I FEEL a strong sense of disappointment that so little has been achieved in manned space flight in the 50 years since Armstrong and Aldrin first stepped on the moon. Skylab, then the Shuttle and now the International Space Station, all involving only low earth orbits, represent so little to show for half a century.

Almost 30 years ago aerospace engineer Robert Zubrin showed how using derivatives of then current Shuttle technology a crewed mission to land on Mars was not just possible, but also affordable for the United States. He subsequently published the Case for Mars, setting out for a layman how it could be done.

The recent film The Martian gives a realistic idea of the lander and Mars habitat modules for such a mission, although its portrayal of the the spacecraft for transit is exaggerated.

Thanks to private enterprise, launch costs have plummeted over recent years. Space X now quotes a price of only $90 million for 13 tons to Mars.

Putting people on Mars is no longer prohibitively expensive and is well within current technical capability. If the West led by the US does not dare to dream and to do, I have no doubt that others, China most likely, soon will.

Otto Inglis, Edinburgh EH4.

ONE aspect of the Moon landing of 1969 that doesn't seem to have been mentioned in recent articles commemorating the enterprise is the suggestion by sceptics that it was all an elaborate hoax.

This scepticism was quite widely publicised at the time, and the doubters included some respected scientists not at all notorious for making eccentric claims in green ink.

I don't pretend to know the truth of the matter, but couldn't help noticing that the sceptics' observations of incongruities in the pictures were never met with reasoned explanations, but only with indignant expostulation and cries of "conspiracy theorist!", as though the existence of such theorists proved conspiracy to be impossible.

Robin Dow, Rothesay.