The harsh radiation environment anticipated during the Europa Jupiter System Mission (EJSM) presents a significant challenge to develop radiation-hardened notional instruments. A high-performance, radiation-tolerant detector is required for the time-of-flight laser altimeter system on the Jupiter Europa Orbiter (JEO), which will perform critical characterization of Europa's topography, ocean tides, and ice shelf. Avalanche photodiodes (APDs) are conventionally chosen as detectors for standard laser altimeter systems. However, the performance of APDs degrades significantly after exposure to high levels of radiation. Aerius Photonics proposes to develop a novel radiation-tolerant detector that is suitable for use in space-based laser-altimeter systems by integrating a Vertical-Cavity Semiconductor Optical Amplifier (VCSOA) with a PIN photodetector. The resulting device, known as a Vertical-Cavity Amplifying Detector (VCAD), is expected to provide high-gain, high-speed, low-noise detection and demonstrate significant improvements in radiation tolerance over APDs. The optical preamplification provided by the VCSOA, along with its operation as a forward-biased majority-carrier device, renders the VCAD system insensitive to radiation-induced increases in detector dark current noise and receiver electronics noise. The VCAD is also expected to be significantly less susceptible to single event transients (SETs) than an APD. Aerius Photonics has expertise in VCSOA development and has already demonstrated basic radiation tolerance of VCSOAs to 300 krad with gamma radiation and to 300 krad with 63 MeV protons. In Phase I of this program, Aerius will design, fabricate and characterize VCADs that have been exposed to a more comprehensive radiation test plan that will include conditions anticipated on the EJSM.