Historical Technology Overview
WIS™
Wireless Instrumentation System
The
success of the WDAS experiment spurred
NASA to award a series of Phase III contracts to apply the technology
to environmental monitoring on the International Space Station
(ISS). Invocon designed and built wireless data acquisition
systems that have successfully flown on multiple ISS Assembly
flights. Invocon is currently contracted to support flight operations.
The system is divided into three types of hardware.
- Internal Wireless Instrumentation System—IWIS™
- Shuttle Wireless Instrumentation System—SWIS™
- Floating Potential Probe—FPP
IWIS, the internal, synchronized system, is deployed by the astronauts inside the partially completed ISS to collect data on the impulse response of the structure. This synchronized data is used to verify the structural integrity of the ISS on orbit. It will also be used to update models predicting the modal response of the ISS. Complete understanding of the resonant modes of the structure will allow effective planning of the re-boost and Reaction Control System (RCS) firing sequences when the Shuttle is docked with the Station. Since this data will change as the Station is assembled, it is important to keep this data current with each addition to the Station. The wireless nature of the data acquisition network minimizes the time necessary for deployment and recovery of the system. Further, some of the RCS test firings must occur when all airlocks between modules are closed. A wired system would not have the flexibility needed to accommodate mission changes and data acquisition windows of opportunity.
The
SWIS or Shuttle-based system includes data gathering
units that are installed on the outside of the Station modules
prior to launch. Other data units are installed on the
Shuttle sill longeron. As the ISS modules are removed
from the Cargo Bay and transferred to the assembly point on
the Station, the SWIS data gathering units transfer sensor data
from the ISS module to the Crew Compartment of the Shuttle where
the data is downlinked to Mission Control for use by the flight
controllers. In the event the WIS data gathering modules
on the ISS loads are blocked from a direct line-of-sight to
the Crew Compartment, the units on the sill longeron act as
relays for the data. The SWIS system deliveries commenced in
fall 1998. SWIS initially launched in September of 2000. Both
IWIS and SWIS system units are currently installed on the ISS.
The Floating Potential Probe (FPP) was launched on ISS
flight 4A and installed on-orbit to measure the floating potential
of the Space Station relative to the local plasma environment.
The measurements verify proper operation of ISS systems designed
to maintain the potential within acceptable ranges and prevent
arching. Invocon delivered a wireless system based upon
the SWIS/IWIS systems that provides for data storage at the
probe and data transfer from the P6 photovoltaic truss element
to a computer inside the Unity node of the ISS. The data
is then displayed for the crew and downlinked to the ground
for analysis.(Invocon developed the communication system for
FPP. Other NASA contractors developed the solar power supply
and sensors.)
General WIS Parameters
- Programmable Sample Rates: 4.5Hz - 1KHz or 12Hr - 2sec sample periods
- Sensor Types: Strain, Temperature (RTD) and Acceleration
- Up to 64 channels per unit
- Approximate Size: Expandable from 9cm x 15cm x 11cm
View the full WIS Technology Profile (WIS.pdf)