LOX/LH2 motors have a good enough Isp figure that they can take the hit in performance -- the Vulcain 2 runs between about 360 at sea level and 420-odd in vacuum, comfortably outperforming vacuum-specific kerosene/LOX designs at all altitudes. The SpaceX Merlins are actually quite poor performers for kerosene/LOX but there may be other trade-offs in terms of construction costs and reusability. They can certainly do the job of getting modest amounts of materiel into orbit.

As for the Raptor engine I'll be interested to see where they go with it. Other people have tried methane/LOX in the past but reported problems. I've heard there is a fuel decomposition problem resulting in coking of the pumps as well as sulphur impurities in the methane causing problems too. What puzzles me is the mention of using a partially-cryogenic fuel mix as an interplanetary engine; LOX is not storable over any sort of a timescale even in space and even methane would require active refrigeration to stay liquid for weeks or months on end during a transfer orbit to, say, Mars.

There are a number of launchers that burn the same engines from ground to true vacuum, indeed the Shuttle's engines burned from launch to orbit insertion (aided by the SRBs in the early part of the flight). Other examples include the Vulcain-2 on the Ariane V and the RS-68A central core stage of the Delta 4 Heavy. Notably all these long-duration burn motors are LH2/LOX which have even better Isp numbers than kerosene/LOX motors.

A modernised version of the F-1 did exist, with much better Isp of 311 seconds at sea level and a greater thrust of 7.25MN at sea level. It could be throttled and pivoted, unlike the brute-force-and-ignorance of the fixed F-1. It's called the RD-171. It spawned a series of cut-down versions flying today such as the two-chamber Atlas RD-180 and the single-chamber Angara RD-191/Antares RD-151.

As for the Saturn V, the first stage spent 10% of its burn time and fuel just clearing the tower so vacuum performance was not really a mission-critical factor in the F-1's development and design. It was laid out in the early days of rocket development where "design" involved slide rules and large sheets of drafting parchment -- the idea of CAD, computer modelling, 3-D printing of engine parts, modern engineering materials etc. were science-fiction dreams whereas they had to bend metal then and there.

What is your evidence that there is no demand for large objects in orbit?

My evidence is that there is actually, in reality, no demand for large objects in orbit. I qualify this statement by saying there's no money being fronted up to buy heavy lift launches of large objects in the 50-tonne region other than the SLS project (which is itself an assembly of small-objects-to-orbit). Wishful thinking, paper exercises and want-to's don't count as a "demand".

I understand SpaceX has some people interested in buying launches of the Falcon Heavy but they're constellations of small satellites, not unitary vehicles. As far as I know nobody's yet cut a cheque for such a launch since the Falcon Heavy's initial proving flight is getting pushed further and further down the calendar due to circumstances.

It didn't need to be since it never ran in true vacuum. The F-1 was actually optimised for reliability and not-killing-the-passengers hence its abysmal performance by today's standards. Even the SpaceX Merlin 1-D has a better Isp figure than the F-1.

F-1 - Isp (sea level) = 263 seconds.

Merlin 1-D Isp (sea level) = 282 seconds.

RD-180 Isp (sea level) = 311 seconds.

If Spacex could lift 200mT to LEO for costs that are comparable to today's heavy launches, would new uses arise?

Such as? The only unitary large-lift mission I can think of is a single-mirror super-Hubble space observatory which has its own problems -- building a one-piece very large mirror, say five metres in diameter that could survive 3G-plus during launch, vibration etc. isn't going to be easy or light. The James Webb is using folding mirror segments and will have an effective diameter of 6.5 metres when deployed and it fits in a regular launcher fairing.

We've got better at doing things in space in the past fifty years, we don't have to go back into the Jet Age to justify Big Dumb Boosters.

As an aside, large amounts of stuff needed in orbit is actually fuel for satellite manoeuvering, deep-space probes, a future manned return to the Moon etc. A remarkable amount of the mass delivered into LEO and GEO today is cheap fuel at a delivery cost of $5000/kg. What I'd like to see Musk doing is working on a robot fuel production system based on, say, Ceres or other water and carbon rich asteroids, bringing back tankers full of fuel to Earth orbit. That way he could go to Mars without having to lift a thousand tonnes of fuel up from the ground in expensive boosters.

Sure there's an interest in big launches, big-mirror observatories and the like. What there isn't are the bucks to pay for them and the need for multiple launches a year that would justify spending tens of billions to develop a 50-tonne class launcher which would only fly once a year, if that.

At the moment humanity is launching about ten to twelve vehicles a month -- December 2015 was a recent activity peak with eighteen launches, three of them within the same 24-hour period. The next large scientific payload I know of is the James Webb telescope which will fly on an Ariane V in 2018, and that's only 6.6 tonnes.

ESA are blowing the cobwebs off their own heavy-lifter, the ES variant of the Ariane V for a couple of missions to launch four Galileo satellites at a time but apart from its original purpose to fly the ATV resupply vehicles to the ISS nobody needing a 20-tonne unitary lift has been buying flights on it, while the regular ECA variant of Ariane (10 tonnes to GTO, usually two GEO satellites plus SYLDA carrier) and the smaller Vega have full order books.

this would still be a major item on the list of things you need to do in order to hurl big stuff into Earth's orbit more affordably. There are long waiting lists of customers for such capability.

There isn't a large pent-up demand for "big stuff" in orbit, at least nothing that anyone's willing to pay even $5000/kg for. The demand for launches of up to fifteen tonnes a lump is handled by the current fleet of rockets. Very occasionally the US spy industry wants to put a unitary big-mirror observation satellite up and that can run to 20-25 tonnes. In those cases the Delta Heavy is used, the only time it is ever launched as far as I know.

The human race has got very good at throwing up small lumps of stuff into orbit and putting them together there afterwards -- the ISS is over 400 tonnes of small lumps, none of them over ten tonnes in mass when they were on the ground. A heavy lifter is not really needed for day-to-day operations or even a blue-sky Manned Mars mission, it's achievable with today's hardware and without the cost overheads of developing new heavy launchers with little or no other commercial sales to pay for them.

this is a portable aircraft with a good carry capacity.

The new version of the Russian Mi-26 heavy-lift helicopter can, reportedly, lift 25 tonnes, significantly more than the Airlander. Existing models of the Mi-26 can carry 20 tonnes of cargo, land on large ships, don't need lots of prepared ground to operate from etc. There's talk of an evolutionary new version to be developed jointly by Russia and China which would be able to lift 33 tonnes but it's still on the drawing board.

The Airlander folks have glossy brochures extolling later development versions of their airship which reputedly would be able to carry up to 60 tonnes of cargo but it's taken them all this time to get their first prototype into the air. I wouldn't hold my breath waiting for that larger version to make its first flight.

Yes, longer-wavelength radars can indeed detect stealthy aircraft. Warships with sea-sweeping radars can often spot such aircraft. The problem is they can't hand off an accurate location and track to the anti-aircraft missile radars which need to be much higher frequency to determine the aircraft's position to within a few centimetres so they can actually hit it. Those missile system radars are what the stealth profiles and skin coatings are designed to be near-invisible to and they do that job very well. At the same time active radars are a perfect target for anti-radar missiles of the sort the F-35 carries among other payloads. In addition it can network its own radar detection systems, handing off radar targets to other aircraft such as the F-14 which can't approach a defence area too closely because they would be detected and fired upon.

Combined-cycle gas turbines (CCGTs) can reach 60% efficiency but they're more complicated than a simple once-through gas turbine of the sort that's likely to be fitted to a truck like this. CCGT power plants boil water to steam with the turbine exhaust and use a secondary steam turbine to generate more electricity hence the 60% figure but they are bigger, heavier and more complex than any conceivable mobile power plant.

Some Lidl stores do have self-checkouts. I was in one today and used a self-checkout there. However the Lidl store I go to most often doesn't have self checkouts and I can spend more time waiting in the queue for a manual checkout than I did shopping for the half-dozen or so items I usually buy. The till operators are pretty quick but there are never enough of them on duty to save on overheads and the store is always busy because of the low prices.

A thousand tonne train of railcars pulled up a slope 100 metres in height, assuming no losses (spherical cow assumptions here but bear with me) will require Mass x Gravity x Height = 1 billion joules = 270 kWhr which at commercial rates for electricity is worth maybe $20 or $30 US. That's not a lot of energy storage given the capital cost of track and equipment and recurring maintenance costs etc.

The Falcon 9 launcher built and flown by SpaceX burns over 200 tonnes of fossil fuel kerosene in every flight.

The big problem with iCar is that obeying the Holy Jobs design rules there will be no holes in the bodyshell large enough for people to get in and out. The solution (so to speak) to this will be the iChipper(tm) with a flexible hose and a unique patented nozzle coupling in the side of the iCar. It will require an up-to-date version of iTunes to get back out of iCar.