The L'LORRI Instrument

Mar 31, 2021

L’LORRI, which some team members affectionately call the “eagle eyes” of the mission, is Lucy’s most sensitive camera.

L'LORRI SPECIFICATIONS

Mass: 12.0 kg
Power: 10.6 W
FOV: 5.1 mrad
Instantaneous field of view (IFOV): 5.0 μrad
Diameter of primary mirror: 8.2 in (20.8 cm)
Focal length: 103 in (262 cm)
Resolution: 15xIFOV μm
Wavelength range: 450-850 nm
Pixels per image: 1024x1024
Frame rate: up to 1 Hz

This panchromatic (black-and-white) camera is a type of Ritchey–Chrétien telescope, the same kind of telescope as the Hubble Space Telescope. In a Ritchey–Chrétien telescope, light travels down the tube and is reflected by the hyperbolic primary mirror, then travels back down the tube and is reflected by the hyperbolic secondary mirror. The secondary mirror focuses the light, and the light travels through an opening in the primary mirror. In L’LORRI’s case, it then passes through a set of lenses. The image is recorded with a charge-coupled device, the light-sensitive device used in digital cameras in place of film.

Ray diagram of the L'LORRI Instrument
Optical diagram of the L'LORRI instrument Credit: David Dezell Turner

One of L’LORRI’s objectives is to produce clear images of the Trojan asteroids, despite the fact that they are extremely dark. From 1000 km away, L’LORRI will be able to clearly see craters with a diameter of 70 m (i.e. 14 m per pixel), which would be like standing at one end of a football field and being able to see a fly at the other end! L’LORRI’s detailed images will help us understand the surface geology of the Trojan asteroids. For instance, the images will provide information about the Trojans’ craters, thus giving a record of nearby asteroid populations over the course of history. L’LORRI will also search the Trojans for any rings, satellites, or activity. L’LORRI’s ability to see faint targets from far away also makes it perfect for optical navigation. L’LORRI will help Lucy navigate to a point in space, then T2Cam (with its much wider field of view) will help the instruments accurately point toward the targets.

Since L’LORRI is panchromatic (and thus built to detect the entire visible spectrum), L’LORRI does not use optical filters. L’LORRI also has no moving parts, which reduces the risk of part failure during the mission. Despite being such a powerful telescope, L’LORRI doesn’t even use a focusing mechanism! Though extreme temperature differences in space could cause a device like this to defocus (since the optical system would be expanding and contracting as the temperature changes), most of L’LORRI’s optical system is made of silicon carbide, which does not expand or contract much when faced with temperature changes, and also quickly disperses heat to reduce temperature differences.

L'LORRI image of Aarokoth
L'LORRI image of Arrokoth from New Horizons. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

L’LORRI is built by a team at Johns Hopkins Applied Physics Laboratory, under the leadership of Harold Weaver (Instrument Principal Investigator) and Neil Dello Russo (Instrument Deputy Principal Investigator). The instrument is based on New Horizons’ LORRI instrument, which is responsible for most of the incredibly detailed images of Pluto and the Kuiper Belt object Arrokoth. Though a few changes were made to New Horizons’ LORRI for the Lucy Mission (such as replacing its composite baffle with stronger aluminum), L’LORRI retains much of its predecessor’s tried-and-tested design.