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If you're going to put 20 million tons of perfectly identical gram-sized craft into orbit somewhere, it seems a lot more sensible to launch a factory to the Moo

If you're going to put 20 million tons of perfectly identical gram-sized craft into orbit somewhere, it seems a lot more sensible to launch a factory to the Moon rather than launch all that mass from Earth. The CO2 added to the atmosphere from burning 2 billion tons of rocket fuel cannot be negligible.

ef4 9y ago
When you build them on earth, you aren't using "a factory", you're using a supply chain with thousands of factories and millions of people. A factory that can go from regolith all the way to spacecraft is still very speculative. As for 2 billion tons of rocket fuel, it's not trivial but it's something less than 5% of one year's current CO2 emissions, and we're talking about spreading it out over a couple decades.
sp332 9y ago
This is addressed in the paper. It's even addressed in the abstract of the paper. Edit: Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. The paper says that if there are rockets involved, they will be used outside of the atmosphere.
- robotresearcher 9y ago
  > It's even addressed in the abstract of the paper. Where? edit: located below (italics added) thanks. The environmental costs of launch are considered. I can't see the environmental impact of manufacture considered explicitly, though. Abstract: If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. The concept considered here is to block 1.8% of the solar flux with a space sunshade orbited near the inner Lagrange point (L1), in-line between the Earth and sun. Following the work of J. Early [Early, JT (1989) J Br Interplanet Soc 42:567–569], transparent material would be used to deflect the sunlight, rather than to absorb it, to minimize the shift in balance out from L1 caused by radiation pressure. Three advances aimed at practical implementation are presented. First is an optical design for a very thin refractive screen with low reflectivity, leading to a total sunshade mass of ≈20 million tons. Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. Third is an implementation of the sunshade as a cloud of many spacecraft, autonomously stabilized by modulating solar radiation pressure. These meter-sized “flyers” would be assembled completely before launch, avoiding any need for construction or unfolding in space. They would weigh a gram each, be launched in stacks of 800,000, and remain for a projected lifetime of 50 years within a 100,000-km-long cloud. The concept builds on existing technologies. It seems feasible that it could be developed and deployed in ≈25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time.
  - Footkerchief 9y ago
    The issue being addressed: > The CO2 added to the atmosphere from burning 2 billion tons of rocket fuel cannot be negligible. The quote from the abstract that addresses it: > Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. More detail later in the paper: > Because of its enormous area and the mass required, shading from space has in the past been regarded as requiring manufacture in space from lunar or asteroid material and, thus, as rather futuristic. Here we explore quantitatively an approach aimed at a relatively near-term solution in which the sunshade would be manufactured completely and launched from Earth, and it would take the form of many small autonomous spacecraft (“flyers”).
  - snakeboy 9y ago
    The quote from the parent comment is about halfway through the abstract you just quoted...
grinich 9y ago
Certainly not negligible, but it's only about 5% of our total annual carbon emissions. https://mobile.nytimes.com/2017/06/26/climate/carbon-in-atmosphere-is-rising-even-as-emissions-stabilize.html https://mobile.nytimes.com/2017/06/26/climate/carbon-in-atmo...
wcoenen 9y ago
To make carbon-neutral rocket fuel, synthesize methane from CO2[1] that is extracted from the air. Both SpaceX[2] and Blue Origin[3] are currently developing methane-fueled rocket engines. [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction [2] https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) [3] https://en.wikipedia.org/wiki/BE-4 https://en.wikipedia.org/wiki/BE-4

ef4 9y ago

When you build them on earth, you aren't using "a factory", you're using a supply chain with thousands of factories and millions of people. A factory that can go from regolith all the way to spacecraft is still very speculative. As for 2 billion tons of rocket fuel, it's not trivial but it's something less than 5% of one year's current CO2 emissions, and we're talking about spreading it out over a couple decades.

sp332 9y ago

This is addressed in the paper. It's even addressed in the abstract of the paper. Edit: Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. The paper says that if there are rockets involved, they will be used outside of the atmosphere.

robotresearcher 9y ago
> It's even addressed in the abstract of the paper. Where? edit: located below (italics added) thanks. The environmental costs of launch are considered. I can't see the environmental impact of manufacture considered explicitly, though. Abstract: If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. The concept considered here is to block 1.8% of the solar flux with a space sunshade orbited near the inner Lagrange point (L1), in-line between the Earth and sun. Following the work of J. Early [Early, JT (1989) J Br Interplanet Soc 42:567–569], transparent material would be used to deflect the sunlight, rather than to absorb it, to minimize the shift in balance out from L1 caused by radiation pressure. Three advances aimed at practical implementation are presented. First is an optical design for a very thin refractive screen with low reflectivity, leading to a total sunshade mass of ≈20 million tons. Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. Third is an implementation of the sunshade as a cloud of many spacecraft, autonomously stabilized by modulating solar radiation pressure. These meter-sized “flyers” would be assembled completely before launch, avoiding any need for construction or unfolding in space. They would weigh a gram each, be launched in stacks of 800,000, and remain for a projected lifetime of 50 years within a 100,000-km-long cloud. The concept builds on existing technologies. It seems feasible that it could be developed and deployed in ≈25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time.
- Footkerchief 9y ago
  The issue being addressed: > The CO2 added to the atmosphere from burning 2 billion tons of rocket fuel cannot be negligible. The quote from the abstract that addresses it: > Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. More detail later in the paper: > Because of its enormous area and the mass required, shading from space has in the past been regarded as requiring manufacture in space from lunar or asteroid material and, thus, as rather futuristic. Here we explore quantitatively an approach aimed at a relatively near-term solution in which the sunshade would be manufactured completely and launched from Earth, and it would take the form of many small autonomous spacecraft (“flyers”).
- snakeboy 9y ago
  The quote from the parent comment is about halfway through the abstract you just quoted...

grinich 9y ago

Certainly not negligible, but it's only about 5% of our total annual carbon emissions. https://mobile.nytimes.com/2017/06/26/climate/carbon-in-atmosphere-is-rising-even-as-emissions-stabilize.html https://mobile.nytimes.com/2017/06/26/climate/carbon-in-atmo...

wcoenen 9y ago

To make carbon-neutral rocket fuel, synthesize methane from CO2[1] that is extracted from the air. Both SpaceX[2] and Blue Origin[3] are currently developing methane-fueled rocket engines. [1] https://en.wikipedia.org/wiki/Sabatier_reaction https://en.wikipedia.org/wiki/Sabatier_reaction [2] https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) [3] https://en.wikipedia.org/wiki/BE-4 https://en.wikipedia.org/wiki/BE-4