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Comment Re:Cue the flood... (Score 1) 193

Surely you can cite some of these "early attempts at production of fusion power", right?
ITER is the first experimental reactor intended to produce power. Most of the research devices don't even use real fusion fuel...they know fusion works, it's the plasma physics they are researching, and building a big power-producing reactor, handling tritium, and dealing with fusion neutrons is unnecessary for that and far beyond the budgets typically allocated to fusion experiments.

Comment Re:Stupid article (Score 1) 226

They save mass that conventional rockets expend almost immediately in their flight, pay a big price in aerodynamic drag instead, and additionally pack on lots of extra mass in air breathing equipment and various HOTOL related structure that they then need to take to orbit. They compensate for that and for the efficiency losses of SSTO by claiming a structure and thermal protection system that are basically magic, and gloss over all the additional operational expenses. And no, they don't avoid the need for payload integration.

SpaceX has the advantage of having a vehicle that actually exists, and they're not content to stop with first stage reuse. The successor to the Falcon 9 will be fully reusable, and far simpler and cheaper to develop, not to mention actually operate.

Comment Re:Stupid article (Score 0) 226

And one of limited real world value. LOX is dirt cheap, and launchers have to leave the atmosphere after a short amount of time in order to reach orbital velocity. They add on all sorts of complexity and losses to enable use of atmospheric oxygen. They are accepting increased vehicle and operational costs in order to reduce the tiny fraction of launch costs that come from the propellant. This simply isn't going to result in inexpensive spaceflight.

Of course, the rest of the vehicle is a fantasy structure of a carbon fiber spaceframe with gigantic liquid hydrogen tanks on the inside and an eggshell-thin ceramic heat shield suspended around it on wires, with insulation and active cooling systems in between. It might be physically possible for a structure that fulfills their requirements to exist, but can it actually be manufactured, let alone maintained and flown? (And of course, if they do manage to work these things out, the same techniques will become available to conventional rockets, along with some things like partially pressure-supported tanks that aren't usable on Skylon due to the bending loads from its horizontal launch...)

Air breathing engines are better suited for cruise than for acceleration to anything approaching orbital velocity, and with the need for LH2, it's probably not aimed at anything commercial...instead, things like hypersonic drone bombers. Skylon is just PR.

Comment Re:For future reference, (Score 1) 221

Whether it slows it down or not as an intermediate step is entirely irrelevant. Kinetic energy is proportional to the square of velocity. Applying a given increment in velocity (as a jet engine of any sort needs to do to produce thrust) costs more energy at higher initial velocities.

Comment Re:For future reference, (Score 1) 221

These issues arise because the engine takes in air as reaction mass and ejects it at higher speed to produce thrust...they apply to anything that breathes air. No fancy internal thermodynamic cycle can get around this. Ultimately, accelerating that flow of reaction mass by a given amount takes more power as the initial velocity of that reaction mass with respect to the craft increases. The only way around this is to not breathe air.

The fact that their engine is absolutely dependent on large quantities of liquid hydrogen is also not promising when it comes to economics...

Comment Re:Only good for "Near Space", not orbital re-entr (Score 1) 62

It reminds me of Branson crowing about how environmentally friendly and efficient their hybrid motor is. "We have reduced the [carbon emission] cost of somebody going into space from something like two weeks of New York’s electricity supply to less than the cost of an economy round-trip from Singapore to London."

Never mind that spaceflight would have to scale up many orders of magnitude to be a meaningful contributor to carbon emissions, that there are few rockets that emit as much carbon for their performance as their hybrid, or that they produce fewer emissions simply because they aren't doing anywhere near as much.

Comment Re:not really Re-entry? (Score 1) 62

It never gets anywhere close to orbital speed. SS2 is to max out at about 1 km/s. It also won't even reach the Karman line, they're aiming for the 50 mile/80 km altitude where Air Force pilots get astronaut wings via a purely bureaucratic definition.

It's a rocket plane. A rocket AIRplane. It's not a spacecraft, and the technology is not relevant to spacecraft.

Comment Re:Long shot (Score 1) 87

If they get Skylon up and flying, they'll have a horrendously complex, expensive, and fragile launch vehicle which is utterly unscalable and inflexible in the range of orbits it can target. More likely, it'll never get up and flying, but suffer the fate of every other super duper spaceplane project, turning into nothing but a big money sink.

The horizontal takeoff and "looks like a plane" aspect is cargo cult engineering based on what looks cool in sci-fi and what works for aircraft performing an entirely different task. Air breathing buys you next to nothing in the end, and costs a great deal. Liquid hydrogen is a pain to use, it's hazardous and it's awkwardly low-density. Carrying extra liquid hydrogen for cooling and a bunch of extra air-breathing equipment and aerodynamic structures in order to use atmospheric oxygen diluted 4:1 with nitrogen which must be dragged up to the speed of the vehicle before being used, all to avoid carrying a bit of liquid oxygen, is not the path to cheap spaceflight.

You can make a reusable vehicle without using exotic propellants, without carrying wings and landing gear to orbit, without any of the Skylon's other magic technologies. SpaceX is a lot closer to doing this than Skylon is to even having a working engine.

Comment Re:Can someone please explain (Score 1) 86

That's not quite correct. Essentially every geostationary satellite has to make such a correction (though not all geosynchronous satellites are geostationary). The orbital mechanics involved make it easier do do for higher altitude destination orbits, though...and starting further away from the equator certainly isn't a benefit.

It would also be prohibitively costly to make a plane change for a satellite in low Earth orbit directly with rocket thrust, but such orbits precess around Earth's axis with time. If you can get the inclination right and have time to wait, it's possible to instead alter their period so they precess faster or slower and eventually reach the desired plane. This is used by Iridium to get in-orbit spares where they need to be:

Again, though, starting out far from the equator is only useful if you're targeting highly inclined/retrograde orbits.

Comment Re:Falcon Heavy will land 3 boosters per mission (Score 1) 72

The video has them all landing together largely for dramatic effect (or to avoid modeling an ASDS). For most real launches, the center core will be much too far downrange and moving too fast to return to the launch site, and will have to land on an ASDS positioned out at sea. The smaller side pads are intended as fallbacks in case the center pad is unreachable or otherwise out of commission. They'll probably use two ASDSs for the center and one side core until they get a second land-based landing site constructed.

Comment Re:Since they are on the ocean... (Score 3, Informative) 72

Rockets are fragile, they can't take much mistreatment. A net would at most catch some debris...they don't want debris, they want a rocket. And in normal operation, they should be able to soft land upright on the platform, so a net would be an unnecessary complication in the best the worst case, the net system gets in the way and causes a landing failure.

Comment Re:It's all about economics (Score 1) 45

It's not clear that the total cost of implementation will be cheaper. Sattelite launches cost $50-250 million each...

LauncherOne is targeting $10 million per launch and would put up 2-3 satellites with each will be one of the most expensive ways to lift mass to orbit at roughly $44000/kg, and still won't be nearly as bad as you state. The Soyuz launches, with over 30 times the payload capacity, would put up many more satellites at far lower cost per satellite.

So what? That has nothing to do with whether the economics of this are workable or not.

You wouldn't have to ask that question if you'd bothered to read the entire text you were responding to. The rural population is not "by definition" small, it is a substantial fraction of the global population.

Comment Re:"Acquired" 65 rockets? (Score 1) 45

And apparently options for 100 more. 139 flights on a launcher that doesn't exist yet, from a company that has never launched anything.

Look at SpaceX...the Falcon 9 has been extremely successful, but it's not the rocket they started with. Their first launcher, the Falcon 1 had multiple launch failures and was ultimately scrapped along with the planned Falcon 5 in favor of the more efficient and capable Falcon 9. Depending on the Falcon 1 being a massive success when it was still a paper rocket would have been rather foolish.

Comment Re:Iridium Redux? (Score 2) 45

The satellites are cheaper, more capable, and far more numerous, and there's a lot more of a market for low latency internet access that doesn't have to follow fiber links on the ground than there was for the capability to make an occasional call with an expensive, clumsy sat-phone.

And cities cover a tiny fraction of the Earth's surface. Around 20% of the population of the US lives in rural areas, and the fraction is much higher in developing countries. It's also not just people in remote areas that will be interested in this, the low, perdictable latency will be of interest to financial institutions, among others.

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