Главная Случайная страница



Text 1. How the Hubble Telescope Will Die

If we do nothing, the Hubble Space Telescope will fall to Earth in 2024.

It is in an orbit roughly 560 km above the Earth and circles the Earth once every 97 minutes. While for most intents and purposes the Hubble Space Telescope can be considered to be in space, it actually lies in what is known as the thermosphere: the largest and most tenuous part of the Earth's atmosphere. The thernosphere is roughly one million times less dense than the atmosphere at sea level, yet it is enough to affect the orbits of satellites that fly within it.

Any satellites in low Earth orbit experience a small but significant resistance as they fly over the planet's surface, slowing them down and decaying their orbits. If not corrected, or periodically 'pushed back up' by a rocket or the Space Shuttle, the satellites at this altitude are eventually doomed to fall to Earth and burn up in the atmosphere.

The Space Shuttle has its own engines and isn't in orbit long enough to be affected by this drag but the International Space Station and the Hubble Space Telescope are affected, and they must be periodically pushed into higher orbits to correct for their orbital decay.

To complicate matters, the amount of drag on the Hubble as it orbits within the thermosphere isn't constant. It varies with the 11 year sunspot cycle. As the Sun becomes more active, the atmosphere of the Earth swells and reaches farther out into space than it otherwise would. This increases the density of the air that Hubble must fly through, slowing it down further, lowering its orbit and ultimately shortening it's lifespan.

Hubble has no jets or engines of any kind for propulsion, so throughout its life, it has relied on the Space Shuttle to grab onto it and move it to a higher orbit. Now that NASA has suspended the Shuttle program, no more launches are scheduled to service the most powerful telescope ever built. The Hubble Space Telescope is on its own.

That doesn't mean however, that NASA has not planned for its demise. On the last servicing mission, astronauts placed a ring, known as the Soft Capture Mechanism to the back end of the spacecraft. This ring will give future robotic spacecraft an easy place to grab onto.

Because the Hubble is so large and heavy, it will not completely burn up when its orbit decays and it re-enters the Earth's atmosphere. This presents the danger that pieces could fall over populated areas.

To ensure a safe re-entry, the Hubble Robotic and De-orbit mission is building a robotic spacecraft designed to grab onto that ring, attach itself to it and guide the re-entry of the Hubble onto a safe trajectory.

While the details of when this mission will be launched is unclear, one thing IS clear: with the demise of the Space Shuttle program, no more manned missions to boost the Hubble into a higher orbit are imminent and any chances of saving it will probably rest with robotic craft. The last days are in sight for the most important scientific instrument ever constructed.

If we do absolutely nothing, that last day will arrive in 2024. If we have the will, there is plenty of time to arrange an alternative. The Hubble Space Telescope stands at the pinnacle of a pantheon of great space telescopes. It has done more to advance our understanding of our place in the universe than any that has come before or since, and at a cost that is microscopic compared to other budgetary expenses.

Because of public outcry, NASA reversed a previous position not to service the Hubble and managed one more fix. Is it possible to design a robotic spacecraft to grab Hubble and bring it home?

Check your comprehension

~ Why can the Hubble Space Telescope fall to Earth in 2024?

~ Does the Hubble Space Telescope have its engines?

Text 2. A Brief History of Engineering

In the old days, 1325 AD to be more precise, an engineer was defined as “a constructor of military engines”. Back then engineering was divided into two categories: Military Engineering and Civil Engineering. The former involved the construction of fortifications and military engines, the latter concerned non-military projects, for example bridge building. This definition is now obsolete, as engineering has broadened to include a myriad of disciplines.

The exact origin of the word ‘engineering’ comes from the era when humans applied themselves to skilful inventions. Man evolving further in the world invented devices such as the pulley, the wheel and levers. The word engineer has its root in the word engine, which comes from the Latin word ingenium, which means “innate quality particularly of mental power”. And thus the word engineer emerged as a person who creates nifty and practical inventions.

Today an engineer is described as someone who has acquired and is applying their scientific and technical knowledge to designing, analysing and building useful, helpful and functional works. This would involve structures, machines and apparatus, manufacturing processes as well as forecasting their behaviour in particular environmental conditions. This is all accomplished with functionality, operational economics and safety to life and property forefront in mind.

Check your comprehension

~ What is the origin of the word “engineering”?

~ Is division of engineering into two categories: Military Engineering and Civil Engineering still true today?

Engineering is a broad discipline with many subdisciplines dedicated to various fields of study with regards to particular types of technologies or products.

Engineers may begin their career being trained in a specific discipline, but because of the engineering jobs they take-on, they often become multi-disciplined having worked in a variety of different fields.

The field of engineering has traditionally been divided into the following engineering job categories:

  • Aerospace Engineering
  • Chemical Engineering
  • Civil Engineering
  • Electrical Engineering, and
  • Mechanical Engineering.

However, since the human race has been swiftly advancing with regards to technology, new branches of engineering are being developed. Engineering jobs can now also be found in the following fields:

· Computer Engineering,

· Software Engineering,

· Nanotechnology,

· Molecular Engineering,

· Mechatronics and many more!

Although all these fields may be defined differently, there is generally a great overlap, particularly in the fields of physics, chemistry and mathematics. Engineering jobs usually entail applying physics and mathematics to problems in order to discover viable solutions or to make improvements. Where a number of different solutions are available, engineers evaluate these options and the required outcome in order to identify the best route to follow.

The earliest recorded civil engineer was an Egyptian known as Imhotep. It is believed that Imhotep designed and built the great pyramid of Djoser, also known as the Step Pyramid. Imhotep was one of Pharaoh Djoser’s officials and it is possible that he was the first person to make use of columns in architecture. The Step Pyramid was built in Egypt in about the time period 2630 – 2611 BC and can be found at Saqqara.

Imhotep would probably be absolutely fascinated with the leaps and bounds engineering has taken in the last 4000 years – although he might have a few secrets to share himself!

Check your comprehension

~ Knowledge of which subjects is crucial for engineers in different fields?

~ Who was the earliest civil engineer?


Unit 4

Последнее изменение этой страницы: 2016-08-11; просмотров: 240

lectmania.ru. Все права принадлежат авторам данных материалов. В случае нарушения авторского права напишите нам сюда...