Introducing PolyCam, MapCam and SamCam, the three UA-built cameras that will guide the OSIRIS-REx spacecraft to its target asteroid, Bennu, and document the sampling mission.
Soon after the OSIRIS-REx spacecraft blasts into the sky over Cape Canaveral, Florida, in September 2016 and glides through space while Earth is shrinking to a mere dot in the black void, it will rely on a sophisticated set of electronic eyes designed and made by UA scientists and engineers for all tasks during its mission.
Later this month, the OSIRIS-REx Camera Suite, or OCAMS, will be delivered to the Lockheed Martin spacecraft assembly facility in Littleton, Colorado, to be integrated into the spacecraft structure, ahead of schedule.
OCAMS is a set of three cameras designed to support the mission to the asteroid Bennu through all of its phases, from approach to sample collection.
“The camera suite on board the spacecraft is similar to a lookout perched in the crow’s nest of a tall ship,” said OCAMS instrument scientist Bashar Rizk, who has been with the OSIRIS-REx team nearly from the beginning in 2006. “This scout must observe Bennu as we approach, survey and recon the asteroid, and tell the ship’s navigator where the hazards are located.”
The design of OCAMS will allow the mission to image Bennu from spotting the target asteroid over an initial distance of more than a million miles all the way to monitoring the sampling process 10 feet from Bennu’s surface, Rizk said.
Rizk said the overall design principle of the three cameras, which have been designed, constructed and tested over the past four years at the UA’s Lunar and Planetary Laboratory, is not unlike that of the human eye.
“The three OCAMS cameras differ from each other, but they belong to the same family,” he said. “They use identical detector assemblies — ‘retinas,’ if you will — to record the images they acquire. They each possess mechanisms actuated by identical motors — think ‘muscles’ — and they share the same unified electronics controller that serves as their ‘brain.'”
Together, these three visual siblings greatly increase the spacecraft’s ability to successfully navigate, explore and sample Bennu. By supplying OCAMS under a $40 million contract from NASA, the UA provides a sizable contribution to the OSIRIS-REx mission in addition to leading the mission and serving as its headquarters.
OSIRIS-REx will be the first U.S. mission to return samples from an asteroid to Earth. The spacecraft is scheduled to bring back a sample of at least 60 grams (2.1 ounces) for study.
OSIRIS-REx carries five instruments that will remotely evaluate the surface of Bennu. The mission will help scientists investigate the composition of the very early solar system and the source of organic materials and water that made their way to Earth, and improve the understanding of asteroids that could impact our planet. The spacecraft will reach Bennu in 2018 and return a sample to Earth in 2023.
Scooping up a sample from a space rock hundreds of millions of miles from Earth is no small feat. The complexity of the mission is one of the reasons the spacecraft is fitted with three cameras. The other is redundancy: The cameras can provide backup if the need arises.
“Our mission tries to attempt a lot of things at the same time,” Rizk said. “Navigation, mapping, reconnaissance, sample site selection, sampling — we do it on the same trip, so we need to understand what is going on at the asteroid at all times, so we can make decisions in real time when we’re there. The most important goal of these cameras is to maximize the chances of successfully bringing back a sample.”
Here are the basics on the three cameras and their respective functions:
- PolyCam: Similar to a scout’s spyglass, this instrument is essentially an 8-inch telescope that doubles as a microscope. It will be the first to spot the asteroid from a million miles away. Once closer, PolyCam will help identify dangerous areas on the asteroid’s surface by spotting and mapping large boulders and rocks, and characterize a dozen prospective sample sites in detail. It has a focus mechanism that converts it from a telescope into a microscope, “allowing our scout to scrutinize the tiniest rocks and pebbles on the asteroid to ensure that they are small enough to fit into the sample head,” Rizk said. “It is this dual nature —telescope turned microscope — that gives the PolyCam its name, because it’s the polymath among the three OCAMS instruments.”
- MapCam: The medium-resolution Mapping Camera, or MapCam, will search for potential hazards to the spacecraft, such as small rocks trapped in Bennu’s orbit, or outgassing plumes. MapCam will map the entire surface of Bennu from a safe distance of three miles, watching Bennu spin through a whole asteroid day every four hours and 20 minutes.
- SamCam: Once a suitable sampling site has been identified, the Sampling Camera, or SamCam, continuously documents the spacecraft’s final trip onto the asteroid’s surface and the sampling sequence. OSIRIS-REx is equipped to make three attempts at scooping up a sample of material from Bennu’s surface. SamCam watches as the spacecraft’s sampling arm touches the surface and jets of nitrogen gas blow pebbles and dust into the sampling chamber. During sampling, SamCam wears “safety goggles” in the form of one of three filters that are placed in front of the lens. “Some of the filters carried by the cameras have power like reading glasses,” Rizk said. “SamCam has one that allows it to look as closely as six feet from the sample canister to make sure the sample is in there before it gets sealed in the return capsule.”
PolyCam’s optics and structure were made through a joint program between the UA College of Optical Sciences and LPL, while SamCam and MapCam were made exclusively by LPL. Only the detectors itself were acquired from outside the UA, Teledyne DALSA’s custom division in Waterloo, Ontario, while Space Dynamics Laboratory of Utah State University Research Foundation in Logan, Utah, provided the detector read-out assemblies. LPL engineers and technicians also completed the final assembly of all OCAMS components, ensured their functionality and calibrated them.
Now that OCAMS is being delivered to be readied for its journey into space, it leaves a lasting legacy for the UA: PolyCam’s focus mechanism has been patented as LPL’s first patent, and while the team that built the cameras has done its work, an engineering center will remain at LPL to take on outside work from companies such as Raytheon and others.
“It has been a good collaboration,” Rizk said. “One of the advantages of the University is that it pools expertise, in this case Steward Observatory, LPL and the College of Optical Sciences, to accomplish things no single unit could accomplish on its own.”
OCAMS benefited from the UA’s long and rich heritage in space science and space hardware. Its design was informed by DISR, the Descent Imager/Spectral Radiometer carried by the Huygens probe, which landed on and provided the first images from the surface of Saturn’s moon Titan as part of the Cassini mission. For that project, Rizk worked with Peter Smith, who would later become principal investigator of the Phoenix Mars Lander mission, and also with Chuck Fellows, who would later become program manager for OCAMS. Also leading an experiment on Phoenix was Bill Boynton, who is currently the OSIRIS-REx mission instrument scientist.
“Peter and Bill assembled a high-powered crew of engineers for Phoenix, many of which are on the OCAMS project,” Rizk said. “We’re like a family, we have many ties and shared technical experience. That’s very important on a project like this.”
The UA’s involvement in the Huygens probe led to several Mars missions, such as Pathfinder, the Phoenix Lander and HiRISE — and now OSIRIS-REx, Rizk said.
“What really carries over is the people working on those things,” he said, “and their combined lab facilities, expertise and acquired experience.”
The OCAMS team is led by Fellows, deputy program manager Cat Merrill, Rizk and Christian d’Aubigny, who serves as the deputy instrument scientist and lead optical engineer.
“I have especially enjoyed working with our students,” Rizk said. “At least a dozen undergraduates have been working on this project, and they get to do everything from systems engineering to mechanical engineering, from electronic engineering to testing, all the way to business management.”
Source: University of Arizona