Derek27 wrote: ↑Sun Jul 11, 2021 8:59 pm
It's like ballistic missiles. If you can get well above the atmosphere you can travel faster and further. Ronald Regan gave a speech talking about getting people from US to Japan in 2 hours. A bit premature but it's probably on its way.
Regan was right but very premature.
For travel above the Earth's surface nothing can really compete with jet engines and rocket engines. Both require oxygen to enable their fuel to burn and provide power. The main difference between them is a jet engine uses the oxygen in the atmosphere and is therefore restricted in altitude while a rocket engine carries it's oxygen in supplementary tanks and is mixed with it's fuel which increases weight.
Hypersonic travel is broadly defined as being in excess of Mach 5 (Concorde maxed out at just over Mach 2). There are many initiatives developing on the theme.
The problem with the rocket approach is the power required to lift the craft into sub-orbital altitudes. Branson's craft does it but only for a small number of people at a time and is given a piggy-back to save on the fuel weight required to lift it through the thicker atmosphere at lower altitudes ... but it's a start.
The problem with the jet approach is the higher you go to reduce the drag on the plane the less oxygen is available to allow the fuel to burn. It is a big problem that is proving very difficult to overcome. "The greatest speed ever reached by a manned aircraft that is not a spacecraft [i.e. atmosphere breathing] is 7,270 km/h (4,520 mph) (Mach 6.7) by USAF Major William J. Knight in the experimental North American Aviation X-15A-2 on 3 October 1967 over the Mojave Desert, California, USA." (
https://www.guinnessworldrecords.com/wo ... t-aircraft) Yes 1967!
After more than 50 years that record still stands!
They have a jet engine able to hit very high speed (Scramjet). The NASA X-43, reached a speed of Mach 9.68 at 109,440 ft (33,357 m), which works out to an airspeed of around 10,800 km/h (6,700 mph), on 16 November 2004. The problem with a scramjet is at such high speeds the combustion chamber gets hot enough to melt itself! A British company, Reaction Engines, based in Oxfordshire, has successfully tested a pre-cooler to counter this but not yet at full operating spec. However there is a second problem with the scramjet, it needs to be flying faster than Mach 4 before you turn it on! So presently a vehicle with such an engine would need a secondary power supply to get it to that speed so the scramjet can take it faster ... more weight, more problems!
We will get there, it will be slow and probably not in my lifetime and not in that of many of you but it will happen, one day.