From: jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins)
Subject: Rosetta summary
Organization: University of Illinois at Urbana
Date: Wed, 8 Apr 1992 22:37:41 GMT

	A few people mailed me privately on topic relating to the comet
discussion that's been going on.  Since they didn't know about Rosetta, and
many other people don't seem to, I though someone should post a summary.

	Rosetta (as in the stone) is one of the 4 major missions planned in 
ESA's Horizon 2000 program.  It is designed to return comet samples to Earth
for study.  They would need substatial help from the international community,
and are planning on major help from NASA (does this sound familiar? :)

	The mission is to return core samples (10kg), volatile samples (.1kg)
and nonvolatile surface samples (1-5kg) for study of compostion, structure
etc.  Naturally, this means a fairly complex return vehicle that has to 
maintain low temps during reentry.
	In situ science includes high precision orbit determination and
study of emission patterns, analysis of coma and nucleus during entry phase,
and studies related to sample aquisition.  The baseline mission does not
include much in the way of surface science, since the main mission is to return
the samples, but they are considering a surface package that would remain on 
the comet long term.	
	Several comets with perihelion under 1.5 AU and aphelion under 6 AU
are possible targets. I won't include names or dates since thay are likely to
be out of date.
	The vehicle consists of three parts.  A Mariner Mk II type carier
provided by NASA, a lander which has the sampler, major payload equipment and
the landing/anchoring system (this stays on the comet) and finally, the
aerocapsule, which is attached to the carier.  Launch is planned for a Titan IV
Centaur, with one Earth swing by and about a four year flight.
	Target aquisition would take place a few million kilometers out, and
R would approach the sunlit side over a period of 25 days.  At this point, the
distance is about 100,000 km, folowed by another 25 day period during which 
R slowly approaches, starting observations 5000km out.  This gives it about
5-10 days to observe as the comet rotates under it.  At 100 km out, R stops
and ground control decides on a landing site.  After about 15 days, during 
which camera resolution is about 1m, R begins hyperbolic flybys over potential
sites during good lighting conditions.  Minimum altitude is 20 km.  When the
landing site is determined, a penatrator with a radio beacon is impacted in
the target zone, and R eventaully lands nearby (within 20 m)  If microwave
instruments indicate than the surface is too rough or that sampling won't be
possible, R aborts to a higher altitude and waits for Earth input.
	Landing gear includes harpoons under tension to keep the spacraft from
flying off when torque is applied to samplers.  Two surface samplers, 50cm x
10cm diameter will be filled with material within a 1m radius.  Two to six
core samples (dug in the same place to increase depth) will be be taken over
a period of ten days.  If landing or sampling is impossible, a backup system
is included.  R hovers above the comet, and a spin stabilized harpoon collects
a sample.  
	After sampling is complete, the carier and return capsule take off at
10 m/s and move away from the comet for 10 to 20 days.  Then the Earth return
procedure is implemented.  3 years later, the craft returns on a trajectory 
that misses Eath by 1000 km.  24 hours before reentry, the RTG is ejected.
The craft then maneuvers onto a re-entry trajectory. 2 hours before reentry,
the carrier seperates and burns out of the reentry trajectory, leavin the
return vehicle to enter the atmosphere.  Deccelleration must be below
50-100 g and thermal flux must be kept very low.  At 25 Km altitude, the 
parachutes deploy, and the vehicle lands within 20km of its target destination.

		Hope this helps,
			Josh Hopkins

Source, ESA Bulletin, August 1989.