DerekL1963

They don't. The theory is that once the samples are gathered, that fact can be used to justify funding for the next stage (getting them to orbit). Once they're in orbit, that serves as justification for going out and fetching them from orbit... lather, rinse, repeat. It's all an attempt to hide the cost and complexity of a sample return mission. Rather childish really.

Polywell has been three years away ever since the late 00's.

Not even close - the loss wasn't caused by a bug. The loss was caused by a configuration error.

Sure looks like LC-39. It's almost certainly LC-39 since all the other pictures are from the same area (KSC / VAB area). That's not a launch complex, that's one of the mobile launchers... specifically MLP-1

It's not 100% certain this is true, an angel might have come forward... But what is certain is that without NASA money, Musk was within hours of having to choose whether Tesla or SpaceX would be thrown overboard. https://www.bloomberg.com/graphics/2015-elon-musk-spacex/

[snip] No, it isn't good at all. The second stage was the key limiter of the -14's performance.

Presuming NSWR works as theorized, but I'm not aware of any actual formal analysis of their performance. (Zubrin's paper is not formal analysis, it's the scientific equivalent of a bar napkin.) Which sounds impressive if your goal is high ISP and high exhaust velocity. But in terms of actual performance, the things that interest people designing actual spacecraft and missions... it's not all that useful. It's thrust makes an ion engine look like a cluster of S-IC stages.

According to what I've seen, the belief is that the -15 is -14 with an improved second stage.

Yes, the events that lead up to the final disaster took place over tens of minutes. The actual accident occurred within a few tens of seconds of the control rods starting to move. The power surge that lead to the explosion only spanned a few seconds between the rods being jammed in place and the first explosion. In the same way, the events that lead up to Challenger's loss (exposure of the o-rings to subzero temperatures) started almost twelve hours before launch. The actual damage took around a minute after ignition to start fully manifesting (venting gasses from the SRB impinging on the ET). Six seconds later the ET begins to fail and leak... Six seconds after that, structural failure (the RH SRB tearing loose) begin... and then the actual breakup spans four seconds. But nobody would claim the Challenger accident took twelve hours, would they? Misunderstanding the difference between the "events leading up to the accident" and "the actual accident" had lead you to a mistaken impression over the speed of the reactor's response to control inputs. And yes, a full start-up takes a significant period of time... But the majority of that time is spent running down a checklist and performing tests to verify the reactor is ready to start and all systems are operational. During the actual startup, they shim the rods out of the core very slowly to ensure the measured conditions match the calculated conditions - and they heat the reactor very slowly both to avoid thermal shock and to avoid sudden changes in reactivity and response. (Basically staying well the heck away from any condition that might lead to prompt critical. Prompt critical means a Very Bad Day is in the offing.) Again, these bear no relation to normal operations and have lead you to a mistaken impression of actual throttle response time. Not to mention, unless reactors responded quickly, we'd never be able to scram them...

Challenger was destroyed when the ET broke up due (essentially) to the aft end falling off, throwing the Orbiter into the airstream. The stack had no time to turn before it was completely shredded due to these forces. (That's why the pictures show the trails of the SRB continuing more-or-less on trajectory.)

o.0 No, try more like "seconds to tens of seconds (at worst)" - changes in moderation take effect fast (hence Chernobyl), and in reactors are really only limited by thermal inertia.

I'm going to think "what? I need to take a much closer look at this thing that looks like nothing natural and get as many other people to look as possible". Doubly so if a few days observation shows that it's orbital path comes anywhere near a planet or other body I'm interested in not having something collide with.

Well, duh. I never claimed otherwise. And only an idiot would handwave away a problem as "only engineering". Engineering at this level is hard. Here in the real world, we're going to have mass and volume limits. It simply isn't that easy. Here in the real world, Mars has an atmosphere. An atmosphere and flight conditions that are all but impossible to duplicate on Earth. Sure, we landed the Shuttle after a few tests... But those came after the better part of century's experience with terrestrial aerodynamics. And a couple of decades worth of practical work on high speed aerodynamics. And the better of a decade of practical work on lifting bodies. And extensive flight experience with tailless and delta wing vehicles of a wide variety of sources. We not only have but an infinitesimal amount of experience on Mars - but nobody seems to plan on getting any. With only one except that I'm aware of, the plan is to commit to no-return for the first time the very first manned landing. In theory, yes. That doesn't mean it's practical. There's a ton of known unknowns that we haven't even begun to address.

In theory. In practice... not so much. We still don't have a demonstrated long duration life support capability. (The ISS systems have required far too much repair work.) Nor have we worked out how to land and return yet. And that's setting aside the usual problems involved in transforming 'technology' into useable designs, and transforming designs into actual flight hardware.

That's for level track designed for (relative to a launch assist system) low acceleration, low speed, and low loads. Apples and oranges. And that's before figuring in that a launch assist system will be at least two parallel tracks for stability. 0.o Buildings (even these types) are simple and cheap. The labor alone (even including the internal systems) would be a fraction of that a kilometer of track requires.

It's not the operating costs that kill you - it's the cost of the not cheap part, the construction of the track. That's not a consensus, it's a stone cold fact. The various forms of assisted launch only make economic sense when you have a high enough flight rate to amortize the capital costs of construction.

That would make you a minority of one... Nobody else treats an ejection charge as the first stage.

The gas generator system on a US SSBN is actually rather clever... What amounts to a good sized solid rocket motor fires into a baffled tank filled with water. This water flashes into steam, and the mix of steam and cooled rocket exhaust is ducted into the eject chamber. So much this. Catapult schemes save fuel by adding complexity. Adding complexity (especially complexity with a huge up front capital cost) is rarely a good idea.

When you work on/with something for almost a decade, one gains a certain fondness for it. That's all I can say...

It's my avatar... (You didn't specify what it was launching...)

Which calculation fails to take into account the insulating effect of ice and leakage of heat from the Earth's core.

Not very, because the neutron shielding you'll require will make the fusion volume very small indeed. It'll probably drive it's own cooling fan though.

Ultimately, that's the real problem with SLS - it is useful, even if for a niche... But that niche is something NASA rarely if ever does anymore, big, expensive, battlestar class planetary probes.

Only if someone is observing the satellite and its vicinity and can command it to execute an avoidance burn when an incoming ASAT is detected. Or, to put it more simply, it's much more complex than just outfitting the satellite with thrusters. They're just the end effectors of a much larger and more complex system.

The damage mechanism from big lasers isn't melting. It's shock - the laser vaporizes the surface of the target, and the rapid expansion of the vaporized material is the equivalent to setting off a high explosive charge.