4K video to be streamed from Orion using lasers & off-axis Cassegrain telescopes

[gary]

Providing sufficient communications bandwidth to and from the Moon
during upcoming missions is not easy.

All forms of communication are limited not only by the laws of physics,
but as electrical engineers are well aware, by the fundamental laws of
mathematics.

In an article today at the Institute of Electrical and Electronics Engineers
(IEEE) Spectrum magazine web site, Michael Koziol provides a detailed
report on how the Orion spacecraft to be used on the Artemis 2 mission to
the Moon will use S-band radio communications but will complement
that with laser system called Optical to Orion, or O2O.

O2O's main task will be to stream 4K ultrahigh-definition video from the
Moon to the viewing public back on Earth.

Originally Posted by Michael Koziol , IEEE Spectrum

Before O2O can even be tested in space, it first has to survive the journey. Laser systems mounted on spacecraft use telescopes to send and receive signals. Those telescopes rely on a fiddly arrangement of mirrors and other moving parts. O2O’s telescope will use an off-axis Cassegrain design, a type of telescope with two mirrors to focus the captured light, mounted on a rotating gimbal. Lincoln Lab researchers selected the design because it will allow them to separate the telescope from the optical transceiver, making the entire system more modular. The engineers must ensure that the Space Launch System rocket carrying Orion won’t shake the whole delicate arrangement apart. The researchers at Lincoln Lab have developed clasps and mounts that they hope will reduce vibrations and keep everything intact during the tumultuous launch.

Once O2O is in space, it will have to be precisely aimed. It’s hard to miss a receiver when your radio signal has the cross section the size of a large country. A 6-km-diameter signal, on the other hand, could miss Earth entirely with just a slight bump from the spacecraft. “If you [use] a laser pointer when you’re nervous and your hand is shaking, it’s going to go all over the place,” says Cornwell.

Orion’s onboard equipment will also generate constant minuscule vibrations, any one of which would be enough to throw off an optical signal. So engineers at NASA and Lincoln Lab will place the optical system on an antijitter platform. The platform measures the jitters from the spacecraft and produces an opposite pattern of vibrations to cancel them out—“like noise-canceling headphones,” Cornwell says.

One final hurdle for O2O will be dealing with any cloud cover back on Earth. Infrared wavelengths, like the O2O’s 1,550 nm, are easily absorbed by clouds. A laser beam might travel the nearly 400,000 km from the moon without incident, only to be blocked just above Earth’s surface. Today, the best defense against losing a signal to a passing stratocumulus is to beam transmissions to multiple receivers. O2O, for example, will use ground stations at Table Mountain, Calif., and White Sands, N.M.

Full story, pictures here :-
https://spectrum.ieee.org/telecom/wi...-to-phone-home