Time-Resolved Infrared Spectrophotometric Observations of High Area to Mass Ratio (HAMR) Objects in GEO

Transcription

1 Time-Resolved Infrared Spectrophotometric Observations of High Area to Mass Ratio (HAMR) Objects in GEO 61 st International Astronautical Congress IAC-10-A September-1 October 2010 Mark Skinner 1, Ray Russell 2, Rick Rudy 2, David J. Gutierrez 2, Daryl L. Kim 2, Kirk Crawford 2, Steve Gregory 1, Tom Kelecy 1 1 Boeing LTS, 2 The Aerospace Corp. BOEING is a trademark of Boeing Management Company.

2 Agenda HAMR objects Brief description of the Aerospace Corporation s Broadband Array Spectrograph Sensor (BASS) On-sky system calibration results using resident space objects Results of observations of HAMR objects by BASS IR Visible Multi-spectral Summary

3 HAMR: High Area-to-Mass Ratio objects A population of deep space objects thought to have origins from sources in the GEO belt [Schildknecht, et al.] Area-to-Mass Ratio from 0.1 to ~10 s of m 2 /kg Solar Radiation Pressure (SRP) disturbs orbital parameters SRP perturbs orbital period, inclination & eccentricity with big variations over days-toweeks scale

4 SRP induced motion depends on physical and thermal characteristics of HAMR objects Objects pictured are MSG-II cooler & baffle cover, ejected near GEO [Ortega et al.] 0.8 m 2 cooler cover, 2 m 2 baffle cover Only two objects we observed that we have any a priori information on Utilize as pseudo-calibration objects, but with caveats Area, Temperature, albedo, emissivity, etc., important to modeling interaction with SRB to determine motion Copyright C R 2009 A/m Boeing. All rights values reserved. ranging from to over 4 m 2 /kg

5 Broadband Array Spectrograph System (BASS) sensor suite

6 Spectrophotometry with BASS at AEOS Single aperture obtains mm range Liquid Helium cooled sensors & internal optics FOV of ~5 arc seconds AW ~ cm 2 sr Princeton CCD camera & filter collect 1.5 arc minute fields simultaneously with IR spectra Utilize a Lyr, a Boo, a Tau, a CMa, & b Gem as IR calibrators

7 On-sky system calibration using orbiting cal spheres

8 CalSphere properties Lincoln Cal Sphere 1 (Norad 1361) [3/23 & 3/25/09] 1.0 m 2 (projected area) aluminum sphere Emissivity (from references (IR Handbook, CRC): ~0.04 for microns Highly reflective; 57.5% (Hall et al.) CalSphere 4(A) (Norad 1520) [4/2/09] m 2 (projected area) white-painted sphere Emissivity ~95% for BASS wavelengths 1/10 area, 20x emissivity compared to LCS Coefficient of absorption ~55% for white paint Using these data allows us to estimate expected T color and emissivity Area projected for the calspheres

9 2 Observations of Lincoln Cal Sphere 1

10 Observation of CalSphere 4(A) Much lower temperature than the LCS 10% of the projected area of LCS, but much higher (~20x) emissivity

11 BASS IR & Visible observations of HAMR objects

12 BASS observed 12 different HAMR objects, from 1-4 times each Observations: September, October 2009, February 2010 Overlap with other groups observations, but no same objects Objects A & B are cooler & baffle covers, C-L unknown Collected about 40 nod pairs (~17 minutes) of IR spectral data per object per observation Fluxes change on timescales of ~seconds excluded nod pairs with flux < W/cm 2 in 8-13 micrometer band Time-averaged spectra to reduce noise

13 IR measurements yield characteristic sizes and temperatures Sizes ~1 - ~several square meters MSG-II Object A: 2 ± 1.5, B: 1 ± 0.7 Literature values are m 2 & 0.8 m 2 Temperatures ~ K Flux from an object correlated with projected area and emissivity Power law index is lower than similar relationship for LEO objects (0.9) [Skinner et al.]; reason not understood at this time

14 Objects T color, from IR Spectra, provide insight into physical parameters No apparent correlation between object size and temperature Objects exhibit low thermal mass when they exit shadow, they appear to rapidly come to thermal equilibrium

15 Striking visible CCD photometry light curves I I Same object (I) taken 2 nights apart 29 th : compare with ea projected ~19 m 2 ; 31 st : ~4.4 m 2 Different orientations of the object Complex, periodic light curves 29 th : main peak at 21.1 seconds period, with a secondary peak at 11.6 seconds period 31 st : not well sampled for good power spectrum

16 Visible light curves, collected simultaneously with IR spectra, probe reflected radiation B C Integration times from seconds Visible calibration using Landolt Standard field SA92 Optical Cross Section: OCS=(R object ) 2 * (Msun-Mobject) & a D A=4p*OCS/f f: phase angle scattering function for the object; in general unknown simple models for f do not allow recovery of albedo-area products that match known objects A or B, or from IR spectra Calculated characteristic sizes and/or albedos are too small. Research into this matter continues.

17 Comparison of visible Optical Cross Section and IR earea projected size estimation finds correlation between the two measurements Plot of earea projected v. optical cross section Have 8 visible light curves taken at same time as IR spectra OCS related to albedoarea by unknown phase angle scattering function, f OCS values are not the physical areas of the objects One point that lies above the curve may have a very low albedo

18 Simple thermal model allows parametric estimation of RSO temperatures Power absorbed = Power emitted: a i p r 2 F = e 4 p r 2 st 4 Assumes object in thermal equilibrium a i =absorption in visible, = 1-a D Plot T v. e, for various a D Lower temperature objects (~200 K) are constrained to have both a high emissivity and a high albedo For objects with higher temperatures (>300 K), a lower range of values of emissivity is required for the range of possible albedos; ε= ~0.2- ~0.5. assumption of often-used albedo=0.1 is not allowed for many of measured temperatures; some are constrained to have higher albedos

19 Conjecture/Summary/Conclusions Could many of the HAMR objects be thermal blankets? High Area-to-mass ratio C R A/m values for MSG-II rigid covers are ~0.035 m 2 /kg Other objects observed range up to 4 m 2 /kg Common on satellite exteriors; held on by velcro Thermal insulation; limit conductive paths to satellite Engineered thermal surface, 2 types typical: gold : low e, high a D, -> high Temperature black : high e, low a D, -> low Temperature Sewn together layers of kapton & scrim, somewhat rigid Conform to satellite surface simple to complex shapes Visible light curves show ~rigid body tumbling Sizes up to several square meters Typical for areas to be covered on satellites Observer bias against smaller objects (sensitivity limits) Low thermal mass of individual layers Thin, light layers of metal-coated film and insulators Outer layer comes to thermal equilibrium quickly after shadow exit Thermal blanket area-to-mass ratio: ~4 m 2 /kg Example: 1000 Å Al + 75 m Kapton + 10x 7.5 m Kapton + 50 m Kapton r Al = 4 g/cm 3, r Kapton =1.42 g/cm 3 -> 0.27 kg/m 2 -> 3.7 m 2 /kg Picture from: http: //science.ksc.nasa.gov/ payload/ missions/ cassini/ images/ captions/ KSC-97EC-0728.html BASS has observed 2 MSG-II covers plus ~10 unknown HAMR objects Fall 09, Spring 10 observing runs time-averaged thermal spectra Estimate T color, earea visible light curves OCS Rotational power spectrum Simple thermal model constrains e & a D Planned improvements Faster, more sensitive CCD camera Grism for low resolution visible spectra Need additional observations, especially with simultaneous visible & IR Coordinate campaigns with other groups

20 Selected References Based on data from the Maui Space Surveillance System, which is operated by Detachment 15 of the U.S. Air Force Research Laboratory's Directed Energy Directorate. This work is supported at The Aerospace Corporation by the Independent Research and Development Program. Schildknecht, et al., Properties of the High Area-to-mass Ratio Space Debris Population in GEO, AMOS Technical Conference., Wailea, Hawaii, Sept, Kelecy, Tom, et al., Solar Radiation Pressure Estimation and Analysis of a GEO Class of High Area-to-mass Ratio Debris Objects, AAS , AAS Astrodynamics Specialist Conference, Mackinac Island, MI, August Hackwell, J.A., et al., A low resolution array spectrograph for the 2.9 to 13.5 micron spectral region, Proc SPIE 1235 (1990). Skinner, et al., Time-Resolved Infrared Spectrophotometric Observations of IRIDIUM satellites and related Resident Space Objects, IAC-09-A6.1.17, International Astronomical Congress 60th meeting, October 2009, Daejeon, Republic of Korea. Ortega, J., et al., Mechanisms and pyros subsystem for the METEOSAT second generation, Space Mechanisms and Tribology, Proceedings of the 8th European Symposium, held 29 Sept. - 1 Oct., 1999 in Toulouse, France., 438, 1999., p.169 Africano, J.; Kervin, P.et al., Understanding Photometric Phase Angle Corrections, Proc. 4th European Conference on Space Debris (ESA SP-587) April 2005, ESA/ESOC, Darmstadt, Germany. Editor: D. Danesy., p. 141 Donabedian, M. & Gilmore, D., ed., Spacecraft Thermal Control Handbook: Cryogenics. Aerospace Press, El Segundo, CA., The Aerospace Corp. maintains a public website with information about BASS at: The authors would like to thank Mr. Brandon Kaneshiro for help with some of the data collections. Special thanks to Mr. Mark Bolden and Dr. Skip Williams for help with this effort. Additionally, and as always, we would like to thank the AEOS telescope operators for their help and support.