Risks of Space Travel

When a spacecraft (or any other object) enters the Earth's atmosphere, it experiences a dramatic range of Forces, Temperatures and Pressures. All of these have the capability to injure or kill astronauts, and so spacecraft designers have to go to great lengths to build craft capable of withstanding these conditions.

The video below shows the conditions NASA's new Orion Capsule will experience during re-entry.

Effect of Temperature

When a object enters the atmosphere, it can be travelling at incredibly high speeds (Orion will re-enter at over 20,000 mph), which when passing through the increasing dense air, will cause the spacecraft to reach incredibly high temperatures (over 2,200 K). Without protection, the spacecraft would burn up on re-entry, and so the spacecraft has to be protected using a heat shield.

A Spacecraft's heat shield consists of thousands of small tiles made of fibre-glass, epoxy resin and other heat resistant materials. The heat shield protects the spacecraft due to its very high Specific Heat Capacity. This means the tiles can absorb a large amount of Heat Energy, preventing the capsule itself from overheating.

The tiles are also ablative, which means they are designed to burn off during re-entry, which takes more Heat Energy away from the spacecraft itself.

The video below shows a brief description of the science of heat shields.

Calculating the Effects of Re-Entry

When a spacecraft enters the atmosphere, it loses an incredible amount of Kinetic Energy, which following the law of conservation of Energy, is converted into Heat Energy.

The following calculation allows the change in the spacecraft's Temperature to be found:-

1. Calculate the loss of Kinetic Energy (1/2mvu2 - 1/2mvv2).

2. Loss in Kinetic Energy = gain in Heat Energy.

3. Use Eh = cmΔT to find change in Temperature.

A spacecraft of mass 5000 kg enters the atmosphere at a speed of 1000 ms-1 and is slowed by the atmosphere to a speed of 300 ms-1. If the Specific Heat Capacity of the materials used to build the spacecraft's heat shield is 12000 Jkg-1°C-1, what is the temperature increase of the heat shield?

Lost Ek = (0.5 x 5000 x ( 1000 )2 ) - ( 0.5 x 5000 x ( 300 )2)

Lost Ek = 2.5x109 - 2.25x108

Lost Ek = 2.275x109 J

Eh = cmΔT

ΔT = Eh / cm

ΔT = 2.275x109 / (12000 x 5000)

ΔT = 38 °C

The Dangers of Space Flight

As can be seen above, one of the major challenges of space flight is building a spacecraft that can withstand the heat of re-entry. This requires the use of materials and shapes to reduce the Heat transfer to the craft itself.

This is, however, not the only risk of space flight. In order to withstand the extremes of temperatures and pressures experienced in space, specialised protective suits must be worn. The image below shows how the Apollo-era spacesuit was designed to protect its wearer:-

The video below shows the effect of exposure to space on the human body.

Dangers of Space Flight Case Study : Space Shuttle Columbia

On February 1st, 2003 the NASA Space Shuttle Columbia was destroyed during re-entry of the Earth's atmosphere, with the loss of all seven astronauts on board. The images below show the Columbia during its final take off, as well as a close-up of the section of foam that became detached during launch.

During take-off, a small section of the protective foam from the shuttle's main fuel tank broke free and struck the underside of the Space Shuttle. This impact most likely caused a 15-20cm diameter hole in the protective heat shield (black sections of above images). This foam detachment was observed on the launch cameras but at the time, the damage was not understood and it was decided to continue with the mission as normal.

Upon re-entry, this hole in the heat shield allowed superheated gases (at temperatures over 2,200 C) to enter the wing of the shuttle, causing the shuttle to break apart whilst travelling at speeds of ~Mach 19, killing all on board.

The video below shows footage of the foam Impacting the Shuttle as well as recreations of the likely effects:-

The video below gives a much more in-depth look into the causes of the loss of the space shuttle Columbia:-