Re-Entry into Earth's Atmosphere: Understanding Space Ship Speed

In summary, a space ship re-enters the Earth's atmosphere at a great rate of speed by emitting part of itself (burnt fuel) at a very high rate of speed. The acceleration of the mass of the fuel to high speed generates a force that propels the spaceship forwards, and the spent fuel backwards.
  • #1
leemuhammad
2
0
How Does a Space Ship reenter the Earth's atmosphere at such a great rate of speed? I understand speed in this way W=F x D. there is nothing in space for the ship to propel itself off to build this great speed.
 
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  • #2
Have you ever considered the change in gravitational potential energy?
 
  • #3
leemuhammad said:
How Does a Space Ship reenter the Earth's atmosphere at such a great rate of speed? I understand speed in this way W=F x D. there is nothing in space for the ship to propel itself off to build this great speed.

You forgot two important factors:

1. The ship already has a large speed to begin with. Just think of how fast the ship has to move to maintain an orbit at that distance above the earth. If it is stationary with respect to the earth, it'll fall towards the earth. So using basic mechanics, you can easily calculate the speed that it needs to maintain to use the central force from the earth.

2. When it is coming back down to earth, a radial component of the velocity increases mainly due to gravity. Drop a ball and its velocity increases at it races towards the ground. So if it doesn't have any "lift" or thrusters, it will increase in speed by itself due to gravitational force.

Zz.
 
  • #4
leemuhammad said:
There is nothing in space for the ship to propel itself off to build this great speed.
No one answered the last question. The spaceship emits part of itself (burnt fuel) at a very high rate of speed. The acceleration of the mass of the fuel to high speed generates a force that propels the spaceship forwards, and the spent fuel backwards. The higher the speed of the propellent, the more efficient the rocket engine is (more energy gained per amount of spent fuel emitted).

When launching a space ship, the more final speed you need, the more fuel you need, but the fuel also adds weight. Using solid rocket boosters on the shuttle helps since they are only accelerated to a sub-orbital speed before being detached after they are spent. It took a huge rocket and a lot of fuel to put a man on the moon. The Saturn V weighed 6 million pounds, and started with just 7 million pounds of thrust at lift-off. Again, multiple stages were used, and detached.

To save fuel and costs, rather than use even more fuel to slow down a space ship, the ship is only partially slowed, then relies on aerodynamic drag to do most of the braking, which generates a lot of heat and was the cause of destruction of one of the shuttles. The fastest piloted re-entry speed ever was the Apollo 10 mission where the return was made when the moon was further from Earth than the other mission.

Here is a link to the fastest speeds of manmade objects:

http://www.aerospaceweb.org/question/ spacecraft /q0260.shtml

Fastest land based objects are rocket sleds, here's another link:

http://www.46tg.af.mil/world_record.htm
 
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  • #5
Jeff Reid said:
No one answered the last question.

I did!

If you follow your scenario, if you do a "burn" to increase your speed, you'll never get back to Earth from that orbit, unless you turn your ship and point it directly at the earth, which isn't how it is done.

What is done instead is to slow down the ship so that it start falling out of orbit towards the earth. But by doing this, you also pick up a radial component of the speed, meaning you start to fall faster towards the Earth simply via gravity. So the ship can simply "propel" itself using the gravitational field.

Zz.
 

1. What is re-entry into Earth's atmosphere?

Re-entry into Earth's atmosphere is the process of a spacecraft or space shuttle returning from space and entering the Earth's atmosphere. This is a critical stage of a space mission, as the spacecraft must withstand extreme temperatures and pressure changes in order to safely reach the Earth's surface.

2. How fast do space ships travel during re-entry?

Space ships can travel at speeds of up to 17,500 miles per hour during re-entry. This high speed is necessary for the spacecraft to overcome the Earth's gravitational pull and re-enter the atmosphere.

3. What factors affect the speed of a spacecraft during re-entry?

The speed of a spacecraft during re-entry is affected by several factors, including the angle of entry, the composition of the atmosphere, and the weight and design of the spacecraft. The angle of entry is particularly important, as a steeper angle can increase the speed of the spacecraft, while a shallower angle can decrease it.

4. How is the speed of a spacecraft during re-entry controlled?

The speed of a spacecraft during re-entry is controlled through a combination of aerodynamic forces, such as lift and drag, and the use of thrusters or parachutes. These systems help to slow down the spacecraft and reduce its speed to a safe level for landing.

5. What are the potential dangers of re-entry into Earth's atmosphere?

Re-entry into Earth's atmosphere can be a dangerous process, as the high speeds and extreme temperatures can put a lot of stress on the spacecraft. If the spacecraft is not properly designed or if there are any malfunctions in the systems, it can lead to structural damage or even the loss of the spacecraft and its crew. That is why careful planning and preparation is essential for a successful re-entry.

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