0 answers
36 views

Dragon launch escape: roll control?

Dragon’s four superdraco pods are positioned well for pitch and yaw control, but not for roll control. So I’m wondering how they’ll control for roll during launch escape—or if they’ll even control for ...
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2 votes
1 answer
87 views

Dragon launch escape: is nose cone ejected for parachute deployment?

Dragon’s landing parachute is stowed roughly in the nose cone hinge area, and this leads me to believe the nose cone has to open for the chute to deploy. In normal operations, I believe the nose cone ...
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2 votes
1 answer
105 views

Dragon Superdracos: how much MMH/NTO propellant?

How much Monomethylhydrazine + Dinitrogen tetroxide (MMH/NTO) hypergolic propellant does the Dragon crew module carry and how much burn time does that afford them during launch escape if one is ...
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5 votes
1 answer
142 views

Do Falcon 9 grid fins lock up during reentry?

Do Falcon 9 grid fins lock up when extended during reentry? Or do they rely on aerodynamic forces to keep them extended once they're deployed? Could the fins flail down during the reentry burn when ...
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2 votes
2 answers
229 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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3 votes
0 answers
70 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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3 votes
0 answers
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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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3 votes
0 answers
98 views

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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2 votes
1 answer
194 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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1 vote
1 answer
100 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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3 votes
2 answers
469 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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0 votes
1 answer
53 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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1 vote
0 answers
394 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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1 vote
0 answers
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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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7 votes
1 answer
425 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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3 votes
0 answers
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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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0 votes
1 answer
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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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0 votes
0 answers
43 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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2 votes
1 answer
296 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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3 votes
2 answers
279 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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