Discovery Science: Transport Technology – To Outer Space and Back Again

Transport Technology – To Outer Space and Back Again

Carrying a space vehicle into Earth’s orbit requires a vast amount of energy. On its return, the kinetic energy of the space vehicle is reduced through friction with the air in the Earth’s atmosphere.

Satellites and astronauts are transported into space by means of a launch vehicle, but it is not enough just to carry the vehicle to the altitude of its intended orbit. Once there, it must be accelerated to the required orbital speed.

For instance, for a low orbit at an altitude of 186 miles (300 km) this needs to be almost five miles per second (eight km/s).

Examples of orbital maneuvers

If a space vehicle is to move from a lower to a higher orbit, its engine needs to “burn” for a specific period. A higher speed extends the orbit into an ellipse. At the highest point of the elliptical trajectory, the engine is started up again. The thrust must accelerate the space vehicle to exactly the speed required for the new orbit. During a rendezvous maneuver, space vehicles are guided toward each other along their orbits.

If need be. they can then be coupled mechanically. This facilitates servicing satellites in space and is also used to transport equipment and astronauts to the international space station. During such a rendezvous, it is common for one space vehicle to be passive, while the other space vehicle approaches it.

The movements of the pursuing vehicle must be closely controlled so that positions, speeds, alignments, and rotations of the vehicles correspond with each other. This complicated maneuver is monitored via radar by ground stations and the pursuing vehicle.

Atmosphere reentry

The vehicle’s return to Earth is initiated in orbit by igniting the deceleration engine. Entering into the Earth’s atmosphere is a critical maneuver because the spacecraft is moving at such great speed. Friction with the denser air in the atmosphere results in the extreme heating of the craft, while also braking the speed.

The heating and braking of the spacecraft are dependent on both the speed and the angle of reentry. Braking action can be severe for a manned capsule. This can be mitigated, however, by shaping the capsule to create a slight buoyancy effect. Although part of the frictional heat is dissipated by the air current, a heat shield is essential if the space vehicle is not to burn up on reentry.

So-called ablative cooling uses materials, which will melt off or vaporize and so remove heat in the process. For instance, the charcoaled ablation shield of the Apollo capsules maintained inside temperatures below 80.6°F (27°C), while outside temperature were in excess of 3632°F (2000°C). Another possibility is protective heat tiles, such as those that have been used on the space shuttle. Finally, space capsules land by means of parachutes.

On some capsules, ground impact is reduced by firing additional braking rockets when the capsule is close to the ground. The space shuttle has the advantage that it can land like an aircraft. The disadvantage is its greater starting weight and it is greater technical complexity.


IF THE STARTING location is close to the Equator, the rocket is already moving at the rotation speed of the Earth, and thus requires less energy for acceleration.

THE FUEL needed to overcome the gravitational force of the Earth and the resistance of the air can often make up about 90 percent of the starting weight of a rocket.