The nominal boundary between "regular" GO proposals and Large Projects (including Large Projects, Very Large Projects and X-ray Visionary Proposals) was set at 300 ks in Cycle 2. LPs are scrutinized in more detail than regular proposals: they are evaluated in two topical panels (rather than just one) and the highly ranked LPs are discussed at the Big Project Panel (BPP), consisting of the topical panel Chairs and ~3 independent pundits. The average number of Large proposals per cycle was 54 in Cycles 2-6 and has risen to 81 proposals per cycle in Cycles 12-17.
We recognize that as the Chandra mission matures there has been a shift to larger proposals. It is important for the Big Project Panel to focus on the largest programs, those that will be the core of Chandra's legacy. Thus a primary motivation for moving the LP boundary is to decrease the number of LPs and hence reduce the workload of both the topical panels and the Big Project Panel.
Proposers who have projects in the 300-400 ks range may wish to consider the following:
In Cycle 17, 6.0 Ms was awarded to Large projects and 10.4 Ms to regular GO proposals. In Cycle 18 we expect ~4 Ms to be available to the Big Project Panel for LPs and ~12.2 Ms to the topical panels. These allocations are adjusted ~ a week before the peer review to account for the actual observing efficiency during the current cycle. The unlikely event of adjustments >5% will be announced to the community.
There is a perception that proposals that ask for ≥ 25% of the total allocation of a single panel (~800 ks) have low success rates. This drives proposers to tailor their requests to fall into the LP category ("it will be easier to get a small LP than a large GO proposal"). The expectation that a "small" LP will have a better chance of success than a "large" GO proposal is not necessarily correct. Figure 1 shows the percentage of accepted proposals as a function of requested exposure time for Cycles 12-17. The grey shaded area shows proposals that fall in one of the LP categories and are reviewed by two panels and the BPP. Historically, proposals that fall into one of the LP categories are the most competitive.
Figure 1
