karn@petrus.UUCP (Phil R. Karn) (03/01/86)
Posted: Sat Feb 22, 1986 2:54 AM GMT Msg: KGIG-2396-4697
From: TOKAMOTO
To: DOCS
Subj: JAS1.DOC
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I J A S - 1 I
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Introduction:
JAS-1 is an amateur radio satellite, promoted by JARL as
a joint venture with NASDA. NEC constructed "system"
units (space frame, power supply etc.), while JAMSAT,
with its selected volunteer JAS-1 project team,
designed and built the "mission" units (transponders,
telemetry/command and house keeping micro-computer) and
ground support systems.
JAS-1 has been completed and has passed all the
necessary tests. It is in a clean room waiting for
the launch, currently scheduled for August 1986.
The outline of this unique satellite is explained in the
following.
Many thanks to Harold Price, NK6K, for his assistance
in the preparation of this article.
February 11, 1986
N6MBM/JA2PKI
Tak Okamoto
191 Pinestone,
Irvine, CA 92714
Hamnet : 72307,3224
Telemail : TOKAMOTO
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JAS-1 Mission Objectives:
1. JAS-1 will provide reliable world-wide amateur radio
communications.
2. JAS-1 will enable radio amateurs to study tracking
and command techniques.
3. JAS-1 will offer an in-space "proving ground" for
radio amateur developed and built transponders and sub-
systems.
4. JAS-1 will provide NASDA an opportunity to carry out
a "multi-payload" launch using their new "H-1" launcher.
(NASDA has never engaged in a multi-payload launch, thus
the JAS-1 project will offer NASDA an excellent
opportunity by providing them with an active payload
having its own telemetry-beacon and transponder for
ranging.)
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1. Form and general dimensions:
The spacecraft takes the form of a 26-facet
polyhedron, which measures 400 mm X 400 mm X 470 mm
and weighs 50 kilograms.
2. Launch and Orbit:
JAS-1 will be launched into a circular low-earth orbit,
which will be non-sun synchronous and non-polar.
Launch vehicle : H-1 2 stage rocket
Launch number : Test Flight # 1
Launch site : Tanegashima Is. Japan
Launch date : August 1986
Estimated inclination : 50 degrees
Estimated altitude : 1500 k.m.
Estimated period : 120 minutes
Estimated window per pass : 20 minutes/pass
Estimated passes per day : 8 passes/day
3. Designed life:
Estimated lifetime is 3 years
4. Special Features of JAS-1:
JAS-1 carries two separate mode J transponders. One is
a linear transponder, and the other is a digital
"store-and-forward" transponder mainly for non-real-time
communication between stations located in different time
zones.
The reasons for selecting mode J for this first Japanese
amateur radio communications satellite are:
a) It is becoming increasingly difficult to use 145-MHz
for a satellite downlink because of man-made electrical
noise and other interference.
b) The planners of JAS-1 wanted to provide a successor
to AMSAT OSCAR-8's mode J, which was originally
developed by JAMSAT's engineering team back in 1976.
c) 435 MHz is much quieter than 145 MHz as a
downlink band, it is comparatively free from man-made
noise and sky-temperature effects.
The digital transponder will provide "error-free"
information exchange.
5. Transponders:
a) The linear transponder = mode JA :
The passband will be 100 kHz wide. The transponder
will have an output of 1 watt p.e.p. Ground stations
will need an uplink power of 100 watts e.i.r.p.
The sidebands will be reversed, i.e., the uplink is LSB,
the downlink is USB. There will be a 100 mW c.w. beacon
switchable to PSK when needed.
Uplink pass band : 145.90 MHz - 146.00 MHz
Downlink pass band : 435.80 MHz - 435.90 MHz
Beacon freq. : 435.795 MHz
Translate freq. : 581.80 MHz
b) The digital transponder = mode JD :
There will be four 145 MHz band input channels using
Manchester coded FM for the uplink. Ground stations
will need 100 watts e.i.r.p. There will be one
downlink channel in the 435 MHz band using PSK, the
output will be 1 watt RMS.
Channels are :
Uplink channel 1 : 145.850 MHz
,, channel 2 : 145.870 MHz
,, channel 3 : 145.890 MHz
,, channel 4 : 145.910 MHz
Downlink channel : 435.910 MHz
The data format is HDLC. The protocol is AX.25 Level 2
Version 2. The data transfer rate is 1200 bps for
both uplink and downlink.
The reasons for not using Bell-202 type FSK modulation
are:
a) To reduce the parts count onboard JAS-1. Using
Manchester coded FM for uplink reduces JAS-1's onboard
decoder chip count by 16.
b) To improve the downlink margins. Due to JAS-1's
tight power budget, only 1 watt is generated by the
downlink transmitter. A more efficient modulation
scheme like PSK is required.
JAS-1 will be a store and forward system but not a
real time digipeater. Digipeating is not an effective
use of a low orbit satellite such as JAS-1, which has a
limited communication foot print and visibility time.
JAS-1 has 4 uplink channels for 1 downlink channel.
This is because the difference of channel efficiency
between uplink and downlink. An uplink channel is
shared by several ground users. Since the ground users
can't hear each other, and are listening to the downlink
channel anyway, the uplinks are subject to packet
collisions. This scheme is called "Pure ALOHA", and is
known to have a theoretical maximum channel throughput
of 18.4%. The JAS-1 downlink is 100% efficient, since
only JAS-1 transmits there. To balance capacity, as
well as add redundancy, four uplink channels are used.
The combined uplink efficiency is then 4 * 18.4% or 76%.
The remaining downlink time is used for general messages
and telemetry data.
JAS-1 will accept a connect from only one station at a
time with the software scheduled for initial use.
Multiple connections will be supported in subsequent
software updates. General packet operation is scheduled
to begin in November 1986.
6. Digital Hardware:
The microprocessor is a MIL-STD-883B screened NSC-800
running with a 1.6MHz clock. This is the only
processor on board. It controls the digital transponder
and also acts as an IHU (Integrated Housekeeping Unit).
The on-board memory has a 1.5MB physical storage
capacity. 48 chips of NMOS 256K DRAMs are used.
A hardware based error-detection/correction circuit is
incorporated to protect the entire 1.5 MB and provide
an 1 MB error free memory area. The system program
occupies some 32KB, the rest is used for message
storage.
The memory unit is physically divided into four
identical 256KB memory cards, any one of which can
be assigned as the system area. Up to three cards can
be turned off. This design provides system redundancy
and allows command stations to control power consumption
without a total loss of service.
JAS-1 has five hardware HDLC controllers. Four of them
are for the uplink channels and one is for the downlink
channel. In total, these controllers consist of some
140 CMOS MSIs, yet their power consumption is less than
that of a single NMOS LSI HDLC controller like WD-1933.
JAS-1 does not have any ROM but has simple hardware boot
strap circuit instead. This design is to increase
system flexibility and reliability.
7. Power system:
25 of JAS-1's 26 faces are covered with a total of 979
pieces of solar cells. They will generate 8.5 watts of
power at the beginning of life.
JAS-1 employs 11 Ni-Cd battery cells with a capacity of
6 AH. These supply 14 volts average to JAS-1's main
power buss. The 14 volts is converted and regulated to
+10V, +5V and -5V.
8. Antenna system:
JAS-1 has three antennas.
2 m reception antenna
Slant 1/4 wave Mono-pole Isotropic -4 dBi gain
70 cm transmission antenna
Mode-JA : Slant Turnstile L.H.C.P. +Z axis +3 dBi gain
Mode-JD : Slant Turnstile R.H.C.P. -Z axis +3 dBi gain
9. Attitude control:
Forced shaking using the earth's geomagnetic field.
JAS-1 has two 1 ATm sq. permanent magnets in its Z axis.
10. Telemetry:
Analog system telemetry has 12 analog channels and 33
system status flags. This telemetry can be sent without
the help of the NSC800 microprocessor and will be
turned on automatically by the separation from the H-1
launcher. The telemetry is sent on the 100mW beacon on
435.795MHz in CW, switchable to PSK.
Digital system telemetry has 29 analog channels and 33
system status flags. This software driven telemetry can
be sent in any format, and can include short text
messages. This telemetry can be sent on either the mode
JD downlink channel (435.910MHz) or the mode JA CW
beacon (435.795MHz).
11. Command:
A simple 3-channel tele-command system is used for
global control functions, e.g. JA transponder
"ON"/"OFF", JD transponder "ON"/"OFF" and independent
"ON"/"OFF" of the A-0 beacon. An additional 37 channels
are available mainly for controlling the digital
transponder.
Onboard command from the NSC-800 is also available.
12. Ground stations:
Mode-JA:
A ground station setup which was used for Amsat Oscar-8
mode-J can be used for JAS-1 mode-JA. A station with a
10 watt 2 m SSB transmitter and a 10dBi beam for uplink;
and a 70 cm receiver (with low NF) with a 15dBi beam for
downlink; should be adequate for this job.
Mode-JD:
In addition to the mode-JA set up, FM mode is required
for the 2 m transmitter.
Since JAS-1 uses the standard AX.25 protocol and 1200
bps data rate, ground stations will be able to use a
TAPR-style TNC, a 2 m FM transmitter and a 70 cm
receiver without modification.
The JAS-1 modem, a special interface board, will be made
available containing the Manchester modulator and an
audio PSK demodulator allowing connection to the
"modem disconnect" connector of a TAPR-style TNC.
The modem also connects to the audio input and PTT of
the 2m FM transmitter and to the audio output and
frequency control (option) of a 70 cm SSB receiver.
Although JAS-1 will be available to individual access,
the general amateur community will benefit from
"JAS-1 gateways". Messages relayed through gateways
can be sent worldwide and is as easy as sending
messages to distant stations via a W0RLI HF gateway.
13. Outline of project history/schedule:
November 1982 : Freezing of conceptual/preliminary design
December 1982 : Preliminary Design
April 1983 : Detail Design
- June 1984 Engineering Modules Integration & Test
Ground Support System Integration
July 1984 : Flight Model #1 Integration & EIC/MIC
- December 1984
January 1985 : Flight Model #1 General Test
- March 1985
January 1985 : Flight Model #2 Integration & EIC/MIC
- August 1985
August 1985 : Flight Model #2 General Test
- November 1985
November 1985 : Software development.
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References:
JARL News, JAS-1 User's Guide (Those are available only in
Japanese.)