Vectors by Charles Sheffield

Author:Charles Sheffield
Language: eng
Format: mobi, epub
Tags: Science Fiction, American, Fiction, General
ISBN: 9780441860579
Publisher: Baen Books
Published: 1979-11-30T05:00:00+00:00

Lead

200

11.4

0.18

Gold

1,400

19.3

0.73

Aluminum

2,000

2.7

7.4

Cast iron

3,500

7.8

4.5

Carbon steel

7,000

7.8

9.0

Manganese steel

16,000

7.8

21.

Drawn tungsten

35,000

19.3

18.

Drawn steel wire

42,000

7.8

54.

Iron whisker

126,000

7.8

161.

Silicon whisker(SiC)

210,000

3.2

660.

Graphite whisker

210,000

2.0

1,050

Fictionite

2,000,000

2.0

10.000

Not surprisingly, we won't be trying to make a Beanstalk support cable from lead. As we can see from the table, even the best steel wire that we can find has a support length only one hundredth of what we need. The last entry in the table, Fictionite, would be perfect but for one drawback: it doesn't exist yet. The strongest materials that we have today, graphite and silicon carbide whiskers, still fall badly short of our requirements (for Earth, that is. A Mars Beanstalk has a minimum support length of only 973 kms. We could make one of those nicely using graphite whiskers).

Does this mean that we have a hopeless situation? It depends what confidence you have in the advance of technology. Table 2 lists the strength of materials that have been available at different dates in human history. There is some inevitable arbitrariness in making a table like this, since no one really knows when the Hittites began to smelt iron, and there must have been poor control of times, temperatures and purity of raw materials in the Bronze Age and early Iron Age. All these factors have a big effect on the tensile strength of the products.

It is tempting to try and fit some kind of function to the values in the table, and see when we will have a material available with a support length of 5,000 kms. or better. It is also very dangerous to even think of such a thing. For example, consider a fit to the data of the form: Strength = B/(t - T), where B and T are to be determined by the data, and t is time in years before the year 2000 A.D. This fits the data fairly well if we choose B = 525,000 and T = 17.5 years. Unfortunately, such a form becomes infinite when t = T. If we were to believe such a fit, we would expect to have infinitely strong materials available to us some time in 1982!

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