The paper describes the system design considerations and design activities performed at Spar Aerospace in the last 18 months in support of the development of a Canadian Mobile Communication Satellite (MSAT). Recent evolving international agreements and events of importance to MSAT are the emergence of the U.S. Operator and the Mobile WARC 1987. Their impacts on the system requirements and system design are discussed. Solutions to these new requirements are implemented into the 9 Beam baseline design. The system design and the parallel technology development permit the support of a commercial flight program

Hing, Kunvana

Moody, Harry J.

English

NASA Technical Reports Server

N88-25741
CONSIDERATIONS FOR SPACECRAFT DESIGN FOR M-SAT
KUNVANA HING, System Engineering; HARRY O. MOODY, Advanced Systems,
Spar Aerospace Limited, Canada
SPAR AEROSPACE LIMITED
21025 Trans Canada Highway
Ste-Anne-de-Bellevue, Quebec H9X 5R2
ABSTRACT
The paper describes the system design considerations and design
activities performed at Spar Aerospace in the last eighteen months in
support of the development of a Canadian Mobile Communication
satellite (M-SAT).
Recent evolving international agreements and events of importance
to M-SAT are the emergence of the U.S. Operator and the Mobile WARC
1987. Their impacts on the system requirements and system design are
discussed.
Solutions to these new requirements are implemented into the 9
Beam baseline design. The system design and the parallel technology
development enable Spar Aerospace to be ready to support a commercial
flight program.
INTRODUCTION
Canada has been persuing for some years the study of systems and
technology for a Canadian Mobile Satellite System (M-SAT). Agreements
between the Department of Regional Industrial Expansion and Spar
Aerospace has provided funding for the 'development of the M-SAT space
segment, work which_is reported in this paper.
Since July 1986, a.number of events in the _nited States and in
Canada a have quickened the pace of commercial M-SAT development.
Recently evolving international agreements and events have added other
considerations to the system design. Of particular importance has been
the emergence of the U.S. Operator and the des£re of the U.S. and
Canadian Operators to provided interoperable systems, The Mobile WARC
conference in 1987 has established the L-band as the frequency band for
mobile satellite service and has added some complexity to the L-band
power end frequency flexibility requirements.
This paper will describe the current work at Spar Aerospace on the
development of an all L-band system where the above requirements have
been considered.
a Kidd, 1987 P_ECEDiN_ F_G_ t_[.ANK t_OT RLMED
431
https://ntrs.nasa.gov/search.jsp?R=19880016357 2020-03-20T06:51:42+00:00Z
SYSTEMREQUIREMENTS
Basic System Desiqn Requirements and Guidelines
The system design based on Canadian requirements of the L-band M-
SAT space segment are to provide full Canadian coverage, full
CONUS/AIoska backup coverage and to provide sufficient capability to
support 60,000 Canadian Users with a ten year lifetime.
The system design resulting from these requirements is to stay
within the following guidelines:
1) The spacecraft should be designed such that it can be
launched by an Ariane IV vehicle as part of a dual launch.
However, the spacecraft should be configured to take
advantage of evolving expendible launch vehicle systems.
2) The payload mass should be maintained below 350 kg (770 ibs)
without margin and the payload DC power should be maintained
below 2500 Watts without margin.
3) The payload should be configured for a typical three axis
body stabilized spacecraft.
4) The overall system should be designed for a mix of service:
40% transportable and 60% ground mobile, with 12 dBi and 9
dBi respective mobile Qntenna gain.
This is to constrain the final design of the payload while maintaining
the desired performance. Spacecraft with the above weight and power
capabilities are now being built for the lates£ generation of domestic
communication satellites.
Impacts of Mobile WARC 1987
Prior to Mobile WARC 1987, the system design and the technology
development have been based on a 9 MHz continuous spectrum in
accordance with the Federal Communication Commission (FIG) b frequency
allocation. However, a two segment L-band allocation for LMSS spanning
29 MHz has been established by Mobile WARC 1987.
There is some indication that the M-SAT operators might want to
provide service In four bonds, namely, MMSS, AMSS and the two segments
of spectrum allocated to LMSS by Mobile WARC 1987 c, for the first
generation system.
This new requirement along with the need for flexibility for
evolvin_ user demands and distribution lead to the follow_ng update of
the pre WARC design:
b Brassard, "1988
c WARC MOB-87
432
Impacts of Mobile WARC 1987 (cant'd)
1)
2)
s)
4)
5)
6)
7)
Minimization of back-haul spectrum and optimization of L-band
spectrum efficiency/flexibility.
Interaction (trade-offs) between back-haul power and L-band
spectrum efficiency/flexibility.
Local Oscillator frequency generation and IF plan to take
into account the much larger number of sub-bands required.
Intermodulatlon analysis taking into account the
discontinuous nature of signal spectrum in the new frequency
pian.
A wider instantaneous bandwidth (i.e. 29 vs 9 MHz) is
required for the L-band high power amplifier.
Passive Inter Modulation (PIM) performance of L-band antenna
components taking into account the reduction of PIM order
from 15th to 7th.
L-band input/output filter performance taking into account
the wider operating bandwidth and the narrower separation
between transmit and receive bands.
Impacts of the Interoperable North American System
The emergence of the U.S. Operator has brought up the following
additional considerations to the M-SAT space segment design:
1) The system design should involve both a Canadian and U.S.
spacecraft with a primary mode of servicing their respective
territories. Prior to launch of the second spacecraft, or in
the case of one of the spacecraft failing, either spacecraft
should be capable of providing both a Canadian and a U.S.
service up to the capacity of a single spacecraft.
2) The concept should allow the two spacecraft to occupy orbital
slots separated by up to 20 degrees of longitude.
3) The spacecraft hardware for both the Canadian and the U.S.
spacecraft should be functionally identical.
The first and third considerations have no technical impact on the
system design. The mass, power, coverage and frequency reuse provided
in the basic design requirements are sufficient to cover these new
items.
The second consideration requires some adjustment to the 9 Beam L-
band antenna coverage pattern.
433
SYSTEMDESIGN
Concept Trade-off
Two candidate system concepts for the M-SAT space segment have
been considered: the conventional spot beam approach (with varying
amounts of overlap) and the scanning system employing the Frequency
Addressable Beam (FAB) technique. Prior to Mobile WARC 1987, a
complete trade-off study had been made between the 9 Beam concept and
the FAB concept. The following parameters have been studied:
1) DC Power
2) Spacecraft mass
3) System capacity
4) System reliability
5) System flexibility including
- Operation with two co-located satellites
- System growth potential
6) Technical risk including
- PIM
- Deployments
The study result has shown that neither of the two schemes offers
overriding advantages. However, after Mobile WARC 1987 and the
decision to provide full 29 MHz service, the 9 Beam concept appears to
be a better candidate due to its PIM performance (separate versus
common transmit/receive antenna in view of the lower order PIM). All
efforts have been shifted to cover various design aspects of the 9 Beam
concept.
434
CONCLUSION
A 9 Beam system meeting all the basic design requirements and
guidelines, had been defined prior to Mobile WARC 1987 d. Solutions to
the considerations discussed earlier, are being implemented to the
baseline design to make it compliant to the requirements as currently
understood. Spar Aerospace is considering applying for a patent on the
design concept to provide power flexibility.
A parallel technology development of payload units, in support of
the system concept, is well advanced at Spar Aerospace e.
Possible ...v-_,m__÷ions_v_ of _k^_,,_requirements suc,h as the addition of
Mexican coverage can easily be implemented in the updated baseline
design.
The system design activities and the parallel technology
development enable Spar Aerospace to be ready to support a commercial
flight program.
REFERENCES
Kidd, A.M., Karlsson, I., Whittaker, N., 1987. M-SAT System and
Payload
Development. The Canadian Satellite User Conference, pp. 594-
599.
Brassord, G., 1988. L-Band linear high power amplifier using Class C
transistors. R.F. Expo '88.
Final Acts of WARC MOB-87
Cox, R.P., Zacharatos, J., Williamson, B., Morgan, C., Cox, J.R.G.,
1988.
System Trade Off for a North American Mobile Satellite. AIAA 12th
ICSSC.
Karlsson, I., Patenaude, Y., Stipelman, L., 1988. Antenna System for
M-SAT Mission. JPL Mobile Satellite Conference.
d Cox, 1988
e Karlsson, 1988
435


Considerations for spacecraft design for MSAT

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