The design of nearly all Earth-orbiting spacecraft includes some sort of added shielding that protects the spacecraft against impacts by meteoroids and orbital debris. The effectiveness of the shielding is typically assessed using ballistic limit equations (BLEs) that are developed using data from high-speed impact tests on key spacecraft components and elements. These equations predict whether or not a particular system or structural element will sustain a critical failure following a specific impact event. As such, they are essential components of spacecraft system design as well as any quantitative spacecraft risk assessments that may need to be performed as part of that design process. Previous high-speed impact test programs have typically used medium-to-high density materials as surrogates for the kinds of materials that populate the orbital debris environment surrounding the Earth. However, with the advent of several new interplanetary spacecraft being designed, it is important to be able to predict and assess the performance of candidate spacecraft shields under impacts by projectiles made of materials that such spacecraft might be expected to encounter throughout their missions. To begin to address that issue, we assess how well a frequently used BLE, the New Nonoptimum (NNO) BLE, is able to predict the response of a commonly used shielding system when it is subjected to less dense materials that are often used as surrogates for icy meteoroids. In the end, it is shown that this BLE might require some modification when used to predict the response of such a system under the impact these kinds of projectiles.