Photonics Not Lost in Space

Gaynell Terrell

The "better" part of "faster, better, cheaper" as it applies to NASA's mandate for low-cost space missions is better technology to send back ample information from those hard-to-scratch parts of our galaxy.

There's a place for photonics in this formula, said scientists attending the fourth International Conference on Low-Cost Planetary Missions in May at the Johns Hopkins University Applied Physics Laboratory. The International Academy of Astronautics sponsored the conference.

Speakers said low-cost space missions depend on reducing the scope of science objectives, when necessary; keeping the spacecraft simple and easy to test; and using or modifying existing technology. Professor Maria Zuber of the Massachusetts Institute of Technology in Cambridge said that there is still a place for large-scale space missions but that advancing space science also calls for small, limited missions that go a lot of places.

Photonic instruments are already blazing trails in low-cost space missions, said conference speaker Andrew Cheng, project scientist with Johns Hopkins. Since February, the Near Earth Asteroid Rendezvous spacecraft has orbited asteroid 433 Eros, its laser rangefinder busily mapping high-resolution topographical landmarks. The rangefinder is a direct-detection lidar system with a GaAs diode-pumped Nd:YAG laser. A separate receiver contains an extended infrared avalanche-photodiode detector with a 7.62-cm clear aperture Dall-Kirkham telescope. In this case, photonics is saving money by using one high-performance instrument for several functions.

"Laser radar is proving to be very crucial to the navigation of the spacecraft -- it tells you how high up you are. A camera can't tell you how far away you are, and radio tracking all by itself does not do the job," Cheng said.

The Near Earth Asteroid Rendezvous spacecraft includes a laser radar to map the surface of asteroid 433 Eros and help steer the spacecraft.

Other participants lobbied for lightweight optics in space, saving money because less rocket power is needed to launch them. Robert C. Romeo, president of Composite Mirror Applications Inc. of Tucson, Ariz., said it is possible to replicate multimeter telescope mirrors, which combine very low areal density, large apertures, high surface smoothness and high optical quality -- all sufficiently lightweight for launch by a (relatively small) Pegasus rocket.

"We have been looking at our costs compared to other lightweight optics," Romeo said. "We have replicated optics -- we make sure one master is in good shape -- and that works very well as far as costs go." The company is working with Goddard Space Flight Center in Baltimore to develop a robotic telescope that can be deployed on the moon.