Comparing NEO Search Telescopes

Abstract

Multiple terrestrial and space-based telescopes have been proposed for detecting and tracking near-Earth objects (NEOs). Detailed simulations of the search performance of these systems have used complex computer codes that are not widely available, which hinders accurate cross-comparison of the proposals and obscures whether they have consistent assumptions. Moreover, some proposed instruments would survey infrared (IR) bands, whereas others would operate in the visible band, and differences among asteroid thermal and visible-light models used in the simulations further complicate like-to-like comparisons. I use simple physical principles to estimate basic performance metrics for the ground-based Large Synoptic Survey Telescope and three space-based instrumentsSentinel, NEOCam, and a Cubesat constellation. The performance is measured against two different NEO distributions, the Bottke et al. distribution of general NEOs, and the Veres et al. distribution of Earth-impacting NEO. The results of the comparison show simplified relative performance metrics, including the expected number of NEOs visible in the search volumes and the initial detection rates expected for each system. Although these simplified comparisons do not capture all of the details, they give considerable insight into the physical factors limiting performance. Multiple asteroid thermal models are considered, including FRM, NEATM, and a new generalized form of FRM. I describe issues with how IR albedo and emissivity have been estimated in previous studies, which may render them inaccurate. A thermal model for tumbling asteroids is also developed and suggests that tumbling asteroids may be surprisingly difficult for IR telescopes to observe.

Modeling the Performance of the LSST in Surveying the Near-Earth Object Population

“…The distribution of V magnitudes turns over sharply at V ∼ 23.5 − 23.75. This is inconsistent with Figure 7 in Myhrvold (2016), who assumes 50% limiting magnitudes ∼ 0.8 mag fainter than our computations indicate.…”

“…The limiting magnitudes and solar elongation coverage presented here are at odds with Myhrvold (2016); his Figure 7 shows much fainter limiting magnitudes than presented here. While Myhrvold (2016) cites the possibility and capability of LSST observing at much smaller solar elongations, this is inconsistent with the published cadences provided by the LSST project and would potentially interfere with its other science goals. Additionally, Myhrvold (2016) incorrectly assumes that an object need only be detected once for it to be counted as discovered, cataloged, and tracked.…”

“…While Myhrvold (2016) cites the possibility and capability of LSST observing at much smaller solar elongations, this is inconsistent with the published cadences provided by the LSST project and would potentially interfere with its other science goals. Additionally, Myhrvold (2016) incorrectly assumes that an object need only be detected once for it to be counted as discovered, cataloged, and tracked. LSST aims to have less than 5% of the focal plane lost due to gaps, bad pixels, or dead detectors.…”

Thermal Modeling of Comet-like Objects from AKARI Observation

“…It is, however, possible to approximate it using the so-called standard H, G magnitude system (Bowell et al 1989). In this system, the phase function of a general asteroid is empirically determined, and the Bond albedo for a Lambertian sphere with phase correction is written as (8) Although Bowell et al (1989) Myhrvold (2016) found that the best fitting function had (C 1 , C 2 ) = (0.286, 0.656). We confirmed the latter result and used it throughout this study.…”

Thermophysical Modeling of Asteroid Surfaces Using Ellipsoid Shape Models

“…Multi-wavelength, photometric infrared observations of asteroids provide essential information about the thermophyiscal properties of their surfaces. A handful of both simple thermal models (Harris, 1998;Lebofsky et al, 1978Lebofsky et al, , 1986Wolters and Green, 2009;Myhrvold, 2016) and more sophisticated themophysical models (TPMs; Spencer et al, 1989;Spencer, 1990;Lagerros, 1996;Delbo' et al, 2007;Mueller, 2007; have been established as effective means of modeling thermal infrared observations of asteroids. The general purpose of a thermal model is to compute surface temperatures for an object, which are in turn used to calculate the emitted flux at the desired wavelengths (see , for a recent review).…”