Mechanical Structure discussions to go here
Inspection of PLUME skeletized structure
Approximate Budgets following the MRR:
|Subsystem||Mass (g)||Power (W)||Volume (mm x mm x mm)||Cost (£)|
|PAY||160||-0.6 continuous||PMT's = 2 x (50.0 +/-0.5 x 50.0 +/-0.5 x at least 12-16)||1600 approx|
|CAM||20||-0.1||20 x 20 x15 approx||?|
|PSU (incldng BATT)||164.19||+1,4 continuous||9216||?|
|Antenna||50||n/a||50 x 50 x 10 stored (2 ariels of 90 x 90 x 5 deployed)||350 - 550|
|OBDH||74||0.008||96 x 90 x 16.5||?|
|ADCS||6||-0.13/0.55||Board: 50 x 50 x 10||?|
|BUS||170||n/a||100 x 100 x 100||?|
|Total||858.19||0.24/-0.83||106 x 106 x 106 stored||?|
Table 1: Up to date budgets for the mass, power, volume and cost of each subsystem
These figures do not include margins.
They are of a square ring design and the figure in the table is their outer dimensions. They have an inner diameter of 90mm, so the volume was calculated by subtracting a cuboid of 90mm x 90mm x 5mm from a cuboid of 94mm x 94mm x 5mm. (This gives a value of 3680mm3)
Breakdown of PSU mass:
|Power Control Board||50|
Table 2: Mass breakdown of PSU subsystem
The estimates for masses for the battery and solar panels are based on technical specification. The control board is an estimate based on Clydesat.
On the link above (user manual) there's a 57 page document from pumpkin inc all about the cubesat kit. Basically the structure is divided up into slots, roughly either 4 or 5. The bootom slot (slot 0) takes the flight module, that takes up the bottom 25mm of the cubesat.
It has been suggested that, for reduced mass and improved fittings within the cubesat, Carbon fibres could be used in place of the Aluminium frame. Or maybe a half Aluminium half Carbon fibre combination.
I looked at the flight regulations from the P-POD bus and I'm not sure this is faesable. One of the specifications our cubesat has to meet is that, if made from an alternative material, it has to have a Coefficient of Thermal Expansion (CTE) similar to that of Al 7075-T73. The value for this I found, from Aerospace Metals, was 23.6 x 10-6m.m-1.oC-1. After looking for similar values for Carbon fibre, I found several qouting a CTE of about 0.54 x 10-6m.m-1.oC-1. The other consideration is that Carbon fibre is not isotropic in its thermal properties, so this would vary greatly upon direction. Without finding a really different Carbon fibre with a CTE of about 23-25, I think it's unlikely we can get approval from the P-POD technicians.
Carbon fibres are not a viable option for the BUS structure
Centre of Mass:
The centre of mass of the overall structure must lie within 2cm of the structures geometric centre.
This simplified model has been created using an excell spreadsheet. Currently using an orbital height of 1000km the maximum dayside temperature is 315K and the minimum nightside temperature is 228K. For details look at the Thermal Modeling Paper and the Excel Worksheet.
A simple radiation environment evaluation has begun. This can be found here. This is a page that ALL subsystems should have a look at when considering radiation susceptibilty.
Dimensions of the PCBs in millimetres and the mechanical interfaces can be found here.