NASA Technical Reports Server (NTRS) 19950016401: Geolocation applications of the Gonets LEO messaging satellites

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by  NASA Technical Reports Server (NTRS)

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N95- 22818
GEOLOCATION APPLICATIONS of the GONETS LEO MESSAGING $;ATELLIT_S
V.N. Vlasov, NPO-PI, Moscow, Russia
Javad Ashjaee, Ashtech
1170 Kifer Road
Sunnyvale, CA 94086
[phone]
FAX [phone]
INTRODUCTION Further improvement of the space
segment could provide some relief for cash-
Geostationary satellites carry a
strapped, low-density user populations. Some
majority of the international tele-
visions have been put forth of massive
communications traffic not carried by
spacecraft with 30 m antennas, huge solar
transoceanic cable. However, because the
arrays generating several kilowatts and
radio path links to and from geostationary
spacecraft masses exceeding 4 to 6 metric
satellites total at least 70,000 km and because
tons. Realistically however, the costs of
of inherent on-board spacecraft power
building and launching such massive, complex
limitations, earth stations used in conjunction
payloads renders this possible approach to
with geostationary satellites are usually large
some future era. It will clearly be impractical
and expensive. This limits their installation to
for the near term.
areas with a well-developed industrial and
economic infrastructure. Low Earth Orbiting (LEO) satellites
offer a practical solution to this dilemma for
This reality helps perpetuate a chicken-
many potential applications.
egg dilemma for the developing countries and
All LEO communications fall into one
isolated regions. Economic integration with
the developed world requires being or two categories depending on the services
"networked". But for many developing they provide and their technical sophistication:
entities, even the initial price of entry exceeds
• data transmission
their modest resources.
• voice communications
Exclusion from the global information
GONETS PACKET DATA RELAY LEO
highways virtually assures retardation of
SYSTEMS
economic growth for developing nations,
remote and isolated areas. The category including projects such as
Gonets, Leosat, Orbcomm, Starsys, Vitasat
Very Small Aperture Terminal (VSAT)
[1-2] can provide the following services:
earth stations are often thought of as a
solution for networking developing regions. • Digital data transmission of:
But economic considerations often forecloses text, imagery, databases,
this option. If VSAT size and cost is to be environmental data to/from control
minimized, powerful spot beams from the and sensors; Supervisory Control
satellite need to be focused on relatively small and Data Acquisition (SCADA)
regions. This is not often feasible because of • Paging
the high cost of the satellite itself. To • Remote geolocation
dedicate a high power spot beam to a small
Many applications do not require
region is usually not economically feasible.
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unin_ptable links. Unlike a voice mass and low orbital altitude allows a single
telephon_nversation wherein a real-time launcher to carry several spacecraft thus
link is essential, many data transmission reducing the overall cost of the space
applications allow for some enroute delay. segment.
Non-realtime data forwarding is vastly more
2. Ground terminals can be small, simple,
cost-effective than providing realtime links.
inexpensive and user-friendly devices lowering
All this considered, a practical, useful, maintainability requirements and the training
low-cost, packet LEO data transmission of the "maintainers" themselves.
network needs to be based on the following
Thus, the foregoing principles allow
principles:
the development of affordable LEO satellite
1. The use of a quasi-random constellation of networks for packet data transmission at an
satellites each of which has attitude control estimated cost of between $50 and $200
mechanisms but no station/orbit keeping million depending on the range and
facility. The number of satellites then complexity of services provided. Such
depends on the specific orbital parameters and networks are end-user oriented and do not
the allowable message delivery transit time require developed terrestrial land-line
from originator to addressee. infrastructure. They thus provide instant
network connectivity in "islands" of often
2. The use of VHF/UHF links (130-400
urgent communications requirements. The
MHz) allocated for mobile satellite
time required to establish a node on any
communications together with polar, circular
square meter of earth is the time needed to
orbits (700-1500 km). This allows global
open an attache case and turn on a switch.
coverage and the use of simple, 0-3 dbi, low
gain _omni" antennas, 2-10 W transmitters The "Gonets" LEO system is
and very simple (gravitational) quasi-passive thoroughly based on the foregoing design
spacecraft attitude control. philosophy and first principles. Gonets is
programmed to be operational with an
3. The use of packet transmission mode to
eventual total of 36 satellites organized as six
minimize power consumption of both the earth
planes of six satellites beginning in 1994 and
and space segments and to allow effective
building to a 1996 full operational
spectrum sharing by multiple users. The
constellation.
packet protocol minimizes channel contention
and reduces overhead by simplifying channel In the current system development
control and supervisory intervention. phase, the "demonstration" phase called
"Gonets-D" has already been placed in orbit.
4. The use of an orbital constellation with
Two Gonets-D satellites were launched in
quasi-random access windows is extremely
July, 1992 and have since provided scores of
easy to control and operate using a single
demonstrations around the world.
master control center.
Gonets-D has been demonstrated to
When realized in a practical network,
various governments, industry, and financial
these basic principles yield the following
institutions in Russia, other CIS countries, as
results:
well as in Australia, India, Africa, and
1. Satellites can be very small (50-200 kg) elsewhere. A major series of Gonets-D
and inexpensive capitalizing on the latest demonstrations is planned in Western Europe
achievements in micro-miniaturization and
later in June and South Asia in the July-
satellite technology. Relatively low spacecraft August time frame.
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Thedemonstrationsystemwill be board memory. When the message addressee
expanded by Smolsat later in November or is heard by the carrying satellite, the message
December 1993 to include an additional 6 addressed to him is downlinked to that station.
satellites with 3 in each of the two orbital
Even in its late developmental phase
planes. That system, called Gonets D-l, will
(1993-94), Smolsat will be offering precise
be capable of supporting up to 30,000 portable
geolocation services for mobile users by
transceive terminals and a virtually unlimited
relaying Global Positioning System
number of SCADA terminals.
(GPS)/Global Navigation System (GLONASS)
The Gonets-D1 advanced development derived vehicle position data to corresponding
demonstration system has the following central service stations via Gonets-D1 by
performance values: using a synthesis of Gonets and GPS terminals
in a convenient package.
• 2 hours maximum access wait at the
0.8 probability level Vehicles and other mobile platforms
(be they icebergs or high-value cargo) which
• 3-6 hours average maximum
require highly accurate location determination
message in-transit delays depending
reporting will use a synthesis of GPS/Glonass
on the system completeness (number receivers and GONETS transceivers to
of spacecraft in service at that point
provide this information to managers. The
The above limitations resulted in the GPS/Glonass-Gonets synthesis will provide the
following communications protocol. facility to accurately and quickly telemeter the
location and status of a vehicle anywhere on
Communication between any two
earth to a command center with an accuracy
stations simultaneously in the 5000 km
within several meters.
diameter footprint is quasi-realtime, quasi-
While these terminals locate the vehicle
bent-pipe mode.
(or other mobile object), status and/or
The satellite periodically sends a
message traffic is transferred to central
preamble signal carrying data necessary to
stations via Gonets user terminals. A standard
establish radio contact with a user. Users can
RS-232C interface is used to connect the
exchange information when they are both in
various equipment.
the footprint of the satellite using the preamble
DIFFERENTIAL NAVIGATION
which contains the necessary subscriber
identification information (callsign) and the
Commercial GPS/Glonass navigation
particular geographic area information. The
receivers are limited to the GPS standard
geographic area identification can be both
position service (SPS) accuracy of 100 meter
satellite and Area Station (AS) generated. The
available worldwide for civil use and similar
latter is simpler and therefore employed by the
accuracy for the Russian Glonass system.
Gonets system.
Navigation receivers which use
Various types of data transfers between
differential corrections can significantly
User Terminals (UT) (UTl-satellite-UT#) and
improve performance. Typical differential
to a Stationary User Terminal (SUT) linked to
GPS accuracy is from 0.5 to 5 meters.
the Area Station (UT2-satellite-AS 1 SUT).
Differential Glonass accuracy can expect
Users not simultaneously in the similar improvements over autonomous
footprint of a satellite use the store-and- receiver operation. [4]
forward mode for communication. Data
The accuracy of differential navigation
received by the satellite is stored in the on-
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is limited by the distance between the base continuous reception of differential corrections
station and remote receiver, the age of the and other applications need a correction at a
differential correction data (update rate), and distinct location or time. Some users require
the differential data link. knowledge of the position of the remote units.
The corrections remove most of the These user requirements can be met
error from the major error sources affecting simply with just a GPS/Glonass receiver and
the accuracy of satellite-range measurements: Gonets user terminal. Gonets protocol is built
satellite orbit estimation, satellite clock into the standard interface of the Ashtech
estimation, ionospheric error, and tropospheric GPS/Glonass-Gonets capable receiver.
error. After the correction is applied, the
Users requiring map or navigation
residual error is on the order of one milli-
displays can add a common personal computer
meter for every kilometer of separation
to the basic configuration. Geographic
between the base and remote receiver. [5]
information systems (GIS) could use a bar
It is estimated that over 500 base code reader to easily enter attribute
differential stations would be required to cover information for the landmark.
the United States. Techniques are being
Typical applications include:
investigated which may reduce the number of
worldwide accident investigation (aircraft,
base stations required to provide differential
ship, oil spills, earthquakes, hurricanes, and
range corrections for a wide area.[6][7]
other infrastructure damage), worldwide
The differential corrections must be rescue operations, locating & tracking
transmitted to the remote receiver at a data icebergs, exploration geophysics, oil rig
update rate sufficient to eliminate the effects positioning, vessile docking, channel
of time varying satellite errors and dredging, installing remote communications
atmospheric effects. Update rates from two to sites, harbor depth mapping, and a host of
six seconds are sufficient to minimize these many other GIS applications.
effects.
Vehicle tracking systems or fleet
The differential data message can also management systems could perform worldwide
include information on the integrity of the tracking and route management control of
differential corrections and the real-time health vehicles (ship, truck, automobiles, and
of the navigation satellites which is critical for aircraft). It is even possible to apply this
some applications. technology to unmanned ships traversing the
oceans. The system could then be used by a
The differential data link requires
pilot to safely navigate the harbors.
selection of an appropriate transmission
frequency to assure reception at the remote Agricultural equipment would benefit
receiver and meet local governmental licensing from accurate position data for planting,
requirements. The selection of a Goners applying fertilizers and pesticides leading to
system as the data link provides an ideal improved yields. Navigation and control of
solution to these problems. unmanned combines and tractors may also be
feasible.
GEOLOCATION APPLICATIONS
All users would have confidence they
Applications for differential navigation
can depend on the accuracy of the
encompass a wide range of user needs and
GPS/Glonass-Gonets position data from the
uses. Equipment complexity is dictated by
health data built into the satellite differential
user requirements. Some applications require
correction messages.
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Table 1. GONETS Technical Data
GONETS Orbital Specifications Maximum power density:-37.8dBW/Hz
General Orbital Characteristics: EIRP:+5.19 dBW
Type:LEO, polar Typical earth station:Type UT-P
Inclination angle: 82.6degrees
Period: 114minutes Space-to-Earth Direction
Apogee: 1420km Spacecraft Characteristics
Perigee: 1420km Maximum gain: +2.0dBi
Footprint:5000km Polarization:RHC
Characteristics of the GONETS-D Orbits Service area: Regions 1, 2, 3
Number of satellites: 2 Type of service: EG, EU, CP
International Designators: Frequency range: 258.900 - 259.100 MHz t
Cosmos 2199, Object 22036 261.085 - 261.1350 MHz*
Cosmos 2201, Object 22038 262.900 - 263.100 MHz t
Launched: 13 Jul 92 from Plesetsk 264.400 - 264.600 MHz t
312 - 315 MHz t
GONETS Spacecraft General Specifications Emission designator: 20KOGlW, 10KOG1W
Bus Description; Total peak power: + 10.0 dBW
Mass:225kg Maximum power density: -37.4 dBW/Hz
Dimensions: Lengthl50cm Space station EIRP +7.6 dBW
Diameterl00cm Receiving system noise temp: 490 OK
Max span, antennas deployed: 140 cm
Attitude control: Gravity gradient boom, Communications Link Parameters
magnetic assisted General:
Attitude accuracy:5 - 10degrees UHF uplink, UHF downlink
Power: Signaling rate: 2.4 kbps*
Orbital average power: 45W 2.4, 9.6, 64 kbps *
Peak power available: 160W Modulation: DPSK
Thermal control:Maintains 0 - 40 °C Coding: Reed-Solomoncoding (32,38), M=8
Launcher:Cyclone 6 per launch Decoding: Viterbi (R= 1/2, K=3)
Link Margins:
GONETS Communications Characteristics Portable terminal UT-P 5-7 dB
Subscriber/user terminal characteristics Fixed terminal UT-S 5-7 dB
Earth-to-Space Direction Link control protocol: DAMA using
Maximum gain: +2.0dBi FDMA/TDMA
Polarization:RHC Marker signal present
Service area:Regions 1, 2, 3 Aloha mediated assignment channel
Class of station: CP, TG, TU Channelization (36 satellite network system):
Receiving system noise temp: 700 °K Preamble signals: 72 physical chan
Frequency range:259.450 - 259.550 MHz t Signal communications: 10,800 TDMA chart
261.850 - 262.150 MHz t Data channels: 72 physical chan
264.375 - 264.525 MHz* Packet transmission: 21,600 16kbit slots/min
387 - 390 MHz
Emission designator:20KOG1W
Total peak power: + 10.0 dBW
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Network Performance: * GONETS-D only
System Throughput at 13% 3x10E04 Mbit/day * GONETS-D1 only
or 3x10E06 pages/day
(GONETS)
Number of users: Up to 1,000,000
Wait time: 20 minutes @ 0.8 probability
Delivery time (worst case): 1 hour
Program Phasina:
Phase Event Schedule Capacity On-board memory
(pages/day) (MByte per
satellite)
Launch of two Gonets-D
(demonstration) 13Ju192 3x10E2 0.019
Launch of 6 Gonets D-1
(isolated user groups) Nov. 1993-
Jan. 1994 1.2x 10E4 2
Full GONETS
constellation 1994-1996 3x10E6 8/16
Start of commercial use 1994/5
Pro_orammatics:
Organizations in consortium:
- SMOLSAT (Moscow): Program management
- NPO AM (Krasnoyarsk): spacecraft bus; system/launch integration
- N-PO PI (Moscow): spacecraft subsystems
- Izhevsk Radio Manufacturer: communications payload, user terminals
- Kievpribor Manufacturer: communications payload
References GLONASS/GPS Positioning, Proceedings of
ION GPS-92, September, 1992.
[1] L.A. Taylor, B.T. Kulick, Smallsats:
Proposals and Prospects for Mobile [5] T. Hunter, Real-Time Differential GPS
Communications, Phillips Business with Ashtech XII, Ashtech technical
Information Inc., 1992. application note, 1991.
[2] Electronic Communications Technology, [6] Changdon Kee, Algorithms and
Satellite Communications and Computer Implementation of Wide Area Differential
Networks, vol. 28, Moscow, 1992. GPS, Proceedings of ION GPS-92,
September, 1992.
[3] Project 21, Inmarsats' program for
personal mobile satellite communications, [7] Dariusz Lapucha, Multi-Site Real-Time
London. DGPS System Using Starfix Link; Operational
Results, Proceedings of ION GPS-92,
[4] First Experiences with Differential September, 1992.
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