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In season 1 of the 2018 Lost In Space Series which aired on Netflix the last Episode has the Robinson family using the by-products of living beings (faeces) as biofuel. If we were to use the same thing, i.e convert human and animal waste into rocket propellant, could we then propel our rockets to space?

  • If so, how much raw materials and biofuel would've been required?

  • If not then why? What would be the obstacles?

  • Might this also help deal with sewage problems?


not the original Lost in Space

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    $\begingroup$ The V2 rocket of WWII used alcohol as fuel, potatos were fermented and distilled. $\endgroup$ – Uwe Jan 31 at 13:30
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    $\begingroup$ Though i'm not going to cobble together an answer, I will point out that poop is full of useful organic chemicals that your ecological life-support system would like; an important thing if you're on a space craft with no opportunities for resupply for an indefinite time. Lots of other places to get fuels, oxidisers and reaction mass in space, but getting manure is quite a lot more challenging! $\endgroup$ – Starfish Prime Jan 31 at 15:58
  • $\begingroup$ I don't watch TV these days and I was confused at first because the first season of Lost In Space ended in 1966 and back then they didn't talk about poop during prime time TV, though I'm sure it got obliquely referred to in jokes on late night TV (e.g. Johny Carson). I made a few small edits to your post, I hope you don't mind. $\endgroup$ – uhoh Feb 25 at 0:31
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First, Season 1 of Lost In Space:

In episode 9, the protagonists discover that their spaceship can be fueled with "petrified biomass" which has built up over hundreds of years in the cave. If I remember correctly, there was also some 'secret ingredient' that made this specific bat guano from that specific cave have the right minerals or chemicals in it or whatever. Point is, Lost in Space is not really science fiction but rather science fantasy (a fantasy story with a spaceships/future setting).

Secondly, using biomass as fuel for rockets:

When talking about fuel, specific energy is a very important metric. Certain things, such as jet fuel or coal have a high specific energy density that they contain a lot of potential energy per unit mass. That's why these are used in power plants and engines.

Some specific examples from Wikipedia:

  • Jet Fuel: 43 MJ/kg
  • Coal: 30 MJ/kg
  • Dried cow dung: 15 MJ/kg
  • Ethanol: 30 MJ/kg
  • Biodiesel: 42 MJ/kg
  • Glucose: 15 MJ/kg
  • Liquid Methane: 55 MJ/kg
  • Liquid Hydrogen: ~130 MJ/kg
  • Uranium: 80620000 MJ/kg
  • Deuterium: 579000000 MJ/kg

As you can see, dried dung doesn't have that much specific energy (comparatively), and this makes sense if you think about it: Creatures eat food to consume energy and excrete that which they can't extract energy from. Evolutionary, a creature which doesn't extract as much energy as possible from it's meal is at a disadvantage.

Unless the "petrified biomass" somehow contained a high amount of radioactive isotopes, there is no fuel which could power the ships as it does in the show. Real spaceships (capable of launching from an Earth-like planet) are usually >90% fuel by volume and mass. In the show, fuel tanks are a small part of the spaceship and the spaceships are clearly able to hover and preform SSTO maneuvers with ease. Something like that requires advanced nuclear technology or clarke-tech (magic).

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    $\begingroup$ The old rocket fuel alcohol should be mentioned too. $\endgroup$ – Uwe Jan 31 at 13:30
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    $\begingroup$ Most of rocket mass is actually oxidizer. And guano contains nitrates, which are often precursors to some common oxidizers, so that's probably the (remote) source of the idea. But in general, yes, specific energy is a good way at looking what is possible and what is not. (OTOH if the ship contained a good source of energy, say, fusion, but required reaction mass, waste products would work as well as anything.) $\endgroup$ – SF. Jan 31 at 14:58
  • $\begingroup$ @SF. that's a bunch of BS (humor!) I'm trying to figure out if there is a new question possible here or in Chemistry SE about nitrates and hydrocarbons, but asking anything touching on fertilizer and energetic reactions might raise some eyebrows. What a load of guano: 5 facts you didn't know about bird poop $\endgroup$ – uhoh Feb 25 at 3:08
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The way it was done in lost in space was pure science fiction as their engine technology is totally different, and that plot aspect was never really explained, so it's really a plot device (not that there's anything wrong with that, I'm not above doing it myself).

In reality it is possible to create biofuel from waste, for example:

  • Collecting Methane from cattle farms and landfill. This is a gas, so it's not a convenient rocket fuel as it isn't that dense but there are designs to use it in cryogenic form. There are also processes which can change gas fuels to liquid ones. This was done by Germany in WWII to convert natural gas into aviation and other fuels as they lacked sufficient access to oil fields. These methods are expensive and inefficient, but they do work
  • HydroThermal Liquifaction (HTL) can take wet sewage and using high heat and pressure create a "bio-crude" which can be refined into biodiesel or other fuels. Biodiesel is very similar to kerosene, which is used as a rocket fuel, so it is viable. In practice this is still under development

So actual rocket fuel from waste is entirely possible. Oxidizer on the other hand is a different story.

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  • $\begingroup$ There are various methane-fuelled rocket designs about. It can be used as-is, but I think it is somewhat inconvenient to store compared to other hydrocarbon fuels. $\endgroup$ – Starfish Prime Jan 31 at 14:13
  • $\begingroup$ Thanks for pointing that out @StarfishPrime, I've edited accordingly. $\endgroup$ – GdD Jan 31 at 14:19
  • $\begingroup$ Liquid oxygen separated of air is bio oxygen if you use bio fuel to operate your air separation plant. Plants made all the oxygen in the air. $\endgroup$ – Uwe Jan 31 at 14:59
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    $\begingroup$ I don't want none of that bio-oxygen @Uwe, we should get it from Texaco like god intended! $\endgroup$ – GdD Jan 31 at 15:05

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