![]() Specifically, it’s important that at least one of the probes passes near to the asteroid. For smaller asteroids, the deployment randomness becomes more important. For asteroids with radii of 2.5 km, the simulations suggest that OpGrav would enable us to determine the mass of the asteroid to within 1% of the true value. Each bar gives the results for a selection of flyby velocity and asteroid radius. Here, performance is defined as the percent error of the result provided by simulated measurements after being processed by the OpGrav algorithms. That is, the top of the bar corresponds to the performance that was achieved by at least 90% of the simulated cases. The bottom, middle, and top of each bar is associated with the 10th, 50th, and 90th percentile results. In this case, we modeled the long-range imager that is flying on the New Horizons spacecraft.Įach bar is associated with 200 simulations of the same flyby scenario, but with a randomly drawn deployment profile. The figures below show the results of these simulations, where 3 probes are deployed and tracked with an optical imager. They also varied the deployment characteristics to represent practical limitations of targeting, pointing, and pre-flyby asteroid knowledge. For this flyby scenario, we simulated varying speeds of the spacecraft and sizes of the asteroid. As an example, we developed a hypothetical trajectory that passes by an asteroid in an orbit similar to Eros. They use simulations to characterize the performance of this concept under different conditions. These angular measurements are ingested into an optimal estimation tool that statistically infers the small body’s mass. From sets of images, they can record the angular locations of the probes with respect to the stars throughout the encounter. Theu call this approach Optical Gravimetry, or OpGrav. The most near-term, lowest risk approach is to use an optical imager on-board the host spacecraft. They have evaluated a suite of possible tracking methods to enable this mass measurement, including optical imagers, radiofrequency (RF) beacons and receivers, and active radar or lidar. ![]() * Finally, many probes can be deployed to obtain sets of independent measurements, which enable cross-validation of the results. This can be limited in traditional approaches. * The location of the probes flyby can be tailored to maximize the measurable deflection. Traditional methods use tracking from Earth, where the spacecraft is typically millions to hundreds of millions of kilometers away. * The measurements of the probes’ locations relative to the host spacecraft are accurate because the tracking range is within 100’s or 1000’s of kilometers. * The probes can pass very close to the asteroid’s surface, where they experience a much higher acceleration than the host spacecraft. This approach offers a high accuracy mass measurement for a variety of reasons: By measuring the deflection in each probe’s motion, we can achieve a very sensitive mass asteroid measurement, exceeding current capabilities by roughly an order of magnitude. The probes are deployed from a spacecraft and tracked as they pass near to the small body. Swarm Flyby Gravimetry is a concept to determine the mass of asteroid or comets during flyby using a collection of small, disposable tracking targets called probes.
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