Welcome to the NASA Goddard Space Flight Center
where we're building the
Laser Communication Relay Demonstration (LCRD).
LCRD is a technology demonstration mission
that will use infrared lasers to send
and receive data above gigabit
per second in a relay capacity.
Multiple systems going to the payload
LCRD will carry two optical modules or telescopes
where the data encoded lasers will be
transmitted and received
and two integrated modems to modulate the data
onto the waves.
Two control electronic
boxes command the optical modules
while a switching unit provides the ability to
relay between the two sides of the payload.
Today we're going to take a
closer look at the optical modules and
how we're developing those. Come on in.
Russell is the lead for LCRD's optical module
development and he's going to show us how
things are going today. How are you doing Russ?
Great, you ready to take a look at the optical modules?
Let's do it.
Now can you tell me about the optical module?
What is it and what does it do?
So the optical module is the device that points
the down link beam at the ground station
and it also gathers the light coming up
from the ground station to the payload
it responds to commands from the controller
electronics and it's connected to modem
via these two optical fibers.
Ok, I see now so
can you break it down a little bit for me,
I know there's a lot of smaller assembly
that go into the overall optical module,
like the gimbal, what's the gimbal what does that do?
The gimbal is right over here.
The optical module has a two-axis gimball.
One of the actuators controls east-west
pointing when we're on orbit and the
other one controls north-south.
They both take extremely small steps
OK, so mounted on the gimbal is
the optical head, which is a combination of
a few sub-assembles.
What are those sub-assembles and what do they do?
The Optical head is made up of the solar window assembly
the optical assembly,
which we can't see
and the Inertial Stable Platform
and the solar window assembly has a large mirror
with a special optical coating.
It's a mirror and most wavelength but it lets
the LCRD wavelengths pass through.
OK, alright, so I know in Lasercom
you need the steady and stable beam in order
to hit the ground station.
How do you account for that on the spacecraft?
How do you keep the beam steady?
That's the job of the Inertially Stable Platform (ISP)
so the optical assembly is mounted on the ISP
and the ISP has some sensors that measures
tip and tilt.
It also has some actuators that are controlled
by the controller electronics
and those are commanded to minimize tip and tilt.
OK, so I hear that the optical assembly is the
most complex and complicated part of the
optical module. Why is that?
Why is it so complicated?
It is complicated. It's made up of two different things
there's a telescope that sits up front
and then a small optics assembly in the back.
The small optics assembly has
several optics that about the size of a dime
each have their own special coating
that rowdy different LCRD wavelengths
where they need to go
and they're also
actuators the small optics assembly that
move the fibers around that are carrying
the data.
OK, speaking of actuators I heard that
there's this rubber o-ring that's around the latch
and in order to deploy the optical module
you have to use paraffin actuators
to deploy it, can you talk to
me about that? What are the paraffin actuators?
Sure we need to have the OM
like this stowed at launch that way the
latch covers the solar window assembly
and supports the optical head
and when we get on orbit we warm up the wax and
one of the paraffin actuators down here.
When it warms up it acts as a pin puller
the latch rotates back and then we can begin operations.
Awesome! Can go check out the test set up?
Sure!
Thanks!
Now this is a really impressive setup is
this where you test the optical modules?
It is, we put the optical module right
here on the jitter table and for some
tests we use these small shakers to disturb
the optical modules. We need to make sure
that the Inertial Stable Platform is
doing its job.
Our host spacecraft has moving parts
which generate disturbances.
OK, and over here I noticed that there's
these really cool looking mirrors.
Why do you need so many of them?
Well these large flat mirrors are for aligning the optical
modules to the optimal test set
and we have three of them because we want to be
able to set up two optical modules
for testing at the same time.
Awesome!
And I noticed the thermal vacuums is in here too.
Besides when the optical modules are integrated
with the payload and the payload goes
off to be made it with the host
spacecraft with the optical modules ever
leave the cleanroom?
The only time to leave is for vibration testing
and that's because we don't need the optical test set
for that.
For everything else we need the OTS
it's very big, it took a long time to assemble
in the line
so instead of moving the OTS, we bring the test
equipment in here,
including the thermal vacuum chamber.
Russ, thank you so much for letting us come in here today
and learn more about the optical modules
Want to learn more about LCRD?
Visit LCRD.GSFC.NASA.GOV