The power budget represents the satellite as a set of loads for finding EPS requirements.
Worst Case Loads
The following table is the full accounting of the worst-case loads in the system.
|System||Peak Power (W)||Voltage Bus (V)||Peak Load (A)||Citation|
|UHF TX||4.68||3.9||1.2||RF Budget|
|UHF RX||0.3393||3.9||0.087||RF Budget|
|RF Sensors & LEDs||0.234825||3.3||0.0712||RF Budget|
|VHF RX||0.45||5.0||0.09||RF Budget|
|VHF TX||1.14||5.0||0.228||RF Budget|
|OBC||0.390||3.3||0.118||Kabir on Slack|
|Reaction Wheels||2.0691||3.3||0.627||ADCS PDR|
|GPS||1.7985||3.3||0.545||OEM-7 Data Sheet|
|Deployment||0.00064||CC||2.0||Steven's Old Data, also see heading below|
|Camera FPGA||3.3||3.3||1.0||TE0725 Datasheet|
|Camera Sensor (Visible)||0.891||3.3||0.270||OV5642 Datasheet|
|Camera Sensor (IR)||0.891||3.3||0.270||OV5642 Datasheet|
|Cell Line Heater||No Data|
The overall worst-case peak power draw is therefore 17.0226W, not yet accounting for the unspecified cell line heater and EPS. The quiescent power draw of various EPS functions are effectively inefficiencies in delivery and assumed to be negligible compared to the worst-case total load. The additional heater power is assumed to be within qualification margins, and if it is not then the biological payload will be changed to a less temperature-sensitive culture. With a 10% qualification margin, the power sources must be able to provide a peak of 18.7248W intermittent power.
Worst Case Bus Loads
The summed peak powers and currents per bus are tabulated below.
|Voltage Bus (V)||Peak Load (A)||Safety Factor||Qualification Load (A)|
Nichrome Deployment Power Rough Estimation
The nichrome wire is a one-shot burning deployment mechanism that draws 2A for approximately one second before self-destructing. However, this experimental figure was determined under normal atmospheric conditions, and is likely far less efficient than in a vacuum due to the additional convective cooling. Nevertheless the 2A figure will be used for approximating the power draw until a vacuum test is conducted. At worst, the error in the number will just give a margin of safety.
If the system is approximated as a 1m long nichrome wire, the resistance is 0.160 milliohms. Resistive power loss can be found as (I^2)R, and if the resistive loss is assumed to be equal to the power draw, then the draw is (2.0)(2.0)(0.000160) = 0.00064W.
The only known continuous loads are the OBC and the losses in the EPS. As the EPS is unspecified a large 10% delivery loss is assumed. Therefore 0.429W is required continuously to keep the satellite alive. Applying a 10% qualification margin, the power system will be designed assuming a constant 0.4719W load.