Energy and Human Ambitions on a Finite Planet, 2021a

4 Space Colonization 66
Americans get to space on Russian rockets. How believable do
you think they would be, <strong>and</strong> what assumptions might be made
to reconcile the shock?
12. Prior to exposure to this material, what would you honestly have
said in response to: How far have humans been from the planet in
the last 45 years;
a) 600 km (about 1
10
Earth radius; low earth orbit)
b) 6,000 km (roughly Earth radius)
c) 36,000 km (about 6 R ⊕ ; around geosynchronous orbit)
d) 385,000 km (approximate distance to the moon)
e) beyond the distance to the moon
Explain what led you to think so (whether correct or not).
13. List at least three space achievements that impress you personally,
even if they do not bear directly on colonization aims.
14. In the enumerated list beginning on page 60, which item is most
surprising to you as not-yet accomplished, <strong>and</strong> why?
15. List three substantive challenges that prevented successful longterm
operation of the artificial biosphere project [31].
[31]: (2020), Biosphere 2
16. Since Figure 4.5 spans the range of atmospheres found in our solar
system, we can imagine how likely it would be that a r<strong>and</strong>om
planet might happen to be livable for humans. 32 Imagine throwing
a dart at the diagram to get a r<strong>and</strong>om instance. How likely are we
to hit the comfort zone of Earth, by your estimation?
32: . . . just in terms of temperature <strong>and</strong>
pressure; ignoring composition <strong>and</strong> a host
of other considerations!
17. Come up with three examples (not repeating items in the text) of
feats that are technically possible, but not common or practical.
18. For some perspective, imagine you were able to drive your car
up a ramp to an altitude characteristic of low-earth orbit (about
320 km, or 200 miles). It takes about 5 × 10 10 J of energy 33 to win 33: We’ll encounter gravitational potential
energy later, but this quantity is computed
as mgh with m ≈1,500 kg.
the fight against gravity. Meanwhile, each gallon of gasoline can
do about 25 × 10 6 J of useful work. How many gallons would it
take to climb to orbital height in a car? Roughly how many miles
per gallon is this (just counting vertical miles)?
19. In Problem 18, we ignored the energy required to provide the
substantial orbital speed (∼ 8 km/s, but will not need), which
essentially doubles the total energy. 34 How much gasoline will it
now take, <strong>and</strong> how massive is the fuel if gasoline is 3 kg per gallon,
compared to the 1,500 kg mass of the car?
34: The same amount of energy to climb
against gravity must go into accelerating to
speed (kinetic energy).
i Given this mass of fuel, <strong>and</strong> its significance
compared to the car’s mass, we can
see that we’ve underestimated the fuel required
since we’ll have to put substantial
additional energy into lifting the fuel away
from the earth.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.