Jacques van Oene
November 29th 04, 10:12 PM
SPC Report November 2004
29 Nov 2004 15:00
Mission Status
The Cassini-Huygens spacecraft was successfully inserted in orbit around
Saturn on 1 July and continues to perform nominally. On 30 June, coming from
below, it crossed the rings with its High-Gain Antenna oriented such as to
shield the most delicate parts of the spacecraft from being hit by ring
particles.
After the 1st ring crossing, the main engine fired for 96 minutes to slow
down the spacecraft and put it in orbit around the ringed planet. At
periape, above the rings, Cassini-Huygens was less than 18000 km above
Saturn's cloud top. Once the engine burn was over, the planned science
observations started. A series of spectacular images of the rings were
obtained before the spacecraft re-oriented itself with its High-Gain Antenna
forward for the second ring crossing. Further observations of the rings were
then obtained and provided excellent data on the ring dynamics, their
interaction with the moons, and composition variation across the various
rings.
Science observations highlights
Phoebe: On 11 June, during its approach to Saturn, Cassini-Huygens flew by
Phoebe, a distant moon in retrograde orbit around the planet. The closest
approach distance was 2000 km. Spectacular data were obtained of what is
most likely a captured object.
Titan: Within 36 hours of Saturn orbit insertion, a series of distant
observations of Titan were made on 2 and 3 July. During this first so-called
"untargeted" encounter, Cassini-Huygens' closest approach to Titan was 339
000 km. Observations of the atmosphere, including detailed observations of a
highly variable methane polar cloud, were acquired. Tantalizing images of
the surface were obtained by both the Camera (ISS, Imaging Science System)
and by the Visual Infrared Mapping Spectrometer (VIMS). Within 2 months, the
Titan data set was carefully analysed together with the relevant latest
ground-based observations to validate the atmosphere engineering model used
for the design of Huygens. The observations confirm that the atmosphere
structure is well within the envelope of the engineering model, in fact very
close to the nominal profile. The methane and the argon concentration
uncertainties have been reduced respectively to the range 1-3 % instead of
1-5% and 0-7% instead of 0-10 %. A model update of Titan's atmosphere is
being worked as an input for the final Huygens performance validation before
separation.
Saturn: Images of Saturn's atmosphere are regularly obtained while
Cassini-Huygens is far from the planet. Lots of atmospheric details are seen
in the images, in particular from the southern hemisphere due to current
viewing geometry.
Rings and moonlets: Cassini discovered one, possibly two moonlets in the F
ring region, and a ring of material associated with Saturn's moon Atlas,
between the A and the F rings. The search for new moonlets and the study of
their interaction with the rings is a key scientific objective of the
Mission. Significant results have already been obtained. Searches will
continue for further detections of the newfound body or bodies seen in
association with the F ring. If the two objects indeed turn out to be a
single moon, it will bring the Saturn moon count to 34. This newly
discovered ring adds to the growing number of narrow ringlets around Saturn.
Cassini results are regularly released on a daily basis on the NASA/JPL web
site: http://saturn.jpl.nasa.gov/. A selection is also posted on ESA's
Huygens science web site http://saturn.esa.int. A series of papers are in
preparation for publication in "Science" before the end of 2004.
Huygens operations and engineering activities
On the operations side, two Huygens probe in-flight checkouts have been
performed since Saturn orbit insertion, on 14 July and on 14 September. They
confirm that the Probe is in good health. A special test was performed on
each of the five Lithium sulphur-dioxide batteries on 19 September to remove
the passivation chemical layer that formed over the years since their
manufacturing. This first of the two so-called "battery passivation"
activities demonstrated that all five Huygens batteries are healthy and
fully charged.
On the engineering side, the work undertaken over the last few months to
validate Huygens's performance during entry is nearing completion. The heat
flux and integrated heat load expected to be experienced by Huygens during
entry have been re-evaluated and their impact on the Thermal Protection
System (TPS) and parachute deployment re-assessed. This work is supported by
several expert groups in Europe and in the USA and by Huygens prime
contractor Alcatel and its subcontractor EADS. The work is expected to be
concluded by end of October. The objective of the on-going work is to
re-assess the margins that were included in the Thermal Protection System
and to verify that the TPS can cope with the updated entry aerothermodynamic
environment. One of the main objectives of the study is also to verify
whether the entry corridor is well centred with respect to the Huygens TPS
performance with a nominal entry angle of -65°.
Upcoming activities
On 23 August, the third largest manoeuvre performed by Cassini-Huygens near
apoapse during the first 117-day orbit around Saturn placed the spacecraft
on its nominal trajectory for the first close encounter with Titan on 26
October, with a planned closest approach at 1200 km. The 2nd close encounter
with Titan is planned on 13 December at an altitude of about 2200 km. After
release, Huygens trajectory will bring it within 60 000 km of the large moon
Iapetus. During the validation process of the Huygens trajectory at JPL, it
was found that the mass uncertainty of Iapetus may have an impact on
Huygens's targeting accuracy. An alternative reference trajectory is being
investigated at JPL that would move Huygens away from Iapetus to about 120
000 km and increase the accuracy with which the Huygens probe will be
delivered to Titan. The new reference trajectory incorporates updated
orbiter andmajor satellite ephemerides. The major changes from the previous
reference trajectory are a decrease in the altitude of the second Titan
flyby (Tb, 13 December 2004) from 2200 km to 1200 km, and an increase in the
altitude of the fourth Titan flyby (T3, 15 February 2005) from 1000 km to
1577 km. The improved satellite ephemerides resulted in small changes to the
timing of events such as Titan flybys and Saturn periapses. The need to
change to the alternative trajectory and the Orbiter science impacts are
being evaluated. A decision is expected by late October at the latest.
Huygens Mission Readiness review
An independent ESA/NASA Mission Readiness Review of Huygens is being
conducted. Preliminary review activities started in early October. The
Formal Kick-Off meeting will take place on 21 October. The final board
meeting is currently planned at ESTEC on 11 November.
Upcoming events
The main upcoming events are:
First targeted Titan flyby (@ 1200 km altitude) on 26 October
Probe checkout #16 on 23 November
Go-NoGo decision for Huygens baseline mission: 6 December 2004
Second targeted Titan flyby (@ 2200 km altitude, may be reduced to 1200 km)
on 13 December
Go-NoGo for Probe separation preparation activities: 17 December
Probe separation on the 25 December (separation window extends several days)
Probe entry on 14 January 2005; Titan flyby at 60000 km
Third low altitude Titan Flyby (@ 1000 km altitude, may be increased to 1577
km) on 15 February 2005.
--
--------------
Jacques :-)
www.spacepatches.info
29 Nov 2004 15:00
Mission Status
The Cassini-Huygens spacecraft was successfully inserted in orbit around
Saturn on 1 July and continues to perform nominally. On 30 June, coming from
below, it crossed the rings with its High-Gain Antenna oriented such as to
shield the most delicate parts of the spacecraft from being hit by ring
particles.
After the 1st ring crossing, the main engine fired for 96 minutes to slow
down the spacecraft and put it in orbit around the ringed planet. At
periape, above the rings, Cassini-Huygens was less than 18000 km above
Saturn's cloud top. Once the engine burn was over, the planned science
observations started. A series of spectacular images of the rings were
obtained before the spacecraft re-oriented itself with its High-Gain Antenna
forward for the second ring crossing. Further observations of the rings were
then obtained and provided excellent data on the ring dynamics, their
interaction with the moons, and composition variation across the various
rings.
Science observations highlights
Phoebe: On 11 June, during its approach to Saturn, Cassini-Huygens flew by
Phoebe, a distant moon in retrograde orbit around the planet. The closest
approach distance was 2000 km. Spectacular data were obtained of what is
most likely a captured object.
Titan: Within 36 hours of Saturn orbit insertion, a series of distant
observations of Titan were made on 2 and 3 July. During this first so-called
"untargeted" encounter, Cassini-Huygens' closest approach to Titan was 339
000 km. Observations of the atmosphere, including detailed observations of a
highly variable methane polar cloud, were acquired. Tantalizing images of
the surface were obtained by both the Camera (ISS, Imaging Science System)
and by the Visual Infrared Mapping Spectrometer (VIMS). Within 2 months, the
Titan data set was carefully analysed together with the relevant latest
ground-based observations to validate the atmosphere engineering model used
for the design of Huygens. The observations confirm that the atmosphere
structure is well within the envelope of the engineering model, in fact very
close to the nominal profile. The methane and the argon concentration
uncertainties have been reduced respectively to the range 1-3 % instead of
1-5% and 0-7% instead of 0-10 %. A model update of Titan's atmosphere is
being worked as an input for the final Huygens performance validation before
separation.
Saturn: Images of Saturn's atmosphere are regularly obtained while
Cassini-Huygens is far from the planet. Lots of atmospheric details are seen
in the images, in particular from the southern hemisphere due to current
viewing geometry.
Rings and moonlets: Cassini discovered one, possibly two moonlets in the F
ring region, and a ring of material associated with Saturn's moon Atlas,
between the A and the F rings. The search for new moonlets and the study of
their interaction with the rings is a key scientific objective of the
Mission. Significant results have already been obtained. Searches will
continue for further detections of the newfound body or bodies seen in
association with the F ring. If the two objects indeed turn out to be a
single moon, it will bring the Saturn moon count to 34. This newly
discovered ring adds to the growing number of narrow ringlets around Saturn.
Cassini results are regularly released on a daily basis on the NASA/JPL web
site: http://saturn.jpl.nasa.gov/. A selection is also posted on ESA's
Huygens science web site http://saturn.esa.int. A series of papers are in
preparation for publication in "Science" before the end of 2004.
Huygens operations and engineering activities
On the operations side, two Huygens probe in-flight checkouts have been
performed since Saturn orbit insertion, on 14 July and on 14 September. They
confirm that the Probe is in good health. A special test was performed on
each of the five Lithium sulphur-dioxide batteries on 19 September to remove
the passivation chemical layer that formed over the years since their
manufacturing. This first of the two so-called "battery passivation"
activities demonstrated that all five Huygens batteries are healthy and
fully charged.
On the engineering side, the work undertaken over the last few months to
validate Huygens's performance during entry is nearing completion. The heat
flux and integrated heat load expected to be experienced by Huygens during
entry have been re-evaluated and their impact on the Thermal Protection
System (TPS) and parachute deployment re-assessed. This work is supported by
several expert groups in Europe and in the USA and by Huygens prime
contractor Alcatel and its subcontractor EADS. The work is expected to be
concluded by end of October. The objective of the on-going work is to
re-assess the margins that were included in the Thermal Protection System
and to verify that the TPS can cope with the updated entry aerothermodynamic
environment. One of the main objectives of the study is also to verify
whether the entry corridor is well centred with respect to the Huygens TPS
performance with a nominal entry angle of -65°.
Upcoming activities
On 23 August, the third largest manoeuvre performed by Cassini-Huygens near
apoapse during the first 117-day orbit around Saturn placed the spacecraft
on its nominal trajectory for the first close encounter with Titan on 26
October, with a planned closest approach at 1200 km. The 2nd close encounter
with Titan is planned on 13 December at an altitude of about 2200 km. After
release, Huygens trajectory will bring it within 60 000 km of the large moon
Iapetus. During the validation process of the Huygens trajectory at JPL, it
was found that the mass uncertainty of Iapetus may have an impact on
Huygens's targeting accuracy. An alternative reference trajectory is being
investigated at JPL that would move Huygens away from Iapetus to about 120
000 km and increase the accuracy with which the Huygens probe will be
delivered to Titan. The new reference trajectory incorporates updated
orbiter andmajor satellite ephemerides. The major changes from the previous
reference trajectory are a decrease in the altitude of the second Titan
flyby (Tb, 13 December 2004) from 2200 km to 1200 km, and an increase in the
altitude of the fourth Titan flyby (T3, 15 February 2005) from 1000 km to
1577 km. The improved satellite ephemerides resulted in small changes to the
timing of events such as Titan flybys and Saturn periapses. The need to
change to the alternative trajectory and the Orbiter science impacts are
being evaluated. A decision is expected by late October at the latest.
Huygens Mission Readiness review
An independent ESA/NASA Mission Readiness Review of Huygens is being
conducted. Preliminary review activities started in early October. The
Formal Kick-Off meeting will take place on 21 October. The final board
meeting is currently planned at ESTEC on 11 November.
Upcoming events
The main upcoming events are:
First targeted Titan flyby (@ 1200 km altitude) on 26 October
Probe checkout #16 on 23 November
Go-NoGo decision for Huygens baseline mission: 6 December 2004
Second targeted Titan flyby (@ 2200 km altitude, may be reduced to 1200 km)
on 13 December
Go-NoGo for Probe separation preparation activities: 17 December
Probe separation on the 25 December (separation window extends several days)
Probe entry on 14 January 2005; Titan flyby at 60000 km
Third low altitude Titan Flyby (@ 1000 km altitude, may be increased to 1577
km) on 15 February 2005.
--
--------------
Jacques :-)
www.spacepatches.info