Original URL: http://www.theregister.co.uk/2011/11/02/space_airships/

Record flight is step toward HYPERSONIC SPACE AIRSHIP

Ion-drive dirigibles to orbit from aerial 'Dark Sky' base

By Lewis Page

Posted in Science, 2nd November 2011 13:02 GMT

Inventors in America are claiming an altitude record for airships after a recent test flight in which an unmanned electrically-propelled helium dirigible successfully manoeuvred under power at 95,085 feet above the Black Rock Desert in Nevada. The "Tandem" craft is intended to demonstrate the first stage of radical plans which would see enormous, permanently inhabited "Dark Sky Stations" floating high in the atmosphere at the edge of space - to act as bases for radical hypersonic airships which would slowly fly themselves into orbit over a period of days using hybrid ion drive propulsion.

Somewhat more conventional extreme-high-altitude airships along the lines of the Tandem, flown above Nevada on October 22, would serve as shuttles carrying people and cargoes from the surface up to the colossal, mile-wide Dark Sky air/spaceports floating at 140,000 feet up.

The "Airship to Orbit" scheme comes to us from American DIY volunteer space collective JP Aerospace, founded by engineer John Powell, which has been developing high altitude balloons, rockets and combo rocket/balloon missions (aka rockoons, or in the parlance of our own Special Projects Bureau, ballockets) since 1979. JP Aerospace has now moved on beyond conventional rockoon flights to work on the use of small unmanned Dark Sky Stations as bases for vertical rocket launches starting from high up on the edge of space.

Both the Tandem and the prototype Dark Sky Station already flown use conventional helium balloons for lift, linked together by lightweight carbon-fibre trusses slung beneath. The Tandem features electrically driven propellors designed for the thin air found up at 100,000 feet and higher. One particularly neat trick is JP Aerospace's use of tied-down bags on the ground in which to inflate their balloons, meaning that there's no need to wait for windless conditions to make a launch.

Future manned ground-to-Dark-Sky ships and Dark Sky bases would use similar but more polished structures which would resemble huge cylinders of helium with lightweight keels running along them. Technically the ships would not be blimps – that's the term for airships without a rigid structure, which maintain their shape purely by internal pressure – but semi-rigids.

According to Powell, the two different types of ship and the intervening aerial base stations are vital as neither craft could survive the flight regime of the other. The vast, flimsy orbital vessels would be torn apart by the dense winds of the lower atmosphere, and the sturdier surface-launched jobs could never reach orbital velocity.

Behold the Mach 20 hypersonic hybrid ion rocket semi-rigid airship!

The underlying concepts at least of the surface-to-base craft and the Dark Sky outposts themselves seem to be feasible, but JP Aerospace has understandably yet to really do much in the way of flight tests on the mighty orbital rocket airships. Are they really feasible? Can massive gossamer envelopes full of helium gradually boost themselves up to Mach 20+ using slow-acting electrical ion drives (such as those used to keep low-flying satellites up to orbital speed despite drag from the upper traces of the atmosphere)? Even though there's very little air up there, surely a giant, hypersonic rocket airship is a big ask.

Powell recently gave an interview on the subject to nextbigfuture.com, in which he points out that upper-atmosphere weather balloons have already achieved Mach 10 as long ago as the 1960s, so that in his view Mach 20 isn't impossible with modern materials. In fact in his judgement what's called for is not a super-low-thrust but ultra-efficient ion drive, nor a conventional chemical rocket, but rather a hybrid of the two - which he describes as "the most efficient chemical rocket ever, or the least efficient ion rocket". The key issue will be whether enough electrical power can be stored at a low enough weight - either using fuel cells or batteries, solar panels can't do the job - to get the ships up to orbital poke. One cunning aspect of the plan is that the ships will not need any heat shield for re-entry as they will slow down so gradually (using drag in the evanescent upper atmosphere) that no appreciable heating will result.

Powell and his crew certainly don't lack for ambition. The idea is that the mighty Dark Sky floating spaceports would also carry telecoms equipment and tourist hotels to generate additional revenue on top of that gleaned from orbital launch. Their analysis suggests that the hypersonic airships could haul cargo into space for as little as $100 per pound in the near term and eventually just $1 per pound - and Powell sees manned flights to the Dark Sky region as soon as 2013, and permanent inhabited bases there from 2021. He says that JP Aerospace never makes a flight unless it will pay for itself, with revenue coming so far from advertising, telecoms experiments and aerospace tests for companies such as Lockheed.

It's interesting stuff, but progress has been slow - 33 years after commencement Powell and Co and are still doing small unmanned tests on the more achievable parts of their scheme. Larger craft such as the "Ascenders" - more like the massive V-shaped craft envisaged for the future ground-to-Dark Sky leg - are not flying at the moment. We probably shouldn't hold our breath waiting for the hypersonic space airships.

Even so, Powell's team is plainly one to watch, especially in light of the Reg's own aspirations in the rockoon/ballocket space plane arena. ®