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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 ...
Dragongeek's user avatar
  • 19.1k
92 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 ...
ForgeMonkey's user avatar
  • 7,119
89 votes
Accepted

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 ...
Jack's user avatar
  • 9,956
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 ...
Xerxes's user avatar
  • 730
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'...
Bret Copeland's user avatar
61 votes
Accepted

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 ...
Russell Borogove's user avatar
59 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 ...
Rikki-Tikki-Tavi's user avatar
59 votes
Accepted

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 ...
DaGroove's user avatar
  • 1,334
50 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 ...
Jörg W Mittag's user avatar
50 votes
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Why was there only a single Falcon 9 landing on ground-pad in 2021?

Whenever possible, SpaceX prefers Return To Launch Site (RTLS) landings over Autonomous Spaceport Droneship (ASDS) landings, since they get the booster back immediately instead of having to wait for a ...
Jörg W Mittag's user avatar
48 votes
Accepted

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 ...
Saiboogu's user avatar
  • 6,417
46 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 ...
Quietghost's user avatar
  • 2,476
45 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 (...
jkavalik's user avatar
  • 5,128
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 ...
geoffc's user avatar
  • 79.6k
45 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 ...
Graham's user avatar
  • 1,920
44 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 ...
Mark Adler's user avatar
  • 58.2k
44 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 ...
Uwe's user avatar
  • 49k
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 ...
geoffc's user avatar
  • 79.6k
41 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 ...
GdD's user avatar
  • 20.3k
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 ...
awksp's user avatar
  • 1,079
39 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 ...
DrSheldon's user avatar
  • 48k
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 ...
PearsonArtPhoto's user avatar
  • 121k
37 votes

What's the technology behind the floating landing pads?

tl;dr summary: the technique for dealing with rough seas is to not deal with rough seas. We often see ships destroyed by storms and waves as tall as dozens of meters, so how does SpaceX keep these ...
Jörg W Mittag's user avatar
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 ...
DarkDust's user avatar
  • 12.5k
34 votes

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

According to the official NASA press release, pyrotechnic guillotines were used: The footage ends with Perseverance’s aluminum wheels making contact with the surface at 1.61 mph (2.6 kilometers per ...
DrSheldon's user avatar
  • 48k
34 votes
Accepted

Could Ingenuity survive if Perseverance failed?

No. Perseverance is the communications relay for Ingenuity. Ingenuity uses essentially ZigBee to communicate, the same protocol that possibly your smart bulbs use. ZigBee has a range of about 300m ...
Jörg W Mittag's user avatar
33 votes
Accepted

What work needs to be done before reusing Falcon 9?

At the moment no one knows, since no one has done quite this task before. SpaceX is learning alot with each recovered core. In this image of three of the recovered cores in the LC-39A HIF building ...
geoffc's user avatar
  • 79.6k
33 votes

Did the soft-landing rockets malfunction in the Soyuz (expedition 50 crew) landing?

The "three second" item is incorrect. In general (and this can be confirmed by watching multiple landings), the rockets fire approximately half a second before landing. Maybe they meant to say "...
Tristan's user avatar
  • 17.3k
32 votes

Why was it necessary to program InSight with an ability to land in dust storms?

InSight doesn't enter Martian orbit before EDL; it plows straight into Mars' atmosphere from interplanetary space. Thus, the time of landing is pretty much un-alterable after its final midcourse ...
Russell Borogove's user avatar
32 votes
Accepted

Land a cubesat on the moon with ion engine

Not a soft landing. A soft landing requires the spacecraft having a thrust-to-weight ratio greater than one (otherwise it just falls faster and faster). Ion engines have a very low thrust to weight ...
SE - stop firing the good guys's user avatar

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