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100 votes
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Why doesn't the Falcon-9 first stage use three legs to land?

I can't speak for why SpaceX made the decision. However, while three legs won't wobble, four legs are less likely to tip over. SpaceX has demonstrated tipping over is a major problem. Dr. Peterson of ...
Schwern's user avatar
  • 8,016
67 votes
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Why doesn't SpaceX land boosters in Africa?

The boosters do not have the range to get to Africa because they aren't going fast enough. If you look at the graphic below it shows a Falcon Heavy mission. The side boosters do not get very far ...
GdD's user avatar
  • 20.3k
43 votes

Why is the Falcon Heavy center core recovery done at sea?

Because of accidents of geography and history. Both of the main US launch sites are where they are because rockets occasionally crash, and, for fully fueled heavy lift vehicles, worst-case impacts ...
GremlinWranger's user avatar
38 votes

Why do rockets not glide back?

As with most things space, it all comes down to tradeoffs. The most efficient rocket is one that is purely expendable and has no mass that does not contribute to getting the payload towards orbit. If ...
GremlinWranger's user avatar
34 votes

Why won't they recover the Falcon 9 from CRS-14?

Earlier on Musk indicated it may be possible to fly a block 3/4 booster more than twice but it would depend on the missions flown, with LEO missions like this Commercial Cargo mission being easier ...
Evan Steinbrenner's user avatar
32 votes
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What makes 21st century fairings so valuable that they'd potentially be recovered and re-used?

It is not so much that in the 21st century it is hard or expensive to make a fairing. Rather they are just REALLY REALLY big. 13 meters by 4.6 meters. That is about 40 feet long, and 14 feet wide....
geoffc's user avatar
  • 80k
29 votes
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Why does this boat have a landing pad? (SpaceX's GO Searcher) Any plans for propulsive capsule landings?

No, the pad will not be used for propulsive capsule landings. As requested by NASA, SpaceX have stopped pursuing propulsive capsule landing. The landing legs have been removed from the design, for ...
Hobbes's user avatar
  • 128k
25 votes
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Why won't the SLS boosters be recovered?

The usual answer - $. Booster recovery was only marginally worth it for STS - once you witnessed how every screw and nut was taken apart, cleaned, and reassembled, you began to wonder why not just ...
Organic Marble's user avatar
25 votes

Why doesn't the Falcon-9 first stage use three legs to land?

A stool with three legs that are rigid, are of a fixed length, and have a fixed orientation with respect to the seat of the stool is superior to a chair with more than three rigid, fixed length, fixed ...
David Hammen's user avatar
  • 75.3k
25 votes

Why did they use uprighting bags in different sizes for the Apollo CM?

This is explained in the Apollo Program Summary Report. A floating command module has two stable positions; stable II is upside-down and undesired. It was discovered that three identical uprighting ...
DrSheldon's user avatar
  • 48.1k
24 votes

Why doesn't SpaceX land boosters in Africa?

In addition to the other answers, a fixed site in Africa would limit the available launch inclinations to a narrow band. A ship can be positioned anywhere in the ocean.
Hobbes's user avatar
  • 128k
24 votes

Why no parachutes in the Orion AA2 abort test?

The test they were doing didn’t require parachutes. Data-taking ended right after the capsule separated from the tower. Since the capsule’s behavior after that was not part of the test, it could be an ...
Bob Jacobsen's user avatar
  • 12.7k
23 votes

What makes 21st century fairings so valuable that they'd potentially be recovered and re-used?

The fairings are large structures, made in a way that's difficult to automate. The structure consists of an aluminium honeycomb core with carbon fibre inner and outer panels laminated onto it. Carbon ...
Hobbes's user avatar
  • 128k
22 votes
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Why is the first stage from the Falcon 9 SES-12 mission not recovered?

If you check the Reddit Wiki listing all the SpaceX Falcon 9 first stage cores, you will see that they are flying the Block 3 and Block 4 boosters only twice. What is interesting has been that they ...
geoffc's user avatar
  • 80k
21 votes

Why doesn't SpaceX land boosters in Africa?

Aside from the technical aspects, Africa is comprised of a couple of dozen different countries, all with their own rules and politics, but none of which would appreciate a botched booster landing in ...
Sebastiaan van den Broek's user avatar
21 votes

Why did they use uprighting bags in different sizes for the Apollo CM?

The first Block I version of the capsule used three bags of the same diameter (43 inch). The later Block II used one smaller bag (34 inch). The volume of the small bag was 49.43 % of the larger ones. ...
Uwe's user avatar
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20 votes
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What was the point of the re-entry and landing burn of the first stage of the GovSat-1 launch?

SpaceX was testing a more efficient, faster landing technique. The test produced useful telemetry data. See Musk's tweet and photo. Normally, the terminal phase of Falcon 9 first-stage landing ...
Russell Borogove's user avatar
20 votes

What would have happened if an Apollo/Gemini/Mercury splashdown hit a ship?

In the Apollo era, landing guidance had gotten quite precise and there wasn't a "huge flotilla" waiting; Apollo 8's recovery force was the largest, with 6 ships waiting for it in each of two ...
Russell Borogove's user avatar
18 votes

Why did the Falcon Heavy center core fall off the ASDS OCISLY barge?

The reports indicate the seas were high enough they did not want to send people on board to weld it down. Further reports suggest the seas were up to ten foot swells, and remember that the ASDS ...
geoffc's user avatar
  • 80k
18 votes
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Were these Apollo 14 and 15 recovery images taken (by a Navy frogman) using an underwater camera?

The answer is on this National Geographic page about the best pictures from NASA's official photographer Bill Ingalls: If you love space, odds are you’ve admired the work of Bill Ingalls. He has been ...
Uwe's user avatar
  • 49.2k
16 votes

Why do rockets not glide back?

Wings are heavy. They also add mass to the rocket's structure, because it is loaded horizontally when flying with wings rather than vertically as it is at launch. At the time Energia was developed, ...
Skyler's user avatar
  • 461
15 votes
Accepted

Is the Falcon Heavy booster much simpler to land than the Falcon 9 first stage?

The FH side boosters should be almost equivalent to the F9 first stage (at least the Block 5 ones) - the difference will be mostly in mount points and the nosecone instead of the interstage. The ...
jkavalik's user avatar
  • 5,138
15 votes

Why no parachutes in the Orion AA2 abort test?

From the article: Tuesday’s launch was more focused on testing the launch abort system itself. The parachutes on Orion have been tested 47 times.
ulatekh's user avatar
  • 251
14 votes

Why is the Falcon Heavy center core recovery done at sea?

It is purely down to trajectory. The side cores detach relatively early after the launch. This means that they are not so high nor do are they travelling so fast Eastbound. There is therefore ...
Roger Lucas's user avatar
13 votes
Accepted

Why won't they recover the Falcon 9 from CRS-14?

SpaceX designed the Falcon 9 for reuse. They have several iterations, starting with the 1.0 design (with the tic-tac-toe grid of engines). The switch to the 1.1 design with the Octaweb, was ...
geoffc's user avatar
  • 80k
13 votes

Why is the Falcon Heavy center core recovery done at sea?

Falcon is launched over sea, partly for safety reasons (to avoid rocket stages falling on people's houses - which happens in China). The first stage is in a ballistic trajectory and simply does not ...
Ags1's user avatar
  • 1,341
12 votes

Do 'size of a bus' sized F9 fairings ever float after impact? Are they navigation hazards?

The fairing consists of an aluminium honeycomb sandwiched between carbon fibre sheets. The amount of air trapped in the honeycomb determines if the structure will float, but as we don't know how thick ...
Hobbes's user avatar
  • 128k
12 votes

Why doesn't SpaceX land boosters in Africa?

We saw with the Falcon Heavy third flight (STP-2 mission) that the center core landing was attempted at 1240KM from launch, which is the farthest recovery attempt to date. A consequence of the ...
geoffc's user avatar
  • 80k
12 votes

Why no parachutes in the Orion AA2 abort test?

This is not a complete answer as I do not know the status of the parachute development, but here are some reasons a parachute is not needed: Ejected Data Recorders: These ~20 data recorders, ...
CourageousPotato's user avatar
11 votes
Accepted

Do 'size of a bus' sized F9 fairings ever float after impact? Are they navigation hazards?

Finally can answer this definitively, yes, they do float and I can prove it! Mr Steven failed to catch the fairing in its net, which looks like this: But after the water landing it was fished out. ...
geoffc's user avatar
  • 80k

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