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posted by janrinok on Saturday November 29 2014, @04:14AM   Printer-friendly
from the but-I-still-can't-say-his-name dept.

As a follow-up to the "poop-powered bus", the Univerity of Florida claims:

GAINESVILLE, Fla. --- Buck Rogers surely couldn’t have seen this one coming, but at NASA’s request, University of Florida researchers have figured out how to turn human waste -- yes, that kind -- into rocket fuel.

Adolescent jokes aside, the process finally makes useful something that until now has been collected to burn up on re-entry. What’s more, like so many other things developed for the space program, the process could well turn up on Earth, said Pratap Pullammanappallil, a UF associate professor of agricultural and biological engineering.

[...]“We were trying to find out how much methane can be produced from uneaten food, food packaging and human waste,” said Pullammanappallil, a UF Institute Food and Agricultural Sciences faculty member and Dhoble’s adviser. “The idea was to see whether we could make enough fuel to launch rockets and not carry all the fuel and its weight from Earth for the return journey. Methane can be used to fuel the rockets. Enough methane can be produced to come back from the moon.”

Abstract can be found here, along with the paywalled full research paper.

Related Stories

Bus Powered by Human Poop Begins Service this Week in UK 24 comments

El Reg reports

[The week of November 23,] punters [traveling] between Bristol and Bath will be able to ride on a bus ultimately powered by human poo, the first ever such service in the UK.

The 40-seater "Bio-Bus" will run up to two times a day and is expected to carry around 10,000 passengers a month by tour operator Bath Bus Company. It can travel up to 300km on a full tank of pressurised methane, which is produced from the equivalent annual waste of five people.

The Bio-Bus will be powered by people living in the area "including quite possibly those on the bus itself," said Mohammed Saddiq, GENeco general manager - the company which generates the biomethane gas that will fuel the service. This is done at the Bristol sewage works.

[...]17 million cubic metres of biomethane is generated a year at the Bristol plant. GENeco said this could power 8,300 homes, though in fact most of it is used to power the treatment plant itself. However there is a surplus of biogas left over for projects such as the Poo Bus.

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  • (Score: 2) by Jeremiah Cornelius on Saturday November 29 2014, @04:19AM

    by Jeremiah Cornelius (2785) on Saturday November 29 2014, @04:19AM (#121026) Journal

    In the house.

     

    Now that we've gotten that over, carry on!

     

    --
    You're betting on the pantomime horse...
    • (Score: 0) by Anonymous Coward on Saturday November 29 2014, @09:47AM

      by Anonymous Coward on Saturday November 29 2014, @09:47AM (#121061)

      Ok... I guess I can call my morning toilet visit my "hour of power".

  • (Score: 2) by novak on Saturday November 29 2014, @04:47AM

    by novak (4683) on Saturday November 29 2014, @04:47AM (#121029) Homepage

    Methane is a pretty good rocket fuel, and without paywall access I can only assume they are talking about using it as the only fuel.

    The thing is, you can make almost anything burn in the presence of an oxidizer like pure oxygen. Things like plexiglass and salami have been used to make so-called hybrid rockets, which have a solid fuel grain with a port that the oxidizer is blown through. I was originally envisioning a solid fuel grain made out of logs...

    --
    novak
    • (Score: 4, Informative) by gman003 on Saturday November 29 2014, @06:09AM

      by gman003 (4155) on Saturday November 29 2014, @06:09AM (#121041)

      I've been thinking about it ever since SpaceX announced they're going to use it on the Raptor, and more and more it seems like a brilliant idea that's obvious in retrospect (SpaceX isn't the first one to do this, but it is a pretty recent development).

      Rocket performance is governed by two equations. The first is for thrust - F=M*Ve. So a heavier exhaust molecule will give more thrust than a lighter one, at the same exhaust speed. The second is for specific impulse (efficiency per fuel mass), Isp = Ve/G, once again proportional to the exhaust velocity.

      However, exhaust velocity is in turn proportional to the combustion temperature and exhaust mass (other factors apply, but those dominate), and temperature is bound mostly by material science at this point. So with the same temperature, you can get either an inefficient, high-thrust rocket by using heavier exhaust, or a more efficient, low-thrust rocket by using a lighter exhaust. That's why solid rockets are generally used in the lower atmosphere, where thrust really matters but efficiency doesn't. Those have a lot of heavy atoms involved, like aluminum, which gives them a pretty huge amount of thrust. Deep-space rockets, where efficiency is everything and low thrust doesn't matter because you can just run the engines longer, tends to use hydrogen, the lightest element there is.

      Most LH2+LOX rockets actually run with excess LH2 - there's some hydrogen just going through the combustion chamber, being heated up and exhausted, without actually burning to water. Semi-famous rocket scientist John Clark once joked that if it were possible to keep monatomic hydrogen stable, and then "burn" H+H=>H2, you would get the most efficient rocket possible. Sadly, that isn't possible.

      LH2 does have some drawbacks - an extremely low density, and a need for heavy insulation on the tankage. Most LH2+LOX rockets actually run with less excess hydrogen than the theoretical ideal, because the mass of the extra tankage would balance out the efficiency increase.

      Methane hits a very good compromise. With only one carbon to four hydrogens, it's a very hydrogen-rich hydrocarbon compared to RP-1 (which is about 1:1 on a molar basis). Yet it achieves far higher densities, and does not require as much insulation as LH2 (-160C, compared to -180C for LOX and -250C for LH2). With the tankage advantage, it might even be more efficient (in terms of dV) than LH2, even in orbit. Considering how much hype diborane got as a rocket fuel/additive, and how that has a slightly *worse* mass-per-hydrogen ratio than methane, I'm surprised it took this long to start seriously looking at methane. Oh, and it's cheap, too - maybe not as cheap as RP-1, but cheaper than LH2 for certain.

      I can't see any downsides with recycling astronaut's waste into methane for rocket fuel. Sure, you'll need to carry oxidizer for it, but you were going to need that anyways. For truly long-term missions, this basically turns the food supply into the fuel supply, with astronauts as a "preburner" of sorts.

      • (Score: 5, Informative) by novak on Saturday November 29 2014, @06:58AM

        by novak (4683) on Saturday November 29 2014, @06:58AM (#121044) Homepage

        Yeah, methane is ok. I think the real reason that solid fuel rockets are so common is more simplicity than thrust. Conceptually, rockets are not much more complex than a bomb to comprehend, but it can still be very hard to build them. Liquid fuel rocket engines require extreme turbopumps to supply them with fuel and must also be able to maintain stable combustion. How to force combustion stability is far from a solved problem. The F1 (Saturn V's larges engine) was designed by actually detonating small bombs in different areas and measuring how well the resulting instabilities were damped out.

        The difference between a good LO2+LH2 engine and a solid fuel booster in terms of efficiency is about two, the solid fuel rocket weighing in around 200, and the liquid around 400. So that literally means that if it costs $5000 per lb to get to orbit, you could cut that in half with a liquid fuel rocket. That would be WELL worth doing, but it's not simple and it's certainly not cheap to build liquid fuel engines, so you wind up spending the money you saved on fuel on engines. It's also less reliable, although solid fuel rockets are actually kind of comically easy to damage.

        Something actually be pretty great is making a hybrid methane rocket. Hybrid rockets have notable advantages in safety (compared to both solid and liquid) and simplicity (as compared to liquid rockets). They usually come out between the two in terms of efficiency, but typically suffer from very low thrust, around an order of magnitude lower than a comparable solid fuel rocket. This is essentially because the mass flow rate is driven by the rate at which the surface of the fuel can be burned up as the oxidizer flows over it. Somewhat less typical solid fuels like frozen methane can burn faster because they melt and vaporize, allowing much more rapid mixing and higher thrust. If I were at home I'd dig up my copy of "fundamentals of hybrid rocket propulsion" and quote you actual numbers, but for now you'll just have to trust me anecdotally (or scour the internet, if you prefer). I'm not specifically familiar with methane but paraffin is a tamer favorite among hybrids that melts, and a good paraffin GOX engine can result in comparable thrust to a solid ammonium perchlorate solid fuel engine, though it would typically be a little lower.

        --
        novak
        • (Score: 1) by khallow on Saturday November 29 2014, @04:02PM

          by khallow (3766) Subscriber Badge on Saturday November 29 2014, @04:02PM (#121130) Journal

          The difference between a good LO2+LH2 engine and a solid fuel booster in terms of efficiency is about two, the solid fuel rocket weighing in around 200, and the liquid around 400. So that literally means that if it costs $5000 per lb to get to orbit, you could cut that in half with a liquid fuel rocket.

          There are three very important things to note here. The efficiency is for vacuum not Earth's surface. In practice, one can achieve about 50-70% better efficiency in one atmosphere of pressure from the liquid propellant engine than the solid fuel motor (due I gather to the larger chamber pressure of the latter).

          Second, efficiency is a matter of the net exit velocity of the engine (the numbers you quote are typical specific impulse (ISP) numbers with dimension inverse second (s^(-1)), multiply by the acceleration of Earth (9.8 m/s^2) to get actual exhaust velocities). There are other important factors such as thrust/weight. Solid fuel motors tend to have better thrust to weight ratios. That means such a rocket can expend less thrust countering the pull of gravity. Gravity losses are a significant loss in rockets launching from Earth's surface (but not an object that is already in freefall).

          Third, cost is not at all proportional to ISP. Having double the ISP means that you can move, for the same mass fraction (final "dry" mass divided by original, fueled or "wet" mass) expended, double the delta v which can for very low mass fractions result in a huge difference. For example, if a certain delta v yields 10% dry mass, then halving the delta v yields a final dry mass of 1% (think of it as having to stack two rockets one on the top of the other, each with 10% dry mass and the entire second fueled rocket being the complete dry mass of the first rocket). You can have a vastly higher cost per kg of payload, if the delta v is high enough.

  • (Score: 0) by Anonymous Coward on Saturday November 29 2014, @04:52AM

    by Anonymous Coward on Saturday November 29 2014, @04:52AM (#121031)

    How long until we can use actual humans to power machines...

    ... so that finally some humans on this planet have a worthwhile purpose and ACHIEVE

    Yes, I do work in IT with substandard performers. Why do you ask?

  • (Score: 2) by bradley13 on Saturday November 29 2014, @11:47AM

    by bradley13 (3053) on Saturday November 29 2014, @11:47AM (#121075) Homepage Journal

    There seems to be a whole slew of these stories in recent times. This is all nothing new: anaerobic fermentation of biological waste produces methane. This has been known since the first bubble swamps were observed, and there are plenty of viable approaches to controlling the process.

    "We were trying to find out how much methane can be produced from uneaten food, food packaging and human waste"

    Just ask any biogas producer and get your answer. The only difference here is, perhaps, the precise mix of materials.

    They haven't done anything along the lines of producing a compact, self-contained processing unit, or talked about capturing and compressing the gas, or indeed solved any of the other difficult problems that would be required for actual use in space.

    Sorry, this is just as unimpressive as the "poop bus"...

    --
    Everyone is somebody else's weirdo.
  • (Score: 2) by wonkey_monkey on Saturday November 29 2014, @03:34PM

    by wonkey_monkey (279) on Saturday November 29 2014, @03:34PM (#121122) Homepage

    ...so get your ass to Mars.

    --
    systemd is Roko's Basilisk
  • (Score: 2) by arslan on Sunday November 30 2014, @09:42PM

    by arslan (3462) on Sunday November 30 2014, @09:42PM (#121330)

    Haven't read the summary or the article yet, but lets talk about getting my shit up to space!