FalconSat-1 is the first of a series of small satellites, designed, built and operated by cadets at the US
Air Force Academy, Colorado Springs, CO. The overall science objective of the mission is to determine
the effects of S/C charging in the LEO environment. Other objectives are to demonstrate/validate the
S/C design and to provide a hands-on experience for all students involved.
The S/C structure is nearly cubical
in shape with dimensions: 46 cm x 46 cm x 42.5 cm. The solar arrays
(GaAs cells of 19% efficiency) are body-mounted providing 24 W of
power, in addition there is a battery with 10 NiCd cells (4.4 Ah). The
bus design features a stack assembly into which the subsystems are
mounted. The mass of the microsatellite is 52 kg. 1) 2) 3)
Figure 1: Illustration of FalconSat-1 (image credit: USAFA)
The S/C is spin-stabilized at about
10 rpm pointing toward nadir (a minimal pointing of ±25º is
required in the direction of S/C velocity vector). The ADACS (Attitude
Determination and Control Subsystem) measures attitude with a
three-axis magnetometer; a torque rod functions as an actuator,
damping is provided by hysteresis rods. The launch vehicle imparts an
initial spin on S/C separation. In
addition, nylon solar radiation paddles are used to maintain the
initial spin rate. By using magnetometer data contained in the
telemetry stream, the satellite can be commanded to operate the torque
necessary to align itself with the Earth's magnetic field lines. Due to
the shape of the Earth's field lines,
the spacecraft executes a "flip," turning 180º over at each
crossing of the equator, when the torque rod is
operating on a 100% duty cycle.
The C&DHS (Command and Data
Handling Subsystem) consists of three main components, the flight
computer (FC) and two embedded controllers. The flight computer is a
NEC V53 space-qualified
flight computer with 1 MB of EDAC program memory and a 4 MB RAM disk. A
real-time multitasking operating system is used. The AX.25 protocol
stack is implemented.
Figure 2: Block diagram of the C&DH subsystem (image credit: USAFA)
Launch: A launch of
FalconSat-1 took place on Jan. 27, 2000 (UTC) with a converted
missile (Minotaur) from VAFB, CA.. The Minotaur of OSC is a four-stage
vehicle with the first and
second stages being Minuteman-II stages; the two upper stages come from
OSC's Pegasus launcher.
FalconSat-1 was part of the JAWSAT multi-payload adapter and launched
with the following satellites: ASUSat-1, OPAL (PicoSat, Artemis,
StenSat), OSCE, MASat, and JAWSAT.
Orbit: Sun-synchronous orbit, altitude = 770 km, inclination = 100.2º, period = 100 minutes.
RF communications are provided in UHF (downlink) at 400.475 MHz and in VHF (uplink) at 148.030
MHz. The data rate for transmit and receive is 9.6 kbit/s. The signal modulation scheme employs
GMSK (Gaussian Minimum Shift Keying). - The ground station for FalconSat-1 is located at USAFA
providing monitoring and control of the spacecraft.
Mission status: The FalconSat-1 spacecraft failed on-orbit soon after deployment, apparently due to
a power failure. No useful science data was returned, despite repeated recovery attempts. The mission
was declared a loss after about a month in orbit.
USAF press statement of June 2002 said: "While FalconSat-1 was a
technical failure, it was a resounding academic success. Cadets
participated in all phases of the mission from conceptual design
though assembly, integration, testing, launch and on-orbit operations."
CHAWS-LD (Charging Hazards and Wake Studies - Long Duration experiment) developed by the
Physics Department at the Academy and supported by DoD. The objective is to measure electric
charge characteristics of the S/C. Voltage and current sensors, made of sheets of stainless steel (and an
electric circuit board stacked together with aluminum and Teflon spacers), are installed on the four
sides of the S/C.
The sensors are made of sheets of stainless steel and an electric circuit board material stacked together
with aluminum and Teflon spacers. Each sensor requires a 10 cm x 10 cm opening on the inside surface
of the spacecraft structure and a 9 cm x 9 cm opening on the outside of the structure. One voltage and
one current sensor are mounted in the center of each side of the spacecraft. The surface of the voltage
sensors, which is exposed to the plasma, is the metalized surface of a circuit board. The exposed surface
of the current sensors is an electro-formed stainless steel mesh. The detector electronics are sealed
from the space environment.
Figure 3: Layout of the CHAWS-LD sensors (image credit: USAFA)
As FalconSat moves through the space plasma, it creates a wake region behind it, in which primarily
electrons accumulate. Hence, the electrically isolated sections of the voltage sensors on the wake side
are negatively charged. The current sensors reject electrons and collect ions from the space plasma,
providing a current that is correlated to the ambient plasma density. The relative amount of current
collected by each sensor provides in addition information about the S/C attitude relative to the plasma
flow. Data measurements can be made at 5 or at 10 Hz. A series of measurements is taken over the
course of one or more orbits. - One voltage and one current sensor are center-mounted at side of the
S/C. The surface of the voltage sensors, exposed to the plasma, is the metalized surface of the circuit
board. The exposed surface of the current sensors is an electro-formed stainless steel mesh. The data
collected from each sensor are stored in the memory of the flight computer. They can be transmitted to
the ground during station passes.
1) R. Chari, "Pre-Flight Characteristics of the US Air Force Academy's FalconSat-1," Proceedings of the 13th AIAA/USU
Conference on Small Satellites, Aug. 23-26, 1999, Logan UT, SSC99-VII-8
3) B. Bush, T. L. Lawrence, M. J. Meerman, "The Undergraduate Satellite and Rocket Design, Fabrication, Launch and Operations
Program at the United States Air Force Academy," Space 2004 Conference and Exhibit, Sept. 28-30, 2004, San Diego, California,
This description was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" - comments and corrections to this
article are welcomed by the author.