231339
222576
Skywatching

Old tech takes us into space

A few days ago, a SpaceX launcher and spacecraft took four astronauts to spend several months on the International Space Station.

The new space systems are safer, more efficient and more sophisticatedly controlled, and boosters can fly home and land for reuse. However, today's launches look much like those of the '50s and 60s. Basically, as yet we have not come up with anything better than the multi-stage rocket, where one rocket piggybacks others partway up.

Surprisingly, the first multi-stage rockets were invented in the 14th Century by the Chinese. They mounted several small rockets on the front of a big one. When the big rocket had burned all its fuel, the smaller ones fired off, having been given a leg up.

Modern multistage space vehicles are still based mainly on the ideas of two people: Konstantin Tsiolkowsky and Wernher von Braun.

If we want to get to the International Space Station, for example, we need a space vehicle system that can lift what we want to deliver to a height of about 410 kilometres and accelerate it to a speed of almost eight kilometres a second.

This takes a lot of fuel, and since a rocket spends most of its operational time in the extreme upper atmosphere and in space, it has also to carry the oxygen needed to burn that fuel.

Then, to contain it we need tanks. To deliver it to the engines we need pumps. The whole lot needs to be supported in a structure that can accommodate accelerations many times that of gravity, handle severe vibrations and stresses, and function in space.

This means lots of weight. Even so, in a modern rocket, the weight of fuel and oxygen can be up to several times the total weight of the hardware.

As the fuel and oxygen are consumed, the tanks become increasingly empty, and more and more of the structure becomes dead weight. There is no point in carrying it all into orbit, and indeed, as yet we have not been able to make a single-stage rocket that is a useful means of getting out into space.

We have standardized on the use of multi-stage rockets. We make a stack of rockets and put what we want to deliver into space, the payload, usually on top.

At launch, we fire the bottom, or first stage. Because it has the most weight to lift, it is usually the biggest. Sometimes we need to strap on additional rockets — boosters — in order to get more thrust. The first stage gets us to 50-80 km, above most of the atmosphere and up to a speed of a several thousand kilometres an hour.

When its fuel and oxygen is all used up, the first stage is dropped. In the past it used to be discarded. In the modern, SpaceX system, some fuel and oxygen are retained in the first stage and used to land it safely back on Earth.

Since this is a large and expensive piece of hardware, being able to reuse it leads to large cost savings. The second stage now fires. At the same time the path of the spacecraft is tilting down, until when it reaches orbital speed, it is moving parallel to the ground.

When this has exhausted its fuel, or the required velocity has been reached, it too is discarded. Leaving it attached to the spacecraft just means more dead weight to manoeuvre and also the risks associated with any unburned fuel.

The spacecraft is now freely in orbit. It is equipped with low-power thrusters that can be used to make the small changes in speed, direction or attitude needed to rendezvous with the space station. If we want to go further, for example, to the Moon, we can add an extra stage.

Reducing the amount of excess weight we have to lift or accelerate reduces costs and in many cases make the missions possible. Even after decades, the ideas of Tsiolkowsky and von Braun still define how we access space.

  • After dark, Saturn and Jupiter lie close together, low in the southwest
  • Mars is rising in the east.
  • Venus lies in the dawn glow with Mercury below and hard to spot. 
  • The Moon is Full on the 30th. 

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



More Skywatching articles

232645
About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



229862
The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

Previous Stories



228921
227490


232116