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102 votes

Why is an airbag landing on the moon not viable?

During the Pathfinder landing the airbag system hit the ground at about 20m/s. This seems fast but compared to other space speeds, it's very slow. When the pathfinder rover arrived to land at Mars, it ...
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93 votes

How does the SpaceX Falcon 9 first-stage straighten for landing?

Ironically, the answer is in his own (or rather SpaceX's) video. Still from 0:49 of the video showing cold gas thruster firing The first stage of the Falcon 9 uses a set of nitrogen cold gas ...
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90 votes
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Difference between BlueOrigin and SpaceX rocket landings?

You see that tiny thing on the far left? That's the Falcon 1. It's a comparable size to Blue Origin's New Shepard spacecraft and SpaceX's Grasshopper (which accomplished a similar feat 6 times, around ...
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  • 1,174
90 votes
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Why was it necessary to program InSight with an ability to land in dust storms?

Because it's at the end of a 6 month cruise and there's no turning back. InSight will not enter closed orbit around Mars - its trajectory is hyperbolic so either it misses Mars entirely or it enters ...
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70 votes

How were Perseverance's cables "cut" after touching down?

I believe the mechanism is this pyro-cutter, photographed by Emily Lakdawalla here. Specifically, I think they were manufactured by PacSci EMC, since they brag about it in this Facebook post. If you'd ...
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70 votes
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Why were the Space Shuttle Orbiter's landing gear not level?

There are really two questions here: why is the main gear long, and why is the nose gear short? The main gear for most aircraft are designed to carry most of the aircraft's weight and therefore they'...
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64 votes
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Why does the SpaceX reusable launcher use vertical rather than horizontal landing?

In two words: Precision landings. Underlying all of SpaceX's decisions is the desire to go to other planets, especially Mars. For exploring the solar system, Elon Musk feels that precision landings ...
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  • 756
59 votes
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What technological breakthroughs were required to land booster stages?

SpaceX's demonstrated booster-landing ability isn't the result of a breakthrough but rather a bunch of small incremental improvements. The major limitation has been funding and the will to make it ...
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59 votes
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Why can't Falcon 9 fairings touch the water?

The fairings are not boats. While they appear to float (at least for some time), there will also be water on the inside of the fairing. That results in some issues. Inside the fairing, there are ...
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  • 1,324
58 votes
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How does the Falcon 9 first stage avoid burning up on re-entry?

The heat of re-entry is highly dependent on speed. The second stage of the rocket is responsible for providing most of the speed needed for orbit, after the first stage lifts it out of dense ...
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58 votes

Why was Venus rather than Mars targeted for the first interplanetary landings?

The reason is delta-v, which is a crucial concept in Spaceflight. It means change in velocity, and is the primary 'currency' that space mission have to expend in order to reach places in the solar ...
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50 votes
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Why were Space Shuttle astronauts able to walk off the orbiter?

Look at the STS-122 video. How many astronauts do you see? I see six. Seven astronauts landed with STS-122. The six you see were the crew of STS-122 who spent twelve days in space. They could walk ...
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49 votes

Difference between BlueOrigin and SpaceX rocket landings?

Here is an image of the two trajectories. (From Reddit) Here is a nice infographic explaining the differences between the two. Kudos for both images above to Jon Ross of ZLSA Design. And here is ...
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48 votes
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Falcon 9: engines stabilize spin

The other answers are great demonstrations of F9's capabilities, but I'll be the contrarian here and say they're all wrong and perhaps Elon oversimplified things for a tweet. This was a one engine ...
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  • 6,377
48 votes

Why not land SpaceX's Starship like a plane?

There is not enough air on Mars. You would need absolutely humongous wings. There is no air at all on the Moon. Surely SpaceX can find a quick and easy way to get Starship vertical and in position ...
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45 votes
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Is there any way to land a rover on the Moon without using any thrusters?

It is not practical to use this approach from orbital (1.6km/s) or escape velocity (2.4km/s), for two major reasons. The first is the acceleration reason. The kinematic for bringing objects to a stop ...
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  • 2,416
45 votes

Is Crew Dragon flawed? Is it just an improvisation with no future?

It seems like you are considering design for re-use as a flaw. The Super Draco engines are kept since they can be reused. They need them for abort, so unless they ditch them, they cost payload mass ...
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44 votes
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Why the soot pattern on the nosecone of Falcon Heavy side booster?

It was charred by the center core after separation: (Source: SpaceX FH launch webcast) Looking at it I would expect one side to be charred too but it may not be - the nose cone is afaik composite (...
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  • 5,027
44 votes
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Why not land SpaceX's Starship like a plane?

You're basically describing the Space Shuttle. The Space Shuttle wasn't even a good solution when it was designed. It had precisely one goal - to look like a plane for the image of the Air Force. As ...
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  • 1,728
43 votes
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Why is an airbag landing on the moon not viable?

Actually there’s no reason that an airbag system could not be used on the Moon, nor that it could not be a good design decision in some circumstances. The MPF and MER airbags took out the last 10 to ...
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  • 57.5k
42 votes
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How are the SpaceX Falcon 9 Mod 3 and Mod 4 grid fins different?

Ok, I asked so I could use these awesome photos in an answer... I confess. The material has changed from Aluminium with an ablative paint to bare titanium. The specific shape, size, and mount points ...
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  • 76.4k
42 votes

Why were contact sensors put on three of the Lunar Module's four legs? Did they ever bend and stick out sideways?

Some pictures from Apollo 11 of the landing gear – struts, footpads and contact probes. Three Apollo 12 images: Two Apollo 14 footpad images: An Apollo 16 image: The two probes bend straight up on ...
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  • 46k
40 votes
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What is the largest hurdle of the mission to Mars?

The minimum-fuel (Hohmann transfer) travel time to Mars is about 8 months each way. It's possible to shave some off that time by using more fuel, but fuel-to-payload ratio is among the biggest ...
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40 votes

Why can't Falcon 9 fairings touch the water?

In addition to the water damage is the impact damage: the fairings wouldn't "touch" the water they'd hit the water, even with parachute retardation. A net slows deceleration down and spreads it more ...
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  • 18.7k
39 votes
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What was the fate of the main core of the first Falcon Heavy launch?

The core has been lost, according to the technical stream: If you wait until ~38 min and 30 seconds, the announcer says "We lost the center core". Update: Elon ...
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  • 1,039
38 votes
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Why were contact sensors put on three of the Lunar Module's four legs? Did they ever bend and stick out sideways?

It is correct that the probe on the forward footpad was omitted to avoid interfering with the ladder: The probe located on the forward landing gear was deleted because of a concern that the failed ...
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  • 46.3k
37 votes

Why was Venus rather than Mars targeted for the first interplanetary landings?

We didn't know how hostile Venus's surface was, until we had landed there. The atmosphere of Venus makes it easier to land there than Mars. From Wikipedia, we learn: Before radio observations in ...
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  • 118k
36 votes

Did Apollo have braking rockets for soft landing on Earth?

No, the Apollo Command Module (the part that made it back to Earth) did not have braking rockets. Instead, it had several parachutes and landed in the water. The descent was first slowed by two drogue ...
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  • 12.2k
35 votes
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Could the Space Shuttle have landed on any long runway other than those specially reinforced at Kennedy (TTS), and Edwards (EDW)?

STS-3 landed at White Sands runway 17. In addition to Kennedy, Edwards, and White Sands, several sites were selected as targets for a transoceanic abort landing (TAL), but no launch ever had to ...
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35 votes

How does the Falcon 9 first stage avoid burning up on re-entry?

Here's an image of the bottom of the stage before launch. As you can see, the entire bottom is covered in white panels. I suspect those panels are a heat shield. This SpaceX press release on the ...
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