Providing High-Resolution Intelligence
Technological constraints, pressing defense needs and high costs – these are
just a few of the challenges facing the employees of the space activity at
Elbit Systems. Exclusive interview
Ami Rojkes Dombe | 2/09/2015
http://www.israeldefense.co.il/en/content/providing-high-resolution-intelligence

In the early 1980s, pursuant to the peace agreement with Egypt, the Israel
Ministry of Defense (IMOD) decided Israel should enter the space business.
The need was immediate. Owing to the agreement with Cairo, the State of
Israel could not employ intelligence aircraft over Egyptian territory.Space
remained the only domain where sovereignty was not an issue. As part of the
national effort, the El-Op Company (currently a part of the Elbit Systems
Group) was ordered to develop the camera for Israel’s optical surveillance
satellites.


“In those days only the superpowers were involved in this activity, so the
knowledge gained up to that time was not available or accessible to the
Israeli engineers, who had to invent and develop everything from the ground
up,” explains Ilan Porat, Head of the Space Unit at Elbit Systems. “The
objective was to provide high-resolution intelligence for military purposes.
Our primary client, then and now, is IMOD.”

The space unit of Elbit Systems, headed by Porat, is located at the Science
Park in Rehovot. Even the entrance to the building states that this is a
national asset. Numerous certificates of merit issued by IMOD for various
developments are posted on the walls, as a monument commemorating the
engineering and scientific potential of this small country. “We squeeze out
of our systems the maximum resolution for the given size and weight,” says
Porat. “The launcher is relatively small, because of the fact that owing to
our location and geopolitical constraints imposed on Israel, we are forced
to launch westward, contrary to the physical advantage of launching
eastward – just the opposite of the rest of the world.

“These constraints compel us to work with a compact, lightweight camera.
Israel is unique with regard to the weight and size considerations in the
development of satellite cameras, and is a global leader in the ratio
between the weight of the camera and its relative performance. Israel is
also among the world leaders in resolution, along with such countries as the
USA and France.

“One thing must be said: the development of cameras for satellites is not a
viable business economically,” explains Porat. “Export is practically
nonexistent, and financing is provided mostly by IMOD. Additionally, there
is a financing mechanism intended to retain national knowledge centers or in
other words – retain the professional personnel of this field. This involves
funding in ILS that does not come from US foreign aid. These funds enable us
to develop the building blocks of the next generation of space cameras for
the State of Israel.

“There is nothing unusual about it. Most of the world’s space industries do
not generate profits. It is a highly competitive field that demands massive
resources as well as political flexibility. The French, for example, develop
satellites for their military and market them worldwide. In Israel that is
not the case. The Americans operate in the same way. In those countries, the
defense ministries are in charge of marketing the satellites, sometimes with
the assistance of the top political echelon. In Israel it works differently,
and as there is no export activity, this field must rely on government
funding.”

Camera Development

The space cameras made by El-Op weigh only a few dozen kilograms only. The
first system developed at Elbit had a lens diameter of 30 centimeters which
provided a resolution of 2 meters (the minimum size of an identifiable
ground object). Subsequently, they moved up to 50 cm diameter, which enabled
a resolution of 70 cm. In the third and present generation, lens diameter is
70 cm and resolution is 50 cm. The latest camera weighs less than 100 kg. As
the lens diameter increases, the camera becomes larger and heavier.

Another point that must be remembered is that no corrections or repairs may
be made in space. If anything goes wrong during the launch or while the
camera is operating in space, the satellite will become space waste. Porat
explains that the challenge is to develop and adjust such a system on the
ground, under gravity conditions. In space there is no gravity, and as a
result optical components tend to warp. As there is no place in the world
where this may be tested, El-Op invests considerable efforts in proper
design and evaluation of the effect of the absence of gravity on the system
once it arrives in space.

Additionally, in order to test the camera while simulating the working
conditions in space, Elbit designed a special testing facility, the size of
a three-story building. Construction was completed about three years ago,
and the new facility is used to test the camera before it is installed in
the satellite. The testing is based on the simulation of extreme space
conditions, including vacuum, temperature, radiation, vibrations and other
parameters.

One of the elements of the simulation facility is a collimator. Its function
is to inject targets into the camera from a simulated distance of 600
kilometers, which is the distance between the satellite and planet Earth.
The collimator is a sort of an inverted telescope – a specially
requisitioned Israeli development. Porat explains that in order to test the
camera for a resolution of 50 cm, a more accurate measurement array is
required (you cannot measure a meter with a meter). In other words, the
measurement and testing array for the space camera should possess the
stability and accuracy characteristics that are equal to a resolution of 5
cm from a distance of 600 km. In order to overcome the natural vibrations of
the planet as well as interference caused by moving trains, vehicles, noise
sources, etc. – the array ‘rides’ a 250 ton concrete slab that floats over
pneumatic feet and is not connected to the floor. All of the assemblies of
the measurement array are not connected to the floor either, so as to
isolate them from vibrations and external interference.

Elbit specified the requirements for the simulation facility, including the
thermal vacuum compartment, the floating concrete slab and its feet, the
collimator and other elements, and these were subsequently manufactured by
various manufacturers in Israel and overseas. The construction process took
about three years to complete. Along with the actual construction of the
building, the entire array had to be integrated as it was delivered by the
various manufacturers and tested for flawless operation. “There are fewer
than five such installations worldwide,” says Porat. “Space is a difficult
environment to operate in. If you face the sun, the camera might heat up and
reach extreme temperatures in minutes, which could lead to warping and
irreversible damage to the optical components – even to melting.

“On the other hand, the rest of the sky is at a temperature of absolute
zero, which will cool the camera components to temperatures that are lower
than those where the camera can survive. Consequently, we are required to
come up with an accurate thermal design which includes a strict thermal
control system while the camera is in space. Another aspect is the radiation
in space, which damages the electronics and optical components. The optics
should also survive the high acceleration rates that develop during the
launch. It all adds up to a fairly complex simulation challenge.”

Developing a camera generation takes about ten years. Duplicating an
existing camera takes about three years. This includes the final testing
that takes about six months in the simulation facility. The main lens is
processed with a deviation measured by atoms. There are no such
off-the-shelf products on the market, they explain at Elbit. Additionally,
owing to the very high optical sensitivity, mirror quality must be excellent
and distortion must be minimal. The acceptable deviation of the mirror
position is measured in microns (thousandths of a millimeter).

In order to reduce the camera size, Elbit uses optics that are based on
mirrors rather than on lenses, which enables them to reduce the camera
length by more than 10 times. In other words, an optical length of 10-15
meters is minimized into less than one meter. Each mirror has a specific
magnification factor and a specific shape, so every distortion or deviation
will be magnified accordingly.

In order to reach high accuracy rates and light weight, Elbit developed some
highly specialized machines. One of them machines the rear part of the
mirror. This machining method uses an ultrasonic technique which enables,
theoretically, the removal of layers only a few molecules thick. Porat
explains that this was the life’s work of a German engineer who aspired to
be able to etch serial numbers on diamonds. He worked on this technology for
30 years, but then laser technology appeared and the whole project went down
the drain. Elbit took his technology and used it as a basis for the
development of this tool. You start off with a mirror weighing 120 kg and in
the end remain with a mirror weighing only 20 kg. “Why are there no such
machines anywhere in the world? Because no one needs them except Israel,”
says Porat.

Another device polishes the mirror using a specialized magnetic fluid. In
this way, no pressure is exerted on the mirror. This method was developed
abroad for the polishing of flexible contact lenses. Elbit took the idea and
developed it into a device for polishing nearly hollow mirrors (after the
machining stage, the rear part of the mirror looks like a honeycomb). The
entire process is computer controlled, thereby making it possible to reach a
maximum error of a few atoms. At the end of the process, the mirror is
coated with a reflective finish so as to enhance reflection. In order to
exploit most of the energy received from the light reflected off the Earth,
each one of the camera mirrors must produce maximum reflection. The entire
machining, polishing and coating process takes about one year to complete.

After the camera is installed in the satellite and launched into space, the
only parameter that may be corrected is focus, using an assembly that
remains adjustable even when the camera is in space by a suitable command
from the ground. All of the other elements remain fixed. If anything moves
on the way to outer space, the camera will not work and the satellite will
become space waste.

Can the satellite track moving targets?

“This only happens in Hollywood,” says Porat. “The satellite covers the
distance from sunrise to sunset within a few minutes (depending on the
altitude of its orbit). If you want to track a target, you need to see it
constantly. Consequently, even in an optimal profile, the theoretical
maximum interval for tracking a target is a few minutes over the course of
an hour and a half, which is the time it takes the satellite to complete a
full circle around the Earth. Tracking moving targets is science fiction. It
is impossible for a satellite to track a moving target in real time. Even
then, the angle, as well as the range, will change significantly during the
actual photography cycle. The only way to remain permanently above a given
area is using a geostationary orbit, which is above the equator at an
altitude of almost 36,000 kilometers (like the communication satellites).
From these ranges, it is impossible to provide photographs with usable
resolutions unless you have a camera whose lens diameter is dozens of
meters.

Nanosatellites?

Admittedly, using nanosatellites is a new and “sexy” activity, but for space
photography you need a large lens. Porat explains that there are thoughts of
splitting the main mirror into several small satellites, but the problem is
maintaining the relative accuracy so that they work in harmony. “We do not
know how to do that yet. It would be feasible in the future, but that will
take time,” says Porat. “There are also thoughts about deployable optics,
namely the optical array will be launched into space in a retracted state,
to be deployed in space. Once again, in this case, too, system accuracy is a
sensitive issue.

“One of the possible uses of nanosatellites is testing electronics for space
use. In the past, we used to purchase space-standard products.
Unfortunately, these products are costly, and companies stopped
manufacturing such parts as it is not profitable and there is hardly any
demand for them. Today, both we and other manufacturers go to military or
civilian components and subject them to a series of tests for withstanding
space radiation. If you have a cheap nanosatellite whose launching is also
cheap, you will be able to use it to conduct such resistance tests in
space.”

How much Resolution is Enough?

One of the questions in the context of photo-surveillance satellites
concerns the resolution that is sufficient in order to provide good
intelligence. Well, the answer depends on the person being asked. Some
terrorist organizations collect intelligence using the Google Earth service.
Another option is to purchase photographs on the commercial market. Even
countries use this option and today it is possible to purchase satellite
photographs in black and white, as well as in color, from commercial
companies worldwide, with a 50 cm resolution and more recently even with 25
cm resolution.

Assuming there are no size or weight restrictions that apply to the camera,
according to statistical calculations, the optimal resolution that may be
achieved is around 10-15 cm, owing to the atmospheric transmittance
limitation. This is a physical limitation that applies to space photography
through the atmosphere, owing to the turbulence phenomenon. Turbulence is
the result of changes in air density (winds, jet streams, temperature
differentials, humidity, etc.) in the atmosphere which prevent the image
reflected off the ground from reaching the aperture of the space camera with
sufficient quality. The most advanced country with regard to this aspect is
the USA.

“The more you improve the resolution, the more pixels you will require, as
otherwise your coverage area will be too small,” explains Porat.
“Eventually, there is a trade-off between resolution and coverage area. If
you want to scan a whole country and you only have a small coverage area, by
the time you scan it again it will no longer be the same country.”

Although resolution is normally the issue being addressed, Porat insists on
directing the spotlight at the data processing capability. “A
third-generation camera (<50 cm) generates data at a rate of almost 6
gigabytes/second. You must do something with it,” explains Porat.
“Admittedly, there are compression and storage mechanisms onboard the
satellite, but eventually, you have to get the data to the ground, as
otherwise, why would you launch a satellite in the first place? Today, with
a compression ratio of 1:6 or 1:7, you lose some of the resolution and
sometimes some of the details, but that is acceptable. The question is how
the interpreters on the ground can deal with this amount of data.

“The satellite completes a full circle around the Earth every ninety
minutes, travelling at a speed of about 7 km per second. Assuming the size
of the Dan region is about 15x15 km, photographing it will require two
seconds of photography out of ninety minutes. Consider the number of people
who would have to sit down to interpret that. Within ninety minutes you
should interpret 12 gigabytes of data. If you fail to do it, you will not be
able to notice the changes. The entire chain should be ready for such a
satellite. Admittedly, the advantage of a satellite of this type is the
ability to photograph at near real time, but it all depends on the
interpretation capability – that’s where the bottleneck is located.”