This is probably stupid but could someone please clarify. Can we source our own materials for the payload equipment, for example thespray tank, or is it mandatory for us to use one of the samples provided in the background, thanks. Also, we noticed that each of the 400 squares on the map provided is larger than an acre, and is rather 1.6 acres, so does anyone know if this was simply an error and we are to assume each square is one acre or if we are to just extrapolate all of the measurements up to 1.6 acres from 1 acre.
You can absolutely source your own equipment for any of the components to be used in your design solution (this is highly encouraged since technology and methods evolve very rapidly). Just make sure you document the cost, requirements, and rationale supporting your decision (i.e., each component used in design) in your Engineering Design Notebook (see template document, section 2.2 selection of System Components).
In regards to the sizing of the grid squares and challenge area, the sizing of each square of 264x264ft (69,696 sqft or 1.6 acres each) was intentional as the total of all equals an area 640 acres or 1 mile x 1 mile ([20 x 264] x [20 x 264] = 27,878,400 sqft = 1 sq mile). This adds an additional layer of complexity to the challenge, which is also accounted for in the base calculations in both the Cost Calculator spreadsheet and the Calculations subsection of the Detailed Background document (see XII Calculations starting on p. 78). So in your design and analysis you will need to extrapolate for measurements of each affected area/grid square being 1.6 acres. Please review the Calculations subsection of the Detailed Background document very thoroughly as you proceed.
Good luck in your development of a proposed solution.