Payload Design
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Contents |
Characteristics
Goals
- For the overall project goals, see Clothos Science Program.
The science payload for the Clothos project is intended to take a biological and environmental profile of the atmosphere. It consists of an air sampler, an environmental monitoring (sensor) package, and a deployment and recovery (e.g. parachute) system. It is intended to be deployable, with minor adjustments, on a wide range of platforms at different altitudes, including low-flying zeppelins, mid-range weather balloons, and high-altitude rockets.
Payload Systems
Environmental monitoring
We need to measure temperature, pressure, airspeed (the velocity of the sampler relative to the air it is passing through), relative humidity, and radiation (UV).
Temperature: A variety of relatively inexpensive sensors are available; however, most RH sensors include temperature measurements.
Pressure: See velocity.
Velocity: This is traditionally measured using a combination of pitot tubes and converted from pressure.
RH: We are covering a very wide range of water content and temperature.
Radiation: Ocean Optics makes relatively small and inexpensive spectrometers that we've successfully used on previous balloon flights. The USB-controlled ones (example) essentially require flying an embedded Linux system to implement. They make self-contained ones (the Jaz line) which can communicate using Ethernet and also store data to a separate SD card, but are bulky and more expensive. Since the Ocean Optics spectrometers use relatively newer techniques their reliability is occasionally challenged, so it is best to combine them with a low-end traditional sensor to provide verification data.
Air sampling
We plan to sample for airborne particulates (in our case, bioaerosols) during a descent via parachute. Sampling during descent ensures that we are entering clean air. It also means the expected sample density proceeds from low-density to high-density, which is preferable. During a descent from 225k ft (~70 km), we pass through essentially two different regions. The atmosphere undergoes a dramatic thickening between 65k-75k feet (approximately 20-23 km). Above that, we will be falling through very low-density air at supersonic (~Mach 2) speeds. In this area, the expected sample density is very low (one of our goals is to determine where in this area the detectable threshold lies). Below that, we will be subsonic and falling at increasingly slow speeds through increasingly dense air. (In between, we decelerate rapidly, try not to get too hot, and don't do anything.) Here, the expected sample density is significantly larger (the tropopause, around 15 km, acts during calm weather as a cap on particulate dispersal) and in fact is greatly concentrated in the last 1 km or so.
At high speeds, our own velocity is sufficient to impact even small-size particles (our range of interest is about 0.5-15 µm) on our sampler, and we can use a simple inlet/filter/exhaust system to trap particles on a filter. At low speeds, it's necessary to force (pull) air through the filter to impact particles that small; this can be most simply done by using evacuated cylinders. We plan to re-use the same valved nozzle/inlet system to expose each of a series of filters during specified altitude intervals. This can be done using either a rotating disc array of filters, or with an array of valves such as the ones manufactured by Scanivalve. Thus the sampler consists of the inlet system, vacuum chambers, exhaust(s), their valves, filters to capture biological particles, and the controls necessary to detect altitude and swap valves/filters. We may get altitude from the pressure taken in the environmental monitoring package, the GPS used for deployment/recovery, or as a separate function.
Sterility is also a concern. Ideally the individual cylinder/valve/filter assemblies will be small enough to fit in an autoclave. The one we currently have access to at ARC has a maximum dimension of ~38 inches (~95 cm). We will experiment with autoclaving them inside sterile plastic bags and opening (rupturing) the bags at altitude. Other plans include seeding the outside of the sampler with sterile glass or latex microbeads to detect any contamination paths during flight and possible in-flight sterilization. If
Deployment and recovery
The payload package is intended to ride up on its platform (e.g. a rocket) remaining inactive and sterile during ascent. It should then be deployed (dropped or separated) from the platform and descend by means of a drogue parachute. It should take samples at specified altitudes or intervals during the descent, including during the last kilometer before landing. The payload should survive landing intact and with the sterility of the samples preserved. It should be easily locatable (via GPS or a beacon) and recoverable (e.g. not sink if expected to land in water). It will then be transported to the lab, where its filters and samples are removed for analysis, and should be able to be decontaminated, reinitialized, re-sterilized, and prepared for another flight.
The rocket platform already has a custom, highly-sensitive GPS implementation which we hope to leverage for tracking and locating the payload.
A significant concern is the heat generated during descent and deceleration. As previous flight profiles indicated that the payload will be supersonic during initial descent and will, between 75-55,000 ft (~23-16 km), decelerate dramatically as the atmosphere thickens towards the tropopause. To be safe, the samples should not be exposed to temperatures greater than 40ºC. (We can recover DNA from dead, intact specimens, but not from decomposed or otherwise destroyed samples.) We already anticipate tapping expertise at NASA on supersonic decelerators.
Support, communications, etc.
In the interests of preserving some useful results even if sterility is lost, no analyzable samples are detected, or the payload itself cannot be recovered, we would like to relay as much of the environmental data back during descent as possible. The radiation data is of most interest as it directly affects other projects potentially related to this flight.
We also anticipate flying a CCD to take high-quality still pictures and hopefully some video. This is useful both for public interest and fundraising purposes, but also helps to correlate spectometer readings with visible light conditions to correct for interruptions such as shadowing from the parachute, icing, or passing through clouds.
Analysis
Initial analysis can be done simply by removing the filters, sectioning them, staining a subsection, and viewing them under a microscope. This will help determine how many samples have been collected on a given filter and of what type. We can then proceed to traditional methods of identification such as culturing. We also have access to significant expertise in newer, culture-independed methods of analysis such as single-cell PCR and genomics, which will allow far more rigorous identification and categorization of any new or existing species of microbes found.
