THE BASELINE ARIANE
The Ariane 5 launcher is designed to
place various payloads automatically into orbit as
cost-effectively as possible: satellites, space station
elements, cargo vessels, etc.
The basic design favours economics and very secure operation.
Although radically different from Ariane 4, it is a simple,
robust design, drawing on proven technologies and incorporating
the long experience of previous programmes.
MAIN CRYOGENIC STAGE (EPC)
The main cryogenic stage, or core
stage, primarily comprises a large aluminium alloy tank, a
thrust frame that transmits the engine’s thrust to the stage,
and a forward skirt, which interfaces with the upper composite
and transmits the thrust from the two giant solid boosters.
The tank comprises two compartments containing 157 tonnes of
very low temperature cryogenic propellants. The cryogenic engine
can be steered in two axes for flight control, via the engine
actuation unit. It delivers about 100 tonnes of thrust.
The core stage operates continuously for 600 seconds, providing
most of the kinetic energy needed to place a payload in orbit.
When it shuts down, the launcher is at an altitude of 130 to 420
kilometres, depending on the mission. This stage is not placed
into orbit, but falls back naturally into the sea.
SOLID BOOSTERS (EAP)
Each of the two solid boosters
contains some 240 tonnes of solid propellant. These are the
largest solid rocket motors ever built in Europe.
The motor comprises a casing made of seven steel cylindrical
sections, and a nozzle mounted on a flexible bearing, that can
be steered up to 6 degrees by the nozzle actuation unit. The
propellant is loaded in three segments.
Each MPS solid rocket motor delivers thrust ranging from about
540 tonnes at lift-off to a maximum of 600 tonnes (1,320,000
lb.). Each MPS generates as much thrust as an Ariane 4 at
lift-off. The two solid boosters are ignited a few seconds after
ignition of the main cryogenic stage, to make sure that the main
engine is operating correctly.
With a combined thrust of 1,200 tonnes – as much as ten
supersonic Concordes! – the two solid boosters provide some 90%
of the total lift-off thrust. They burn for about 130 seconds.
After burnout, they are separated from the main stage by a
pyrotechnic system at an altitude of 55 to 70 kilometres
(depending on the mission). They continue on a trajectory
peaking at 80 to 140 kilometres, then deploy parachutes and fall
back into the sea about 150 kilometres from the launch base.
They are regularly recovered for inspection and analysis.
STORABLE PROPELLANT STAGE (EPS)
The storable propellant upper stage
completes the orbital injection of the payload(s) into the
targeted orbit(s), and ensures payload separation and
orientation. Built by Astrium, the storable propellant stage
comprises an array of four tanks containing up to 9.7 tonnes of
conventional propellants (MMH and N204), plus an engine that can
be restarted twice and delivers vacuum thrust of 2.7 tonnes. Its
nozzle is gimballed in two axes for thrust vector control.
For missions into low Earth orbit, the launcher flies
ballistically before ignition of the upper stage. This stage
operates for about 1,000 seconds on a GTO mission. Its restart
capability can be used to optimise the orbital injection of
payloads, depending on the type of satellite and the targeted
orbit. It also clears the payload’s orbit after separation,
especially on LEO missions for injection of elements within a
future space station’s manoeuvring range.
VEHICLE EQUIPMENT BAY
Astrium is in charge of production of
the vehicle equipment bay (VEB), which is composed of a
cylindrical structure and a cone supporting the upper stage and
part of the electrical equipment needed for each mission.
In fact, the VEB contains most of the flight control and
telemetry equipment. It also contains the hydrazine
thruster-based attitude control system, which includes two sets
of nozzles for launcher roll control during the powered phases,
and for attitude control of the upper composite during payload
release. The maximum specified operating time for the VEB is
about 6,900 seconds (used during LEO missions).
SATELLITE SUPPORT STRUCTURE (SPELTRA)
Speltra, the French acronym for Ariane
launch external support structure, enables the simultaneous
launch of several payloads. For launch, the different payloads
are mounted either on or inside the Speltra, depending on their
shape and mission requirements. The Speltra is manufactured by
ARIANE DUAL LAUNCH SYSTEM (SYLDA)
The Sylda dual launch system also
enables the simultaneous launch of two payloads. It is an
internal structure, located inside the fairing. Depending on the
satellites’ shapes and mission requirements, they are placed on
top of or inside the Sylda. It is manufactured by Astrium, and
is available in six different versions of different heights, to
make optimum use of the upper part of the launcher.
The cone-shaped fairing protects the
payload during its passage through the atmosphere, while also
maintaining the required launcher’s aerodynamics. It is released
about 200 seconds after lift-off, at an altitude of
approximately 110 kilometres. The Ariane 5 fairing is built by
Oerlikon Contraves, and the pyrotechnic separation system is
made by EADS LAUNCH VEHICLES. Three different fairing models are
planned: short, medium and long.