Rumor has it that the Aurora aircraft makes a contrail like that.
Supposedly it is powered by a pulse jet engine or some sort of external
combustion powerplant.

For an example of the contrail check out-
http://wave.prohosting.com/aurora85/...contrails.html

If you start looking into into the Aurora, make sure you get out your
tin foil hat--- conspiracy theories abound.

However, maybe it is just aliens. tin_foil_hat=on

Len

Big John wrote:
AW&ST, 26 Apr 04

21 March the characteristic con trail of sequential puffs was observed
over CO. Along side this con was a normal con which was appeared to
be an escort bird.

As the puffs came out, it was seen that there were two adjacent puffs
that quickly merged into a single puff. From this it is assumed that
the vehicle is twin engined and both engine's fire at the same time
due to the puffs joining. The observer called them a "string of
pearls" across a large arc of the sky.

Neither aircraft could be seen or heard from the 8000 feet elevation
where the observer lived in the mountains east of SLC, so were at a
very high altitude.

One of these days the black veil will break and we will see what this
vehicle is.

Big John