Wednesday, March 06, 2013

TO URANUS




The giants guard vast hoards of treasure....

...but if you get too close, they will crush you!!!

Of these four great giants,
Uranus is probably the most hospitable.

Discovered by Herschel. Uranus is the seventh planet from the Sun and the third-largest and fourth-most massive planet in the solar system. Sir William Herschel discovered it on March 13, 1781; this was the first discovery of a planet with a telescope.
Named by Bode. Since Herschel discovered this planet, he considered naming it after his sponsor, King George III. However, Johann Bode (recall Bode's Law), suggested "Uranus", the mythological father of Saturn and grandfather of Jupiter.
Naming the Moons. 
In 1851, Herschel's son Sir John Herschel had became a well known astronomer; and he gave the four then-known moons their current names. He departed from traditional mythological names and turned to the works of Shakespeare and Pope. He named Titania and Oberon (spotted by William Herschel on March 13, 1787) for the king and queen of the fairies from Shakespeare's "A Midsummer Night's Dream". Ariel and Umbriel (discovered by William Lassell in 1851) were spirits in Pope's "The Rape of the Lock". In 1948, Gerard Kuiper (recall Kuiper Belt) discovered Uranus's last large moon and named it Miranda from Shakespeare's "The Tempest". Uranus has 27 known natural satellites. Orbit Uranus revolves around the Sun once every 84 Earth years with an average radius of about 20 AU.
Axial Tilt Differs
 Perhaps the most unusual feature is its axis of rotation. Unlike any other planet, Uranus lies on its side with an axial tilt of 98 degrees with respect to the plane of the solar system. Other planets rotate like tilted spinning tops; however, Uranus rotates more like a tilted rolling ball. Why this strange axial tilt?? Some scientists speculate an Earth sized protoplanet collided with Uranus many eons ago.
Visible without a Telescope.
Though undiscovered til relatively recently in human history, Uranus is sometimes visible to the unaided eye. At opposition, Uranus is visible to the naked eye in dark, non-light polluted skies and becomes an easy target even in urban conditions with binoculars.
Size: Uranus' mass is roughly 14.5 times that of the Earth, making it the least massive of the giant planets, while its density of 1.27 g/cm³ makes it the second least dense planet, after Saturn.
Composition: Ice Uranus is made primarily of various ices, such as water, ammonia, and methane. The total mass of ice is between 9.3 and 13.5 Earth masses. Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses. The remainder of the mass (0.5 to 3.7 Earth masses) is rocky material.
Distinctive Color: Third most abundant element of the Uranian atmosphere is the hydrocarbon, methane (CH4) which give's Uranus its distinctive cyan color. [Most and 2nd most abundant elements are hydrogen and helium respectively.]
Planetary rings
Uranus has a faint planetary ring system, the second ring system to be discovered in the Solar System after Saturn's. William Herschel claimed to have seen rings at Uranus in 1789. During the centuries since, rings at Uranus had been largely discounted; however, recent discoveries indicate ironic agreement with his findings.
Visible Features
Uranus does have some distinct visible features, but much less then the other gas giants. One possible explanation is that Uranus' internal heat is much lower than other giant planets.
Bands in Southern Hemisphere. In 1986, Voyager 2 images showed the southern hemisphere of Uranus as two regions: a bright polar cap and dark equatorial bands with a boundary at about −45o latitude. The Southern Collar straddles the latitudinal range from −45o to −50o; it is the brightest large feature on the visible surface of the planet.
Dark Spot. Uranus's dark spot was first observed by ACS on HST in 2006.
Why go??
Uranus might be the best place in the solar system to get He3, a helium isotope. This substance is rare on Earth, but it's plentiful in the gas giants. If He3 became abundant on Earth, then fusion energy would become viable, and plentiful, "green" energy would become a reality. Primary Assumption - Economic Incentive. A significant factor for large scale interplanetary travel will be that He-3 will likely prove to be an economic incentive to travel to the gas giant planets of our Solar System. Sunlight will not provide sufficient power for habitats orbiting the outer planets such as Jupiter and beyond. Fortunately, the gas giants have gigantic reservoirs of He-3 which could then be used to power the same habitats which house the people mining He-3 from the gas giant atmospheres.
Energy and Value from He3
He-3 can combine with deuterium (H2, an isotope of hydrogen) to give off a proton and he-4 (normal helium) as well as a good energy return. This nuclear fusion reaction produces plentiful, "clean" energy without the hazardous side effect of neutron radiation common to other types of fusion reactions or other radioactive byproducts of today's fission-powered plants.
1 kg of helium-3 reacts with 0.67 kg of deuterium to yield about 19 megawatt-years of energy output. Thus, one boxcar of He3 (about 25 tons) would power the United States for an entire year (without the smog and acid rain). If all the electricity in the United States is $75 billion, the He3 can be valued at $3 billion per metric tonne or $3,000,000 per kg.

TABLE-1: Selected Fusion Sites

Other economic analysises compare He3 to oil . As an optimal reactant for a safe thermonuclear fusion process, He3's energy value in today's dollars is $5.7 million per kilogram when compared to the oil's energy potential.
Unfortunately, He-3 is extremely rare on Earth, but large quantities are needed to solve Helium-3 (He-3) is abundant on the lunar surface. However, there would be several problems with Luna as our primary source of He-3.
  • Concentration of helium-3 in the lunar regolith could be very low, perhaps one part in 100 million.
  • Constructing a conventional mine on Luna would require tremendous resources. Once completed, a Lunar mine would require constant maintenance. (See Mining the Sky... by John Lewis, p.137-141.)
  • Melting the regolith would likely require huge solar reflectors orbiting the moon. This begs the question: "Why not use the solar power directly?"
Therefore, Prof. Swindle says for a lot of He3; the best place won't be the moon: "The really big source is way out." In our quest for helium-3, we'll travel to the gas giants, whose helium-rich atmospheres are very similar in chemical composition to the sun.
Gas Giants
The biggest gas giants are Saturn and Jupiter. They are both closer then Uranus, and they definitely have much more He3. However, neither Saturn nor Jupiter would be the optimal choice; they both have huge masses with strong gravity with high escape velocities. Also, they are both very active planets with lots of radiation hazards.As for Neptune, it is similar in size as Uranus with similar escape velocity (slightly higher), but the Neptunian system is much farther then Uranus. (30 AUs vs. 20 AUs for Uranus).
Of the four gas giants, Uranus is much calmer with the lowest escape velocity. Disregarding travel time, Uranus is our first choice.

TABLE-2: Potential Helium-3 in Gas Giants

Planet
Dist.
to Sol
Planet Mass
Escape Velocity
Est'd Mass of Helium-3
Est'd Energy Capacity
He-3 from Uranus
Since Uranus has the lowest escape velocity of the four gas giants, it might be the optimal mining site for helium-3. Mining operations would require a mix of artificial intelligency and human activity. Thus, human settlements would be requirements. There are several alternatives for this.
  1. Uranus' natural satellites could serve as bases for human settlements.
  2. An alternative is to place floating cities in its atmosphere. By using gigantic balloons filled with hydrogen, large masses suspend underneath at roughly the Uranian altitude closest to Earth gravity.
  3. A more practical alternative would involve a habitat along the lines described by Dr. O'Neill, in his book, High Frontier. Such habitats could be manufactured in a near Earth, solar orbit, then moved to orbit in the Uranian system. Such habitats could be lived in and worked on during the trip. They could be very comfortable; a cylindrical habitat could even simulate gravity with the right amount of spin. They might need a supply of He3 and water to provide life support and plentiful energy.
(Earth=
1.0 AU)
(M = 1 Earth mass)
(Earth's e=11.2 km/sec)
(mT = metric Tonne)
(1 yr = Earth ann'l use)
Jupiter
5AU
318×M 
59.5 kps
350×1012mT
65×109 yr
Saturn
10AU
95×M
35.5 kps
104×1012mT
19×109 yr
Uranus
20AU
15×M
21.3 kps
16×1012 mT
3×109 yr
Neptune
30AU
17×M
23.7 kps
19×1012 mT
3.5×109 yr

Getting There
Current Technology vs. Achievable Technology.
Today, current technology spacecraft use transfer orbits to travel to Uranus or other planets for flight times of several years. Fortunately, transfer orbits don't require much fuel.  Unfortunately, their lengthy zero-g, flight durations are only practical to transport Artificial Intelligence (AI) entities (i.e., robots).
Achieveable technology could provide shorter duration, g-force flights.  A Manhatten Project type effort could readily achieve space borne, particle accelerators to produce constant acceleration to destinations throughout the Solar System; thus, humans could routinely travel to the planets within weeks or even days.
Current Technology
Hohlman transfers are a special case of transfer orbits (least fuel required). Following table uses the simple formula for Hohlman transfers to compute typical travel times from Earth's orbit to each of the giants.
AU = 149,597,870.7 km
tYr=(1+aAU)3/2

5.656
Current technology trips would take too long for any commercial enterprise to yield profitable results. Thus, trips to any of the gas giants will never become routine if travel times take years. Recurring travel by humans would have to concentrate on Jupiter in spite of the enormous dangers involved with Jupiter's very high gravity.
Dest.
Semimajor
Axis
Travel Time
Planet
AUs
kms
Days
Months
Years
Jupiter
5.2
777.9×106
997
32.8
2.73
Saturn
9.54
1,427.2×106
2,210
72.6
6.05
Uranus
19.18
2,869.3×106
5,855
192.4
16.03
Neptune
30.06
4,496.8×106
11,181
367.3
30.61
Observed
aAU
km/AU×aAU
tYr×365.26
tYr×12
tYr
Several Feasible Technologies for interplanetary travel are demonstrated in the movie "2001: a Space Odyssey". In this 1968 epic science fiction film by MGM (directed by Stanley Kubrick and written by both Kubrick and Arthur C. Clarke, eminent scientist and author), the ship, Discovery One, travels from Earth to Jupiter with two astronauts manning the ship and three scientists in cryogenic hibernation.Transporting humans for years inside a small vessel is overwhelmingly impractical (cryogenic or conscious). Even though the two astronauts had the famous HAL as a diversion (HAL was an onbound computer system which killed all but one of the onboard humans), 2.7 years (typical flight time to Jupiter) is way too long to live in a zero-g environment. The 16+ years to travel to Uranus would be out of the question. Spending years in cramped quarters at zero-g would be far worse then prison. Such a trip is feasible but not very practical.
However, practicality increases substantially for a vessel which offers Earth like gravity and comfortable living quarters for over a million occupants. Such a vessel, Class III Habitat, is described by O'Neill in his book, "High Frontier". In his book, "Mining the Sky", John Lewis describes how such enterprises can make handsome profits.

TABLE-4: DIFFERENT VALUES FOR G.

Different Units of g
g10 m/sec

sec
864 km/sec

day
0.5 AU/day

day
0.289%c

day
"km/sec" enables a direct comparison of ship's inflight velocity to escape velocities of Earth (11 km/sec) and other planets. Escape velocity for Uranus is about 21 km/sec
"AU/day" is convenient because distance to nearby planets is conveniently measured in AUs and g-force flight times will take days. "%c" reassures us that relativity is not a factor for g-force accelerated interplanetary flights. For example, ship doesn't reach one percent of light speed (1% c) until after three days of g-force acceleration.
For routine travel between Earth and gas giants, achieve a technology where interplanetary trip takes days versus decades. Given that extraordinary achievement, energy gathering enterprises could bypass Jupiter and Saturn and travel on to Uranus to for a more hospitable environment.
Accordingly, Thought Experiment (TE) assumes our spacecraft to constantly accelerate at g-force for extended periods. Thus, TE assumes for every second of powered flight, spacecraft applies sufficient propulsive force to increase velocity 10 meters per second.
For extended durations, it might become convenient to express the g value with different units. (See table at right.)
TE further assumes that space borne particle accelerators could provide the propulsion required for reliable g-force throughout extended flights. Since earth bound accelerators have been with us for many years, TE assumes such propulsion to be an achievable technology.


TABLE-5: G-FORCE FLIGHT PROFILE

Earth
Departure Leg
Uranus
Return Leg
Earth
Assume Phase Distance:
dP = 10 AU
Compute Phase Time:
tp=(2 × dP )

g
tp= (2 × 10 AU)

0.5 AU/day2
tp = 6.3 days
Compute Final Velocity:
VFin = g × tP
VFin = 864kps

day
×6.3days
VFin = 5,445kps
For Phases II and IV:
VFin = V0 - g × t
VFin  = 5,445kps - g × 6.3days
VFin = 0 kps

Phase 1
M

I

D

W

A

Y
Phase 2
Uranus
Phase 3
M

I

D

W

A

Y
Phase 4
End
dP
10 AU
10 AU
Dest
10 AU
10 AU
Return
tP
6.3 Days
6.3 Days
Dest
6.3 Days
6.3 Days
Return
VFin
5,445kps
0 kps
Dest
5,445kps
0 kps
Return


Departure
Phase I: Accelerate to Midway
Phase II: Decelerate to Dest.


Destination
Phase III: Accelerate
back to 
Midway
Phase IV: Decelerate
back to
Dept.

Return

DEPARTURE LEG
Ph. I: Accelerate to Midway: Constant acceleration rapidly increases speed at 864 kilometers per second (kps) per day.  If vessel accelerates for 6.3 days; then, velocity reaches an incredible 5,445 kps (almost 2% of light speed, .02c).
Ph. II: Decelerate from Midway to Destination: Vessel's enormous speed must decrease to accomplish mission at destination. To maintain g-force, absolute value of Phase II's deceleration must equal absolute value of Phase I's acceleration. Thus, keep same g-force but turn the vessel completely around to reverse direction of propulsive force.
RETURN LEG
Ph. III: Accelerate back to Midway: See Ph. I (above).  TE assumes achievable technology will create particle accelerator with capabiity to continue flow of high speed particles for as long as needed.
Ph. IV: Decelerate from Midway to Return to Departure: See Ph. II (above).  Reverse direction of propulsion vector by turning vessel 180°.
A transfer orbit to Uranus will take years.
If a trip takes years, we're compelled to go to closest destination (optimal or not) and deal with the situation as is. Thus, transfer orbits would compel us to try to get take our treasure from the closest but least hospitable gas giant, Jupiter. Perhaps there is a better way.
However, g-force propulsion can greatly reduce trip time; as short as 2 weeks.
For such a short duration, we can choose to bypass the two nearest gas giants and proceed directly to the most hospitable. TE assumes this to be the case, let's consider the Earth-Uranus mission a bit more closely.

TABLE-6: FUEL REQUIREMENT, %TOGW

Constant g-force throughout the flight requires a constant transformation of mass to energy.
Our thought experiment models this fuel consumption according to following assumptions.
1. Exhaust Particle's Velocity (VExh). Assume VExh to be .866c (86.6% light speed). At this relativistic speed, exhaust particle mass doubles from its original size at ingest.
2. Daily Difference (Δ). At the speed/size of these exhaust particles, previous work enables us to further assume one day of g-force acceleration requires fuel consumption of 0.166% of the spaceship's mass. Thus, Δ = 0.166%GW/day.
3. Efficiency Factor. Design flaws and peripheral energy requirements will necessitate additional fuel consumption. Since we have no way of knowing how efficient our spaceship will be, we arbitrarily assume same quantity of fuel for peripheral needs as for propulsion needs. Thus, 0.166% of ship's daily GW is consumed for propulsion and same amount is also consumed for peripheral needs.  Thus, we'll double the daily difference; thus, 2Δ is daily consumed.
4. Daily Gross Weight (GWt). If spacecraft's initial Gross Weight (GW0) is 100%; then, GW at end of day 1 (GW1) is 1-2Δ = 100% - (2×.166%) = 99.668% of GW0 (also known as Takeoff Gross Weight (TOGW)). For time (t) in cummulative days of g-force powered flight: GWt = (1-2Δ)t
5. Fuel Requirment as Percentage of TOGW (%TOGW). To determine quantity of fuel required for a multi-day space flight, use the formula: %TOGWt = 100% - GWt .
Phase 1Phase
2
U

R

A

N

U

S
Phase
3
Phase
4
E

A

R

T

H
Phase
Time
(tP)
6.3
Days
6.3
Days
6.3
Days
6.3
Days
See TABLE-5: G-FORCE FLIGHT PROFILE
tP=(2 × dP/g)
Cumm
Time
(tC)
6.3 Days
12.6 Days
18.9 Days
25.2 Days
Running total of flight time.
tC=tP + tC-1
Gross
Weight
(GWt)
97.9%
95.9%
93.9%
92.0%
Ever decreasing GW.
GWt = (1-2Δ)t
let t = Cumm time (tC)
Percent Takeoff Gross Weight
(%TOGW)
2.1%
4.1%
6.1%
8.0%
Ever increasing
%TOGW.
%TOGWt =
100% - GWt
On site operations.
Once there, spacecraft could drop off a habitat full of humans, robots, equipment, and supplies needed to harvest vast quantities of He3 then immediately return.

William Herschel

"Man Who Discovered Uranus"

Musician Born. William Herschel, one of history's greatest astronomers, was born at Hanover, on November 15, 1738. His father, Isaac Herschel, was an accomplished musician but not wealthy. Isaac left few worldly goods to his heirs, but he passed on genius to William and William's younger sister, Caroline. Later, Caroline faithfully chronicled her famed brother's life.
This modest family circle dispersed at the outbreak of the Seven Years' War in 1756. The French invaded Hanover, then part of the British dominions. Young William Herschel had become a regular in the regimental band of the Hanoverian Guards, but circumstances compelled this young musician into combat in the battle of Hastenbeck. After this disastrous battle, he deserted his unit and fled to to England. Many years later, Herschel became the famous astronomer, and King George the Third pardoned him.
Became Astronomer. In England, Herschel's studies progressed from music to mathematics to astronomy; eventually; Herschel come to spend every spare moment on astronomy and making his own telescopes. In 1774, William first glimpsed the stars with his own instrument. Thereafter, he used his telescopes every night the weather allowed.
Caroline Herschel - Invaluable Assistant. Herschel frequently continued his observations throughout a long winter's night from dusk till dawn accompanied by Caroline. While William attended to his daily labors, Caroline carefully transcribed the observations made during the previous night and prepared everything for observations to follow on the ensuing evening.
Discoverer of Uranus After surveying thousands of stars, he noticed a different "star" in 1781. This object had a disc with a definite, measurable size, which was totally different. He further noted a definite shift of its position relative to the stars. Thus, he initially reported it (on 26 April 1781) as a "comet". However, Bode concluded that its near-circular orbit was more like a planet than a comet. The object was soon universally accepted as a new planet.
Royal Astronomer. King George III heard of Herschel's achievements and invited him to Windsor. Herschel brought his famous telescope to exhibit the new planet to the King. After this meeting, Herschel could do exclusively astronomy for the rest of his life. King George granted Herschel the title of Royal Astronomer with many admirable entitlements including an adequate salary for Caroline. Freed from his other duties, Herschel immediately began constructing the great telescopes at Windsor. For more than thirty years, he and his faithful sister continued their rigorous observation schedule. Their many Royal Society papers described numerous objects such as double stars; nebulae and clusters; objects first revealed to human gaze due to their efforts. However, the discovery of Uranus remained his most noteworthy achievement.
Herschel married late in life; yet, he lived to see his only son, Sir John Herschel, also become a famous astronomer. After the elder Herschel died in 1822, his illustrious sister Caroline returned to Hanover, where she lived for many years with much deserved respect.



VOLUME I: ASTEROIDAL
VOLUME II:  INTERPLANETARY
VOLUME III: INTERSTELLAR



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