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PICO SATELLITE CONCEPT OF TU-BERLIN

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					          PICO SATELLITE CONCEPT OF TU-BERLIN
                             Hakan Kayal, Klaus Briess
                             Technical University of Berlin
                      Institute of Aeronautics and Astronautics
                              Department of Astronautics
               Hakan.Kayal@TU-Berlin.de; Klaus.Briess@ilr.tu-berlin.de


ABSTRACT

One of the latest manifestation of miniaturization in space applications is the
development of standardized pico satellites. The so called CUBESAT’s for example,
which are standardized picosatellites have a size of only 10x10x10 cm³ and a
maximum mass of 1 kg. They are based on concepts of California Polytechnic State
University and Space Stanford University. Pico and nano satellites will be developed at
the Institute of Aeronautics and Astronautics of the Technical University of Berlin as
one of the major working topics within the department of astronautics.
   The basic vision behind the objective is to use pico satellites for demanding
scientific and technological applications at a very low cost. The development of pico
satellites is currently in an very early phase. It is however conceivable that reliable and
powerful platforms will emerge from today’s efforts, which will enable a large number of
applications for pico and nano satellites. The range of potential applications will include
areas such as earth observation, space science, astronomy and on-orbit verification of
new technologies. Another additional advantage of developing pico satellites at the TU-
Berlin is the opportunity to give hands on experience to students on complete satellite
missions, including design, test, production and operations.
   Enabling technologies for demanding applications will surely make use of MEMS
based components. Especially in the fields of attitude control, communication and
propulsion there is a need for new developments in order to enable demanding
applications with pico satellites. TU-Berlin is working on various concepts for the
development of such components at various levels and under the involvement of
external cooperation partners, companies and students.
   This paper will give an overview of current and future activities of the TU-Berlin
related to the development of pico and nano satellite mission concepts.


1. CURRENT SITUATION

More then 40 developers worldwide are working currently on CUBESATS with different
objectives. Based on concepts of California Polytechnic State University and Space
Stanford University, the CUBESAT specifications define the overall dimension, mass
and other interfaces, in order to fit the satellite into a deployment mechanism called P-
POD. Besides this specification, developers are free in the design of the satellite
functions.
   All activities onboard a CUBESAT are strongly limited by the available space and
electrical power. These two aspects are dominating and limiting all functions.
   While one of the most common aspects is, that students are involved it the
development and operation of the CUBESAT’s, many of them are rather at a very early
development stage. For example, most of the CUBESAT’s have either no attitude
control or very limited attitude control capabilities, which is a precondition for rather
demanding applications. The most important reason is the lack of adequate attitude
control sensor and actuator elements.
   But not only attitude control is an important issue for future pico satellites with
demanding applications. Communications at higher bit rates is also an important issue,
especially for downlink. In most cases, current projects make use of low bit rate
communications between 1,2 kBit/s and 9,6 kBit/s. As soon as the need for the
transmission of images or other scientific data with higher volume is given, downlink
capability on at least S-Band with adequate formatting and coding is required.
   Onboard processing of data is the next point, where many considerations are
necessary within an CUBESAT environment. Demanding CUBESAT applications
require high processing capability at very low available electrical power. Today,
microprocessors get always faster and consuming lower power but their suitability in
the space environment must be proved. Also different redundancy and power saving
mechanisms for pico satellites must still be tested is space. As stated in the objectives,
pico satellites are ideally suited to make such tests in orbit.


2. OBJECTIVES

The main objectives for the development of pico satellites at the TU-Berlin are as
follows:

• Development and in orbit verification of new space technologies

There are an increasing number of new micro technologies, which can be interesting
for space applications. These technologies will help reducing the total mass and
volume of spacecrafts, if they can be used in the space environment. There are two
different direct consequences. The first consequence is, that spacecrafts using micro
technologies will be more capable, because they will have more payload capacity
without degradation of supporting bus functions. The second one is, that new
applications for pico satellites will emerge, which were not possible before due to the
lack of such components.
    The needed micro components must be tested and verified in space. Pico satellites
are ideal platforms for this purpose, because, they can be built at a very low cost and in
large quantities. Micro electro mechanical systems (MEMS), micro propulsions,
onboard navigation, high end onboard processing and autonomy are some examples
for such micro components, for which we can observe an demand for on orbit
verification.

• Analysis of anthropogenic effects on earth

Today earth observation from space is done by means of a variety of satellites.
Depending on the requirements, this can be very large platforms like envisat or nano
satellites. A number of anthropogenic effects for example changes in the atmosphere
could also be observed by pico satellites when they become reliable. An advantage of
pico satellites is, that the cost of deploying a number of pico satellites is very low
compared with larger satellites. Thus pico satellite constellations or formations may be
a very useful tool for observation of anthropogenic effects on earth.
• Observation of phenomena’s on earth and in space

There are various phenomenons on earth and in space, which require a nearly
continuous, worldwide observation in order to be detected and analyzed. A typical
example are lightning’s on the upper atmosphere. For the detection and counting of
such events, it is necessary to have a satellite constellation in order to increase the
chances to catch an event. In the future, when pico satellite technologies allow a
precise attitude control, also a combination of pico satellites for observation of a single
target will be possible with high resolution.

• Education of students

The practical education of students on satellite complete missions is an important
aspect of pico satellite missions. The students are involved in the planning,
development, construction, test and operation of the pico satellites in orbit and gain
valuable experience for their later profession.


3. MISSION CONCEPT OF TU-BERLIN

The first generation of pico satellites of the TU-Berlin will follow the CUBESAT
standard. This defines the overall characteristics of the satellite of max. 1kg mass and
dimensions of 10 x 10 x 10 cm³. Detailed specifications are available in order to make
the satellites compatible with CalPoly’s orbital deployment mechanism (P-POD). This
compatibility is a requirement in order to be launched and deployed using a P-POD.
   One cost reduction factor in the operation of CUBESAT’s is to use amateur radio
frequencies, which is common praxis. Provided that legal requirements are met and
coordination actions are taken successfully by licensed amateur radio operators, it is
possible to use these frequencies without high license fees. However amateur radio
specific functions must be implemented into the spacecraft to make use of this option.
   The CUBESAT’s of TU-Berlin will also make use of this option, whereby a high
degree of compatibility with
amateur        radio      satellite
communication standards will
be implemented to involve
external ground station capacity
into the mission concept.
Regarding mission operations
this is of big value, especially,
but not only in the LEOP and
emergency cases.
   Mission operations will be
performed by the mission
control center at the TU-Berlin
(Figure 1) and a network of
cooperative ground stations will
be connected to exchange
satellite data as shown in
Figure 2.                              Figure 1 Mission control center of TU-Berlin
                                     TUB




                                        Earth

                         Ext. GS


                                                 Ext. GS




Figure 2 Principal illustration of the ground station network for the pico satellites
                                     of TU-Berlin



4. SATELLITE CHARACTERISTICS

The pico satellites will have all necessary subsystems, such as:
   •   Power
   •   Onboard Data Handling
   •   Telemetry and telecommand
   •   Attitude & Orbit control
   •   Thermal control
   •   Structure & mechanisms
   •   Payload
Depending on the specific mission, different payloads will be integrated. The satellites
will have a high degree of modularity in order to exchange the payload easily.


5. CONCLUSION

The development of pico satellites is currently at its very early stages. Demanding
scientific and technological applications at a very low cost will however be possible in
the future using new technologies from today’s intensive efforts in the field of
miniaturization.
    TU-Berlin is contributing to these efforts with its own pico satellite studies and
projects together with partners from industry and students. The work will be focused on
different key issues such as precise attitude control and reliable board computers as
well as high performance communication and propulsion systems for pico satellites.

				
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posted:8/4/2011
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