# Small Satellite Tools for High-Resolution Infrared Fire Monitoring
## 9 Innovative Tools to Increase the Agility of Small Satellites
### High Agility of Prospective Small Satellites with IR Sensors  
Design proposals for compact multi-spectral VIS-NIR and MIR/TIR push-broom sensors based on mega-pixel detector arrays of the COTS type are discussed in [16; 17]. The high agility of such a single-satellite sensor system, with (intelligent pointing may be, for instance, the use of information on the cloud cover and cloud-free regions for the pointing of the sensor's Line of Sight (LoS) in a wide Field of Regard (FoR)) of the sensor's Line of Sight (LoS) in a wide Field of Regard (FoR), is illustrated in Figure 22. In this example, the LoS of the push-broom sensor is moving forward with a speed of \(\sim\)27 km/s, which is approximately four times higher than the speed of the satellite over ground (\(\sim\)7 km/s). This high agility is possible due to the use of:  
* a cooled CdHgTe matrix detector array in combination with stripped filters in the multi-spectral MIR/TIR sensor (allowing for fast sampling with overlaps also for supplementary data binning); and
* HTWs as the key actuators to enable fast and agile pointing of the sensor's LoS.  
The area covered by the sensor in Figure 22 is approximately two times larger than the area that the sensor would cover in the \"classic\" push-broom mode, where the sensor's LoS is moving forward with the speed of the satellite over ground (\(\sim\)7 km/s).  
A Scan/Tilt Mirror System (STMS) for optical payloads on small satellites of, for instance, the BIROS type is shown in Figure 23. This system allows us to conduct either a wide-swath push-whisk-broom scan or to tilt the LoS of a push-broom sensor. The STMS comprises a mechanism for the compensation of the torque moment occurring during the angular movement of the mirror.  
Figure 21: A transparent view of the BIROS RGB camera of type VRm DFC-42 with a baffle in front of the entrance lens.  
Figure 23: Scan/Tilt Mirror System (STMS) for small satellites equipped with a mechanism for the compensation of the torque moment [18], consisting of the following numbered main parts: 1—mirror, 2—two masses compensating for the mass of the mirror, 3—encoder wheel, 4—rotating part of the drive, 5 and 8—flying cone wheels of the towed differential transmission, 6—fixed mounted part of the drive, 7—torque-compensating masses, 9—axis, 10—body-fixed cone wheels of the towed differential transmission, 11—angular encoder.  
Figure 22: Illustration of intelligent and agile pointing of the Line of Sight (LoS) of a push-broom sensor in a partly cloud-covered scene [17].  
Figure 24 illustrates the push-broom, whisk-broom, and push-whisk-broom scan modes of an imaging Earth observation sensor.  
The utilization of the STMS will allow **us** to implement either an along-track tilt or an across-track wide angle scan, both conducted (i) with one satellite sensor system, and--before the start of one of the two sampling modes--(ii) by an initial \(\sim\)(+/\(-\))90\({}^{\circ}\) angular movement of the satellite around its nadir-oriented Z-axis. Figures 25 and 26 illustrate this STMS function for the along-track tilt and the across-track scan, respectively.  
Figure 24: Three typical scan modes of an imaging Earth observation sensor: push-broom (left, with an array detector), whisk-broom (middle, with a single detector), and push-whisk-broom (right, with an array detector).  
Figure 25: Illustration of the along-track tilt of a push-broom sensor’s LoS by the STMS.