SCOUT: EVA Capabilities of the Space Construction and Orbital Utility Transport 2004-01-2295
The University of Maryland has performed a detailed design for the space equivalent of an atmospheric diving suit. The Space Construction and Orbital Utility Transport (SCOUT) is a small single-person spacecraft, with all necessary utilities for extended sorties away from the host station. Through a pair of AX-5 style space suit arms integrated into the cabin wall, as well as a trio of dexterous manipulators, the SCOUT operator can directly interact with the work site environment, performing spacecraft servicing, structural assembly, or other tasks traditionally done by an astronaut in a space suit. Originally designed as an augmentation to the NASA Gateway station architecture for the Earth-Moon L1 system, studies indicate that a SCOUT-type EVA system would represent a substantial benefit to International Space Station operations as well. Due to the integrated robotics system, ISS extravehicular operations, which nominally require two EVA crew and one IVA robotics operator, can be done with a single SCOUT pod unaided.
One of the requirements to allow safe single-pod operations is a high-reliability system to ensure crew survival. To this end, SCOUT incorporates several design features to increase mission assurance and maximize the probability of crew survival following a catastrophic failure. Since SCOUT is designed around an 8.3 psi cabin pressure, there are no prebreathe requirements prior to start of operations. This will allow a second SCOUT pod to be kept on “ready alert” at the station, with its operator performing other tasks but ready to react in a contingency. The second SCOUT safety feature is the adoption of an innovative “bail-out” system. In the event of a failure which renders SCOUT uninhabitable, in less than a minute the operator can deploy an emergency bail-out system, normally kept in a small package on the SCOUT hull. A single valve actuation will inflate an all-fabric escape suit, consisting of a simple cylindrical body with polycarbonate face plate and adjustable-length arms, mounted to the SCOUT cabin via a pressure hatch. The operator will then move into the escape suit, close the hatch, then detach from SCOUT. The system provides three hours of life support, along with SAFER-style cold gas thrusters for mobility. Between the second SCOUT pod on ready alert and the self-rescue capability of the escape suit, a probabilistic risk assessment shows a 99.9% chance of performing a 600-EVA mission model without loss of crew.
Additional systems have also been designed to extend the operating range of the SCOUT system. A docking module was designed to support two SCOUT pods, providing docking interfaces to the host station and SCOUT-specific resupply/repair capabilities. The docking module docks to space station through the use of an International Space Station common berthing mechanism (CBM). An extended mission package provides support for SCOUT in remote operations, extending sortie times from 11 hours to several days. In conjunction with an orbital maneuvering vehicle, the extended mission package would allow an ISS-based SCOUT to be used for human servicing at geostationary orbit, and from an L1 base would allow SCOUT operations in lunar orbit.