The SEH electronics package, including the original sounding rocket skin, is contained in the adjacent 5.0 cubic foot canister and provides the interface to the Hitchhiker Carrier system electronics. The Helium Double Ionization Cell, shown above, is one of three integral flux measurement instruments contained within the SEH experiment. The Helium Double Ionization cell is used to determine the helium photoionization rate. The photoionizatoin rate is them used to calculate the total number of photons in the emission lines between 50 - 504 Angstroms. The Helium Double Ionization instrument contains a reservoir of helium that is released, via ground command, into the ionization cell.
Photons enter the ionization cell and collide with helium atoms.
Those photons in the emission line of interest are absorbed by the helium atom creating an electron and helium ion pair. A power supply collects the free electrons and collectors 1 and 2 collect the free helium ions. If too much helium has been introduced into the cell, then secondary and possibly tertiary collisions will occur between these electron ion pairs and the extra helium gas creating erroneous readings. Moreover, if too little helium is introduced into the cell, than photons will not collide with the helium gas again obfuscating the intended results. To circumvent these possibilities, a radiation pressure gauge, which utilizes a tritium source, provides a measure of helium in the cell and is telemetried to the ground enabling realtime adjustments to the gas pressure.