textfiles/bbs/KEELYNET/GRAVITY/statpwr.asc

463 lines
20 KiB
Plaintext

(word processor parameters LM=8, RM=78, TM=2, BM=2)
Taken from KeelyNet BBS (214) 324-3501
Sponsored by Vangard Sciences
PO BOX 1031
Mesquite, TX 75150
August 7, 1990
Courtesy of NASA BBS at 205 895-0028
T H E S P A C E S T A T I O N
P O W E R S Y S T E M
The Space Station represents the commitment of the United States to
a lasting future in space. This future will be ripe with
intellectual and technical challenges. It will hold vast opportunity
for commercial profit and preservation of the nation's economic
vitality. It will be both a research facility in space and a
stepping-stone to long-term human space exploration and discovery.
The Space Station demonstrates that America's significant
achievements in space lie ahead of us, not behind us. The Station
also symbolizes our nation's desire to cooperate with others in
mutually beneficial civil space activities.
Canada, the European Space Agency, and Japan have already responded
positively to the U.S. invitation to participate in the development
of the Station. Formal agreements are being negotiated and are near
completion.
If the negotiations are successful, their involvement will lead to
unprecedented international cooperation, toward the peaceful
exploration and utilization of the space environment.
During the early planning stages of the Space Station Program,
before the first engineer was allowed to set pencil to paper, two
major questions had to be answered:
o Who will use the Space Station?
o What resources will have to be
provided to those users?
A detailed survey of the technical community showed that five types
of experiments would most likely be performed on the Space Station.
o Observational sciences (astronomy and Earth
observations)
o Life sciences
o Materials sciences
o Servicing/repair, and
o Technology development/testing
Page 1
The major resources these potential users demanded were found to be:
o Power
o Volume
o Crew time
The quantitative evaluation of these user requirements defined the
ground rules for the engineering studies that led to the system
definition and preliminary design of the Space Station baseline
configuration.
____________________________________________________________________
S P A C E S T A T I O N B A S E L I N E
C O N F I G U R A T I O N
Photovoltaic Power Array
[][][] [][][] High Gain [][][] [][][]
[][][] [][][] Antenna [][][] [][][]
[][][] [][][] Radiator \ |{ [][][] [][][]
[][][] [][][] \ __ ___ |__ [][][] [][][]
[][][] [][][] ## | |___|J | ## [][][] [][][]
[][][] [][][] ## |E | |E | ## [][][] [][][]
|\|\|\|\|\|\|\|\|\|\|\|==|M |___|M |==|\|\|\|\|\|\|\|\|\|\|\|
[][][] [][][] |__|___|__| [][][] [][][]
[][][] [][][] | | |H | [][][] [][][]
[][][] [][][] | |___|M | [][][] [][][]
[][][] [][][] |__|___|__| [][][] [][][]
[][][] [][][] / [][][] [][][]
[][][] [][][] US Laboratory Module [][][] [][][]
EM = European Module
JEM = Japanese Experiment Module
HM = Habitation Module
____________________________________________________________________
THE SPACE STATION POWER LEVEL
Electrical power, in many respects, is the most critical resource
aboard the Space Station. Electricity is essential to supporting
human life in space. It allows a multitude of systems on board Space
Station to operate, support, and produce.
Whether electricity is used to power life support systems, to run a
furnace making crystals, to manage a computerized data distribution
system, or to operate a centrifuge, electricity is the key.
The more electricity available, the more work possible, and the more
flexible the entire array of Space Station activities becomes. A
comfortable amount of power allows men and women to utilize their
own most precious resources: observation and innovation.
Page 2
Adequate power allows a crew, in orbit, and a variety of
researchers, using telescience capabilities from the ground, the
opportunity to make instantaneous observations and responses.
In a severely power-constrained environment, flexibility and
spontaneity are diminished. This, in turn, limits the invaluable
utility of a permanent human presence in space.
In addition, power runs the infrastructure of the hardware and
software that supports the entire facility. For this reason, Space
Station power systems and power-level projections have been an
important focus of attention during Phase A and Phase B definition
and design stages.
The power level given as the ground rule in the "reference
configuration," the starting point for analytical studies during the
Space Station Concept Definition and Preliminary Design Phase (Phase
B), was 75 kW with growth capability to 300 kW.
The Space Station assembly sequence supplied 25 kW of photovoltaic
power by the second flight. This 25 kW of power would support
general station-keeping requirements and early payloads that would
be provided during the assembly phase of the program.
An additional 50 kW of solar dynamic power was planned downstream in
the assembly sequence, raising the total power supply to 75 kW, the
baseline level for the permanently manned phase.
This figure was based on the projected needs of the future Space
Station user community and early estimates of the housekeeping
power.
A review by Congress of Space Station concluded that the preliminary
power of 25 kW was insufficient to adequately support early
payloads.
As a result, the initial power level was increased to 37.5 kW of
photovoltaic power. With the addition of the 50 kW of solar dynamic
power intended for the later stage of the Station development, the
total power level for the program climbed to 87.5 kW.
It should be noted that the absence of a permanent crew in such a
configuration makes crew time the most critical parameter and
severely limits the kind of experiments that can be performed.
The Space Station review ordered by the NASA Administrator at the
end of Phase B resulted in several changes to the Phase B results,
including a reordering of the assembly sequence to allow for early
user operation and confirming power at 87.5 kW.
A subsequent cost review resulted in the "phased" approach to
construction of the Space Station. Early calculations of power
needed in this approach yielded 50 kW.
Further examination of user and housekeeping requirements, however,
resulted in an increase of that figure to 75 kW for Phase I and an
additional 50 kW (125 kW total) for a future Phase II.
Page 3
THE SPACE STATION POWER SYSTEM
The only continuously available source of energy in this solar
system is the Sun. The Sun's energy is available in the form of
light and heat; however, spacecraft need electricity.
Accordingly, NASA has pioneered and is continuing to develop
technologies to efficiently convert the Sun's energy (light and
heat) into electrical power.
Some materials, such as silicon and gallium arsenide, can directly
convert light to electricity. Hence, "solar cells" can be made from
these materials.
The efficiency of energy conversion by this method is not very high;
it ranges from 5 to 10 percent. The cells, however, can be assembled
into "arrays" and these can be used to generate high power levels.
In fact, the 75 kW required for the Space Station Manned Base and
the power for the Polar Platform will be generated entirely by solar
arrays.
A spacecraft in orbit around the Earth is not always in direct
sunlight. Thus, energy has to be stored to provide a continuous
source of electricity.
Storage is usually accomplished by using batteries, which is the
method of choice for Space Station. The Space Station "photovoltaic
power module" contains both the solar arrays and the batteries.
____________________________________________________________________
SPACE STATION PROGRAM
S O L A R P O W E R O P T I O N S
(PHOTOVOLTAIC)
Sunlight
| | |
| | |
| | |
v v v
_________
|_________| Solar Cell
\ \
| Direct Current (DC)
| Electrical Power
__________ | ___________
| |____|_____| |
| Battery | | Power |
|__________| | Converter |
|___________|
\ \
Alternating Current (AC)
Electrical Power
(SOLAR DYNAMIC)
Receiver/Thermal Storage
\ ______
| | Sunlight
__________| | /
| |______| /
| ' /
| ' /
v ' /
| ' /
| ' /
| \_____|/____/ Mirrors
|
| ______________________
|________| |
| Turbine/Generator |
|______________________|
\ \
Alternating Current (AC)
Electrical Power
____________________________________________________________________
The photovoltaic power system is well understood and has the
advantage of being off-the-self technology. Its disadvantage is the
large size of the arrays required to generate sufficient power.
In addition, the large weight and relatively short lifetime (about
five years) of the batteries is a disadvantage.
The Space Station will operate in low Earth orbit (about 220
nautical miles). In this, or any other near-earth orbit, there is a
certain amount of "drag," i.e. resistance to the progression of the
spacecraft.
As a consequence, the spacecraft tends to slow down. This results
in a loss of altitude, a gradual progression towards an ultimate de-
orbit.
To prevent the Station from eventually reentering the atmosphere,
periodic reboost of the spacecraft is necessary. This requires a
resupply of propellant: the larger the area, the larger the drag,
and the more reboost propellant is needed.
Resupply of the propellant is needed. Resupply of the propellant is
part of the life-cycle cost.
Decreasing the area of the spacecraft minimizes drag. The largest
area of the Space Station is the solar arrays. Early design concepts
indicated that a reduction in the area of solar arrays represented
life-cycle cost reduction.
However, a newer design concept has mitigated the increased life-
cycle costs associated with reboosting, by using a hydrogen fuel
obtained from surplus supplies of water. Therefore, the size of the
solar array no longer drives life-cycle costs as directly.
Another source of life-cycle cost is the need to replace the
batteries after five years. The use of a long-life energy storage
system represents life-cycle cost savings.
A solar dynamic power system might provide a solution for these
problems. This technology, far different from the photovoltaic
system, utilizes the Sun's heat instead of its light for the
production of power.
Heat is collected in the focal point of a mirror. Power is then
generated exactly the same way as on an earthbound power station: by
heating a fluid, which in turn rotates a turbine.
Since a heat/gas-driven turbine is a much more efficient power
converter than a sunlight-driven solar cell, the mirror (the largest
part of the solar dynamic system) would have to be only one-fourth
the area of a solar array to generate the same amount of power from
the Sun's light.
There are several different engines that can be used for the
generation of power within the solar dynamic system. They are
similar in that they are "closed cycle," i.e., they recycle the
working fluid. These engines are usually known by the names of
their inventor. For use on Space Station, the Brayton Cycle engine
has been selected.
The energy storage device used for a solar dynamic power system is
superior to a photovoltaic system because heat is stored rather than
electricity. Heat is cheaper and far more simple to store for
subsequent use.
Storage can be accomplished by taking advantage of the heating, or
fusion, of inorganic salts. On the sunny side of the Earth, heat is
absorbed by the salt and it melts. On the dark (cold) side the salt
freezes and gives up its heat to the working fluid of the engine,
ensuring continuous operation.
S U M M A R Y
An abundant supply of power is one of the top priorities for users
of the Space Station and therefore, of highest priority for the
Space Station Program.
It was for this reason that the original "hybrid" power system was
chosen: it provided early power to the user by using off-the-self
photovoltaic/battery technology, then adding the more "growable,"
but higher risk, solar dynamic system later. This concept was
revised in light of budget realities. By using only photovoltaic
modules in Phase I, NASA will be able to meet budget restrictions
without sacrificing the needs of the users.
The ability to utilize solar dynamic systems with lower life-cycle
cost will be added in the future as the Space Station evolves.
Page 6
SOLAR POWER OPTIONS: ADVANTAGES DISADVANTAGES
--------------------------------------------------------------------
Photovoltaic o Large Data Base for o Limited Data on
Small Rigid Arrays Hi Voltage Arrays
with Batteries
o Tolerant of Pointing o High Life Cycle
Errors Cost
o Flexible Array o Development Risks
Demonstrated Large Array &
Energy Storage
o Technology Well o Large Drag Area
Understood
--------------------------------------------------------------------
Solar Dynamic o High Efficiency o Limited Phase
Change Data
o Terrestrial Data o High Development
Base Cost Than
Photovoltaic
o Low Life Cycle Cost o More Sensitive to
--Low Drag Area Pointing Error than
--Low Production PV Cost
o Not Demonstrated in
Space
--------------------------------------------------------------------
Hybrid o PV Power for Early o Requires
Development Station Buildup
and Logistics
Support of Both
Systems
o SD Low Cost Power as
Requirements Increase
o Low Life Cycle Cost
o Diverse Power Sources
THE SPACE STATION POWER SYSTEM, NASA
--------------------------------------------------------------------
If you have comments or other information relating to such topics as
this paper covers, please upload to KeelyNet or send to the Vangard
Sciences address as listed on the first page. Thank you for your
consideration, interest and support.
Jerry W. Decker.........Ron Barker...........Chuck Henderson
Vangard Sciences/KeelyNet
--------------------------------------------------------------------
If we can be of service, you may contact
Jerry at (214) 324-8741 or Ron at (214) 484-3189
--------------------------------------------------------------------
Page 7