Hot answers tagged

26

I reviewed the video frame-by-frame. The stage falls on the collapsed leg (which was hot enough to be on fire during the landing). The leg penetrated the RP-1 tank. The tank is under pressure, so it ruptures violently and takes the oxygen tank with it. You have both gushing out under pressure (i.e. at high speed) over a hot deck and towards the even hotter ...


26

I bet that's every rookie US Navy pilot's thought too on their first carrier landing approach. Thing is though, that unlike aircraft, Falcon 9 first stage can't really maintain altitude before landing. Even single of its nine Merlin engines throttled all the way down is too powerful for hovering on nearly empty tanks and landing is really going to be more of ...


18

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 barges are very large and flat. They did not use the Octobgrabber/Xoomba, because the attach points it uses on a Falcon 9 core, are modified and not available on a ...


16

Old/Original Proposal for Second Stage Reuse Second stage reuse for Falcon 9 was a planned feature that has been discontinued. In this old render(Shows a Falcon 9v1.0 with square engine block) you can see a reuse plan very similar to what you described. The second stage nozzle would retract into the tank structure, small legs would deploy, and smaller ...


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....


14

Consider what is happening. A rocket firing a 175,000 lb thrust engine, (throttled down as low as it can go, so let's call it 100,000 lbs thrust) is pointed at, and getting closer and closer to a flat surface 170x300 feet in size floating on the ocean. The engine thrust is vibrating the platform so much they lose satellite lock. To put that in scale: A ...


12

If you look and listen closely to the video, you'll hear two bangs, not one: First, the LOX tank at the top of the rocket ruptures. Since it's pressurized, it doesn't just spill out, but quite loudly shoots liquid oxygen in all directions. But no explosion, only a small fire, likely combusting residue kerosene on the engine. A moment later, the kerosene ...


11

The issue is interesting, since the Bezos patent is specific about the barge and the rocket handshaking and talking directly to each other. But SpaceX is contesting the patent (obviously, since they are actually doing it). Almost certainly the initial location is sent by Mission Control, refined the whole time. The ASDS is set to maintain a location, the ...


10

According to Musk at the post CRS-8 briefing: Both (ship and rocket) is going to an absolute position. So the ship is holding to the absolute GPS position, with relative GPS and today it was holding to the accuracy of below a meter. It has four engines all of which can rotate 360 degrees and operating continuously to hold the position, to hold both ...


9

The Marmac 300 barge, which was modified into ASDS JRTI is made out of steel. There has been a lot of modelling and debate in the NasaSpaceflight.com forums trying to estimate how thick. Current thinking seems to come out around 25-35mm (1 inch to a bit thicker) steel. The heat load of a landing stage is not really that high. A single Merlin 1D at 70% ...


9

Looking at that video I'm not sure you're describing it accurately. I don't think it's actually 90 degrees from the fall direction. It's pretty much sideways but I'm not sure it's entirely sideways. If there was even a small component in the needed direction I can see the computer firing it because it wasn't programmed to recognize impossible--it saw it ...


8

Based on a rumour, who so far has been accurate the following is reported: The wings have been boxed in for added strength on both the original and new wing sets. They are attached by welding only; no hull penetrations needed. Only penetrations are through the barge decks, for fresh water ballast, which helps stabilize in towing. Ballast water is also used ...


8

After reviewing the "landing" video it seems like the Falcon 9 was trying to compensate for the tiny size of JRTI. This simply is not the case. SpaceX has stated that the rocket was trying to compensate for a slower-than-expected throttle response. They know what the problem is, and they very likely know how to address the problem. The target is plenty big ...


8

Seems like on the BulgariaSat-1 launch, the booster landed hard and used up the emergency crush core in the landing legs. This is the design case for the Xoomba, to provide extra support to a rocket that might need it. (Also to allow securing the stage, before crew get on board, perhaps in bad weather). Photos of OCISLY coming into Port Canaveral with the ...


7

SpaceX has a number of problems they need to resolve. Surviving re-entry with a first stage, finding a target to land on. Controlling it all the way down. The last step is actually landing it. The ultimate goal is to do it on land, but they need to prove to the FAA that they are safe to come in over land. The fact that they have hit the JRTI twice (...


7

Their eventual goal is to "land" on land anyway. For that, they need FAA clearance, and in order to get that, they don't need to prove that they can "land", only that they can kinda-sorta crash into the landing site in such a way that the explosion doesn't harm anyone else than them. Which they have already done with the current barge system.


7

The landing had tighter timing than usual (see Why were three engines used for the F9 1st stage landing burn (BulgariaSat-1)?), which means less room for corrections. Elon Musk tweeted: Rocket was suddenly slammed sideways right before landing. Heavy gust or something malfunctioned onboard. Reviewing telemetry. Assuming the booster did work correctly, it ...


6

It is currently unknown (1 week before the Dec 16th launch/landing date) where they will do the checkout and refurbishment work. So some questions to answer your question. (There may be an ethnic joke lurking in here) First set of questions: Will they tow the barge back to port (Which port?) upright? Or will they somehow lower it onto it's side? Using a ...


6

SpaceX has not yet published the specific locations for landing for CRS-7, however we can make a reasonable guess by looking at the previous landing attempt. Here is the Hazard Map of the previous landing attempt It outlines the Keep Out Areas SpaceX requests for each launch. The orange area is for early termination safety. The red area is the expected ...


6

I don't have any citation, but the first stage is doing all its own guidance and control; it would be insane to do it any other way. The "acquisition" called out at about 80km altitude is acquisition of signal, not of control. What exactly is being signalled and how the ASDS makes use of it is unclear. I've heard (again, without citation) that both the ...


6

The barge would need some kind of flame trench, and you'd need some kind of rain bird system to absorb the acoustic energy reflected off the barge surface, otherwise you risk damage from the rocket's own exhaust and loudness. You'd also definitely want to put a fairing on top of the interstage, meaning you need a crane (maybe on a second servicing vessel ...


6

‘Autonomous’ is misleading. The ASDS ships are towed into position by an ocean going tug, and are supported by the Go Quest support ship. Once in landing position, the ASDS operates independently for the landings but then the support ships come in, and the fleet returns to port. It does not appear the ASDS ships are designed to be left at sea unattended ...


5

The basic answer is, as others have said, JRtI doesn't need to be larger. SpaceX can find it, reach it, and put the stage engines down on it. The fact that their already highly-successful recovery tests have not yet quite delivered an intact stage is not a problem. I'm answering mostly to respond to the idea that the technique chosen is a "suicide burn". ...


5

SpaceX have already proved very accurate spot landings can be achieved with their Grasshopper. Their next step is to prove it can be done with a vehicle that can't hover, and that sort of vertically timed landing doesn't really need a pad of a certain size; just good control over vertical speed (especially deceleration). So, the size of the barge is pretty ...


5

The stage and ship both navigate to a preprogrammed GPS coordinate. It seems that GPS datum cannot be changed in-flight. Last-minute corrections are done via a radar on the stage. AOS by the drone ship is one-way communication (stage telemetry going to the ship). (I know, using a forum post as a source. It's corroborated by another post in the L2 ...


5

One possible thing which might help is to switch to methalox on the second stage to get additional performance to pay for grid fins and a heat shield. The subscale raptor engine they tested back in September 2016 has a thrust of 1MN, which is similar to the uprated thrust of the vacuum merlin 1D. The engine is also of a similar size. The dimensions of the ...


5

Liquid Oxygen has an expansion ratio of 1:861 (This means that 1 liter of liquid oxygen is equivalent to 861 liters of gaseous oxygen). Having worked with it on military aircraft, and witnessed a VERY SMALL amount being introduced to a flame source, I can tell you it very much could have just been the LOX going up. (I won't speculate if that's what it ...


4

Combustibles (oil, fat or grease, but also asphalt) in contact with liquid oxygen may explode on ignition or impact. See these links 1, 2, 3, 4, 5, 6, 7. This NASA document is about tests on compatibility of runways to LOX. A very impressive cite from the NASA document: "A detonation was reported to have occured when a man walked across a gravelled ...


4

There are two ASDS ships. Just Read the Instructions (JRTI) which was first deployed on the Marmac 300 hull, never successfully landed a stage, had its wings removed and moved over to a newer hull (Marmac 303 I think), then shipped through the Panama Canal to the Pacific. In the Pacific, JRTI has landed the Jason-3 and Iridium-Next first cores as of Jun ...


3

It's likely that the most efficient flight path is the mirror of the one that got the 1st stage to the barge in the first place - a powered ascent phase to high altitude (a little ways out of the atmosphere) followed by a ballistic coast phase, hypersonic reentry, and powered descent and landing. I did some number crunching, making a lot of unwarranted ...


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