The International Space Station

In 1984, President Ronald Regan announced a goal of developing a permanently inhabited station in orbit. This led to the International Space Station (ISS), man’s outpost to space which includes 16 Nations from around the world that have come together to build the elements needed to complete this cosmic outpost.  The ISS is the largest artificial body in orbit.  It is 357 feet in length, about the size of an American football field.  It comprises of pressurized modules for astronauts to live in, external trusses for propulsion, and solar arrays for power.  The ISS was taken into space piece-by-piece and gradually built in orbit.  Current plans call for the space station to be operated through at least 2020.  According to deputy head of Rosksmos space agency Vitaly Davydov in 2011, the ISS will be sent into the ocean after 2020.

ISS

Image from https://en.wikipedia.org/wiki/International_Space_Station

Introduction

The ISS is a livable human-made satellite that orbits Earth at an altitude of about 400 km. [1] It is the single most expensive engineering project in human history and one of the most complex pieces of machinery ever assembled.  The ISS is a huge space laboratory where astronauts and scientists can learn more about living in space and the effects of zero-gravity.  The station also provides valuable opportunities to test spacecraft systems and equipment and act as a staging base for possible missions to Mars and the Moon.  As a permanently occupied outpost in outer space, it serves as a stepping-stone for further space exploration. [2]

In 1984, President Ronald Regan announced a goal of developing a permanently inhabited station in orbit. This lead to the combined man power that has gone into building, launching, and in-space assembly of the ISS represents the biggest construction project in history.  Five international partners include NASA of the United States, CSA of Canada, Roskosmos of Russia, European Space Agency (ESA) made up of agencies from France, Brazil, Malaysia, South Korea, and Italy, and JAXA of Japan.  When completed in 2004, the ISS contained 14 modules including science laboratories and living modules.

The International Space Station

To stay in orbit, an object must be traveling at a constant speed over Earth’s surface. For the ISS, which orbits at a height of about 200 miles, that’s roughly 17,500 miles per hour. [5] Aerospace engineer and re-entry specialist William Ailor of the Aerospace Corporation stated that to counteract its orbital drag, mission controllers must use propellant in attached spacecraft to periodically loft the station to a higher orbit.  Without those propellant burns, the station would eventually drop from orbit.

The ISS is the largest artificial body in orbit. It is 357 feet in length, about the size of an American football field.  It comprises of pressurized modules for astronauts to live in, external trusses for propulsion, solar arrays for power.  Zarya was the first module of the ISS to be sent to space.  It was launched into space on a Russian Proton rocket on November 20, 1998.  Zarya provided propulsion, altitude control, communications and electrical power.  NASA launched its own module named Unity two weeks later using the Space Shuttle Endeavor.  Unity was attached to the Zarya module.

Unity was equipped with all the requirements for long-term human living.  The first ISS crew mission was called Expedition 1 in October 2000.  Three Russian cosmonauts docked and entered the ISS on November 2000.  The space station has been continuously occupied since.  A six-person expedition crew typically stays four to six months aboard the ISS.  [2] The ISS has been visited by astronauts and cosmonauts from 15 different nations.

The ISS was taken into space piece-by-piece and gradually built in orbit. [2] The assembly was done by a 55-foot robot arm assembly is capable of lifting 220,000 lbs.  [2] Crews are responsible for maintaining the station.   The ISS has 2 bathrooms, a gym and more room than a 6 bedroom house.   The ISS operates as a full research facility with technology such as 3-D printing, autonomous Earth imaging, laser communications and mini-satellite launchers.

The ISS is located 400 km above Earth. It is man’s outpost to space which includes 16 Nations from around the world that have come together to build the elements needed to complete this cosmic outpost.  This is a world combined effort to leave Earth for the first time.  The estimated cost of 16 billion dollars and weight more than 420,000 kg.  The ISS orbits the Earth every 92 minutes, 16 times per day.  It travels at 27,724 km per hour.  That means the crew members on board the ISS experience a sunrise or sunset every 92 minutes.  It can be seen from nearly every area of Earth at some point in time.

If the crew needs to evacuate the station, they can return to Earth aboard two Russian Soyuz vehicles docked to the ISS. [2] Current plans call for the space station to be operated through at least 2020.  According to deputy head of Rosksmos space agency Vitaly Davydov in 2011, the ISS will be sent into the ocean after 2020.  The plan is for the ISS to have a controlled fall.  The structure will be deorbited in a controlled way.  NASA officials have stated that bringing the space station down will be a long and involved process that will begin about one year from it’s planned re-entry. [4]

Re-Entry into Earth’s Atmosphere

Meteorites burn up when they fall into the Earth’s atmosphere, this basically has to do with the sheer size of the meteorite and kinetic energy, you know, because the large meteorite is going incredibly fast. So when a meteorite enters the Earth’s atmosphere, most of the heat is due to the air that the meteorite runs into. In a sense, the air does not have time to get out of the way, so the air starts to compress and heat up. We’re talking temperatures exceeding 3,000 degrees. Now if the meteor happens to be small enough, then it will burn up entirely before reaching the lower atmosphere.

That got me to thinking, what about all of the satellites up there? They don’t stay up there forever, right? So do they just completely burn up when eventually falling back to Earth? Well a little more research and I found that the newer satellites are actually designed to burn up completely upon re-entry. And the older ones? Well if they are big enough, most of the satellite will burn up, but some of the remaining pieces will actually land on Earth. Let’s take the NASA satellite UARS (Upper Atmosphere Research Satellite) for example. This 6.5 ton satellite actually plunged to Earth in 2011. Luckily UARS crash-landed into the South Pacific Ocean. UARS was not the first, or the last piece of man-made space hardware to come crashing back to Earth.

The Eventual Retirement of the ISS

It is obvious that over the years NASA has learned how spacecraft break up in Earth’s atmosphere. Space station controllers will dock an unmanned vehicle to the forward end of the laboratory.  At the right time they will burn its propellant at full blast and sink the entire complex deep into the atmosphere.  As the ISS plows through the thin other atmosphere at hypersonic speeds, cone-like shock fronts will surround parts out in orbit.  Air molecules will compress, collide, emit infrared radiation, and heat pieces of the space station upward of 3,000 degrees Fahrenheit.  [5]

Bigger modules will heat up and begin to soften or melt as the plunge continues. The space station’s metallic joints should break apart next.  And when the weakened structures sinks into thicker parts of the atmosphere, deceleration up to eight times stronger than Earth’s gravity will rip the components to shreds. [5]

Between 10 and 40 percent of the space station’s mass should drop back to Earth. Pieces that do survive will either be those dense enough to not fully melt or break apart, or those shielded by components that bore the brunt of atmospheric reentry. [5]

References

[1] International Space Station. (n.d.). Retrieved August 26, 2015.

[2] Sharp, T. (2015, March 19). International Space Station: Facts, History & Tracking | Space.com. Retrieved August 26, 2015.

[3] International Space Station User’s Guide. (n.d.). Retrieved August 25, 2015, from http://www.spaceref.com/iss/ops/ISS.User.Guide.R2.pdf

[4] Wall, M. (2011, September 24). How Will the International Space Station Fall to Earth? | NASA & International Space Station | UARS, Space Junk & Orbital Debris | Space.com. Retrieved August 26, 2015,

[5] By Dave Mosher, for National Geographic News PUBLISHED August 09, 2011. (2011, August 9). Space Station to Fall to Earth-Find Out How and Where. Retrieved August 26, 2015.

[6] Bracket, A. (2011, September 20). Why do satellites & meteors “burn up” entering atmosphere. Retrieved August 26, 2015.

 

Author: Claude