ethan@utastro.UUCP (Ethan Vishniac) (03/15/86)
[Suddenly a bug rang out!!]
I have in my hand a preprint from someone in my own department (Michael
Harris). On the assumption that he would like the publicity and because
it might start a good discussion in the group I am posting the abstract
of the paper and a brief synopsis of its contents.
On the Detectability of Antimatter Propulsion Spacecraft
It is shown that the NASA Gamma Ray Observatory will be able
to detect large interstellar spacecraft at distances up to 300pc by
the gamma ray emission from the propulsion system alone. The distance
limit is set by the possibility of recognizing such objects by their proper
motions.
In this paper Michael Harris points out that alien spacecraft using an
antimatter drive will have large proper motions and be quite conspicuous.
Assuming that the velocity is close to the speed of light and that GRO
will have a lifetime of 10 years then the two instruments with the
best angular resolution can see motion at distances of 100 pc (EGRET)
and 300 pc (BATSE). This assume purely tangential velocity.
Stellar motions are not in excess of 10 arc seconds per year or 2 arc minutes
over the lifetime of the GRO. In contrast the angular resolution of the
instruments is 1.6 degrees and 0.5 degrees. We see that we are angular
resolution limited and that a 15 fold increase in distance might be possible
before confusion sets in. Moreover the large proper motions are due to
nearby stars and they are not effective sources of gamma rays. The luminosity
of a given spacecraft is obviously a matter of conjecture. However, reasonable
numbers would make them easily detectable.
--
"Ma, I've been to another Ethan Vishniac
planet!" {charm,ut-sally,ut-ngp,noao}!utastro!ethan
ethan@astro.UTEXAS.EDU
Department of Astronomy
University of Texasphoenix@genat.UUCP (phoenix) (03/19/86)
In article <512@utastro.UUCP> ethan@utastro.UUCP (Ethan Vishniac) writes: > > I have in my hand a preprint from someone in my own department (Michael >Harris). On the assumption that he would like the publicity and because >it might start a good discussion in the group I am posting the abstract >of the paper and a brief synopsis of its contents. > > > On the Detectability of Antimatter Propulsion Spacecraft What about alien starships using a non-anti-matter drive? (There are most probably other types of star-drive as well...:-)) -- The Phoenix (Neither Bright, Dark, nor Young) ---"A man should live forever...or die trying." ---"There is no substitute for good manners...except fast reflexes."
ethan@utastro.UUCP (Ethan Vishniac) (03/24/86)
In article <2586@genat.UUCP>, phoenix@genat.UUCP (phoenix) writes: > > What about alien starships using a non-anti-matter drive? (There are most > probably other types of star-drive as well...:-)) > -- Invisible aliens and nonexistent aliens have many points in common, the most obvious being that it`s hard to publish papers about them in a refereed journal. -- "Ma, I've been to another Ethan Vishniac planet!" {charm,ut-sally,ut-ngp,noao}!utastro!ethan ethan@astro.UTEXAS.EDU Department of Astronomy University of Texas