Monday 1st September 2008 Meeting Report
Going To The Stars - Speaker: Colin Johnston (Armagh Planetarium)


The 2008-2009 season got off to a “flying” start with a lecture about the prospects for future interstellar space flight, a subject which almost all astronomy buffs will have come across at some time or another, usually in the annals of science fiction or so-called science faction. Most members had been looking forward to this lecture since it was announced, and over 30 people attended. No-one was disappointed.

Colin started by giving an overview of the extraordinary recent advances in the search for planets around other stars. In 1995, there were no definite exoplanets known, now there are over 300. The search is now concentrating on trying to identify Earth-like planets, rather than the Jupiter-mass planets which have been discovered so far. A recent discovery of a possible candidate orbiting the star Gliese 581 promises more discoveries in the near future.

After a brief discussion about the units of measurement used by astronomers, Colin went on to the main part of the lecture, by describing four different types of proposals for interstellar travel, starting with the Orion project originally conceived by the United States Airforce in the 1950’s. the Daedalus project, a proposal by the British Interplanetary Society in the 60’s, and two later proposals, a Lightsail, and a Bussard interstellar ramjet.

The first of these, Orion, looked for all the world like a gigantic flying observatory, with a crew of 150. The name was later revived for a NASA project which involved a spaceship propelled by nuclear bombs being discharged from a hole at the back and exploding, pushing the spaceship along. The Daedalus project relied on a credible method of nuclear fusion being invented. All these proposals were quickly discarded as being impractical.

The lightsail is an idea which has appeared in various guises over the years. It is based on the premise that the solar wind and sunlight itself could be utilized to drive a solid thin sail. NASA went as far as to produce a prototype, named ECHO 1. The main drawback would be the enormous size of the sail required, although in space, the sail could be many kilometres broad.

The ramjet proposal is based on the idea of collecting fuel in a giant scoop as the vehicle travels through space. It is a common misconception that space is a complete vacuum, in fact, there is both gas and dust, although this would only come to maybe 1g of material for every 100o cubic kilometres. As with the lightsail, the scoop would need to be enormous in order to gather enough material. Both the lightsail and the ramjet are ideas whose time may come in the future.

Colin ended by discussing the effects of long space journeys, especially if those journeys could take place at near light speed, with regards to the effects of relativity, and concluded by pointing out that when it is possible to build interstellar spacecraft, they will probably be nothing like we can imagine now. He noted that when Galileo drew his plans for a flying machine, he could not have envisaged the modern helicopter or aeroplane. A lively question and answer session followed the lecture.


References and further reading for Starships talk
General (Virtual Planetarium) (fictional starships) (sceptical speculations on colonising space by SF author Charles Stross)

Orion (a sceptical view of the concept)


Light Sail (paper by Robert Forward, inventor of the concept)

Bussard Ramjet (time dilation calculator)

Books (available through libraries and
Gilster, Paul, Centauri Dreams
Zubrin, Robert, Entering space
Mallove, Eugene F.  and Matloff , Gregory L, The Star Flight Handbook
Schmidt, Stanley and Zubrin. Robert,  Islands in the Sky
Dyson, George, Project Orion
Nicholson, Iain, The Road to the Stars
Sagan, Carl, Cosmos

Science Fiction
(I don’t claim that these novels have any great merit as literature but they deal with concepts covered in this talk in an interesting and entertaining way. )
Forward, Robert L, Rocheworld (laser light sail)
Niven, Larry and Pournelle, Jerry, The Mote in God’s Eye (an alien-built laser light sail)
Niven, Larry and Pournelle, Jerry, Footfall (Orion)
Anderson, Poul, Orion shall rise (Orion)
Anderson, Poul, Tau Zero (the Bussard Ramjet novel)
Niven, Larry, A world out of time (Bussard Ramjet)
Heinlein, Robert, Time for the Stars (relativistic interstellar travel)
Stross, Charles, Accelerando (a light sail appears midway through the story– complete novel can be downloaded from




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