Hi! Per NSF guidelines: An organization may submit only one invited SBIR/STTR Phase I proposal submission windw. An organization must wait for a determination from NSF (e.g., Award, Declination, or Return without Review) on any NSF SBIR/STTR Phase I pending proposal before submitting a new proposal in the next window. This eligibility constraint will be strictly enforced. In the event that an organization exceeds this limit, the first proposal received will be accepted, and the remainder will be Returned without Review. Declined proposals require a new invited Pitch while proposals Returned without Review may be submitted using the same invited Pitch (within the one-year eligibility from date of the original proposal invitation).
Thus, if the first proposal is rejected, you can submit a new pitch. If invited, a new/revised proposal can be submitted. If awarded, with a small company having several employees, even changing to a new topic area, it will be really difficult to receive another award. Hope this helps!