by Duncan Lunan

Balloons in Space

Professor A. M. Low, one of the founders of the British Interplanetary Society, deserves to be remembered for his accurate prediction, in The Next 50 Years  (1939), that the first attempts to reach the Moon by rocket would be made 20 years later.  Like other BIS founders including Arthur C. Clarke, he also wrote science fiction.  Less memorable, except for its oddity, was his young adult novel Adrift in the Stratosphere, published in 1937  (Fig. 1), but probably written a good deal earlier.  (Short review:  “I couldn’t put it down.”)  Among its curious features, he populated the upper atmosphere and near space with monsters, as Sir Arthur Conan Doyle had done earlier  (‘The Horror of the Heights’, 1913)  and Charles Fort had postulated around 1930.

He correctly foresaw that rockets launched from high-altitude balloons would generate considerably more thrust, but his strange idea was that actual rockets would be fired from tubes around the balloon’s gondola, giving it a boost in the opposite direction, like the recoil of the ‘Bazooka’ World War 2 anti-tank missile launcher.  (That was supposed to be recoilless, but according to my late father, who had fired one, it was anything but.)  Even stranger, Low appeared to think that the stratosphere extended to the inner planets;  later in the novel, two French balloonists come to grief as they approach Venus.

The greater thrust of rockets at altitude was harnessed in the ‘Rockoon’ experiments of the 1950s  (Figs. 2 & 3), culminating in Project Farside, where 4-stage solid rockets were launched through the carrier balloons at high altitude  (Fig. 4), and as the name implies, the ambitious aim was to get high enough to photograph the other side of the Moon  (Fig. 5).  Farside rockets did reach heights of 4000 miles during the International Geophysical Year, 1957-58, but their achievements were overshadowed by the launches of the first artificial satellites.  (Lloyd Mallan, Space Satellites, 1957;  Wernher Buedeler, Operation Vanguard – Earth Satellite, 1957.)

Low was also right to predict that the first off-Earth deployment of balloons would be over Venus, and there would be two of them,  In 1986, the small international flotilla of probes to Halley’s Comet included the two Soviet Vega probes  (Fig. 6), which made gravitational slingshots around Venus  (Fig. 7)  and released two French balloons into the atmosphere  (Fig. 8).  They only lasted about a day, but they did maintain contact with landers on the surface  (Fig. 9), and more advanced concepts have been planned for years now. 

At the surface of Mars, the atmospheric pressure is only 1% of Earth’s, equivalent to an altitude here of 100,000 feet, around the ceiling of US balloon research in the 1950s.  (Curiously, the Chinese ‘Spy Balloon’ just shot down in US waters was only at 60,000 feet, an altitude reached by British Canberra jet bombers around 1960 and easily within reach of today’s fighters and missiles.)  Hot-air balloon flight on Mars is just possible, with hydrogen as the lifting agent.  In the 2000s, the Scottish Branch of the Mars Society had a discussion project, ‘Building the Martian Nation’, which envisaged building a settlement on Lunae Planum, in a lava-flooded crater which we called ‘Glasgow Bay’ because of its size  (Fig. 10).

The region had many attractive features including shielding from cosmic radiation by the crater wall, ‘pedestal craters’ indicating underground water, likewise clay deposits detected by Mars Express, and sulphur deposits in the nearby Juventus Chasma.  But we were concerned that the roughness of the surrounding terrain  (Fig. 11), particularly indications of fissures running north to south, might inhibit exploration and expansion from the settlement. 

As a possible solution Gordon Ross, then at the Industrial Design Unit of Glasgow School of Art, designed a 2-person disc-shaped Mars airship, powered by solar cells on its upper surface.  Landing away from the settlement, it could be covered in soil which was cemented in place.  When the disc was then deflated and removed, the resulting dome could be sealed and pressurised for use by future explorers, protected by the laminated soil from solar flares and cosmic rays.  Erik Wernquist’s 2015 film Wanderers, which I cited last week, includes somewhat larger ‘Mars blimps’ approaching the rim of Victoria crater, which was explored by the Curiosity rover in 2007 (Fig. 12).

In the 1970s, as I’ve previously mentioned, the British Interplanetary Society’s Project Daedalus proposed to fuel an interstellar probe with 50,000 tons of deuterium and helium-3, extracted from the atmosphere of Jupiter.  The collectors would be very large hydrogen-filled ‘aerostats’  (Fig. 13).  In the discussions which led to my 1983 book Man and the Planets, we suggested that Waverider ‘Flying Factories’ would be more practicable.  (See ‘Flight in Non-terrestrial Atmospheres’, ON, December 4^th 2022.)  But less demanding balloon exploration of Jupiter’s atmosphere would certainly be possible  (Fig. 14), and was featured in Arthur C. Clarke’s story ‘A Meeting with Medusa’, as well as in The Medusa Chronicles, (Gollancz, 2016), the book-length sequel by Stephen Baxter & Alastair Reynolds.

Describing the coming Dragonfly rotorcraft mission to Titan last week, I mentioned that originally it was to be battery-powered and recharged from a nuclear-power balloon in Titan’s atmosphere.  Although the Titan Montgolfière has been eliminated from the Dragonfly mission, it may well be reinstated as a relay between future floating probes in Titan’s lakes and orbiter spacecraft overhead  (Fig. 15).  Titan blimps are equally possible  (Fig. 16).

The atmosphere of Saturn itself has other intriguing possibilities.  Saturn is the only planet whose overall density is less than water, and it’s often remarked that Saturn could float in a sufficiently large bathtub  (although, as the Jet Propulsion Laboratory’s Warren James pointed out, when you took it out again it would leave a ring). As a result, gravity at the visible surface is only 1g, the same as Earth’s.  Erik Wernquist’s Wanderers ends with a sequence of crewed blimps floating in view of the rings and the planet’s shadow on them  (Fig. 17).  Exploration and even settlement at greater depth is possible, but as I pointed out in Man and the Planets, “Who could bear to lose sight of that stupendous arch, curving from one distant horizon to the other, with the meteors falling below it from the D-ring and the curtains of the polar aurora shimmering at one’s back?”

Looking at closer possibilities brings us back to Venus.  NASA is already flying prototype Venus balloons  (Fig. 18), and among many concepts for a new phase of Venus exploration are a balloon at a height of 50 km, to detect Venus-quakes at ground level  (Fig. 19), and floating power sources for surface probes and rovers  (Fig. 20).   Which of these will become reality remains to be seen. 

NASA’s Langley Research Centre has come up with a much more ambitious plan called HAVOC  (High Altitude Venus Operational Concept), which would deploy blimps into the Venus atmosphere  (Fig. 21)  and cluster them to build floating settlements  (Fig. 22). 

It’s not clear how they manage to have blue sky above them, given that the 1-atmosphere pressure level is deep in the clouds, and the JPL retro space tourism poster refers more realistically to a ‘Cloud 9 Observatory’  (Fig. 23).  It could be a precursor to the ‘Cytherea Station’ featured in Bob Buckley’s novel World in the Clouds  (1980), illustrated for Analog by Vincent di Fate  (Fig. 24), or to a more ambitious Russian proposal for a cloud city  (Fig. 25).   It could also lead to the less salubrious, multi-tiered Venus society of Derek Künsken’s The House of Styx, A Venus Ascendant Novel, (Solaris, 2021). and that’s a review we might look at later.

But before we leave Venus, there is one other remarkable possibility to discuss.  In ‘Flight in Non-terrestrial Atmospheres’, I wrote, ‘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!’

In 1961 the late Carl Sagan made headlines with a proposal to give Venus a breathable atmosphere by seeding the clouds with blue-algae  (Fig. 26).  It depended on the clouds being water ice, and was ruled out when they turned out to be sulphuric acid smog  (though the idea lived on in the literature for years, regardless).  With the resources of the Asteroid Belt to draw on in the future, our suggestion was to manufacture pumice-type boulders, like Saturn’s moon Hyperion  (Fig. 27), with an alkaline composition, and drop them by space elevator.  As they floated in the clouds like the ‘Laputa’ of Gulliver’s Travels, interaction with the acid could release water to trickle down and sustain blue-green algae in their spongy interiors.  If each floating islands had an interior processing area of 1 square kilometre, and we could keep 115 million of them active at a time, we calculated that we could give Venus an oxygen atmosphere in ‘only’ 3.172 million years. 

To do it in, say, 1000 years, comparable to estimated timescales for terraforming Mars, would need ‘billions and billions’ of them, to quote Sagan himself, giving new meaning to the fliers’ adage, ‘Beware of clouds with rocks in them’.  If you could drastically increase the processing area inside them, that would make it easier.  In any case you would either need a lot more of them at the start, or a different strategy towards the end, as the concentration of acid in the clouds diminished – assuming that there was enough of it in the first place for the algae to transform all the carbon dioxide… It’s not as easy as it looked at first glance, but it did lead on to some very interesting thoughts about what to do with Venus afterwards.  But that, as they say, is another story, for another time.