Skylon

SpaceX Discussion Thread

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Every time I try to replicate an F9 hoverslam I get a lot more 'F9' than I bargain for :wink: 

Edited by Skylon

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I completely forgot about this launch!

Now seen the webcast and I have to say this is, by far, the best camerawork so far. Stage separation was awesome.

I do wonder what kind of equipment they used to get that shot at 100+ km...

Also, first stage telemetry all the way down, which makes me convinced Elon Musk is following these forums...

JK, ofc

Edited by Shpaget

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Yes, I'm pretty sure that black would be a problem with cryo propellants. But it would save on scraping off the soot before each flight.

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4 minutes ago, Nibb31 said:

Yes, I'm pretty sure that black would be a problem with cryo propellants. But it would save on scraping off the soot before each flight.

Then the guy with the low-skill but still awesome job of power washing boosters has to collect welfare.

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Only 3 days in and already 150 new posts! Amazing!

Congrats to SpaceX for landing yet another first stage!

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May 15th, then May 31 are on the schedule for SX... that'd make 3 in a month if they manage to not be delayed (lol).

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5 minutes ago, tater said:

May 15th

If that gets delayed, I'm pretty sure it'll launch by ~the 20th

5 minutes ago, tater said:

then May 31 are on the schedule for SX... if they manage to not be delayed (lol).

Ha, good luck with that! 

54 minutes ago, Shpaget said:

...which makes me convinced Elon Musk is following these forums...

JK, ofc

Actually, someone should tag him on twitter and tell him to make a KSP forum account (he seems to be pretty active on twitter) :D 

Spoiler

I would do it, but I don't have a twitter account

 

Edited by TheEpicSquared

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8 hours ago, Ultimate Steve said:

That ground based boostback coverage was really cool!

Yeah, I've not been following the news much, so when I watched the replay and saw it was boost back to land... BOOST BACK TO LAND! Wow. Cool tech.

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I had no idea the scale of the re-entry burn plume.  I kept thinking that looks like one of my KSP launch failures.

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Hi, I've always been suspicious of the SpaceX reusability strategy, because you get the most efficiency out of the last drops of fuel in a tank, so leaving that unused for landing is setting aside a lot of delta v, isn't it? Thus, they have to build a much larger rocket than they could have built otherwise, introducing a question of cost vs. benefit. Is there anywhere that I can go to see where people have done the actual math to prove that making a larger rocket in the first place (in order to have enough fuel to land the first stage) does not end up costing more money overall than ditching the first stage would cost?

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36 minutes ago, Crimeo said:

Hi, I've always been suspicious of the SpaceX reusability strategy, because you get the most efficiency out of the last drops of fuel in a tank, so leaving that unused for landing is setting aside a lot of delta v, isn't it? Thus, they have to build a much larger rocket than they could have built otherwise, introducing a question of cost vs. benefit. Is there anywhere that I can go to see where people have done the actual math to prove that making a larger rocket in the first place (in order to have enough fuel to land the first stage) does not end up costing more money overall than ditching the first stage would cost?

It's a contentious topic, and this thread (well the one before it anyway) has literally hundreds of pages of people arguing both sides fairly convincingly.

Edited by Steel

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34 minutes ago, Crimeo said:

Hi, I've always been suspicious of the SpaceX reusability strategy, because you get the most efficiency out of the last drops of fuel in a tank, so leaving that unused for landing is setting aside a lot of delta v, isn't it? Thus, they have to build a much larger rocket than they could have built otherwise, introducing a question of cost vs. benefit. Is there anywhere that I can go to see where people have done the actual math to prove that making a larger rocket in the first place (in order to have enough fuel to land the first stage) does not end up costing more money overall than ditching the first stage would cost?

Well, I don't have actual math right this second, or links to sources, but here's me:

If you want to build a bigger rocket for reusability, you need to do a few things: Make a longer fuel tank and uprate the thrust of the engines. That, and the landing gear. Lengthening the fuel tank by a few meters is probably at most 3-4 million dollars of aluminum, composites, and electronics. In order to uprate the engines, if you're lucky all you need to do is make the turbopumps spin faster. If you do this too many times you may need to build a bigger pump, a longer nozzle, and maybe wider propellant pipes. I'm probably missing a few things, but that probably covers most of it.

That is a lot of money, let's say a high estimate of 20 million dollars per flight. Let's say, for example, the Falcon 9 with the upgrade costs 62 million dollars (which is what it costs today) and that it would cost 42 million without the upgrade.

The reusable first stage costs 35 million dollars (number I saw somewhere, + or - 7 million), let's assume that an unupgraded one would be about 20 million dollars (with 15mil of the upgrade going to the first stage, and 5mil to the second stage).

So, in an unupgraded expendable flight you would spend 42 million dollars launching a rocket and not get anything back. On an upgraded flight, you would spend 62 million dollars and get back a 35 million dollar first stage. Even if it costs 5 million dollars to refurbish, that's still a net cost of 32 million dollars, ten million dollars less than without the upgrade. Also, the Falcon 9 is already one of the cheapest rockets on the market, even without reusability.

Another point, Falcon 9 can theoretically launch 22mt to LEO (in expendable. The max for reusable is something like 12-ish mt), but it has never had the need to do so. The most it has ever launched in one shot is 9600kg, which was the Iridium NEXT 1 mission to LEO. That's less than half of the maximum payload. There isn't really that many super heavy satellites out there (yet), so that leaves SpaceX with plenty of margin to experiment with reusability.

 

I mean, there's also the R&D costs to factor in, but reusability should pay off in the long term provided SpaceX can get the stage one refurbishment price below 15 million dollars per stage, which I'm pretty sure they can.

There's also other benefits to reuse other than cost: you get data on hypersonic retropropulsion, you can (in theory) achieve very short turnarounds, and it's just plain awesome to see one of those things landing.

 

As @Steel has said, you could just as easily argue for the other side.

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18 hours ago, Crimeo said:

Hi, I've always been suspicious of the SpaceX reusability strategy, because you get the most efficiency out of the last drops of fuel in a tank, so leaving that unused for landing is setting aside a lot of delta v, isn't it? Thus, they have to build a much larger rocket than they could have built otherwise, introducing a question of cost vs. benefit. Is there anywhere that I can go to see where people have done the actual math to prove that making a larger rocket in the first place (in order to have enough fuel to land the first stage) does not end up costing more money overall than ditching the first stage would cost?

Look at it this way: they can launch heavy payloads as a fully expendable booster, or they can launch smaller payloads and recover the booster. They only have to build one size of rocket that way. Same as they only make one engine model (with different engine bells) for both stages, to save costs. Economies of scale are also at work here: it's not going to cost much less to make a smaller rocket.

Edit: Finally got to watch the video. That was beautiful!

Edited by StrandedonEarth

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@Ultimate Steve makes sense to me. Besides, these guys came up with an idea of a 40-metre rocket going into space and back on its own. I will just assume they know what they are doing and what they want to achieve.

I feel like even if they don't succeed there are other space companies trying to do the same or better. Whatever happens it's a win-win scenario for the future of spaceflight.

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3 hours ago, Crimeo said:

Hi, I've always been suspicious of the SpaceX reusability strategy, because you get the most efficiency out of the last drops of fuel in a tank, so leaving that unused for landing is setting aside a lot of delta v, isn't it? Thus, they have to build a much larger rocket than they could have built otherwise, introducing a question of cost vs. benefit. Is there anywhere that I can go to see where people have done the actual math to prove that making a larger rocket in the first place (in order to have enough fuel to land the first stage) does not end up costing more money overall than ditching the first stage would cost?

I think a lot of SpaceX's reasoning has to do with fixed costs and launch cadence. It's not necessarily about saving money on the individual rockets, but rather about saving time. If they can refurbish and reuse a first stage 10 times in the time it would normally take them to build one (I am pulling numbers out of the air here), that would allow them to maintain a higher rate of launches and thus spread out their fixed costs, reducing the price of each individual launch. 

If memory serves, this was the primary driver for trying to recover the fairings. They simply take too long to manufacture. 

I don't know that anyone knows for certain where the breaking point is in the numbers. SpaceX certainly thinks there is value in reusability, but I think their business model is still an experiment at this point. Even if it doesn't work out though, SpaceX has successfully disrupted an industry in desperate need of disruption. 

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How much performance can F9 Block 5 or any future upgrade get by replacing internals with proposed lightweight ITS tanks (carbon-fiber) instead of normal tanks(Al-Li) nowadays? Because if recovery will get usual, they can make more expensive rocket, when they know it will come back. Launching expensable only with the older normal rockets instead of new...

I'm bad at numbers, have somebody an idea?

Edited by Toonu

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Just had a quick go at reducing the dry masses of F9FT by ~25%.

1st stage : isp 298, prop 411t, dry 23t  down to 17t.

2nd stage : isp 348, prop 107.5t, dry 4.2t down to 3.2t. 

Fairing 2t.

Payload (for ~9170m/s) goes from 23t to 25t.

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20 minutes ago, RedKraken said:

Just had a quick go at reducing the dry masses of F9FT by ~25%.

1st stage : isp 298, prop 411t, dry 23t  down to 17t.

2nd stage : isp 348, prop 107.5t, dry 4.2t down to 3.2t. 

Fairing 2t.

Payload (for ~9170m/s) goes from 23t to 25t.

Ok, not so much worth it then. Even when it will be reusable or...not? 

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GTO expendable (11638m/s) goes 8.3t to 9.8t.

GTO reuse (12465m/s) goes 5.5t to 6.8t.

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8 hours ago, Ten Key said:

I think a lot of SpaceX's reasoning has to do with fixed costs and launch cadence. It's not necessarily about saving money on the individual rockets, but rather about saving time. If they can refurbish and reuse a first stage 10 times in the time it would normally take them to build one (I am pulling numbers out of the air here), that would allow them to maintain a higher rate of launches and thus spread out their fixed costs, reducing the price of each individual launch. 

If memory serves, this was the primary driver for trying to recover the fairings. They simply take too long to manufacture. 

I don't know that anyone knows for certain where the breaking point is in the numbers. SpaceX certainly thinks there is value in reusability, but I think their business model is still an experiment at this point. Even if it doesn't work out though, SpaceX has successfully disrupted an industry in desperate need of disruption. 

The numbers look pretty good too:

Whether you could get the same savings by building a slightly smaller disposable booster? My gut feeling is no, particularly with SpaceX's emphasis on commonality of components, but that's not backed up by any hard data.

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The economics of reuse have been something everyone has wondered about since the idea came up. The "don't throw away a multi-million dollar vehicle every use" certainly makes sense at a gut level, but we honestly won't know until they start flying reasonable numbers of reused boosters (including any possible increase in failure rates).

As Musk has said, to be meaningful the reuse cannot involve doing much work to the vehicle, he said in that TED talk that you don't send your airliner back to Boeing between flights.

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One thing to consider in looking at the economics of reuse is that the initial version of Falcon 9, v1.0, had a lower payload flying expendable than Falcon 9 FT has flying reusable. Granted, Falcon 9 v1.0 didn't have the extensive development investment that F9FT has behind it. But since SpaceX can almost certainly refurbish F9FT for MUCH cheaper than the cost of a new Falcon 9 v1.0 (or something like Falcon 5), I think the argument closes rather well.

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