Aerospace and Electronic Systems Magazine April 2018 - 17
The following are among the biggest challenges in implementing a commercial VLC system:
C
C
C
The hardware implementation and the miniaturization of a
high-power, high-bandwidth system
The difficulties presented by atmospheric distortion and the
compensation techniques necessary to counteract these impairments
The relatively poor signal-to-noise ratio (SNR) of noncoherent carriers compared to laser-based systems
In this article, we address all three issues and discuss the payload that is being prepared for the Calypso 1U CubeSat (Figures 1
and 2). Verification of this system in orbit on a spacecraft of this
size and power constraint will allow it be easily adapted for larger
CubeSats and various mission requirements.
MISSION GOALS
The primary goal of the Calypso optical payload is to demonstrate
the commercial viability of a fully optical spacecraft, complete
with uplink and downlink. At the same time, a number of exciting
technologies have presented themselves
through the adoption of VLC. The mission also has the following goals:
C
C
C
commercial, off-the-shelf [COTS] components have a spectral
spread of around 15 nm). At the same time, the design is restricted
by a wider beam. Nevertheless, LEDs allow for higher power density for its footprint compared to laser-based systems. To this, we
have chosen a peak electrical power of 140 W and average operational power of 15 W, with an electrooptical efficiency of 70%,
well within the feasible limits of a 1U CubeSat.
The gain of the transmitter and receiver are given by the following [6]:
G (tx) =
16d 2
λ2
πd
G (rx) =
λ
2
A 400-km circular orbit is used, with a maximum link angle from
zenith, of 40°, a beam divergence of 20°, and a homogeneous
power distribution. As a result of the relatively large beam width,
we approximate the aiming loss to 1 dB resulting from receiver
tracking inaccuracies. A 30-cm (12 inch) commercially available
telescope is used as the receiver, and 700 photons/bit is assumed.
To measure atmospheric attenuation through power monitoring on
the precalibrated transmitter
To train and evaluate a deep learning system for optical communication error correction
To evaluate the feasibility of differential phase delay correction
using two ground stations
LINK DESIGN
SNR is a prime concern on the spacecraft downlink due to the low monochromaticity of single-color LEDs (most
APRIL 2018
Figure 2.
Internal layout of the Calypso 1U CubeSat.
IEEE A&E SYSTEMS MAGAZINE
17
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