[meteorite-list] Rosetta: The Big Burns - Part 3

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 18 Jun 2014 15:30:36 -0700 (PDT)
Message-ID: <201406182230.s5IMUaZ0000979_at_zagami.jpl.nasa.gov>

http://blogs.esa.int/rosetta/2014/06/17/the-big-burns-part-3/

Rosetta
The Big Burns Part 3
June 17, 2014

It's burn week in space again!

On Wednesday, 18 June, Rosetta will conduct the third in a series of
three "Big Burns", which are themselves part of the ten-burn series of
orbit correction manoeuvres (OCMs) that are taking us to arrival at
comet 67P/C-G on 6 August.

We've dubbed these three the "Big Burns" because, well, they're big.

The first two, on 21 May and 4 June, used 218 kg and 190 kg of
propellant, respectively, and delivered a delta-v (change in velocity)
of 289.9 and 269.5 m/s, respectively.

Both delivered results to within just a few percent of the planed
delta-v, indicating that, so far, everything is working nominally with
the spacecraft's propulsion system, even though it is working well
outside its design range.

"The series of ten OCMs during May to August has to deliver a total of
about 775 m/s delta-v, and we've already achieved about three-quarters
of that," says Sylvain Lodiot, Rosetta Spacecraft Operations Manager.
"We continue monitoring all the OCMs very closely."

Thruster commands will execute automatically

The burn tomorrow is set to achieve a delta-v of 88.7 m/s and should run
for 136 mins: 41 secs; it gets under way at 15:17 CEST (13:17 UTC). The
burn will be commanded automatically by a series of commands that will
be uploaded on 17 June.

The manoeuvre will be conducted with ground station coverage provided by
ESA's 35m deep space station at New Norcia, Australia

Telemetry (status information from Rosetta's systems) will be monitored
in real-time; the radio signals must travel 24 min:22 sec to cover the
enormous distance from Rosetta, currently about 2.9 AU (434 million km)
from Earth.

[Graphic]
Rosetta OCM plan as of 17 June 2014. Note that future OCMs will be
adjusted based on the actual performance of past burns.

As with past OCMs, the rest of the series will be adjusted based on the
actual performance of the previous burn and the continuous improvement
of our knowledge of the comet's orbit; the comet's trajectory is being
regularly refined by analysing images taken with the OSIRIS camera
<http://blogs.esa.int/rosetta/2014/05/15/comet-67pc-g-is-becoming-active/>
and the navigation camera.

The rest of the spacecraft's systems - including power, thermal,
attitude and orbit control, data handling and communications - are
operating as expected.

ESA's Heavy Metal tracking station

It's interesting to note what happens at the New Norcia ground station
to get ready for Rosetta tracking passes, lining up the 580-tonne
moveable antenna and support structure to point at the spacecraft.

"There are 45 minutes of preparation required at the ground station
prior to each pass," says Gabriela Ravera, the Ground Operations Manager
supporting the Rosetta mission.

"This includes configuring the station to support Rosetta [setting the
uplink and downlink frequency -- Ed.], confirming the Spacecraft
Trajectory Data Message, commanding the massive 35m dish antenna to
point to the correct point in the sky, configuring the station's front
and back end, warming up the amplifiers, calibrating the ranging signal
and then reporting readiness for the track."

These activities are coordinated and implemented by the Estrack Control
Centre at ESOC, where operators are on shift 24 hrs/day year-round.

Gabriela says ESA deep-space stations have a redundant "hot-backup"
chain of hardware connected to the antenna so as to minimise the chance
that any telemetry or data would be lost.

The station sends commands to Rosetta at 2 kbps , and transmits with 10
kW of power.
Received on Wed 18 Jun 2014 06:30:36 PM PDT