17 September 2013

Trajectory to the moon

1950s era comic depicting the general expectation for space travel -- a space age which never came to pass because of deadly space radiation and other problems that have not yet been overcome
In getting from the ground to space the boosting rocket must provide the energy for lifting the mass, overcoming gravity and air resistance and getting up to orbital speed.  It's a big job that takes a big rocket. Apollo's rocket was one of the biggest, the Saturn V:

It's a biggy: the Saturn V

13 September 2013

Space reentry vehicles, part 7

Part 7: Pressure

At subsonic speed, below Mach 0.3, the pressure of the air coming into the hull of an aircraft is roughly 1/2ρv2 where ρ is the density of the fluid medium; for air at sea level = 1.225 kg/m3.  The equation for compressible flow given for above Mach 1 speeds goes as the power of 3.5 rather than 2 and rises much more quickly.

12 September 2013

Space reentry vehicles, part 6

Part 6: Control


After atmospheric reentry the heat shields on the bottom of space reentry capsules have a characteristic burn pattern that starts at a point off centre and emanates to the edge. 

Gemini heat shield after reentry

The central point of the burn pattern is the stagnation point where the air isn't moving parallel with respect to the surface but hits it at right angles.  The temperature and pressure is at a maximum at the stagnation point such as the following diagram depicts:

02 September 2013

Space reentry vehicles, part 5

Part 5: More on the detached shock wave


The term detached shock wave originally referred to an undesirable aerodynamic effect that was found in supersonic projectiles such as bullets.  This type of shock wave was of interest because it had a lot more drag and aerodynamic instability than an attached one.

The first aircraft designed to be supersonic, the Bell X-1, was modelled after the shape of a 0.5 calibre Browning machine gun bullet, which was known to be stable in supersonic flight.