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The volume of space between the Earth’s surface out to geosynchronous orbit is enormous—equivalent to 240,000 times all the Earth’s oceans. Yet the number of objects calling that volume home is growing all the time—not just with satellites but with debris of all kinds, natural and manmade. And keeping track of it all is becoming a real-time, non-trivial challenge. “That is why the U.S. Department of Defense has made space situational awareness a top priority and why few areas of DARPA research are as important to the future of U.S. and global security as helping to secure this most strategic frontier,” said Dr. Steven Walker, DARPA Deputy Director, at the Transition Ceremony for the Space Surveillance Telescope.
Space situational awareness (SSA) is the foundational element of space security, and it entails keeping track of all natural and artificial space objects, energy and particle fluxes and understanding how the space picture is changing over time. SSA is a system of systems dealing with space surveillance, space weather and NEOs. Comprehensive SSA requires a networked system of radars and electro-optical sensors.
The US Space Surveillance Network (SSN) is the principal system used to detect, track and identify objects orbiting earth. It has the best set of SSA capabilities, operating a global network of 30+ ground based radars and optical telescopes and 2 satellites in orbit. It maintains the most complete tracking database of 23,000+ space objects bigger than 10 cm. SSN largely relies on phased array radars that are also used for early missile warning sensors .The data is fed to the Joint Space Operations Center (JSpOC) in California that provides a range of data and services for US government, satellite operators, and public.
Ground-based telescopes have long been the workhorses of astronomical research. Compared to space-based telescopes, ground-based telescopes have much to offer. They can be built bigger and for less money. They’re easier to maintain and upgrade. Practically speaking, they also have a much lower risk of being damaged by one of the 500,000 pieces of debris flying through the cosmos—or space junk. But increasingly, scientists and engineers are turning to space as the new frontier for advanced telescopes. The trend toward space telescopes began in the 1960s, when astronomers started attaching giant balloons to telescopes as a means to carry them above Earth’s lower atmosphere.
When a telescope on the ground looks to the cosmos and takes a picture, the light it captures has first travelled through air in the atmosphere. If that air is at all turbulent, it blurs the light. This is termed “atmospheric distortion.” It’s the reason stars seem to “twinkle” when we look at them from Earth, and also the reason many ground-based telescopes can’t take super-sharp images of objects in space. Newer, more advanced ground-based telescopes implement adaptive optics, a technique to sharpen blurry images right as they’re being taken.
An adaptive optics system uses lasers, supercomputers, and an array of mirrors to correct atmospheric distortion. To sharpen an image with adaptive optics, astronomers will pick a point of light, called a “guide star.” They’ll measure and monitor how its light waves bends as they move through Earth’s atmosphere, and then send that information, via supercomputer, to the telescope’s mirrors. In response, the mirrors bend in a way that straightens out the light waves as they are reflected onto the telescope. Of course, there isn’t always a guide star near enough to the object that an astronomer is studying, and, in that case, astronomers use lasers as a guide star instead.
Space Based Space Surveillance
The Space Based Space Surveillance (SBSS) operates 24-hours a day, 7-days a week collecting metric and Space Object Identification data for man-made orbiting objects without the disruption of weather, time of day and atmosphere that can limit ground-based systems. SBSS has a clear and unobstructed view of resident space objects orbiting earth from its 390-mile altitude orbit.
SBSS communicates information through the world-wide Air Force Satellite Control Network and commercial Unified Space Network ground stations and then to Schriever Air Force Base, Colo., where operators oversee the day-to-day command and control operations of SBSS. This satellite system can monitor very small objects all the way out to the Geosynchronous belt. SBSS provides the data necessary to predict the trajectories of these objects, which gives experts an idea if an orbiting satellite may collide with another orbiting object, which allows time for evasive action to be taken in order to avoid collisions.
SBSS was launched from Vandenberg AFB, Calif., Sept. 25, 2010. The first signals from the space surveillance satellite were received a short time later at the Satellite Operations Center at Schriever AFB. U.S. Air Force Space Command declared that the SBSS satellite reached Initial Operating Capability on Aug. 17, 2012. SBSS is the follow-on to the Midcourse Space Experiment (MSX) satellite, which was the first space-based sensor to contribute to the Space Surveillance Network after initially being a technology demonstration to identify and track ballistic missiles during their midcourse flight phase.
SBSS uses a visible sensor mounted on an agile, two-axis gimbal, which allows ground operators to quickly move the camera between targets without having to expend time and fuel to reposition the entire spacecraft.
Boeing awarded $21.2M contract to maintain surveillance satellite
Boeing has been awarded a $21.2 million contract modification for sustainment and development for the Air Force’s space based surveillance system , the Department of Defense announced in Dec 2019. The modification funds systems engineering, operations, operations support and contractor logistics support for the Space Based Space Surveillance Block 10.
The SBSS Block 10 was launched in 2010 and became operational in 2013. It watched the geostationary orbit arc where most military and civil communication satellites are stationed. The total cumulative value of the contract to date is is $129.9 million. The deal obligates $2 million at the time of the award. Work on the satellite will be performed at El Segundo, Calif., and Colorado Springs, Colo., and is expected to be completed by 2022.
DEMI (Deformable Mirror) is a tiny military CubeSat satellite, owned by DARPA, the Pentagon’s research division, and launched from the International Space Station that will use its camera to focus on the dim, distant objects in space that usually get washed out by nearby stars or other larger objects. DeMi is drastically smaller than famous space cameras like the Hubble Space Telescope, but DARPA is counting on its ability to focus on overlooked celestial bodies to vastly improve the images scientists can capture.
Space based surveillance technologies
A recently deployed DARPA CubeSat seeks to demonstrate technology that could improve imaging of distant objects in space and allow powerful space telescopes to fit into small satellites. DARPA’s Deformable Mirror (DeMi) CubeSat deployed from the International Space Station July 13, beginning the technology demonstration of a miniature space telescope with a small deformable mirror called a microelectromechanical systems (MEMS) mirror.
DeMi made first contact about a week following launch, demonstrating the expected power from its solar arrays, as well as correct spacecraft pointing and stable temperatures. The team will focus on payload checkout over the coming days. Deformable mirrors can adjust the shape of their reflective surfaces to correct for the effects of temperature and mechanical changes on a space telescope, improving image quality. The experiment will measure how well a MEMS deformable mirror performs in space, from the rocket launch through its time in orbit experiencing the thermal and radiation environment.
“Space telescopes currently in orbit are limited in ability to detect and distinguish small, dim objects next to large, bright objects – for example, dim exoplanets next to bright stars. Deformable mirrors have proven successful in ground-based applications, but their performance has not been tested in long duration space operations,” said Stacie Williams, the program manager for DeMi in DARPA’s Tactical Technology Office. “Our goal is to demonstrate the benefits of a MEMS deformable mirror to actively correct the images of distant objects in space.”
The primary mirror of the DeMi telescope is about an inch wide, and the deformable mirror surface is about the size of a dime. The DeMi payload can observe stars with the telescope and use an internal laser for calibration measurements of the deformable mirror. When the payload observes stars, the deformable mirror will keep the star centered on the imaging camera. The MEMS mirror has 140 actuators, tiny moving surfaces that control the mirror shape. Calibration measurements will track the performance using about 50 actuators over time in the space environment.
DeMi also aims to demonstrate wavefront correction, where the payload measures the wavefront, or shape of misalignments in the optical system. The deformable mirror corrects these errors by changing shape, acting like the opposite of a distorting funhouse mirror. After making observations, the DeMi spacecraft will downlink images from the wavefront sensors so operators can monitor the deformable mirror behavior from the ground.
These changes are needed because when you’re in orbit, conditions can be rough. One side of your satellite can be burning hot in the sun, while the other can be freezing cold. As the temperature changes, the parts change size and move. Rotating and thrusting can make things vibrate as well. “All of these disturbances make tiny little speckles on the pictures that you’re taking,” says Kerri Cahoy, an associate professor of aeronautics and astronautics at MIT.
To fix this, the mirror can sense errors in the picture, and bend to correct them. It does this by analyzing the light as it hits the mirror. Printed circuit boards send signals to rods, which adjust the shape of the mirror accordingly. It doesn’t need to move a lot: we’re talking 10 to 20 nanometers. But these slight changes could combat any distortion in the light the telescope is picking up. “One nice thing about this type of technique is that the contrast is so good,” says Paula do Vale Pereira, an MIT PhD student and mechanical lead on the project.
The DARPA DeMi team includes Aurora Flight Sciences; Massachusetts Institute of Technology, which designed and built the optical payload; and Blue Canyon Technologies, which designed and built the spacecraft bus. DeMi arrived to the space station in February aboard a cargo resupply mission, packed into a NanoRacks CubeSat Deployer. The mission is anticipated to last about a year.
DARPA CubeSat experiment may support future Space Force initiatives
A new CubeSat experiment by the Defense Advanced Research Projects Agency (DARPA), designed to explore the use of microelectronic materials in extra-terrestrial environments, could pay dividends for future capabilities fielded by the US Space Force and the Pentagon’s Space Development Agency.
DARPA’s Deformable Mirror (DeMi) CubeSat programme was launched from the International Space Station (ISS) in July 2020. The deployment of the DeMi CubeSat kicked off the initial phase of the agency’s technology demonstration of the microelectromechanical systems (MEMS) mirror, mounted inside a CubeSat-deployable miniature telescope, a DARPA fact sheet stated. The agency’s Tactical Technology Office is the directorate spearheading the DeMi CubeSat and MEMS mirror demonstration programmes.
“This [launch] is exploring how to produce very high-quality optical characteristics, optical apertures using microelectronic materials” that can withstand the rigors of operating in a space environment, DARPA Acting Director Peter Highnam told a small group of reporters on 30 July.
Specifically, the microelectronic elements integrated into the MEMS mirror will be able to responsively adjust the angle and shape of the mirror’s reflective surface, the fact sheet stated. The reactive responses in the MEMS mirror are designed to counter dramatic changes in temperature or mechanical changes aboard the telescope itself, it added. Those temperature or mechanical changes can negatively affect the imagery produced by the telescope or the equipment itself.
“This is us de-risking things,” in terms of ensuring the quality of the telescope’s imagery and the durability of the system, Highnam said regarding the need for the DeMi CubeSat programme. “These and other technologies we are doing are guaranteed to be of great use to the Space Force” in conjunction with the Pentagon’s Space Development Agency, he added.
References and Resources also include:
https://www.darpa.mil/news-events/2020-07-28
