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 #25 November 21, 2017

2 Energy Elsewhere

3 There are many reasons to go into space Satellites, for many applications: communications, entertainment, GPS, surveillance, telescopes. Resources, such as those found on so-called Near Earth Asteroids or NEAs. Solar power stations. Exploration and science Planetary defense: deflecting would-be meteor strikes. Expanding humankind s presence in the Universe. Surviving as a species is something happens to the Earth?

4 Lest you think I was kidding about planetary defense!

5 Gerry O Neill s vision for space utilization Space habitats Mining off planet and mass drivers

6 Gerard O Neill invented the modern collider used in particle physics Fermilab, near Chicago, the Large Hadron Collider, or LHC at CERN are both examples

7 From NYT in 2009

8 More recent plans to build space-based solar power stations Note date of 24 April IEEE is a main-stream organization for electrical engineers. Just because they have plans does not mean they will follow through. Even so, it shows the ideas are real and being seriously explored.

9 So.. why is it hard to get up into space?

10 So.. why is it hard to get up into space? The answer?, the Earth s gravity, and just getting to low Earth orbit, or LEO is the hardest part.

11 Putting things in low Earth orbit (LEO) This is a problem that was considered by Newton... For one thing, they must be going fast enough that as they fall, they follow a circular path.

12 How fast is fast enough? For example, the International Space Station, which orbits at about 250 miles above the Earth s surface, travels at around 17,150 mph.

13 SpaceX Falcon 9 Resupply of the International Space Station Notice that mostly, the payload is boosted sideways, NOT up!

14 SpaceX Falcon 9 Resupply of the International Space Station Notice that mostly, the payload is boosted sideways, NOT up!

15 Dragon Capsule arrives at ISS from same mission The Dragon Capsule is the only commercially built spaceship that can reenter the Earth s atmosphere and return cargo.

16 Dragon Capsule arrives at ISS from same mission The Dragon Capsule is the only commercially built spaceship that can reenter the Earth s atmosphere and return cargo.

17 Why is landing the Grasshopper much easier than landing a booster? Answer? SPEED!!! The Grasshopper was not reentering the atmosphere from an altitude of 80 km (50 miles) at Mach 10!

18 Why is landing the Grasshopper much easier than landing a booster? Answer? SPEED!!! The Grasshopper was not reentering the atmosphere from an altitude of 80 km (50 miles) at Mach 10!

19 Strategy for soft-landing of booster stage ~Mach 10 ~6000 mph ~10,000 km/hr Note the key is getting RID if speed, which requires lots of energy (and thus engine burns).

20 Historic event: the first stage of CRS lands softly at Cape Canaveral This is the first time a rocket has delivered satellites into orbit, and then returned to land at the point from which it took off.

21 Historic event: the first stage of CRS lands softly at Cape Canaveral This is the first time a rocket has delivered satellites into orbit, and then returned to land at the point from which it took off.

22 Landing on a drone ship at sea

23 Landing on a drone ship at sea

24 The view from the booster

25 The view from the booster

26 So what are we talking about for an orbiting solar power station? Assume we want 1 GW (109 Watts) of power generation. In space, the sun shines 24/7, so we take Intensity = 1,400 W/m2 Area = Power efficiency x Intensity Area = 10 9 Watts 0.20 x 1,400 W/m 2 = 3.6x10 6 m 2 = 1.9 km x 1.9 km So a 1 GW power generating station would need a collection area of roughly 2 kilometers by 2 kilometer... that is pretty big! (at least for space)

27 Consider the scale of the International Space Station (ISS) 109 meters A square array would be 20 times the width (400 times the area) of the ISS. The construction crew required would be way too large to live on the ISS. The ISS cost over $100 Billion, so..

28 FYI You can see the ISS from Charlottesville! Just google spot the station and the first hit brings you to an interactive website where you can get up-to-date observation info

29 So how much energy per kg? Energy = ½mv 2 Energy per unit mass = ½mv 2 /m E/kg = ½v 2 = ½(7.9 x 10 3 m/s) 2 E/kg = 31.2 x 10 6 J/kg This is for an orbit essentially skimming the Earth s surface.

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