AIAA 2 nd Responsive Space Conference AIAA-RS2 2004-3004 ORBITAL RECOVERY S RESPONSIVE COMMERCIAL SPACE TUG FOR LIFE EXTENSION MISSIONS Dennis Ray Wingo, Orbital Recovery Corporation Orbital Recovery Limited London, UK 2nd Responsive Space Conference April 19 22, 2004 Los Angeles, CA
Copyright Orbital Recovery 2004, Published by AIAA 2 nd Responsive Space Conference with Permission 1 AIAA-RS2 2004-3004 ORBITAL RECOVERY S RESPONSIVE COMMERCIAL SPACE TUG FOR LIFE EXTENSION MISSIONS Dennis Ray Wingo, Orbital Recovery Corporation, London, UK ABSTRACT Orbital Recovery Corporation (ORC) and its UK subsidiary Orbital Recovery Limited (ORL) are in the developmental stage of an orbital space tug called the Orbital Life Extension Vehicle (OLEV), whose purpose is to mechanically mate with an existing communications spacecraft in GEO or GEO intended orbit, take over north/south and east/west station keeping as well as attitude control. The OLEV is designed as a secondary payload on an Ariane V launch vehicle and carries a Hall Effect Thruster (HET) to execute GTO to GEO orbit raising, rendezvous and docking, and operations of the coupled spacecraft pair. The OLEV does not transfer fuel or otherwise interface with the parent spacecraft. The OLEV is designed to mate with any three axis stabilized spacecraft and has sufficient supplies to keep a 3000 kg parent spacecraft in geostationary orbit for up to an additional ten years of life. MARKET CONCEPT The life extension of GEO orbit spacecraft is desirable to satellite operators for the increased revenue potential that such life extension provides. The proof principle of this is the operation of numerous spacecraft well beyond their contracted lifetimes. This is typically accomplished by rationing the last year(s) of station keeping fuel by eliminating north/south station keeping which demands ten times the impulse that east/west station keeping requires (~40 meters/sec vs. ~3 meters/sec). This results in an inevitable increase in orbital inclination due to the gravitational influences of the Moon and Sun at GEO altitude (~33,000 km). While the increase in inclination requires spacecraft users to purchase considerably more expensive antennas to track the changing inclination, the lower revenue charges by the operators more than offset this cost. It is clear that a great proportion of existing spacecraft in GEO are actually in inclined orbits. Table 1 gives the numbers of GEO and inclined orbit operational spacecraft as of June 2003. i Region GEO Inclined (160 W-71 E) 65 19 (71 E-0 E) 59 25 (0 W-61 W) 36 14 (61 W-160 W) 60 8 Table 1: GEO vs. Inclined Orbits Out of a total of 286 operational spacecraft 66 of them are operating in inclined orbits. A few of these spacecraft such as the old NASA Tracking Data Relay Satellites (TDRS) are used for communications with the South pole installations during the descending nodes but for the most part these inclined birds are used for customers within the normal range of a geostationary comsat. Some of these spacecraft, such as the SBS IV/HGS-5, launched on the Space Shuttle in 1984 (a Hughes 376 spinner), are as much as nearly 20 years old and still functional and producing revenues. ii The design life was 8 years. The question that came to our minds was can we, in a cost effective manner, build a space tug that could extend GEO assets lifetime and keep them in GEO where their revenue streams would be much higher than for the
inclined birds? Some companies make considerable revenue from inclined birds but their revenues are only a fraction of the revenues obtained from operating in the stationary belt. In our business development we had to come up with a metric to determine what cost effective meant. Our design guidance was to posit the simplest on orbit servicing system possible and limit customers to those with the most valuable commercial assets. The spacecraft that fit these parameters are three axis stabilized commercial GEO comsats with a revenue of at least $40-50M dollars per year. To us this meant that we had to achieve a cost target for our system that was no more than a year to a year and a half of revenue for the operator. This would give an operator a revenue of between $200-$500M over the life extended mission between conservative and optimistic assumptions. It turns out that out of the existing 286 commercial comsats in orbit today over 50 of them that fit our metrics will need replacing by 2009. We have to provide a clear value to the customer and providing a three to six times revenue return of our price qualifies. Business with governments are handled on the same basis as with commercial customers with pricing based upon our commercial pricing and not the other way around. Cost is the fundamental driver of our business and if we can not sell the OLEV for a commercially attractive price that customers are willing to pay then we do not have a business. Costing like this for the commercial market is much more understandable to investors as these are metrics that anyone can analyze. Government development efforts have different metrics that are difficult for Wall Street to measure and forecast. Government customers are an additional source of revenue but our business cannot be justified on that basis. DESIGN TRADE STUDIES With cost efficiency as the principal system architectural driver we undertook a detailed design that worked for lower cost at each stage. We decided that in order to meet any reasonable overall cost target, we had to go with a secondary launch to GTO. With Arianespace we found a reasonably priced secondary launch that went to our desired orbit and with a payload weight of up to 1000 Kg. That put an upper limit on our size, which ruled out chemical propulsion systems. Time is also a factor and we needed a system that was controllable in GEO in a robust enough fashion to do the docking with the only aperture available on the zenith face of a commercial comsat, the liquid apogee motor. In looking at available systems, one based upon Hall Effect Thrusters (HET s) seemed to have better overall performance than gridded ion in terms of handling the extra mass for attitude control and station keeping of a comsat as well as our asymmetrical load on the parent spacecraft. This then drove the size of the solar arrays to the 4-5 kilowatt range in order to minimize transit time between GTO and GEO. In an unexpected development, during our concept design study the Institute for Robotics and Mechantronics DLR (German Space Agency), demonstrated to us their advanced development of a complete rendezvous and docking solution for GEO, including a capture tool that would allow us to dock to the apogee motor and imaging software to guide the system. We have an exclusive commercial license for this solution and have integrated this into our design. This agreement and the hardware and software supplied allows us to decrease schedule risk, increase our credibility by leveraging the extensive design experience at DLR, as well as allowing for a greater definition of the cost and configuration of the system early on in the design process. 2
With these general conclusions we drew up a strawman design and did preliminary costing of subsystems and components to determine raw costs. We added to this the expected cost of manufacturing, launch, and insurance and came up with a number within the cost cap chosen as our market viability point. We then rolled the requirements that came from our study into a document that became the foundation of our RFP to potential suppliers. In the fall of 2003 after an evaluation period for proposal responses, we chose Dutch Space of Leiden, the Netherlands, because their solution was almost ideal for our purposes. OLEV DESIGN The OLEV is based upon a modification of the design of the cone adapter between the 2624 millimeter base of the Ariane V upper stage and the standard 1194 millimeter Marman adapter between the cone and the primary payload(s). Figure one illustrates the concept and placement within the Ariane V system. spacer used for these secondary payload missions. The solar array is a six-petal design, carrying triple junction Emcore solar cells to maximize power to approximately 4 kilowatts. Adding more power is possible but this is beyond our baseline model. Figure 2 shows the available area inside the Ariane V adapter. Figure 2: A 5 Secondary Payload Volume This arrangement solves a host of problems for Orbital Recovery s application, including providing a large surface area interface between the OLEV and the parent spacecraft. The spacecraft has a wide rear surface necessary to provide a moment arm for the station keeping thrusters, already incorporates Hall thruster technology, (as a result of a prior B0 study), and has the ability to incorporate the Capture tool and rendezvous and docking software from DLR. Figure three gives a general picture of the layout of the spacecraft. Figure 1: OLEV on the Ariane V The OLEV carries the standard Ariane V cone adapter above its own internal structure. The solar arrays and other deployables reside underneath the spacecraft in an area that is a Figure 3: OLEV Internal Configuration The OLEV carries the standard hardware expected on a GEO comsat and is rated for a 3
twelve year lifetime. This includes two hundred and sixty kilos of xenon gas for the GTO to GEO transfer and enough fuel to station keep a 3000kg comsat mass for up to ten years with margin. The attitude control system is oversized in order to be able to maintain the +/- 0.035 nadir pointing required by the largest comsats. For electronics we are using a spacecraft processor built by Swedish Space, that already has proven much of our orbit raising mission profile in the SMART-1 mission by ESA. The Dutch Space OLEV design meets all of our overall cost targets within an acceptable margin. At the present time we have just started a B1 design study in cooperation with ESA under the ARTES4 public/private partnership program whereby an ESA fund matches the funding provided by the private entities (Dutch Space and ORL). This fund is set up to help to enable companies within the European Union (EU) to generate new aerospace business for EU based companies. Threde, of Munich, Germany under a commercialization agreement with the German government. The flight and ground software will also be supplied through Kayser Threde from DLR. The capture tool houses six sensor heads located at 120 degree angles apart. These sensors give feedback to the teleoperator or to the autonomous software to determine where within the volume of the apogee motor the capture tool is located. The locking mechanism, when fully inserted into the apogee motor crown, has a crown mechanism that, using a set of spreading pins, forms a tight mechanical connection between the capture tool and the apogee motor. Figure 5 gives is an illustration of the capture tool and sensors inside of an Apogee motor. ROBOTIC PAYLOAD The robotic payload on the OLEV is being supplied principally by DLR. This comprises both hardware (capture tool) and software (model matching software, sensor feedback software from the capture tool, and telepresence software) to allow ORL engineers to guide the OLEV to a docking or under autonomous operation. Figure 4 shows the capture tool already built by DLR. Figure 4: DLR Capture Tool This capture tool will be flight qualified and flight copies will be manufactured by Kayser Figure 5: Capture Tool In Apogee Motor The Dutch Space design of the OLEV supplements this connection by pulling the capture tool down to contact the ring or a plate offset from the ring (avoiding the ejection springs) in a manner under revision during the B1 study. The software from DLR acts as a feedback mechanism between the sensors located in the capture tool and the imaging system. The 4
software works with a standard 2D imaging system and uses a software model of the parent spacecraft and pattern matches that to the images received from the camera system. Range and range/rate data can be generated by the software based upon inputs from the imager to allow the software to control the rendezvous phase. Under consideration is a laser rangefinder to supplement the imaging system. Figure 6 is an example of the output of the imaging and pattern matching software. OLEV will take approximately 120-150 days from separation to achieving GEO orbital altitude. It will take approximately 120-140 kilos of Xenon to get to GEO. Figure 7 is a representative transfer from GTO to GEO simulated for us by SAIC and confirmed by Dutch Space. Figure 7: GTO to GEO Transfer Figure 6: DLR Pattern Matching Software DLR at their Institute for Robotics and Mechatronics has a full simulation laboratory where an extensive amount of work has been carried out in developing the simulation for this mission. The software acquired under license by ORL is a major factor in reducing our development time and will allow the team led by Dutch Space to concentrate on integrating the total system rather than designing from scratch a very sophisticated robotic hardware and software system. OLEV MISSION The OLEV mission begins with the separation of the spacecraft from the Ariane V launch vehicle. Solar arrays and antennas are deployed, initial system tests accomplished and the Hall thruster system enabled. The The transfer time is influenced by the beta angle during the climb as well as the orientation of the orbit with respect to the Earth s umbra and penumbra shadow. Also, it is strongly desired to gain perigee altitude as quickly as possible to get above 10,000 km. Based upon data from the ESA Spacecraft SMART-1 this is the altitude where solar array degradation falls off to a low value. RENDEZVOUS AND DOCKING The rendezvous and docking sequence begins at an altitude slightly above GEO and behind the parent spacecraft. This is the classical R bar approach used by NASA in several docking approaches with the Shuttle. The R bar approach precludes plume impingement on the parent spacecraft by the Xenon from the Hall thrusters. Approach is accomplished by using GPS or spacecraft orbital determination and by knowing the location of the parent spacecraft within a GEO box of 80 X 80 X 40 km. The spacecraft also knows the attitude of the parent (usually nadir oriented to within 0.7 degrees). This is the baseline that may be refined during the B1 study period. 5
After the OLEV closes to within 40 km visual indications are used to guide the spacecraft closer to the parent. It may be possible to use the parent s transponders as a homing beacon or use a laser rangefinder at this distance. After the parent is positively acquired and the distance closes to less than 400 meters the on board imaging system will be used to guide the parent to docking. One dramatic difference in performing a docking at GEO altitude is that the order of magnitude of forces (differential orbital velocity) is approximately 256 times less than in a LEO orbit such as the International Space Station. The final stage is at 4 meters and closer where the Hall effect thrusters may not have the control authority to move the spacecraft around. The Dutch Space led team in the B1 study is currently investigating a cold gas system to control the spacecraft for the last 4 meters. The OLEV is oriented in a nadir/zenith orientation and closure to within the apogee motor is accomplished. The LED s indicate the depth within the nozzle and when the crown mechanism has passed the throat of the nozzle the crown locking mechanism is actuated. After a positive lock is accomplished the capture tool is retracted at its base and latches are deployed from within the OLEV to provide a three point positive latch with the parent spacecraft Marman clamp underside surface. Detailed design of this mechanism is in progress. This provides a multipoint interface that allows the capture tool and the apogee nozzle to carry only a fraction of the total loads of the coupled system. Figure 8 gives an illustration of the configuration of system just prior to docking. Figure 8: OLEV Prior to Docking At the moment of capture the on board attitude and station keeping control system is disabled. The OLEV then takes complete control of both the attitude and station keeping of the coupled spacecraft pair. COUPLED SYSTEM OPERATION For the coupled system to correctly operate the OLEV must dock to the center of mass in the X/Y plane leaving only a Z offset to be corrected. In order to provide maximum revenue, the attitude control of the coupled mass must be as good as for the original system. For some spacecraft this is as fine as +/- 0.035 degrees in all three axes. Station keeping must also be accomplished for the coupled mass for as long as ten years after docking with enough reserve to allow for moving to the final disposal orbit. 6 Station keeping for east/west station keeping is accomplished by the use of the Hall thrusters in the nadir or zenith direction,
depending on the position in the GEO box that the spacecraft wants to stay in. Station keeping in the north/south direction has to be through the center of mass of the coupled system. The coupled system center of mass shifts due to the depletion of the xenon fuel during the life of the life extension mission. This represents the most challenging technical aspect of the OLEV design because an exact representation of the parent spacecraft is not known to sufficient precision prior to docking. This will be compensated for by designing for the worst case, with single or dual axis gimbals on critical thrusters. After a check out and training period the operation of the coupled system is turned back over to the satellite operator or their designated contractor. Orbital Recovery does not intend to operate customer satellites but will provide a full compliment of engineering backup should any problems occur. One strategic consideration is that Orbital Recovery will always retain the capability to undock the spacecraft from the parent comsat. This is in the case of missions where the comsat dies before the exhaustion of xenon fuel in the OLEV and we have delivered the defunct spacecraft to the junk orbit. The customer shall not have the ability to do this, only Orbital Recovery, in order to absolutely maintain control of the operation of the system when in free flight mode. OLEV AS A RESPONSIVE SPACE SYSTEM The OLEV has great potential as a responsive space system for commercial as well as government customers. In the commercial realm, in space insurance is at a historic high today. We are in discussions with a potential customer to provide a OLEV to dock with a retiring commercial asset that has been replaced with a new model of similar specifications. This gives the customer effectively a one spacecraft deductible on their yearly insurance. In effect if the primary spacecraft fails for any reason, the customer simply brings the retired spacecraft back online. Basically this is a hot spare that would cause an outage of a few hours versus the long periods of time and the expensive acquisition of spare capacity on a competitor s spacecraft fleet. Another method for providing responsive space capacity for commercial fleet operators is to provide a OLEV on orbit to backup any fleet operator s propulsion related difficulty. This capability results in lower insurance rates and a higher level of customer availability. This same rational could easily apply to government customers. At this time there are several semi-retired TDRS spacecraft in inclined orbits that could be rehabilitated or as existing operational assets are retired they could be life extended as either a hot spare or as an augmentation of the existing fleet. NASA at the current time is having a great deal of difficulty related to ISS communications capability. A system such as ours would solve this problem at a fraction of the cost of augmenting the existing TDRS system. For other government customers in GEO similar benefits would accrue. The USAF is in the midst of a massive upgrade in communications capability via the Transformational Communications Architecture. Recent reports indicate that this program, as well as the Advanced EHF system are having schedule and cost issues. A OLEV could dock with an existing Milstar spacecraft and extend its life to compensate for shortfalls in expected AEHF production, or to keep the multi billion dollar Milstar spacecraft in service beyond their expected fuel lifetime. The cost metrics that make our system a favorable alternative in the commercial arena 7
are multiplied by the ratio of the cost difference between the OLEV and the spacecraft that they extend the life of. Figure 9 is an illustration of the OLEV as a free flyer being deployed from an Ariane V. Figure 9: OLEV Post Deployment Going a step beyond simple life extension commercial customers in the future as well as the U.S. government could buy OLEV vehicles and have them on station above the GEO belt or below the GEO belt to rapidly respond to failures of upper stages or the on orbit propulsion systems of their assets. The government in operational structure has the same issues as a commercial fleet operator. The OLEV could be placed into orbit on contingency in order to provide rapid response capability to recover a critical asset who s life has been curtailed by a propulsion related problem. Today in GEO orbit there are no less than seven commercial spacecraft with recent partial or total failures of the propulsion system that could be mitigated by the use of the OLEV. Two years ago a delivery of TDRS-I to GEO orbit from GTO was delayed by several months due to a flaw in the spacecraft propulsion system. Before that, the European Artemis spacecraft was left in an improper transfer orbit between GTO and GEO by a failure of the Ariane V upper stage. On that same flight an Orbital Sciences light 8 GEO sat was left in an unusable orbit without the propulsion capability to achieve GEO with any usable life. Since then the 5000 kilogram Astra 1K was stranded in a LEO orbit by the failure of the upper stage of the Proton rocket. In the late 1990 s a U.S. Navy spacecraft was left in an unusable orbit. On average an upper stage propulsion failure occurs every 18 months. The OLEV could also be placed on station in GEO to respond within a couple of weeks to a problem that could cripple a critical space asset during a period of increased operational tempo. Also, the existence of contingency OLEV spacecraft would provide considerable increased operational flexibility in mission planning by allowing planning beyond the depletion of the existing on board fuel supply of multi-billion dollar communications assets. The OLEV could also be used for responsive operation with large LEO government assets. In general, the OLEV is too expensive for commercial LEO assets but it would be suitable and cost effective to add life or contingency propulsion for expensive government LEO assets. Beyond GEO, a OLEV could be used by NASA in the case of the failure to deploy of the petals of the James Webb space telescope. For other applications the OLEV has the potential to grow into a very capable responsive in-space servicing system. Discussions are underway now with potential customers for providing power for the Boeing 702 spacecraft with large solar array degradation problems. As the OLEV matures it may be possible to change the way that GEO spacecraft are procured in order to facilitate their servicing by the OLEV Mark II system that could replace components, provide extra power, or life extension. Going beyond this even it can be forecast that the existence of proven, cost effective on orbit servicing spacecraft could change the market
metrics for GEO spacecraft by allowing the designs to be less long lived, with servicing built in. This would reduce cost dramatically for the manufacturer and the customer. The overall point here is that the mere existence of a proven Orbital Recovery product in this market will begin to open the door to new ideas and applications that formerly have been beyond the grasp of the existing way of doing business. The key is cost effectiveness and cost effectiveness is enforced by the commercial market that has little stomach for expensive solutions and long term R&D projects. Making money is the key parameter for success in commercial space. With our success we can help make space more profitable for commercial interests and more responsive for everyone. i www.lyngsat.com ii http://www.skyrocket.de/space/doc_sdat/asiasat-3.htm 9