AEROSPACE

2.  Pre-launch activities of space segment
construction can extend over a significant
period (1 to 3 years).
 The fundamental level of spacecraft
construction commences(start) with the
building of equipments.
 This is generally known as unit level
construction.
 The unit level equipments are first tested
independently, then assembled(‫جوڑنا‬) into
subsystems which are subjected to further
testing.

3.  After this, the subsystems are mounted upon
the mechanical structure to form the system
which will be launched, the spacecraft.
 The spacecraft structure is composed of two
prime elements:
 Service module (SM)
 Communications module (CM).
 The two structural modules are constructed
independently and then integrated to form
the satellite.

4.  When the satellite is complete, it undergoes a
test programme that verifies that the on
board satellite subsystems can operate
together without any incompatibilities.
 The programme then goes on to simulate the
expected environments which the satellite will
experience during its launch and in-flight
life.
 This is a qualification process to prove that
the spacecraft is ready for its launch and
working life.

5.  A significant number of construction
activities take place in a laboratory
environment.
 The laboratory environment is strictly
controlled regarding temperature, humidity,
and cleanliness.
 This is because some units of the spacecraft
can be delicate(‫عمدہ‬), and if environmental
limits are exceeded, damage can occur.

6.  A special room is dedicated for that normally
termed as “CLEAN ROOM”.
 Special filters are fixed on the roof of that
room known as “HEPA FILTERS” (High
Efficiency Particulate Filters).
 These filters have been assigned quality
standards.
 For example 500, 000 dust particles per
cubic and 100, 000 dust particles per cubic
feet etc.


8.  Here 100, 000 dust particles per cubic feet
has more quality standards than 500, 000
dust particles per cubic feet etc.
 The quality standards vary purpose to
purpose.
 Pre launch operations of the satellite should
include rehearsals of post launch activities
and include worst case situations.

9.  If all goes well when the satellite is in orbit,
there will be the possibility for less satellite
control activities than during its testing and
prelaunch verification.
 The task of integrating and testing spacecraft
subsystems to form the spacecraft is often
known as spacecraft level (system) assembly,
integration, and testing (AIT).

10.  A verification of operation can be sufficient if
a full performance test has been made during
unit or subsystem level testing.
 In such cases, the spacecraft system level
operation can be termed as verification,
hence the emergence of the term spacecraft
level (system) assembly, integration, and
verification (AIV).
 AIV can be considered to be a derivative of
unit or subsystem level AIT.

11.  From a spacecraft operation standpoint, the
electrical models which were operated by
telemetry and telecommands could be
termed:
 Engineering model (EM)
 Qualification model (QM)
 Flight model (FM)

12. This model was constructed to enable
electrical designs to be verified at system
level.
 Any design anomalies would be corrected and
implemented on the next development
model, the qualification model.

13.  Constructed with components that would be
subjected to environmental conditions that
are greater than those expected.
 QM operations were a stage of total system
level design qualification which included
thermal and structural aspects.

14.  The flight model is the operational spacecraft
which would be launched.

15.  With the experience gained from historical
testing methods, it is now possible to
construct prototype flight model (PFM)
spacecraft.
 As the name implies, these are prototypes
which will be launched, and therefore, obviate
the need for the construction of EM and QM
spacecraft, thus giving cost saving
incentives(‫رغیب‬َ‫ت‬).

16.  A PFM spacecraft will first be operated in a
laboratory environment and then, if this is
successful, a repeat of the operations will be
made in the differing and more demanding
environments of launch and space
simulations(‫ونہ‬ُ‫م‬‫.)ن‬
 These satellites have been operated in
simulated launch and space environments
which have normally included two prime
environmental tests.

17.  These tests simulate the expected vibrations
that will be experienced by the satellite
during launch.
 Vibrations caused by the operation of the
launch vehicle engines can be transmitted to
the satellite.

18.  The environmental conditions of a vacuum
with solar simulations are produced in a test
chamber.
 The satellite is placed in the chamber which is
pumped down to a vacuum. Lamps provide
illumination which is a simulation of the Sun.

19.  For some of the tests, the solar simulators
are not used, thereby simulating a shadow
condition for when the satellite is not
exposed to the Sun.
 In summary, thermal vacuum tests
necessitate placing the satellite in a vacuum
and varying the temperatures over a range,
typically 80°C to — 130°C for geostationary
orbits.