SHERPA: a responsive multi-mission space tug
The shuttle expendable rocket for payload augmentation (SHERPA) is a rocket-powered orbital transfer system for small satellites. It is currently being developed by the Air Force Research Laboratory Space Vehicles Directorate (AFRL/VS) to support the need of the Department of Defense (DoD) space test program (STP) to deploy satellite payloads to higher orbits. SHERPA, a space tug, mass of 56 kilograms and is capable of boosting a 125-kg satellite payload from an orbit of 350 kilometers to 700 kilometers. The STP utilizes a variety of systems to fly its payloads. Although the current plan for the SHERPA flight demonstration is to use the canister for all payload ejections (CAPE), opportunities exist to also launch as a secondary payload aboard an expendable launch vehicle (ELV). The SHERPA team, consisting of AFRL/VS and several small business innovative research (SBIR) contractors, is designing the core technologies for this effort to be as modular as possible to allow use of these individual technologies in other applications. The planned demonstration SHERPA fly as a secondary payload and deploy after the space shuttle has completed its primary mission. After SHERPA and its satellite payload have separated from the Shuttle, it loiters on orbit until it is adequately separated from the shuttle and international space station (ISS). The SHERPA orient the payload stack and fire its propulsion system to enter a Hohmann transfer orbit. This boost requires a total change in velocity of 240 meters per second (m/s) and includes a one-degree plane change for collision avoidance. After the stack has coasted to the final mission orbit apogee, the propulsion system fires again, inserting the satellite payload into its final mission orbit. SHERPA will then separate itself from the satellite payload and fire a collision/clearance avoidance maneuver (C/CAM), ensuring it is clear of the satellite and guaranteeing the pressurized propulsion tanks are emptied as much as possible before re-entry. After this final maneuver, SHERPA is in its lowest possible orbit and ready for rapid re-entry.
SHERPA: A Flexible &amp; Responsive Small Satellite Transport Vehicle
SHERPA1,2, the Shuttle Expendable Rocket for Payload Augmentation, is a highly capable propulsive satellite. The SHERPA is currently approaching a PDR level design. The SHERPA can perform a wide range of missions including orbit transfers, small satellite maneuvers, space situational awareness missions, and serve as a platform for experiments. The SHERPA has three versions: The Mark I, is a propulsion unit, the Mark II is a standalone propulsive satellite, and the Mark III, a self contained long-duration propulsive satellite. Each version can support either an electric or chemical propulsion module. The SHERPA integrates several Air Force Research Laboratory developed technologies into one unique package. The SHERPA can also fulfil a number of other mission needs as a low cost satellite bus for the DoD Space Test Program
DEPLOYMENT AND RELEASE DEVICES EFFORTS AT THE AIR FORCE RESEARCH LABORATORY SPACE VEHICLES DIRECTORATE
Small satellites require a variety of release devices to accomplish mission-related functions such as separation from the launch vehicle, separation from each other, and deployment of instruments. This paper summarizes low-shock non-pyrotechnic separation efforts that are being managed by the Air Force Research Laboratory Space Vehicles Directorate (AFRL/VS). The AFRL/VS has been actively developing low-shock, non-pyrotechnic spacecraft release devices to mitigate problems associated with traditional pyrotechnic release devices. Specifically, pyrotechnic devices produce high shock, create unnecessary contamination, and have costly handling requirements due to their hazardous nature. Small satellites are particularly susceptible to shock related failure because of the close proximity of sensors and instruments to the shock source. Reducing shock-induced loads on the spacecraft dramatically lowers the overall cost of a spacecraft's design, testing, and operation. Lower loads allow spacecraft components, such as solar arrays and other flexible structures, to be made lighter and use less expensive materials. This results in both smaller mass and reduced production costs. The AFRL/VS is sponsoring the development of several innovative technologies that can provide solutions to these problems. The devices are being designed to replace existing separation and deployment systems.