re-entering the atmosphere

In space there is no air resistance to oppose motion, so the Space Shuttle orbiter could travel at very high speeds, up to 17,000 mph!  At these speeds, the orbiter experienced enormous air resistance as it descended into the Earth’s atmosphere at the end of its mission.

Air resistance is just like any other form of friction – it converts kinetic energy into heat energy.  The effect of this heat energy is demonstrated in this video clip taken by a Canadian police car camera.  It shows a meteor burning up in the atmosphere above Edmonton.

Thankfully most meteors do burn up in the atmosphere, although the dinosaurs were not so lucky.

The high temperatures created during re-entry ionised the gas around the orbiter and this is often seen as a bright light in NASA cockpit videos, such as the one shown below.

To protect the vehicle and its crew from these high temperatures, the underside of the orbiter was covered by a layer of heat resistant tiles called the thermal protection system.  This NASA clip explains how the tiles are constructed and arranged on the underside of the orbiter.

When Columbia was launched in 2003, something fell against the insulation on the left wing and knocked off some of the tiles.  This hole in the thermal protection system caused Columbia to explode over the US as it re-entered the atmosphere.  There is a wikipedia article about the Columbia disaster.

Video footage of NASA’s Houston control room from the morning of the disaster was included in the BBC Horizon documentary Final Descent – Last Flight of Space Shuttle Columbia.

WARNING: This last film is an excerpt from the Horizon programme and includes genuine cockpit video that was found in the wreckage, with some clips of the crew’s final minutes before they were killed.

There is a good description of the Space Shuttle at How Stuff Works.

Before the space shuttle, each spacecraft was designed to be used only once and it was only the capsule containing the crew that returned to Earth. This was a small conical vehicle that had a thick heat shield on its base to withstand the heat of re-entry.

drawing of Apollo capsule re-entering the atmosphereartist’s impression of Apollo capsule re-entering the atmosphere

An ablative heat shield was used for these capsules. The material covering the base was designed to heat up until it sublimed (changed from solid to gas). The latent heat of sublimation is much greater than that required for fusion or vaporisation, so much more heat energy could be absorbed by the shield material as it changed state. Obviously there is a catch…the longer the shield protects the astronauts, the thinner it becomes! Here is an image of a Gemini IV capsule on display at the Smithsonian National Air and Space Museum showing what was left of the heat shield after successful return to Earth.

Gemini IV crew capsule photo: Richard Kruse

 

transit of Venus

I set my alarm clock for 4am and was disappointed to find a sky full of clouds that would prevent us from viewing the transit of Venus from Thurso and the surrounding area. 

The BBC Horizon programme broadcast last night was very good.  You can still catch it on iPlayer for the next week or download it using the link below.

very large telescope

I found a brilliant timelapse video on the Popular Science site.  It shows the Very Large Telescope (VLT) at work in Chile.

Here are some VLT links to explore

You can get a pdf summary of the VLT from the European Southern Observatory (ESO), the organisation that runs the VLT, by clicking on the download link below.

Endeavour takes antimatter hunter to the space station

image by NASA

A few weeks ago we were all ready to look up for an evening sighting of the space shuttle Endeavour as it separated from its external fuel tank while passing over the UK.  That launch was delayed but NASA is set to try again today.

Endeavour is the newest vehicle in the shuttle fleet.  It was built as a replacement for Challenger.  This will be Endeavour’s last mission and its task is to carry the Alpha Magnetic Spectrometer (AMS-02) up to the International Space Station.

Launch is scheduled for 1.56pm UK time and you can watch it live on NASA TV.  Alternatively, you can watch the launch as a webcast from CERN, starting at 1.45pm.

AMS is designed to search for antimatter, a substance first proposed by British Physicist Paul Dirac.

Physicists believe that there should be a balance between matter and antimatter .  The problem is that we live in a universe that seems to be made from matter, not matter and antimatter, so the question is…

where did all of the antimatter go?

Particle physicists at CERN’s Large Hadron Collider have an experiment that is looking for an answer to this question.  The particle physics research teams at CERN were given the job of building the AMS, which was transferred to the Kennedy Space Centre earlier this year.

The videos below are from CERN’s multimedia library for the AMS project and will give you an idea of the role of AMS.  The first film is less than one minute long and designed to act as a trailer for the project.  The second is longer (15 minutes) and has several interviews with key project staff.