Rocket engine operation method
Pressure-fed rocket cycle. Propellant tanks are pressurized to directly supply fuel and oxidizer to the engine, eliminating the need for
turbopumps
.
The
pressure-fed engine
is a class of
rocket engine
designs. A separate gas supply, usually
helium
, pressurizes the propellant tanks to force fuel and oxidizer to the combustion chamber. To maintain adequate flow, the tank pressures must exceed the combustion chamber pressure.
Pressure fed engines have simple plumbing and have no need for complex and occasionally unreliable
turbopumps
. A typical startup procedure begins with opening a valve, often a one-shot pyrotechnic device, to allow the pressurizing gas to flow through check valves into the propellant tanks. Then the propellant valves in the engine itself are opened. If the fuel and oxidizer are
hypergolic
, they burn on contact; non-hypergolic fuels require an igniter. Multiple burns can be conducted by merely opening and closing the propellant valves as needed. If the pressurization system also has activating valves, they can be operated electrically, or by gas pressure controlled by smaller electrically operated valves.
Care must be taken, especially during long burns, to avoid excessive cooling of the pressurizing gas due to
adiabatic expansion
. Cold helium won't liquify, but it could freeze a propellant, decrease tank pressures, or damage components not designed for low temperatures. The
Apollo Lunar Module
Descent Propulsion System
was unusual in storing its helium in a
supercritical
but very cold state. It was warmed as it was withdrawn through a
heat exchanger
from the ambient temperature fuel.
[1]
This is a diagram of the pressure fed, reusable
Orbital Manouevering System
pod, of which there were two on either side of the shuttle’s
stabiliser
. It was used on the
Space Shuttle orbiter (or simply Space Shuttle)
for
orbital insertion
, manoeuvring the orbiter in space, and the deorbit burn. The
AJ10-190
engines could be reused for up to 100 missions.
Diagram of an
RS-25 (or Space Shuttle Main Engine)
, that used a
twin shaft staged combustion cycle
. There were three of these on the back of the orbiter. Comparing the diagram of the RS-25 to that of the Orbital Manoeuvring System (OMS), it is clear that the RS-25 engine is far more complex. The record for the most space shuttle missions an individual RS-25 engine has been used on is 19.
Spacecraft
attitude control
and
orbital maneuvering
thrusters are almost universally pressure-fed designs.
[2]
Examples include the Reaction Control (RCS) and the
Orbital Maneuvering (OMS)
engines of the
Space Shuttle
orbiter; the RCS and Service Propulsion System (SPS) engines on the
Apollo Command/Service Module
; the
SuperDraco
(in-flight abort) and
Draco
(RCS) engines on the
SpaceX Dragon 2
; and the RCS, ascent and descent engines on the
Apollo Lunar Module
.
[1]
Some launcher
upper stages
also use pressure-fed engines. These include the Aerojet
AJ10
and TRW
TR-201
used in the second stage of
Delta II
launch vehicle,
and the
Kestrel
engine of the
Falcon 1
by SpaceX.
[3]
The 1960s
Sea Dragon
concept by
Robert Truax
for a
big dumb booster
would have used pressure-fed engines.
Pressure-fed engines have practical limits on propellant pressure, which in turn limits combustion chamber pressure. High pressure propellant tanks require thicker walls and stronger materials which make the vehicle tanks heavier, thereby reducing performance and payload capacity. The lower stages of
launch vehicles
often use either
solid fuel
or
pump-fed
liquid fuel engines instead, where high pressure ratio nozzles are considered desirable.
[2]
Other vehicles or companies using pressure-fed engine:
See also
[
edit
]
References
[
edit
]
External links
[
edit
]
|
---|
Concepts
| |
---|
Physical propulsion
| |
---|
Chemical propulsion
| State
| |
---|
Propellants
| |
---|
Power cycles
| |
---|
Intake mechanisms
| |
---|
|
---|
Electrical propulsion
| Electrostatic
| |
---|
Electromagnetic
| |
---|
Electrothermal
| |
---|
Other
| |
---|
|
---|
Nuclear propulsion
| Closed system
| |
---|
Open system
| |
---|
|
---|
External power
| |
---|
Related concepts
| |
---|
|