∫Department of Aerospace
Engineering
Background
Within the past several years,
the University of North Dakota (UND) School of Engineering & Mines (SEM)
has been developing a focus on spacecraft design, particularly in the area of
sensor data acquisition. The school has
been collaborating with the Upper Midwest Aerospace Consortium (UMAC), also
headquartered at UND, in taking an incremental approach towards reaching its goal
of launching an Earth-observing, remote sensing satellite by the end of the
decade.
Undergraduate and graduate
engineering students at UND have already built and launched three spacecrafts
via weather balloons, and they are currently involved in several more-advanced
remote sensing development efforts. The
first of two spacecraft projects in a series known as “Scorpio” was completed
during the summer of 2000, in which seven
undergraduate students built a remote sensing payload that was suspended from a moored weather balloon. This payload was able to collect and transmit
real-time health and atmospheric data.
The second Scorpio payload, built during the 2000-2001 academic year,
was launched using a free-flying weather balloon. This payload was again able to downlink
health and environmental data in real time, with the significant addition of
transmitting a picture taken by an on-board digital camera. The
third
spacecraft, the Zippy Aerospace Module Broadcasting Observed Not-so-bad Images
(ZAMBONI), was based on a double-size CubeSat developed during the 2002-2003
academic year. This payload was
successful in acquiring digital images and transmitting them over amateur radio
frequencies in real-time. ZAMBONI was
launched twice using a free-flying weather balloon in the spring and summer of
2003. These projects are evidence of the
growing systems engineering capability within UND SEM Engineering, necessary
for the design of small satellites.
Figure 1 shows ZAMBONI in its balloon testing enclosure, along with a
digital picture captured during the June 2003 flight [1].
Undergraduate
and graduate students within the UND SEM are currently involved in three remote
sensing projects, which will result in professional-grade instruments:
1.) The Student Tracked Atmospheric Research
Satellites (Starshine) project, initiated by the United States Naval Research
Laboratory (USNRL), gives middle-school, high-school, and college students an
opportunity to assist in the construction of an orbiting satellite and to receive
telemetry data.
2.) The Airborne Environmental Research Observational Camera (AEROCam)
project, operated with UND SEM, UMAC, and the John D. Odegard School of
Aerospace Sciences at UND, is a four-band, multi-spectral digital imaging
system which is installed and operated in a Piper Arrow single-engine aircraft.
3.) The Agricultural Camera (AgCam) project, a joint venture between
UND SEM and UMAC, is a two-band multi-spectral digital imaging system that will
be mounted inside the pressurized International Space Station’s Window
Observational Research Facility (WORF).
It is anticipated that AgCam will be shipped to NASA in early 2004 for a
launch on the Space Shuttle.
These systems
engineering projects have been extremely educational for both students and the
faculty. In order to build a
professional-quality remote sensing instrument, expertise is required from many
disciplines, especially electrical and mechanical engineering. To date, all projects have involved students
and faculty from UND Electrical and Mechanical Engineering, with assistance
from students majoring in Computer Science, Space Studies, and Business
Administration [3]. As a National
Science Foundation Research Experiences for Undergraduates (REU) site, UND has
been able to bring students in from around the country to work on these aerospace
projects.
Ongoing Work
UND has
a goal of launching and operating its own orbiting remote-sensing satellite by
the end of this decade. However, the
university needs to start with a relatively low-risk and inexpensive orbiting
spacecraft. The UND CubeSat Project fills
this gap in the evolution from airborne to space-borne remote sensing. CubeSat To Accept Any Payload (CTAAP) is the
second iteration of UND’s CubeSat Project.
It will contain many similar components as a commercial satellite, but
it will be developed at a much lower cost (under $10,000) and with a significantly
lower risk than its more expensive counterparts. If mission failure occurs, the loss will not be
as substantial due to the smaller initial investment. The CTAAP and ZAMBONI projects represent a
significant step in the growth of spacecraft systems engineering at the
Although
size and weight must be carefully conserved on a CubeSat mission, important
experiments are possible with this picosatellite. ZAMBONI was a good stepping stone to begin
the CubeSat project at UND. While the
satellite was functional, the goals of ZAMBONI were not practical due to the
following reasons:
1.)
The
expense of launching a double CubeSat is beyond the scope of a
university-funded program
2.)
Transmission
through amateur packet radio was too slow for satellite-imaging to be practical
3.)
The
structure was bulky
Because of these problems, the
ZAMBONI project was abandoned and CTAAP was conceived. CTAAP will be a standard size CubeSat with a
mass of 1 kg and dimensions of 10 cm x 10cm x 10cm. A graphical representation of CTAAP is shown in
Figure 2. This picosatellite will be a
vehicle to accept various payloads using industry-standard transfer protocols. It will be designed with a fully functional
communications system, budgeted power, mass, and volume for a funded payload. The primary goal with the completion of CTAAP
is to achieve a launch through sponsorship by a company or U.S. Government
laboratory. Payloads will most-likely
require low-earth environmental testing in an orbit.
Potential
payloads include:
1.) Various sensors to measure temperature, voltage,
current, radiation, etc.
2.)
Microchips and GPS sensors for developmental and environmental testing
3.) Low cost environmental testing of materials
4.) Attitude control system
CTAAP will be designed to accept a payload with:
1.) Volume: 6.35 cm x 7.62 cm x 1.59 cm
(2.5 in x 3 in x 0.625 in)
2.) Mass: less than 200 g (7 oz)
3.) Power Consumption: less than 250 mW
Engineering Design
Figure 3
shows the planned subsystem interfaces for CTAAP and its ground control station:
and Custom TNC
Figure 3: CTAAP subsystem interfaces.
Telecommunications
will be conducted using custom and commercial-off-the-shelf (COTS) components,
with uplink and downlink frequencies in the UHF/VHF amateur frequency bands. The use of the amateur radio frequencies will
allow operators from around the world to receive CTAAP’s data using
commercially-available equipment. If
necessary, the communications system may be modified to utilize frequency bands
beyond those of amateur radio in order to allow encryption protecting of proprietary
information. The ability to transmit
uplink telecommands will be restricted to designated personnel.
Testing
Testing
plays a crucial role to ensure the reliability of any engineering project within
its intended operating environment. Commercial
testing typically involves an extensive amount of time and money, both of which
are extremely limited in an academic institution. A commercial test chamber to test
temperature, pressure, and humidity costs approximately $50,000 [5]. An inexpensive means of environmental testing
is necessary for university-funded space project.
At the University of North
Dakota, high-altitude balloon launching has been adopted as a primary means of
system testing. Balloon launching has
proven to be a very effective, yet inexpensive approach to simulate space
conditions. The balloon launches
conducted by UND have provided students and faculty with valuable design experience
and evaluation data for various environmental parameters while operating a
remote-sensing system.
Balloon
launches enable a payload to travel beyond the troposphere and into the upper
stratosphere, with altitude ranges of approximately 30 ~ 40 km (100,000 ~
130,000 ft). The atmospheric conditions
at approximately 30 km (100,000 ft) are 1 kPa and -50°C. At this altitude, the payload is exposed to a
pressure of 0.0098 atm. A balloon launch
is an accurate method of testing a payload in the following space environments:
cold, pressure, radiation, solar-power output and communications link. However, it is not an accurate means of
testing vibration, heat, and outgassing. The materials for a typical balloon launch conducted
by UND High Altitude Balloon Group carry a cost of less than $500. The cost of a 3000 g meteorological balloon
is about $200 while the helium required to launch an 8 kg payload costs $130. The balance includes travel costs to and from
the site, and costs associated with tracking the balloon.
The
University of North Dakota has conducted four successful balloon launches focusing
on spacecraft design, particularly in the areas of sensor data acquisition. Each balloon launch had its successes and
failures. The failures have assisted in the
follow-on designs, creating a more robust, reliable system with each iteration.
The
most
recent ZAMBONI balloon launch in June 2003 was the most successful of all the UND
SEM launches made possible by the experience gained from previous launches. In the first launch of ZAMBONI, the satellite
did not function as expected. This was
attributed to the communications subsystem and electrical connections failing
in the extreme cold. A system shutdown
and restart occurred due to an electrical connection failure, causing the
communications subsystem to remain offline.
All electrical connections were replaced, and an automatic power-up for
the communications subsystem was developed.
After these problems were addressed, ZAMBONI was launched for the second
time resulting in flawless operation.
Launch and Future Directions
While a full-scale
free-flying satellite project is still a long-term goal of UND, the CubeSat
project is immediately attainable. A launch
of CTAAP will be coordinated along with other university-built CubeSats from
around the world [4]; each team expects that launch costs will be approximately
$40,000. In order to gain sufficient
design, build, integration, test, launch, and operations expertise, UND
Engineering foresees several builds of CTAAP prior to embarking on the
development and launch of a small satellite.
The future iterations of CTAAP will provide the designers with a
relatively low-risk, low-cost means of testing various systems in space, such
as a nanotechnology-based attitude control system or constellation satellite
communications and control cannot be fully tested on the ground. When UND eventually kicks off its remote
sensing satellite development mission, the project will commence with
confidence that it can be successful from both scientific and engineering
perspectives.
References
[1] Christopher J. Schmidt, Jonathan A. Lovseth,
Melissa A. Barnum, Jayson F. Clairmont, Patricia E. Langwost, Nicholas E.
Hulst, Kelani J. Parisien, Joseph R. Rydel, Darryl Sale, Richard R. Schultz,
Chang-Hee Won, Arnold F. Johnson, and William H. Semke, “Systems Engineering
Pedagogy Through Balloon-Launched Spacecraft.”
In Proceedings of the 2001
National Conference on Undergraduate Research,
[2] Nicholas E. Hulst, Jason Gullicks, Jacob Johnson, Gary Lauinger,
Dustan Larson, and Sarah Lemcke, “The Airborne Environmental Research
Observational Camera (AEROCam): A
Multispectral Digital Photography System for Remote Sensing.” In Proceedings
of the 2002 National Conference on Undergraduate Research,
[3] Chang-Hee Won, Darryl Sale, Richard R.
Schultz, Arnold F. Johnson, and William H. Semke, “Spacecraft Systems
Engineering – The Initiation of a Multidisciplinary Design Project at the
[4] Jordi Puig-Suari, Clark Turner, and Robert J.
Twiggs, “CubeSat: The Development and
Launch Support Infrastructure for Eighteen Different Satellite Customers on One
Launch.” In Proceedings of the 2001 Small Satellite Conference (on CD-ROM),
[5] Yang, Chheang, contacted Envirotronics,
[6] Christopher J.
Schmidt, Jonathan C. Fargo, Nicholas E. Hulst, Katie C. Kirchner, Jonathan A.
Lovseth, Jason T. Senti, Warren J. Wambsganss, David L. Heckmann, Arnold F.
Johnson, Richard R. Schultz, and William H. Semke, “Satellite Systems Engineering at the University of North Dakota.” August, 2002.
Acknowledgements
This work has been supported by a number of
federal agencies as well as the assistance of four organizations on the
National Science Foundation award number ECC-0139185,
"REU Site: Engaging
Undergraduates in Multidisciplinary Remote Sensing Image Acquisition and
Analysis Research at the
Rockwell
Collins Charitable
"Avionics and Spacecraft
Systems Engineering at the
NASA Experimental Program to Stimulate Competitive
Research
(EPSCoR) grant number NCC5-582, "NASA EPSCoR-UND
CubeSat."
Nordlie, John.