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 ...
- 18k
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 ...
- 7,139
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 ...
- 1,234
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 ...
- 9,976
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 ...
- 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'...
- 1,954
61
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 ...
- 167k
59
votes
Accepted
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 ...
- 167k
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 ...
- 8,414
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 ...
- 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 ...
- 18k
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 ...
- 18k
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 ...
- 79.3k
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 ...
- 6,427
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 ...
- 2,466
46
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 ...
- 1,940
45
votes
Accepted
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 (...
- 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 ...
- 79.3k
44
votes
Accepted
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 ...
- 58.5k
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 ...
- 48.8k
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 ...
- 79.3k
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 ...
- 19.9k
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 ...
- 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 ...
- 47.7k
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 ...
- 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 ...
- 18k
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 ...
- 12.5k
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 ...
- 126k
34
votes
Difference between BlueOrigin and SpaceX rocket landings?
Blue Origin's flight was straight-up, straight-down, with a fairly small rocket that can't carry much useful payload. It's a great demonstration of technology, but it's only practical for space ...
- 167k
34
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 ...
- 79.3k
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