|
People: Jason-1 & TOPEX/Poseidon Mission Planning and Sequence Team (MPST)
Team members: Sophia Malloy, Laurie Francis, Sandhya Guduru and Ron Bailey
Overview: The Mission Planning and Sequence Team, (MPST), is composed of four
Sequence Integration Engineers. The team has three types of tasks to ensure that information
flows smoothly between the TOPEX/Poseidon and Jason-1 ground system and the TOPEX/Poseidon and
Jason-1 satellites. These tasks are sequencing, software development and maintenance, and
scheduling TDRSS and LEOT communications.
Sequences are sets of instructions, (known as "commands") that are sent to both the
satellite and the Ground System which consists of a number of earth based processors.
Commands control things such as the time at which sequences are transmitted from the
ground system to the satellite, the play-back of data from the satellite to Earth, and
fine-scale changes to the satellite's orbit. Sequences are sent to the satellite about every 7
days. Building a sequence is largely automated and is done on a computer, but there are
many different combinations of complex commands. Once a sequence is built it is tested
to make sure it will do precisely what is needed. Great care is taken to ensure that the
satellite and its instruments are commanded to do exactly the right thing.
Software development and maintenance is necessary to ensure that operating the spacecraft
is as efficient as is possible. Computer code for new instructions has to be built as
conditions change in space and as the spacecraft ages. Scheduling communications between
the ground system and the TOPEX/Poseidon and Jason-1 satellites is the third major area
of work for this group. Arrangements have to be made with TDRSS, LEO-T and NASA's Deep
Space Network (DSN). TDRSS is the Telecommunications and Data Relay Satellite System in
space; LEO-T is the Low Earth Orbit Telecommunications system; the DSN is an international
network of communications facilities on the ground at Goldstone, in California's Mojave
Desert; near Madrid, Spain; and near Canberra, Australia.
A more complete picture of major roles of the MPST:
- Producing an "integrated sequence of events"
for monitoring of satellite performance. The term "integrated" means that the final sequence
of events includes commands and other information for both the TOPEX Ground System and satellite.
Ground System events would include such things as times when data are to be transmitted to or
received from the satellite. Satellite events would include such things as data playback times,
orbit maintenance maneuvers, etc.
- Coordinating and implementing routine
activities. This includes such things as regular uploading of command sequences to the
satellites and playback of science and engineering data from the satellites. The MPST leads
the sequence review process. All command sequences must be thoroughly reviewed and tested on
the ground before they are sent to the satellite.
- Maintaining and monitoring compliance with
the Mission Plan. The Mission Plan is a document that is generated early in the development
stage of a mission. It tells, with quite some detail, how the mission will be conducted. For
example, on TOPEX/Poseidon, the Mission Plan dictates how much time will be allotted on the
altimeter antenna to the NASA and CNES altimeters, respectively. Although the Mission Plan is
updated periodically, it remains the guiding document throughout life of the project.
- Performing TDRSS/LEO-T and NASCOM scheduling
and supporting the Flight Control Team in carrying out the TDRSS schedule. Operation time on
the TDRSS, LEO-T and the NASA Communications Network must be tightly scheduled in advance
because of the competing requirements of other missions and activities.
- Command sequences for the satellites. These
are uplinked every seven days, however, the process of generating a sequence can take as long
as three weeks. This includes one week for generating a request for time on the TDRSS and LEO-Ts,
one week for negotiating and processing of the requests, and one week for generation of a
sequences for both satellites, project review and approvals. This complicated process is made
somewhat easier by a number of things. First, sequence activities and schedules are repetitive
to a large extent. Secondly, routine sequence activities are handled internally within the MPST,
without higher, management approval being required. Thirdly, the MPST Sequence Integration
Engineers have automated many of the steps in the process. These factors, among others, have
resulted in a reduction of the staffing requirement for MPST of over 80 percent since the
beginning of the operations phase.
|
