89

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 3 years ago, but didn't *technically* enter space). You see those 3 in the middle? That's what SpaceX landed today. Grasshopper / Blue Origin were ...


63

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 are extremely important. The precision landing requirement means that you want to start slowing the spacecraft before you reach the surface, which points ...


54

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 atmosphere. Falcon 9 separates its first and second stages at relatively low speed, so its reentry starts off drastically slower than a reentry from orbit -- about ...


54

The diameter of the stages is the largest size that can be transported by road without extensive "outsize load" issues (permits, having to move traffic lights and signs out of the way etc.). This makes the rocket much cheaper to transport. The fairing size (5.4 m) is dictated by the standard satellite diameter set by the Shuttle and Ariane 5.


46

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 another fun size comparison (source unknown): This video especially where I cued that link, should also show an aspect of the discussion.


34

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 tourism. Today's Falcon flight was a paid orbital payload mission. In order to get the payload to orbit, the first stage has to not only bring the second stage to ...


33

It is unnecessary to use anything but the rockets. For the same reason a helicopter uses its engine and rotor to land. It would be a bit ridiculous to land a helicopter with parachutes and airbags, wouldn't it? Boeing CST-100 will use parachutes and airbags to land, and Elon Musk made fun of it in an interview, saying that its drop test landing looked like ...


32

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 introduction of the Falcon 9 v1.1 refers to a heat shield. The reference is a bit oblique, but I think this refers to the first stage. Here's the same area ...


31

That is my estimation of CoG of nearly empty Falcon 9 booster. On the left is GoG with legs opened, on the right with legs retracted. The landed vehicle is pretty stable. It could withstand the winds of 50 m/sec (97 knots!), if sliding is prevented. There are relatively narrow limits on horizontal component of landing speed as well as on rotational velocity ...


30

Nobody knows, but it seems pretty safe to assume, for a while, things will continue as normal. SpaceX will continue launching rockets and attempting to land them. They will take the one they have (and any more they acquire) and analyse them extensively to determine if they are, in fact, flightworthy again and what effects being used has had on their ...


27

Blue Origins Flew to just over 100 km (100.5), just enough to say it went to space. Landed at the same site, presumably went straight up and down. Carried a suborbital payload. Announced only after the fact. SpaceX Separation from 1st stage at 79.3 km, 5929 km/hr (From webcast video) At that point, the upward speed was about (86.6-75.3)/7 or 1.6 km/ ...


24

I think that's the fairing (the shell around the satellites on top of the second stage). The fairing separates into 2 halves, those are the only objects large enough to be visible in this photo. At T+3:18 of that video, you can hear one of the technicians say "Fairing separation confirmed". Right after that, the first bright object separates from the ...


23

                     Key phases in the launch-and-landing plan for SpaceX Falcon 9 rocket. Image credit: Jon Ross, NBC News.com After the first stage main engine cutoff, cold gas N2 thrusters are used to rotate the booster into the direction of flight, they ...


23

The plan as has dribbled and drabbled out from Musk's various statements is that the fairings are large and light, thus reentry heating is not too bad on them. They do not need to do a re-entry burn as the first stage seems to require, in order to slow down enough that hitting the atmosphere does not melt the entire structure. Then once in thicker air, a ...


22

SpaceX have tried using parachutes for landing the first stage, but they weren't happy with the results. A landing with airbags is more complicated: you need to attach parachutes to at least two locations (top and bottom of the stage). You still don't have fine control over the landing location. You need to land on a barge to prevent soaking the stage in ...


21

Torque and/or mass. You can go with small reaction wheels which can only barely affect the attitude, or with massive ones, which... still barely affect the attitude. They are good for satellites that stay in the orbit for years, where you can afford hours per maneuver, but need years of operation. Meanwhile, RCS will run out of fuel quite fast, but it can ...


19

The first several attempts to recover the Falcon 9 did include water landings: (Image source) However there are many problems with water landings. There's no way for the Falcon 9 to remain upright on water. To get an idea of the magnitude of the problem, try standing by a swimming pool and falling forward face first into the water. It's going to hurt. Now ...


19

An earlier plan, years ago, when they thought they would have landed much sooner was to take the used first stage to SpacePort America in the Mojave Desert, after inspection, and refly it there several times. But current plans seem to be focused on expediency and they will use it for fit checks and ground support equipment tests at the LC-39A pad they are ...


18

According to Spaceflight 101, the fueled mass of the first stage is 403 tons, and empty mass 18 tons. Its specific impulse ranges from 282 to 311 seconds going from sea level to vacuum, implying exhaust velocity of 2766-3050 m/s. Plugging those values into the rocket equation gets you somewhere between 8600 and 9500 m/s of delta-v. I don't know the exact ...


16

It seems to me very unlikely that this would actually occur. One would have to get the fuel out to the barge, fill the rocket, monitor the mission to return, and run the risk of losing the rocket, etc. The cost to have the barge return is minimal in comparison, and in fact, the cost is probably about the same regardless of if there is a booster on top or not....


15

SpaceX has leased LC-13 on the Florida coast, and renamed it Landing Complex 1. Then renamed to Landing Zone 1. They are building 5 landing pads there, but the Environmental assessment (the document you have to get to be able to start building and construction) says they will only land one at a time. (So Heavy's three cores not quite yet). Gwynne Shotwell ...


13

No. The booster did not even have landing legs. To loft the two payloads with a total mass of 4,159 Kilograms into a Supersynchronous Transfer orbit required almost the entire performance of Falcon 9, not permitting the first stage to attempt a boost-back and propulsive landing because it had to burn its entire propellant load during the primary mission ...


13

There's not much reliable data out there to estimate this ourselves, and SpaceX isn't exactly forthcoming with details. Or perhaps they would be, but media aren't asking the right questions during press conferences. So far, the only somewhat reliable data point is the canceled recovery attempt during the DSCOVR launch on February 11, 2015; According to ...


13

Dry mass of the first stage from SpaceFlight101 suggests 25,600 kilos. Dry mass of the second stage is 3,900 kilos, and 92,670 kilos fueled. Ignoring payload, that is one heck of a top heavy vehicle, an empty first stage, and a fully fueled second stage, almost 4 times the mass in the second stage. The current control facilities (Cold gas thrusters, Grid ...


13

Landing legs catching fire as they extend in the final second prior to landing isn't really unexpected, so they would be designed to withstand that. And this being potentially a problem unless engineered around it has already been made more than apparent during Grasshopper and F9R Dev test flights. Adiabatic flame temperature of RP-1 (rocket grade kerosene) ...


12

Problem the first: The first stage when finished with its mission is not in orbit, nor even close. It somewhat depends, and specifically with a Falcon 9 there is a wider range than usual of first stage MECO stats. They can run it as a F9 expendable, where it is max payload, max thrust, empty tanks. They can run it as a F9 reusable, where they save 15-30% ...


12

They have said that they will reserve around 15% of the fuel capacity of a first stage for reusability operations. At the point they need to impart the Delta-V to return to base, they will thus be 85% empty. Thus the need for only 3 engines instead of the 9 main engines for the retro propulsion burn. I won't try to do the math, but they claim they have, ...


12

The side boosters and the center core will be different. Gwynne Shotwell discussed this in an interview, which you can read a report of in this SpaceNews article. “Falcon Heavy is two different cores — the inner core and the two side sticks,” Shotwell said. “The new Falcon 9 will basically be a Falcon Heavy side booster. So we’re building [only two ...


12

I believe the visual effect is due to the rocket flying a small positive angle of attack at the end of the first stage burn, combined with a steeply foreshortened camera view. According to the simulation data at FlightClub (https://www.flightclub.io/results/?code=SS10), the rocket flies a positive angle-of-attack during the end of the first stage burn, ...


11

The root cause was a propellant valve for the Merlin engine that was slow to respond, so the engine had way too much power in the last few seconds. This results in the bottom of the stage having more lateral speed than it should, so it overshoots the vertical position. The tweet referenced "biprop" (bi-propellant) and the only engine on the stage that ...


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