Overview of the Air Force ESEX Flight Experiment

Transcription

1 549 IEPCG Overview of the Air Force ESEX Flight Experiment A. M. Sutton Phillips Laboratory (AFMC) Edwards AFB, California, USA Therefore, a search is underway for new Abstract technologies that can fulfill the maneuvering requirements and avoid increasing propellant. The most promising near In the post cold war, the United States term solution to this problem is electric Air Force is challenged by the need for propulsion (EP) 1.2. increased maneuverability of the U.S. space assets, and the need to reduce There are, moreover, many payoffs to launch costs. These needs have using electric propulsion for orbit raising. spawned the Electric Propulsion Space EP upperstages can deliver greater Experiment (ESEX). ESEX will address payloads from LEO to an operational key issues associated with high power orbit. Additionally, launch vehicle flexarcjets. Measuring performance in space ibility can be gained on large satellites. A and interactions on the spacecraft of this large satellite limited to a Titian IV with a new plasma propulsion system will conventional upperstage, can be launched provide the first step towards the on a smaller, cheaper, launch vehicle with operational use of high power arcjets. an EP upperstage 3. Currently, the program is nearing completion of the second phase, in which The arcjet appears to be the most likely the subsystems are being built, tested, candidate for orbit raising and manand integrated into a flight unit. In the euvering from amongst the many choices third phase, the flight unit environmental in EP engines. The arcjet is the most tests will be performed. In the last technologically mature and has a relphases, the flight unit will fly aboard the atively high power (10's of kw's). P91-1 spacecraft, the Advanced Research Global Observation Satellite (ARGOS) in A 26 kw arcjet was chosen for the first late Air Force electric propulsion flight experiment for the following reasons: the 26 kw thruster was state-of-the-art at the Introduction time of the inception of the ESEX program; an arcjet of this size can accommodate the current projections of avail- With depolarization of geopolitical con- able space power (30-50 kw); the relflict, the ability to predict the location of atively high thrust makes transfer trip possible military conflict is difficult. This time less than 100 days. Long trip times difficulty has increased the demands on are unattractive to potential Air Force the existing Air Force satellite con- users. stellations and has created the need for increased maneuverability. The increase ESEX is part of the Advanced in maneuverability can be accomplished Technology Transition Demonstration easily by the addition of propellant. (ATTD), which is specifically designed to However, this solution costs dearly in transfer technology from the government limited spacecraft mass allocation, labs to the aerospace community. Copyright International Electric Propulsion Conference. All rights reserved. No copyright is asserted in the United States nder Title 17, U.S. Code. The Government has a royalty-free license to exercise all rights under the copyright claimed herein for Government purposes. All other rights are reserved by copyright owner. This paper is declared a workof the U.S. Government and is not subject to copyright protection in the United States.

2 IEPC The $18.5 million effort is funded by the Phillips Laboratory. TRW is the prime contractor. Olin's Rocket Research Company (RRC), Defense Systems, Inc. (DSI) and Ergo-Tech, Inc. (ETI) are the subcontractors. In addition, RRCs sister company Pacific Electro Dynamic (PED) is subcontracted to build the power conditioning unit (PCU) 4. EMI, since the vacuum chamber walls have a large effect on the plume. A high power arcjet operating at 100's of amperes of current is a great potential source for EMI 6. Although, spacecraft designers can work around EMI, it must first be characterized. ESEX's antennae will measure EMI in the GHz frequency range, corresponding to nominal satellite communication channels. Objective During life tests of the arcjet, tungsten is lost from the electrodes. Tungsten represents a serious contamination issue In order to transfer the high power arcjet for solar arrays and optics. It is assumed successfully into operational use, the this mass is ejected away from the ESEX experiment has to accomplish two spacecraft at close to the arcjet exhaust major objectives. The first is to develop velocity. ESEX will measure the deposreliable flight hardware which will suc- ition of tungsten and other contaminants cessfully complete a test firing in space. impinging on the spacecraft to verify this The second objective is to gather data on assumption. key spacecraft integration issues, verifying that a high power arc plasma The arcjet converts approximately 30 persource can operate without adversely cent of its energy into thrust. Therefore, affecting a spacecraft's nominal oper- about 70 percent of the converted energy ations. is either conducted to the spacecraft as heat or lost into space. Measurements of To successfully demonstrate a high the conducted heat can be made on the power arcjet that can survive launch and ground. However, a large part of the operate reliably in the space environment, expelled energy is radiated heat to the the thruster performance will be quant- spacecraft from the arcjet plume, and can ified and compared with ground measure- not easily be measured on the ground. ments. Ground performance data of EP The radiated heat is affected by plume devices has been historically encumbered size and shape, which is determined by by ground facility errors, creating the the background pressure and vacuum need for flight data 5. Flight performance chamber geometry. ESEX will measure data will include thrust, specific impulse, the amount of thermal radiation impinging and efficiency. Thrust will be derived on the spacecraft during a firing 7. Addifrom measuring acceleration and cor- tionally, measurements of size and shape bined with spacecraft mass. Specific of the arcjet plume will be imaged at the impulse will be derived from the pro- Air Force Maui Optical Site (AMOS), in pellant mass flow rate and thrust. Effi- Hawaii. ciency will be derived from the voltage current product (power) and the thrust data. Host Vehicle The arcjet spacecraft interactions that concern designers are radiated electro- ESEX is one of eight experiments magnetic interference (EMI), plume scheduled to fly in late 1995 on the P91-1 contamination, and thermal radiation. In spacecraft, Advanced Research Global ground facilities, it is difficult to accur- Observation Satellite (ARGOS). ARGOS ately measure plume contamination and is managed by the Space Test and Small 2

3 551 IEPC Launch Vehicle Programs office at the Design Review (CDR), scheduled for Space and Missile Systems Center. November of Phase II will be ARGOS is being built by Rockwell concluded upon completion of the flight International and will be launched by a unit integration. Phase III will consist of Delta II, to a 460 nautical mile, 98.7 deg. performing the environmental and flight inclination orbit. ESEX is scheduled to qualification tests of ESEX. Phase IV fire during the second phase of the flight, will be the integration of ESEX to the alternating with the Critical Ionization ARGOS host spacecraft. Phase V will be Velocity (CIV) gas release experiment. 8 the actual flight and Phase VI the Besides the instruments onboard ESEX, reduction of flight data. ground controllers will be monitoring the state of health of ARGOS. In the event, - -, of an unexpected adverse effect of the arcjet on ARGOS the firing will be "- terminated. Due the robust ARGOS de-. sign and the fact that arcjet operation is not mission essential, the ESEX ex-," I periment offers little risk to the host -- satellite. - _ MEN -umo -cm JIM2 DATA I One concern of ARGOS is the arcjet "" thrust vector alignment. In order for" ' ""' '" " ESEX to make its measurement of thrust, the ARGOS reaction control thrusters will Figure 1 be deactivated during the ESEX firings. Schedule ARGOS will control its attitude with three reaction control wheels. If the thrust vector of the arcjet is misaligned with Subsystems respect to the spacecraft center of gravity, the reaction wheels could be saturated and ESEX is comprised of four major subcause ARGOS to tumble. The arcjet can systems. The propulsion subsystem; the only be aligned on the ground to the diagnostics subsystem; the command and geometric center of the constrictor, and it control subsystem; and the power subis assumed that the thrust vector goes system. In figure 2 an exploded view of though that center. ARGOS will be the ESEX components are shown. sending data of the change in reaction mnit &, wheel momentum as part of its state-ofhealth and this will verify the assumption. -A AnIMUIA SIP^a t tile Schedule This effort is divided into six phases (fig. '"i'" 1). In phase I, the initial design was "" completed and reviewed at the Preliminary Design Review (PDR), in " " July In phase II, TRW and its " """"" team have been fabricating and testing "A'atn«.. each subsystem. A comprehensive tm0a - review of the fabricated hardware test Figure 2 results will be conducted in a Critical Subsystem Layout 3

4 IEPC The propulsion subsystem consists of the downsizing to a smaller launch vehicle is arcjet, PCU, and propellant feed possible. subsystem (PFS) 9 ' 0. Currently, engineering models of all of these components The Air Force believes that EP have been built and will be tested in an technology will be important in a future integrated mission simulation test at where the U.S. will rely more on its RRC 11. Upon successful completion of space assets and allocate fewer dollars to this test, flight versions of these com- perform those missions. ESEX will adponents will be built and delivered to dress the key issues associated with the DSI. operation of single high power arcjet or multiple low power thrusters. The ESEX The diagnostic subsystem consists of the program is an important first step towards video camera, radiometers, thermoelect- fielding an electric orbit transfer vehicle rically cooled quartz crystal micro- and an electric orbit repositioning satel- -balances (TQCM's) and EMI antennae lite. and electronics. Most of these components are built and undergoing tests as flight hardware. References The command and control subsystem or unit (CCU) will communicate with ARGOS via a MIL-STD-1553B data bus. 1. J. M. Jones, R. S. Einhorn, The A prototype of this unit is built and USAF Electric Propulsion Systems undergoing testing. The CCU will be Activities, 1993, Phillips Laboratory, refurbished for the flight. AIAA , Jun 93. The power subsystem consists of the 2. J. E. Pollard, et al, Electric Propulsion Power Integration Unit (PIU) and the Flight Experience and Technology silver zinc batteries. The PIU distributes Readiness, The Aerospace Corp., El and conditions the 28 VDC power from Segundo, CA, AIAA , Jun 93. ARGOS to all the ESEX subsystems. The PIU also contains the charger to 3. T. M. Miller, R. S. Bell, Assessment perform the 100 hour recharge of the of the Economic Benefits of Solar Electric batteries between firings. A prototype of Orbital Transfer Vehicles, McDonnell the PIU is built and undergoing testing, Douglas Aerospace, Huntington Beach, but will be refurbished for flight. En- CA, AIAA , Jun 93. gineering model batteries have been delivered to RRC for the integrated mission 4. J. M. Jones, et al, The USAF Electric simulation, and the flight cells have been Propulsion Systems Activities, Phillips construction. Laboratory, AIAA , Jul 92. Conclusion 5. W. D. Denininger, 30-kW Ammonia Arcjet Technology, JPL, Pasadena, CA, Final Report, Jul 1986-Dec There are many payoffs in the develop- 6. L. K. Johnson, et al, Frequencyment of electric propulsion technology, domain Electromagnetic Characteristics of In station-keeping, mission lifetimes can a 26kW Ammonia Arcjet, The Aerospace be increased. In orbit maneuvering, more Corp., El Segundo, CA, AIAA , maneuvers can be performed with the Jun 93. same propellant load. In orbit raising, more payload may be accommodated or 4 7. M. M. Kriebel, N. J. Stevens, 30-kW Class Arcjet Advanced Technology Transition Demonstration (ATTD) Flight

5 553 IEPC Experiment Diagnostic Package, TRW, Redondo Beach, CA, AIAA , Jul F. J. Agardy, R.R. Cleave, A Strategy for Maximizing the Scientific Return Using a Multiphase Mission Design for ARGOS, The Aerospace Corp., El Segundo, CA, AAS , Aug C. E. Vaughan, J. P. Morris, Propellant Feed Subsystem for a 26 kw Flight Arcjet Propulsion System, Rocket Research Co., Redmond, WA, AIAA , Jun C. E. Vaughan, et al, Design, Fabrication and Test of a 26 kw Arcjet and Power Conditioning Unit, Rocket Research Co., Redmond, WA, IEPC , Sep R. S. Adland, et al, Integrated Mission Simulation of a 26 kw Flight Arcjet Propulsion System, Rocket Research Co., Redmond, WA, AIAA , Jun 93. 5