[sci.astro] CRAF/Cassini Update - 11/09/90

baalke@mars.jpl.nasa.gov (Ron Baalke) (11/11/90)

                         CRAF/Cassini Status Report
                             November 9, 1990

   The good news concerning the CRAF/Cassini mission, is that it looks like
both missions will be funded.  Congress approved both missions earlier in the
year, but during the recent budget negotiations, it looked like that the CRAF
portion was not going to be funded.  The total budget for both missions is
1.6 billion dollars, with 145 million needed in the 1991 fiscal year budget to
get the projects started.  Only 95 million was approved - being 50 million
short, things were looking grim for the CRAF mission, as the Cassini mission
has priority.  However, most of the 50 million has since been restored which
should enable the start of both the CRAF and Cassini missions.

     The CRAF/Cassini missions will be the first to use the next generation
spacecraft using the Mariner Mark II design.  The CRAF spacecraft
(Comet Rendezvous Asteroid Flyby) will meet with the Comet Kopff near
the orbit of Jupiter and travel along side it for at least three years.
It will also launch a penetrator which will directly sample the comet's
nucleus.  On the way to to Comet Kopff, CRAF will flyby the asteroid
Hamburga.  JPL is currently in negotiations with the McDonald's hamburger
franchise to arrange some kind of advertising deal (this is no joke).

         Key Scheduled Dates for the CRAF Mission
         --------------------------------------------
           08/22/95 - Titan IV/Centaur Launch
           01/22/98 - 449 Hamburga Asteroid Flyby
           08/14/00 - Comet Kopff Arrival
           08/20/01 - CRAF Penetrator to Kopff
           03/31/03 - End of Primary Mission


     The Cassini mission will go to Saturn, using gravity assists from the
Earth and Jupiter.  This trajectory is called EJGA (Earth-Jupiter Gravity
Assist).  A probe named Huygens will be dropped off at Saturn's largest moon,
Titan.  The Cassini mission is an international mission.  The European
Space Agency (ESA) will supply the Huygens probe, Germany will supply the
propulsion module, and Italy will provide the High Gain Antenna, sun sensors,
and radio science instruments.  ESA has already approved the science
instruments that will be on the Titan probe.  NASA has selected the science
instruments that will be onboard the Cassini orbiter; however, this list is not
quite official yet -- it is sitting on the desk of Richard Truly, NASA's
administrator, awaiting his signature.

         Key Scheduled Dates for the Cassini Mission (EJGA Trajectory)
         -------------------------------------------------------------
           08/22/96 - Titan IV/Centaur Launch
           03/29/97 - 66 Maja Asteroid Flyby
           06/08/98 - Earth Gravity Assist
           02/06/00 - Jupiter Gravity Assist
           12/06/02 - Saturn Arrival
           03/27/03 - Titan Probe Release
           03/29/03 - Orbiter Deflection Maneuver
           04/18/03 - Titan Probe Entry
           06/30/03 - Iapetus Flyby
           05/20/04 - Dione Flyby
           09/12/04 - Enceladus Flyby
           08/14/05 - Iapetus Flyby
           12/31/06 - End of Primary Mission

     The Maja asteroid that Cassini will encounter is a type C asteroid, 39
kilometers in size.

     When Cassini arrives at Saturn in December, 2002,  it will perform a
SOI (Saturn Orbit Insertion) burn.  The spacecraft will actually pass through
the outer rings of Saturn during SOI, passing between the F and G rings at a
distance of 2.6 Saturn radii from the planet.  After SOI, the
Huygens probe will be released on the subsequent orbit.  Two days after
probe release, the Cassini orbiter will perform a deflection manuever.  This
deflection maneuver serves two purposes: it ensures the Cassini orbiter
doesn't follow the Hugyens probe into Titan, and it positions the orbiter to
lag behind the probe about 3.5 hours so that science data can be received
from the Huygens probe as it descends into the atmosphere of Titan.  It will
take the Huygens probe about 3 hours to parachute all the way down to the
surface of Titan; if the probe survives the landing, valuable data will
continue to be transmitted back for about 30 more minutes.  No more data will
be returned to the Cassini orbiter from Huygens on any subsequent orbits, as
the battery onboard Huygens will have rundown by then.

    During its four year orbital tour of Saturn, Cassini will make 60 orbits
of the planet.  Compare this with Galileo, which will make about 10 orbits
around Jupiter in two years.  Galileo has the luxury of using gravity assists
of the four large Galileon moons (Io, Europa, Ganymede and Callisto), while
at Saturn, there is only one large moon, Titan, that Cassini can take
advantage of.  Because of this, Cassini will make close flybys of Titan on
35 of the 60 orbits.  Each Titan flyby is designed so that the Cassini
will be deflected a little further out of Saturn's ecliptic plane, so that
at the end of four years, the spacecraft will be in polar orbit around
Saturn at an inclination of between 80 to 90 degrees.  A polar orbit puts
Cassini into a unique advantage point where many star occultations can be
observed through Saturn's rings.  Cassini will be carrying a Titan Radar
Mapper which it will use to map the surface of Titan during its numerous
flybys of the moon.  The Titan Radar Mapper is a SAR (Synthetic Aperture
Radar), similiar to the one used by the Magellan spacecraft at Venus.

     Also, still being looked at, are alternate trajectory routes to Saturn.
A VEJGA (Venus-Earth-Jupiter Gravity Assist) trajectory has been developed
which would use an additional gravity assist of Venus.  This trajectory has
the advantage of reducing the launch energy, which in turn, means a heavier
payload can be launched.  Note that the VEJGA trajectory is only preliminary,
and the EJGA trajectory is still the official route that Cassini will take.

         Key Dates for the Cassini Mission (VEJGA Trajectory)
         ----------------------------------------------------
           11/28/95 - Titan IV/Centaur Launch
           12/04/96 - Venus Gravity Assist
           07/05/98 - Earth Gravity Assist
           11/11/98 - Clarissa Asteriod Flyby
           03/28/00 - Jupiter Gravity Assist
           12/07/03 - Saturn Arrival

     This trajectory will have Cassini pass near the Clarissa Asteroid, a
type F asteroid which is 21 kilometers in size.
      ___    _____     ___
     /_ /|  /____/ \  /_ /|
     | | | |  __ \ /| | | |      Ron Baalke         | baalke@mars.jpl.nasa.gov
  ___| | | | |__) |/  | | |___   Jet Propulsion Lab | baalke@jems.jpl.nasa.gov
 /___| | | |  ___/    | |/__ /|  M/S 301-355        |
 |_____|/  |_|/       |_____|/   Pasadena, CA 91109 |

sysmgr@KING.ENG.UMD.EDU (Doug Mohney) (11/12/90)

In article <1990Nov11.001924.10302@jato.jpl.nasa.gov>, baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
>
>nucleus.  On the way to to Comet Kopff, CRAF will flyby the asteroid
>Hamburga.  JPL is currently in negotiations with the McDonald's hamburger
>franchise to arrange some kind of advertising deal (this is no joke).

Does this mean that Ron Baalke will be replaced by Ronald McDonald for our news
postings ? :-)

>     Also, still being looked at, are alternate trajectory routes to Saturn.
>A VEJGA (Venus-Earth-Jupiter Gravity Assist) trajectory has been developed
>which would use an additional gravity assist of Venus.  This trajectory has
>the advantage of reducing the launch energy, which in turn, means a heavier
>payload can be launched. 

Could a Venus assist get the probe there faster instead of trading off for a
heavier playload?

rice@dg-rtp.dg.com (Brian Rice) (11/13/90)

In article <0093F8EE.D9E16A40@KING.ENG.UMD.EDU>, 
sysmgr@KING.ENG.UMD.EDU (Doug Mohney) writes:
|> In article <1990Nov11.001924.10302@jato.jpl.nasa.gov>, 
|> baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
|> >
|> > On the way to to Comet Kopff, CRAF will flyby the asteroid
|> > Hamburga.  JPL is currently in negotiations with the McDonald's 
|> > hamburger franchise to arrange some kind of advertising deal 
|> > (this is no joke).
|> 
|> Does this mean that Ron Baalke will be replaced by Ronald McDonald 
|> for our news postings ? :-)

JPL: "Junkfood Promotion Lab."

Seriously, I think Ron just threw this in to see whether or 
not people were really reading his articles.  Either that or 
NASA really wants to have CRAF do a gravity-assist flyby 
someplace, and they're counting on the added mass of the 
Happy Meal to justify it.
--
Brian Rice   rice@dg-rtp.dg.com   +1 919 248-6328
DG/UX Product Assurance Engineering
Data General Corp., Research Triangle Park, N.C.

hthomas@irisa.fr (Henry Thomas) (11/13/90)

In article <7034.273fd310@abo.fi>, mlindroos@abo.fi writes:
|> In article <1990Nov11.001924.10302@jato.jpl.nasa.gov>, baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
|> > 
|> >                          CRAF/Cassini Status Report
|> >                              November 9, 1990
|> > ...take the Huygens probe about 3 hours to parachute all the way down to the
|> > surface of Titan; if the probe survives the landing, valuable data will
|> > continue to be transmitted back for about 30 more minutes.  No more data will
|> > be returned to the Cassini orbiter from Huygens on any subsequent orbits, as
|> > the battery onboard Huygens will have rundown by then.
|> > 
|> 
|> 30 minutes! Why can't we send an advanced long-life, Viking-style probe
|> to Titan instead?! The Viking lander was "only" about twice as heavy as the 
|> Huygens probe will be so the lack of a powerful-enough launcher surely cannot 
|> be the reason? Is this just because of financial considerations again, or...?

The reason is maybe that we have NO data of the condition down there: 
	- Is there any *solid* ground ?
	- pressure ?
	- temperature ?
So with no information, it seems difficult to design a long-life probe.
A similar(?) problem occured on Venus, where the probes Venera 11-14 lasted only a few hours. The first ones didn't reached the ground because theirs parachutes where destroyed by the acid atmosphere. 
On mars, the informations where much more complete, because the ground had been observed by many orbital probes: it was visible.

There was an excellent article in the ESA journal (?), some month ago about "Cassini Probe  Huygens Entry techniques" .


-- 
-- E-mail: Henry.Thomas@irisa.fr 
Henry Thomas - IRISA Campus Universitaire de Beaulieu 35042 RENNES CEDEX FRANCE
Phone: (+33)99 36 20 00 +549  Fax: (+33)99 38 38 32  Telex: UNIRISA 950 473F
X.400: C=FR;ADMD=ATLAS;PRMD=irisa;S=hthomas  Telex:/X121=842950473/@atlas.fr

mlindroos@abo.fi (11/13/90)

In article <1990Nov11.001924.10302@jato.jpl.nasa.gov>, baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
> 
>                          CRAF/Cassini Status Report
>                              November 9, 1990
> ...take the Huygens probe about 3 hours to parachute all the way down to the
> surface of Titan; if the probe survives the landing, valuable data will
> continue to be transmitted back for about 30 more minutes.  No more data will
> be returned to the Cassini orbiter from Huygens on any subsequent orbits, as
> the battery onboard Huygens will have rundown by then.
> 

30 minutes! Why can't we send an advanced long-life, Viking-style probe
to Titan instead?! The Viking lander was "only" about twice as heavy as the 
Huygens probe will be so the lack of a powerful-enough launcher surely cannot 
be the reason? Is this just because of financial considerations again, or...?

MARCU$

joshi@public.BTR.COM (Nikhil R. Joshi joshi@btr.com) (11/14/90)

In article <1990Nov13.104319.11134@irisa.fr> Henry.Thomas@irisa.fr writes:
>>In article <7034.273fd310@abo.fi>, mlindroos@abo.fi writes:
>>
>> 30 minutes! Why can't we send an advanced long-life, Viking-style probe
>> to Titan instead?! The Viking lander was "only" about twice as heavy as the
>> Huygens probe will be so the lack of a powerful-enough launcher surely cannot
>> be the reason? Is this just because of financial considerations again, or...?
>
>The reason is maybe that we have NO data of the condition down there:
>
>	- Is there any *solid* ground ?
>	- pressure ?
>	- temperature ?
>

 Was the Viking lander at least partially solar powered?  If so, that
 explains it's long life.  The solar flux at Saturn isn't nearly great
 enough to power even an orbital probe like Voyager, let alone a lander
 after being attenuated by Titan's atmosphere.   But then why can't we
 put an RTG like Voyager's on the probe?

 Nikhil Joshi
 joshi@btr.com

hthomas@irisa.fr (Henry Thomas) (11/14/90)

In article <1990Nov13.104319.11134@irisa.fr>, hthomas@irisa.fr (Henry Thomas) writes:
|> In article <7034.273fd310@abo.fi>, mlindroos@abo.fi writes:
|> |> In article <1990Nov11.001924.10302@jato.jpl.nasa.gov>, baalke@mars.jpl.nasa.gov (Ron Baalke) writes:
[deleted]
|> |> 30 minutes! Why can't we send an advanced long-life, Viking-style probe
|> |> to Titan instead?! The Viking lander was "only" about twice as heavy as the 
|> |> Huygens probe will be so the lack of a powerful-enough launcher surely cannot 
|> |> be the reason? Is this just because of financial considerations again, or...?
|> 
|> The reason is maybe that we have NO data of the condition down there: 
|> 	- Is there any *solid* ground ?
|> 	- pressure ?
|> 	- temperature ?
|> So with no information, it seems difficult to design a long-life probe.
|> A similar(?) problem occured on Venus, where the probes Venera 11-14 lasted only a few hours. The first ones didn't reached the ground because theirs parachutes where destroyed by the acid atmosphere. 
|> On mars, the informations where much more complete, because the ground had been observed by many orbital probes: it was visible.
|> 
|> There was an excellent article in the ESA journal (?), some month ago about "Cassini Probe  Huygens Entry techniques" .
|> 

Here are some excerpts from this article

ESA Journal  1989, vol 13 pp 175--190 "Cassini/Huygens Entry and Descent Technologies" G Scoon, G, Whitcomb, M Eiden, A. Smith

"The main objectives of the probe's mission  will  be the determination of the chemical composition of the atmosphere and the measurement of  winds and temperature  and pressure profiles from an altitude of 170 km down to the surface" ... " Althoug