Energy. on this world and elsewhere. Instructor: Gordon D. Cates Office: Physics 106a, Phone: (434)

Transcription

1 Energy on this world and elsewhere Instructor: Gordon D. Cates Office: Physics 106a, Phone: (434) Course web site available at click on classes and find Physics or at Lecture #27 May 3, 2016

2 Announcements Last quiz Similar in format to the most recent quiz, 25 questions, multiple choice. Will have several questions requiring small calculations. Sample/practice problems will be provided in the review sheet. Material will emphasize stuff not already covered, again will be spelled out on the review sheet.

3 Final Paper Announcements Four to five pages, style along the lines of a briefing. In other words, you already have the persons attention. You can imagine your audience, but be clear who that is. Choose a particular primary energy source, or one of several suggested topics. Choose one or two issues related to that source/topic. Develop a solution(s) to the issue, which could include the possibility of phasing something out (such as fracking, synthetic crude from tar sands, etc.).

4 Short/Medium-term reasons to develop space Orbiting solar power stations Mining Asteroids (at least two companies already exist) Valuable metals such as gold, platinum, silver, iridium and others. Other elements that are in limited supply such as rare earth s Water, that could be converted into rocket fuel (hydrogen and oxygen) to enable refueling without launching fuel from the Earth. Space manufacturing where zero-gravity is an advantage. Eventually make satellites in space? Colonization

5 Video from the company Planetary Resources

6 Issues when living in space Artificial gravity - probably necessary for long-term habitation. Radiation shielding - important issue for anything other than low-earth orbit. Space manufacturing - probably unavoidable once commercialization becomes truly large scale.

7 Artificial gravity Spin the spacecraft so that the centrifugal force causes artificial gravity. If you ve ever been on certain amusement park rides, you know this is not always a good idea. Quote from O Neill s book.

8 Artificial gravity in the movie 2001 Something as small as this would need to spin way too fast. If we assume a 10 meter radius, the period of rotation would be around 6 seconds.

9 O Neill s Island One Spherical living space is one mile in circumference (radius of around 256 meters). If spun with a rotation period of 30 seconds, the artificial gravity would feel like earth s along the equator. Living space is shielded against radiation. Agriculture conducted in unshielded toruses. Zero-g industry at each end. Solar collectors provide energy. Radiators dissipate excess heat. So something around 250 meters is the smallest size that is safe against motion sickness.

10 O Neill s Island One Would house around 10,000 people

11 Constructing Island I Mass ~ 3 x 10 9 kg Mass of USS George Washington (Aircraft carrier): 1.1 x 10 6 kg Island I is x28 bigger!!! From the surface of the Earth Days of Oil = (251 MJ/kg)(3x10 9 kg) (6000 MJ/barrel)(19x10 6 barrels/day) = 6.6 days From the surface of the Moon Days of Oil = (7.1 MJ/kg)(3x10 9 kg) (6000 MJ/barrel)(19x10 6 barrels/day) = 0.19 days = 4.5 hours Even launching from the Earth s surface, at $100/barrel, the cost would be $12.5 billion. Clearly, energy is not the dominant cost for constructing something like Island I.

12 Cost of Constructing Island I Mass ~ 3 x 10 9 kg Mass of USS George Washington (Aircraft carrier): 1.1 x 10 6 kg Island I is x28 bigger!!! Cost of oil, if sending everything up from the Earth: $12.5 Billion Cost using current market price for payloads heading to GEO: $180 Trillion Cost if payload costs go down by factor of 100: $180 Billion Maybe launching from the moon isn t so crazy. Need to imagine a whole new way to develop extraterrestrial construction projects, perhaps self-replicating construction robots?

13 The Stanford Torus Diameter of 1.9 km This gives a rotation period of 1 minute for 1 g (Earth gravity) Was imagined to house between 10,000 and 140,000 inhabitants. One of many ringshaped space stations imagined over the years.

14 Inside the Stanford Torus

15 What limits the size of space colonies with artificial gravity? Answer: tensile strength Required tensile strength = Radius x (density of material) x g artificial The strength of the material out of which the space habitat is constructed rises linearly with the radius of the spinnig structure.

16 What limits the size of space colonies with artificial gravity? Island Three contains two cylinders, each with a diameter of 4 miles (radius of 3,220 m) and a length of 20 miles. land area up to 250 mi 2!! Required Tensile strength = 3,220 m 2710 kg/m m/s 2 = 86x10 6 N/m 2 Density of aluminum Acceleration of gravity on earth Aluminum starts to deform around 95x10 6 N/m 2 - still (marginally) possible with Al!

17 What is the most the human race might be able to do to provide itself with energy?

18 Paper by Freeman Dyson in Science, vol. 131, pg (1960)

19 Paper by Freeman Dyson in Science, vol. 131, pg (1960) Dyson then examines the available energy (that coming from the star), the available material (he considers the mass of Jupiter as being typical), and the time it would take, from an energy perspective, to disassemble Jupiter and rearrange the solar system. He then concludes that:

20 Paper by Freeman Dyson in Science, vol. 131, pg (1960)

21 Paper by Freeman Dyson in Science, vol. 131, pg (1960)

22 Dyson Spheres A solid spinning object would tear itself apart. Instead, a system of many orbiting objects could be used.

23 Dyson Spheres have inspired science fiction... Larry Niven s Ringworld, spinning to achieve artificial gravity, would actually not work. A system of objects, however, could be feasible.

24 Even Star Trek episodes... This is a YouTube clip of a Star Trek episode along with some commentary...

25 Dyson Spheres Dyson himself states: I do not argue that this is what will happen in our system; I only say that this is what may have happened in other systems.

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27 So... is there a moral to this (Physics 1110) story?

28 Society grew through the industrial revolution using cheap energy from coal, oil, and more recently, natural gas.

29 The fossil fuels are scarcer now, and we should expect prices to fluctuate, but ultimately climb quite high.

30 The time scales over which fossil fuels will become expensive is unclear, and depends on many factors. Regardless of price, we are paying a steep environmental price for the continued use of fossil fuels, and this is true independent of global warming

31 There is a huge amount of energy available in our solar system if we develop the technology to harness it. The times scales for this are long, so we should start now.

32 I truly believe that history will judge this time period by how we deal with the issue of shifting our energy infrastructure, and the way in which it impact our planet.

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