Agile Space Launch
Steven Weis and Lisa Berenberg
Aerospace has been providing systems engineering support to the Space Test Program, the Operationally Responsive Space Office, and the Air Force Research Laboratory, in an effort to rapidly launch and deploy satellites in the evolving agile space environment.
The Delta IV heavy completed a demonstration flight from Cape Canaveral in December 2004, carrying the student-built Nanosat-2. The launch vehicle did not reach the intended orbit, so Nanosat-2 was unable to complete its science objectives. (Photo courtesy of Boeing) |
Agile launch is one component required to support the goals of the Operationally Responsive Space (ORS) Office, whose mission is to rapidly augment DOD space systems to support the warfighter in near real time. For ORS, "rapidly" is defined as mission call-up to launch in a matter of days or weeks. The target launch time for augmentation missions is six days. Typical DOD missions currently take years and even decades to become operational on orbit, so the ORS goal is an ambitious one. Agile space launch involves planning, acquiring, and executing a launch quickly, but more than that, it requires flexibility in mission design, availability of multiple spacelift options, and a readiness to seize opportunities.
The Aerospace Corporation has provided systems engineering support to the ORS Office since its founding in May 2007. Aerospace has also provided systems engineering and mission assurance support to the DOD Space Test Program (STP) since its inception in 1965. STP is the primary provider of mission design, spacecraft acquisition, integration, launch, and on orbit operations for DOD space experiments and technology demonstrations. The typical mission timeline is three years from start to on-orbit operability, and for two recent missions, the timeline was under 12 months from call-up to launch.
These two recent missions, Kodiak Star and Nanosat-2, illustrate the successful application of the principles of agile space launch. For the Kodiak Star mission, STP and NASA, in approximately 11 months, identified and prepared a payload to fly aboard the Athena I launch vehicle. The Nanosat-2 spacecraft, in storage for a year, was reconfigured in four months to fly on the Delta IV heavy-lift vehicle demonstration in 2004.
These two launches, as case studies, provide valuable insights into how to reach the ambitious launch goal of six days. For both missions, Aerospace was a key member of a small team that provided systems engineering support directly to the Air Force mission manager, and then supported the readiness review process with a mission risk assessment to the Air Force mission director.
A survey of current launch vehicles that endeavor to have a "rapid" launch capability is also useful in understanding how far the industry must come to meet the six-day goal. For example, the Minotaur family of vehicles, which use surplus ballistic missile components, provides low-cost, reliable space launch capability to meet U.S. government small-satellite requirements. The Falcon 1 and Raptor series launch vehicles provide additional launch options for small payloads from STP and other DOD programs. Aerospace was a member of the government team developing the payloads that flew on the eight Minotaur missions to date and is involved at varying levels in five of the seven Minotaur missions next scheduled for flight.
STP is also working to use the excess capability—the additional launch vehicle performance and volume margin not used by the primary mission—on launches of government Evolved Expendable Launch Vehicles (EELV) to fly both research and operational payloads. Aerospace was instrumental in the design and development of the EELV Secondary Payload Adapter (ESPA) and supported its demonstration flight on the STP-1 mission in March 2007.
With this new effort to pursue the tenets of agile space that will reduce the timeline for spacelift from years to days to support the ORS mission, benefits to the entire U.S. space industry could be realized, including a reduction in costs, a standardization of interfaces, and a streamlining of processes.
Responsive Payloads: Two Case Studies
Kodiak Star
The Kodiak Star mission launched in September 2001 provides a useful case study in responsive mission design and interagency collaboration. Originally scheduled for August 2001, the mission was supposed to be the first orbital launch from the Kodiak Launch Complex on Kodiak Island, Alaska. However, NASA's primary payload, the Vegetation Canopy Lidar, had been canceled because of developmental problems. NASA needed a replacement—one that could be ready soon enough to maintain the launch date. At an industry conference in August 2000, representatives of NASA's Expendable Launch Vehicle office met with members from the STP mission design office to discuss a possible solution. Within a month of this first meeting, NASA and STP had identified four spacecraft that could meet the orbital constraints and tight schedule: Starshine 3, PICOSat, PCSat, and SAPPHIRE.
The Kodiak Star spacecraft is readied for encapsulation in the fairing as it is prepared for launch. The payloads aboard this mission included the Starshine 3, sponsored by NASA, and the PICOSat, PCSat, and SAPPHIRE, sponsored by the Department of Defense Space Test Program out of Albuquerque, New Mexico. (Photo courtesy of NASA) |
Starshine 3 (Student Tracked Atmospheric Research Satellite Heuristic International Networking Experiment), developed by the Rocky Mountain NASA Space Grant Consortium and the Naval Research Laboratory, was a one-meter sphere covered with approximately 1500 aluminum mirrors. Students throughout the world would track the satellite through the glinting of sunlight off the mirrors and publish the data collection over the Internet. When it was proposed for the Kodiak Star mission, completed mirrors were available, but the main structure had yet to be manufactured.
PICOSat, built by Surrey Satellite Technology Ltd. of the United Kingdom for STP, flew four scientific payloads, including one provided by the Aerospace Space Science Applications Laboratory. When it was selected for the mission, the satellite was completely assembled and tested and waiting for a launch opportunity. Partially funded by the Office of the Secretary of Defense Foreign Comparative Test Office, PICOSat demonstrated the viability of using a commercial-off-the-shelf microsatellite platform to provide cost-effective and timely access to space for DOD space experiments. Aerospace provided systems engineering support to STP throughout the development and testing of PICOSat, maintained continuity during the transitions between Air Force program managers, and ultimately assumed day-to-day management responsibility of PICOSat because of Air Force personnel shortfalls.
The other two STP-sponsored spacecraft aboard Kodiak Star had an educational component and were used to train students in spacecraft operations. The first, PCSat (Prototype Communications Satellite), was designed, built, and tested by midshipmen at the United States Naval Academy. It was still in the design stage when it was selected for the mission. The second, SAPPHIRE (Stanford Audio Phonic Photographic Infrared Experiment), was built by students at Stanford University, with preflight integration and postlaunch operations support provided by Washington University in St.Louis.
Like PICOSat, SAPPHIRE was "on the shelf," waiting for a launch opportunity. For these student-built spacecraft, Aerospace worked with the spacecraft teams to identify risks and implement mitigation plans to keep the mission on schedule, and provided technical assistance in the development and verification of the requirements in the interface to the launch vehicle.
 PCSat-1 (Prototype Communications Satellite) was built at the U. S. Naval Academy with student participation throughout its development. The mission demonstrated a low-cost approach to satellite design. PCSat-1 completed its eighth year in orbit in Sept. 2009. (Photo courtesy of US Naval Academy) |
To adapt the existing launch vehicle hardware to fly the four new spacecraft, Lockheed Martin designed, manufactured, and tested a unique payload upper deck for the Athena I in just five months to support the spacecraft fit check in March 2001. Lockheed Martin also wrote new flight software to allow the launch vehicle to deploy the three STP satellites into an 800-kilometer orbit, then maneuver into a 500-kilometer orbit for the release of Starshine 3.
Each spacecraft, after completing environmental testing, was delivered to the payload processing facility at the Kodiak Launch Complex and integrated onto the payload upper deck starting the final week in July 2001. Aerospace supported the launch site activities for all three of the STP-sponsored spacecraft, and provided on-console support to the Air Force mission manager during launch operations. After a series of terrestrial and space weather delays, and travel limitations imposed in the aftermath of September 11, launch of the Kodiak Star mission occurred on September 29, 2001, with the launch vehicle achieving the desired parameters for both targeted orbits.
Nanosat-2
The Air Force Space and Missile Systems Center (SMC) tasked STP in June 2003 to investigate the feasibility of flying an auxiliary payload on the EELV Delta IV heavy demonstration, scheduled to launch in June 2004. Nanosat-2 was ultimately selected. Nanosat-2 had originally been planned to launch aboard the space shuttle in the Shuttle Hitchhiker Experimental Launch System, but after significant delays in the shuttle manifest, Nanosat-2 was put into storage to await other flight opportunities.
Nanosat-2, actually a stack of three space vehicles, was developed under the University Nanosatellite Program, a joint program of the Air Force Research Laboratory, the Air Force Office of Scientific Research, and the American Institute of Aeronautics and Astronautics. Constructed by student teams at the University of Colorado, New Mexico State University, and Arizona State University, Nanosat-2 was designed to demonstrate two different low-shock separation systems for small satellites and perform collaborative formation flying. All three spacecraft and the associated interface hardware had been assembled and tested when selected for the demonstration.
 Kirk Nygren and Lisa Berenberg with the Nanosat-2 payload mated to the Demosat as it is prepared for launch on the Delta IV heavy demo vehicle. |
After call-up on January 23, 2004, the satellite had four months until it had to be mated to the DemoSat, the main payload of the mission. After an initial kickoff meeting with the mission team, including the government agencies and contractors representing both the satellite and launch vehicles, the Nanosat-2 stack was reduced from three spacecraft to two. Satellite and launch-vehicle work began immediately. The satellite was refurbished and cleaned February 2–25 and reassembled February 26–27; electrical checks were completed March 8–12. Meanwhile, the launch vehicle team was developing a one-of-a-kind adapter to mount the satellite to the DemoSat, designing unique mechanical, electrical, and environmental interfaces.
On March 29, the launch vehicle interface requirements were completed, and the satellite began testing to the new requirements. Random vibration and sine tests were conducted April 5–9, electromagnetic interference testing April 14–23, and shock testing May 3–7. Nanosat-2 was mated to DemoSat May 3—7, and on June 28 encapsulation inside the fairing was completed. The Nanosat-2 team managed to go from storage to mate in 115 days, with approximately half that time spent waiting for the definition of the interface for the launch vehicle.
During this four-month effort, Aerospace served as the systems engineering liaison between the Air Force Research Laboratory and the launch vehicle contractor, with personnel from what is now the Space Innovation Directorate supporting STP and personnel from the Launch Operations Division supporting the Air Force Launch and Range Systems Wing.
After the physical integration was completed, the Aerospace focus shifted to mission assurance, with an emphasis on ensuring that the presence of the nanosat payloads would not adversely affect the primary goal of the Delta IV heavy-lift demonstration mission. Particular emphasis was placed on the qualification of the satellite and the robustness of the separation system, including a new separation-signal timer box. After a thorough Aerospace review, including the requirement for additional separation system ground testing, Aerospace deemed the nanosat system low risk for launch.
The Delta IV heavy demonstration was launched December 21, 2004. During launch, sensors in the Delta IV common booster cores incorrectly registered depletion of propellant, resulting in a premature shutdown of all three stage-one engines and a significant performance shortfall. Nanosat-2 was successfully separated from DemoSat, but in a lower orbit than expected, and was unable to complete its remaining science goals.
Responsive Launch Vehicles
Minotaur
Orbital Sciences Corporation, under the U.S. Air Force Orbital/Suborbital Program contract, develops and provides launch services for government-sponsored payloads using a combination of government-supplied Minuteman and Peacekeeper rocket motors and commercial launch technologies. The use of surplus ICBM assets significantly reduces launch costs while leveraging the heritage of proven systems.
Orbital's Minotaur I is a four-stage launch vehicle using surplus Minuteman solid rocket motors for the first and second stages, combined with the upper-stage structures and motors originally developed for Orbital's Pegasus XL vehicle. Minotaur I can launch payloads up to 580 kilograms into low Earth orbit, and has had 100-percent success after eight missions.
Minotaur IV uses the three solid rocket motor stages from the Peacekeeper ICBM and a commercial solid rocket upper stage to place payloads up to 1730 kilograms into low Earth orbit. The first flight of Minotaur IV is scheduled for 2009. Minotaur V is a five-stage derivative of Minotaur IV using two commercial upper stages to launch small spacecraft into high-energy trajectories.
The Minotaur launch vehicles have a standard 18-month procurement cycle. Studies show this cycle could be reduced to 12 months without any new processes or hardware; however, this is still a 52-week cycle, as opposed to the one-week ORS target. Additional reductions in schedule are being investigated, including ideas such as "stockpiling," where the launch vehicle is completely assembled and tested and just awaits a spacecraft; automating mandatory analyses such as coupled loads and range-safety corridor development; and using dedicated personnel—possibly Air Force personnel—to perform the work required to launch a mission on a "24/7" basis. Aerospace is helping the ORS Office evaluate contractor studies.
The Minotaur 1 through 5 vehicles with their corresponding application and performance information. Aerospace was a member of the government team developing the payloads that have flown on the eight Minotaur missions to date and is involved at varying levels for flights of five more scheduled for launch. |
Falcon 1
To provide additional launch options for small spacecraft, the Air Force also has the Responsive Small Spacelift program, designed to provide military customers with low-cost, responsive (12 to 18 months) commercial launch services. Three launch vehicles are available on the contract: Falcon 1, Raptor I, and Raptor II.
SpaceX (Space Exploration Technologies Corporation) is developing the Falcon family of low-cost, liquid-fueled launch vehicles. Falcon 1 is a two-stage launch vehicle, which, in September 2008, became the first privately developed liquid-fueled rocket to orbit Earth. The first stage is powered by a single regeneratively cooled Merlin 1C engine developed by SpaceX. The primary structure uses a SpaceX-developed flight-pressure-stabilized architecture, which has high mass efficiency relative to traditional structures while avoiding the ground-handling difficulties of a fully pressure-stabilized design (some rockets, such as the Atlas II, are unable to support their own weight on the ground and have to be pressurized to hold their shape). The second stage is powered by a single Kestrel engine, also developed by SpaceX.
Launched from SpaceX's launch facility in the Kwajalein Atoll, Falcon 1 can place up to 420 kilograms into low Earth orbit. An enhanced version, Falcon 1e, with estimated availability beginning in 2010, will be capable of launching payloads weighing up to 1010 kilograms.
From the beginning of the Falcon program, SpaceX has advocated a streamlined process for spacecraft integration and interface analyses through standardization and limiting the analysis cycle to one iteration—the verification cycle when all the models are mature. These ideas should continue to reduce the Falcon I integration cycle to bring it closer to the ORS goal.
The STP-1 payload stack being encapsulated at Astrotech in Titusville, Florida. |
Raptor
Also available on the Responsive Small Spacelift contract are two air-launched vehicles, Raptor I and Raptor II, built by Orbital Sciences. Raptor I, derived from the Pegasus XL, is dropped from Orbital's L1011 "Stargazer" aircraft, providing the flexibility to launch from worldwide locations with minimal ground support requirements. Like Pegasus XL, Raptor I is a winged, three-stage solid rocket booster capable of delivering up to 475 kilograms into low Earth orbit. Raptor II is an air-launched version of Orbital's three-stage Taurus-Lite launch vehicle. Flown to the launch location inside a C-17, the Raptor II is extracted from the aircraft, slowed and stabilized using a parachute system, and ignited in a nearly vertical position. It can deliver up to 250 kilograms to low Earth orbit.
Since both Raptor vehicles are air-launched, they can achieve low-inclination orbits and can potentially reduce cycle time by removing the constraints of ground-based range infrastructure. The use of air-launched vehicles is being studied closely by the ORS Office to see what advantages they may have over ground-based launchers.
EELV Secondary Payload Adapter
As early as 1997, STP and the Air Force Research Laboratory began developing the capability to fly up to six auxiliary payloads on Atlas V and Delta IV. The result was the EELV Secondary Payload Adapter (ESPA), first flown on the STP-1 mission in March 2007. Aerospace was part of the ESPA development team from the concept stage, providing systems engineering and mission assurance support.
The ESPA is installed below the primary payload to provide rideshare opportunities for 180-kilogram spacecraft that fit inside a volume of 24 by 28 by 38 inches. This mass and volume constraint has now become known as the "ESPA class." To simplify the inclusion of the ESPA on future missions, STP, the EELV program office, and United Launch Alliance are working to develop a standard service option for government launches. This service would include all of the necessary interface hardware (ESPA ring, auxiliary payload separation systems, and harnessing) along with the required mission integration analyses.
Enablers for Future Agile Space Launch
Changes to the Mission Design Paradigm
The standard integration timeline for small launch vehicle missions is 12 to 18 months from contract award to initial launch capability. This schedule is driven primarily by the launch vehicle hardware procurement cycle, and to a lesser extent, by the design methodology used on most missions. Advanced procurement of long-lead items can accelerate the hardware delivery, but accelerating the mission integration timeline requires a change in philosophy.
The standard mission design methodology selects a launch vehicle while the spacecraft is still in the preliminary design phase based on its expected final mass and desired orbit. The spacecraft is then designed to meet the specifications of the selected launch vehicle and to survive the launch environments. This paradigm greatly limits the ability to change the mission should the need arise.
A more agile approach incorporates innovative design practices on both the spacecraft and launch vehicle sides of the interface. Designing and testing a spacecraft to levels that envelop multiple spacelift options would provide more flexibility in launch manifesting. For example, Nanosat-2 had been tested to space shuttle requirements, giving confidence that it could survive on the EELV Delta IV heavy. SAPPHIRE was designed and tested to be compatible with almost any potential launch option.
Changes to Spacecraft Systems
STP has embraced this new paradigm in the procurement of the so-called Standard Interface Vehicle--essentially a generic spacecraft bus with a standardized payload interface. The Standard Interface Vehicle contract was for the purchase of up to six space vehicles that would be compatible with five different launch vehicles--the Minotaur I and IV, Pegasus, and the Delta IV and Atlas V ESPA. This allows for "next available opportunity" manifesting.
Designing a spacecraft to multiple launch vehicle standards allows it to be built and "put on the shelf." The approach is clearly feasible: two of the four satellites on the Kodiak Star mission (SAPPHIRE and PICOSat) and the Nanosat-2 spacecraft were complete and ready for the next available launch opportunity.
Still, there are drawbacks to this "satellite-on-the-shelf" approach, such as component degradation, continuous testing requirements, and technology obsolescence, to name a few. To combat these issues, the Air Force Research Laboratory has come up with an innovative spacecraft design and manufacturing concept known as plug-and-play. Analogous to the home personal computer, where all the components fit together regardless of the manufacturer through the use of a common interface (the USB, or universal serial bus), the plug-and-play satellite program has developed a standard interface for all the avionics on the bus. Through the use of this interface, components can be kept on the shelf, and by using a dedicated space-vehicle integration facility, a unique satellite that meets mission requirements can be designed and assembled in six days.
Changes to Launch Systems
Once the issue of standardization of physical interfaces is resolved, additional changes to launch-vehicle systems will be required to meet the six-day launch goal. As with satellites, one way to meet the six-day goal is to build the launch vehicle and then place it in storage to await a payload. Drawbacks to this concept are not hard to imagine, including the significant investment in explosive storage requirements and the testing and component life issues similar to those of the satellites. However, even with this stockpiling of launch vehicles, numerous preparations remain, such as the development of the flight software to fly the correct trajectory to the correct orbit, analysis of coupled loads to ensure no structural coupling between the satellite and launch vehicle, and development of guidance and control algorithms, to name a few.
These preparations currently must be done serially, starting with coupled loads analysis, then guidance and control, and then flight software; the process takes about three months. The introduction of automated software development tools could bring this cycle time down to days, and is absolutely necessary for the ORS Office to meet its goals.
Changes to Launch Range Infrastructure
The last piece of the launch timeline, and the one that has not been addressed by any missions to date, is that of range infrastructure—specifically in the area of flight safety. The range infrastructure required to launch national space systems is very extensive; thus, in the United States there are only two ranges that launch national security space missions—Cape Canaveral in Florida and Vandenberg in California. One way to limit the range interface timeline would be to remove a mission from the range, but though that may save some time in the areas of ground interfaces, flight safety must always be ensured. Studies in this area are in their infancy, and the conclusions of these studies will be reviewed carefully.
Agile Space—A Multifaceted Issue
The three military offices at Kirtland Air Force Base in New Mexico—STP, the Air Force Research Laboratory, and the ORS Office—are working together to define solutions to the ORS goal of a six-day mission timeline. The concept of agile launch implies it is not a single mission component that will meet this ambitious goal, but rather a collection of innovations across all mission components--spacecraft, launch vehicles, and launch ranges--and across all engineering disciplines--mechanical and electrical interfaces, software, and systems engineering.
In supporting all of these offices, Aerospace is uniquely positioned not only to ensure coordination across the effort, but to help define the architecture of the effort. Various government and industry organizations have been considering components of agile launch for years, but the ORS mission has only been codified for two years; so, the effort is really in its infancy. In the future, the ORS Office may transform some of the tenets of agile launch discussed in this article into flight demonstrations, and when that happens, it may well revolutionize the way space missions are conceived and executed.
