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starship-design: FW: Transforming Spacecraft Economics Via On Orbit Assembly
Transforming Spacecraft Economics Via On Orbit Assembly
by Dennis Wingo
Los Angeles - Jan 30, 2002
Since the dawn of the space age, the Defense Department (DoD), NASA,
commercial aerospace companies, and entrepreneurial efforts have spent vast
sums in continuing efforts to lower the cost of launch vehicles.
Traditionally, DoD and NASA have also sponsored the introduction of new
spacecraft architectures, technologies, and systems. The many advances in
the fields of Earth orbiting satellites and interplanetary spacecraft have
revolutionized our lives. However, today an impasse is approaching in terms
of the cost, schedule and utility of spacecraft.
Per unit spacecraft costs are rising dramatically for DoD, NASA, and other
government customers. Congress cancelled the Discoverer II program due to
concern over rapidly rising costs. Extremely important strategic defense
programs such as SBIRS Low and SBIRS High are in deep trouble due to cost
spiral. Commercial satellite costs are also rising as well as we cram more
and more capability and complexity on launch vehicles and in their limited
payload sections. Multiple failures of multi-hundred million dollar comsats
on orbit and the spiraling per unit cost has driven several communications
enterprises out of business in the last few years.
The remaining commercial space companies cannot afford, nor will their
stakeholders allow them to take large risks for the benefits that
revolutionary approaches afford. Due to these issues and others commercial
space is no longer growing as it has for decades and is actually in decline.
This is where the government, seeing the long term benefit to the nation,
can invest in dramatically improved technologies and systems that can break
this impasse.
This method is the on orbit assembly of spacecraft from components and
subsystems carried into space in energy absorbing packaging. The dynamic
vibrations associated with the launch environment are mitigated by the
enclosure of spacecraft subsystem elements in energy absorbing packaging
just as fragile cargo on earth are packaged before air or ground shipment to
preclude damage from excessive shock and vibration.
These subsystem elements are then launched on the Space Shuttle or any
vehicle that can dock at the International Space Station (ISS). These
subsystem elements are assembled into a full spacecraft. The resulting
spacecraft are then tested and deployed from ISS either upward or downward
depending on the presence of a propulsion system on board.
On orbit assembly can fundamentally change the economics of spacecraft by
changing or eliminating constraints associated with their design,
construction, and test. SkyCorp intends to prove the utility and cost
effectiveness of this approach by the only method that is truly convincing:
building and launching a test spacecraft.
Background Rational
In thirty years we will no longer build spacecraft on the Earth
There are two fundamental constraints that rule the world of a spacecraft
designer and drive the total cost.
1. Dynamic and Acoustical Acceleration Environment.
Acceleration stresses induced from the launch of a rocket are several times
the force of gravity. What's more, the dynamic vibrations of the launch
vehicle structure are considerably more severe than the acceleration rate.
This is due to the low frequencies associated with large volumes of fuel
flowing into the engines and other mechanical vibrations. These vibrations
mechanically couple into the spacecraft bolted to the top at resonant
frequencies below fifty hertz. A fundamental design requirement for
spacecraft engineers is to build structures and appendages stiff enough so
that these frequencies are not amplified by the spacecraft structure to
damage or destroy it. Also, the acoustical environment caused by the payload
shroud passing through the atmosphere at high velocities imparts a spectrum
of medium frequency white noise. These vibrations can set up mechanical
resonances with appendages such as antennas, solar arrays, and sensors.
These resonance frequencies also affect internal components such as
electronic circuit boards and other internal mechanical components. These
acoustical resonances provide a second related design constraint upon
spacecraft designers.
Spacecraft designers have dealt with the vibration issue by building stiff
structures with hard attach points for appendages. These stiff structures
are based upon fundamental geometrical constructs such as the cube and
cylinder. Spacecraft appendages are stiffened by securing them with
explosive bolts that are commanded to blow after the spacecraft is released
from the launch vehicle in orbit. This is an expensive process for an
environment that a spacecraft sees for less than fifteen minutes.
2. Geometrical Constraints Driven by Fairing Dimensions
The cylindrical geometry of the inside of a launch vehicle payload shroud
severely constrains design options for the spacecraft designer. This is
especially true for large and high powered satellites such as military
reconnaissance or geosynchronous comsats. Indeed the primary technical
constraint on the future growth of these satellites is the inability to
remove heat from the geometrically constrained spacecraft bus. This is due
to the limited surface area available from the fundamental geometrical
constructs used. All payload shrouds are cylindrical due to the aerodynamic
shape that is required for the launch vehicle to efficiently penetrate the
atmosphere. Therefore the size of spacecraft is a direct function of the
size of the fairing.
A systems analysis performed by SkyCorp has determined that an average of
50% of the cost of a spacecraft was associated with the launch environment
and the geometrical constraints of the fairing that are unnecessary for
space operation
The SkyCorp SkySat Methodology
As a Shuttle, ELV, and sounding rocket payload developer the author has been
exposed to almost every conceivable launch environment. This experience
showed that the design of satellites is primarily driven by the launch
environment and only secondarily by the space environment. Therefore,
eliminating dynamic and acoustic loads will have large payoffs in terms of
the design, manufacture, test and deployment of spacecraft. Additionally, if
the designer is freed from the geometric constraints of the payload fairing,
new capabilities and weight efficient architectures can be implemented.
In considering the above in designing spacecraft the author has developed a
new methodology that can considerably reduce the cost, increase the
capabilities, and decrease the development time for spacecraft. The term
developed for it is the SkySat on orbit assembly method. In the SkySat
method the designer takes each significant subsystem of a spacecraft and
physically breaks it down into components that can be stored in energy
absorbing material encased in a container. These sub assemblies are carried
to orbit on the Shuttle or expendable launcher. The cargo must be taken to
ISS, another manned space facility or the Shuttle itself to be assembled,
tested, and deployed.
Human-Supervised Deployment
Human-supervised deployment leads to large material gains in total system
reliability. Booms, antennas and solar arrays will be extended while a crew
person is standing by. The crew person will have tools ready to fix
deployment glitches. Considerable time and money can now be saved in the
design/build/test process and mission success no longer rests on the perfect
functioning of a mechanical latch or a pyrotechnic release system.
The SkySat Methodology and NASA
The advent of ISS and its continuous occupation has established a "beachhead
in the sky" that did not exist before for the U.S. space program or for
commercial companies wishing to take advantage of such a facility. ISS was
originally supposed to support a hanger whereby very large space structures
could be built. With the program changes, this feature went away. It is our
intention to reopen that door by proving the viability and cost effectivenes
s of our approach. It is the intention of SkyCorp to garner enough business
building spacecraft on orbit to be able to justify and fund the construction
of a commercial hanger as a module for ISS.
The "SuperSat" Demonstrator
Our candidate spacecraft for a demonstration of on orbit assembly builds
upon previous work by SkyCorp and LunaCorp for a spacecraft called SuperSat.
Since early 1999 over $300k has been spent developing the on orbit assembly
technology in general and $150k specifically on the Lunar mission. The
specific utility of this spacecraft is to demonstrate and validate
conclusively the cost effectiveness of the on orbit assembly method.
Spacecraft Specifications
The SuperSat spacecraft weighs 55% of the only comparable spacecraft, NASA's
Deep Space 1. The spacecraft has over 200% of the power and 50% more on
board propulsion capability. Below in Table 1 are the general specifications
of the SuperSat spacecraft.
Sub System Specified Performance Parameter
Propulsion 270 millinewton 2050 Isp Stationary
Plasma Thruster
Fuel 18 km/sec total impulse Xenon 83 Kg
Weight 225 kilograms wet weight Lightweight Structure
Communications 25 megabits/sec Phased Array spot
Data Handling Multiprocessor Embedded Power PC Linux Based
Data Storage 77 Gigabytes Flash Disk
Navigation Autonav to Lunar Orbit SkyCorp/SAIC Custom
Attitude Control Pulse Plasma/Momentum General Dynamics/
Dynacon
Imaging System HDTV Quality Twin CCD megapixel.
A Fundamental Transformation of Costs vs. Capabilities
The SkySat methodology basically gives spacecraft builders the cost
advantages of a small-sat approach with the capabilities of much larger
systems. Small spacecraft typically do not have large antennas, solar
arrays, or large area sensors. The SkySat method is suited to the
development of the large apertures and substantial electrical power of
deployable elements in a cost effective manner.
Benefits
Examples of the new abilities include:
Low-cost high-capability radar and communications spacecraft can be
proliferated, ending coverage gaps. Shortened development cycles support
rapid technology deployment.
A dramatic reduction in the time between the identification of need to
flight.
Production spacecraft could be stockpiled on orbit for rapid deployment.
A LEO constellation of large-aperture high-power communications satellites
can support worldwide broadband data links to mobile ground units and
remotely piloted vehicles.
It is the intention of SkyCorp to become a major player in the development
of low cost high capability spacecraft for the defense and commercial
markets.
Commercial and NASA Benefits
The SkySat methodology can bring many benefits to NASA and commercial
customers to reduce the cost and improve the reliability of spacecraft. Some
examples include:
NASA has recently had to cancel a contract to build three communications
relays in Mars orbit. This was due to significant cost growth. Our
preliminary estimate is that we could build all three as simple variants of
the SuperSat, assemble and launch for a lower cost than the original Mars
microsats while dramatically improving their overall performance and data
rate.
Several different lightweight spacecraft for inner and mid solar system
studies could be built using the methodology at considerable savings to the
government.
On orbit assembled spacecraft could also allow the deployment of low cost
LEO constellations. The Internet in the sky idea of Teledesic faltered due
to the high cost of satellites built in the traditional way. The cost
effectiveness of our method multiplies with a linear scaling of the number
of satellites deployed
Project Risk
Our preliminary work over the past three years has given us at least a 80%
confidence in the cost of the mission and as much of the remaining risk as
is possible to retire will be done during a study potentially funded by
DARPA and our commercial partners. The technological risk is fairly low in
that even though we are using a lot of new technology and software, much of
this has been proven on Deep Space 1, and the propulsion system that we are
using is human safe and has had several times more testing than our mission
requires.
Conclusion
We have an opportunity to launch the spacecraft on the Space Shuttle in 2003
to ISS. This is an ambitious approach but we feel that this is an
opportunity to really show that we can build a spacecraft of this complexity
on an accelerated schedule.
This spacecraft is the prototype of an entire family of high capability
spacecraft with benefits that serve a broad range of customer needs. It is
our intention to license the technology to proliferate it through our
aerospace industrial base. We do intend to move forward to develop our own
module for ISS a where this technology can be fully brought into its own.
It is our thought that sans propulsion, batteries, and solar arrays that
spacecraft should not cost any more than high performance computers and
telecommunications systems built on Earth. This will allow the vast
proliferation of spacecraft on orbit and will finally allow the
implementation of a global wireless Internet as well as their NASA and
military utility. With the cost reductions that we anticipate with the full
adoption of our methods we feel that in thirty years we truly will not build
spacecraft on the Earth.
Dennis Wingo is a principal with SkyCorp Inc and can be contacted via
media@skycorpinc.com
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