Waverider, Part 2 – Flight in Nonterrestrial  Atmospheres,

or, The Hang-Glider’s Guide to the Galaxy

by Duncan Lunan

VESSEL – the Venus Surface Sustained Exploration Lander

At the Venus surface pressure is 91 atmospheres, and the temperature is over 600^o C.  In the first of my stories for Sydney Jordan’s Lance McLane strip in the Daily Record  (‘The Phoenix at Easter’, 1982-83, set 100 years on), there was an underwater test of a crewed Venus explorer.  It was manufactured in Earth orbit  (Fig. 1), using exotic materials, and simulating Venus-temperatures would be easy using solar mirrors.  But in pressure tests, if anything went wrong, a tank at 91 atm with vacuum outside would make a very effective bomb, or a missile if it merely sprang a leak!  It would be safer to test VESSEL on Earth at an appropriate depth in water.  The seafloor off Easter Island, with a depth of three-quarters of a mile, would be an ideal testing ground. 

The Venus surface has been flooded by lava flows, within the last 10 million years, and there’s great debate about whether volcanic activity continues.  The Venera 11 and 12 probes detected intense lightning activity and Pioneer Venus Orbiter located it at two mountainous, volcanic features, implying that they were active at the time and would be prime targets for exploration  (Fig. 2).  The Venera lightning frequency reached 25 strikes per second, and in 91 atmospheres’ pressure the shockwaves from lightning bolts or volcanic outbursts would act like depth-charges.  VESSEL would have to be at least as heavily armoured as a military submarine, rather than lightly built like a bathyscaph  (Fig. 3).  Even so, VESSEL’s crew compartment would have to have very efficient shock-absorbers.

Helium lift cells would require only 1.6% the volume of a dirigible’s on Earth   (S.W. Greenwood, ‘Extraterrestrial Atmosphere Transport Considerations’, Journal of the British Interplanetary Society, Feb. 1974)  but 3 to 4 times the propulsive thrust would be needed – electric motors, as there’s no chemical energy for propulsion in a carbon dioxide atmosphere, and probably propellers  (Fig. 1), though Darren Gillett, who prepared technical drawings of the VESSEL, gave it jets – and a fusion power plant to make them effective!  (Fig. 4)   

VESSEL would be brought down by Waverider, the atmosphere-entry design of the late Prof. Terence Nonweiler, which would remain aloft almost indefinitely in the Venus layers which he described as “embarrassingly thick”  (Fig. 5).  It could be carried as streamlined ‘deck cargo’, or faired into a cargo bay  (Fig. 6).  At the cloudbase pressure is 7.5 atm, and as it’s ragged and turbulent, a release point below them would give VESSEL a smooth descent and minimise acid attack on the Waverider while it waits in unpowered hover.  At 2 to 3 atm a Waverider’s stalling speed would be so low that “you could get out and walk beside it”  (Nonweiler), and because any surrounding medium slows down the exhaust gases of a rocket, a Venus booster would be 2 to 4 times bigger than for Earth launch  (Syvertson).  Instead, VESSEL would drop ballast at the end of its surface mission and return to the Waverider, which would have its own electric motors and lift cells to take it up to the 1-atm level or higher before engaging rocket thrust.  Using a forced-orbit flightpath, inverted, just above the cloud tops, at 25 times the speed of sound, with external fuel burning in the hypersonic shockwave, the ‘roll to heads-up’, to escape, would not be a simple manoeuvre like the Space Shuttle’s at Pitch-over, but would require a ‘conical roll’, devised by Gordon, flying round the inside of the shock cone while keeping the nose on the line of flight.  But there is an alternative…

Because of its slow, retrograde, 243-Earth-day rotation, a space elevator synchronised with the Venus surface and tethered to it would be impossibly long, and subject to severe solar perturbations.   But the Venus clouds rotate much faster, taking only four days to circle the planet.  So the equivalent of a terrestrial space elevator, in a 24-hour orbit around Venus, could have its tip suspended above the clouds at a relative velocity of only 250 miles per hour.  Releasing payloads into the Venus atmosphere and recovering them on rocket thrust would then be comparatively easy!

The Dick-Dick, A Soft Option for Mars.

At the surface of Mars atmospheric pressure is only 1% of Earth’s, equivalent to a terrestrial altitude of 32 km:  to lift a given payload the wing area has to be 47 times the terrestrial equivalent.  In 1983 Gordon Dick  (now Gordon Ross)  designed the Mars aircraft which I christened the ‘Dick-Dick’  (Fig. 7).  (Its base would of course be known as the Dick-Dick Dock.  If built of wood, with a lightweight structure for Martian gravity, it would be the Hickory Dickery Dick-Dick Dock, and if the area around it were terraformed it would be Hickory Dickery Dick-Dick Dock Green.)  In 1985 we featured the Dick-Dicks in a story for Lance McLane called ‘Sails in the Red Sunset’.  For story purposes the wings were shortened to allow them to attack Marsbase and fight gliders in the air  (Fig. 8 – see ‘Sailplanes on Mars”, ON, 4^th July 2022), but they couldn’t do it in real life. 

The Dick-Dick uses gas pressure to control the shape of flexible airfoils, of lightweight, high-strength materials such as nylon and Kevlar, rolled up and packaged up to six at a time for dispatch to Mars  (Fig. 9). 

The wing is lightweight for long-duration, low-sink-rate gliding, but it has an electric motor powered by solar cells on the upper surface, controlled by an autonomous onboard computer.  A camera system activated near nightfall by the diminishing light levels, would find touchdown sites on high ground to pass the night  (Fig. 10).  With its very low stall speed, the flexible wing would be very manoeuvrable even at low speeds, with a very low sink rate, so with this phototropic evening programme it should be able to alight on high ridges or peaks and take off again at sunrise.  During the night the gas in the wings would contract, re-expanding to raise them after dawn – flocks of them on the crags of the great volcanoes, waiting for the sunrise  (Fig. 11), though with their very large wingspans, they’d be more like the pteranodons of Walking with Dinosaurs than like roosting seabirds.

Gordon has since come up with more ‘soft options’ for Mars flight.  One is to reduce the Dick-Dick’s wingspan and the risk of damage at landing and takeoff, with a triplane design.  As ‘Alba’ is the old name for Scotland and ‘Ross’ was the new name for Gordon, it seemed inevitable that it would become known as the ‘Albatross’, although the First World War allusion is not entirely accurate.

A Flying Factory for Jupiter

When I began writing stories for Lance McLane, Sydney Jordan went along with my suggestion that the main drives for the starships Faith, Hope and Charity, holding Solar System settlement together after an explosion on the Sun, were developments of the pulsed fusion propulsion devised for the British Interplanetary Society’s ‘Project Daedalus’ interstellar probe study.  An interstellar probe would be sent within 60 years – a human lifetime – to Barnard’s Star, and the 50,000 tonnes of deuterium and helium-3 required as propellant was to come from the atmosphere of Jupiter  (A.R. Martin, ed., Project Daedalus, British Interplanetary Society, 1978.).  Callisto is the only one of the big moons to orbit outside Jupiter’s ‘supralethal’ radiation belts, so the operation would be run by remote control from there  (Fig. 12). 

In ASTRA’s Interplanetary Project, leading to my books New Worlds for Old and Man and the Planets  (1979 and 1983), we realised that there was an easier way.  In the BIS proposal, the factories gathering the Daedalus propellants were to be ‘aerostats’, huge hot-air balloons – minimum diameter 212 metres, to support 85-tonne nuclear-powered factories  (Fig. 13).  With 10% excess lift capacity, it was calculated that they could beat the downdraughts of the dark belts, which would be of order 25 metres/sec..  (R.C. Parkinson, ‘Propellant Acquisition Techniques’, in Project Daedalus above).

However, to expect nothing worse in the atmosphere of Jupiter seems optimistic, and Gordon Dick and I decided to use a Waverider instead.  With 290 kph airstreams meeting in opposite directions, the Voyager photographs in 1979 showed turbulence features typically 100 km across  (Fig. 14), and above the visible clouds Clear Air Turbulence may be extensive.  At Mach 6, which was the design speed of the Royal Aircraft Establishment Waverider airliner  (see Part 1), an aircraft would simply slice through turbulence, and if the factory maintains that speed, incoming shuttles won’t have to slow down any further  (the shockwave typically detaches from a Waverider leading edge at around Mach 2.4), and more importantly outgoing shuttles will not have to use so much of the fuel they came for, to get away.  Docking and undocking shuttles, in a gravity 2.535 times Earth’s, will paradoxically be easier with a factory in powered flight than with the underside of an aerostat which will be stationary in its airstream  (Fig. 15). 

Gordon designed a caret Waverider flying factory with a docking boom on top of the fin  (Fig. 16), approached as in mid-air refuelling on Earth, so that the shuttles don’t have to enter the shockwave over the factory’s upper surface, and Darren Gillett came up with a variant using the University of Maryland’s alternative design  (Fig. 17).

The extra large engine intake also brings in atmosphere for processing, eliminating the load on the compressor which is the first stage of processing on the aerostat.  The gases are liquefied in a compression turbine, then separated from ordinary hydrogen in a fractionating column.  On Earth that column would be at least 12 m. high  (R.B. Hinckley, R.C. Reid, P.E. Glaser, ‘Recovery of Deuterium in the Atmosphere of Jupiter’, Second Conference on Planetology and Space Mission Planning, Annals of the New York Academy of Sciences, 163, Article 1).  Jupiter’s gravity may be some help here, but it gives an idea of how big the factory has to be.  Further treatment would then be needed to separate the deuterium from the helium and the helium-3 from the ‘normal’ helium-4;  but those stages might be done in space, if industrial uses of helium-4 made it worth shipping out from Jupiter, as Isaac Asimov suggested  (‘The Element of Perfection’, in View from a Height, Dobson, 1964).

From the upper atmosphere, to get into close orbit around Jupiter takes 42 kps, and to escape altogether needs 60 kps, but Jupiter’s 12.6 kps equatorial spin provides a quarter of the orbital velocity and a 290 kph airstream in the same direction supplies 0.08 kps;  hypersonic factory flight can add up to 3 kps more.  A shuttle can reach 10 kps in the atmosphere on scramjet thrust before engaging rockets, but a further 19 to 20 kps is still needed to reach orbit.  Ideally the shuttles would be a nuclear-powered version of Alan Bond’s HOTOL or his more recent Skylon design.  Gordon assumed that each pickup carries 60,000 lbs. of cargo, a typical payload for the Space Shuttle, so 1800 to 2000 flights would accumulate 50,000 tons of propellant, enough to send a habitat to the stars.  

As I’ve pointed out in previous articles, space habitats’ shielding against cosmic rays will allow them to come into close orbit around Jupiter  (Fig. 18).  Because Jupiter’s magnetic field is generated not in the core, but in the liquid hydrogen layer overlying it, the field isn’t concentric with the planet, there’s an ‘eccentric cam effect’ – a radiation-free zone, extending to 7140 km above the clouds on one side of the planet, rotating with the invisible ‘System III’ of Jupiter’s interior.  From a habitat in it, a manned, unshielded vehicle can descend into the atmosphere.  Factory operations would normally be automated, but living space for a crew of two in the factory nose, with access from the fin, allows emergency repair.  The factory’s wing-loading allows for extended glide at below design Mach number, for that.  If it fails and the crew can’t get back to their shuttle, the escape system for’ard might be a capsule with a deployable hot-air balloon.

At the visible surface gravity is 2.535 g;  but standing up in a fairground rotor is a common test of strength, and the Red Arrows routinely perform sustained 10g sequences.   Pilots could be acclimatised to it in centrifuges, or just by driving round the axes of their habitats at high speed, as the Skylab astronauts simulated gravity by running round a ring of lockers.  With 90 km-deep sky to play around in, there are bound to be pilots who find some excuse to get down there.  

The Lucifer Plane and the Altair, the All-Terran All-Terrain Aircraft

When Gordon and I first submitted our F.I.N.T.A. article to Analog, it featured only VESSEL, the Dick-Dick and the Flying Factory.  But Analog editor Stanley Schmidt asked us also to consider worlds which would be like Earth, yet sufficiently different to need different designs.  The conditions allowing human occupation of planets were examined by Stephen H. Dole in the fascinating book Habitable Planets for Man  (Blaisdell, 1964).  The allowable range was from 0.04 of Earth’s mass to 2.35, to retain a breathable atmosphere at one end and to keep surface gravity below 1.5g at the other  (Fig. 19).  The lower limit of atmospheric pressure is set by mountaineering experience, the upper by deep-sea diving, with partial pressures of oxygen and other gases adjusted accordingly.  The temperature range has to permit water to exist as solid, liquid and gas… and when we look at the effect all this has on aircraft design, the answer is that if something will fly on Earth, it’ll fly on any other Earthlike world, with more or less payload depending on the exact set of conditions.

For Stanley we came up with a world younger than Earth, perhaps larger  (though not too large), with more radioactive material in its crust, and lots of volcanic activity, keeping the continents sterile though life in the sea generates a breathable atmosphere.  Our imagined settlers would terraform isolated valleys for their survival  (Fig. 20). 

With all that thermal lift around, the occupants could use hang-gliders for transport  – and they’d need them, because settlements would be separated by impassable badlands.  An atmosphere entry vehicle should also be able to withstand temperatures inside the crater of a volcano;  but could it be lightweight and robust enough to do both?  Following a suggestion by L.H. Townend, Gordon was already working on his new family of flex-wing Waveriders  (see Part 1), particularly the space shuttle and planetary probe carrier, and he now devised two more flexible Waverider shapes, the Lucifer Plane and the Altair, allying his previous experience in sails and hang-glider design to Nonweiler’s theory. 

The Lucifer plane is almost entirely carbon fibre, and its wings are a carbon-fibre mesh which will let enough plasma through to survive the heat of entry (Fig. 21), like Gordon’s other flex-wing designs.  For a ballistic vehicle a mesh parachute increases the landing ‘footprint’;  you might think that for a Waverider they contract it, since the lift of the wing is reduced, but as drag is also reduced the crucial lift/drag ratio is little altered.  The leading edges, spars and struts are cooled during atmosphere entry by liquid hydrogen.  On the way into atmosphere, the fuselage is uppermost and the wing is a double-cavity Waverider.  Once in the troposphere, in a manoeuvre which will require careful timing and judgement, the pilot rolls it on to its back, adjusts the geometry of the leading edge by varying the spread of the fan, and rotates the cockpit 180 degrees so that he or she is no longer upside-down.  With that, and the tail assembly rotated for landing, the plane is in hang-glider mode  (Fig. 22).

The three structural differences between the Altair and the Lucifer plane are the radial reinforcement battens; the struts telescopic as well as hinged;  and the diamond-section box on top of the wing  (in its hang-glider mode), into which the sail rolls like a blind  (Fig. 23).  Gordon added these features to allow the wing a much wider spread, to allow for a range of atmospheric densities;  for instance, in this design the sail billow can be varied, by altering the tension on the battens, to increase or decrease lift in response to different atmosphere compositions or wind conditions.  Even at that, to gain enough lift on Mars with a wingspan which will work elsewhere, the body has again to be lightweight and we have a carrier for one or two persons at most.

So it’s a scout ship, or a millionaire’s plaything;  Stan did say he wanted something to be used by explorers in other planetary systems.  (We know several people who want one, but none of them offered to put up the development cost!)  That leads us to the rotating, dual-purpose rudders and multi-purpose landing gear.  Once down on the surface, with the appropriate rudder and undercarriage combination, it’s possible to roll up one half of the wing, swing the other half to the vertical, rotate it to catch the wind, and sail off as a land-yacht, ice-yacht or boat.  (Fig. 24 – Did I mention that Gordon used to design and build sails, as well as hang-gliders?)

For electric propulsion in those modes, the Altair could have flexible solar cells like the Dick-Dick’s;  though they wouldn’t work in thick cloudy atmospheres like Venus’s or Titan’s.  But in any case neither Lucifer Plane nor Altair will do for Venus, what with the low surface winds, the need for armour, lift cells and ballast, and the sulphuric acid which would turn the carbon-fibre construction to candy floss.  And Venus is described in most textbooks as a terrestrial planet, on the grounds of size and mass.  So there are two options, to make the Altair truly all-Terran as well as all-terrain:  we can produce a material which will let the plane go to Venus, yet still fly in all those other atmospheres;  or we can just make Venus and any sister worlds habitable, so making their atmospheres ‘terrestrial’ in the sense we began with.

Afterword

All the vehicles above are described in much more detail, in Duncan Lunan and Gordon Dick, ‘Flight in Non-Terrestrial Atmospheres, or the Hang-glider’s Guide to the Galaxy’, Analog Science Fiction/Science Fact, January 1993.  Duncan’s story ‘The Phoenix at Easter’ ran in the Daily Record, 1982-83, reprinted with Notes and with ‘Hawke’s Wings: VESSEL’. in Jeff Hawke’s Cosmos, Vol. 9 No. 3, January 2016.  ‘Sails in the Red Sunset’ by Duncan and Gordon Ross  (then Gordon Dick)  ran in the Daily Record, 1985, reprinted in Jeff Hawke’s Cosmos, Vol. 10 No. 2, August 2017, with ‘Hawke’s Wings: the Dick-Dick’.  Flying Factories were covered in ‘Hawke’s Notes:  Chalk Circle’, Jeff Hawke’s Cosmos Vol. 8 No. 1, July 2013.  Notes on the Lucifer Plane appeared with Duncan’s story ‘Riding the Fire’, in The Elements of Time, Time Travel Stories by Duncan Lunan, Shoreline of Infinity, 2016, illustrated by Sydney Jordan  (Fig. 25).