Whipple Shields and Radiators
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Categories: Modern, Not an expert

Whipple Shields and Radiators

A screenshot of the homepage of http://projectrho.com/public_html/rocket/ with digital art of a torchship against the background of a planet overlaid with equations

In fall 2021, Winchell ‘Nyrath’ Chung [Patreon] – [hellbirdsite] was diagnosed with terminal cancer. As of April 2022 it is in remission. His site Project Rho is one of the great Internet preservation projects: it collects material in various essays, books, and Internet posts and organizes it so it can be turned into something more digestable one day. In his case, that material is calculations and speculations about how high-powered spacecraft would work, especially in combat. This week I will talk about some of the things I learned from worldbuilding geeks which I did not learn from science fiction stories.

We all learned in school that converting energy between forms produces a certain amount of waste heat. And whenever we use a thermos, we see that vacuum is an excellent insulator. So a spacecraft with a giant fusion plant, amazing total-conversion drive, or fearsome chemical-powered lasers would produce a lot of waste heat and need a way to dispose of it before the crew boiled. The obvious solution is to have a system of radiator fins which dissipate that waste heat over as much area as possible. In a high-powered spacecraft, the fins would often glow red hot. Since they need to have maximum area for their weight, the fins would be unavoidably fragile. So high-powered spacecraft cruising between planets would be surrounded by a delicate armature of glowing radiators, and when they engaged in combat they would have to decide whether to risk boiling or risk having the radiators shot away.

Whipple shields are the standard way of armouring objects in space against impacts. Since there is negligible friction in space, objects can reach tremendous relative velocities. Armouring against impacts with a single thick plate would require prohibitive weight. So back in 1947, astronomer Fred Whipple suggested using several layers of aluminum, possibly reinforced with synthetic fibres, to break up impactors into a scattering of small fragments which can be stopped by the inner layers. Whipple shields take up some bulk, but not much mass.

Radiators and Whipple shields are well known to geeks who like to imagine how the spacecraft in old hard science fiction would work (including projects like GURPS Transhuman Space, the wargame Attack Vector: Tactical, and the computer game Children of a Dead Earth). But they are very scarce in actual fiction.

Learning about Whipple shields reminded me of how aggressively retro the science fiction of the middle of the 20th century was. Desert Mars and jungle Venus remained popular tropes in the 1950s, but back in 1907, naturalist Alfred Russel Wallace had showed that Mars was too cold and its air too thin to have liquid water. General relativity was published in 1915, but faster-than-light travel remains a beloved trope (even though these days most writers are more sensible than Robert A. Heinlein and don’t have viewpoint characters dance rhetorical rings around believers in relativity).

Ultravelocity projectiles, shaped charges, and directed energy weapons obey different physics than arrows and bullets. The Whipple Shield was proposed in 1947! Already in 1956, the designers of the Leopard I tank were told to keep the weight around 30 tons like a medium tank and only armour it against 20 mm cannon fire. They did not know any effective way to armour against shaped charges. Today tank armour consists of layers of metal, ceramics, glass, and rubber separated by air gaps. But most science fiction games still envision armour as putting as much hard dense mass between the baddies and the squishy bits as possible. Their vision of armour is anchored in the Second World War or even earlier.

Many stories about space wars are excuses to recycle tropes from 19th and 20th century warfare. The Honor Harrington stories are a famous example, but Star Wars episodes 5 and 8 even had literal bombing raids where attackers drop projectiles and watch them fall onto their targets. Space pirates keep crawling over the gunnels despite fun-ruiners trying to push them back with cries of “the economics don’t make any sense and there is no way to escape with your booty!” Space is a different environment than seas, rivers, or oceans, and space technology is very different from the technology of the Age of Sail or the Age of Steam, so there is no reason to believe that anything would exactly recapitulate itself. Naval warfare in the 19th century did not recapitulate Hellenistic galley warfare or Viking Age lashing the ships together and drifting towards the enemy!

But radiators give one excuse to adapt those old tropes! Character have to choose whether to extend their radiators (and risk them being shot off) or slowly cook to death. They have to choose whether to generate heat and upset their heat balance. That has some things in common with submarine warfare in WW II, where a submersed submarine below Schnorkel depth had a limited supply of air and battery power and could not use its powerful diesel engines. Choices with consequences make good stories. And red-hot radiators are spectacular looking, and spectacular images have always been a key part of science fiction. So I really do not know why they never became a big part of written science fiction.

Science fiction set in space rarely pays any attention to science in defining how its spacecraft work. And the rare stories which do pay attention generally add or remove a few zeros and embrace a few magical technologies such as hyperdrives, Ansibles, or Langston Fields. The geeks and dreamers who created the knowledge behind Project Rho were trying to make their imaginations realer than most of the writers who inspired them. And yet they did something wonderful.

Edit 2023-01-18: Added a link to Project Rho

(scheduled 28 June 2022)

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