According my understanding of aerothermodynamics . . .
infinity divided by zero?
No, you have to study my writings about it. Very popular.
Very popular, very wrong.
Maybe you should enlighten us on your "understanding of aerothermodynamics"?
OK - here we go!
A
re-entry is done by a spacecraft or an ICBM returning to Earth from space at high speed that manages slowing down and land in 10 to 30 minutes. The first
re-entry with a human aboard was done by Juri Gagarin 1961 ICBM style with start on Earth and a landing on Earth a little later. It was a communist hoax! It never happened in reality! It was Fake News! Pure propaganda.
The velocity at beginning of any
re-entry at top of atmosphere (altitude 120 000 meters) - the re-entry interface - differs considerably depending on where the space craft comes from. It is suggested that a manned spacecraft arrives with speed >21,000 m/s, when coming from planet Mars, >11,000 m/s, when coming from the Moon or only about 8,000 m/s, when coming from Earth Parking Orbit, EPO. Reason for different re-entry velocities is that Earth gravity has accelerated the spacecrafts during different times; weeks for a spacecraft coming from Mars, days for a spacecraft coming from the Moon and hours for a spacecraft trying to descend from a space station in EPO or 30 minutes for an ICBM descending from its top altitude You must arrive at the starting point of a re-entry at the right time! If you arrive 10 seconds too early or late, you miss the end point - the landing zone or target - by 80 000 - 210 000 meters! What the change of direction (°/s) is better forgotten. Spacecrafts are supposed to land at 0 speed so parachutes are required at the end. ICBMs will just go faster and faster during re-entry. During re-entry there is always a break in communication between spacecraft or ICBM.
Assuming that it is possible to steer the spacecraft or ICBM to arrive at the correct location, at the right moment, at the right direction at the upper atmosphere in Earth 3D space (it isn't), it is suggested that suddenly a big brake force (!) develops out of nowhere up in the sky which slows down the spacecraft to land in front of a welcome committee with a brass band. It is suggested that this big brake force is due only to contact between the spacecraft or ICBM and air or atmosphere but it is
aerothermodynamics nonsense.
It cannot happen in reality!
Only brain washed people believe it!
The first
re-entry in history after a trip to the Moon was Apollo 8 on December 27, 1968. Apollo 8 was a small spacecraft capsule/command module without toilet. At 139h15m after start (and no visits to the toilet) Apollo 8 was 94 800 kms from Entry Interface 6h30m away. Speed was only 2 650 m/s. 37 minutes later Apollo 8 was 88 900 kms from Entry Interface with speed 2 740 m/s. During the next 6 hrs velocity increased all the time, e.g. 63 minutes later at140h55m - 78 300 kms from Entry Interface - speed 2 926 m/s, 124 minutes later at 142h59m - 56 340 kms from Entry Interface - speed 3 443 m/s, 37 minutes later at 143h36m - 49 000 kms from Entry Interface - speed 3 680 m/s, 37 minutes later at 144h13m - 41 255 kms from Entry Interface - speed 3 993 m/s, 25 minutes later at 144h38m - 35 188 kms from Entry Interface - speed 4 276 m/s, 31 minutes later at 145h09m - 28 254 kms from Entry Interface - speed 4 712 m/s, 23 minutes later at 145h32m - 21 531 kms from Entry Interface - speed 5 265 m/s, 13 minutes later (1 hr 1 m to Entry Interface) at 145h45m - 17 800 kms from Entry Interface - speed 5 588 m/s, 27 minutes later at 146h12m - 9 167 kms from Entry Interface - speed 7 103 m/s. At 146h31m the Service module was dumped (it burnt up in the atmosphere). Command module continued alone at increased speed. Reason why velocity increased and direction turned down to Earth was that Earth gravity force accelerated Apollo 8 straight down all the time!
Re-entry Interface at 120 000 m altitude was apparently reached at 146h46m - speed was then 11,040 m/s! Maybe they were above Tokyo at that time? With that speed straight down Apollo 8 would have hit the Ginza after 11 seconds. It didn't happen. Apollo 8 flew off towards Palmyra island in a remote area of the Pacific Ocean (where nobody could watch)!
What happened then, i.e. the real
re-entry trajectory from Entry Interface to splash down is not really known. It was an
aerothermodynamics mystery. There was a break in communication but at 146h54m - drogue chutes were out at 7 000 m altitude (we are told) (speed estimate 200 m/s?), at 146h55m - chutes were deployed and at 147h00m - splash down - December 27, 1968 (at 15.51.42 UTC local time), pos 8°8'N 165°1' W. Hole in one! Just in front of awaiting US navy ships and a brass band playing! The Apollo 8 crew could finally go to the toilet.
How Apollo 8 managed to slow down from 11 040 m/s speed to 0 in 14 minutes (or 840 seconds) at 13.14 m/s² has never really been explained. It was due to
aerothermodynamics of course but how? Everyone was so happy that it just happened, so nobody ever asked ... how? Actually no
re-entry took place at all. It was just a Hollywood show! Apollo 8 command module was dropped from a US airplane that took off from an airbase nearby.
Willy Low was happy! Americans believed anything 1968! The US Space Program was a success! Even if it was 100% fakery!
If e.g. Apollo 11 with mass 5 500 kg would start its
re-entry with a speed of about 11 000 m/s, when arriving in and dipping into the upper, very thin atmosphere at say 120 000 meters altitude - the
re-entry interface - with a certain direction relative ground and, if you intend to slow down at a constant 18.0 m/s² deceleration during about 10 minutes, you must apart from the brake force in the opposite direction of travel also counter the 9.8 m/s² vertical downwards pull of Earth gravity. It would appear that the constant, total force suddenly applied to
re-enter and land must be of the order 130 900 N (that corresponds to 23.8 m/s² deceleration) during 10 minutes and you should of course wonder where it comes from.
Aerothermodynamics? That force will also change your direction!
Can a force of 130 900 N (or 13 tons) just suddenly appear out of nowhere up in the sky at 120,000 m altitude?
It is suggested that this brake force consists of aerodynamic drag and lift but there is no air at 120,000 m altitude to provide any drag and lift.
Aerothermodynamics!
Regardless, drag/lift forces are functions of spacecraft shape and flow, velocity and air density, which are changing all the time, i.e. the forces are not constant and so it is impossible to predict the brake trajectory of the re-entry from when the variable drag/lift forces are applied. You have not got a clue, where you will end up! It means that you will start to spin and burn up.
Furthermore it is suggested (already 1966) that a future spacecraft arriving from Mars at 21 000 m/s speed will bounce (LOL) on the top of the atmosphere, skip out and do a second
re-entry (terminal control) a little later, i.e. the brake force lifts the spacecraft back into space again at first contact with the atmosphere.
But how do you control and determine such a high speed, skip out
re-entry? Can you do it braking or speeding up with a rocket engine?
In order just to prepare a re-entry from EPO you must ensure that you arrive on time at the location to start
re-entry at the exact speed/direction. If you are too early or too late to start your re-entry, you must slow down or speed up before to arrive in order not to make a mess of the rest.
It is not easy. It is in fact very difficult. The only way to slow down is to fire your rocket engine. Apollo 11 didn't have any but the Shuttle had:
To adjust re-entry speed at around 8 000 m/s velocity only from EPO costs plenty fuel. Say that your Shuttle arrives at 8 050 m/s speed with kinetic energy 32 401 250 J/kg, but that it should arrive at 7 950 m/s speed and kinetic energy 31 601 250 J/kg to succeed the complete
re-entry. The difference in kinetic energy is then 800 000 J/kg.
Have you got the fuel to adjust the speed 100 m/s? The answer is simple.
Konstantin E. Tsiolkovsky has established that the change in velocity, delta-v, of a spacecraft in vacuum space (no influence of gravity of adjacent planet Earth) is a function of the mass ratio (spacecraft mass before, m
0 and after, m
1 firing the rocket engine, difference m
0 - m
1 being the fuel mass ejected as exhaust gas and the exhaust velocity v
e of gas leaving the spaceship rocket nozzle.
Delta-v = v
e ln (m
0/m
1)
Example - here we want to slow down a 78 000 kg (m0) Shuttle (with fuel) entering the atmosphere backwards at a almost horizontal speed of 8 050 m/s (no influence of gravity) to 7 950 m/s to ensure arriving at the re-entry location. The fuel aboard is ejected at a velocity v
e of say 4 000 m/s. Delta-v is 100 m/s!
Then ln(m
0/m
1) = 0.025 and m
0/m
1 is about 1.025315!
It means that you need ~2.5% of the spacecraft mass or 2 000 kg of fuel just to slow down 100 m/s or 1.25% of the speed!
If your rocket engine is an old one with v
e only 2 800 m/s, then ln(m
0/m
1) = 0.035 and m
0/m
1 is about 1.03636!
It means that you need ~3.6% of the spacecraft mass or 2 800 kg of fuel just to slow down 100 m/s!
And you have to fire the rocket engine in exactly the right direction at the right time/location! Otherwise you brake out of correct direction! And will miss the target.
Let's face it. You cannot do it. You cannot carry the fuel required! You cannot aim the brake force in the right direction.
How Apollo 11 without any rocket engine aboard managed to arrive at the
re-entry start point in the upper atmosphere at the right time/speed/direction in 1969 is a mystery. Or not! It was all fantasy!
All re-entries since 1961 are hoaxes! You are going too fast and do not know your speeds, positions and directions at any moment and cannot adjust anything, as you do not have the means to do it.
The re-entry was an integral part of the 1957-1991 US/USSR fake 'space race', i.e. simple propaganda. The Russians just said it was dead easy and the Americans agreed. But it was and is impossible.
Etc, etc. Guess where above is from!