X-Ray Calorimeter ~ Concept Presentation ~

1. X-Ray Calorimeter ~ Concept Presentation ~ Micrometeoroid Damage Assessment Ivonne Rodriguez Feb 17, 2011

2. Objective • The objective of this analysis is to provide a preliminary probability of damage to major instrument components due to micrometeoroid (MM) impacts at L2. • Results are used in reliability analysis. • They are also useful to identify surfaces that may need additional shielding, if any. • This analysis is preliminary, and based on empirical equations and environmental models. It can be re-evaluated and refined as the design progresses.

3. 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.

4. 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.

5. Analysis Results, Hardware Scenarios: - 3 yrs nominal mission; 5 yrs mission - With and without MLI with Kevlar P = Probability of Penetration * Maximum size in Athena concept.

6. 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 FMA is not part of this study. For the purpose of this calculation, the AXSIO FMA is assumed, although it is known that its focal length is longer. It is recommended to update the results when the spacecraft configuration is known and details of the current FMA configuration become available. • 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. • It is important to differentiate between the probability of a particle to enter the FMA, which depends on particle flux (slide #8) and the probability of the particle to reach the detector once it has entered the FMA, which depends on instrument geometry (next slide). • 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).

7. 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. • Unknown values: • R2. Assumed R2 is little less than R1 (assumed 1mm less). • amax. Assumed 1.2⁰ because it is the highest value that results in a positive P(0<θ< a) Once the total effective area is obtained, the analysis proceeds as in the hardware section (P=FxAxT).

8. Probability of Particle Entering the FMA Values from AXSIO FMA: Effective area Ap: Probability of filter impact by particle size, for 3 yrs and 5 yrs: • Note that the maximum probability of impact is for particles of the order of 1 μm, which are not likely to produce permanent damage. • 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.

9. Conclusions and Future Work • The micrometeoroid environment at L2 (interplanetary space) represents low risk for the X-Ray Calorimeter’s dewar, electronic boxes, and harness. The highest probability of penetration of the components under study was less than 1%, assuming worst case. • Electronics boxes can be located in the dewar side of the instrument panel without significant probability of damage, even assuming a minimum wall thickness of 1.27 mm. • Since the location of the electronics boxes and harness is not firmly determined yet, the direction of the MM flux is not taken into consideration (Assumed omnidirectional flux). • This is conservative, because once the location of the components is determined, potential shielding effects can be taken into consideration (reducing the exposed area). • The use of a MLI with a Kevlar layer covering the X-Ray Calorimeter dewar and electronics boxes slightly reduces the probability of penetration by MM. • The Kevlar is a good addition to the MLI as additional protection, but is not necessary, as the probability of damage without it is low (interplanetary MM particle flux and size below those of the orbital debris environment at LEO). • The probability of a particle striking the filter from the inside (through the FMA) is highly dependant on the FMA configuration (R1, R2, spacing), more than on the calorimeter dewar itself. The results shown here are representative, as a first approximation, and it is recommended to update them with current FMA values when available. • Future work: Run a more detailed analysis when the design matures.

10. Additional charts

11. Data and Results Table (1 of 3) Electronics Boxes, Dewar, and Filter Wheel Cover: no Kevlar\MLI • The sizes of the electronic boxes are taken from the largest and smallest boxes in the Athena configuration. The probability is low enough to allow margin for larger dimensions. • The Dewar and the Filter Wheel Cover are assumed to have a cylindrical shape, and the cross sectional area is used for computations.

12. Data and Results Table (2 of 3) Electronics Boxes, Dewar, and Filter Wheel Cover, with Kevlar\MLI • For the scenario where electronic boxes are located inside the spacecraft structure, the values are not recalculated (not affected by external MLI). • Recalculated values are indicated by a blue cell. • See other notes in previous chart.

13. Data Results Table (3 of 3) • Assumed a copper wire with a diameter of 1 mm and a length of 1.33 m (approximated circumference of the mid-section cylindrical wall, to account for routing) and a 0.2 mm insulation layer. • The resulting probability of a single wire can be multiplied by the number of wires we want to assume for now. This is conservative, because it does not account for shielding due to location of other components or due to bundling. Harness, no Kevlar\MLI: Harness, with Kevlar\MLI: