3 ms·

My friend was wondering why we don’t use ATP as rocket fuel? You can’t get any better than the energy currency of the cell.

comicjk 7y ago
Yes, you can, much better in fact. ATP makes sense in the specific context of the inside of cells, but it doesn't compare to e.g. methane + liquid oxygen in terms of cost or performance.
ethbro 7y ago
Think about it this way: are cells in the business of needing the maximum amount of energy per volume / weight, at the expense of explosive instability? Or would the be better off making a trade off for less efficient performance in exchange for more stability and biocompatibility?
caf 7y ago
Ignition! devotes an entire chapter (Chapter 7) to the topic of propellant performance. One crucial point is that you are aiming for as high an exhaust velocity as possible, and that means that all else being equal you want exhaust products with both a high heat of formation and low molecular weight. It's not just about the energy balance (not that ATP is particularly outstanding on that measure anyway).
thereisnospork 7y ago
> You can’t get any better than the energy currency of the cell. laughs in FOOF https://blogs.sciencemag.org/pipeline/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride https://blogs.sciencemag.org/pipeline/archives/2010/02/23/th... biochemical compounds suffer from all sorts of annoying limitations which stem from being made by a living creature (such as not turning aforementioned living creature into a cloud of steam.)
yetihehe 7y ago
I briefly remember April Fools article about using pure adrenaline as a rocket fuel. Comparative tests suggested it's so potent, that just the amount of adrenaline produced by astronauts during launch could lift whole rocket 4m off the ground.
jcranmer 7y ago
ATP is closer to a battery than a fuel. Most enzymes use an ATP->ADP+P step to deliver energy, so the respiration process in the mitochondria produces ATP from ADP+P. The actual biological fuel is glucose, and the oxidation of glucose in successive stages is turned into usable energy.

comicjk 7y ago

Yes, you can, much better in fact. ATP makes sense in the specific context of the inside of cells, but it doesn't compare to e.g. methane + liquid oxygen in terms of cost or performance.

ethbro 7y ago

Think about it this way: are cells in the business of needing the maximum amount of energy per volume / weight, at the expense of explosive instability? Or would the be better off making a trade off for less efficient performance in exchange for more stability and biocompatibility?

caf 7y ago

Ignition! devotes an entire chapter (Chapter 7) to the topic of propellant performance. One crucial point is that you are aiming for as high an exhaust velocity as possible, and that means that all else being equal you want exhaust products with both a high heat of formation and low molecular weight. It's not just about the energy balance (not that ATP is particularly outstanding on that measure anyway).

thereisnospork 7y ago

> You can’t get any better than the energy currency of the cell. laughs in FOOF https://blogs.sciencemag.org/pipeline/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride https://blogs.sciencemag.org/pipeline/archives/2010/02/23/th... biochemical compounds suffer from all sorts of annoying limitations which stem from being made by a living creature (such as not turning aforementioned living creature into a cloud of steam.)

yetihehe 7y ago

I briefly remember April Fools article about using pure adrenaline as a rocket fuel. Comparative tests suggested it's so potent, that just the amount of adrenaline produced by astronauts during launch could lift whole rocket 4m off the ground.

jcranmer 7y ago

ATP is closer to a battery than a fuel. Most enzymes use an ATP->ADP+P step to deliver energy, so the respiration process in the mitochondria produces ATP from ADP+P. The actual biological fuel is glucose, and the oxidation of glucose in successive stages is turned into usable energy.