## 1 Introduction
### Medical Screening and Certification Prior to Space Travel  
When considering preflight medical screening and certification, the requirements and recommendations vary based on the duration of space travel. Suborbital spaceflight, part of the new era of space travel, has participants launching to the edge of space (defined as the Karman line, 100 Km above mean sea level) for brief 3-5 min microgravity exposures. Orbital spaceflight, defined as microgravity exposure for up to 30 days, involves healthy individuals with preflight medical screening. In addition to a physical examination and metabolic screening, preflight medical screening assessing aerobic capacity (VO2 max), and muscle strength and function may be sufficient to ensure proper conditioning prior to mission launch [11; 12; 13; 14]. Age-appropriate health screening tests (e.g., colonoscopy, serum prostate specific antigen in men, and mammography in women) are generally recommended for astronauts in the same fashion as their counterparts on Earth. In individuals with cardiovascular risk factors or with specific medical conditions, additional screening may be required [15]. The goal of these preflight screening measures is to ensure that medical conditions that may result in sudden incapacitation are identified and either disqualified or treated before the mission begins. In addition to the medical screening described above, short-duration space travelers are also required to undergo acceleration training, hypobaricand hypoxia exposure training, and hypercapnia awareness procedures as part of the preflight training phase. In preparation for long-duration space travel, astronauts generally undergo a general physical examination, as well as imaging and laboratory studies at the time of initial selection. These screening tests would then be repeated annually, as well as upon assignment to an International Space Station (ISS) mission. ISS crew members are medically certified for long-duration spaceflight missions through individual agency medical boards (e.g., NASA Aerospace Medical Board) and international medical review boards (e.g., Multilateral Space Medicine Board) [16; 17]. In order for an individual to become certified for long-duration space travel, an individual must be at the lowest possible risk for the occurrence of medical events during the preflight, infight, and postflight periods. Following spaceflight, it is recommended that returning astronauts undergo occupational surveillance for the remainder of their lifetime for the detection of health issues related to space travel (e.g., NASA's Lifetime Surveillance of Astronaut Health program) [18]. Table 1 summarizes the preflight, inflight, and postflight screening recommendations for each organ. Further research utilizing data from either long-term space missions or simulated environments is required in order to develop an adequate preflight scoring system capable of predicting inflight and postflight health outcomes in space travelers based on various risk factors. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scheme** & **Pre-Flight** & **In-Flight** & **Post-Flight** \\ \hline \multirow{8}{*}{Physical Fitness Assessment} & Cardiovascular fitness: VO2 max & \multirow{8}{*}{Cardiovascular fitness: Flight} & \multirow{8}{*}{Functional fitness assessment: R+7, R+30} \\  & measured cycle ergometry & & \\  Flexibility: Sit \& reach; & day (FD) +30, +120, return day & \\  & shoulder flexibility & (R) \(-\)30 VO2 max & \multirow{8}{*}{Cardiovascular fitness: R+7, R+30} \\  & Muscular strength and & & \\  endurance: Maximum & FD+3 through day prior to & & \\  push-ups in 2 min; maximum & & return.