The Flight
There are many critical phases that occur in a mission for a manned lunar landing.
The above figure shows the route the space vehicle will take. The heavy lines represent short accelerated maneuvers.
PRELAUNCH
In this phase, extensive tests are done on all equipment to ensure there are no last minute problems.
LIFTOFF!
The thrust produced here by the Saturn rocket is 34 million Newtons!!!
MANEUVERING AND ENTERING ORBIT
In this stage, the original Saturn rocket’s entire fuel supply has been used up. The system is now jettisoned.
5 rockets, producing a combined thrust of 4.5 million Newtons, is now used to bring the vehicle close to orbital altitude. The vehicle has left the atmosphere at this point, reducing aerodynamic pressure to zero and maneuvering thrusters have that much less to fight against from now on.
The Saturn rockets are swiveled and directs the space vehicle to enter a standard Earth orbit. To control the general direction of the vehicle, thrusters producing up to .9 million Newtons are used. Roll control is taken care of by smaller thrusters, capable of producing a force of 670 Newtons.
STANDARD EARTH ORBIT
At an altitude of 185 km, the orbital engine shuts down and leaves the vehicle in a circular orbit.
TRANSLUNAR INJECTION
The trajectory that will be taken will allow the vehicle to do what is known as a free return. The vehicle will go in front of the moon and be captured by its gravity well and enter orbit around the moon. With this proximity to the moon, it is possible to orbit it despite the large mass of Earth being so near.
LUNAR ORBIT INSERTION
All has gone well and the vehicle is about to enter orbit around the moon. A few midcourse corrections have been made so that it has arrived at this point. Navigation is done using ground data and on board data collected during flight. To align or "superimpose" the data, star sightings are used as they are more or less fixed points in the "sky". The thrusters being used now have a thrust of 98’000 Newtons.
LUNAR ORBIT
The lunar orbit is approximately 150km above the surface of the moon.
DESCENT INJECTION
This portion of the flight will be to launch the space module that will be land on the moon. The transfer orbit of the module will have an altitude of 15km. It is not actually a true orbit as it will begin to dive very soon due to the gravitation pull of the moon. This orbit is know as a Hohman transfer orbit.
DESCENT AND LANDING
Fuel of allowance here provides for 2 minutes of "hover" ability before touchdown must be accomplished or the landing aborted. The craft has to be near vertical and at a low velocity.
ASCENT AND RENDEZVOUS
The ascent is timed so that it is nearly identical to the descent except in direction. This brings the module to an entering orbit trajectory. The main vehicle will be there to rendezvous with the module.
TRANSEARTH INJECTION
While the lunar landing module was on the surface and the vehicle was it orbit, measurements had been taken to allow for a return to enter Earth orbit. The flight here is very similar to the translunar flight and after the initial thrust to escape the moon’s orbit, the rest of the flight is again more or less powered by the gravity of Earth and the moon. Corrections will need to made as they approach the Earth to allow the vehicle to reach Earth at a safe entry corridor. The entry must not be too high or too low. A high entry will cause the vehicle to skip out of the atmosphere (much like skipping stones on water). A low entry will result in extreme atmospheric drag and pressure against the hull of the vehicle.
ENTERING THE ATMOSPHERE AND LANDING
The landing site is a water one. This is both practical and logical. There is already plenty of water and the composition of water allows for a softer landing. As well, water does not cost anything as a special landing pad would. The large area that water occupies also lessens the calculations necessary on the already tiring crew of the vehicle and the staff at the Command Centre.
The primary concern is the dissipation of energy during entry. Proper navigation can minimize such effects. Drag parachutes are deployed once safe entry into the atmosphere has been established.