Earth from space station?

-  1785  -  Earth from Space Station.  How many times does the Earth rotate  while making a single orbit around the Sun?
-
-----------------  1785  -  Earth from Space Station
-
-  How many times does the Earth rotate making a single orbit around the Sun?
-
------------------  -

-
-  That was a trick question.  Only Turner and Nathan got it.
-
-  This picture is Earth from the International Space Station.  The Earth spins on its axis below while the station  orbits every 96 minutes.  So day night on the station is far different than from Mother Earth.
-
-  How about how many days in a year?
-
-  Everyone knows there are 365 days in a year and a few know that every 4 years there are 366 days making it a Leap Year.  So, a year on average must be:
-
------------------------  Year  =  365.25 days
-
-  Well that depends on how you measure it.  The path that the Earth travels around the Sun is a near circle ( slightly elliptical but not much).  If you measure 360 degrees of a full circle of the Eliptic, as the orbit is called you get:
-
-------------------------- Year  =  365.24219 days
-
-  Now, if you don’t measure 360 degrees from the Earth but you measure when the Earth’ s orbit returns to the same background of the farthest stars you get:
-
----------------------  Year  =  365.256363004  days
-
-  What if you just measure exactly 12 cycles of the phases f the Moon ( Lunar Cycles) you get:
-
-----------------------Year  =  354.37 days
-
-  The Moon’s orbit is not a perfect circle either.  Like the Earth’s orbit that is an elliptical orbit meaning that at some times it is closer to the Sun and conversely sometimes farther away.  Closest orbit is called the “ Perihelion”.  Now the time for the Earth to return to same closest point your get:
-
---------------------  Year  =  365.259636 days
-
-  Ok, then there is the Moon eclipsing the Sun.  Called the Lunar Node, or the Eclipse Year.  The time for one Lunar Node it the next you get:
-
-----------------------  Year  =  346.620075883  days
--
-  Ok, I give up.  Let’s just average it all out and agree to make the year 365.25 days.  That is close enough for government work.  It is just politics.
-
-  Lunar years are easier to define since we only have one Moon.  Note the number of decimal points on the above number.  But, how confusing would it be on Mars that has 2 moons.  It gets worse:
-
------------------------     Mars  =        2 moons
------------------------     Pluto  =        5 moons
------------------------     Neptune  =  14 moons
------------------------     Uranus  =    27 moons
------------------------     Saturn  =     62 moons
------------------------     Jupiter  =    67 moons
-
-  It becomes more complicated calculating the days in a year living on those planets.  Measured in Earth years you get:
-
------------------------     Mars       =        1.881 years
------------------------     Jupiter      =    11.86 years
------------------------     Saturn      =    29.42 years
------------------------     Uranus     =    84.01 years
------------------------     Neptune  =     164.8 years
------------------------     Pluto       =    248 years
-
-  Ok I give up again.  Get past Pluto into the Kuiper Belt and you get to a “year of years” to get around the Sun.  It is past my bed time, Good night.  Tomorrow is another day.
-
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What was the 5th planet to be discovered?

-  1784  -  What was the 5th planet to be discovered?  This is about the Dwarf Planet Ceres that was discovered in 1801.  We had a spacecraft visit it this year making some startling discoveries.
-

-----------------  1784  -  What was the 5th planet to be discovered?
-
-  I bet you can not name it?
-
-  Earth, Venus, Mars, Jupiter, ????????
-  
-  It was discovered in the year 1801.
-
-  It got demoted to an asteroid in 1850 having been a planet for 50 years.   It was the largest asteroid.  It got promoted to a Dwarf Planet at the same time that Pluto got demoted from a Planet to a Dwarf Planet in 2006.
-
-  Ok, our 5th planet  was the Dwarf Planet, “ Ceres”
-
-  Discovered in 1801 in the Asteroid Belt between Mars and Jupiter.  Ceres remained a “planet” for some 50 years until it got reclassified to become the largest asteroid.  Ceres is 600 miles in diameter.  Pluto is 1,473 miles in diameter.
-
-  The next biggest asteroid is “ Vesta” that is 360 miles in diameter, but still considered an asteroid.
-
-  When the Dawn Spacecraft approached a Ceres orbit in 2015 it discovered a proto-planet that looked very much like Pluto.  Ceres was likely even formed in the icy regions of the Kuiper Belt like Pluto before it was somehow flung into the Belt of Asteroids.
-
-  Dust rains onto everything in the Asteroid Belt where there are millions of asteroids in orbit.  This dust turns surfaces into darker shades of gray.  So, when bright white spots were discovered on Ceres astronomers were surprised.  That meant Ceres might have volcanic activity that is creating spots younger than the rest of the surface.  Ceres was expected to be too small and cold to contain any volcanic activity.
-
-  Now astronomers think Ceres may have an interior packed with water ice even though its surface is perfectly dry.  If water ice did sublimate to the surface it would leave salt behind.  The white salt is likely “ Epsom salt”, or,  magnesium sulfate.
-
-  Ok, the white spots were the most interesting mysteries but Ceres had some other surprises.  It hosts a lone mountain that is 21,000 feet tall.  That is higher than North America’s highest peak.  This mountain peak is not surrounded by any related impact that might explain how it was formed.  So, it remains a mystery how it got here.
-
-  Ceres has a crater that is 175 miles across and 9 miles deep.
-
-  This little proto-planet is definitely more active and dynamic than astronomers expected.
-
-  Here are some previous reviews about Ceres before the Dawn arrival:
-
-  #1618 -   Ceres is icy compared to Vesta that is a dry asteroid.  It is 4% the mass of the Moon and orbit’s the Sun in 4.6 years.
-
-  #847  - Ceres shares its orbit around the Sun with over a million asteroids that are all larger than 0.6 miles.  Three other asteroids are over 250 miles in diameter:  Vesta, Pallas, and Hygrea.
-
-  A small number of these asteroids have orbits that cross Earth’s orbit.  These are impacts waiting to happen.  I hope you get to read this before one of them hits us.
-
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How fast would a space station have to spin to reproduce Earth’s gravity?

-  1783  -  How fast would a space station have to spin to reproduce Earth’s gravity?  This review goes through the math for centripetal force in a rotating space station.
-

-----------------  1783  -  How fast to spin to reproduce gravity?
-
-  Jeff’s question:  How fast would a satellite ( space station ) have to spin to reproduce gravity the same as felt on the surface of the Earth?
-
-  This is a simple problem of calculating Centripetal Force.  Here’s how:
-
-  Say we have a space station that is a hollow circular tube that has a radius to the outer wall of 50 meters.  We rotate the orbiting tube at some constant speed.  What speed is needed so the astronaut walking on the outside wall weighs the same as he does back home?
-
-  The acceleration of gravity on the surface of Earth is 32 feet per second per second.  Regardless of mass all things fall at that same acceleration:
-
-----------------------------  a  =  32 ft/sec^2
-
-  When an object in circular motion is at a constant rotating speed it is constantly accelerating because its velocity is constantly changing direction.  Speed is the absolute magnitude , but , velocity is a vector with magnitude and direction.
-
---------------------------  Speed  =  “v”
-
---------------------------  Radius  =  “r”
-
-  The vector of acceleration is “a”
-
--------------------------  a  = - v^2 / r
-
-  The minus sign means the vector is pointing outward for the center of the circular motion.  Newton’s second law of motion is Force  =  mass * acceleration.
-
--------------------------  F  =  m * a
-
---------------------------  a  =  v^2  /  r
-
------------------------  F  =  - m* v^2  /  r
-
-  The astronaut in the space station standing on the outside wall of the tube has a mass “m”
-
-  The space station radius is “r”  (50 meters)
-
-  The speed of rotation is a constant  = “v”
-
------------------------  a  =  m * v^2 / r
-
-  On the surface of Earth the acceleration of gravity is called “g”,  G-forces.  Therefore:
-
------------------------  a  =  m * g
-
-  Put the two equations equal to each other:
-
------------------------  m * g  =  m * v^2  / r
-
-  This equation  reduces because mass cancels from both sides of the equation.  All mass falls at the same acceleration.  Drop an iron bowling ball and a plastic bowling ball from the tower of Pizza and they both hit the ground at the same time. So, would a feather, but you would have to remove all the air.
-
----------------------------  g  =  v^2 / r
-
----------------------------  v^2  =  g * r
-
-  Converting “g” to the metric system:  g  =  32 feet / sec^2  =  9.8 meters / sec^2
-
------------------------  v^2  =  9.8 m / s^2  *  50 meters  =  490 m^2 s^2
-
-----------------------  v  =  22 m / sec
-
-  That is about 50 miles per hour.  22 m/sec  *  mile /  1610 m  * 3600 sec / hour  =  49.5 miles / hour.
-
-  That is spinning pretty fast.  I think astronauts will need to get used to operating in a little less gravity.  Work would be a lot easier.  Requires less energy to move around.
-
-  Jeff, does that answer your question?
-
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How huge is the Universe?

-  1782  -  Telescopes looking back in time.  Astronomers can almost see all the way back to the beginning.  13.82 billion years later the Universe has cooled and expanded to become enormously huge.  This review attempts to try and put that into perspective.
-

-----------------  1782  -  Telescopes looking back in time.
-
-  What happens if you focus a telescope at a single spot in the dark sky and collect all the light for 140 hours?  The long time exposure collects enough light to image thousands of never before seen galaxies.
-
-  This Hubble Deep Field exposure took 150 orbits staring at a single spot of the dark sky just above the Big Dipper ( Ursa Major Constellation).  4 different filters were used, ultraviolet, blue, yellow and far red.  This 140 hours of exposure was first competed in 1996.
-
-  The image from this time exposure was a view 11 billion years backwards in time.  The early galaxies were smaller in size, irregular, and knotty in shape.
-
-  How do astronomers know that these faintest galaxies are actually 11 billion lightyears distant and less than 2 billion years old?
-
-  Looking past our Solar System, past distant galaxies, past distant galaxy clusters, we enter a deep universe populated by super clusters of galaxies, long filaments interconnecting them, and colossal voids of near empty space in between.
-
-  We are part of the Virgo Supercluster.  We used to think that it was the largest gravity bound group inside the expanding universe.  Our home VirgoSupercluster is 100,000,000 lightyears across.  However, new discoveries have found we are bound to other superclusters that together span 500,000,000 lightyears across.  The larger group is named “Laniakea”.  It is the Hawaiian word for “ immense heaven”.
-
-  These distance measurements are made using the brightness of light and the broadening of the spectrum wavelengths of electromagnetic radiation traveling through expanding space.  For example:  Astronomers measure the relative motion of these galaxies by the shift in frequency of a particular wavelength of radiation.  Blue shifted galaxies are moving toward us and red shifted galaxies are moving away from us.  Astronomers use the strength of radio waves to estimate how much energy the galaxies release in visible light.
-
-  When all this data is collected together what emerges is galaxies huddling together in super clusters with massive voids of space in between them.  The clumps of galaxies are inner connected by “strings” of galaxies.  The image becomes one of a Cosmic Web.
-
-  The Dark Matter that astronomers can not see appears to be occupying a thicker scaffolding supporting the cosmic web.  Dark Matter is only detected by its gravitational interactions with normal matter.  This unknown material holding filaments and superclusters together has 5 times the mass as the “Normal Matter” that we can see.
-

-
-  Astronomers discovered that more distant galaxies had a light spectrum shifted into the red and infrared wavelengths meaning the farther galaxies were moving away faster than the nearer galaxies and the Universe was therefore expanding.
-
-  The most common element in the Universe is hydrogen and hydrogen atoms most commonly emit and absorb the single wavelength of 91.2 nanometers.  This causes a break in the continuous light spectrum.  Observing this hydrogen break in galaxy light that are 11 billion lightyears away has a redshift emitted in the ultraviolet and detected in blue wavelengths.  Some detected wavelengths have shifted all the way to the infrared wavelengths.  Traveling across expanding space expands radiation into wider and wider wavelengths.
-
-  Looking into the depths of the expanding Universe has brought other new discoveries.  For Example:  The peak star formation occurred 10 to 12 billion years ago.
-
-  A huge hole in the Universe was discovered dwarfing any other structure. It is nearly a billion lightyears across.  This region is devoid of stars, gas, and any ordinary matter, and any Dark Matter.  It is located 6 to 10 billion lightyears away and astronomers have no explanation for its existence.
-
-  Still another problem persists:  When astronomers create a detailed inventory of all the matter and energy evidence they can “see” they come up with only 5% of what their calculations say should be out there.  95% of the Universe is “missing”.  The ratios of matter to energy tell us that 22% of this is missing Dark Matter and 73% is missing Dark Energy.  It is the enormous amount of Dark Energy that is expanding the Universe at an ever acceleration rate.
-
-  Gravitational Lensing has been the primary tool used to confirm these discoveries.  When light passes a massive object like a cluster of galaxies and other unseen Dark Matter the light is bent just like a light beam passing through a glass magnifying glass.  The amount of bending is used to calculate the amount of total mass that is there.   And, that total mass is 5 times more than can be seen.
-
-  Some of this Dark Matter could be neutrinos.  But, neutrinos account for a very small part of the total missing mass.  The larger part is still unknown and dubbed to be “ WIMPS”., weakly, interactive, massive particles.  WIMPS have yet to be discovered.  They exist in theory only.
-
-  Dark Energy on the other hand is large scale “ anti-gravity” that is pushing galaxy clusters apart.  We know what it does, but, have no idea what it is.
-
-   The picture started 13,820,000,000 years ago.  The Universe expanded and cooled to 3,000 degrees Kelvin ( 4,900F) in just 380,000 years.  At that point vibrating protons could grab nearby vibrating electrons and form neutral atoms of hydrogen.  When these two charged particles were neutralized light photons were set free to escape into this “first light“.  Previously these photons were pin balls bouncing continuously between the sea of charged particles.
-
-  Today astronomers can see this escape event as a sea of cool microwave glow ( Cosmic Microwave Background radiation).  It occurred 380,000 years after the Big Bang.    The 3,000 Kelvin radiation has since expanded and cooled to 2.73Kelvin.  The radiation wavelengths stretched out in the expanding Universe from gamma rays to now microwaves.  The tiny differences in temperature in this cooling and expanding sea of particles allowed the denser regions to condense into galaxies and the lesser dense regions into voids.
-
-  These first galaxies were a million times smaller than our today’s Milky Way Galaxy.  These small irregular galaxies formed a billion years after the Big Bang.  3 billion years later you see the Universe we have today.  4.32 billion years after the Big Bang I am sending you this review of how it all happened to bring us to where we are today.
-
-  Today the Universe is immensely huge, beyond comprehension.  If the Sun is a grain of sand the Milky Way alone would be 40,000 miles across.
-
-  The Universe extends 13.8 billion lightyears in all directions in time and distance.  That is 13,800,000,000 lightyears with each lightyear being 6,000,000,000,000 miles.  And, during the time for that light to reach us the Universe has expanded to 93 billion lightyears across as that more distant light is still traveling to reach us.  And, 93 billion lightyears of Universe is only the “Visible Universe”.  The Universe beyond that horizon is so distant and expanding so fast the light will never reach us.  The furthest expansion is moving away faster than the speed of light and still accelerating.  More of that Universe that we can see in moving into that part of the Universe that we will  never see.  Light only travels 186,000 miles per second. Expansion faster than that means the light never, never gets here.
-
- In this real sense the Universe appears to be dieing?
-
----------------------------------------------------------------------------------------
-  The Hubble Space Telescope orbits Earth every 96.6 minutes.  See Review #1780 to learn how this calculation was made.  (math).
-
-  Astronomers have detected active Blackholes scattered across this Cosmic Web.  The most distant Blackholes existed only 750 million years after the Big Bang. That is 13 billion lightyears away and 13 billion years ago.  These bright active Blackholes are called “ Quasars”.
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1781-Learn about Pluto

-  1781 - In 2015 our spacecraft visited Pluto making many new discoveries that surprised astronomers.  In 2016 the data will still be arriving and more discoveries are expected to arrive.  Stay tuned Pluto is complex.
-

-----------------  1781 -   Learn about Pluto.
-
-  Our New Horizon spacecraft visited the dwarf planet Pluto on July 14, 2015.  It was a flyby mission.  Measurements lasted for several months and it will take over a year to download all the new data.  It takes a signal 4.6 hours to reach us and the 12 watt transmitter is transmitting at only 2,000 bits per second.
-
-  Pluto was bigger and stranger than all the astronomers expected.  We had Pluto’s diameter at 1,467 miles.  New measurements put the width at 1,473 miles which is 30% smaller than our Moon, (2,152 miles).
-
-  See Review #1724 to learn more about the New Horizon mission itself.  It was launched in 2006 at 35,880 miles per hour and it took 9 years to reach Pluto..  The flyby skimmed the surface just 7,770 miles altitude.
-
-  Astronomers from afar expected Pluto’s surface to be a frozen, cratered and totally dead as a planet.  What they discovered was a young surface with smooth frozen plains and icy mountains as high as our Rockies.  There were dunes, glacial lakes and ice that has recently flowed.  Smooth surfaces were estimated to be only 100 million years old on top of regions the were billions of years old.
-
-  Something internal has warmed the planet to create these unexpected features.
-
-  Pluto has a rich atmosphere that extends 80 miles above its surface.  Wisps of nitrogen atmosphere could be detected 1,000 miles above the surface.
-
-  Pluto has 5 moons, Charon, Styx Nix Hydra and Kerberos.  Charon is 751 miles in diameter.  The other 4 are only a few dozen miles in diameter.
-
-  Pluto was recently designated as a “ Dwarf Planet” not belonging to the other 8 planets in our Solar System.  Pluto then became a member of the Kuiper Belt of objects.  The next larger Kuiper Belt object so far discovered is Eris with a diameter of 1,445 miles.
-
-  Pluto has a calculated density of 1.86 grams per cubic centimeter which means it is about 60% rock and 40% ice in composition.  Pluto’s atmospheric pressure is only 0.001% that of the pressure at sea level on Earth.
-
-  Pluto’s surface is many times more complex than astronomers expected.  There are canyons, polar caps, broad equatorial dark plains, ice mountains, ice plains, craters and glaciers.  There are convections on the icy plains that indicate an unknown source of heat inside the planet.  There are clear signs of ice flows down the mountains likely due to the presence of liquid nitrogen.  Pluto’s gravity is only 6% that of Earth’s.
-
-  As of August 2015  95% of the measurement data is still on the spacecraft.  It takes a long time to download at 2,000 bits per second.
-
-  Other Reviews available about Pluto written before the New Horizon visit:
-
- #1724  -  New Horizon spacecraft weighs 934 pounds carrying 7 measurement instruments including a 8.2 inch telescope.  Camera resolution is to 70 meters per pixel up to 65,000 pixels.
-
-  #1632  Astronomers have found over 1,000 “ dwarf planet size” objects in the Kuiper Belt.  Pluto orbit’s the Sun twice for every 3 times Neptune orbits the Sun.  One orbit takes 248 years.  Pluto’s average temperature is -380 F.
-
-  #1727  -  Pluto and Charon  -  this review shows how the flyby measurements were used to calculate the mass of the planet and the moons. (math)
-
-  #1129  -  Reasons why Pluto was kicked out of the Solar System. (politics)
-
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1780 How Fast to Orbit

-  -----------------------  # 1780  -  How Fast to Orbit?  Speed is what it takes to go into orbit.  I does not matter how big you are, just how fast you are going.  This Review does the calculations.
-    

-  Gravity Probe B is a satellite in orbit 400 miles up.  ( See Review # 1536 to learn the Gravity Probe B mission).  How fast must the satellite be going in order to stay in this orbit.  A satellite in orbit is weightless because it is continuously falling around the Earth.  Its orbit is falling around the curvature of the Earth.  The rate of falling is determined by the acceleration of gravity, not the mass of the satellite.  It is a constant.  The rate of falling is the same for every mass that is in free fall and is at the same distance from the center of Earth, or,  the center of gravity.  The acceleration of gravity near the Earth is 32.2 feet per second per second.  (that is 9.8 m/sec^2)
-
-  The satellite , like the Moon, and the Planets obey Kepler’s laws of motion.  The cube of the radius of orbit is proportional to the square of the period of orbit.  Let’s start with the Moon, that is also in free fall around the Earth:
-
------------------  The period of the Moon’s orbit is 27.32 days.
-
------------------  The radius of the Moon’s orbit is 239,509 miles.
-
-  The cube of the period is proportional to the square of the period:
-
-  ------------------  (239,509 )^3  =  K* ( 27.32 days)^2
-
--------------------  13/57 *10^15  =  K * (7.464*10^2)
-
-  “K” is the constant of proportionality depending on the units of measurement used, and,  we do not have to know that to solve the period for the satellite.  We know that regardless of mass the ratios are the same.
-
-------------------  Satellite Radius^3 /  Moon Radius^3 //  Time, Ts^2  /  Moon Period^2
-
--------------------  Period for the satellite  =  Ts
-
--------------------  Radius of orbit for the satellite is 400 miles plus the radius of the Earth 3957 miles equals 4,357 miles.
-
-  Now equate the two ratios and solve for Ts:
-
--------------------  (4.357*10^3)^3  /  2.39509 *10^5)^3   =   Ts^2  /  (27.32)^2
-
--------------------  6.02*10^-6  =  Ts^2  /  7.46*10^2
-
-------------------  Ts^2  =  44.93*10-4
-
--------------------  Ts  =  6.7 *10*-2 days
-
--------------------  Ts  =  1.61 hours    (   96.6 minutes )
-
-  The time for one complete orbit of the satellite is 1.61 hours.  Now if we know the distance traveled in one complete orbit we can calculate the speed.
-
-  The distance of the orbit is the circumference of a circle which is 2 * pi * r.  The velocity of orbit is distance / time.
-
------------------  v  =  d / t  =  2*pi *r  /  t  =  2*pi*(4,357 miles)  /  1.61 hours.
-
-------------------  v  =  17,004 miles per hour.
-
-  However, this assumes we have a perfect circle for an orbit.  What would be the effect if the satellite had a slightly elliptical orbit?  An elliptical orbit requires that it travel a greater amount of distance in the same amount of time, so it must be going faster during part of the orbit.  Can we do this calculation without assuming the perfect circle orbit?
-
-  With the elliptical orbit the radius of orbit,” r“, changes with the function of time, t. If we construct a coordinate plane with the radius connected from the center of the Earth to the point on the orbit , we can make the radius to to be hypotenuse of a right triangle.
-
-----------------  hypotenuse  =  r
-
-----------------  opposite side  =  r * sin a,   where  “ a “ is the angle
-
-----------------  adjacent side  =  r cos a
-
---------------  Using the Pythagorean Theorem:  r^2  =  (r*sin a)^2  +  (r*cos a)^2
-
-  The radius is rotating as the points move around the elliptical orbit.  The radius is a function of time, r(t), depending on the angularly velocity of rotation.  The angular velocity =  da / dt.  The rate of change of the angle with time.  Restating the distance equation in terms of changes with time:
-
--------------------- r(t)^2  =  (r * sin da /dt * t )^2  +  ( r*cos da/dt * t)^2
-
-  The speed of the satellite is constant, but, the velocity of the satellite is constantly changing, because the direction of travel is constantly changing.  Velocity is the rate of change of distance.  v(t)  =  dr /dt.  If we take the derivative of both sides of the above equation:
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----------------  v(t)^2  =  ( dr/dt)^2  =  r^2 cos a^2  (dc/dt)^2  +  r^2 *(- sin a)^2  ( dc/dt)^2
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-   Where:  the derivative of sin a =  cos a dt
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-   Where: the derivative of cos a  =  - sin a dt
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-  Speed is the absolute magnitude of velocity.  So, the square of velocity gets us an absolute magnitude and is equivalent to speed.
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------------------------  (cos a)^2  +  (sin a)^2  =  1
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-  Again this is the Pythagorean theorem:  opposite^2 / r^2  +  adjacent^2 / r^2  =   1
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-------------------  v(t)^2  =  r^2 ( da/dt)^2
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------------------  v  =  r * da/dt
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-------------------  velocity  = radius * angular velocity
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------------------  (da/dt)^2  =  v^2 / r^2
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-  Acceleration is the rate of change of velocity.  acceleration  =  dv / dt  =  r * (da/dt)^2
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------------------------------  acceleration  =  r * v^2 / r^2
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------------------------------  acceleration  =  v^2 / r
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-----------------------------  In the case of a satellite in continuous orbit the acceleration of orbit must balance with the acceleration of gravity, g.
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-------------------------------acceleration  =  g  =  32.2 feet/sec^2
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------------------------------  v^2  =  g*r
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-  The constant acceleration of gravity near the Earth is 32.2 feet per second per second, or 79,036 miles per hour ^2
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---------------------------  v^2  =  32.2 feet /sec^2  * 4.357*10^3 miles * mile / 5,280 feet * (3600 sec)^2 / hour ^2
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--------------------------  v^2  =  344.4 *10^6 miles^2 / hours^2
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-------------------------  v  =  18,557 miles per hour.
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-  The assumption here is that the acceleration of gravity is 32.2 feet /sec^2 at 400 miles altitude.  Assuming that is near to the Earth.  The other assumption was that the orbit was a perfect circle.  Both need some tweaking to get a more accurate answer to how fast the satellite is traveling.  All velocity is relative depending on your assumptions.  But, the satellite must be traveling about 18,000 miles per hour.  It will be traveling slightly faster if its orbit gets closer to Earth and slightly slower when farther away from Earth.  Now you know “how fast to orbit”
-
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---   Some reviews are at:  --------------     http://jdetrick.blogspot.com -----
--  email comments, corrections, request for copies or Index of all reviews
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 -----   707-536-3272    ----------------------   Friday, December 4, 2015  -----
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Our next trip to Mars?

-  1779  -  Trip to Mars.  How will we visit this planet?  What are the risks of such a trip?  We need to send robots first to do our exploring.  The next one will leave March, 2016
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-----------------  1779  -  Trip to Mars.
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-  Not in my day, but, someday astronauts will visit Mars.  Probably a one way trip first time, but, the trick is to keep astronauts alive while they are there.
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-   It will take several months of space travel to reach Mars.  Let’s say you make it there and are orbiting the planet.  Landing on the surface is the next trick.  Mar’s atmosphere is 100 times thinner than Earth’s atmosphere.  Parachutes will not work.  Power thrusters must slow the heavy space craft down then stand on its tail to gently reach the surface.
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-  Estimates are that this spacecraft needs to be carrying 20 to 30 tons of astronauts and supplies to start a planetary habitat. A well designed decelerator is needed to slow down this much mass and land it safely.
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-  Next trick is how to stay alive once on the surface?  It is cold.  The average temperature is -81F, but, depending on time and location it can range form +86 at the equator to -284F at the poles.  The thin atmosphere means astronauts will feel rapid temperature changes much more harshly.  New and better space suits and habitats need to be designed.
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-  Food and supplies are required similar to a research outpost in the Antarctic.  Resupply missions would take months to complete.  Self-sustainability will require some form of interplanetary farming.  If 80 square meters can be dedicated to plant growth it would be like a pot farm with artificial lighting, water pumped form sub-surface, carbon-dioxide pumped from the 4 man crew.
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-  Crew produced CO2 will work but be insufficient to support the crop growth needed.  Some new technology is needed to scrub CO2 out of the gases in the Martian atmosphere.
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-  Plants are also needed to resupply oxygen for the 4 man crew.  This technology needs tight control as well.  In a closed environment the crew has the risk of oxygen toxicity.  And, oxygen is very flammable.  It needs to be managed carefully.  One management technique would be to have the capability to split CO2 into oxygen and carbon monoxide.
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-  Surviving in this man-made habitat will certainly be challenging.  But, let’s get back to the voyage to get there.  It takes a complicated spacecraft.  Even assuming it all works it has to avoid space debris and intense radiation.  High energy Cosmic Rays can easily penetrate the walls of a spacecraft.
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- Cosmic Rays also penetrate the brain and destroy brain cells.  Astronauts may loose a functioning keen mind to operate what’s needed.  Longer exposure may create cancer.
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-  Many of these obstacles need to be overcome not limited to shelter, food, water, air to breath, communication , exercise, social interactions, medicine, ……….  The biggest obstacle to be overcoming failures.  We can not think of everything.  We will need to be prepared to deal with surprises.
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-  Stay tuned, Space-X and Elon Musk will have a proposal for a Mars trip this year.   Andy Weir will have a book and a movie coming out that will focus on some of the worst case scenarios.  Some future generation will see it happen for real.
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-  In the meantime we need to send robots to do our exploring.  Next March, 2016, we will launch another spacecraft ( robot) called “ Insight”.  It will take 7 months to get to Mars.  About the size of a car it will land with instruments designed to study the internal structure of the planet.
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-  Mars is less geologically active than Earth having no plate tectonics.  It therefore retains a more complete record of the planetary history of our solar system.  Seismographs will measure the size, thickness, and density of the core, mantle and crust.  It may even discover underground water reservoirs.  Other instruments will measure the rate at which heat escapes from the planet’s interior.
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-  The study will determine the solid-liquid state of the core.  It will determine the composition and structure of the mantle and crust.  It will measure the rate of meteorite impacts on the surface.
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-  All this data is designed to tell the story of the origins of the Solar System.  All this data will be immediately available to everyone interested.  Students can learn their own solar system history lessons.  We better learn a lot before sending our first astronauts there.  It is a risky trip.
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-----------------  RSVP, Pass it on to whomever is interested. ----------------
---   Some reviews are at:  --------------     http://jdetrick.blogspot.com -----
--  email comments, corrections, request for copies or Index of all reviews
-  to:   -------    jamesdetrick@comcast.net  ------  “Jim Detrick”  -----------
-  https://plus.google.com/u/0/  -- www.facebook.com  -- www.twitter.com
 -----   707-536-3272    ----------------------   Saturday, May 30, 2015  -----
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