OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is a NASA asteroid-study and sample-return mission. The mission’s primary goal is to obtain a sample of at least 60 g (2.1 oz) from 101955 Bennu, a carbonaceous near-Earth asteroid, and return the sample to Earth for a detailed analysis. The material returned is expected to enable scientists to learn more about the formation and evolution of the Solar System, its initial stages of planet formation, and the source of organic compounds that led to the formation of life on Earth.
OSIRIS-REx was launched on 8 September 2016, flew past Earth on 22 September 2017, and rendezvoused with Bennu on 3 December 2018. It spent the next several months analyzing the surface to find a suitable site from which to extract a sample. On 20 October 2020, OSIRIS-REx touched down on Bennu and successfully collected a sample. Though some of the sample escaped when the flap that should have closed the sampler head was jammed open by larger rocks, NASA is confident that they were able to retain between 400 g and over 1 kg of sample material, well in excess of the 60 g (2.1 oz) minimum target mass. OSIRIS-REx is expected to return with its sample to Earth on 24 September 2023 and subsequently start its new mission to study 99942 Apophis as OSIRIS-APEX (‘APophis EXplorer’), arriving at that asteroid in 2029.
Bennu was chosen as the target of study because it is a “time capsule” from the birth of the Solar System. Bennu has a very dark surface and is classified as a B-type asteroid, a sub-type of the carbonaceous C-type asteroids. Such asteroids are considered primitive, having undergone little geological change from their time of formation. In particular, Bennu was selected because of the availability of pristine carbonaceous material, a key element in organic molecules necessary for life as well as representative of matter from before the formation of Earth. Organic molecules, such as amino acids, have previously been found in meteorite and comet samples, indicating that some ingredients necessary for life can be naturally synthesized in outer space.
The cost of the mission is approximately US$800 million, not including the Atlas V launch vehicle, which is about US$183.5 million. It is the third planetary science mission selected in the New Frontiers program, after Juno and New Horizons. The principal investigator is Dante Lauretta from the University of Arizona. If successful, OSIRIS-REx will be the first United States spacecraft to return samples from an asteroid. The Japanese probe Hayabusa returned samples from 25143 Itokawa in 2010, and Hayabusa2 returned from 162173 Ryugu in December 2020. On 10 May 2021, OSIRIS-REx successfully completed its departure from Bennu and began its two-year return to Earth.
The Lunar Reconnaissance Orbiter (LRO) is a NASA robotic spacecraft currently orbiting the Moon in an eccentric polar mapping orbit. Data collected by LRO have been described as essential for planning NASA’s future human and robotic missions to the Moon. Its detailed mapping program is identifying safe landing sites, locating potential resources on the Moon, characterizing the radiation environment, and demonstrating new technologies.
Launched on June 18, 2009, in conjunction with the Lunar Crater Observation and Sensing Satellite (LCROSS), as the vanguard of NASA’s Lunar Precursor Robotic Program, LRO was the first United States mission to the Moon in over ten years. LRO and LCROSS were launched as part of the United States’s Vision for Space Exploration program.
The probe has made a 3-D map of the Moon’s surface at 100-meter resolution and 98.2% coverage (excluding polar areas in deep shadow), including 0.5-meter resolution images of Apollo landing sites. The first images from LRO were published on July 2, 2009, showing a region in the lunar highlands south of Mare Nubium (Sea of Clouds).
The total cost of the mission is reported as US$583 million, of which $504 million pertains to the main LRO probe and $79 million to the LCROSS satellite. As of 2019, LRO has enough fuel to continue operations for at least seven more years, and NASA expects to continue utilizing LRO’s reconnaissance capabilities to identify sites for lunar landers well into the 2020s.
NASA’s Starling mission is advancing the readiness of various technologies for cooperative groups of spacecraft – also known as distributed missions, clusters, or swarms. Starling will demonstrate technologies to enable multipoint science data collection by several small spacecraft flying in swarms. The six-month mission will use four CubeSats in low-Earth orbit to test four technologies that let spacecraft operate in a synchronized manner without resources from the ground. The technologies will advance the following capabilities: swarm maneuver planning and execution, communications networking, relative navigation, autonomous coordination between spacecraft.
The Starling mission will test whether the technologies work as expected, what their limitations are, and what developments are still needed for CubeSat swarms to be successful.
Distributed spacecraft are advantageous because they can act in unison to achieve objectives. Incorporating autonomy allows these missions to act cooperatively with minimal oversight from the ground. Autonomy ensures that a mission continues to perform through periods when communications with a spacecraft from the ground is temporarily unavailable because of distance or location. Spacecraft swarms operating at great distances from the Earth must act more autonomously due to the delays in time communicating with Earth ground stations.
Clustering satellites into a swarm requires planning and executing multiple maneuvers for each spacecraft. Managing these operations from the ground becomes impractical as the size of the swarm grows or the time delay in communicating with the spacecraft increases. The Starling mission will test technologies that traditionally run ground-oriented operations but are now shifted to operate onboard the spacecraft.
Having the spacecraft in a swarm operate autonomously is essential to making distributed spacecraft missions affordable and highly scaleable. Starling is a first step in developing this new mission architecture that could eventually allow for autonomous swarms of many spacecraft and at greater distances from Earth.
The four 6-unit CubeSats (each about the size of two stacked cereal boxes) will fly in a Sun-synchronous orbit more than 300 miles above Earth and no more than 170 miles apart from each other. The spacecraft will fly in two formations. First, they will begin in line, or in-train, like a string of pearls. Then, the CubeSats will move out of the in-train configuration and into a set of stable relative orbits known as passive safety ellipses.
The following four technologies will be tested:
Reconfiguration and Orbit Maintenance Experiments Onboard (ROMEO): In each phase, cluster flight control software will initially operate in shadow mode, autonomously planning maneuvers while the CubeSats are controlled from the ground. Once validated, ROMEO will demonstrate execution of swarm maintenance maneuvers from aboard the spacecraft without ground intervention. The performance of those maneuvers will then be evaluated.
Mobile Ad-hoc Network (MANET): The CubeSats will be able to communicate with each other via two-way S-band crosslink radios/antennas, adapting a ground-based network protocol for reliable space communication across any spacecraft node within the swarm. If one spacecraft communications node fails, the communications route automatically reconfigures to maintain full communication capabilities for the remaining operational swarm of spacecraft.
Starling Formation-Flying Optical Experiment (StarFOX): Using commercial star trackers, which are onboard cameras that measure the position of stars, each spacecraft determines its own orientation relative to the stars. An advanced navigation algorithm utilizes this orientation data and star tracker images to visually detect and track the other three spacecraft within the swarm to perform relative-position knowledge tests. The goal is for each spacecraft to achieve onboard awareness of its location as well as the location of the other three spacecraft.
Distributed Spacecraft Autonomy (DSA): This experiment will demonstrate autonomous monitoring of Earth’s ionosphere, the layer between our atmosphere and the beginning of space, with a spacecraft swarm. This is intended as a representative measurement to demonstrate autonomous reactive operations for future missions. Starling’s dual-band GPS receivers are used to measure the density of atmospheric regions. Each orbiting Starling spacecraft constantly changes position relative to the atmospheric phenomenon and the GPS satellites. Therefore, the most interesting source of information changes over time, requiring changes to the monitoring strategy in response to observations. DSA onboard software will autonomously coordinate the selection of the best GPS signals, across all Starling spacecraft, to accurately capture regions of higher or lower ionospheric density. This is accomplished by first sharing information over the crosslink network to maintain a consistent state, then selecting the GPS signals to prioritize and share in the future. The ability to evaluate data as it is collected, balance promising observations with coverage to ensure other interesting information is not missed, and autonomously coordinate measurements, is an enabling technology for future science missions.
It’s important to note that although Starling is being tested in low-Earth orbit, the technologies apply equally as well to deep space applications. In the future, constellation-like swarms of autonomously operating CubeSats could provide NASA and commercial missions in deep space with navigation services akin to GPS and communications relays provided by Earth’s network of communications satellites. Distributed spacecraft can also work together to collect multi-point science data and prepare for exploration missions by positioning multiple small spacecraft to function as one very large observation instrument. This could support the identification of resources for long-term presence on the Moon. Another example of this cooperative work might include telescopes mounted on multiple small spacecraft and trained on a particular observation target, creating a larger field of view than possible with a single telescope.
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