Deep Space 1
NEW TECHNOLOGIES FOR SPACE RESEARCH: DEEP SPACE 1
With the advent of the new millennium, NASA established a flight program to test new technologies that would enable in the future more unmanned missions within a reduced budget. The first of these test spacecraft was "Deep Space 1".
The smaller the spacecraft, the smaller the launch vehicle can be, and this can significantly reduce the cost of a mission. "Deep Space 1" has a new type of communications radio with a mass half of what previous equipments had. Also are very miniaturized two scientific cameras for visible light, another for infrared light, that can detect the composition of different minerals by their colors, and another to study the composition of vapor and dust, in ultraviolet light. The four of them can share a single telescope, 10 cm in diameter. Another small equipment combines multiple sensors to detect particles such as electrons and atoms nuclei. Also are smaller the electric energy distributors, and even the walls of the spacecraft are constructed so as to serve as circuitry plates for various electronics.
The spacecraft has a high-frequency transmitter that allows that ground antennas smaller than traditional ones be used to receive data. It also allows that communications be carried out at high speed, and therefore be short, permitting that several spacecraft could use in succession the same station on Earth. To avoid controllers having to regularly monitor the spacecraft to know its health status, it has the capacity to self-diagnose failures. It can distinguish minor faults from more serious faults, and even failures that may put the mission in danger, and decide whether to seek help immediately, or in medium term, or just in long-term. Radio signals transmitted by this function can be easily interpreted by secondary ground stations.
In traditional spacecraft each activity is programmed one by one, action by action, instrument by instrument, from Earth. "Deep Space 1" receives only general orders on specific objectives of the mission, and its computer autoprograms itself alone, without help, elaborating the sequence of commands to be sent to each of the instruments and other systems. This also allows it to act immediately upon noticing any problems or obstacles for the mission, without waiting several minutes, or even hours, for the solution to come from Earth.
Perhaps the most interesting part of its automated systems is the autonomous navigation. Normally, ground antennas are used to know where each spacecraft is in space and follow its trajectory, but with so many simultaneous missions out there this becomes increasingly difficult. The "Deep Space 1" uses its cameras to locate, beside stars, various well known asteroids, and by comparing the positions of these in space, the computer can work out where the spacecraft is at all times. By performing more of these determination of positions over time, it is possible to know in which direction the spacecraft is moving, and how fast. Consequently, the computer can order the engines any corrections deemed necessary, all without human intervention.
It is very important that electricity consumption be low, in order to carry more instruments and other systems. Various components of "Deep Space 1" were specially manufactured to have extra-low consumption. And it has innovative solar panels, covered with many small cylindrical lens to focus sunlight and help generate much more electricity than conventional designs.
"Deep Space 1" became famous as the first spacecraft to use an ion propulsion engine. It works by tearing electrons from a gas, xenon in this case, so that the atoms are left positively charged. Then a positively charged plate and another negatively charged one strongly accelerate these atoms out of the ship, creating momentum. Torn out electrons are discarded in that same gas jet. The system produces very little thrust, but it is ten times more efficient in the use of propellants than conventional chemical motors, saving much mass. This engine emits an eerie blue light, and stays on for much longer: in the "Deep Space 1" it was calibrated to spend its propellant gas very slowly over several months of continuous operation, enough time to change the speed (and trajectory) very considerably.
All these technologies were tested since launch, in October 1998. By July 1999, the spacecraft flew past asteroid (9969) Braille, and in September 2001 it passed by comet 19P/Borrelly, occasion in which it got the best pictures from a comet nucleus obtained so far.
In November 1999, "Deep Space 1" lost its main orientation detector, the star tracker camera. After months of intense work, the ground crew figured out how to point the spacecraft without it. The failure of this off-the-shelf, commercial device exemplifies that Space Exploration is always risky business, be it with new or old technology. Anyway, "Deep Space 1" was able to validate the innovations it was designed to test-fly.
Now science missions can adopt these new technologies. At this point the probe "Dawn" is orbiting the giant asteroid (1) Ceres, after studying the interesting asteroid (4) Vesta, two of the largest known asteroids. This spacecraft has ion engines, and other technologies tested and approved by the "Deep Space 1".
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Originally published in "Panal" magazine, number 156, October 2006, page 21. Poster: This whimsical image dealing with NASA's Deep Space 1 mission was developed in cooperation with Spectrum Astro Inc., Gilbert, AZ, JPL's primary industrial partner in Deep Space 1 spacecraft development. Credit: National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California / Spectrum Astro / International Technology Education Association. © 1996 Spectrum Astro, Inc., then owned by General Dynamics, now owned by Orbital Sciences Corportation. With permission from Orbital Sciences Corporation.