The asteroid explorer/sample return mission is designed in the context of both scenarios and is the first phase of a long range plan for humans to utilize asteroid resources.
The report concentrates specifically on the selection of the most promising asteroids for exploration and the development of an exploration scenario. Future utilization as well as subsystem requirements of an asteroid sample return probe are also addressed.
Project STONER is divided into two primary areas: asteroid selection/mission design and explorer spacecraft design. The asteroid selection team has narrowed the possible 4800+ known asteroids to ten, considering physical attributes of each candidate asteroid as well as mission trajectory and V requirements. From that group of ten, a final asteroid was chosen for more in-depth study.
The mission design team formulated mission scenarios and -- working with the other teams -- investigated possible problem areas and contingency plans. In the design of the spacecraft, subsystems that have been studied are: GNC, communications, automation, propulsion, power, structures, thermal systems, scientific instruments, and mechanical retrieval devices.
The Hawking spacecraft, designed to study an asteroid and return a sample to Earth, was named after Steven F. Hawking as a tribute to his continuing efforts to expand the limits of manıs understanding of the universe. The Hawking is an adaptation of the Mariner Mk II series of spacecraft. Utilization of the Mariner Mk II design can accelerate development of the spacecraft and significantly reduce cost.
The Hawking spacecraft consists of three component vehicles: orbiter, lander and the sample return craft (SRC). Each of these vehicles has specific mission objectives and contributes directly to the fulfillment of the primary mission goal: return a sample of asteroidal material to the earth for analysis. Analysis of the samples is crucial in determining the composition of different taxonomic classes, and is a necessary step before utilization of asteroids can begin.
The sample return mission scenario consists of nine phases, the successful completion of each being critical to the overall mission:
Hawking is launched into LEO orbit aboard an existing launch vehicle.
Hawking is injected into the interplanetary transfer trajectory by its upper stage.
Phase 3: During the interplanetary cruise, the spacecraft performs radio science experiments and studies of the solar wind.
Hawking inserts itself into the asteroidıs orbit, positioning itself several asteroid radii ahead of the body and slightly to the sun side. This position allows the spacecraft to map the asteroid, determine its rotational axis, and locate scientifically interesting features, all to help determine a desirable landing site.
The Hawking Explorer Spacecraft
Once a landing site is chosen, the lander/SRC separates from the orbiter. The orbiter remains several asteroid radii away to serve as a relay for the lander/SRC and to provide reconnaissance for the rovers. The lander/SRC approaches and docks with the asteroid using its attitude control thrusters.
Samples of scientific interest are identified and retrieved by either the robotic arm or the rovers, and placed in the SRC.
The SRC is launched from the lander in a non-destructive manner (ie., springs, pneumatic pistons) so the lander can remain intact to perform more analysis of the asteroid. At an altitude of approximately 0.5 km above the lander, the SRC rotates and fires the booster's engines to inject itself into the transfer trajectory back to Earth.
After the injection burn, the booster stage is jettisoned and the communication antenna and solar panels are deployed. During the interplanetary cruise of the SRC, the integrity of the sample is maintained by minimizing g-loads during maneuvers and keeping the sample at a low temperature.
Upon arrival at Earth, the SRC inserts itself into a highly elliptical orbit. After accurate ground-based orbit determination, the SRC circularizes into LEO where it waits for pick-up by either the Space Shuttle or Space Station Freedom.
There are many benefits to be gained from studying asteroids. Presently these bodies have been almost totally neglected in the exploration of the solar system. It is believed that because of their primitive state they hold clues to the formation of the solar system. Also, utilization of asteroids as a future space-based source of raw materials could reduce the total cost of future space missions.
Last Modified: July 3, 1998
CSR/TSGC Team Web