Why the ideal interplanetary ship still needs people

I set my novella ‘Missionary‘ in a future where ordinary people had to find the strength to do extraordinary things. I also wanted it to be interstellar.

Gravitational lens attributed to the presence of Dark Matter. NASA, public domain.
Gravitational lens attributed to the presence of Dark Matter. NASA, public domain.

Making that meet my other intention to set it in a super-hard science setting, insofar as fiction allows, was a challenge. I solved it by imagining a techno-magical ‘star drive’ that produced instantaneous jumps from one star system to another – but only where space-time was flat. My favourite physicist’s equations suggest the exact opposite, but that wouldn’t work for story plots. The problem with the real option is certain ‘spaghettification’ followed by The End (to outside viewers, the End for the spaghettified stretches, literally, to eternity, and don’t be fooled by the hand-waving of Interstellar, OK?)

I actually wanted a story. This still meant that my starships had to be capable of long interplanetary cruises, and this – certainly – I wanted to make credible in everyday terms that we know to be mathematically and technically possible, even if nobody’s put the money into the R&D (hint, hint). Today’s general concept of a real-world interplanetary ship was invented by Sir Arthur C. Clarke in the 1950s. In hindsight that’s unsurprising. Clarke was a total genius and physics hasn’t changed since, so the current and likely future engineering solution is broadly what he came up with. (Clarke also invented the communications satellite and conceptualised the idea of the modern internet with all its social consequences, including mobile, way ahead of it happening. Just saying.)

The “Star Witch”, setting for my story.

As far as interplanetary ships go, Clarke’s thinking was different from the ‘ocean going’ analogs of his contemporaries – including Heinlein – in which the ship was enclosed within a single hull. Clarke imagined a crew-cargo module, separated from a reactor-fuel module by a long spine.  His concept reached ultimate form in 2001: A Space Odyssey of 1968, where Discovery was broadly to his design, with input from NASA engineer Fred Ordway, who I met once. Really. It was in the same venue where I won a regional science prize, as a teenager, for my study of Einstein and black hole physics. Just saying. And no, I am not Sheldon. Please! It’s Spock, thank you…

The problem with the movie Discovery was that Kubrick hand-waved the practical features, reducing the design to one that wouldn’t work. His amendments involved removing the radiators. We talk about the ‘cold’ of space. Actually, vacuum is an insulator, and if you’ve got a reactor on board, you need to get rid of heat by means other than conduction. Apparently, early designs for Discovery included radiators, but Kubrick wanted a skeletal look. Discovery lacked adequate fuel tanks for the same reason. Kubrick was right artistically – but it wasn’t pure science.

A starscape with a conceptualisation of Kubrick’s “Discovery” and one of its space-pods nearby, an image I made courtesy of the awesome ‘Celestia’ freeware astronomy package and a mod. You have to imagine this to part of the adagio from Aram Khachaturian’s 1942 Gayane ballet suite.

The main science problem was the centrifuge, which simulated 1/6 Earth gravity on a 40-foot (13 metre) diameter. The set was built like a Ferris wheel, full-scale, in Pinewood studios. But it wouldn’t work in free fall (‘space’) because of the way the Coriolis effect tweaks those cute bones and semicircular canals in the inner ear. This is an outcome of conservation of momentum. I’ll go into that in detail in another post (ask). In Discovery’s centrifuge, Frank Poole and Dave Bowman should have been staggering – certainly got dizzy if they stood too quickly.

That effect – not ‘force’ – can be reduced by increasing the radius of the centrifuge. Heinlein knew this, which is why some of his sci-fi ships tumbled end-for-end. The centrifuge radius becomes up to half the length of the ship, just don’t get too close to the centre of rotation. That’s why real-world experiments with simulated gravity in space have involved rotating a spacecraft at the end of a long(ish) cable, counterbalanced by a rocket stage.

I should add that the end-for-end rotation Discovery had in 2010, after the centrifuge transferred its angular momentum to the whole vessel, is wrong. The mechanics of friction transfer were right, but the centrifuge was shown mounted 90 degrees to the long axis, meaning the ship should have been rolling. Just saying…

An “Eagle Transporter” from Gerry Anderson’s mid-1970s “Space 1999”. Another Celestia starscape conceptualisation I constructed.

A lot of sci-fi designs have followed the “reactor module aft with spine and command module forward” concept, especially the ‘Eagle Transporters’ from Gerry Anderson’s Space 1999. These were awesome, apart from infinite fuel supply, artificial internal gravity, operational capability that varied depending on plot, and lack of radiators. OK, they were a bit crap when it comes to physics, but they looked convincing. More to the point, they were set in a compelling human setting. Anderson always nailed what counted when it came to story-telling. And this was pivotal – then, and today.

My take is that this worked visually, but writing is a different medium, demanding a different approach to achieve the same end.

A ‘real’ interplanetary ship wouldn’t look or behave like any of these in detail – as studies show, though none have broken Clarke’s original broad concept. At some distances from the Sun, for reasons involved with equalising solar heating, it would need to roll, as the Apollo CSM did during trans-lunar cruise (‘barbeque mode’). Nor do real spaceships move with prow in the direction of travel and the ‘bottom’ of the long axis of the hull pointing at the nearest horizontal surface. Just about every Hollywood spaceship, including Enterprise, does that. Reality? NASA’s Shuttle orbited ‘upside-down’ and ‘stern first’ – specifically to put the main engines, which weren’t needed to deorbit, in the way of debris. The OMS, which was needed, was a smaller target. Gravity got that one wrong, along with a lot else.

To me, the practical ‘atomic’ interplanetary ship needs a reactor at one end, connected to a spinning ‘minimum-radius’ habitat module by a spine carrying radiators and fuel tanks. The reactor is unshielded apart from a plate, just forward of the reactor module, that creates a ‘radiation shadow’. The longer the spine, the smaller and lighter the ‘shadow shield’. Outside it, the reactor spews radiation without hindrance. A similar system was used in the Convair NB-36H test-bed of 1955-57, where only the crew compartment was properly shielded from the reactor in the bomb bay.

The Convair NB-36H with reactor on board - test-bed for the proposed X-6 atomic powered aircraft. Don't approach from the rear or side, OK?
The Convair NB-36H with reactor on board. It wasn’t atomic powered itself, but the reactor was a test-bed for the X-6 atomic powered aircraft. Seen here with B-50 chase aircraft. Don’t approach from the rear, OK? And is that a town down there? Public domain, via Wikipedia.

The ship I came up with for ‘Missionary‘ included this – all was crucial to the plot. I did the maths to work out the hab module – more in a separate post. But even with ‘atomic’ rockets, mass is at a premium. For reasons subtly explored in the nature of my main character (go read – go figure) – I decided the optimal ship for my imagined future wouldn’t carry fuel for a two-way journey into unknown space. So I concocted a risky yet rational engineering solution, built into the design which, to my knowledge, hasn’t been applied before in science fiction.

Of course it failed, dropping the onus on people, especially my main character. But that’s the whole purpose of fiction.

The results – well, you’ll have to read the story… It’s out now, on Amazon.

Copyright © Matthew Wright 2015


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