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2
Systems Engineering and Operations
BACKGROUND AND STATUS
Major factors in space system costs are the launch and mission operations. Since
the ultimate cost is determined at the time the system is designed, operations must be a
major consideration during the initial systems design. The emerging small spacecraft
industry has been supported to a significant degree by ARPA and BMDO and, to some
degree, by the Small Explorer and the MST! programs. These agencies have largely
abandoned the design, development, and systems engineering practices employed by
producers of large spacecraft systems. The companies that develop small spacecraft
systems are also creating new approaches to launch and mission operations that are
simpler and much less costly per mission than their larger counterparts.
Several companies and consortia are currently engaged in the design of new
communications systems that employ low-Earth-orbit constellations of small, low-cost
spacecraft, which will have graceful system degradation and shorter transmission delay
than is achievable with geosynchronous orbits (Seitz, 1993a; Seitz and de Selding, 19931.
Numerous agencies and companies are engaged in small spacecraft activities. Several
examples are included in Table 2-~. Some of these programs are successfully
demonstrating systems for tracking, telemetry, and mission data operations that employ,
when appropriate, the latest standard commercial communications equipment, data
processing equipment, and software, as well as substantial automation technology, to
reduce cost while maximizing performance. It has been demonstrated that such systems
can provide sophisticated services with high reliability at costs well below those
achievable with the conventional approach, and they can do so in much shorter periods
of time. It also has been demonstrated that a fundamental design philosophy for
minimization of costs is to design, build, and operate the system with minimal personnel
and only the absolutely necessary documentation. Broad application of these techniques
in combination with new technology development programs can have a major impact on
the cost and utility of future NASA and commercial space systems.
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Systems Engineering and Operations
TABLE 2-l Examples of Current Small Spacecraft and Launch Vehicle Activities
13
AGENCY/COMPANY
NASA GSFC
JPL
BMDO/U.S. Air Force Phillips
Lab oratory /IPL
BMDO/Naval Research Laboratory
(NRL)/NASA
ARPA/Defense Systems Incorporated/
U.S. Air Force
Orbital Sciences Corporation
Lockheed/Motorola/Iridium Inc.
Ellipsat
Starsys Global Positioning, Inc.
SMALL SPACECRAFT/LAUNCH
VEHICLE ACTIVITY
Small Explorer Program
Mars Pathfinder
Miniature Sensor Technology Integration
Program (MSTI)
Deep Space Program Science Experiment
(Clementine)
Microsats, DARPASAT
Space Test Experiment Platform (STEP)
Pegasus, Taurus, Orbcomm, Pegastar
LEV- I, IRIDIUM
Ellipso
Starsys
SMALL SPACECRAFT SYSTEMS ENGINEERING
The initial phase of a program is very important in establishing the methods by which
cost will be reduced. Decisions involving trade-offs among mission objectives, mission operation
concepts, system and subsystem performance, life-cycle cost, schedule, risk, and reliability can
have a large impact. These trades should be performed as the first step, before committing to
a specific spacecraft configuration and design approach. By utilizing advanced technology on
small spacecraft, increased capabilities can be achieved for a wide variety of missions, with only
small reductions in performance relative to the performance of large systems. These trade-offs
could result in substantially different system configurations. For example, several small
comnlementarv spacecraft with specific capabilities could be used in combination to achieve the
-or ~ ~ -~--~ -r - ~ - - - - - -- - - - - --- - --
~ . . . . . . ~ . ~ . . . ~ . ~ _ . . . . .
total mission objectives. Alternatively, a higher failure rate could be accepted by using new
technology that has not yet been qualified by space flight but that offers a large advantage in
cost, weight, or performance. A complete backup could be provided in case of failure, and the
cost might still be lower.
Since personnel costs associated with ground operations have been shown to be a major
contributor to space system life-cycle costs, systems trade-offs may require the shifting of
ground functions to the spacecraft for more autonomous, lower-cost space operations (Larson
and Wertz, 1992~. In other cases, however, lower system costs may result from shifting
functionality to Earth-based, yet automated, facilities. Furthermore, since many past failures
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Technology for Small Spacecraft
have resulted due to human error, technology that reduces the number of personnel can
possibly reduce the risk of failure. Some key technologies that may play a role in
determining these trade-offs are miniaturized digital electronics; built-in self testing;
expert systems techniques; high-density, solid-state memory; on-board communications
and data processing; autonomous GPS navigation, guidance, and spacecraft attitude
control; and massively parallel computers employed in open system architectures, often
using commercially available hardware and software.
Another important trade-off concerns selection of the launch vehicle and the
desirability of a spacecraft having compatibility with several different launch vehicles.
The venous launch vehicle options that can be considered are (~) use of one of the
existing or one of several soon-to-be-available small spacecraft launch vehicles; (2) use
of a medium launch vehicle that can launch several small spacecraft at once; or (3) use
of a medium or large launch system (e.g., the Space Shuttle) that can launch a small
spacecraft in conjunction with other payloads.
Currently, models and simulations of the trade-off process cover costs of the
systems engineering, design, and production of the spacecraft with minimal consideration
of the life-cycle costs, which frequently are a large part of the overall commitment.
There is little published data on small spacecraft costs, so there is some probability of
error. However, significant improvement in accuracy over current costing practice could
be achieved with modeling that includes a database of recent small spacecraft costs.
Several other factors not necessarily involving technology have a major impact
on the cost of a small spacecraft program. A number of guidelines to reduce cost of
small spacecraft are listed below:
Use a design-to-cost philosophy, which permits achievement of most of
the original objectives with resources available to the program.
Use small, integrated product development teams for design, manufacture,
test, launch operations, and Hight operations. Preferably, the engineers
who design the system will also use the system. The result is simpler,
easier-to-operate systems, such as the Microsats spacecraft.
Keep outside oversight at an appropriately low level with emphasis on
personal accountability of the individuals doing the work.
Maintain close, well-coordinated relationships among users, operators, and
funding sponsors that enable straightforward and rapid negotiation of key
requirements.
Compare the use of existing launch facilities and infrastructure versus the
employment of small spacecraft launch facilities and innovative mission
operation concepts and architectures.
To the largest extent possible, use off-the-shelf hardware and software.
This may require innovation to allow the use of technology that has not
been flight qualified. For example, the Solar Anomalous and
Magnetospheric Particle Explorer (S AMPEX) program was able to use a
standard commercial microprocessor that was not radiation hardened by
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Systems Engineering and Operations
.
placing it in a location that was protected from space radiation by other
elements of the spacecraft.
Provide as much on-board data storage and processing as possible,
combined with data compression techniques, to minimize the frequency of
ground-station interaction. A large memory also allows more commands
to be installed for later execution and a programmable memory permits
later alteration.
SMALL SPACECRAFT LAUNCH OPERATIONS
The cost of launch operations can be a major factor in total space system costs.
High costs result when a large number of people and extended periods of time are
required to prepare the launch vehicle and the spacecraft after reaching the launch site.
The high cost of such systems requires a highly reliable launch. This demands extensive
oversight and review activities, which place additional burdens on the launch crew. All
launch operations are inhibited by several payload and operational constraints; for
example, the early need of the payload for vehicle integration, inability to access the
payload during the countdown, compliance with range rules and overflight restrictions,
and extensive safely requirements associated with very energetic propellants and
ordnance. Technologies, as discussed below, can be used to ameliorate several of these
constraints and lower the cost of launch operations.
Spacecraft/I,aunch Vehicle Checkout and Health Monitoring
The task of ensuring that the space system is functioning properly is a large
consumer of manpower and equipment. The ability to ship the flight vehicles directly
from the factory to the launch site and to launch without further testing except to verify
interfaces between the spacecraft and the launch vehicle would be optimal. This idea can
be approached through the use of on-board health monitoring and, where economical,
fault correction. The DoD agencies have made extensive use of built-in-test capability to
simplify operations and reduce equipment and personnel requirements in the field for
aircraft and missile systems. Under the National Launch System program, which was
terminated, the U.S. Air Force sponsored architecture and instrumentation technologies
to monitor vehicle and engine system health. Many of these developments could have
application to small spacecraft and launch vehicles. In addition, NASA has ongoing
technology efforts to evaluate architecture, instrumentation, and software for both vehicle
and propulsion system health monitoring. NASA also currently sponsors a center of
excellence at the University of Cincinnati for condition health monitoring.
For those checkout requirements that demand extensive ground equipment, the
number of people and the amount of equipment could be reduced by using a single set
of checkout equipment located at the factory. The equipment could communicate by data
link with the vehicle at the launch site. Data could be transmitted over commercially
15
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Technology for Small Spacecraft
available systems, utilizing, if necessary, data storage and reconstitution devices for
overload conditions. This approach could reduce the number of people at the launch site
who are often idle between launches. For example, the Radio Amateur Satellite
Organization has successfully used personal computers to interface with its spacecraft
during launch and reduce the personnel required.
With the use of existing launch vehicles, if anomalies are detected during the
launch process and a component or subsystem must be replaced, there is often the need
to restart the countdown (or a major portion thereof). The result is long delays, missed
opportunities, consternation, and cost increases. New launch vehicles and components
should be developed that permit component or subsystem replacement without the need
to restart the preparation process from the beginning, while still bearing in mind the
requirements for pad and personnel safety.
Spacecraft/Launch Vehicle Integration
The time required to verify the spacecraft/launch vehicle interfaces during
integration is a function of the complexity of the interfaces. This can be an especially
complicated problem when using a launch vehicle that must accommodate numerous
spacecraft configurations. Several contractors and government agencies are pursuing the
development of standard spacecraft buses. This issue has been addressed to some extent
in the Ariane program by providing a standard interface, which greatly simplifies the
integration of very small spacecraft. However, since there is no coordination between
various agencies and companies, existing launch vehicles must still accommodate several
different spacecraft configurations. Standardization of components and system
architecture offers an opportunity for time and cost savings. Standardization at the
interface level, with the resultant reduction in interface negotiations, documentation
integration, and checkout effort, could produce large cost savings. While this approach
might require some degree of mission-specific cabling, the majority of the interfaces
could be standardized.
Range Safety Considerations
One of the current unavoidable costs in launch operations is that of range safety
tracking, which is done using a series of ground radars that track the launch vehicle's
flight. A range safety officer monitors the trajectory ano initiates a destruct command if
the launch vehicle displays performance that is outside of preset limits. Much ground
equipment and many maintenance and operations personnel could be eliminated if a
highly reliable and accurate on-board system for determination of trajectory were
available. It is conceivable that GPS could be used to perform this function and transmit
the trajectory information to the range safety officer if determined by range safety experts
to be an acceptable alternative to the current practices.
in. . , . ~, ^` .. .. . . . . . ...
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Systems Engineering and Operations
Spacecraft Accessibility and Safety
Some space missions require access to the spacecraft late in the countdown
procedure, for example, to enable insertion of life science experiment specimens or to
repair a spacecraft component. The design of current systems does not permit access
after the payload shroud is installed. Also, access to the pad is severely restricted on
current systems by safety requirements, especially those associated with highly reactive
propellants and ordnance devices. One possible solution to the shroud problem is to
provide a means for installation of the shroud late in the countdown, but this would
require development of attachment methods that are simple, safe, and verifiable. Another
method is to provide access into the spacecraft through the shroud.
Resolution of the ordnance problem is more difficult. Various methods have been
proposed. One requires developing ordnance devices that would be inert until activated
remotely. A possible concept would entail insertion late in the countdown using robotic
devices. Another approach would be to use inert materials such as memory metals (e.g.,
Nitinol), which undergo a phase transformation upon heating, to sever structural
connections.
Significant costs for operation of current systems are the result of safety
requirements associated with the very energetic and environmentally sensitive propellants
used, including the high-energy solid rocket motors. Use of hybrid rockets) wouic}
preclude the need for these extensive safety measures because of the improved operability
offered by the inherent inertness of the propellant elements up to the time combustion is
initiated at launch. The American Rocket Company, with other industry support, has
carried out privately funcled development work in this area for several years. Their
hybrid rocket motor has been test fired, but it is not yet flight qualified (Boyer, 19931.
Additionally, there has been independent research and development work on hybrid
propulsion by other industrial firms and the U.S. Air Force Academy. Recently, an
industry and government consortium was formed for hybrid technology with support
from NASA and DoD under the federal Technology Reinvestment Program (American
Rocket Company, 1994; NASA, 1993b; U.S. Congress, 19931.
Flight Programming
Another major element of launch operations costs (and of flight operations costs)
is the preparation of the flight programming software required for each individual
mission and for each individual launch vehicle. A computer program for flight
programming that would prepare the flight programming software for the launch upon
insertion of several trajectory and launch vehicle parameters could reduce the time and
cost required for this activity. The BMDO/McDonnell Douglas Single-Stage-to-Orbit
project was working on the development of such a program prior to its cancellation
~ Hybrid rockets employ a liquid oxidizer with a solid, inert fuel.
17
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Technology for Small Spacecraft
(Palsulich and Raspet, 19931. At the time of this report, announcements indicate the
single-stage-to-orbit technology efforts will be continued under the auspices of NASA
(lannotta, 1994~. The previously mentioned MST} program also has as one of its
objectives the demonstration of automation of the design of the control software and
flight code software (Mattock et al., 19931.
SMALL SPACECRAFT MISSION OPERATIONS
Mission operations, which include the people, hardware, software, ground
systems, and space assets necessary to conduct day-to-day activities, are a significant life-
cycle cost driver for many space systems. In fact, recent procurements suggest that the
cost of mission operations for longer, more complex missions can equal or exceed
development cost. In the past, mission operators got involved too late in the project
definition phase to have opportunities to reduce the life-cycle cost significantly. For small
spacecraft missions, the mission operations concept and supporting space mission
architecture must be addressed early in the program. In fact, if possible, the spacecraft
should be developed by the team of spacecraft designers and the engineers and
technicians who will operate and use it.
Today NASA maintains and operates a number of facilities for transmitting and
processing spacecraft data. These facilities, which represent the existing infrastructure
for NASA operations, consist of
.
.
~· ~ · · ~
the Tracking and Data Relay Satellite System (TDRSS) network, which
uses large geosynchronous satellites and a major Earth station in New
Mexico (this network services most U.S. low Earth-orbiting spacecraft and
the Space Shuttle);
the Deep Space Network, maintained and operated by JPL for planetary
and high Earth orbit missions;
the Ground/Space Tracking and Data Network, which is made up of
various smaller ground facilities for general tracking and data reception
and retransmission;
the Wallops Island ground station, which is used for the Small Explorer
program; and
a number of services maintained and operated by commercial and common
carriers.
The TDRSS, Deep Space Network, and Ground/Space Tracking and Data Network all
offer some standardized communications interfaces.
During the last decade, the developers and operators of low-cost, small Earth-
orbiting spacecraft systems have avoided using the existing infrastructure. It was found
to be complex, costly, and incompatible with the overall concepts of short development
time and low-cost operations. However, dedicated receiving and tracking facilities on the
ground are too costly if there is a mission requirement for real-time data, and reliance
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Systems Engineering and Operations
must be placed on space-borne systems such as TDRSS. To increase the usage of the
TDRSS for small spacecraft support (particularly for real-time high-data-rate missions)
or to permit high-data-rate transmission directly to the ground (with dedicates! or
specialized ground antennas), several efforts are underway in private industry and in
government to replace the costly, heavy transponders needed today. The private ventures
seem to have reached the limit of corporate independent research and development
funding and may need enhanced government support to take them from laboratory
ventures to flight-qualif~ed status. The Principal companies involved are Motorola
Cincinnati Electronics, and Stanford Electronics. Several NASA facilities (GSFC, JPL,
and Wallops Island) are also interested in developing ways to increase TDRSS's use with
small spacecraft.
Another major cost element in mission operations is personnel. Mission operations
is a labor-intensive activity. Most approaches to reducing its cost involve one or a
combination of the following:
.
.
distribution of ground control functions or portions of them to other areas
(e.g., on-board orbit determination and controls, distributed processing of
remote sensing and scientific data);
standardization of interfaces and communications;
automation of repetitive, labor-intensive functions; and
reuse of existing software, hardware, and procedures.
Distributed Functions
An effective way to reduce mission operations costs is to reduce the number of
functions required of the mission operations team. Application of currently available
technology for on-board orbital position determination would enable the spacecraft to
autonomously determine its orbit parameters and command the proper systems to
maintain the desired orbit parameters, achieving autonomous station keeping. The MST}
program has an objective to demonstrate this capability using an advanced star tracking
system. An on-board GPS receiver could also provide the position information for most
Earth-orbiting spacecraft.
The distribution of payload data analysis also could relieve the mission operations
team of a large workload. Payload data for remote sensing ant} scientific missions could
be processed on-board and the processed data transmitted to the grounc} to reduce
transmission load, and it could be distributed directly to locations where further
processing could be done more cost effectively. The computing power to handle much
of the processing load is readily available. The technical challenge is to develop a data
~ _ _
distribution system that gets the data from the spacecraft to the user's computers In the
appropriate timeframe and medium. For example, the Radio Amateur Satellite
Organization and the NASA Solar Mesosphere Explorer program both have ground
stations that allow experimenters to receive data directly from the spacecraft.
19
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Technology for Small Spacecraft
Standardization
Standardization of certain aspects of mission operations has the potential of
reducing cost. However, imposition of numerous standards carries the risk of overly
restricting the creativity of small spacecraft system design teams and requiring excessive
documentation, which could conceivably result in increased cost. Mandatory standards
should be chosen very selectively, but the availability of standards, which the design
teams could choose to adapt, could have large potential for cost savings. The following
are specific areas of standardization for consideration (Wall and ~better, 19911.
Tracking aM orbit data formats require use of a common data structure
for spacecraft tracking data and a common set of conventions for the
models and coordinate systems used to process the tracking data by all
agencies participating.
Telecommunications characteristics require using common frequency
bands; ground-timing stability criteria; and command, telemetry, and
ranging bandwidths among and within all facilities and agencies
participating.
Sta~ard-format data units require use of a common data structure for
transfer of data between any elements of the ground data system.
Common time-code formats require all spacecraft and ground systems to
use a common format for time and to select that format from a
predetermined set of formats. On-board clocks would be limited to
specific oscillator frequencies, formats, and characteristics.
Packetized2 telecommar~s require all ground-prepared commands for
transmission to a spacecraft to conform to a common data structure,
including frame size and format.
Packetized telemetry requires payload and housekeeping data on the
spacecraft to conform to a common data structure. including frame size
and format.
Telemetry channel coding requires data coded on a spacecraft to select
from a set of acceptable downlink coding algorithms.
~.,
Automation
Automation of carefully selected tasks can reduce the cost of space mission
operations. Typical goals of automation are to reduce life-cycle cost, enhance efficiency,
and reduce the number and frequency of errors. The key is to automate the appropriate
tasks in the spacecraft or on the ground. Candidates for automation are straightforward,
2 Packetized consolidated communications commands that can be accepted or rejected as
a group.
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Systems Engineering arid Operations
repetitive tasks like command verification, trend analysis of spacecraft subsystems, fault
detection, and even operations status briefings. Expert systems may even be useful to
augment the efforts of people performing mission operations.
Reuse of Software, Hardware, and Procedures
Reusing software and procedures for mission operations, if done properly, can
greatly reduce development cost. Many software routines and procedures are resident
within the existing mission operations infrastructure, where they have been developed,
tested, and used to conduct mission operations. A program can realize the greatest
savings by reviewing existing software, hardware, and procedures early in the program
and adopting acceptable items. Spacecraft developers and mission operations teams can
then design other necessary software and procedures to be compatible with the existing
resource. Goddard Space Flight Center, for example, has doubled the amount of software
and procedures they reuse, from 40 percent to 82 percent (Boden and Larson, 19941.
PRIORITIZED RECOMMENDATIONS
In order to enhance engineering and operations of small spacecraft systems, the
Pane! on Small Spacecraft Technology makes the following prioritized recommendations
for NASA:
I. Capabilities and design tools should be developed that facilitate improved
up-front concept development for low-cost small spacecraft missions. These capabilities
and tools should facilitate in-depth trades that result in improving the ability to estimate
and in lowering overall life-cycle costs. Key trades include:
.
Tools that would be useful are
21
operational mission concepts;
many small spacecraft versus larger, fully integrated systems;
the degree of autonomy on the spacecraft and on the ground;
the effect of launch strategy and vehicle selection;
the degree of acceptable risk and approach to reliability; and
dedicated versus shared mission operations facilities.
data bases and cost estimating software that address life-cycle cost
of small missions; and
nationally available data bases for existing parts, components, and
new technologies.
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Technology for Small Spacecraft
2. Technologies and techniques should be developed that would reduce the
required number of mission operations personnel. These techniques include:
.
autonomous orbit determination and correction;
on-board data screening to reduce the amount of data to be
transmitted to the ground; and
communication systems for distribution of mission data clirectly
from the spacecraft to the data users.
3. Technologies and practices required to enable a factory-to-launch sequence
with minimum checkout at the launch site should be developed and demonstrated. These
should utilize expert systems when appropriate, including, as a minimum, the following:
on-board health monitoring and checkout and, where economical,
fault correction, for both the launch vehicle ant! the spacecraft;
techniques for remote system checkout;
automated preparation of flight software for guidance and control
of both the launch vehicle and spacecraft;
a set of standard hardware interfaces for small launch vehicles and
spacecraft;
on-board launch trajectory determination for range safety tracking;
spacecraft accessibility late in the countdown; and
reduction of launch pad safety requirements through use of
technologies such as hybrid propulsion and nonexplosive separation
devices.
4. Data storage and transmission techniques should be developed that meet
the needs unique to small spacecraft. These techniques should utilize:
Tow-cost, miniaturized, high-capacity, reliable data storage devices
efficient, high-data-rate transmission techniques;
better forward error-correction codes; and
efficient protocols for high-speed-data interactive transactions.
~,
5. Standardized communications interfaces for mission control functions
should be developed. Areas for standardization include:
tracking and orbit data formats;
telecommunications characteristics;
standard-format data units;
time-code formats;
packetized telecommands;
packetized telemetry; and
telemetry channel coding.
Representative terms from entire chapter:
launch vehicle
