1. In our previous work,5a high-temperature shock effect on micron-sized particles has been investigated. Subsequently, the effect of heating on silica aerogel and dust particles was studied in Ref. 6 since the sample collector is exposed to significant aerodynamic heating during dust sampling. Based on our previous investigation, it was found that using a silica aerogel sample collector, the sampling time as well as the targeted sample size should be limited. Meanwhile, from the point of view of sample analysis, it is preferable to increase the sampling time in order to capture sample particles larger than 2 µm. Thus, in the present study, possible Martian dust sample size and number within a specified sampling time have first been investigated for the MASC mission. A Martian dust size distribution model of Tomasko7has been applied and the size distribution has been integrated with a 0.5 µm interval. In Fig. 3, the Martian dust distributions at altitudes between 25 and 40 km for an average Martian weather condition are presented. It can be seen that the main particle size is 1-2 µm, and the distribution gradually decreases with increasing the particle size. Based on the proposed flight trajectory in Ref. 4, the descent sampling altitude can be between 30 and 35 km. Thus, for altitudes between 25 and 45 km, dust sampling rates for particle size between 1 and 10 µm in an average Martian weather condition were examined and are listed in Table 1. The relative particle speed to the collector surface and the collector surface area are set to 4.0 km/s and 20.0 cm2, respectively. It was found that in order to capture at least 10 dust samples, the necessary sampling time is 0.01 s for
2. II. Experimental Configurations
3. Aerogel heating tests are carried out in the 750 kW arcjet wind tunnel (AWT) at JAXA. In the tests, aerogel laboratory models are exposed to a high-enthalpy air flow for a short period of time under several heating conditions. The laboratory model of aerogel sample collectors is produced by trimming aerogel test pieces to 13×13 mm2or 8×8 mm2cross section, and the model is put in a 1-mm thick acrylic case so as to utilize the heated models for the following light gas gun (LGG) sample capture simulations. Silica aerogel used in this study has originally been developed in the cosmic ray physics and neutrino astronomy laboratory at Chiba University, and 0.02, 0.03, and 0.04 g/cm3low-density SAs are used in this and the following tests. Low-density carbon aerogel has also been developed by Hatakeyama et al., and several CA test pieces with the density between 0.025 and 0.15 g/cm3are compared to investigate the density dependence in this work. CASA sample collector laboratory models have been produced by cutting and shaping both CA and SA manually. The SA layer has been trimmed by using elaborate surgical knives, and the thin CA layer has been trimmed to be 0.75-3.5 mm thickness by using sandpapers. In the arcjet tests, six aerogel laboratory models can be put in a stainless container without any adhesive applications, and the assembly is then flush-mounted on a water-cooled wedge holder with its surface covered by a 1 mm-thick copper plate (see Fig. 5).
4. In order to characterize the arcjet test flow at a position where the aerogel laboratory models are heated, local heat flux values have been measured by using slag calorimeters prior to aerogel heating tests. Three slag calorimeters are put on a copper container in a straight line for the purpose of getting the spatial variation of heat flux values along the centerline of the wedge holder. At the reverse side of the slag, a type-K thermocouple is embedded to measure the slag temperature. With -10◦of the angle between the wedge holder surface and the freestream direction, the heat flux values were found to be approximately 103, 78.8, and 53.2 kW/m2attheupstream, center, anddownstreamsideonthewedgeholder, respectively. Since the heat flux value in the MASC sampling environments is estimated to be approximately 60-90 kW/m2(see Refs. 8 and 9), the wedge angle of -10◦is selected in this study (see Fig. 6). The testing exposure time for the experiment is set to either 10 or 20 s. The effect of aerodynamic heating on CASA surfaces is examined by comparing the weight and aerogel surface condition between before and after heating. The laboratory models are inspected by using a digital microscope (VHX-1000, Keyence) and a SEM (JSM-6010, JEOL) at JAXA. B. Light gas gun sample capture simulations