Herschel and Planck launch timeline (Forwarded)

ESA News
http://www.esa.int

11 May 2009

Herschel and Planck launch timeline

There's a buzz in the Main Control Room as the launch of Herschel and Planck
gets closer. The two satellites are scheduled to launch together at 15:12
CEST [13:12 GMT], 14 May, on an Ariane 5 from ESA's Spaceport in Kourou,
French Guiana. Several critical events are planned leading up to and after
launch.

After launch, Herschel and Planck will be headed to L2, the second Lagrange
point of the Sun-Earth system, where they will operate from independent
orbits.

L2 is a local gravitational point that is fixed in the Earth-Sun system and
is situated on Earth's night-side. It is an excellent location for both
Herschel and Planck: it allows them to shield their sensitive instruments
from solar radiation which may otherwise disturb observations and offers
good sky visibility. If they were placed in orbit around Earth, heat from
our planet, the Moon and the Sun would interfere with the instruments and
telescopes, reducing sensitivity.

Both satellites have now been integrated with the launcher; the combination
measures approximately 11 m in height and 4.5 m in width, with a weight of
about 5.7 tonnes.

The critical milestones before launch include the launch readiness review,
held on 9 May, and roll-out to the launch pad on 13 May. The launch also
marks the beginning of the Launch and Early Orbit phase (LEOP), during which
mission controllers will monitor the satellites 22 hr/day via ESA's ground
stations at New Norcia and Perth, Australia; Maspalomas and Cebreros, Spain;
and Kourou, French Guiana.

The Ariane 5's solid boosters separate about 2.5 minutes into the launch and
the fairing is jettisoned about 50 seconds later. The upper stage separates
and its engine ignites about 9 minutes into the launch.

The velocity of the composite that includes both satellites will be about 10
km/s just before the satellites go their own way. Separation of Herschel
from the upper stage is scheduled for 15:38 CEST [13:38 GMT], about 26
minutes into the launch. The 'Sylda' (a support structure for Herschel that
also forms a protective cover for Planck) will be jettisoned 1.5 minutes
later and Planck will follow at about 15:40 CEST [13:40 GMT], just under 29
minutes into the launch.

Separation will occur above the east coast of Africa, at about 1100 km
altitude for Herschel, and at about 1700 km altitude for Planck, which
separates some 2.5 mins after Herschel. After separation, the two satellites
will have slightly different velocities.

Herschel's final orbit will be a quasi-halo orbit with an average distance
of 800 000 km from L2. The final orbit for Planck will be a Lissajous orbit,
with an amplitude of 400 000 km.

The launcher will set the satellites directly on the path to L2. This means
that no injection manoeuvre will be necessary for Herschel; the satellite
will be close to its halo orbit around L2 right from separation. One major
manoeuvre is planned to fine-tune the orbit about 24 hours after launch.

Planck will also be in orbit around L2 at separation, but since the
amplitude of its orbit is half that of Herschel, engineers will execute
manoeuvres to reduce its orbit to half that of the original. The first
manoeuvre is planned about 30 hours after launch.

An expanded version of the timeline covering all critical events around and
after launch is available at
http://www.esa.int/esaCP/SEMVW10YDUF_index_0.html

[NOTE: Images and related links supporting this release are available at
http://www.esa.int/esaCP/SEMVW10YDUF_index_1.html ]