To survive the physical stresses associated with launch, a spacecraft and its
payload must be solidly built and well tested. Each spacecraft built for an
ESA science mission is unique and so must undergo its own ‘baptism of fire’
to prove that it can withstand the launch and reach its orbit in perfect
shape ready to carry out its mission.
During the past few weeks the structural model of SMART-1, the first in ESA’s
series of Small Missions for Advanced Research in Technology, has undergone
vibration testing at ESTEC — ESA’s space research and technology centre at
Noordwijk in the Netherlands. SMART-1 will test solar electric primary
propulsion as the key technology for future deep-space missions. BepiColombo,
ESA’s mission to explore the planet Mercury, could be the first to benefit
from the SMART-1 mission results.
The SMART-1 structural model was constructed in order to mimic the mechanical
behaviour of the final flight spacecraft. Any mechanical test which must be
performed to verify that the design of the spacecraft is sound is then
performed on this model. The real instruments (the payload) are replaced
by dummy instruments which have the same mass and dimensions as the actual
payload.
Vibration testing involves shaking the ‘spacecraft’ in a way that simulates
the possible types of vibration that the spacecraft will encounter from
launch to operation. Vibrations can also arise from the noise generated
by the launch rocket, which can reach up to 146 decibels. The so-called
‘acoustic tests’ check that these vibrations will not damage the spacecraft.
Engineers are experts in designing the elements that make up a scientific
satellite but since each spacecraft, and its payload, is unique, it is vital
to ensure that the final spacecraft construction can survive the rigors of
its journey into space.
The acoustic test is performed in the Large European Acoustic Facility
(LEAF) at ESTEC. LEAF is a large chamber in which the structural model is
exposed to acoustic noise comparable to several Jumbo jets at a distance
of 30 m. Other vibration tests are performed by clamping the spacecraft to
an electro-dynamic shaker, which loads the 42 kg SMART-1 structure with the
equivalent of over 4 tonnes about 20 times per second. Lower levels of
vibrations are applied up to 100 Hz.
Shock tests are also performed on the structural model. For these tests
Arianespace provides a flight representative adapter with an explosive ring
(called a Shogun). The spacecraft is mounted on it and then the explosives
are fired, generating shock waves of 5000 g.
In parallel with these mechanical tests, electrical and software tests are
performed on the ‘bench test models’ — simplified versions of the final
instruments. With the data accumulated from these tests, final adjustments
to the spacecraft and payload fittings, if necessary, can be incorporated
into the real flight spacecraft.
This autumn, the real SMART-1 will start to take shape and it too will
repeat a series of mechanical, electrical and thermal tests prior to
shipping to Kourou for launch in winter 2002.
The Swedish Space Corporation, as prime contractor for the SMART-1 mission,
is responsible for the development and construction of the SMART-1
spacecraft.
USEFUL LINKS FOR THIS STORY
* SMART-1 home page
* Swedish Space Corporation
IMAGE CAPTIONS:
[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=10&cid=12&oid=27555&ooid=27780]
SMART-1 structural model during testing at ESTEC. A series of tests were
performed on the SMART-1 structural model during the early summer of 2001.
In particular, acoustic, vibration and shock tests were carried out at
ESTEC in order to test the structural integrity of the SMART-1 design.
[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=10&cid=12&oid=27555&ooid=27781]
SMART-1 will undergo a series of structural, electrical and mechanical tests
prior to its launch in 2002. Testing of the structural model was carried out,
during the summer of 2001, at ESA’s space research and technology centre
(ESTEC).
