Back to the Future - Serviceable Spacecraft Make a Comeback


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Ever wonder about the future of space science? Hop inside a time machine that transports you back 40 years and you may get a good idea about where things are headed. History, it would seem, has a funny way of repeating itself.

Serviceable spacecraft — like the NASA-developed Multi-Mission Modular Spacecraft (MMS) and, of course, the iconic Hubble Space Telescope that NASA conceived and developed in the 1970s with servicing in mind — are once again de rigueur. (The serviceable MMS shouldn’t be confused with NASA’s Magnetospheric Multiscale mission, which also goes by the MMS acronym.)

Case in point: As required by Congress in a law passed in 2010 and then amended five years later, NASA is requiring that proposed flagship astrophysics missions support servicing, even if their orbits are up to a million miles away. The agency also released a Request for Information (RFI) seeking ideas for a spacecraft design that it could use for both its proposed Asteroid Redirect Mission (ARM) and as a vehicle for refueling a government satellite in low-Earth orbit.

“The 40-year cycle is starting all over again,” said Benjamin Reed, deputy project manager of the Satellite Servicing Capabilities Office (SSCO) at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. SSCO personnel developed all of the technologies to service Hubble and is now creating and demonstrating next-generation servicing technologies, including validation experiments on the International Space Station. “It worked with Hubble. It would be crazy not to think it would work again. It’s back to the future.”

And according to him, NASA is well along the way to realizing that future — even if it means servicing spacecraft positioned tens of thousands of miles away from terra firma.

What’s Different Today

Satellite servicing certainly isn’t new — as evidenced by the five Hubble servicing missions and the 1984 repair of the Solar Max mission that used the MMS serviceable satellite bus.

What’s different today is where these operations are expected to occur in the future and the technology needed to ensure success. Robotic spacecraft — likely operated with joysticks by technicians on the ground — would carry out the hands-on maneuvers, not human beings using robotic and other specialized tools, as was the case for low-Earth-orbiting Hubble and Solar Max.

“Goddard knows how to service satellites in low-Earth orbits,” said Michael Kienlen, an SSCO engineer who is studying servicing beyond low-Earth orbit. “However, future flagship missions, including the WFIRST-AFTA (Wide-Field Infrared Survey Telescope-Astrophysics Focused Telescope) and other future observatories should operate in more distant orbits.”

WFIRST-AFTA, which NASA plans to equip with an 8-foot (2.4-meter) mirror and a slitless spectrometer and imager, will study dark energy, the mysterious form of energy that permeates all of space and accelerates the expansion of the universe, while providing cosmic surveys. It also will carry a coronagraph that will allow the observatory to image giant exoplanets and debris disks in other solar systems.

Other conceptual missions that various groups currently are studying in preparation for the 2020 Astrophysics Decadal Survey also could operate in more distant orbits.

Although still in the conceptual stage, these missions may carry very large primary mirrors that would allow scientists to study cosmological targets with greater resolution and sensitivity. One possible scientific objective would be to find Earth-size exoplanets [This links to the story about the VNC] in the habitable zone in our solar neighborhood and then identify chemicals in their atmospheres that may indicate the presence of life.

To achieve these ambitious goals, WFIRST and the other conceptual observatories ideally would operate from Sun-Earth L2 (SEL2), a thermally stable sun-Earth orbit roughly a million miles away.

Due to concerns that technologies might not exist to service SEL2-orbiting missions, some have recommended that the observatories fly in geostationary orbit (GEO), roughly 10 percent of the distance to the moon.

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