Kenneth Getzandanner

Recovery of Bennu’s orientation for the OSIRIS-REx mission: implications for the spin state accuracy and geolocation errors

The goal of the OSIRIS-REx mission is to return a sample of asteroid material from near-Earth asteroid (101955) Bennu. The role of the navigation and flight dynamics team is critical for the spacecraft to execute a precisely planned sampling maneuver over a specifically selected landing site. In particular, the orientation of Bennu needs to be recovered with good accuracy during orbital operations to contribute as small an error as possible to the landing error budget. Although Bennu is well characterized from Earth-based radar observations, its orientation dynamics are not sufficiently known to exclude the presence of a small wobble. To better understand this contingency and evaluate how well the orientation can be recovered in the presence of a large 1

Conceptual Design of a Hypervelocity Asteroid Intercept Vehicle (HAIV) Flight Validation Mission

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Mission opportunities for the flight validation of the kinetic impactor concept for asteroid deflection

∘ wobble, we conduct a comprehensive simulation with the NASA GSFC GEODYN orbit determination and geodetic parameter estimation software. We describe the dynamic orientation modeling implemented in GEODYN in support of OSIRIS-REx operations and show how both altimetry and imagery data can be used as either undifferenced (landmark, direct altimetry) or differenced (image crossover, altimetry crossover) measurements. We find that these two different types of data contribute differently to the recovery of instrument pointing or planetary orientation. When upweighted, the absolute measurements help reduce the geolocation errors, despite poorer astrometric (inertial) performance. We find that with no wobble present, all the geolocation requirements are met. While the presence of a large wobble is detrimental, the recovery is still reliable thanks to the combined use of altimetry and imagery data.

An Independent Orbit Determination Simulation for the OSIRIS-REx Asteroid Sample Return Mission

The mitigation of orbital debris was addressed in the most recent release of the National Space Policy directing space faring agencies to pursue technologies that will “mitigate and remove on-orbit debris.” No matter what abatement technology is developed and deployed, still lacking is the remote sensing infrastructure to locate and track these objects with adequate precision. We propose using GSFCs ground-based laser ranging facility to provide meter-level or better ranging precision on optically passive 10-30 cm orbital debris targets with the goal of improving current predictions up to 85%. The improved location accuracy also has the immediate benefit of reducing costly false alarms in collision predictions for existing assets.

Relative Terrain Imaging Navigation (RETINA) Tool for the Asteroid Redirect Robotic Mission (ARRM)

Earth has been struck in the past by near-Earth objects (NEOs) that were sufficiently energetic, in terms of mass and impact velocity, to cause significant damage ranging from local or regional devastation to mass extinctions. Such impact events will occur again in the future and humanity is beginning to see the wisdom in planning ahead to be ready to respond to the next incoming NEO so that we will have the opportunity to mount an effective defense. Some of the key factors in designing planetary defense systems include the size of the incoming NEO and the amount of warning time. The size of the NEO determines how much damage it would cause and places limits on our response options, while the warning time further constrains our options for dealing with the NEO. Opportunities to rendezvous with NEOs at a reasonable propellant mass cost tend to occur infrequently, so for scenarios in which the NEO impact event is known less than 10 years in advance, the most viable option will likely be a hypervelocity intercept in which our mitigation system is guided to intercept the NEO at high relative velocity because the propellant cost to match the NEO’s velocity would be prohibitive. Although large NEOs are capable of causing more damage than small NEOs, the small NEOs are far more numerous and thus a small NEO impact scenario is more likely within a given time frame, all else being equal. Unfortunately, small NEOs are faint in the night sky (because they have relatively little surface area to reflect sunlight) and are therefore harder to discover and track with ground-based telescopes in advance of when they would collide with Earth. Their faintness also makes small NEOs more difficult for a spacecraft to target, especially at high relative velocity. Thus the most challenging NEO mitigation scenario involves a NEO that is small (but large enough to survive atmospheric passage and cause ground damage) and for which we have a relatively short warning time, requiring a hypervelocity intercept for deflection or destruction of the NEO. A spacecraft system capable of reliably handling that scenario would of course be able to handle less stressing cases, i.e., more warning time, lower intercept velocities, and/or larger NEOs. Work was recently performed towards the design of such a spacecraft system by the Mission Design Laboratory (MDL) of NASA Goddard Space Flight Center’s Integrated Design Center (IDC). The MDL assessed the technical feasibility of reliably performing hypervelocity interception of a 50 m diameter NEO and developed a conceptual design for a spacecraft and mission operations support architecture for flight validation of the system. This research was funded by and in support of the recently awarded NASA Innovative Advanced Concepts (NIAC) Phase II study entitled “An Innovative Solution to NASA’s NEO Impact Threat Mitigation Grand Challenge and Flight Validation Mission Architecture Development.” The goals of this research project include designing a two-body Hypervelocity Asteroid Intercept Vehicle (HAIV) that will deliver a kinetic impactor to the target NEO to excavate a shallow crater within which the second portion of the spacecraft will detonate a Nuclear Explosive Device (NED) immediately thereafter to effect a powerful subsurface detonation capable of disrupting the NEO, as shown in Figure 1. Flight validation of this system is crucial because any NEO mitigation system must be thoroughly flight tested before it can be relied upon during a true emergency. To date no such flight validations have been performed. In this paper we present a detailed overview of the MDL study results and subsequent advances in the design of GNC algorithms for accurate terminal guidance during hypervelocity NEO intercept. The MDL study produced a conceptual configuration of the two-body HAIV and its subsystems; a mission scenario and trajectory design for a notional flight validation mission to a selected candidate target NEO; GNC results regarding the ability of the HAIV to reliably intercept small (50 m) NEOs at hypervelocity (typically > 10 km/s); candidate launch vehicle selection; a notional operations concept and cost estimate for the flight validation mission; and a list of topics to address during the remainder of our NIAC Phase II study.