Search

Rapid reconnaissance flyby missions are highly desirable for planetary defense due to their ability to quickly characterize a potentially hazardous asteroid. However, traditional flybys lack the ability to measure some of the most important characteristics of an asteroid: mass, density, and porosity. These highly related features are needed to estimate potential damage to Earth and to plan mitigation strategies. Using standard Earth-based ranging and Doppler tracking of the spacecraft as it flies by is not sufficient for the smaller asteroids that are of most concern for planetary defense. In this study, we apply a new technique, Doppler Gravimetry (DopGrav), to the 2023 Planetary Defense Conference hypothetical impact scenario. DopGrav supplements traditional Earth-based tracking of the flyby spacecraft with Doppler and optical measurements from the spacecraft to one or more test-masses that can pass much closer to the asteroid. We augmented the scenario reconnaissance flyby mission with a 6U CubeSat test mass, and use a similar concept of operations to what was demonstrated by LICIACube and DART. We show that with this addition, it would be possible to measure the mass of the hypothetical asteroid to better than 3% 1 σ. This would greatly increase the utility of such a flyby reconnaissance mission and if the scenario were real it would allow for a much more tailored response to mitigate the asteroid. • Radiofrequency and optical tracking of CubeSat improves asteroid flyby mass estimation. • CubeSat deployment and operations concept similar to those used for successful LICIACube mission hosted on DART. • Doppler gravimetry could measure mass of hypothetical impact asteroid to better than 3% 1 σ. [ABSTRACT FROM AUTHOR]

Double Asteroid Redirection Test will be the first mission to demonstrate and characterize the concept of a kinetic impactor for planetary defense, by impacting the smaller member of a binary asteroid system Didymos. The results of this mission will have implications for planetary defense, near-Earth object science, and resource utilization. This research focuses on the heliocentric transfer phase of the mission. The heliocentric trajectory is evaluated using various objective functions, including a search for the latest possible Earth escape date, the shortest time of flight, and the maximum impact energy. Also included in the search is the potential to use Earth gravitational assists, which proves not to offer any useful advantages. A new way to assess the trajectory's margin for missed thrust is used, which quantifies the ability of the spacecraft to recover its mission following unplanned nonthrusting events, such as safe mode. The baseline trajectory is shown to be capable of recovering from missed-thrust events lasting 14 days using only 1% of its propellant as margin. Finally, contingency trajectories that attempt to impact Didymos at a subsequent perihelion are considered. [ABSTRACT FROM AUTHOR]

The on-orbit deployment of large numbers of nanosatellites is cast in terms of the relative motion equations, augmented with differential drag. Using this framework, a methodology is developed for minimizing the likelihood of recontact or interference among the deployed nanosatellites. This approach is applied to a representative test case derived from the Operationally Responsive Space Office's Launch Enabler Mission, which delivered 28 small payloads to orbit in 2013. By strategically varying the deployment order, timing, and launch vehicle attitude, the net separation among each of the nanosatellites is demonstrated for the first three weeks with minimal close approaches. These results are validated using high-fidelity simulations. [ABSTRACT FROM AUTHOR]

This study presents interplanetary trajectory options for the Double Asteroid Redirection Test (DART) spacecraft to reach the near Earth object, Didymos binary system, during its 2022 Earth conjunction. DART represents a component of a joint NASA-ESA mission to study near Earth object kinetic impact deflection. The DART trajectory must satisfy mission objectives for arrival timing, geometry, and lighting while minimizing launch vehicle and spacecraft propellant requirements. Chemical propulsion trajectories are feasible from two candidate launch windows in late 2020 and 2021. The 2020 trajectories are highly perturbed by Earth's orbit, requiring post-launch deep space maneuvers to retarget the Didymos system. Within these windows, opportunities exist for flybys of additional near Earth objects: Orpheus in 2021 or 2007 YJ in 2022. A second impact attempt, in the event that the first impact is unsuccessful, can be added at the expense of a shorter launch window and increased (∼3x) spacecraft Δ V . However, the second impact arrival geometry has poor lighting, high Earth ranges, and would require additional degrees of freedom for solar panel and/or antenna gimbals. A low-thrust spacecraft configuration increases the trajectory flexibility. A solar electric propulsion spacecraft could be affordably launched as a secondary spacecraft in an Earth orbit and spiral out to target the requisite interplanetary departure condition. A sample solar electric trajectory was constructed from an Earth geostationary transfer using a representative 1.5 kW thruster. The trajectory requires 9 months to depart Earth's sphere of influence, after which its interplanetary trajectory includes a flyby of Orpheus and a second Didymos impact attempt. The solar electric spacecraft implementation would impose additional bus design constraints, including large solar arrays that could pose challenges for terminal guidance. On the basis of this study, there are many feasible options for DART to meet its mission design objectives and enable this unique kinetic impact experiment. [ABSTRACT FROM AUTHOR]

Abstract: Taking inspiration from the orbital dynamics of dust, we find that spacecraft length scaling is a means of enabling infinite-impulse orbits that require no feedback control. Our candidate spacecraft is a 25μm thick, 1cm square silicon chip equipped with signal transmitting circuitry. This design reduces the total mass to less than 7.5mg and enables the spacecraft bus itself to serve as a solar sail with characteristic acceleration on the order of 0.1mm/s2. It is passive in that it maneuvers with no closed-loop actuation of orbital or attitude states. The unforced dynamics that result from an insertion orbit and a launch-vehicle separation determine its subsequent state evolution. We have developed a system architecture that uses solar radiation torques to maintain a sun-pointing heading and can be fabricated with standard microfabrication processes. This architecture has potential applications in heliocentric, geocentric, and three-body orbits. [Copyright &y& Elsevier]

Low-thrust trajectories to the moon are attractive for many proposed and selected SmallSat missions due to their low-fuel requirements and reduced launch cost. However, designing these trajectories is computationally expensive, making design space exploration prohibitively difficult for these low-budget missions. In this paper, we introduce a new method to rapidly produce near-optimal, high-fidelity trajectories in cislunar space using the Q-Law guidance algorithm. By combining forward- and backward-propagated Q-Law, we generate continuous trajectories from an Earth parking orbit to a target lunar orbit. The Q-Law result can then be refined using direct collocation. To demonstrate this process, we solve a problem inspired by the SMART-1 mission and compare to literature results. We then apply this method to two SmallSat mission scenarios and demonstrate that this technique can be used to efficiently explore the trajectory trade space and provide powerful initial guesses for direct optimization. [ABSTRACT FROM AUTHOR]

DART is NASA's demonstration of an asteroid deflection using a kinetic impactor. The spacecraft launched aboard a SpaceX Falcon 9 on November 24th 2021, on a direct collision with the binary asteroid system Didymos planned for September 26th 2022. By impacting the small moon, Dimorphos, DART's objective was to alter the moon's orbit about the larger asteroid by several minutes. The navigation of a ballistic mission is usually relatively simple. Other than heading to a violent demise, this mission had a number of unconventional aspects which gave the navigation team interesting challenges: a tight propellant budget for part of the mission, no reaction wheels which resulted in a noisy spacecraft with the Nav team having to rely heavily on Delta Differential One-way Ranging measurements to identify off line-of-sight Delta-V, and critical operations in the last 30 days of the mission under a new thrusting control mode regime. Optical navigation was a critical element in the success of this mission, contributing to the determination of the spacecraft and target ephemerides for refined targeting maneuvers. After strategic decisions in the final weeks of the missions, DART could have comfortably hit the larger asteroid, Didymos, which increased the probably of impact with its moon Dimorphos. • DART was NASA's demonstration of an asteroid deflection using a kinetic impactor. • This mission gave the navigation team interesting challenges. • Optical navigation was a critical element in the success of this mission. • DART could have hit Didymos, which increased the probably of impact with its moon. [ABSTRACT FROM AUTHOR]

Low-thrust spacecraft trajectory optimization for the many-revolution orbital transfer problem is especially challenging due to the high problem dimension and perturbing accelerations that prevent or complicate accurate analytical solutions. This analysis seeks to simplify the calculation of the nonaveraged spiral trajectory through the use of the well-known Q-Law guidance algorithm. Here, Q-Law is used to seed phases of the direct trajectory optimization problem. We explore the trade space between the fast calculation speed of Q-Law and the time or mass optimality of the full optimization problem using the common example of a geostationary transfer orbit to geostationary transfer. We find that a computationally efficient, near-optimal solution can be achieved by using Q-Law for an initial fraction of a spiral trajectory and direct optimization for the remainder of the trajectory. This reduces the direct optimization problem to a lower dimension and enables the spacecraft to reach a specific final state. Q-Law is particularly effective for portions of the trajectory where there are many eclipses, which can challenge direct optimization methods. [ABSTRACT FROM AUTHOR]

It is challenging or infeasible to precisely measure the mass of small asteroids using the state-of-the-art without a dedicated spacecraft rendezvous mission, which are typically limited to one or a few asteroid targets. Alternatively, spacecraft flyby missions offer the possibility of visiting multiple asteroids but typically lack the sensitivity to measure mass for all but the largest asteroids. In these encounters, Earth-based two-way Doppler is used to measure a change in the spacecraft's velocity imparted by the asteroid. The technique known as Optical Gravimetry (OpGrav) seeks to increase this sensitivity of mass measurements from flyby encounters using optical measurements from the spacecraft to one or more test-masses. In this technique, the spacecraft deploys the test-masses prior to an asteroid flyby and then tracks them before and after the encounter using an on-board telescope. The test-masses can pass much closer to the asteroid than a spacecraft would typically choose such that their trajectories are measurably deflected. This paper provides a quantitative sensitivity analysis of the design parameters most relevant to OpGrav, including asteroid mass, flyby velocity, number of test-masses, test-mass target altitude, test-mass deployment time, and the cadence of optical measurements. Additionally, this paper investigates the effect of practical test-mass deployment errors on the expected mass measurement. Broadly speaking, this analysis shows that OpGrav provides comparable sensitivity to the existing technique at asteroids that are five to ten times smaller in diameter, depending on whether one or three test-masses are deployed. We demonstrate that under realistic mission assumptions, the use of OpGrav would have allowed all previous flyby visits of asteroids, most of which were not able to obtain mass estimates, to achieve better than 25% 1 σ accuracy in mass measurements, representing a significant improvement on the state of the art. • Optical tracking of test-masses greatly improves asteroid flyby mass estimation. • Can obtain mass estimates of asteroids as small as 500 ​m in diameter. • Can obtain mass estimates for flybys up to 20 ​km/s for bodies ≥ 1 ​km in diameter. • Tracking 3 test-masses is necessary for most sensitive measurements. • Optical gravimetry has minimal impact to other spacecraft science activities. [ABSTRACT FROM AUTHOR]

The Asteroid Impact & Deflection Assessment (AIDA) mission is an international cooperation between NASA and ESA. NASA plans to provide the Double Asteroid Redirection Test (DART) mission which will perform a kinetic impactor experiment to demonstrate asteroid impact hazard mitigation. ESA proposes to provide the Hera mission which will rendezvous with the target to monitor the deflection, perform detailed characterizations, and measure the DART impact outcomes and momentum transfer efficiency. The primary goals of AIDA are (i) to demonstrate the kinetic impact technique on a potentially hazardous near-Earth asteroid and (ii) to measure and characterize the deflection caused by the impact. The AIDA target will be the binary asteroid (65803) Didymos, which is of spectral type Sq, with the deflection experiment to occur in October, 2022. The DART impact on the secondary member of the binary at ∼6 km/s changes the orbital speed and the binary orbit period, which can be measured by Earth-based observatories with telescope apertures as small as 1 m. The DART impact will in addition alter the orbital and rotational states of the Didymos binary, leading to excitation of eccentricity and libration that, if measured by Hera, can constrain internal structure of the target asteroid. Measurements of the DART crater diameter and morphology can constrain target properties like cohesion and porosity based on numerical simulations of the DART impact. [ABSTRACT FROM AUTHOR]