Racescort666

That makes sense. The engine was probably one of the more complex parts of the system and the engine supplier (Rocketdyne I think) presumably made the case for sticking with their design and moving forward.

I could be wrong about this but I though Apollo CSM was originally envisioned as a direct ascent vehicle right?

The license was filed with the FCC. That being said, defense is largely exempt from other regulatory practices (if it is an NRO flight or some kind of spy mission) but that doesn't necessarily exempt SpaceX from needing to comply with said regulations using their commercial hardware.

@Ultimate Steve, I don't have a reddit account but would you consider asking if SpaceX considers BFS a viable vehicle for cleaning up space debris? ULA is considering the implications of a 1 up 1 down policy for future vehicles and it seems like BFS would be perfect for such capability. It's gotta pay the bills after all, right?

I figured it was coming as well but I was wondering when the official word came down. I seem to remember some discussion of it back around OTV-5 because I thought OTV-5 was going to be the last launch from 39A. I would be in on a pool. I'll say Late Jan 2018.

I saw that SFN and Reddit had an updated FH launch to "late 2017" so I was trying to find an update of when SpaceX said this. I didn't see anything in this thread unless it got buried in the Mars colonization discussion.

A guy at work asked me "why are you listening to elevator music." So I was like "it's the elevator music that SpaceX plays for people riding the elevator up the service tower before getting into their space capsule."

uh... yeah...

@Grand Ship Builder, phases described as "solid, liquid, and gas" doesn't necessarily give credit considering the complexity of the matter. @IncongruousGoat mentioned helium liquid phases but there are also the many phases of water ice, 17 according to wikipedia. In fact, many alloys also have phase diagrams based on temperature and composition, take this iron-carbon phase diagram for instance: It's basically just steel but it shows how the iron/carbide crystals form in the grain structure, this is really important for steel manufacturing and is essential to the strength of steel. In this case, the 0.76% triple point is noteworthy because it is the percentage of carbon that forms eutectoid steel. Carbon dissolves very readily into gamma phase iron and as it is cooled and converts to alpha phase, the alpha phase and carbide form alternating layers. This makes the steel very hard yet still maintain some of its flexibility.

It's also worth noting that the military has a habit of throwing contractors a bone when they aren't doing well. Ben Rich talks a little bit about it in Skunkworks but once you realize it happens the pieces fall into place for several projects.

So I did some math and you would need 13 (o_O) SNRE engines to match the thrust of an MVac engine. Improved performance is something that people always talk about when discussing NTRs but the cost (that's rarely quantified) is the mass penalty. So here we go: Payload 10 886 kg (constant for this analysis) dV: 7205 m/s (based off of F9 upper stage with the above payload) The goal of this exercise is to concept an NTR upper stage to replace the current F9 upper stage so it has to have roughly the same performance. M1D mass: 490 kg SNRE cluster: 31 200 kg (over 63X the mass) MVac ISP: 348 s SNRE ISP: 900 s The thing that doesn't get talked about is how much tank and fuel you would need to match this dV. All else being equal (including rocket diameter), you get: Fuel mass: 87 646 kg, Not bad considering the F9's 107 990 kg mass but you need to store it. Tank mass: 27 376 kg, If you're following along at home... Total mass: 157 108 kg, way more than the F9's 122 876 kg Also of note, tank length: 117.7 m, more than double the F9 first stage. There's no way this is practical. The easy way to fix this is to increase the tank diameter. Arbitrarily, I chose the same diameter as the F9 payload fairing: Fuel mass: 74 529 kg, still better but lets see how the rest of it stacks up Tank mass: 19 820 kg, still a lot Total mass: 136 435 kg, still more than the current F9 upper stage but possibly in the realm of what the booster can handle Tank length: 49.6 m, longer than the F9 first stage, it might look a little goofy. The last diameter that I calculated was the same diameter as the Space Shuttle ET 8.4 m. I used the ET as my benchmark for tankage mass by area and simplified everything to cylinders. I figured this was a good approximation of how to get a stage mass. There will be other components that factor into the mass but in general, the larger the tank, the more that stuff comes out in the wash. Fuel mass: 67 264 kg Tank mass: 13 954 kg Total mass: 123 304 kg Tank length: 17.1 m Finally something that's reasonable in terms of size and mass but now we have a weird egg shaped tank below the fairing. NTRs are cool and awesome but I don't think they are practical for Falcon 9 unless you wanted to do some sort of NTR kicker stage for an interplanetary mission. Even then, it may be worth considering alternate options. Sorry if this wasn't really relevant to the thread but I had crunched the numbers and decided to share.

From the article: Literally the sound that I made when I read that:

Have they ever flown a 2 engine Centaur on an Atlas V?

Touché

First AMA question, "does 'BFR' stand for 'big (rhymes with trucking) rocket'?"

Comparing anything to a military budget is simply ridiculous. Especially comparing the US space programs to the US military. Why? Well, for starters, the worldwide space programs would not exist without the military. Second, at the height of space program spending, everything had direct military significance. Does putting a man on the moon have military strategy? No, but all of the technology developed to do so did. Does the Space Shuttle building and servicing a continuously manned laboratory have a military advantage? No, but the Space Shuttle itself wasn't designed only for that purpose and was specifically designed for military payloads, hence DoD dollars going directly to the development. On the flip side, congress and the military aren't stupid. The US has many enemies and at the same time has probably the single best military R&D and manufacturing capability in the world, it would be foolish to stop investing in it. Congress knows this and the military knows this. But this capability is not just for domestic R&D and production but also for export capability. I.e. to countries that are friendly to the US but don't have the R&D or manufacturing capability. If approved by congress, of course. This post has gotten too political. Suffice it to say, comparing NASA's budget to the DoD budget is like comparing apples and oranges. They might both be fruit, they might both be healthy foods, but they are different foods for different purposes. As far as NASA's Mars budget goes; sure, they could they could do something crazy and inspiring like spending all of their money on a manned Mars mission. But they would have to sacrifice many other things that offset the cost of pure science missions. This is on top of the fact that (to use another food metaphor) they would be putting all of their eggs in one basket for a comparatively low science return.

Essentially ACES is supposed to be like this, i.e. still usable after payload deployment. ULA has talked about adding the ability to refuel ACES on orbit but I think the biggest advantage that ACES would have is a more reliable disposal burn. ULA has also mentioned a 1 up/1 down launch strategy that a long duration upper stage like ACES would be able to help accomplish. For GTO, everything is in a very similar orbit so it's not too big of a stretch to do something like this.

Is this the same thread that said there's nothing of value in TLI launches? All of these things are starting to blend together. Regardless, ACES is a long duration bigger version of Centaur and ULA makes it sound like it's specifically for TLI and other beyond earth orbit missions. I guess there's no reason it couldn't be used on shorter duration missions since IVF is really what gives it the capability for long duration. Plus IVF is a cost reduction and big complexity reduction from current Centaur systems.

I'm an American too. Working in the auto industry converted me to metric. KSP reinforced it.

Do you mean nitrogen dioxide (NO2) or nitrous oxide (N2O)? Nitrous oxide is common as an oxidizer while nitrogen dioxide is usually considered a pollutant but is also present in RFNA.

I thought part of the drive for FH was for the 6t+ payloads going to GTO to have a chance at reusability. I was under the impression that the weight limit to GTO for reusable was less than 6t (according to wikipedia it is 5.5t). With the introduction of FH, there is now an increased mass to GTO while recovering the boosters.

I was going to ask how you figured that there was only 1 launch until FH. By my count, there's at least 3.

3.8 ft and 2.67 ft That's just a ballpark from scaling the dimensions though. eg. X/10ft 7in = 2.28in/6.35in, solve for X = 3.8.

I was going to say something about ballistic coefficient and boat-tail ammunition but then I came across this picture. Bullets have an interesting trade off between fitting in the cartridge, fitting in the gun (magazine), fitting in the barrel (on the rifling and sealing the bore), and aerodynamics.

I love endurance racing. One of my favorite things to do is play KSP and have one of the big 12 or 24 hour races on.