One approach involves an investigation of alternating current systems for balloon use,
Solid-state tech-
nology has now produced highly efficient light weight inverters that offer to make practicable the use of alternating current devices on balloon platforms,
Devices of this type weighing less than twenty-five pounds can
now deliver 3 KVA of 400 cycle power with close frequency control and efficiencies exceeding 85 to 90 percent.
With respect to high altitude sampling this will allow the use of low-friction, brushless motors delivering a
given horsepower at high efficiencies and lessening the critical heat dissipation problem.
There will be little,
if any, weight penalty in going to AC systems since the somewhat higher total efficiency should result in lower
battery weight.
High altitude operation also offers some interesting advantages with respect to the use of cascade impactors.
At low densities, efficient impaction can be obtained at relatively low jet velocities.
This means that we
may be able to abandonthe relatively inefficient constant volume pumps with their low sampling rate (22 cfm)
and go instead to multistage turbines which will deliver much higher volumes, giving the radiochemists more
adequate samples to analyze.
A second, entirely different approach to high altitude sampling is largely an outgrowth of our past work
with crystalline zeolites.
This involves the idea of using an evacuated zeolite bed as a pump.
If sucha bed is
maintained at liquid nitrogen temperatures (-196°C), ten grams of Linde Type 13X zeolite will adsorb over one
standard liter of dry air at pressure altitudes equivalent to 170, 000 feet (0.5 mm Hg).
verified many times in the laboratory.
This is a fact we have
Furthermore, this process is quite rapid and tests indicate that at
130, 000 feet, 85 pounds of zeolite will be able to adsorb over 100 standard cubic feet of air in less than
100 minutes.
Figure 5 shows in principle the basic features of a particle sampler which utilizes a liquid nitrogen cooled
zeolite pump.
Such a sampler is presently being designed for flight tests in late summer 1961 and this unit is
expected to have the following characteristics:
WEIGHTS
Zeolite Adsorbent
85 lbs
Liquid Nitrogen
45 lbs
Containers and Hardware
70 lbs
TOTAL
200 ibs
PERFORMANCE GOALS
156
Volume Sampled
100 + scf
Sampling Rate
1.0 scf/min
Sampling Altitude
To 140, 000 feet