PCsat OPERATIONS and COMM PLAN
PRELIMINARY DRAFT!
OPERATIONS
OVERVIEW: There are several
modes and operations scenarios on PCsat.
These are SAFE, LOW POWER, NORMAL, GPS, BBS and COMMAND. The following describes the salient features
of these modes:
SAFE
(RESET): PCsat was designed with dual redundant systems, labeled A
and B. To assure reliable ground
command, PCsat powers up or returns to SAFE mode any time the watchdog timers
time-out and reset the TNC. In SAFE
mode PCsat is in its RESET or power-up initial configuration. Any data and/or file messages are lost. Note, the primary mission is real-time
bent-pipe relay, so normally there are no messages or files on board. In SAFE mode, PCsat is configured to
maximize its ability to respond to ground command even in the presence of
multiple failures. The following
conditions are met in SAFE mode:
BATTERIES CROSS CONNECTED: This assures that power will be available to
both A and B systems.
TRANSMITTERS CROSSCONNECTED: This
assures that should one transmitter have
failed, that both TNC's are connected to the remaining transmitter so that we
can still connect to either TNC.
UHF RECEIVERS ON: This assures that if there is some problem
with the VHF receiver on either system, that we still have at least one
receiver per system to establish a command link.
TELEMETRY
ON: Telemetry is set at a 60 second
period.
DIGIPEATING
DISABLED: The real-time digipeating
functions are disabled. No users can use the satellite.
GPS OFF: The auxiliary GPS payload is OFF to minimize
power.
COOLING RADIATOR
is OFF: This minimizes power.
XTAL
FREQUNECY: The default crystal for
Transmitter B is used.
The only problem with SAFE mode is that it is not the lowest
power consumption mode. It operates at
about HALF the nominal design power budget which should be safe enough, but
later in life, as the power budget decreases, and power becomes an issue, then
the UHF receivers may need to be commanded off as soon as a command station is
available to save power.
ENTERING SAFE MODE: Safe mode is entered under these conditions:
* If a TNC fails
to transmit a minimum of once in 90 seconds
* Once every 3
days, if there has been no COMMAND connection.
* By hardware
command via either TNC to RESET the other TNC.
* By software
command via a TNC to RESET itself.
LOW POWER MODE:
The nominal 6 Watt power budget for PCsat is easily managed
via command or by managing the user loading on the packet transponder. The power requirements for PCsat modules are
approximately the following:
MODULE POWER
DEFAULT PERCENT OF POWER BUDGET
---------------
----- ---------- ------------------------------
TNC’s .5W always ON
8%
VHF Receivers .6W always ON 10%
UHF Receivers 1 W default
ON 16%
GPS Receiver 2 W default
OFF 33%
Radiator 3 W default
OFF 50%
Transmitter 8 W variable 13%-50% depending on user load
Under conditions of low power budget, and after all optional payloads are turned off (their defaults), the UHF receivers can be turned off for additional power savings of 8 or 16%. These receivers are secondary to the primary mission of the VHF receivers. The greatest variability of power budget depends on user load on the transponder. This is managed as noted in the OPERATIONAL MODE section.
The optional GPS receiver will only be enalbled when there is a significant surplus of power on a whole orbit basis. The Cooling Radiator is similarly for optional experimentation with the thermal balance of the spacecraft or when excessive temperatures require.
NORMAL MODE:
The normal mode for PCsat is with both A and B systems operational, each
with both the VHF and UHF receivers ON.
Users select the proper uplink appropriate to their application and the
proper PCsat digipeater routing callsign
necessary to be digipeated back down on the proper downlink. The duty cycle for the transmitter and
consequential power budget is based on the assumption that only 10% of the
Earths surface has active amateur satellite users in the footprint.
During passes in these active areas, the upperbound for
transmit duty cycle is 50% since the channel is operated half duplex. But this requires perfect timing from users
and continent wide synchronizing of all users to fractions of a second. The realizable duty cycle is 40% considering
the probability of catching a complete packet on the uplink. The actual duty cycle is expected to be much
less.
Under these conditions, the whole-orbit average transmitter
duty cycle is less than 4% and well within the 50% power budget allocated.
GPS MODE:
PCsat carries an auxiliary GPS experiment to permit PCsat to report its
own APRS position integrated with all the other user GPS position data in the
downlink. Thus, the GPS experiment not
only supports the PCsat primary mission, but also provides meaningful scientific
data on the performance of the GPS on an orbiting spacecraft. The GPS engine
draws a substantial 2 Watts of power which is 30% of the PCsat budget. Careful monitoring of the PCsat power budget
during orbital periods of full sun should permit the GPS to remain ON for
multiple orbits. If the GPS comes on
via SEU or is left on during poor power periods, the switching circuit is self
quenching at at bus voltage of
10% of the time
COMMAND
MODE:
Command mode is entered as soon as a command station connects
to PCsat using the REMOTE SYSOP function in the KPC-9612 TNC. Both the A and B TNC's are completely
independent. Each TNC has both
CONFIGURATION settings and HARDWARE SWITCHES. Thus, to command a TNC, the
command station must connect to that specific TNC via either its dedicated VHF
or UHF receiver. For redundancy, all of
the crtical hardware COMMAND switches are dual connected to each TNC. Thus, either TNC can operate any of the
critical switches.
HARDWARE
SWITCHES:
BATTERY ISOLATE:
This command permits each TNC and transmitter to operate on its own
battery for independence from any possible battery problems on the other side.
TRANSMITTER ISOLATE:
This command permits each TNC to operate with its OWN transmitter
only. This is normal operational mode
and permits each SYSTEM to support multiple mission objectives independently.
UHF RECEIVERS OFF:
The UHF receivers can be individually turned off in order to save power
as needed.
GPS EXPERIMENT: The
GPS receiver can be turned ON or OFF.
The GPS draws 2 Watts or 30% of power budget. The switch circuit fails safe (off) if bus voltage drops below 12
volts.
GPS NMEA: This
switch (if GPS is ON) will enable single packet NMEA GPS data on the 1200 baud
VHF-A channel. These position reports
will normally occur once every 30 seconds.
This switch can only be controlled from TNC-A.
GPS MITEL: This
switch (if GPS is ON) will enable multiple packet data dumps in the MITEL data
format on the 9600 baud downlink of VHF-B.
This switch can only be contro0lled from TNC-B.
COOLING RADIATOR:
This switch enables a 3 watt resistive radiator on the –Z face to
radiate 3 watts of electrical energy from the spacecraft in case of
overheating. A possible 8 degree C
temperature drop might be possible. R=
3*32.4 or 97 Ohms for 2.6 Watts. The
switch circuit fails safe (off) if bus voltage drops below 12 volts.
XTAL FREQUENCY: This
switch can change the frequency of VHF transmitter B from its normal mode on
the North American APRS frequency to the primary downlink of 145.825 in case
the primary transmitter is lost.
TNC
CONFIGURATION:
Each TNC has hundreds of configuration parameters because of
the very capable general purpose applications for AX.25 packet radio
protocol. But for PCsat only the
following TNC functions are important:
DIGIPEATER: This is
PCsats primary mission. Real Time
Digital Relay
TELEMETRY: Necessary
to see conditions on board the spacecraft
COMMAND: Necessary
to change software or hardware configuration
BBS: The 32K
Bulletin Board System can be used for file store and forward, but this is not a primary mission on
PCsat.
ROUTING: As a
digipeater, the routing of packets between the two
receivers
and two baudrates is under SYSOP control.
Routing is
controlled by the use of digipeater callsigns.
CALLSIGNS: Communications with PCsat and between users
on the ground use station addresses of up to 6 characters called
callsigns. The following default
callsigns are assigned to the operation of PCsat:
PARAM CALLSIGN SYSTEM
USAGE
------- --------
--------- ---------------------------------------------
MYCALL1
W3ADO-1 SYSTEM A, Substituted in
user's VHF-VHF relayed packet
Also used for GPS NMEA 1200 baud data.
MYCALL1 W3ADO-2
SYSTEM B, Substituted in user's VHF-VHF relayed packet
Also used for GPS MITEL data at 9600 baud
MYCALL2 W3ADO-11
SYSTEM A, Substituted in 9600 UHF to 9600 VHF packets
MYCALL2 W3ADO-12
SYSTEM B, Substituted in 9600 UHF to 9600 VHF packets
MYREM COMAND-1 SYSTEM A, COMMAND Channel. Password protected.
MYREM COMAND-2 SYSTEM B, COMMAND Channel. Password protected.
MYBBS MAIL-1* SYSTEM A, MAILBOX (not a primary mission)
MYBBS MAIL-2* SYSTEM B, MAILBOX (not a primary mission)
UIDIGI APRSAT* SYSTEM A
VHF/UHF digipeating call. User uses this
path on uplink and PCsat substitutes its own
MYCALL in the downlink
UIDIGI SECRET* SYSTEM B
VHF/UHF digipeating call for Special users.
Callsign substitution of MYCALL2
will occur.
UIDIGI WIDE* BOTH
Alias for terrestrial compatibility
MYGATE XBAUD* SYSTEM A VHF-1200 to VHF-9600 digipeating
callsign
MYGATE XBAUD* SYSTEM B VHF-1200 to VHF-9600 digipeating
callsign
MYGATE XBAUD* SYSTEM A UHF-9600 to VHF-1200 digipeating
callsign
MYGATE XBAUD* SYSTEM B UHF-9600 to VHF-1200 digipeating
callsign
* Functions show with (*) are disabled in SAFE mode.
COMMANDS
TO TRANSITION FROM SAFE MODE TO NORMAL OPERATIONS:
1) CONNECT TO MY
REMOTE (COMAND-1,2). ...
A. HARDWARE
COMMANDS:
1. ISOLATE
BATTERIES CTRL A
ON
2. ISOLATE
TRANSMITTERS CTRL B
ON
3. Turn OFF
UHF Receiver A OUTPUT
0xxxxxxx
4. Turn OFF UHF Receiver B OUTPUT x0xxxxxx
5. Reset OTHER TNC OUTPUT xx0xxxxx
6. GPS ON OUTPUT
xxx0xxxx
7. A: NMEA ON / B:MITEL ON OUTPUT xxxx0xxx
8. Cooling Radiator ON OUTPUT xxxxx0xx
9. Switch B to 145.825 MHz OUTPUT xxxxxx0x
10. Enable
Auxilliary Relay OUTPUT
xxxxxxx0
B. ROUTING
COMMANDS:
1. Enable
digipeating via MYCALL DIGI
ON
2. Enable
digipeating VIA APRSAT and ALIASES
UIDIGI APRSAT, etc
3. Enable
cross speed conversion (XBAUD) MYGATE
XBAUD
4. Enable
Bulletin Board(not primary mission)
PBPERSON off
5. Enable
access to GPS CONOK
ON, CMSG ON
C. TIMING
COMMANDS:
1. Set
TELEMETRY rate TE
N (in 10 secs)
2. Set Beacon
Rate BE E N
(in mins)
3. Set
Bulletin Rates BLT
N
D. CHARACTER
STRINGS:
1. Set Beacon
Text BT ……………
2. Set CONNECT
Text CT ……………
3. Set
BULLETIN Texts (four) LT
N ………
2) CONNECT TO
MYCALLS (W3ADO-1,2 and W3ADO-11,12).
This is not normally done unless there is an auxilliary RS-232 payload
such as a GPS or auxiliary processor.
3) TRANSPONDER
OPERATIONS: Users address the various
transponder paths through PCsat based on the uplink and downlink channel and
the path callsign. To minimize
collisions and contention on the uplink these users are separated amongst the 4
different receivers:
A. 5 Watt HANDHELD USERS:
Receive on VHF-A 1200 baud downlink
1. Handhelds will use the path VIA
APRSAT on the VHF-A Uplink
2. Handhelds may use the path VIA XBAUD
on the VHF-A uplink
to communicate with mobiles directly at 9600 baud
B. 50 Watt MOBILE USERS:
Receive on VHF-A 9600 baud downlink
1. Mobile users will use the path VIA
APRSAT on the UHF-A uplink
2. Mobile users may use the path VIA
XBAUD on the UHF-A uplink
to communicate directly with Handheld users at 1200 baud
C. Internet linked special ground stations or IGates:
1. Igates will monitor the VHF-A
downlink for all packets.
2. Igates will use the path via XBAUD
on the UHF-A uplink to send
messages to Handhelds monitoring the VHF-A 1200 baud downlink
3. Igates will use the path via APRSAT
on the UHF-A uplink to send
messages to Mobiles.
D. SPECIAL EVENTS AND LOW POWER TRACKING DEVICES:
1.
Special tracking devices will be authorized for low power
uplink on the unpublished VHF B command channel via SECRET. Downlink is on the North American 144.39
APRS channel.
2.
Other Special uses, such as tracking the Olympic Tourch, etc
can uplink on VHF B via SECRET or via XBAUD
E. AUTHORIZED PAGING STATIONS:
1. Authorized PAGING stations will use
the unpublished 9600 baud UHF-B on a limited basis to initiate North American
wide Paging on the 144.39 downlink.
Normally the path of XBAUD will be used so that the downlink comes down
on the normal 1200 baud used on 144.39.
2. "Semiprivate" pages would
use XBAUD for the packet to come
down on the unusual 9600 baud on that
frequency.
F. USNA AND AUTHORIZED PAGING STATIONS:
1. USNA will control PCSAT via the
unpublished 9600 baud UHF-B if the UHF receivers are on. Otherwise, it will use VHF-B.
2. If System B fails, USNA will use
UHF-A or VHF-A as needed.
G. RECOVERY FROM SAFE MODE to NORMAL MODE: With all systems and
components operating normally, the
following steps will usually be
taken to re-configure from SAFE MODE:
1.
If power is scarce even with all user load disabled and all
receivers are fully functional, then
the UHF receivers should be
commanded off to conserve additional
power.
2.
The ISOLATE TRANSMITTERS command should be sent to separate
the two transmitters so that signals
intended for the separate
transmitters do not collide with each
other during NORMAL Ops.
3.
The ISOLATE POWER command should be sent to separate the
battery systems. This allows us to watch the degradation of
battery system A by allowing it to run
with the greater load
anticipated on System A. Once System A has degraded below the
point of reliable operation, then the
systems will remain cross-
connected.
5) FAILURE MODES:
Commands are provided for operating with the following failures:
A. LOW POWER
BUDGET
1. Send UHF
Receivers OFF command
2. Send UIDIGI
OFF to disable general users of the APRSAT alias
3. Send DIGI
OFF command to disable all users
4. Increase
TELEMETRY period above 1 minute to 80 seconds.
B. FAILED VHF-A
Transmitter
1. Send Cross
Connect XMTR command (and change XTAL Freq)
C. FAILED VHF-A
Receiver
1. Move
Handheld users to VHF-B uplink (downlink stays on 144.39)
2. Optionally
cross connect XMTRS (which also swaps frequencies)
D. FAILED UHF-A
Receiver
1. Move Mobiles
to VHF-A at 1200 baud
2. Move MObiles
to UHF-B and cross connect XMTRS.
E. FAILED TNC-A
1. Move
Handhelds to VHF-B
F. FAILED
BATTERY-A
1. Send
Cross-Connect-Power command
G. FAILED VHF-B
Transmitter
1. Send
CROSS-CONNECT XMTRS command (downlink now is on VHF-A)
H. FAILED VHF-B
Receiver:
1. Suggest all
special tracking devices move to VHF-A
I. FAILED UHF-B
Transmitter
1. USNA and
Paging applications move to VHF-B
J. FAILED TNC-B
K. FAILED
BATTERY-B
1. Send
Cross-Connect-Power command
6) TOTAL FAILURE MODES:
A. Both Batteries
Fail (May work in Sunlight at lower power)
B. Both TNC's fail
C. Both
Transmitters Fail
D. Solar power drops
below X% of original
E. Both 1-min AND
3-day Fail-Safe-Timers fail and both TNC's lockup.
F. Both VHF
receivers fail and UHF Receivers are off and TNC's both
are OK and the 3-day Fail-Safe-Timers
fail
G. Stuck
Transmitter and both UHF Receivers OFF and TNC's are both OK
will cause Batteries to drain. THus resetting the UHF receivers to ON.
TELEMETRY COMMAND and CONTROL HARDWARE INTERFACES:
PCsat uses an off-the shelf AX.25 packet radio terminal node
controller for all of its communications, telemetry, command and control. The Kantronics KPC-9612Plus is a dual port
version of this popular communications standard, and it includes enough basic
input/ouput capability to handle all of PCsat’s needs. The following table summarizes its capabilities…
Radio Ports:
Radio Port 1: Uplink/downlinks
using AX.25 packet data at 1200 baud
Radio Port 2: Uplink/downlinks
using AX.25 packet data at 9600 baud
Spacecraft I/O ports:
Serial
Port: A bi-directional RS-232 4800
baud serial data port when the TNC is in the CONVERSE mode.
Control Bits: Four
FET switches. Use CTRL A,B/A,B command
Output
Bits: Eight input/output bits. As outputs, these are open collector
switches. Use the OUTPUT bbbbbbbb
command.
Input
Bits: The same eight I/O bits may be
used as inputs if a 10k pullup resistor is used. The state of these bits is shown in the Telemetry packets.
Input
Bit: One additional single input
bit in the telemetry.
Telemetry: There are 5 analog (0-5volt)
inputs. These appear in every telemetry
packet. In PCsat, an external
multiplexer switches 4 banks of 5 values into sequential packets so that 20
values may be read.
PCsat
Functional Descriptions:
Solar
Panels: There are three
types of solar cells on PCsat.
Sides
+/-X and +/-Y: These four sides
contain 4 terrestrial
1W
Teflon coated panels connected as an A system pair and a
system
pair.
+z
Panels: Four space rated
high efficiency glass covered cells
producing
about 1.7 times as much as the terrestrial cells. These
are
also connected as an A pair and a B pair.
-Z
Panel: One custom panel
consisting of a single 16 volt string
supplies
1.4 times the power of the terrestrial cells.
Battery
Charging Circuits: The PCsat charging system was designed with
a 16
volt unregulated bus to be self-regulating.
By using 12
NICAD
cells, with a fully charged open circuit terminal voltage of
16.8
volts, the solar panel output current tapers to under X ma
under
full charge conditions so there is no chance for overcharge.
As a
precaution, there are 4 zener diode shunt regulators that
will
dump any excess current from voltages above 16.9v to ground.
Under
load, the nominal bus voltage will be 14.4 volts.
Power
Regulators: The transmitter is
operated directly from the
unregulated
14.4 volt bus. All other circuits are
powered by dual
redundant
8 volt switching regulators.
Internally, the TNC’s
regulate
down to +5 volts for their use.
Special
Circuits:
Fail-Safe
Reset Timers:
72
Hour fail-safe Reset Circuit:
Transmitter
Synchronizing and Holdoff:
Telemetry
Multiplexer:
Transmitter/Receivers:
Terminal
Node Controller (TNC):
INITIAL CHECKOUT
(FLATSAT on 4-25-2001)
Battery Isolate Test:
B receivers and TNC were not connected
Setup: Supply 16.60 volts on Bat-A. Idle 120 ma. XMT 550 ma
Supply
16.62 volts on Bat-B. Idle 40 ma.
XMT 290 ma
Command
BAT-ISOLATE: XMT-A = 820 ma. XMT-B = 40 ma.
Transmitter Isolate:
Continuity was measured through the TXA and PTT lines between the A and
B side while commanding the XMIT-ISOLATE relay.
Default was 0 ohms.
XMIT-ISOLATE commanded ON was OPEN.
UHF RECEIVER A OFF:
OUTPUT 0xxxxxxx changed UHF-A B+ from 7.6 to 0 v
UHF RECEIVER B OFF: OUTPUT x0xxxxxx changed UHF-B B+ from 7.6 to 0 V
GPS ON: OUTPUT xx0xxxxx changed GPS-ON from 0.3 to 16 v
TNC-RESET: OUTPUT xxx0xxxx Changed pull-up from 5 to 0
NMEA ON/MITEL ON: OUTPUT xxxx0xxx Internal to TNC not yet built
XTAL-B: OUTPUT xxxxx0xx Missing wires in harness
RADIATOR-ON: OUTPUT xxxxxx0x C&C interfacec not built!
AUXILLIAR-A ON: OUTPUT xxxxxxx0 Bad bit from TNC