Direct Energy Transfer System

The node current equations that describe the DET system during the dark portion of the orbit and the illuminated portion of the orbit can be written, respectively, as follows  

The DET power system designers believe that for optimum system reliability, the minimum solar-array size should consist of 110 strings in parallel and 63 cells in series per string, which will involve a minimum of 6,930 solar cells. These solar cells will limit battery charge current to approximately 5.52 amperes. 

---

Several dyes have been found to sensitize the cationic polymerization of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether initiated by diaryliodonium salts (109,110). Acridinium dyes such as acridine orange and acridine yellow were found to be effective sensitizers. One example of a benzothiazolium dye (setoflavin T) was also reported, but no other class of dye nor any other example of a dye absorbing at longer wavelengths were discovered. Crivello and Lam favored a sensitization mechanism in which direct energy transfer from the dye to the diaryliodonium salt occurred. Pappas (12,106) provided evidence that both energy transfer and electron transfer sensitization were feasible in this system. 

The energy transfer efficiency is directly proportional to the spectral overlap, and this also directly affects the Forster distance of a particular D-A pair. Figure 10.5 shows the D and A excitation and emission spectra in an ideal energy transfer system, wherein D and A have very distinct excitation spectra (so that A can only be excited by energy transfer and not by direct photon absorption at the wavelengths used to excite D)—the D emission and A excitation spectra overlap strongly—and the D and A emission maxima are well separated, so that the quenching of D fluorescence and the enhancement of A fluorescence can be individually measured.98 99... 

Excitation of the Lnm ion by a d-transition metal ion is an alternative to chromophore-substituted ligands, and proof of principle has been demonstrated for several systems. The lack of quantitative data, however does not allow an evaluation of their real potential, except for their main advantage, which is the control of the luminescent properties of the 4f-metal ion by directional energy transfer. In this context, we note the emergence of self-assembly processes to build new edifices, particularly bi-metallic edifices, by the simultaneous recognition of two metal ions. This relatively unexplored area has already resulted in the design of edifices in which the rate of population, and therefore the apparent lifetime, of a 4f-excited state can be fine-tuned by energy transfer from a d-transition metal ion (Torelli et al., 2005). 

Fig. 16.10 Energy level diagram for a Gd -Eu system, showing the visible quantum cutting process by two-step energy transfer upon excitation in the Gj levels of Gd. The two energy-transfer steps are indicated by (T) (CR cross relaxation step) and (2) (DT direct energy transfer) Reprinted from Ref. [21], Cop5orght 1999, with permission from Elsevier...

FIGURE 9. Summary of polarization values for the Ca(5 Ipj <- 5 Pj) energy transfer system 0 forward direction and reverse direction. 

The direct energy transfer (DET) system plays vital roles when the satellite is operating in a dark period (absence of sun light) or during the sun-illuminated portion of the flight. Critical components of this system and its block diagram are clearly identified in Figure 2.4. 

Figure 2.5 Block diagram of a direct energy transfer power system aboard a spacecraft. (From Pessin, L., and Rusta, D., "A comparison of solar-cell and battery-type power systems for spacecrafts," IEEE Transactions on Aerospace and Electronic Systems, 1967 IEEE. With permission.)...

---