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Paper Title (use style: paper title) Space Technology 5
Technology Validation Results
Candace C. Carlisle, Guan Le
NASA/Goddard Space Flight Center
Codes 422, 674
Greenbelt, Maryland 20771 USA

AbstractThe Space Technology 5 (ST5) Project is part of
NASAs New Millennium Program. ST5 consists of a
constellation of three micro-satellites, each micro-sat
approximately 25 kg in mass, launched March 22, 2006, on a
Pegasus XL rocket. All ST5 components are low mass, low
power, and low volume. During the three-month flight
demonstration phase, the ST5 team validated the key
technologies that will make future low-cost micro-satellite
constellations possible, demonstrated operability concepts for
future micro-satellite science constellation missions, and
demonstrated the research-quality science capabilities of the
spacecraft. The ST5 mission was successfully completed in June
2006.
I.

I
NTRODUCTION

The Space Technology 5 (ST5) Project is part of NASAs
New Millennium Program. ST5 consists of a constellation of
three micro-satellites, each approximately 25 kg in mass. The
ST5 mission commenced March 22, 2006, with a Pegasus XL
rocket launch, and consisted of 90 days of technology and
science validation operations, followed by 10 days of end-of-
mission activities. During the flight demonstration phase, the
ST5 team validated the key technologies that will make future
low-cost micro-satellite constellations possible, demonstrated
operability concepts for future micro-satellite science
constellation missions, and demonstrated the research-quality
science capabilities of the spacecraft.
ST5s advanced technology components include: single-
card Command and Data Handling (C&DH) computer, low-
voltage power subsystem featuring triple-junction solar cells
and a lithium-ion battery, communications subsystem featuring
a miniature X-band transponder and an evolved antenna
developed using a genetic (or evolved) algorithm, cold gas
propulsion subsystem using a single micro-thruster for both
delta-V and attitude control, 0.5 V CMOS Ultra Low Power
Radiation Tolerant (CULPRiT) logic, Variable Emittance
Coating thermal surfaces, miniature magnetometer, miniature
spinning sun sensor, and a non-bellows nutation damper.
The three ST5 spacecraft were operated as a constellation,
demonstrating model-based operations automation and
ground communication strategies that will be useful for future
missions that plan to deploy multiple spacecraft with minimal
ground support personnel (i.e., lights-out operations).
ST5 validated the three primary areas critical to future
science constellation missions: formation flying, micro-
satellite suitability as a platform for making scientific
measurements, and the autonomous response of the micro-
satellites to science events.
II.

S
PACECRAFT AND
C
OMPONENT
T
ECHNOLOGIES

The ST5 spacecraft represents a significant design effort to
develop a micro-spacecraft with the full subsystem
functionality found in larger spacecraft (see Fig. 1). The
spacecraft was developed in-house by Goddard Space Flight
Center (GSFC), with some components developed by outside
vendors and industry partners.
Each ST5 spacecraft is octagonal in shape, approximately
25 kg in mass, and approximately 53 cm in diameter (solar
panel peak-to-peak) by 48 cm in height (tip of antenna to tip of
antenna). The top deck is removable, allowing access to all
components during Integration and Test. An integral card-cage
provides the structural backbone of the spacecraft, as well as
housing the Command and Data Handling and Power System
Electronics cards. The card-cage structure is lightweight
investment-cast aluminum.
The Command and Data Handling (C&DH) subsystem is a
double-sided single card computer that retains all of the
functionality found on larger spacecraft while consuming little
power (<4 W). It supports all communications activities
between the spacecraft and the ground, as well as
communications within the spacecraft to all of the components.
The Complementary Metal Oxide Semiconductor Ultra
Low Power Radiation Technology (CULPRiT) chip resides on
the C&DH board. CULPRiT allows circuits to operate at very
low voltage. The technology is capable of significant power
reduction over current technology, while achieving radiation
and latch-up tolerance. For ST5, the CULPRiT chip was used
is a Reed Solomon Encoder. CULPRiT performed flawlessly
over the entire mission, transmitting over 330 million telemetry
frames with no voltage or current instability, current increases
related to radiation, or bit errors. Partners in the CULPRiT
development included the Center for Advanced
Microelectronics and Biomolecular Research at the University
of Idaho, AMI Semiconductor, and Picodyne.
The Electrical Power Subsystem, controlled by a single
double-sided power system electronics card, provides electrical
services to all components on the spacecraft and battery-
charging capability, including over-voltage protection.

Fig. 1. ST5 Components.
ST5 includes a solar array composed of 8 body-mounted
panels with a total power-generating capacity of 25 W
(beginning of life) at approximately 10 V. At procurement
time, the triple junction ST5 solar cells were the highest
efficiency available in the USA, and were available only as
research quality cells. The raw cell efficiencies vary from
28.1 to 29.1 percent at 1 sun intensity (without the added
complexity of solar concentrators). The ST5 solar cells were
procured in partnership with the Air Force Research
Laboratory and provided by Emcore.
ST5 energy storage is accomplished using a Lithium-Ion
battery with total usable energy storage of 9 A-h (beginning
of life) at the maximum operating voltage of 8.4 V.
Lithium-Ion represents a dramatic three-fold improvement in
energy density over previous batteries. The batteries on all
three satellites performed flawlessly over the 90-day
mission, with no capacity fade, cell imbalance or voltage
decay. ABSL (formerly AEA Technologies) built the ST5
battery.
The spacecraft is designed with a communication
subsystem operating at X-band for both ground-to-space
(uplink) and space-to-ground (downlink) communications.
The communication subsystem employs a new technology
X-band transponder, built by AeroAstro, to provide uplink
and coherent downlink tracking functionality. Throughout
the 90-day mission, the ST5 transponders were used for
command, telemetry, and radiometric orbit determination
(two-way Doppler).
Two body-mounted antennas, one each on the top and
bottom decks, provide nearly 4 steradian coverage with the
ground. Each antennas boresight is mounted co-linear with
the spin-axis of the spacecraft. Each ST5 spacecraft houses
one quadrifilar helix antenna and one evolved antenna. The
evolved antenna is designed using a computer program based
on a genetic algorithm. The algorithm designs a wire form
radiator, evolving the design based on a fitness function
computed from voltage standing wave ratio and gain scores.
This evolved antenna design method has the potential for
high gain across a wider range of elevation angles and more
uniform coverage than conventional designs (a very uniform
pattern over the 40-80 degree elevation angles of greatest
interest).
The ST5 transponders and antennas performed flawlessly
throughout the mission. This assessment of the transponder
and antenna performance is based on automatic gain control,
receiver carrier loop stress, transmitter output power,
oscillator temperature, received signal strength and bit error
rate.
The spacecraft includes a cold gas propulsion system to
provide attitude maneuvering capability as well as a limited
orbital maneuvering capability. The propulsion subsystem
consists of a tank, a single thruster, a fill-and-drain valve, an
in-line filter and a pressure transducer. The propellant used
for the mission is Gaseous Nitrogen (GN
2
).
The propulsion tank, built by Carleton Technologies, has
a total volume of 146 cubic inches. It is a composite over- wrap (PBO fiber) over a seamless Aluminum 6061-T6 tank,
with a maximum expected operating pressure of 2240 psig.
The ST5 micro-thruster was provided by Marotta
Scientific Controls. This cold gas micro-thruster is capable
of being operated in both pulse and continuous fire modes, to
achieve both delta-V and attitude control, and features very
low power draw and low leakage rates. The latching
solenoid valve design provides an order of magnitude
reduction in power consumption compared to thrusters based
on continuous duty solenoid valves. The ST5 Cold Gas
Micro Thruster far exceeded the original performance goals
(Thrust >2.1N @ 2000 psi and 0.1N @ 100 psi and ISP
Level > 60 seconds), and performed flawlessly from the
beginning of the mission to the end.
The spacecraft is passively spin stabilized, with system
momentum about the major principal moment of inertia axis.
The initial spin-up of the spacecraft is performed by the
spacecraft deployment mechanism.
The ST5 spacecraft employs a passive nutation damping
device. The damper is made from titanium and is
completely filled with a viscous silicone. The damper design
is notable in that it employs very high internal pressures (up
to 10,000 psi) and does not use a bellows. The ST5