Shyam Bhaskaran

Asphaug, E.; Barucci, A.; Belton, M.; Bhaskaran, S.; Brownlee, D.; Carter, L.; Castillo, J.; Chesley, S.; Chodas, P.; Farnham, T.; Gaskell, R.; Gim, Y.; Heggy, E.; Klaasen, K.; Kofman, W.; Kreslavsky, M.; Lisse, C.; McFadden, L.; Pettinelli, E.; Plaut, J.; Scheeres, D.; Turtle, E.; Weissman, P.; Wu, R. ... Deep Interior is a comet rendezvous mission using a high heritage planetary sounding radar to derive a high definition image of the global interior.

Abstract On February 14, 2011 Stardust-NExT flew by Comet Tempel 1, the target of the Deep Impact mission in 2005, obtaining dust measurements and highresolution images of areas surrounding the 2005 impact site, and extending coverage to almost two thirds of ...

The Deep Impact spacecraft flew by comet Hartley 2 on November 4, 2010 as part of its extended mission called EPOXI. Successful navigation depended critically on the quality and timing of optical navigation data processing, since pictures of the comet provided the most precise comet-relative position of the spacecraft. This paper describes the planning, including the picture timing and pointing; the methods used to determine the center of the comet image in each picture; and the optical navigation results, which provided the necessary information to allow the cameras to accurately target the comet for science imaging at encounter.

As the time of the Ida encounter by Galileo approached, some unfortunate circumstances occurred, causing a very worrisome but exciting encounter, especially with regards to navigation. This paper reports on Galileo's orbit determination stratagy during the period after the last Earth encounter through the Ida flyby. Details in the modeling of Galileo's orbit, and in the use of various navigation tools, will be explained and the results of several key orbit solutions will be given.

... than that obtained using a standard Doppler and range fit, but not quite as good as the ADOR solution. The TCA'S are not affected much by anY of the weights or filters, as this parameter is determined primarily by the range data and is accurately solved for in ali cases. ...

Stardust successfully encountered comet 81P/Wild 2 on 2 January 2004 at a distance of 236.4 ± 1 km. All encounter investigations acquired valuable new and surprising findings. The time‐of‐flight spectrometer registered 29 spectra during flyby and measured the first negative ion mass spectra of cometary particles. The dust detectors recorded particles over a broad mass range, 10−11 to 10−4 g. Unexpectedly, the dust distribution along Stardust's flight path was far from uniform, but instead occurred in short “bursts,” suggesting in‐flight breakup of fragments ejected from the nucleus. High‐resolution, stunning images of the Wild 2 surface show a diverse and complex variety of landforms not seen from comets 1P/Halley and 19P/Borrelly or icy satellites of the outer solar system. Longer‐exposure images reveal large numbers of jets projected nearly around the entire perimeter of the nucleus, many of which appear to be highly collimated. A triaxial ellipsoidal fit of the Wild 2 nucleus...

Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1–3. A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation1. NASA’s Double Asteroid Redirection Test (DART) mission is a full-scale test of kinetic impact technology. The mission’s target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the DART spacecraft4. Although past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their t...

With the advent of the Deep Space Atomic Clock, operationally accurate and reliable one-way radiometric data sent from a radio beacon (i.e., a DSN antenna or other spacecraft) and collected using a spacecraft's radio receiver enables the development and use of autonomous radio navigation. This work examines the fusion of radiometric data with optical data (i.e. OpNav) to yield robust and accurate trajectory solutions that include selected model reductions and computationally efficient navigation algorithms that can be readily adopted for onboard, autonomous navigation. The methodology is characterized using a representative high-fidelity simulation of deep space cruise, approach, and delivery to Mars. The results show that the combination of the two data types yields solutions that are almost an order of magnitude more accurate than those obtained using each data type by itself. Furthermore, the combined data solutions readily meet representative entry navigation requirements (in this case at Mars).

A kinetic impactor spacecraft is a viable method to deflect an asteroid which poses a threat to the Earth. The technology to perform such a deflection has been demonstrated by the Deep Impact (DI) mission, which successfully collided with comet Tempel 1 in July 2005 using an onboard autonomous navigation system, called AutoNav, for the terminal phase of the mission. In this paper, we evaluate the ability of AutoNav to impact a wider range of scenarios that a deflection mission could encounter, varying parameters such as the approach velocity, phase angle, size of the asteroid, and the attitude determination accuracy. In particular, we evaluated the capability of AutoNav to impact 100-300 m size asteroids at speeds between 7.5 and 20 km/s at various phase angles. Using realistic Monte Carlo simulations, we tabulated the probability of success of the deflection as a function of these parameters and find the highest sensitivity to be due to the spacecraft attitude determination error. In addition, we also specifically analyzed the impact probability for a proposed mission (called ISIS) which would send an impactor to the asteroid 1999RQ36. We conclude with some recommendations for future work.

<p><strong>Introduction:</strong>  The close approach of asteroid (99942) Apophis on April 13, 2029 presents a unique opportunity to achieve breakthrough science and strengthen planetary defense goals. </p> <p>As discussed in [1], low-frequency (VHF) radar observations can probe the interior structure of small bodies, as demonstrated by CONSERT at comet 67P [2, 3], and the planned JuRa low frequency radar on Hera/Juventas at the Didymos system—target of the DART mission. Radar measurements can determine the distribution of monolithic objects and voids within the body at 10’s of meter scale, which are critical for potential deflection and disruption attempts. This is best accomplished by multi-static, low frequency radar [4].</p> <p>A mission concept to exploit the Apophis opportunity has been developed in a collaboration between NASA/JPL and CNES. The Distributed Radar Observations of Interior Distributions (DROID) mission would rendezvous with Apophis in late Summer 2028, seven months prior to Earth closest approach (ECA) and escort it through the encounter. A possible asteroid flyby on the way would delay arrival to late 2028 but still provide ample time for pre-ECA characterization. DROID’s measurements would determine the interior structure and properties, the body’s shape, morphology and rotation and observe any resolvable changes. DROID provides unique high fidelity in situ data that complements and enhances Earth-based optical and radar observations of Apophis, as well as data collected by OSIRIS-APEX which is due to rendezvous with Apophis 8 days after ECA.</p> <p>As illustrated in Figure 1, DROID’s architecture calls for three spacecraft: an ESPA Grande-class Mothership and two 6U CubeSats. The Mothership carries the CubeSats to Apophis, achieves the rendezvous cruise trajectory, performs high resolution imaging, and acts as a Direct-to-Earth (DTE) node for the constellation. Once Apophis’s physical characteristics (shape, spin, gravity field) are sufficiently characterized, the Mothership deploys both CubeSats, which then insert themselves into coordinated low orbits to perform monostatic and bistatic radar observations.</p> <p><strong>Mission Goals:</strong>  The DROID mission has two primary goals. The first goal is to understand the interior structure of a rubble pile asteroid and implications for its formation, evolution and response to a deflection attempt. Objectives include determining shape and density, and determining the internal size, distribution, and arrangement of blocks and voids within Apophis. \</p> <p>DROID’s second goal is to understand how close planetary encounters affect asteroids. DROID will provide critical pre-ECA imagery of Apophis that are necessary for change detection. Objectives include determining if material moves on the surface of Apophis during the Earth flyby, and determining how the spin state of Apophis changes during ECA.</p> <p><strong>Payload: </strong>Given the goals above, DROID employs four types of payloads distributed over three spacecraft (Figure 1). Objectives requiring surface imaging are to be met with a narrow-angle camera (NAC) on-board the Mothership spacecraft, whose focal plane is to be based on the Advanced CASPEX detector [5]. Additional wide-angle cameras (WACs) are carried on the two CubeSats for optical navigation.</p> <p>The objective to map internal structure is achieved using the Low Frequency Radar (LFR) on the CubeSats. The LFR is baselined as a version of JuRa (60 MHz), [6], modified to operate in a bistatic mode [1]. Inter-Spacecraft Link (ISL) S-band transponders on all three spacecraft perform data transfer between CubeSats and Mothership, and synchronize the CubeSat clocks for accurate bistatic radar measurement. ISLs are also used with the Mothership’s DTE link to map the gravity field.</p> <p><strong>Mission Architecture:</strong> The DROID mission architecture is compatible with either direct launch or rideshare and will utilize heritage bus designs that can achieve the required propulsion performance. DROID’s 3.54 km/s ΔV requirement is similar to that of ESCAPADE, which uses bipropellant propulsion [7], DROID’s reference mission is constrained by a cruise trajectory insertion (CTI) window of about October-November 2027. Details of launch, CTI and cruise are provided in [8].</p> <p><strong>Operations: </strong>DROID arrives at Apophis around August-September 2028 (~December if it performs a precursor asteroid flyby) and executes a 0.30 km/s burn to reduce its relative velocity. During this phase, the Mothership NAC begins preliminary characterization of Apophis’s shape and spin. Approach imaging is then…

In-spiraling supermassive black holes should emit gravitational waves, which would produce characteristic distortions in the time of arrival residuals from millisecond pulsars. Multiple national and regional consortia have constructed pulsar timing arrays by precise timing of different sets of millisecond pulsars. An essential aspect of precision timing is the transfer of the times of arrival to a (quasi-)inertial frame, conventionally the solar system barycenter. The barycenter is determined from the knowledge of the planetary masses and orbits, which has been refined over the past 50 years by multiple spacecraft. Within the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), uncertainties on the solar system barycenter are emerging as an important element of the NANOGrav noise budget. We describe what is known about the solar system barycenter, touch upon how uncertainties in it affect gravitational wave studies with pulsar timing arrays, and consider future t...

Spacecraft landings on small bodies (asteroids and comets) can require target accuracies too stringent to be met using ground-based navigation alone, especially if specific landing site requirements must be met for safe-ty or to meet science goals. In-situ optical observations coupled with on-board navigation processing can meet the tighter accuracy requirements to enable such missions. Recent developments in deep space navigation ca-pability include a self-contained autonomous navigation system (used in flight on three missions) and a landmark tracking system (used experimen-tally on the Japanese Hayabusa mission). The merging of these two tech-nologies forms a methodology to perform autonomous onboard navigation around small bodies. This paper presents an overview of these systems, as well as the results from Monte Carlo studies to quantify the achievable landing accuracies by using these methods. Sensitivity of the results to var-iations in spacecraft maneuver execution error, at...

The Stardust-NExT (New Exploration of Tempel) mission, a follow-on to the Stardust prime mission, successfully completed a flyby of comet Tempel-1 on 2/14/11. However there were many challenges along the way, most significantly low propellant margin and detection of the comet in imagery later than antici-pated. These challenges and their ramifications forced the project to respond with flexibility and ingenuity. As a result, the flyby at an altitude of 178 km was nearly flawless, accomplishing all its science objectives. Lessons learned on Stardust-NExT may have relevance to other spacecraft missions.

The critical aspect of optical navigation (opnav) is the ability to accurately derive the centers of stars and target bodies. Sets of opnav images can be stacked and co-added to reduce noise and improve accuracy. However, this does not capitalize on the additional sampling information that exists due to the sub-integer pixel offsets between images created by spacecraft attitude drift. This paper details how, by utilizing simple subsampling techniques for the New Horizons flyby of (486958) 2014 MU69, this additional spatial information was recovered, thus enabling more accurate centers and earlier resolution of multiple bodies. Introduction. The New Horizons flyby of Kuiper Belt Object (486958) 2014 MU69,1 nicknamed “Ultima Thule” (UT), presented significant challenges when trying to derive accurate opnav observations. At 43 AU away from the sun, there was roughly a 6-hour one way light travel time, with light levels that were less than 0.06% that of at Earth. In order to reduce the ...

The New Horizons spacecraft made its closest approach to Pluto on 14 July 2015. The most significant challenge of this mission was that the Pluto system ephemeris was initially known with a precision of ~1000 km. This needed to be improved significantly on approach in order to meet the science requirements. During the final six months leading to the flyby, a JPL Independent Navigation (INAV) Team was included in the ephemeris knowledge update process as a cross-check on the Project Navigation (PNAV) Team’s results. This paper discusses the INAV team’s experiences and challenges navigating New Horizons through the Pluto planetary system encounter.

The recently discovered asteroid 2011 AG5 currently has a 1-in-500 chance of impacting Earth in 2040. In this paper, we discuss the potential of future observations of the asteroid and their effects on the asteroid’s orbital uncertainty. Various kinetic impactor mission scenarios, relying on both conventional chemical as well as solar-electric propulsion, are presented for deflecting the course of the asteroid safely away from Earth. The times for the missions range from pre-keyhole passage (pre-2023), and up to five years prior to the 2040 Earth close approach. We also include a brief discussion on terminal guidance, and contingency options for mission planning.

Recent advances with space navigation technologies developed by NASA in space-based atomic clocks and pulsar X-ray navigation, combined with past successes in autonomous navigation using optical imaging, brings to the forefront the need to compare space navigation using optical, radiometric, and pulsar-based measurements using a common set of assumptions and techniques. This review article examines these navigation data types in two different ways. First, a simplified deep space orbit determination problem is posed that captures key features of the dynamics and geometry, and then each data type is characterized for its ability to solve for the orbit. The data types are compared and contrasted using a semi-analytical approach with geometric dilution of precision techniques. The results provide useful parametric insights into the strengths of each data type. In the second part of the paper, a high-fidelity, Monte Carlo simulation of a Mars cruise, approach, and entry navigation proble...

Future missions to asteroids and comets will likely encounter a body which is tumbling (i.e., not in principal axis rotation). In this work, simulated images of a tumbling comet are processed by a sequential Extended Kalman Filter (EKF) Simultaneous Localization and Mapping (SLAM) method. The EKF SLAM method uses a limited set of manually identified optical landmarks to estimate the small body spin state and scaled moments of inertia; the spacecraft position and velocity (the spacecraft attitude is provided by an independent attitude determination system); and the surface landmark locations. A method for generating initial landmark surface positions is provided, as well as an interpolation method for the provided spacecraft attitude values. The SLAM method is successful in estimating the spin state of the simulated body, with final smoothed error magnitudes lower than 1 degree for the small body orientation and 2 degrees per day for the small body angular velocity.

Future missions to asteroids and comets will likely encounter a body which is tumbling (i.e., not in principal axis rotation). In this work, simulated images of a tumbling comet are processed by a sequential Extended Kalman Filter (EKF) Simultaneous Localization and Mapping (SLAM) method. The EKF SLAM method uses a limited set of manually identified optical landmarks to estimate the small body spin state and scaled moments of inertia; the spacecraft position and velocity (the spacecraft attitude is provided by an independent attitude determination system); and the surface landmark locations. A method for generating initial landmark surface positions is provided, as well as an interpolation method for the provided spacecraft attitude values. The SLAM method is successful in estimating the spin state of the simulated body, with final smoothed error magnitudes lower than 1 degree for the small body orientation and 2 degrees per day for the small body angular velocity.

Several options are being examined to reduce the costs of spacecraft and deep space missions. One such option is to fly spacecraft in a non-coherent mode, that is, the spacecraft does not carry a transponder and cannot coherently return a Doppler signal. Historically, such one-way data has not been used as the sole data type due to the instability of the onboard oscillator, the use of S-band frequencies, and the corresponding larger error sources which could not be modeled. However, with the advent of high-speed work stations and more sophisticated modeling ability, the possibility of using one-way data is being re-examined. This paper addresses the navigation performance of various one-way data types for use in interplanetary missions.