When we talk of spacecraft acceleration, we usually refer to those fast-moving objects in the orbit going around the earth on a travel mission towards a planet. These spacecrafts obtain their velocity as well as position and direction from the ground stations.
By the use of Doppler Shift, time delay and baseline information, the position, direction, speed and velocity of a spacecraft can be determined with precision in relation to the earth. The speed and direction of the earth are known precisely and thru a combination of this information, you will know your movements in the solar system.
If you are moving accurately, you can utilize the on-board accelerometer. By knowing your rate of acceleration, you can ascertain your velocity. In case you want to know your exact acceleration within the area of the universe, this may not be possible because the accelerometer has no capacity to sense the movements of a planet where you are orbiting.
The instrument will read zero whether you are in space or going around a certain planet. Let us say that you are inside the spacecraft and orbiting the earth, and you want to know your position and how fast you are moving, you can try the optical methods.
By looking at the nearby planets and stars with a high-powered telescope, you can find out where you are. You can search the database that indicate where the stars and planets are located based on space and time and analyze them relative to your position.
Based on Physics, acceleration is the rate of variation in velocity against time. In simple definition, acceleration is the process of increasing the speed of an object. In the case of a car, when it is said that the speed is changing from zero to 60 in 6.7 seconds, this means the car accelerates in 6.7 seconds to reach 60 mph starting from a full stop.
This case indicates a simple acceleration theory; however, in Physics it is more complicated than just ascertaining the speed of a car. Acceleration in Physics involves the increasing, decreasing and changes in the direction of a moving object. Another acceleration determinant is the acceleration caused by gravity.
This can be felt in roller coasters which rarely exceed 60 mph. But when it accelerates from high to low, the acceleration due to gravity is increased creating a dangerous proportion. In the case of spacecraft, acceleration is maintained at a normal level because if it is increased above the normal level, there will be corresponding stress felt by the Astronauts.
Always remember that acceleration is related to injury. This is the reason why the most reliable gauge to an accident experiment is the accelerometer. Heavy acceleration can lead to injury or death. When Princess Diana died in an accident, the acceleration was found at an overwhelming speed that is why it was impossible for her to survive.
This was worsened by the impact of her body to the car which crashed on the outside surface due to her failure to wear seatbelt.