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Experiment/Payload OverviewThe Dust Aerosol Measurement Feasibility Test (DAFT) releases particles in the International Space Station (ISS) atmosphere to test the ability of different equipment to measure the levels of dust and air quality.
Principal Investigator
Payload Developer
ZIN Technologies Incorporated, Cleveland, OH, United States
National Aeronautics and Space Administration (NASA)
Sponsoring Organization:Human Exploration and Operations Missions Directorate (HEOMD)
ISS Expedition Duration:October 2004 - September 2006
10, 13
Previous ISS MissionsThe P-Trak and DustTrak were first tested on ISS Expedition 10.
Our understanding of how fires burn in a spacecraft has evolved since the fire detection equipment on space
shuttle and space station was developed. One thing we have learned is that smoke particles that form in microgravity
can be larger than those formed on Earth. Since smoke detectors are gauged to detect certain sizes of particles,
this knowledge could help design more accurate smoke detectors for future spacecraft. The Smoke and Aerosol
Measurement Experiment (SAME) is planned to gather particulate size information on ISS. The DAFT experiment,
which was initiated after the Columbia accident, is to be used to obtain data in preparation for SAME using very
little upmass.
DAFT is intended to assess and characterize the distribution of particles in the air inside ISS to allow assessment of the suitability
of current shuttle and ISS smoke detectors. This experiment
was begun on Expedition 10 and is planned for completion during
Expedition 13. DAFT is designed to test the effectiveness of the PTrak
Ultrafine Particle Counter, a device that counts ultra-fine dust
particles in a microgravity environment. Most particle counters work
by using a laser to record instances when the beam is interrupted;
however, this method will not record ultra-fine particles that are
much smaller than the wavelength of the light. P-Trak works by
passing dust-laden air through a chamber of vaporous isopropyl
alcohol. When a droplet of alcohol condenses over an ultra-fine
dust particle, the particle becomes large enough to break the light
beam and be counted. The alcohol is then recycled as it condenses
on sidewalls and gravity pulls the alcohol back to the saturator. If
the results are satisfactory, P-Trak will be used in SAME, which
requires counts of particles ranging from 0.2-1 micron.
Extended duration space flight missions with larger vessels will require fire detection systems with increased reliability and sensitivity. In order to provide the data required for that development, SAME needs to utilize the DAFT experiment to provide mitigation against the risk that the P-Trak may not be able to provide the required data.
Additionally, in the event that the experiment is successful, it may be possible to use these devices to provide more detailed information about the character of the particulate in the atmosphere aboard the ISS.
The smoke detectors developed from the results of SAME can also be useful in other extreme environments on Earth, such as submarines or underwater laboratories. Accurate detection of smoke in these environments can save lives.
Since they have no external power requirements, DAFT-1 and DAFT-2 can be operated almost anywhere (where the release of small amounts of alcohol is permitted) within the ISS. Downlinking is performed using a program supplied by the project and installed onto an EXPRESS computer. Three test points can be accomplished by a single crew member in 80 minutes.
DAFT-3 and DAFT-4 needs ISS gaseous nitrogen and therefore require an active nitrogen source, and safety restraint for the fill device. Test point time increases by 15 minutes per point.
The crew member simply assembles the test set up from the included packages, turns the devices on and waits 6 minutes for operation, noting average readings and/or anomalies. Sensitivity to the alcohol content of the atmosphere on board the ISS limits usage of the P-Trak to a maximum of three test points per day. For DAFT-3 and DAFT-4 precautions regarding overfilling the sample bag and preventing potential hose whip exist.
Preliminary results, based on DAFT sessions performed on station in 2005 and 2006, demonstrated that the P-Trak
Ultrafine Particle Counter could be successfully built into the SAME payload, and established the optimal ranges for
particle detection using this instrument. The data collected also indicate very low levels of particulate in the ISS
environment relative to that previously measured on shuttle. This low particulate level is not surprising due to the
small crew size on ISS (two or three vs. the typical seven-person crew on shuttle) and the high-efficiency
particular accumulator (HEPA) filtration system of ISS. It is suspected that the particulate level will rise once station
hosts a larger crew. In later experiment runs, the results indicated that the average size of the particles were larger
on orbit than on Earth. These results could be due to the inefficiency of the large particle filter. Once the median
particulate level throughout ISS is known, it can be used to design future smoke detectors that accurately distinguish
normal dust from the presence of dangerous smoke particles.
A series of events (malfunction of the electronic data transmitted, crew time limits, and an alcohol wick that did not open) shortened the overall experiment, but adequate data was collected to label the demonstration successful. (Evans et al. 2009)