Talk:Space sunshade

What Hermann Oberth wrote

Oberth wrote two pages on a proposal for a space mirror in his 1923 book (which can be obtained from De Gruyter via TWL, in German and English), and expanded it to an entire chapter of his 1929 book. But this can't be considered the inception of the idea of sunshades, if sunshades and mirrors are considered to be different things.

However, in the section on solar system exploration in his 1929 book, on p554 of the English translation, Oberth writes:

"Assuming, however, Venus did rotate about its axis like the earth, then the climate would look somewhat as follows : Quite uniform clouding over on both sides, hence a temperature at the visible surface of 8-20°C and a ground temperature of at least 45°C. Humid-warm, foggy weather, very much rain, frequent thunder (in agreement with this is perhaps the lighting sometimes observed on the night side). In this case, settling on Venus would naturally be out of the question, except if man of later ages found ways and means of keeping part of the sun's rays away from Venus say by rotating umbrellas made of sodium plate."

This is interesting since it's earlier than any reference we have on Terraforming of Venus. But it is just that one sentence, so Oberth's claim as inventor is tenuous. Our article claims that Oberth designed space mirrors that "were intended to focus sunlight on individual regions of the Earth's surface or deflect it into space so that the solar radiation is weakened in a specifically controlled manner for individual regions on the Earth's surface." Only the first part of this sentence is supported by the text. Oberth actually wrote, in his 1929 book:

"By suitably adjusting the single facets, all the solar energy reflected by the sun could be concentrated on a single point on earth or also spread out over wide stretches of land as needed or, if there is no use for it, allowed to radiate into interplanetary space."

Oberth did not anticipate that there would be any need to cool the Earth. He made no suggestion that his proposed space mirror would be useful for this purpose. A sunshade is technically much simpler than his polished, steerable sodium foil space mirror.

I plan to edit the article along these lines. -- Tim Starling (talk) 13:58, 12 July 2026 (UTC)

I just removed the text for now since it's hard to fit a sentence on terraforming Venus into an article that defines its topic as a device for cooling Earth. It would probably be good to broaden the topic of the article, since Terraforming of Venus links here. After Oberth's passing reference to terraforming Venus with a sunshade in 1929 (using a grossly incorrect model for its surface conditions) the topic might not have been revisited until Freitas in 1983. But that still predates the earliest proposal for an Earth sunshade that we know of, by Early in 1989. -- Tim Starling (talk) 00:29, 13 July 2026 (UTC)