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 effectiveness 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.

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.

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:

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 [email protected]

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ROBO SPACE

Humans and Robots: Partners in Space
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