Recent developments for laser communication on CubeSats across interplanetary distances will be presented. A binary polarization-shift-keyed modulation scheme using dual gain-switched diode lasers is developed and demonstrated within an end-to-end link testbed to achieve signal acquisition under extremely poor signal-to-noise conditions (-43.5 dB average signal-to-noise power ratio at a 1-MHz symbol rate) to simulate direct-to-Earth links, while simultaneously targeting a limited SWaP footprint (1.5U envelope). Additional system design and constraints for the compact laser transmitter will be discussed.
The Optical PAyload for Lasercomm Science (OPALS) experiment on the International Space Station (ISS) recently demonstrated successful optical downlinks to the NASA/JPL 1-m aperture telescope at the Optical Communication Telescope Laboratory (OCTL) located near Wrightwood, CA. A large area (200 μm diameter) free space coupled avalanche photodiode (APD) detector was used to receive video and a bit patterns at 50 Mb/s. We report on a recent experiment that used an adaptive optics system at OCTL to correct for atmospherically-induced refractive index fluctuations so that the downlink from the ISS could be coupled into a single mode fiber receiver. Stable fiber coupled power was achieved over an entire pass using a self-referencing interferometer based adaptive optics system that was provided and operated by Boeing Co. and integrated to OCTL. End-to-end transmission and reconstruction of an HD video signal verified the communication performance as in the original OPALS demonstration. Coupling the signal into a single mode fiber opens the possibility for higher bandwidth and efficiency modulation schemes and serves as a pilot experiment for future implementations.
A number of laser communication link demonstrations from near Earth distances extending out to lunar ranges have been remarkably successful, demonstrating the augmented channel capacity that is accessible with the use of lasers for communications. The next hurdle on the path to extending laser communication and its benefits throughout the solar system and beyond is to demonstrate deep-space laser communication links. In this paper, concepts and technology development being advanced at the Jet Propulsion Laboratory (JPL) in order to enable deep-space link demonstrations to ranges of approximately 3 AU in the next decade, will be discussed.
The Optical Payload for Lasercomm Science (OPALS) Flight System on-board the International Space Station uses a charge coupled device (CCD) camera to detect a beacon laser from Earth. Relative measurements of the background contributed by upwelling radiance under diverse illumination conditions and varying surface terrain is presented. In some cases clouds in the field-of-view allowed a comparison of terrestrial and cloud-top upwelling radiance. In this paper we will report these measurements and examine the extent of agreement with atmospheric model predictions.
In mid-2014 several day and nighttime links under diverse atmospheric conditions were completed using the Optical Payload for Lasercomm Science (OPALS) flight system on-board the International Space Station (ISS). In this paper we compare measured optical power and its variance at either end of the link with predictions that include atmospheric propagation models. For the 976 nm laser beacon mean power transmitted from the ground to the ISS the predicted mean irradiance of tens of microwatts per square meter close to zenith and its decrease with range and increased air mass shows good agreement with predictions. The irradiance fluctuations sampled at 100 Hz also follow the expected increase in scintillation with air mass representative of atmospheric coherence lengths at zenith at 500 nm in the 3-8 cm range. The downlink predicted power of hundreds of nanowatts was also reconciled within the uncertainty of the atmospheric losses. Expected link performance with uncoded bit-error rates less than 1E-4 required for the Reed- Solomon code to correct errors for video, text and file transmissions was verified. The results of predicted and measured powers and fluctuations suggest the need for further study and refinement.
From mid-October through mid-November 2013, NASA’s Lunar Laser Communication Demonstration (LLCD) successfully demonstrated for the first time duplex laser communications between a satellite in lunar orbit, the Lunar Atmosphere and Dust Environment Explorer (LADEE), and ground stations on the Earth. It constituted the longest-range laser communication link ever built and demonstrated the highest communication data rates ever achieved to or from the Moon. The system included the development of a novel space terminal, a novel ground terminal, two major upgrades of existing ground terminals, and a capable and flexible ground operations infrastructure. This presentation will give an overview of the system architecture and the several terminals, basic operations of both the link and the whole system, and some typical results.
The Optical Communications Telescope Laboratory (OCTL) located on Table Mountain near Wrightwood, CA served as
an alternate ground terminal to the Lunar Laser Communications Demonstration (LLCD), the first free-space laser
communication demonstration from lunar distances. The Lunar Lasercom OCTL Terminal (LLOT) Project utilized the
existing 1m diameter OCTL telescope by retrofitting: (i) a multi-beam 1568 nm laser beacon transmitter; (ii) a tungsten
silicide (WSi) superconducting nanowire single photon detector (SNSPD) receiver for 1550 nm downlink; (iii) a
telescope control system with the functionality required for laser communication operations; and (iv) a secure network
connection to the Lunar Lasercom Operations Center (LLOC) located at the Lincoln Laboratory, Massachusetts Institute
of Technology (LL-MIT). The laser beacon transmitted from Table Mountain was acquired by the Lunar Lasercom
Space Terminal (LLST) on-board the Lunar Atmospheric Dust Environment Explorer (LADEE) spacecraft and a 1550
nm downlink at 39 and 78 Mb/s was returned to LLOT. Link operations were coordinated by LLOC. During October
and November of 2013, twenty successful links were accomplished under diverse conditions. In this paper, a brief
system level description of LLOT along with the concept of operations and selected results are presented.
The NASA owned Optical Communication Telescope Laboratory (OCTL) telescope located at Table Mountain, CA is
being readied as a backup ground station for the upcoming Lunar Laser Communications Demonstration (LLCD). The
backup ground terminal is called the Lunar Laser OCTL Terminal (LLOT). The 1-m diameter telescope will be
configured as a mono-static transceiver for transmitting a laser beacon and receiving downlink at a data-rate of 39 Mb/s.
Interfaces to an operations center with near-real time exchange of monitored data at OCTL will also be developed. A
system level overview of this backup ground station for LLCD will be presented.
JPL is developing and testing a 10 Gb/s laser communications terminal for use with earth-orbiting spacecraft. The
system consists of an optical transceiver head on a two-axis gimbal with a separate electronics assembly that contains the
avionics, modem and laser. The link is achieved by multiplexing on the flight terminal four 0.5-W lasers in the C-band
that are modulated at up to 2.5 Gb/s; transmitted through a 5-cm aperture; and received by a 1m ground aperture. A
description of the system together with experimental tests of a prototype is presented.
We have developed and tested an optical ranging system using a Pseudo-Random Bit Stream (PRBS) modulation
technique. The optical transceiver consisted of an infrared laser transmitter co-aligned with a receiver telescope. The
infrared laser beam was propagated to a retro-reflector and then received by a detector coupled to the telescope. The
transceiver itself was mounted on a gimbal that could actively track moving targets through a camera that was bore
sighted with the optical detector. The detected optical signal was processed in real time to produce a range measurement
with sub mm accuracy. This system was tested in the field using both stationary and moving targets up to 5 km away.
Ranging measurements to an aircraft were compared with results obtained by differential GPS (Global Positioning
We present results of the acquisition and pointing system from successful aircraft-to-ground optical communication
demonstrations performed at JPL and nearby at the Table Mountain Facility. Pointing acquisition was accomplished by
first using a GPS/INS system to point the aircraft transceiver's beam at the ground station which was equipped with a
wide-field camera for acquisition, then locking the ground station pointing to the aircraft's beam. Finally, the aircraft
transceiver pointing was locked to the return beam from the ground. Before we began the design and construction of the
pointing control system we obtained flight data of typical pointing disturbances on the target aircraft. We then used
these data in simulations of the acquisition process and of closed-loop operation. These simulations were used to make
design decisions. Excellent pointing performance was achieved in spite of the large disturbances on the aircraft by
using a direct-drive brushless DC motor gimbal which provided both passive disturbance isolation and high pointing
control loop bandwidth.
JPL in collaboration with JAXA and NICT demonstrated a 50Mb/s downlink and 2Mb/s uplink bi-directional link with the LEO OICETS satellite. The experiments were conducted in May and June over a variety of atmospheric conditions. Bit error rates of 10<sup>-1</sup> to less than 10<sup>-6</sup> were measured on the downlink. This paper describes the preparations, precursor experiments, and operations for the link. It also presents the analyzed downlink data results.
The OCTL to OICETS Optical Link Experiment (OTOOLE) project demonstrated bi-directional optical
communications between the JAXA Optical Inter-orbit Communications Engineering Test Satellite
(OICETS) spacecraft and the NASA Optical Communications Telescope Laboratory (OCTL) ground
station. This paper provides a detailed description of the experiment design for the uplink optical channel,
in which 4 beacon lasers and 3 modulated communication lasers were combined and projected through the
F/76 OCTL main telescope. The paper also describes the reimaging optical design employed on the
acquisition telescope for receiving the OICETS-transmitted signal and the design of the receiver channel.
Performance tests and alignment techniques of both systems are described.
JPL has developed a series of software and hardware tools to analyze and record data from a 50Mb/s down and 2 Mb/s
up bi-directional optical link with the LUCE terminal onboard the LEO OICETS satellite. This paper presents the data
products for this experiment including the system architecture and analysis of the actual data received.
Video imagery was streamed from the ground to an aircraft using a free-space laser communication link. The link
operated at 270 Mb/s over slant ranges of 5-9 km in day and night time background conditions. The experiment was
designed to demonstrate autonomous link acquisition and served as a first proof-of-concept for a planetary access link
between a surface asset and an orbiter at Mars. System parameters monitored during the link demonstration including
acquisition and tracking and communication performance are discussed.
Optical access links can be used for relaying data from the surface of Mars to spacecraft orbiting Mars. In this paper
considerations related to the concept of operations, link analysis and low-complexity transceiver design required for
future implementation are discussed, along with the description of some prototype transceiver development that has been
We have validated an autonomous acquisition scheme that is critical for achieving data transfer over proximity links
with ranges up to a few thousand kilometers. The sun-illuminated International Space Station (ISS) against a dark sky
background during terminator passes over Southern California was used to validate the autonomous acquisition and
tracking scheme. A root mean square (rms) accuracy of 83 μrad was achieved.
Optical communications is a key technology to meet the bandwidth expansion required in the global information grid.
High bandwidth bi-directional links between sub-orbital platforms and ground and space terminals can provide a
seamless interconnectivity for rapid return of critical data to analysts. The JPL Optical Communications Telescope
Laboratory (OCTL) is located in Wrightwood California at an altitude of 2.2.km. This 200 sq-m facility houses a state-of-
the-art 1-m telescope and is used to develop operational strategies for ground-to-space laser beam propagation that
include safe beam transmission through navigable air space, adaptive optics correction and multi-beam scintillation
mitigation, and line of sight optical attenuation monitoring. JPL has received authorization from international satellite
owners to transmit laser beams to more than twenty retro-reflecting satellites. This paper presents recent progress in the
development of these operational strategies tested by narrow laser beam transmissions from the OCTL to retro-reflecting
satellites. We present experimental results and compare our measurements with predicted performance for a variety of
The requirements and design concepts for a ground-based laser assembly for transmitting an uplink beacon to a Mars
bound spacecraft, carrying a laser communications terminal, are reported. The effects of the atmosphere are analyzed
and drive the multi-beam design.
A laser beam with a pseudo random bit stream pattern amplitude modulation is retro reflected off a target to produce a real time ranging signal using a cross correlation technique. The measured resolution of the system was 0.2 mm with an absolute accuracy of ± 2 mm over 2 m. The use of a modulated retro reflector allows a communications signal to be added to the ranging capability.