The Air Force Research Laboratory (AFRL) is currently engaged in developing and demonstrating several advanced spacecraft and launch vehicle mechanism technologies. A variety of mechanisms are required to accomplish spacecraft and launch vehicle functions such as deployment, articulation, positioning, and isolation. Current off-the-shelf mechanisms such as pyrotechnics, gimbals, paraffin actuators, and electro-mechanical devices may not be able to meet future satellite requirements. For this reason, advanced technologies are needed that will increase mechanism efficiency in terms of cost, weight, reliability/survivability, and power consumption. In addition to developing these technologies, it is necessary to prove them in flight demonstrations in order to make technology transition feasible. This paper summarizes the status of several space-related programs being conducted by AFRL for developing and demonstrating new technology to support future DoD space requirements. One of these flight programs will fly the first whole-spacecraft isolation system on a Taurus launch vehicle in January 1998 and another will demonstrate the first solar array with overall array specific power greater than 150W/Kg in the fall of 2002. This solar array is being developed for flight on the third New Millennium Program technology demonstration flight

Fosness, Eugene R.

Founds, David B.

Madison, Richard

Sciulli, Dino

English

Embry-Riddle Aeronautical University

The Space Congress® Proceedings 1998 (35th) Horizons Unlimited Apr 30th, 1:00 PM Paper Session III-C - Advanced Mechanisms For Space Applications Eugene R. Fosness Richard Madison Dino Sciulli David B. Founds Follow this and additional works at: https://commons.erau.edu/space-congress-proceedings Scholarly Commons Citation Fosness, Eugene R.; Madison, Richard; Sciulli, Dino; and Founds, David B., "Paper Session III-C - Advanced Mechanisms For Space Applications" (1998). The Space Congress® Proceedings. 30. https://commons.erau.edu/space-congress-proceedings/proceedings-1998-35th/april-30-1998/30 This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact commons@erau.edu. ADVANCED MECHANISMS FOR SPACE APPLICATIONSE. Fosness1, R. Madison2, K. Denoyer3, D. Sciulli4, and D. Founds5AbstractThe Air Force Research Laboratory (AFRL) is currently engaged in developing and demonstrat-ing several advanced spacecraft and launch vehicle mechanism technologies. A variety ofmechanisms are required to accomplish spacecraft and launch vehicle functions such as de-ployment, articulation, positioning, and isolation.  Current off-the-shelf mechanisms such aspyrotechnics, gimbals, paraffin actuators, and electro-mechanical devices may not be able tomeet future satellite requirements.  For this reason, advanced technologies are needed that willincrease mechanism efficiency in terms of cost, weight, reliability/survivability, and power con-sumption.  In addition to developing these technologies, it is necessary to prove them in flightdemonstrations in order to make technology transition feasible.  This paper summarizes thestatus of several space-related programs being conducted by AFRL for developing and demon-strating new technology to support future DoD space requirements.  One of these flight pro-grams will fly the first whole-spacecraft isolation system on a Taurus launch vehicle in January1998 and another will demonstrate the first solar array with overall array specific power greaterthan 150W/Kg in the fall of 2002.  This solar array is being developed for flight on the third NewMillennium Program technology demonstration flight.IntroductionSpacecraft require a variety of mechanisms to accomplish mission related functions such asdeployment, articulation, and positioning.  Current technologies for these mechanisms includepyrotechnics, high output parafin, and electric motors.  While successful in many applications,these technologies have drawbacks that make them unsuitable for the increasingly restrictiverequirements of current and future spacecraft.  These drawbacks include generation of highlevels of shock, contamination, short lifespan, low reliability, low efficiency, safety risks, andexcessive weight and volume.  The Air Force Research Laboratory (AFRL) is developing inno-vative technologies for new mechanisms that avoid many of the problems found in currentdevices.  The goal of this research is to develop and transition technologies to advance thestate-of-the-practice in spacecraft mechanisms.  Specific technology areas being researchedinclude launch isolation for satellites, shape memory alloys release mechanisms, light weightsolar arrays, precision gimbals, magnetic bearings for energy efficient reaction wheels and flywheels, and automation of high-level mechanical tasks.Whole-Spacecraft IsolationThe most severe vibration that a satellite experiences during its lifetime occurs duringlaunch. Traditionally, designing spacecraft to overcome launch vibration has meantstructural stiffening and component isolation.  This approach is costly, time consuming,and adds significiant weight.  The AFRL is actively investigating an alternative approach,which involves isolating the whole spacecraft from the structural-borne vibrations duringlaunch.  The objective of the current effort is to reduce the launch-induced, structural-borne dynamic acceleration at the satellite by a factor of 3 to 4, by inserting an isolatorbetween the spacecraft and the launch vehicle.  The AFRL has several programs in thearea of whole-spacecraft isolation, targeting the small to medium class launch vehicles.The first ever whole-spacecraft isolation system will fly on a Taurus launch vehicle inJanuary 1998.  Additional flights that are scheduled to use whole-spacecraft isolationinclude a LMLV-II (Fall 99), Minuteman (Fall 99), and an Evolved Expendable LaunchVehicle (2002).  It is envisioned that a whole-spacecraft isolation system will replace thetraditional adapter used to physically attach a spacecraft to an LV as shown in Figure 1.By integrating an isolation system into the adapter, the whole spacecraft can be effec-tively isolated from launch loads.  Solar arrays and other flexible structures can then bemade lighter and from less expensive materials, resulting in both mass and productioncost savings.  Lower component mass also allows a larger percentage of the payloadweight to be dedicated to scientific equipment.  It is anticipated that the technologiescurrently under development will  reduce costs and the number of failures.  This will beespecially important for launching  large numbers of similar spaccraft such as thoseenvisioned for proposed satellite constellations necessary to form global telecommuni-cation networks.Figure 1.  Launch Vehicle, Spacecraft, and Payload Attach Fitting (Adapter)Release MechanismsSpacecraft require separation and release mechanisms to separate from the launch vehicle anddeploy appendages such as solar arrays.  Pyrotechnic bolts are currently used for most of thesetasks, but their presence on a spacecraft has several negative impacts. Detonating pyrotechniccharges produces high frequency shock, which can damage fragile sensors, electronics, andlightweight structures.  The explosions also release contaminants, which can reduce the effec-tiveness of sensitive optics.  A 1985 survey of pyroshock flight failures (Moening, 1985) foundthat pyrotechnics related problems caused 83 spacecraft failures in 600 launches, and over halfof the failures caused catastrophic mission failure.  In addition to a propensity for these types offailures, pyrotechnic bolts have the potential for accidental explosion.  According to a NASAstudy (Shapio, 1995), this necessitates special handling and storage procedures, significantlyincreasing the cost of satellite integration.To eliminate the problems associated with  pyrotechnic release devices, the AFRL, andLockheed Martin Astronautics have developed a non-pyrotechnic release device that usesshape memory alloy (SMA) technology.  The SMA mechanism retracts a bolt without producingcontaminants or presenting the threat of an accidental explosion.  The mechanisms can betested in-situ, because unlike pyrotechnic bolts, SMA mechanisms can be reset.  This meansthat the same bolts used in ground tests can be used in the actual flight.  Release is not instan-taneous (> 50ms), but is still fast enough to allow sufficiently synchronous release of multiplebolts.  An additional advantage of SMA devices is that they reduce shock produced duringrelease by an order of magnitude over pyrotechnic bolts.  To demonstrate this, shock spectra,shown in Figure 2, were experimentally measured for several release mechanisms:  a pyrotech-nic device, a non-pyrotechnic device, and two SMA mechanisms (Carpenter, 1996).  The SMAactuators keep the acceleration (shock) below 500g, avoiding the need for space qualificationtesting, while the non-SMA mechnisms do not.  Because of their advantages over currentrelease devices, the new SMA mechanisms will be demonstrated as an experiment on theMightysat 1 spacecraft in 1998.Figure 2.  Typical Shock Response Spectra for Two Conventional and two Shape MemoryActuated Release DevicesLightweight Solar ArraysConventional solar arrays typically use Silicon or Galium Arsinide cells supported by rigid honeycombsubstrates.  Rigid panel composite facesheet thicknesses (around 0.010”) and honeycomb densities (1.6kg/m3) have reached their practical producible limits, capping rigid panel solar array technology at aspecific power of roughly 50 watts per kilogram.  A revolutionary solar array approach is required to meetthe evolving DoD and NASA specific power (>150W/kg), packaging (300 W/m2), and stowage (<0.15 m3for 750 W array) requirements.  The AFRL, NASA Langley, DARPA, and Lockheed Martin are jointlydeveloping and demonstrating advanced technologies for solar array applications.  These technologieswill be combined to reduce cost, weight, and risk, while increasing reliability and power from solar arrays.The technologies developed in this program will be integrated into a solar array with specific powergreater than 150W/Kg.  Two arrays will be designed, fabricated, and tested by Lockheed/Martin, thenflight qualified and flown as two experiments in the Third New Millennium Program technology demonstra-tion.  The first experiment will be two 20 cm by 50 cm panels on NASA’s Earth Observation 1 (EO-1) inthe fall of 1999.  The second will be a full size solar array, like the one in Figure 3, on NASA’s EO-2spacecraft in 2001.Figure 3.  Advanced Solar Array TechnologiesSpacecraft Sensor Gimbal/Bearing SystemAnother AFRL technology area of recent interest is the development of a long life, high reliability,ultra-smooth, fault tolerant, low cost gimbals for slow scan sensors.  As DoD, NASA, and com-mercial payload requirements increase, so does the need for precise, vibration free, sensorgimbal functionality and reliability.  Conventional gimbals are limited by their susceptibility tomechanical wear, need for lubricants, and inherent vibration.  Eventually, performance require-ments will exceed the capability of current gimbals.  Recent advances in electromagnetic sus-pension technology provide an alternative to electromechanical designs for satellite sensorgimbal mounting.  Suspended gimbals will be immune to the problems limiting current designs.Momentum StorageThe AFRL is developing advanced technologies to more efficiently store momentum in rotatingwheels.  Spacecraft attitude control mechanisms typically use such wheels to store angularmomentum and generate torques.  More efficient storage will allow wheels to be used not onlyfor attitude control but also as energy storate devices (mechanical batteries).  One importanttechnology is high precison magnetic bearings, such as those depicted in Figure 4.  Magneticbearings are not required to construct momentum wheels and multi-functional flywheels, butincorporating them will significantly decrease friction and vibration in the wheels.  This in turnwill increase energy efficiency and lifespan, allowing higher rotational speeds.  The latter iscritical, given that flywheel rotor speeds must exceed 40,000 rpm for weight-efficient energystorage (Ginter and Mahoney, 1997).  In addition to developing low-power magnetic bearings,the AFRL has several other ongoing efforts.  These include rotor health monitoring, a new formof homopolar magnetic bearing, and new touchdown bearings that can withstand launch shocksand high speed operation.  Additional areas of interest are containment of flywheels duringfailure and advanced composite materials for rotors.Figure 4.  Magnetic Bearings and Flywheel Rim for Spacecraft ApplicationsAutomationThe AFRL is also investigating automation of high level mechanical functions for on-orbit space-craft maintenance.  Maintaining spacecraft by resupply, retrofitting, and repair can increase thelife span of a satellite and result in lower life-cycle-costs.  This is particularly true of geosynchro-nous satellites, because of the high cost of launching replacement support structure and theneed to tow abandoned satellites to a parking orbit.  To date, spacecraft have been maintainedby extravehicular activity (EVA), limiting the set of maintainable satellites to those in the feworbits accessible to the space shuttle.  Astronauts or ground operators could extend their rangeby teleoperating robotic manipulators on spacecraft or maintenance spacecraft dispatched toaid ailing spacecraft.  An extension of this idea is to automate these manipulators and craft, tooperate without human intervention.  This offers significant benefits when communicationsdelays, limited communications bandwidth, or low duty cycle would prevent a humanteleoperator from working effectively.  Several technologies are required to meet identifiedmaintenance needs such as resupply, retrofitting, inspection, decontamination of solar cells andsensors, assembly and repair of structures, and debris collection.  Technologies being investi-gated include autonomous navigation, collision avoidance, path planning, and robotic endeffectors for tasks such as docking, cleaning, and grasping.ConclusionThis paper summarizes several technology areas that the AFRL is currently investigating toadvance spacecraft mechanisms.  The near-term goal of these technology programs is toadvance the state-of-the-practice rather than the state-of-the-art.  This is especially true in thearea of whole-spacecraft launch isolation.  Spacecraft have been launched for decades withoutthe benefits of even rudimentary isolation from launch vehicle loads.   The insertion and accep-tance of whole-spacecraft isolation came about only after a very simple, lightweight passivedesign was recently introduced. This approach was taken to lower risk concerns that a fullyactive system might generate, despite the promise of superior performance.  By incrementallyadvancing this technology, AFRL has been successful in inserting isolation technology onseveral different launch vehicles, with the first demonstration in January ‘98 on a Taurus launchvehicle.  Because of the program success, several launch vehicle manufacturers have indicatedthat they intend to insert this technology into their launch vehicle fleet as well.  To extend thetechnology further and achieve greater performance, AFRL is now developing active/passive(hybrid) whole-spacecraft isolation.In addition to launch isolation, this paper also discusses AFRL research in the areas of SMArelease mechanisms, lightweight solar arrays, precision gimbals, magnetic bearings for fly-wheels and reaction wheels, and mechanical automation.  Continuing work in these areas willprovide technology that will meet the increasing requirements of spacecraft mechanisms.  It isexpected that the successful implementation of these programs will have an impact on all futuremilitary and commercial spacecraft programs by providing more efficient and reliable spacecraftsystems.References1. Moening, C. J. “Pyroshock Flight Failures,” Proceedings of 31st Annual Technical Meeting ofthe Institute of Environmental Sciences (IES), 3 May 1985.2. Shapio, W., F. Murry, R. Howorth and R. Fusaro, “Space Mechanisms Lessons LearnedStudy:  Volume I – Summary,” NASA Technical Memorandum 107046, September 1995.3. Carpenter, B. F., “Shape Memory Actation and Release Devices”, USAF technical report PL-TR-96-1123, October 1996.4. Carpenter, B. F. and T. Gillespie, “Lightweight Flexible Solar Array”, Lockheed Martin whitepaper, August 1996.5. Ginter, S. and D. Mahoney, “An Assessment of Flywheel Energy Storage System Reliability”,USAF technical report PL-TR-97-1039, February 1997.           11.  Research Structural Engineer, AFRL/VSDV, Kirtland AFB, NM  87117-5776.             22.  Research Computer Engineer, AFRL/VSDV, Kirtland AFB, NM  87117-5776.               33.  Research Aerospace Engineer, AFRL/VSDV, Kirtland AFB, NM  87117-5776.              43.  Research Aerospace Engineer AFRL/VSDV, Kirtland AFB, NM  87117-5776.54.  Deputy Chief, AFRL/VSDV, Kirtland AFB, NM  87117-5776.

Paper Session III-C - Advanced Mechanisms For Space Applications

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Paper Session III-C - Advanced Mechanisms For Space Applications

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