X-ray Calorimeter

1. X-ray Calorimeter Orbital Debris and End of Mission Plans Ivonne Rodriguez 2 – 6 April, 2012

2. Orbital Debris and EOMP Agenda • Orbital Debris Requirements Overview • Micrometeoroid Damage Assessment • Conclusions • Acronym List • Backup Material

3. Orbital Debris Requirements per NASA-STD-8719.14: Most Requirements Do not Apply to L2 Missions (See Backup charts for complete requirements)

4. Probability of Damage due to Micrometeoroid Environment: General Procedure • The number of impacts, h, is given by: • h = F x A x T, where: • F is the particle flux in impacts/m2/yr • A is the cross-sectional area of the component in m2 • T is the mission lifetime in years. • The probability of penetration is given by: • P = 1-e(-h) • The flux F is obtained from the Grün interplanetary meteoroid flux based on the minimum particle diameter (critical diameter) capable of penetrating the surface under study. • The critical diameter is computed from ballistic limit equations. For this study, the software BLA (Ballistic Limit Analysis) was used to obtain the critical diameter. • In the Grün model, the micrometeoroid (MM) flux is averaged for a year, and is assumed to strike normal to a flat surface in random orientation. • This analysis covers the metering structure, representative components inside the bus and detector. Analysis of external calorimeter structure and electronics boxes was covered on the IDL study.

5. Increased Damage to Metering Structure with Reduced Thickness • Metering Structure perforation • Probability of penetration by micrometeoroids: varies with facesheet thickness. • Smallest particle capable of penetrating the structure, worst case = 0.046 cm diam. • Failure is defined as penetration of the two facesheets. • Instrument bench perforation • Probability of penetration of both facesheets by micrometeoroids: 1.4% for 3 years, 2.3% for 5 years. • Smallest particle size capable of penetrating the panel = 0.088 cm • Calorimeter and electronic boxes reduce the exposed area. • Effect of MLI included.

6. Bus: Propellant Tank and Battery • Propulsion tank and battery box are selected as representative of components located inside the bus. Radials and other internal structure limit the damage, so for the purposes of this analysis only the flux coming from one deck panel and one closeout panel is taken into consideration.

7. Calorimeter Damage from The FMA Side • The probability of damage to the filter from particles coming from the Flight Mirror Assembly (FMA) side is a separate case from the hardware assessment for the following reasons: • While in the hardware assessment a failure is defined as penetration of a wall or surface, in this case a particle impact to the filter not always produce permanent damage. Depending on the size of the particle, the result may vary from a temporary production of bright pixels to penetration of the filter. • It does not involve a direct hit by the particle, but is the result of scattering through the FMA. • Note that the results depend on the specific FMA configuration. • The particle reaching the filter might be ejecta produced by the impact with the mirror foil (the MM vaporizes), or the scattered MM after impacting the mirror foil. • The analysis is limited to the particles that reach the detector once it has entered the FMA, which depends on instrument geometry (next slide). Not all particles striking the FMA may reach the detector. • Computation of the mirror effective area is based on Carpenter, et al, Effects of Micrometeoroid and Space Debris Impacts in Grazing Incidence Telescopes, from Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray, Proc. of SPIE Vol 6266, 62663K (2006).

8. Analysis Assumptions and Equations Mirror effective area based on the probability of an entering particle to reach the detector or filter. • R1 = front radius of the nth mirror shell’s parabolic mirror. • R2 = radius at the interface between the two hyperbolic and parabolic mirrors. • An = on-axis component of the mirror area. • A = on-axis area of the nest of n mirrors. • a = Minimum scatter angle required to hit the detector or filter. • P(0<θ< a) = probability that a particle is scattered by an angle which is less than some upper limit a. • Phit = probability that a particle will strike the detector or filter. • Anp = on-axis “effective” area for a single mirror shell. • Ap = total on-axis “effective” area for the telescope. • Assumed values: • R2 : Assumed 1mm less than R1. • a: Assumed 0.7⁰ (Swift, XMM) Once the total effective area is obtained, the analysis proceeds as in the hardware section (P=FxAxT).

9. Probability of Particle Reaching the Detector Values for FMA: Effective area Ap: Probability of filter impact by particle size, for 3 yrs and 5 yrs: • As expected, the probability decreases significantly with increased size. • An impact by a particle of about 1 mm is capable of penetrating a 3-mm thick filter. However, the probability for that scenario is very low.

10. Conclusions and Comments • No issues in terms of orbital debris and end of mission plans. Most requirements do not apply. • Content of X-Ray Gratings presentation and conclusions apply to this configuration. Disposal recommendations: give a soft “push” at EOM to help the spacecraft to drift away from L2 and make it easier to prove that the spacecraft will not come back to Earth vicinity. • The bus structure provides adequate protection to internal components. • The probability of at least one particle reaching the detector is 12% for 3 years and 19% for 5 years. Minimum particle diameter, and most likely size to strike the filter, is 1 μm, which is not expected to produce permanent damage to the surface.

11. Acronym List • BLA – Balistic Limit Analysis • LEO – Low Earth Orbit • EOM – End of Mission

12. Backup Material

13. The Grün MM Flux Model • Gives the flux of sporadic and stream MM averaged for a year. Assumes all impacts are normal to the surface. • Omnidirectional; assumes maximum flux in every direction (Conservative). • Assumes the surface is a flat plate in random direction. In this case, boxes are represented as 5 flat surfaces (one side is attached to the instrument panel) and cylinders as 2D projections (cross-sectional area), excluding the top (protected by radiator) and bottom. • Easy to codify in Excel or other math software. • Less detailed than the most recent MSFC’s Meteoroid Environment Model 1c (MEM R1c), which is directional. • See NASA TM-4527, Section VII for more details on the micrometeoroid environment.

14. Data Tables and Results, 3 years FMA and Detector

15. Data Tables and Results, 5 years FMA and Detector

16. Requirements

17. 4.3 Assessment of Debris Released During Normal Operations

18. 4.4 Assessment of Debris Generated by Explosions and Intentional Breakups

19. 4.4 Assessment of Debris Generated by Explosions and Intentional Breakups, cont.

20. 4.5 Assessment of Debris Generated by On-orbit Collisions

21. 4.6 Postmission Disposal of Space Structures

22. 4.6 Postmission Disposal of Space Structures, cont.

23. 4.7 Survival of Debris From the Postmission Disposal Earth Atmospheric Reentry Option

24. 4.8 Additional Assessment Requirements for Tether Missions