Elukka

Orion designs had an isp of up to 4000 seconds. They thought it may be possible to raise that to 10 000 - 20 000 seconds through further development. The Daedalus proposal had an isp of 1 000 000 seconds. Orion is not remotely comparable. Of course, we could probably actually build an Orion with current technology... but it's really not good enough for interstellar travel unless you're fine with it taking centuries. There's all sorts of numbers for much higher performance nuclear pulse propulsion floating about, but it's far more theoretical. It probably wouldn't look much like Orion as we know it and you might indeed consider Daedalus one of those advanced nuclear pulse propulsion concepts that have performance closer to the theoretical maximum.

Looking at the earlier discussion (panarchist calculates an isp of 37 000 s), isn't the performance of this a little crazy? As in, 10-20 times better than the real Orion: The Orion people were clear that these numbers were for initial operating capability and they guessed that a few vehicle generations down they could potentially reach 10 000 - 20 000 s isp, so it's not completely insane. I'm thinking also from a gameplay perspective though that it might be interesting to have first gen Orions which would "only" give you maybe double the isp of the stock NTR, and go up from there. That would also give more room for a role for advanced variants like the Mini-Mag. Though maybe the current very high isp is a placeholder until all that advanced stuff is implemented?

I think SSTO and reusability are two goals that make each other harder. SSTO is a performance penalty and reusability is another performance penalty on top of that. You're basically adding two sets of razor thin margins together. If you have two stages you do have two different recovery systems and events, but you have so much more margin to spend on it it's a lot more practical.

It depends a fair bit on just what sort of ship it is. Any sort of electric propulsion, you're gonna need giant radiators. Nuclear propulsion, electric or otherwise, you're well served by having a long spine to put the radiation source further from the sensitive bits. Want to aerobrake on return to Earth or wherever you're going? Something like SpaceX's ITS. (This sort of thing can also be open-topped, sort of like a partial shell around your ship, look up NASA's ellipsled) There's a ton of different designs on Project Rho, including a ship specifically designed to transport crew and cargo to and from the asteroid belt. http://www.projectrho.com/public_html/rocket/realdesigns.php

There's no issue with blood as long as it's contained by your veins. If it isn't, you have other issues. However I can't really begin to think how you might modify humans to survive in vacuum. I imagine it'll do to just make lighter, better-to-wear protective equipment, at least for a very long time.

Well, it wouldn't need all that much delta-v so it could make do with a relatively modest propellant fraction. For example, if you specced it at 3 km/s delta-v (which may be excessive) and used a kerolox rocket of middling performance, you would only need about 65% of the vehicle mass to be fuel. It's certainly possible and not a particularly strenuous mission requirement compared to things like orbital launch.

The core of the US navy is really the carriers, which are the biggest, most expensive warships I can think of by a large margin, and they won't be getting any smaller. It doesn't really seem like the cruisers or destroyers are getting any smaller either. I'm really not seeing this trend.

Depends on your assumption of technology, strategic environment and ship role. What you're asking is impossible to answer because it's a bit like asking what the best design for a vehicle on Earth would be, without knowing if you're talking about a motorcycle or a supersonic airliner.

I really like how they look, visually speaking. My main reservation is dry mass, for the ducts, fuselage and heat shield. I don't know how to try and estimate those myself however.

I'd bet the differences between the F9 and FH center core is the main reason for its delay. Not because it should take so long to develop, but because the F9 has been undergoing constant changes. Imagine if they had implemented the original 1.0 FH on time. They'd then have had two lines of rockets to keep up to date and upgraded to 1.1, Full Thrust, Even Fuller Thrust, etc. Some of those changes, especially 1.0 -> 1.1 were huge and would no doubt have resulted in pretty big changes in the hypothetical early FH too. My guess is they expected the F9 to mature much faster, but considering they've managed to more than double its original payload I can't really blame them for keeping on fiddling with it.

I don't think Falcon Heavy will be replaced any time soon. It'll work, it can be recovered, I just doubt they'll make new multi-core rockets afterwards, at least if reusability works out. For easier reuse you'd rather want a simple two stage rocket like Falcon 9, only bigger, which is what they're doing with the BFR: "At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage." You keep repeating this claim but it's getting no less bizarre. I have no idea what this impression is based on - yes, things get reprioritized, put on the back burner, accelerated. They don't just haphazardly jump from project to project - maybe you're watching whatever they're publicizing most heavily at a time and making the assumption that that's all they're working on now? In particular the idea that they just go for Musk's silly pet projects until he has the next idea seems like something you invented, because I've seen nothing to indicate the company works like this. If it did, they would probably never accomplish anything.

I suspect two reasons - one, it's not necessary for the desired performance on FH, and two, they probably won't make any more multi-core rockets like FH because it's not a great fit for how they've chosen to approach recovery. If my guess is correct on that then crossfeed would represent a technological dead end for them with no further use after FH. That doesn't mean crossfeed is a bad idea - just it's not a great fit for SpaceX at this time.

I was under the impression that whether volatiles pile up on the dark side or remain thawed depends on your assumptions on atmospheric and other conditions.

You would have visible light available for photosynthesis on a brown dwarf. The larger the dwarf, the more visible spectrum light you'd have to play with, but any dwarf will probably generate some suitable light for photosynthesis. (which is apparently possible in the near infrared too: https://en.wikipedia.org/wiki/Chlorophyll_f)

No, that doesn't follow at all. All it means is that a Falcon 9 in expendable configuration can lift 22.8 tonnes. Would an expendable F9 be launched in a future situation where reuse is in full swing and Falcon Heavy operational? Probably not. Does that have any bearing of how much an expendable F9 can lift? No.

From what I figure they're simply the numbers the launchers would have if launched in expendable configuration, i.e. numbers that can be compared to other launch vehicles. I don't get how any of your conclusions follow. I would not expect that they would lie about these numbers either.

This isn't exactly the only place where it's been discussed.

While I agree SSTO doesn't generally make a lot of sense it's an interesting design. I wonder if the ducts could really be as light as you expect though. 25% of two Merlins is only 235 kilograms. Surely they'd be rather heavier than that. I tried a quick google for existing design but the best I got was an uncited claim on Wikipedia that you'd expect a duct-augmented rocket engine to be five to ten times heavier. I can't judge the accuracy of that number but if you made them five times heavier you would still have a payload.if your isp expectations hold.

Yup: Now, previous error aside, this is a pretty high number! Things of note: - It's more than double the 1.0's payload. - It's still in excess of the advertised payload for 1.1 if you apply a 40% penalty for reuse. - In an expendable configuration, it's basically gone from the medium launcher category to the heavy category. It about matches the Proton in payload. It's really incredible how much more performance they've been able to get from this rocket over its lifetime. Also, per the new numbers the Merlin now has a thrust-to-weight ratio of 200.

Well, I'm not unwilling to believe it if there's some further confirmation. It's just the figure is startlingly high. Would be interesting if Falcon actually significantly outperforms a hydrolox rocket in terms of payload fraction. We know they're working on a Raptor-based methalox second stage which would increase its performance but I doubt the numbers are based on that since that hasn't really even been formally announced yet.

I struggle to understand how these numbers are possible and I'm wondering if there isn't a mistake. They have the F9 match the Delta IV Heavy in LEO payload, despite carrying a lesser propellant load and much lower isp engines. We know the Falcon's engines have a thrust-to-weight ratio well in excess of any other engine in operation (and possibly any engine in history) and that its structure is most likely lighter than that of most rockets. However, the only way I can see those numbers is if the F9 has always been much more capable than we've been let on, and the true payload figure for expendable missions was never previously published. I'd still have trouble reconciling it with the Delta IV Heavy. It would imply the effect Falcon's lower dry mass is so significant it outweighs the reduced isp and propellant load.

As I recall there's quite a bit on in-flight forces in the user's guide: http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf Makes sense since you have to know the forces your payload must withstand.

I don't see why it would be so energy-limited. You'd have about as much sunlight as we do on Earth, just longer wavelength. We have organisms on Earth that can photosynthesize in the near-infrared, and that would be much more heavily selected for around a low mass brown dwarf. There will also be visible light. Maybe you'd have somewhat less energy to go around particularly on low mass dwarves compared to Earth but I don't see why you wouldn't have enough for an energy-rich ecosystem based on photosynthesis.

Musk has mentioned a 40% structural safety margin. The first stage also has engine out capability (https://www.youtube.com/watch?v=dvTIh96otDw). For aircraft the FAA apparently mandates a safety factor of 1.5 which the Falcon is rather close to.

The elasticity of the launch market remains to be seen. Various companies have made noises about one possible business made feasible through cheaper launches: Low orbit satellite internet, using thousands of small, cheap satellites rather than a few big expensive GEO satellites. The main advantage is low latency, which might make it competitive with non-satellite internet. Whether that pans out or other ideas pop up, we don't really know yet. SpaceX has talked both realistic near term expectations and highly hypothetical long term expectations for the savings enabled by reuse. Near term, I recall a figure of 30% savings being mentioned. For a potential future launch market with much more launches and a fully reusable F9-scale vehicle they've guessed a launch cost of $5-7 million, or about 90% savings. One thing you gotta give them credit for is they're usually pretty good about marking speculation as such and schedule slips aside they're pretty careful not to make hypetastic claims on things like this. Musk in particular likes to use phrases like "we may not succeed" and "we're trying to" a lot.