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Eagle’s touchdown explained

There’s no mystery to the process by which the Apollo 11 lunar module was able to touch down on the surface of the Moon (‘How did the Eagle Land?’, Letters, April 2016). Apollo’s guidance computer steered the module main engine’s gimbals, and there were 16 ‘puffer jets’ to help keep the lander stable. The system relied on gyroscope technology dating from the earliest age of aviation instrumentation that was brought to new levels of sophistication during development of the Polaris missile in the late 1950s and further refined for Apollo.

Three enormous changes have made this kind of technology widely available today. First, of course, is the massive reduction in cost, size and weight of computing power, allied to similarly astonishing improvements in memory and other aspects of processing performance. Second, we must take into account the development of similarly cheap solid-state motion sensors. Finally, we have the plastics and carbon materials evolution, which enables the construction of strong but ultra-lightweight flying machines at scales ranging from the vast to the miniature.

Nasa has never made any secret of the technologies involved, but one does have to take time and dig into the old manuals. Landing a rocket vertically in the 1960s was “no mean feat.” That, of course, is precisely why it ranks as one of engineering’s greatest accomplishments. What was amazing 50 years ago, surely we should expect to be commonplace today.

Piers Bizony
Bradford on Avon, Wiltshire

Far from being reluctant to release technical data, Nasa has been doing just that for decades, for example in the Apollo 11 News Reference, which can be found online at bit.ly/1UBIiB7. The ‘flying bedstead’ LEM test vehicles made hundreds of successful landings over a period of eight years, so the total of three crashes does not support the claim it was “hopelessly unstable”. While impressive, it is hardly suspicious that Nasa, with its vast resources, should have been able to land a single-use machine on a stable surface in an airless environment in 1969, after over 20 years of VTOL research in more problematic Earth environments.

Neil Armstrong became extremely proficient at flying the test vehicle, which had a downward thrusting jet engine to support five-sixths of its weight and simulate flying in the Moon’s gravitational field. It also had a vertical lift rocket capable of being throttled to support the remaining one-sixth of its weight and manoeuvring thruster ‘puffers’ similar to those used on the LEM.

On the day Armstrong had to eject, all the controls went haywire. Both the vertical-lift rocket and the manoeuvring thrusters used helium gas under pressure to force propellants into the combustion chambers. Because of the strong wind blowing that day the helium was used up more quickly than usual and both the vertical lift rocket and the manoeuvring thrusters started behaving erratically. This was not expected to be a problem on the Moon.

Denis Sharp
Hailsham, East Sussex

Patent value

David Sant’s Comment column on changes to Europe’s patent system (March 2016) encourages me to raise the question of the value of taking out a patent. A patent document describes in great detail how the design works, making it easy for someone to copy it or, worse, to find a way around the design features. Also, the high cost of litigation is likely to ruin the designer if he sues the infringer.

As the engineering director of an induction heating equipment manufacturer, I made a rule that we would never patent our designs but would rather put our efforts into marketing the equipment and earn the reputation of being the world leader in our field.

There was, of course, the argument that someone could copy our design, patent it and sue us for infringement. My argument was that we always told a friendly customer that their equipment was subject to a patent application and that he could be called to give evidence that the delivery date of his equipment represented ‘prior disclosure’. I have been told that this idea may not stand the test of litigation, but, thank goodness, we never had the high cost of having to prove it.

AP Baines FIET

Old lamps make a comeback

The majority of us, I suspect, have done our best to reduce energy consumption and carbon emissions by migrating over the years from tungsten filament lamps to compact fluorescent lamps and now to LEDs.

However, the carbon filament lamp has now re-emerged on the market after an interregnum of about 90 years. Apparently this does not contravene any regulations provided that the packaging bears words to the effect that “This lamp is not suitable for general lighting”. In spite of this I have seen large public areas of pubs and restaurants entirely lit by these lamps.

The carbon filament lamp is grossly inefficient even compared with the tungsten filament lamp. It also has what might once have been regarded as a virtue in that it has an extremely long life; in fact some were almost everlasting.

Even if new legislation is enacted to prohibit their future sale, the ones already in use will still be wasting energy, perhaps into the next century!

Michael Twitchett FIET
Banstead, Surrey

Reusing space junk

The proposal that space junk should be grabbed and pulled out of orbit to burn up in the atmosphere (Letters, March 2016), is very wasteful and short-sighted. Think of the money and effort it took to put it up there in the first place. Think of how we have to build these things from raw materials down here in our gravity well, and then burn vast amounts of energy to get them into orbit.

How about a longer-term view on this? How about a space ‘sheep dog’ vehicle to collect these bits of valuable debris into one place, in a suitable parking orbit. Then all that high-tech material would be out of the way, in a well-known place, with a big radar profile. It would be held together by its own gravity, and would be available for use as raw materials for constructing future space stations, or whatever.

A small but highly mobile robotic vehicle could nudge the pieces of junk together without much interference from the ground. It might take a few years, but it’s better than doing nothing, or risking pieces of junk falling on someone’s head down here on the surface.

Gerald Lambert
By email

Bullet points

Further to the article on new designs of bullets in the February 2016 issue of E&T, when I was in the Cadet Force at school – a long, long, time ago – the fragmentary nature of soft-nosed bullets was well known. Stories circulated, though no one ever admitted to having tried the experiment, that a .22 bullet could be modified by flattening or cutting across the nose. When such a bullet was fired into a tin of Compo processed cheese there would be a small entry hole and, so it was claimed, a large exit hole with cheese spattered around the target end of the range. Such bullets were known as dumdum bullets, after the village of Dum Dum, near Calcutta, where they were first made. It was generally believed that fragmenting bullets were considered so unethical that they were illegal for both civilian and military use.

Brian M Russell

I find the letter from Adrian Jones in the March 2016 issue of E&T saying engineers should be ashamed of more effective bullet designs extraordinary. If you are trying to kill something or someone, a bullet that does that more certainly, quickly and efficiently will cause less pain to the recipient, ie be humane. More importantly, it reduces the possibility of return fire, something those entrusted with protecting our liberty will welcome.

Michael O’Regan CEng MIET
By email

A win-win flooding solution?

Last winter brought devastating floods to the UK and statistics indicate that the problem is likely to get worse. Clearly water management systems, which are expensive, have to be put in place if recurrence is to be avoided. If micro-hydroelectric schemes are incorporated into the water-management systems then the cost is offset by the electricity generated. As the main cost of such a scheme is in the water-management system, which has to be undertaken anyway, the additional cost of installing generators offers a cost-effective way of generating a useful amount of electrical energy from renewable sources.

Generators could be staged at several points along the flow so that energy can be extracted from the water while controlling its flow rate. The electricity produced could pay for maintenance. Providing the sale of electrical energy generated exceeds the maintenance costs the system will eventually pay for itself. Such schemes are likely to be embraced by local residents, and with good planning they could be sensitively incorporated into places of natural beauty.

Roy Gregory CEng FIET
By email

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