| Designation | EMR Type | Photo Cathode | Window Material | Minimum Background-Nmin (per 14 sec) | Maximum Background-Nmax (per 14 sec, outside SAA) | R(Nmax/Nmin) | Corr Factor |
|---|---|---|---|---|---|---|---|
| U1 | FUV | KBr | -- | 17 | 80 | 4.7 | 1 |
| U2 | FUV | KBr | -- | 12 | 60 | 5.0 | 1 |
| U3 | G08 | CsI | LiF | 8 | 42 | 5.2 | 1 |
| V1 | N09 | Bialkali | MgF2 | 3,500 | 11,000 | 3.1 | 0.52 |
| V2 | N09 | Bialkali | MgF2 | 2,000 | 7,500 | 3.7 | 0.68 |
| V3 | D01 | Bialkali | 7056 Glass | 2,500** | 4,500 | 1.8 | 0.20 |
| Designation | Carriage No. | Spectrum Order | Wavelength (Å) | Non-grating Optics Behind Common Entrance Slit |
|---|---|---|---|---|
| U1 | 1 | 2 | 710-1500 | |
| U2 | 2 | 2 | 750-1645 | Dipping Mirror |
| U3 | Fixed | 1 | 1310 Å | Blackened reflecting mirror |
| V1 | 1 | 1 | 1640-3185 | Fabry optics (reflecting), quartz filter |
| V2 | 2 | 1 | 1480-3275 | Dipping mirror, Fabry optics (incl. sapphire prism) |
| V3 | Fixed | 1 | 3428 Å | Reflecting mirror |
| Designation | Scaling Factor | Operating Voltage* | Typical 14-Sec Dark Count Earth Vacuum Tests, -2°C |
|---|---|---|---|
| U1 | 21 | 4.9 KV | 2.0 |
| U2 | 23 | 4.9 KV | 2.8 |
| U3 | 25 | 3.0 KV | 1.4 |
| V1 | 22 | 3.0 KV | 9.1 |
| V2 | 24 | 3.0 KV | 14.2 |
| V3 | 25 | 3.0 KV | 140 |
| Minimum signal | .1 mv U1, U2 |
| .2 mv V1, V2 |
* Photocathode grounded.
** Where counts in other tubes are low, the V3 count rate may be as high as 7500/14 sec, in orbits where the satellite has just passed the SAA.