This paper presents, in general terms, the results of the experiments with NUSAT I. These include what has been learned about the strengths of the original design, as well as improvements being incorporated into NUSAT II, which should be of interest to designers of future Get Away Special ejected satellites. This paper also presents an account of the formation of the Center for AeroSpace Technology (CAST) at Weber State College, which grew out of the NUSAT project, and some potential applications and markets for inexpensive, low orbit satellites which CAST has explored

Bonsall, Charles A.

English

NASA Technical Reports Server

NUSAT Update
By Charles A. Bonsall
Center for AeroSpace Technology
Weber State College, Ogden, Utah
This paper presents, in general terms, the results of
the experiments with NUSAT I. These include what has been
learned about the strengths of the original design, as well
as improvements being incorporated into NUSAT II, which
should be of interest to designers of future Get Away Special
ejected satellites. This paper also presents an account of
the formation of the Center for AeroSpace Technology (CAST)
at Weber State College, which grew out of the NUSAT project,
and some potential applications and markets for inexpensive,
low orbit satellites which CAST has explored.
THE GOALS OF THE NUSAT I PROJECT
NUSAT I was a small, 105 pound satellite ejected from
the orbiter, Challenger, shortly after the launch of mission
51B on April 29, 1985. The principal experiment on board
NUSAT I was an L-band measurement system to determine the
vertical radiation pattern of air traffic control radar
antennas. This information would then be used to optimize
the coverage volume of these radars.
The NUSAT project was organized with three stated goals:
- to provide an exciting, real life educational
experience for students;
- to test the Get Away Special (GAS) canister as a
platform for ejecting small satellites into independent
orbit; and
- to demonstrate a technique for measuring the vertical
radiation patterns of large vertical aperture antennas.
Some implied goals were:
- to test the effectiveness of an ad hoc, volunteer
organization comprised of individuals from academia,
industry and government;
- to enhance awareness of Northern Utah as a center of
aerospace activity; and
- to facilitate networking of aerospace technologists.
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https://ntrs.nasa.gov/search.jsp?R=19870010879 2020-03-20T11:19:33+00:00Z
NUSAT I EXPERIMENT RESULTS
Contact was established with NUSAT I a few days after
launch and continued until July 15, 1985. However, com-
munications during this period were characterized by low
reliability. After a period of optimizing the ground station
facilities and improving operator proficiency, it became
clear that there was at least one problem on board the
satellite. Many possibilities were considered including
antenna orientation, solar cell or battery failure,
interference, abnormal temperatures, and others, most of
which could only be determined by the acquisition of sensor
data. Eventually this data was obtained and indicated that
the system temperatures and voltages were normal. Since
only very short programs could be uploaded successfully,
several other experiments could not be completed before
all contact was lost in July.
Following a thorough recheck of the ground station it
was assumed that the satellite had failed. Nevertheless,
routine attempts to communicate with the satellite continued
with no success. Ironically, during the early evening of
November 23, 1985, while several participants were gathering
to prepare a final, pessimistic report to the Federal
Aviation Administration project coordinator, a half-hearted
attempt to contact the satellite was successful! A number of
new experiments were formulated based upon the observed
system behavior and recently enhanced capabilities of the
ground station, such as doppler compensation under software
control. For example, it was noticed that the ground station
room was unusually cold the night of reacquisition and the
possibility of frequency drift on the satellite was
considered. Eventually, it was determined that the modem
clock on board NUSAT I had shifted and was compensated for by
adjusting the ground station system.
Since last November, communications with NUSAT I have
been very reliable, allowing routine uploads of long programs
and successful downloads of large masses of data. One common
operation has been the downloading of sensor data collected
at various increments during an entire orbit. This has
allowed study of the behavior of the power system while
illuminated and shaded, as well as, analysis of platform
attitude using the light sensor data. Another frequent
operation has been the collecting of L-Band signal data
while using unique interrogation modes from Federal Aviation
Administration and Air National Guard radars in Utah. In
addition, several experiments have been conducted with:
Montana State University, an astronomer in Texas, amateur
radio operators, even successful communications with a
handheld transceiver!
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The results of over a year of operation and experimenta-
tion with NUSAT I support the following conclusions:
i. The GAS canister is an excellent, low cost, vehicle
for injecting a small satellite into low altitude,
circular orbits. NUSAT I was ejected at an altitude of
360 km which had decayed to 305 km by June 1986. The
orbit eccentricity was very low with a difference
between apogee and perigee of about 8 km at that time.
2. It is possible to achieve reliable open-loop tracking
of low orbit satellites using very inexpensive equipment
operated by relatively inexperienced students. But an
onboard beacon would simplify acquisition and tracking.
3. The enhanced flexibility permitted by the totally
programmable philosophy implemented in NUSAT I is
invaluable. Only the communications protocol, timing
functions, security and fail-safe routines are in
firmware on the satellite. All operational programs are
uploaded from the ground station, which has allowed
operational changes and experiments unthought of prior
to launch.
4. Physical accessibility to internal components is an
important consideration in the mechanical design of a
small, but complex, satellite. Several post-assembly
repairs and changes to NUSATI were very difficult to
accomplish.
5. Attitude determination by light sensors alone is a
very complex, inaccurate process, especially when the
spectral and directional characteristics of the sensors
are not thoroughly measured prior to launch ....
6. The time domain pulse discrimination technique used
in the Federal Aviation Administration experiment on
NUSAT I may be inadequate for use in the dense L-Band pulse
environment over the United States and Europe.
NUSAT II DESIGN IMPROVEMENTS
A number of changes are being incorporated into the
design, construction and operation of NUSAT II and subsequent
satellites being planned by the Center for Aero-Space
Technology. Some of these changes are influenced by NUSAT I
experience, others are due to the availability of resources and
devices not available at the time of NUSAT I's design and
construction. These improvements include:
65
i. A full-time, low duty cycle Morse code telemetry
beacon. The transmissions will contain spacecraft
environmental and system parameter data which can be
received by interested parties around the globe without
unique equipment or knowledge. This beacon, combined
with a high gain synthetic aperture antenna system on
the ground, will enhance acquisition and tracking with
less precise orbit predictions than those required for
NUSAT I operations.
2. System redundancy. The availability of more powerful
computers and larger memories requiring less current
permit designs including completely redundant computers,
expanded memory and dual communications systems. In
addition, two isolated battery packs will be installed.
3. A cylindrical form. This will enclose a greater
volume, simplify accessibility during integration and
testing, increase solar panel/antenna area and enhance
attitude control with more flexibility for changing
moments.
4. An improved software communications protocol. A
system employing error correcting codes, packet trans-
missions, etc., will be used to improve communications
reliability under low signal-to-noise conditions.
5. An enhanced attitude measurement/control system which
will increase the usefulness of presently planned experi-
ments and provide experience and data for future satellite
systems. This system will include optical and television
sensors, magnetometers and magnetic torque rods.
6. Support for other experiments. NUSAT II will have
sufficient volume, power and control to support additional
experiments.
7. The Federal Aviation Administration L-Band system
will include the following improvements:
- Two superheterodyne receivers instead of the
present six TRF receivers. This will reduce power
drain and increase system stability and flexibility.
- A frequency domain pulse discrimination technique
using FFT's. This will improve operation in dense
RF pulse environments.
- Greater flexibility in antenna directional
control achieved with a phased array antenna and/or
selective use of attitude controlled gain antennas.
66
8. And, finally, a system and philosophy of project
management that includes closer tracking and reporting
of sub-system progress, uniform documentation standards,
more frequent design reviews and closer coordination
with the senior projects program.
FORMATIONOF THE CENTERFOR AEROSPACETECHNOLOGY
Following the successful design, construction, launch
and operation of NUSAT I, it became apparent that many
individuals wanted to continue their participation in similar
enterprises. In addition, Weber State College experienced
increased public interest and support, greater success
recruiting high quality matriculants interested in aerospace
technology and more success placing graduates in the aerospace
industry. Therefore, several individuals who had been members
of the NUSAT Executive Committee, and a few new participants,
formed the Center for Aero-Space Technology at Weber State
College.
The following is the Statement of Purpose and Goals of
the Center for Aero-Space Technology:
"The Center for Aero-Space Technology is a non-profit
organization of individuals from industry, education and
government in association with Weber State College. The
purpose of the Center is to propose, solicit, design and
manufacture useful aero-space experiments, devices or
systems, or to support similar enterprises in other Utah
schools and organizations.
"The goals of the Center are:
- to generate significant, practical and realistic
technical experiences for students:
- to provide a local center for aero-space technologists
to connect with others of similar interests, share their
expertise with students and associates, and achieve
other personal goals:
- to create an environment in Northern Utah which will
support aero-space industries:
- and, to facilitate public aerospace education in Utah.
"It is envisioned that future projects will be modeled after
the NUSAT I project, in which its goals were achieved through
a combination of student and volunteer efforts, donated
resources and contracts with other organizations."
The Center for Aero-Space Technology is governed by a
Board of Directors from the college, industry and government.
A larger group of aerospace professionals serve as student
group advisors. And the production teams are formed of
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senior project, and other, student groups working with faculty
members and advisors to do the actual design, manufacturing
and testing of systems.
Presently the Center employs a full-time director, a
part-time consultant from the faculty and several part-time
student operators and researchers. Funding for the Center
comes from several sources including: a grant from the Utah
State Board of Economic Development; a third contract with the
Federal Aviation Administration; and a matching grant from Weber
State College. Contracts with the Center are administered by the
Director of Sponsored Projects at Weber State College.
The Center for Aero-Space Technology, as part of the
Western Space Consortium, including Weber State College,
Montana State University, University of Idaho and several
corporations, has applied for a NASA grant under the Centers
for Commercial Development of Space program. The Center has
been invited to participate in two other consortiums one of
which has received, the other has applied for, a similar NASA
grant. The author is chairman of a sub-committee of the
Satellite Operators and Users Technical Committee which is
investigating a potential application for small low orbit
satellites. Other members of the Board of Directors are
pursuing similar projects within their own corporations,
government agencies, SDIO, etc. The Center is continuously
receiving communications from sources as varied as
universities in Pakistan, government agencies in the United
Kingdom, corporations in Japan, as well as, individuals,
corporations, educators and government agencies in the United
States. Some proposals have been beyond our capabilities and
we have referred them to other organizations and others have
been of questionable value, but several are being pursued as
future projects for the Center.
LOWORBIT SATELLITE APPLICATIONS
There are many potential applications requiring small,
low orbit satellites. Some are in the area of communications
and control, such as collecting environmental sensor and
position/movement data from remote locations, remote
management of power and irrigation system resources and many
customized message delivery systems. A large variety of
space-based sensor platforms are needed and a vast number of
military projects require these satellites. A great deal of
research is needed to specify and invent: the optimum
communications systems; inexpensive and simple attitude
determination and control systems; multi-spectrum sensors;
materials testing systems for the low orbit environment;
artificial intelligence for auto-operation of spacecraft
systems; and many more ....
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For example, the Center is working with the Federal
Communications Commission, the Satellite Operators and Users
Technical Committee, and several colleges and corporations to
develop and deploy a low orbit system to locate sources of
interference with geo-stationary communications satellites.
A similar system can be used to improve tracking and locating
systems presently employing a meteorology satellite.
The Center is also pursuing several projects that are of
interest to the Strategic Defense Initiative Organization.
The opportunities to improve existing systems and
develop new systems are endless. There is so much work to be
done that no individual organization needs to fear that
others will steal all the opportunities.
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