ROOM
15
Special Report
Figure 5. Illustration of
how on-orbit assembly
approaches can alleviate
limitations associated
with deploying
communications
satellites to enhance
system performance and
increase revenue return.
increase at end of life enabled by on-orbit
assembly is about US$300 million per satellite.
Figure 5 shows how assembling more antennas
onto a single platform, conducting on-orbit
manufacture and assembly to eliminate the
stresses of launch, and assembling refreshed
payloads onto an existing platform, all contribute
to increased system performance and revenue
return for a communications satellite.
Technical capability status
Having identified the potential benefits of on-orbit
assembly, it is informative to review present status
and future prospects for the technical capabilities
that can be expected. On-orbit assembly of
spacecraft will require development of a number
of technologies and processes involving sensing,
robotics, automation and modular interfaces
between payloads and platforms.
Relevant space activities that represent
intermediate steps to full on-orbit assembly
include on-orbit inspection and servicing of
spacecraft. A significant heritage has been built up
over the last 50 years by astronauts conducting
on-orbit assembly and lessons learned from these
activities will inform future missions and the
development of new techniques.
Capabilities are being developed for automated
on-orbit inspection of spacecraft. In the United
States, the Air Force Research Laboratory (AFRL)
Automated Navigation and Guidance Experiment
for Local Space (ANGELS) spacecraft investigated
technologies and procedures for manoeuvering
and imaging within a few kilometres of an
expended rocket body.
Concepts are also being developed using sensors
for inspection of spacecraft. On-orbit servicing,
including autonomous docking, was demonstrated
by the US Defense Advanced Research Projects
Agency’s (DARPA) Orbital Express in 2007. The
mission involved a surrogate next generation satellite
and a prototype servicing spacecraft. The satellites
docked several times, and the prototype servicer
refuelled the satellite and exchanged modules.
The most impressive example of astronaut-
assisted assembly is the construction of
the International Space Station (ISS), which
involved over 35 Space Shuttle launches and 160
spacewalks spanning 1,061 hours. The station is
the size of a football field weighing over 400,000
kg and encompassing over 900 cubic metres of
pressurised volume, and has been called home by
over 200 people representing 15 countries.
Robotic assembly
A spectrum of robotic assembly techniques could
be used to replace astronaut assembly, from
robots as eyes, subordinates and sidekicks to
robots as surrogates and specialists.
United States’ Orbital ATK’s Mission Extension
Vehicle (MEV) is one example of a servicing
capability. The NASA Restore-L mission is
scheduled for 2020, and involves the refuelling of
Landsat-7 by a MEV. The MEV will autonomously
rendezvous with the Landsat spacecraft and then
tele-robotically cut wires, remove caps and refuel
the satellite. Landsat-7, an unprepared ‘client’ built
long before MEV technology was available, will be
about 20 years old at that point.
Restore-L demonstrates the potential for
robotic servicing to increase the lifespan and
safety of current missions. The Space Dynamics
Department of Germany’s Institute of Robotics
and Mechatronics runs a mission called Deutsche
Orbitale Servicing (DEOS) which involves two
satellites, a ‘client’ and a ‘servicer’. Planned to launch
in 2018, the servicer will chase and rendezvous
with the client, demonstrate refuelling and module
exchange, and then safely de-orbit the client.
DARPA is developing robotic servicing vehicles
for GEO satellites as part of its Robotic Servicing of
Geosynchronous Satellites (RSGS) project. Satellites
in this high orbit will be able to be repaired and
maintained over time, increasing their capabilities
and value to their owners. Under development
since 2016, the planned launch date is 2021.
A spectrum of robotic assembly techniques could
be used to replace astronaut assembly, from
robots as eyes, subordinates and sidekicks to
robots as surrogates and specialists
Constraint
Result
Outcome
New approach
COMMERCIAL COMMUNICATIONS: AFTER OMAS
Small fairing
Stresses
of launch
Cost of
launch
Assemble many
antennas onto
single platform
On-orbit
manufacture
and assembly
Assemble
payload after
7 years
Increased
payload
utilization
Increased
payload
mass
Increased
system
performance
and revenue
return
