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ä /llf#l #> AIAA 98-0288 Experimentation Using the Mir Station as a Space Laboratory G. F. Karabadzhak, Yu. Piastinin, and B. Khmelinin Central Institute for Machine Building (TsNIIMASH) Korolev, Moscow Region, Russia V. Teslenko and N. Shvets Energia Space Corporation Korolev, Moscow Region, Russia and J. A. Drakes, D. G. Swann, and W. K. McGregor Sverdrup Technology, Inc., AEDC Group Arnold Engineering Development Center , Arnold Air Force Base, Tennessee, USA 36th Aerospace Sciences Meetings Exhibit January 12-15, 1998 / Reno, NV For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics 1801 Alexander Bell Drive, Suite 500, Reston, VA 22091 vmr. QUALITY INSPECTED Ö DISTRIBUTION STATEMENT A ~r Approved for public release; Distribution Unlimited . f Experimentation Using the Mir Station as a Space Laboratory4 G. F. Karabadzhak, ** Yu. Plastinin,' V. Teslenkoand J. A. Drakes/ D. G. Swann, andB. Khmelinin N. Shvets and W. K. McGregor* Central Institute for Energia Space Corporation Sverdrup Technology, Inc., AEDC Group Machine Building (TsNIIMASH) Korolev, Moscow Region, Arnold Engineering Development Center Korolev, Moscow Region, Russia Russia Arnold Air Force Base, 77V 37389-9013 USA Abstract option is to actually perform the experiments in the space environment. This allows for an in-sltuevalu- Collaboration is now underway to perform ation of the chemical kinetics leading to the radia- space-based experiments on the interactions of tion that is routinely observed during space flights. rocket plume exhausts and the ambient environment at an altitude of roughly 350 km. The key ele- The Russian Mir station provides an excellent ment in this experiment is the use of the Mir space site for conducting space experiments due to its station as a platform for optical instrumentation. A flexibility and frequent traffic with ground stations. description is given of the modeling and instrumen- As an example, the Mir will be used as an optical tation involved in the execution of this experiment, bench in an upcoming experiment, termed MirEx, to as well as a description of the experiment strategy observe the generation of the OH(A2Z+ -X2n), and some experimental data already obtained. In NO(A2S+ - X2n), and CO(a3n - X12+) radiation in particular, a hypothesized model of the OH(A-X) rocket exhaust plumes and from the interaction of ultraviolet radiation is presented and evaluated. rocket exhaust plumes with the atmosphere. The goal is to determine the chemical excitation path- 1.0 Introduction way that leads to the production of the electroni- cally-excited states. A second objective of this The observation of the emission from electroni- experiment is to evaluate the physical process of cally excited atoms and molecules in the Earth's vibrational and rotational relaxation of triatomic mol- uppermost atmosphere has been performed for ecules such as C0 as they are rapidly expanded 2 centuries. An example of this is the aurora. Other from a high- to low-temperature and density envi- more recently discovered examples include the ronment. In order to accomplish this experiment, a emission from rocket exhaust plumes traveling in dedicated maneuver of a Progress supply ship is the upper atmosphere. It is difficult to recreate the planned for May 1998. The Progress spacecraft will interactions between a rocket exhaust plume and ignite either the small attitude control thrusters or the upper atmosphere environment in a controlled the larger main engine at precise moments during laboratory setting because of the extremely low the undocking trajectory when various portions of density of the atmosphere and the large mole frac- the exhaust plume are within the fields of view of tion of atomic oxygen. In addition, spacecraft are the selected onboard optical instrumentation. orbiting the Earth at speeds of 5 to 10 km/sec, com- pared to the essentially static atmosphere. Hence, Although considerable coordination must be by virtue of the movement of the spacecraft, there performed during the execution of an experiment is a high-velocity, low-density atmospheric wind such as that mentioned above, it has been found blowing into the rocket exhaust plumes. In addition that the Mir station is surprisingly adaptable to such to the continuing work on mimicking the atmo- scientific use. The Mir is already populated with spheric flux in ground test facilities, an additional numerous spectrometers and radiometric imagers, * The research reported herein was performed by the Arnold Engineering Development Center (AEDC), Air Force Materiel Command. Work and analysis for this research were performed by personnel of Sverdrup Technology, Inc., AEDC Group, technical services contractor for AEDC. Further reproduction is authorized to satisfy needs of the U. S. Government. " Member, AIAA. t Senior Member, AIAA. * Associate Fellow, AIAA. Approved for public release; distribution unlimited. This paper is declared a work of the U. S. government and DUG QUALITY IBüPEiMäD d not subject to copyright protection in the United States. 1 American Institute of Aeronautics and Astronautics negating the logistical issue of obtaining flight-rated Table 1. General Characteristics of the Progress instrumentation. Furthermore, the frequent travel of Main Engine the Progress, Soyuz, and U.S. Shuttle to and from Fuel UDMH the Mir station offers the real possibility of deliver- Oxidizer N 0 2 4 ing unique special-purpose instrumentation to the Equivalence Ratio 1.85 station. Chamber Pressure, N/m2 9.00 x105 Chamber Temperature, K 2930 As with any experiment, prior planning is key to Thrust, N 3090 a successful outcome. This includes the ballistic Nozzle Throat Radius, m 0.02445 trajectories for the spacecraft, logistic scheduling Nozzle Area Ratio 48 for the experiments and cosmonauts or astronauts, and a clear hypothesis to examine in the experi- ambient atmosphere. This is because collisions ment. For the case of the MirEx experiment, the among the combustion products themselves are hypotheses have been, and are continuing to be, negligible as the plume expands and the molecules modeled to reliably estimate the instrumentation excited in the near field have already decayed. The settings. Some processes which may dominate in radiation intensities have been evaluated for the NO and CO excitation and decay have been stud- PME plume near field and far field separately. ied previously.1 This paper describes the develop- Among a great variety of possible processes result- ment of the radiative hypothesis for the OH(A) radi- ing in the generation of radiation in the far field, only ation, the modeling of the expected plume-atmo- those are discussed here which produce OH(A2E+) sphere interaction, the assessment of previous molecules, because some experimental data on the data, strategy for experiment execution, and the far-field OH radiation have already been obtained. planned instrumentation. In addition, other types of experiments utilizing the Mir station will be briefly The PME near-field UV and IR radiation intensi- discussed. ties in the molecular bands of NO, CO, C0 and OH 2 have been evaluated over the maps of gasdynamic 2.0 Modeling parameters by an overlay method using the approx- imation of an optically thin plume. The Numerical 2.1 PME Near-Field Radiation Analysis of Real Jets (NARJ) computer code was employed to generate the gasdynamic parameter It is important to understand the size and inten- maps.2 NARJ is a fully reacting, axisymmetric, con- sity of the expected exhaust plume radiation prior tinuum flow solver designed for rocket nozzle and to attempts to measure the radiation. This will be plume computations. Excitation of the plume gas also useful for verification of the models applied. molecular electronic states by solar radiation, geo- Several methodologies have been used to model corona Lyman-alpha, and electronic impact has potential Mir-based plume experiments. The been considered. Chemical reactions resulting in Progress main engine (PME) exhaust was consid- the plume species excitation have not been considered as a primary candidate for observation. The ered because modeling of these processes is not single-nozzle PME utilizes UDMH as the fuel and finished yet. The PME plume spectral brightness, N 0 as the oxidizer, at an equivalence ratio of 2 4 averaged within 5 meters downstream from the 1.85. The area ratio of the PME is 48, with a nozzle nozzle, has been evaluated for the daytime condi- exit diameter of 0.3 m. The Progress altitude at the tion. Table 2 gives the brightness value. The esti- experiment is expected to be between 350 and 400 mated values presented in Table 2 were used as a km. A description of the PME is given in Table 1. reference for the experiment planning and are not considered as final results of accurate modeling. In the near field (order of ten meters from the PME nozzle), the radiation is due to the processes 2.2 OH(A) Excitation Mechanisms in the plume itself. Further downstream from the nozzle exit, the radiation results mostly from the There are a number of possible routes to the interaction of the combustion products with the formation of OH(A2S+) in the rocket exhaust American Institute of Aeronautics and Astronautics Table 2. Estimates of the PME Exhaust Plume Brightness in Various Spectral Regions Molecule CO NO OH C02 CO NO Wavelength, mm 0.14-0.17 0.2-0.23 0.3-0.33 4.2-4.4. 4.5-4.8 5.1-5.6 Brightness, W/sr-^m-cm2 10"6 2 x10-7 5x10"6 io-2 10"3 IO"4 plumes at orbital altitudes, especially in the case of the final translational energy partitioning of Eq. (1), the retrofiring. The most significant constraint on reaction Eq. (2) may or may not be possible. the reaction mechanism is that the very low density will favor two-body reactions over three-body reac- A more attractive alternative to the 0(1D) route tions. Hence, the modeling applied to bow shock is the direct formation of OH(A2I+) from the reac- re-entry vehicles may not be applicable for the tion present plume problem.3 However, one similar fea- ture, at least for retrofirings, to the bow shock prob- 0(3P) + H20 -> OH(A2I+) + OH (3) lem is the high relative velocities between plume An extensive discussion of this reaction has exhaust gas molecules and the ambient atmo- been provided by Kofsky, et al.6 Based upon the sphere. Given an orbital velocity of 8 km/sec and a endothermicity of the reaction, this process has a typical plume exhaust velocity of 3 km/sec, it is threshold relative velocity of 10.4 km/sec. Because possible to obtain relative velocities in the range of the threshold velocity of the reaction is at the 5 to 11 km/sec. The high level of kinetic energy higher range of the expected relative velocities, opens up many possible reaction pathways for OH(A2i;+) formation, depending on the details of this process can be expected to be relevant primarily for retrofirings. The orbital velocity at the Mir the conversion of the kinetic energy into internal orbit is 7.35 km/sec, allowing only molecules flying excitation. in the plume inside the cone with the top half-angle One possibility for creating OH(A2E+) is the two- of 22 deg to the spacecraft velocity vector to over- come the reaction threshold. In addition, only those step reaction of the atmospheric oxygen atoms oxygen atoms may produce OH(A) molecules with plume species such as N , given as, 2 which have not bgien previously scattered and still 0(3P) + (N , O) -» 0(1 D) + (N , O) (1) possess a velocity anti-parallel to the spacecraft 2 2 velocity vector in the spacecraft reference center. 0(1 D) + H -» OH(A2Z+) + H (2) For simplicity, the OH(A->X) is evaluated below for 2 the case of an axisymmetric nozzle with its axis The formation of the first excited state of atomic anti-parallel to the spacecraft velocity vector. oxygen, 0(1D), in a retrofiring plume exhaust has been previously investigated by Murad, et al.4 The 2.3 Rarefied Flow Modeling 0(1D) emission was observed by ground tele- scopes at the US Air Force Maui Observatory The NARJ exit plane result was incorporated (AMOS) during Shuttle vernier engine firings. The into a computer code known as SOCRATES7 engine firings were both wake and ram, and testi- (Spacecraft/Orbiter Contamination Representation fied to the presence of 0(1D) in the plume due to Accounting for Transiently Emitted Species). The the interaction with atmospheric oxygen atoms. In SOCRATES model utilizes the direct simulation the case of 0(3P) and N with a relative velocity of Monte Carlo (DSMC) method to simulate the three- 2 10 km/sec, the energy excess of Eq. (1) is roughly dimensional, rarefied gaseous flow-field properties 3.3 eV, which is an important factor in determining far from the spacecraft. The PME simulation was whether the second step proceeds. The second run with the nozzle exhaust conditions stated in step of the reaction has been investigated in the Table 3. laboratory by Lebehot, et al.5 and presents an energy activation barrier of -2.8 eV, with a net The default atmospheric model of SOCRATES endothermicity of 2.1 eV. Thus, depending upon (MSIS '90) was used to define the ambient species American Institute of Aeronautics and Astronautics Table 3. PME Exit Plane Predictions, as large cell dimensions, however, do not adequately Determined by NARJ provide flow field properties in the near field of the thruster. Therefore, to characterize the near field Altitude, km 350 (exit plane), a third computation was performed Vehicle Velocity, km/sec 8 with a cell dimension chosen to be 1 meter. This Exit Temperature, K 732 gave a total computational space of 16 x 16 meters Exit Pressure , N/m2 1.09 x103 in the cross-sectional plane and 30 meters in the Exit Density, cm"3 1.08 x1017 axial plane (25 m downstream of the exit plane of Exit Velocity, m/sec 2,993 the nozzle and 5 m upstream of the exit plane). Composition, mole fraction: H 0 0.2884 The SOCRATES results for the plume species 2 N 0.2668 densities are shown in Figs. 1 and 2. Figure 1 illus- 2 trates the predicted total density distribution. For CO 0.1891 H 0.1905 clarity, a cut through the three-dimensional solution 2 co 0.0531 domain has been taken along the y = 0 plane (with 2 the orbital velocity vector defining the +z axis), and OH 1.07E-5 H 0.0110 0 9.20E-6 mole fractions and temperatures. For an altitude of 350 km, the atmospheric temperature is 1150 K and the number density is 4.68 x 108 cm"3. The composition is dominated by atomic oxygen, which has a mole fraction of 0.843 at 350 km. Ideally, to properly characterize the entire flow field of the PME, SOCRATES should be run with cell dimensions that are small enough to provide adequate resolution of the flow-field properties over all space. For the exit plane region of the engine, where the flow-field properties change rapidly, this requires cell dimensions of not more than 1 meter. However, the total region of space occu- pied by the plume can be on the order of tens of kilometers. Therefore, because of both computer a. Surface map of centerline plane. resource and time limitations, the full extent of the PME flow field was simulated using several scaled runs. In all cases the code was run until steady state had been fully reached. In particular, two SOCRATES computations were performed with cell dimensions of 10 and 100 m . This gave, for the 10-m case, a total computational space of 160 x 160 meters in the cross-sectional plane and 300 meters (250 downstream of the exit plane and 50 meters upstream) along the 1240 660 500 axial plane. For the 100-m case, the region of Distance, m space covered was 1,600 x 1,600 x 3,000 meters b. Axial Profile (2500 m downstream of the nozzle exit plane and Fig. 1. Calculated total number density of retrofir- 500 m upstream of the nozzle exit plane). These ing Progress plume at 350 km altitude. American Institute of Aeronautics and Astronautics is given as a surface map in Fig. 1a. To better illus- stream of the nozzle exit. The important point to trate the far-field behavior of the density, the grid note is that the atmospheric O atoms do not pass spacing in this figure is coarse, as the first grid through the plume without being scattered by the point after the nozzle exit plane is 50 m down- plume gases. This leaves the region closest to the stream. Clearly the rapid expansion of the plume nozzle comparatively starved for atmospheric O gas into the very low-pressure environment is evi- atoms. In the 1-m spatial-resolution calculations, it dent, along with the interesting fan structure of the can be discerned that the O atom density is ele- plume. In Fig. 1b, a profile has been taken of the vated near the nozzle exit plane due to the O plume density along the +z axis. In contrast to the atoms from the plume itself. surface map shown in Fig. 1a, the profile includes the high spatial resolution solution near the nozzle Assuming the elastic collision with the plume exit and illustrates the very steep decline of the molecules is the main contributor to the attenuation density, ranging over 5 orders of magnitude in the of the directed flux of the oxygen, the number den- first 500 meters The behavior of the other major sity, N0(x),of the reacting oxygen atoms at point x plume species, e.g. H 0, N , H , CO and 0 , fol- on the plume axis may be expressed as : 2 2 2 2 low the same trend as the total number density, N (x)=N exp(-Jo N(x')dx'), ( ) with the only significant difference being the vari- 0 0 el 4 ous scales. This is not unexpected, since the major where N(x) is the total plume number density at species chemistry is frozen in the computation. point x, N is the concentration of the oxygen 0 atoms far away from the spacecraft, and <s is the et elastic collision cross section. Assuming further that OH(A) molecules pro- duced in the reaction Eq. (3) experience only radiative relaxation, the total amount of radiation in the OH (A->X) band per unit volume in the point x may be calculated: Bff = NH o(x) • No(x) • °r(vr) • vr' hv 2 = NH2OW ' N0exp(-Joe|N(x')dx') (5) •o (v)v -hv r r r where v is the relative velocity between the O r atom and the H 0, and o(v) is the excitation 2 r r (reactive) cross section. The dependence of excitation cross section upon the relative velocity for Eq. (3) has been derived in Ref. 6 above, Fig. 2. Calculated atomic oxygen density of retrofiring Progress plume at 350 km altitude. -16 th <j(v) = 5.43-10 (6) In marked contrast to the major plume species r r densities are the atomic O and N densities. Figure th 2 shows a surface map of the 0(3P) atom density, analogous to the map of Fig. 1a. For the O atoms, where o(v) is the reactive cross section in cm2, r r the density is small at the nozzle exit and increases and vh is the threshold velocity of 10.4 km/sec. t to the ambient atmospheric value as the axial dis- The elastic collision cross section can be esti- tance is increased. The trend of the O atom density mated, based upon Ref. 6, as 3 x 10""1 5cm-2. is reversed from the plume species, and illustrates the penetration distance of the atmosphere into the Based upon the arguments presented above, retrofiring plume as roughly to within 500 m down- the radiation power of the plume per unit volume American Institute of Aeronautics and Astronautics may be estimated by Eq. (5). The evaluation made Table 4. BRIZ Spectrometer General for the PME with the number densities computed Characteristics from SOCRATES gave a value for Bff = 0.9 W/sr. Wavelength Region, nm 135-369 Furthermore, differentiation of Eq. (5) with respect Field of View, angular minutes 7 x 40 to the plume axis coordinate, x, gives the coordi- Spectral Resolution, nm 2.4 + 0.3 nate where the specific radiation power is maximal. Scanning Rate, seconds per spectrum 2.0 ± 0.2 For the PME computations above, this value is x Noise Equivalent Radiation declared by m Manufacturer, W/sr-um-cm2 = 630 meters from the nozzle, indicating that the characteristic cross dimension of the glowing X=150nm 10 plume region in this case is approximately -300 X = 250 nm 10 meters. However, even a small angle between the X = 310nm 2x10"8 velocity vector and the plume axis will result in a Dynamic Range 2x104 decrease of x and the characteristic plume m dimension in this waveband. 193-253 nm, 251-311 nm, and 309-369 nm. Accu- racy of the interval limits setting is 2 nm. In princi- 3.0 Instruments and Experimental Scheme ple, no overlapping of the intervals is allowed. Accuracy of the wavelength setting is better than 1 Two spectrometers and an ultraviolet imager nm. Accuracy of the noise equivalent radiation data have been chosen among the onboard instruments as declared by the instrument manufacturer is bet- to perform the rocket motor radiation measure- ter than 30 percent in the region of X =200-369 nm ments. The NO, CO, and OH emissions related to and better than 40 percent in the region of X < 200 the electronic transitions will be measured by the nm. The spectrometer has a built-in calibration VUV-UV spectroradiometer BRIZ. The UV imager source that automatically provides a reference equipped with a 310 to 330-nm narrow-band filter spectrum after every 300 sec of operation. will provide the OH(A) radiation spatial distribution. The IR spectrometer ISTOK will measure the CO 3.2. The UV Imager and NO vibrational band radiation. The UV imager was developed and manufac- 3.1. BRIZ Spectrometer tured at TSNIIMASH in cooperation with the Opti- cal Department of Lebedev's Physical Institute. It The BRIZ is a four-channel scanning polychro- combines a quartz telescope followed by an image mator developed and manufactured in the Optical intensifier and relay lens to interface with a radia- State Institute in St. Petersburg. It is equipped with tion detector. To effectively block the visible radia- four exit slits and four photomultipliers operating in tion a solar blind Cs Te photocathode is used in the photon counting mode. It is mounted on top of 2 the image intensifier. The UV imager is also the SPEKTR-module and connected with cables to equipped with a broad-band color glass UV filter the inside data acquisition and control unit. The and three different narrow-band (8-nm FWHM) instrument line of sight is lying in the XY plane of interference filters. Some general characteristics of the Mir core module along a line that is 10 deg off the UV imager are presented in Table 5. the -Y direction to the -X direction. The instrument line-of-sight direction is fixed. The BRIZ instrument Table 5. UV-lmager General Characteristics works automatically and needs no crew supervi- Operating Wavelength Region, nm 200 - 360 sion. It uses common Mir data storage and teleme- Wide Band Color UV Filter, nm 240 - 360 try systems to downlink the data collected. The Interference Filter's Centers, nm 260, 284, 317 total time of BRIZ operation is about 15 min per Telescope Effective Diameter, mm 55 experiment. This time is restricted by the capabili- Telescope Focal Length, mm 78 ties of the Mir telemetry system. General charac- Field of View, deg 12 teristics of the spectrometer are given in Table 4. Angular Resolution, angular minutes 3.0 The spectrometer measures spectra simulta- Image Intensifier Maximum Gain - 3 x 104 neously in four spectral intervals: 135-195 nm, American Institute of Aeronautics and Astronautics The imager is located inside the Mir station and, P8=S(Xo)jE(Ä.)T(A.)-s(Ä.)-dÄ., (7) can therefore work effectively only when looking through a quartz window. Common photo and where E(X) - star radiation flux, T(X) - filter video cameras are basically used as the detecting transparency, s(X) - image intensifier relative spec- element. Modular design of the UV imager pro- tral sensitivity. vides an opportunity to easily replace the detector 3.3. ISTOK Spectrometer in accordance with experiment requirements. The crew operator can observe the imaging scene The ISTOK instrument was developed and through the detector viewfinder. There was also a manufactured in the Optical Department of Lebe- provision to set the image intensifier amplification dev's Physical Institute of Russian Academy of Sci- gain at the level appropriate to the radiance of the ences in Moscow. It combines several units: opti- object being observed. Crewmembers are trained cal, electronic, calibration source unit, data acquisi- to handle the imager before flight and will be pro- tion and control unit and some others. The optical vided with a specific experiment plan from the Mis- unit is located outside the PRIRODA module on the sion Control Center just before the experiment. rotating platform. Its line of sight may be positioned The use of video tapes and photo films for data before measurement along any preset direction recording, storage and delivery simplifies the data inside the field of regard, which covers all the space acquisition system, but it brings forth severe confined by the +X, +Y, +Z axes of the Mir core requirements to the imager calibration procedure module. The optical unit of the instrument consists when absolute radiation values are to be mea- of two identical channels. The first channel pro- sured. The used films are returned to Earth by the vides the spectrum in the region of X = 4-8 u.m, and next Progress cargo spacecraft flight. The most the other in the region X = 8-16 |o,m. The incoming interesting and urgent data are recorded on video- radiation dispersed on the grating is detected by a tape and may be promptly transmitted to the Mis- 32-pixel linear array of pyroelectric detectors in the sion Control Center terminals in the course of a spectrometer. The spectrometer has a built-in regular TV session. mechanical chopper for the radiation flux frequency modulation. The spectrometer works automatically The Mir station has two quartz windows and and doesn't need crew supervision. Measurements special window adapter for the UV imager mount- are controlled by an onboard control unit which in ing. The line of sight of the UV imager during oper- turn works in accordance with the instructions ation can be either firmly fixed along a specified uplinked from the Mir Mission Control Center during direction with respect to the window axis or con- routine telemetry sessions. All housekeeping and trolled by the crew operator. scientific data are written in the spectrometer digital memory unit onboard the Mir station and stored The absolute sensitivity of the imager is not pre- there until next telemetry session. The spectrome- sented in the Table 5 because it depends on the ter can work continuously for more than 15 min. window transparency and on the particular detec- The operating time is basically restricted by the tor and recording tape characteristics. On those capacity of the data storage system. occasions when absolute values of radiation have to be reduced from the images obtained, the Some general characteristics of the ISTOK imager is accurately calibrated against known radi- spectrometer are given in Table 6. ation from various stars, using the identical experimental arrangement. Analysis of the data obtained 3.4 Strategy of the Experiment from the UV imager for four years of its operation indicates that the spectral response of the instru- Comparison of the expected radiation intensity ment is largely defined by the image intensifier with the instruments' sensitivities and fields of view spectral sensitivity and the filter transparency shows that near-field emissions spectra of the curve in the region X> 270 nm. Therefore, absolute PME exhaust could be reliably measured from dis- response of the instrument at the center of narrow- tances of less than several kilometers. Measure- band filter S(X ) may be derived from: ments of the far-field PME radiation spectra and 0 American Institute of Aeronautics and Astronautics ACS thruster's emissions may require an even Table 6. Some General Characteristics of the smaller distances. Hence, the firing of these ISTOK Spectrometer motors during the spacecraft docking and undock- Operating Wavelength Region, \im 4-16 ing procedures represents an ideal opportunity for Spectral Resolution, \im: observation. Several attempts were made last year in the region 4-8 n.m 0.125 in the region 8-16 urn 0.250 to measure the spectra during the Shuttle and Progress undocking; however, no reliable data Sensitivity Level for 1 -Hz bandpass, W/cm2-sr-|xm: in the region 4-8 |xm 10"5 have been obtained from these attempts. This was in the region 8-16 urn 5x10"6 primarily because in those instances, the space- Dynamic Range >irj2 craft docking and undocking were very intensive procedures, requiring unique station orientation Minimum Time per Spectrum Acquisition, sec 1 and consuming much of the station resources and Field of View, angular minutes 6.5 x 26 crew attention as well. While continuing with the attempts to measure the motor exhaust radiation spectra during undocking, a dedicated Progress plume observation experiment was planned for last fall. Figure 3 helps to understand the strategy of the experi- >%m ment. The black squares in this figure repre- sent points of the Progress trajectory after undocking. Distances on the axes are given in km in the frame system referenced to the Mir station. Also, times after undocking are shown at the picture when the firings will take place. at I n i' * i i „„ The experiment was to be performed right after the Progress undocking. During undocking, the station supports an orbital Fig. 3. Planned Progress trajectory and plume positions orientation (maintains a fixed position refer- during observation event, Earth is below and both enced to the Earth system frame). In this ori- Mir and Progress are moving to the right. entation the X axis of the MIR Core module lies in the orbital plane, and the Y axis either lies in experiment is now being planned for May. the orbital plane or directed perpendicular to it. The Although no reliable spectra have been obtained spacecraft detaches the station mechanically and due to above-mentioned reasons, some data from goes forward and up from the station in the direc- the UV-imager appeared to be quite interesting tion of the velocity vector, flying over the station and demonstrated the ability to perform the plume toward its rear side. In the course of this maneuver, observation experiments onboard the Mir station. the spacecraft was scheduled to perform three dedicated ACS motor firings of about 10-sec dura- 4.0 Results of the Preliminary Experiments tion each. As is seen from Fig. 3, the spectrometers were supposed to measure the exhaust spec- The UV imager filtered in the A. = 280 to 330-nm tra from different parts of the plume while one of wavelength region was used to observe retrofirings the crewmembers manually tracked the spacecraft of the Progress main engine. The main engine ret- with the UV imager. rofirings are being performed each time the Progress de-orbit before its re-entry. The engine The summer accident seriously impacted all operates for about 4 min during this maneuver, and scientific activity onboard the MIR station. The sci- the distance to the spacecraft ranges from about entific program was suspended and only recently 12 km to about 60 km, depending on particular recovered. The dedicated plume observation requirements of the re-entry conditions. The 8 American Institute of Aeronautics and Astronautics spacecraft positions itself before the firing in such a Table 7. Progress Main Engine Plume Observa- way as to keep the X axis (plume centerline) in the tion Conditions orbital plane and parallel to the velocity vector. Sample # Distance to the Angle ß Angle 9, Once the engine is fired, the spacecraft keeps iner- Progress, (see Fig.6), deg tial orientation, resulting in continuous changing of km deg the plume axis direction with respect to the velocity a 15.8 3.6 7.7 b 19.7 -0.2 11.6 vector. The Mir station orientation is normally the c 22.3 -2.4 16.0 inertia! one during the Progress re-entry. However, the station can build, in principle, a specific orientation that corresponds to the observation require- Based on the stellar images analysis, the UV ments and provides proper spacecraft viewing. imager angular resolution was evaluated to be equal about 1.7 • 10'3 rad full-width at half-maxi- The general scheme of the Progress retrofiring mum (FWHM). Allowing for this resolution, the spa- observation is as depicted in Fig. 4. A specific pecu- tial scale of the radiating volume cross section liarity of the observation is that Progress main axis recovered from the images appeared to be about is always located inside the angle ± 20 deg from the 70-80 meters. Assuming the radiation in the con- line of sight, such that the PME nozzle throat may sidered wavelength region is mainly due to the be seen from Mir. Table 7 gives the observation OH(A22+->X2n) transition, its intensity was evalu- conditions and Fig. 5 represents three typical sam- ated based on the imager calibration data. The ples of images obtained in the experiments. intensity appeared to be B = 1.2 ± 0.3 W/sr. The plume images in Fig. 5 are essentially dif- Because of the experiment geometry, the total fused and differ from a star point source image. radiation is a combination of radiation from the combustion chamber/intrinsic nozzle, v ^Ptvynm- Mt*n Ante F as well as the near-field and far-field plume components. The combustion chamber/intrinsic nozzle radiation yield was evaluated, assuming that combus- tions product composition and excited states population, correspond to the local thermodynamic equilibrium condi- Fig. 4. Schematic of viewing geometry of Mir and Progress after tion. The radiation transfer equation undocking. mrad mrad mrad a. Progress b. Progress c.Progress d.Pleiades Fig. 5. Progress plume images and Pleiades stellar cluster image clip (the same magnification). Inten- sity profiles taken approximately at the middle of the images are shown below the image. American Institute of Aeronautics and Astronautics