ROOM
12
Special Report
of constraints imposed by launch vehicle
fairing size and shape. The structures are
packaged more efficiently into the launch
fairing than can be accomplished with a
fully integrated spacecraft
• An ability to achieve increased
flexibility and resilience of spacecraft
assets enabled by assembly involving
additions, replacements and technology
updates of payloads onto a compliant,
orbiting platform
• An ability to create cost savings related to
carrying more useful mass - less packaging
material (structure) for ruggedization, and
less platform material
• An ability to create cost savings through
reduction in the number and intensity
of ground-based tests of space-bound
spacecraft and subsystems
• An ability to create structures that
cannot be created on Earth at all
because of constraints imposed by the
terrestrial gravity.
These advantages, in turn, can provide dramatic
benefits in a number of different ways to a variety
of different space operations.
In astronomy, on-orbit assembly can enable
the construction of telescopes too large to be
fully built on Earth and launched into orbit. High
definition space telescopes (HDST) are very large,
space-based observatories with a number of
primary missions, including characterisation of
exoplanets and the search for life on exoEarths
through the use of spectroscopic bio-markers.
An analysis performed by the Association of
Universities for Research in Astronomy (‘From
Cosmic Birth to Living Earths: The Future of
UVOIR Space Astronomy’, 2015) showed that at
least 30 candidates must be characterised in order
to infer statistically meaningful conclusions about
the prospects for biological life on other planets.
The same analysis revealed that telescope
aperture diameter is the most important
parameter in determining the number of
candidates that can be characterised, and the
relation is plotted in Figure 2. Data points are
included for the Hubble Space Telescope (HST)
and for the James Webb Space Telescope (JWST),
the latter being the next NASA HDST mission
planned for launch in 2018. With an aperture
diameter of 6.5 m, it is estimated that JWST will
identify about 10 exoEarths.
To advance the search for exoEarth candidates
beyond JWST to a level of stronger scientific
rigour, a significant increase in telescope aperture
diameter is required on future HDST missions and
Figure 2 shows that an aperture of 12 m would
yield more than 30 candidates.
The JWST aperture is approaching the size
limit for what can be accommodated within
current launch vehicle fairings; even then, this
size necessitates use of a complicated folding
arrangement, with many associated risks and
ground testing requirements.
While larger launch fairings are being
considered in the development of future launch
systems, significant growth beyond current
capabilities is both technically challenging and
extraordinarily expensive.
The idea is to assemble a large telescope in
space using large hexagonal elements that are
4m across from one flat side to another
Figure 1. Illustration of
how the current approach
for deploying
communications satellites
places limitations on
revenue return.
Above right: Figure 2.
Exoplanet yield as a
function of telescope
diameter (adapted from
AURA, 2015).
Constraint
Result
Implication
Outcome
Current
approach
COMMERCIAL COMMUNICATIONS: BEFORE OMAS
Fairing
diameter
Stresses
of launch
Cost
of launch
Number
of antennas
limited
Antenna
size limited
Maximize size
& number
of antennas
Add parasitic
structural
mass, pre-
launch tests
Limited
payload
utilization
Approaching
single launch
payload limit
Poor payload
performance
at end of life
Limitations
on revenue
return
Desire for
long lifetime
assets
Payload used
for 15 years
Need for
ruggedization
ExoEarth Candidate Yield
Telescope Diameter (m)
90
80
70
60
50
40
30
20
10
0
0
5
10
15
20
25
Stage #3
Stage #2
Stage #1
JWST
HST
