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EVA (Extravehicular Activity) are complicated, time-consuming, resource-consuming, and potentially dangerous activities. They have to be properly planned and prepared and deconflicted from other events.It would take several pages to cover all of the complications that have to be accounted for before sending someone outside. I’m not going to cover all of that. Below are just a subset of factors.The normal process for planning a new EVA starts about eight weeks prior to the EVA. For a specific set of well-defined contingency EVA, that schedule can be compressed to less than two weeks. First, we have to determine exactly what tasks we need the crew to perform, how they will perform those tasks, what tools they will need, what potential safing activities we need to perform, what the translational path will be for the crew, and whether or not new procedures will have to be generated. Often this includes having astronauts in Houston rehearse the planned activity in the pool, to identify risks and complexities.ISS ReconfigurationThe ISS, itself, will need some level of reconfiguration. We will have to incorporate the necessary telemetry packets to ensure all of the required EVA-related telemetry is downlinked to the ground. This can mean taking telemetry away from some other users, which means replanning their work. As EVA is a critical operation, we will have to reserve extra time from the TDRS satellite network, to fill in the standard holes between our nominal satellites. It is critical that we have a good command path to the vehicle during the EVA, so, to protect against failures of the US S-band system, we must also perform pre-EVA Command and Telemetry Checkout to ensure we can send commands via Russian assets.The MSS (Mobile Servicing System) will have to be checked out and the robotic work station setup and checked out.Certain radios that may be along their translation path will have to be deactivated, both to prevent interference and to avoid radiating the crew.If the crew will be working with any electrically powered equipment, outside the ISS, that equipment will have to be safed to ensure there is no risk of electrocution.Environmental FactorsA thermal analysis of the worksite needs to be done to understand the environment the crewmembers will experience. The length of the day/night cycle for the ISS varies, depending on the beta angle. It is more efficient to schedule EVA for times where the day periods are longer.EVA crewmembers are exposed to more radiation that they would be inside the spacecraft. As radiation workers, we have to follow the following rules from U.S. Federal Register, Vol. 52, No. 17:There should be no occupational exposure to radiation without the expectation of overall benefit from the activity causing the exposureNo exposure is acceptable without first examining the justifications behind itSustained effort must be made to ensure that doses are maintained as low as reasonably achievable (ALARA).Similarly, we need to protect the crew, as much as possible, from risk of micro-meteor/orbital debris. We do not schedule EVA during predicted meteor showers and the TOPO flight controllers will perform analyses to ensure there is no known orbital debris in the vicinity during the EVA.What that means is that we have to plan EVA carefully. We need to minimize the crew’s exposure, so we will work to schedule the activity to avoid predicted radiation events and passages through the South Atlantic Anomaly (SAA)Suit PreparationThere is no maintenance team onboard to maintain the suits and tools. The crew have to perform that work and have to inspect their suits and tools to make sure they are in a fully-functional state.For example, the batteries of the EMU (suit) have to be charged prior to the EVA. The batteries are kept discharged during periods of non-use. This minimizes the stress on the electrode-separator system and extends the lifetime. The SAFER (Simplified Aid for EVA Rescue) hardware has to be checked out to ensure it is functional prior to the EVA. This has to have been performed within two weeks of the EVA.PrebreatheThe atmosphere of the suit is considerably below normal atmospheric pressure. If the pressure of inert gases (nitrogen) in the blood is greater than the ambient pressure, bubbles of nitrogen can come out of solution and spread through the blood and tissues of the body, causing DCS (Decompression Sickness). Symptoms of DCS can range from joint pain to convulsive seizures.The purpose of the prebreathe is for the astronaut/cosmonaut to spend some time breathing pure oxygen, prior to the EVA (spacewalk), in order to remove any nitrogen in the blood stream (the ISS cabin atmosphere is about 78% nitrogen, just like the atmosphere on Earth).There are three options for performing prebreathes:In Suit - Prior to the EVA, the crew member breathes 100% oxygen in the spacesuit for about four hours.Campout - the EVA crew members sleep in the partially depressed (down to 10.2 psi) airlock and then for the final hour wear an oxygen mask for an hour.Exercise - the crew member exercises while wearing an oxygen mask and then does a forty minute in suit prebreathe.Other work impactsAn EVA requires three crew-members – two EVA crew (the ones that go outside) and an IVA crew (someone who stays inside but assists where needed such as in suit donning/doffing, airlock preparation, and robotic arm usage. So, whenever an EVA is scheduled, other planned work has to be rescheduled. This impacts a lot of people, such as payload investigators on the ground.

If you’re asking if astronauts can just ask to go outside, what it takes to get that approved? It doesn’t work that way. EVA (spacewalks) are mission critical activities. They are only done to fulfill a mission need. Either something needs to get installed/removed or it needs to get repaired. Those are the only reasons to do EVA. It is too expensive, resource consuming, and dangerous to do for reasons other than mission need.All of the crew are trained to perform EVA. If one is needed, the equipment is deemed operational, and the flight surgeons agree that the latest data shows the crew are healthy enough to do it, it is scheduled, planned, and executed.It would take several pages to cover all of the complications that have to be accounted for before sending someone outside. I’m not going to cover all of that. Below are just a subset of factors.The normal process for planning a new EVA starts about eight weeks prior to the EVA. For a specific set of well-defined contingency EVA, that schedule can be compressed to less than two weeks. First, we have to determine exactly what tasks we need the crew to perform, how they will perform those tasks, what tools they will need, what potential safing activities we need to perform, what the translational path will be for the crew, and whether or not new procedures will have to be generated. Often this includes having astronauts in Houston rehearse the planned activity in the pool, to identify risks and complexities.ISS ReconfigurationThe ISS, itself, will need some level of reconfiguration. We will have to incorporate the necessary telemetry packets to ensure all of the required EVA-related telemetry is downlinked to the ground. This can mean taking telemetry away from some other users, which means replanning their work. As EVA is a critical operation, we will have to reserve extra time from the TDRS satellite network, to fill in the standard holes between our nominal satellites. It is critical that we have a good command path to the vehicle during the EVA, so, to protect against failures of the US S-band system, we must also perform pre-EVA Command and Telemetry Checkout to ensure we can send commands via Russian assets.The MSS (Mobile Servicing System) will have to be checked out and the robotic work station set up and checked out.Certain radios that may be along their translation path will have to be deactivated, both to prevent interference and to avoid radiating the crew.If the crew will be working with any electrically powered equipment, outside the ISS, that equipment will have to be safed to ensure there is no risk of electrocution.Environmental FactorsA thermal analysis of the worksite needs to be done to understand the environment the crewmembers will experience. The length of the day/night cycle for the ISS varies, depending on the beta angle. It is more efficient to schedule EVA for times where the day periods are longer.EVA crewmembers are exposed to more radiation than they would be inside the spacecraft. As radiation workers, we have to follow the following rules from U.S. Federal Register, Vol. 52, No. 17:There should be no occupational exposure to radiation without the expectation of overall benefit from the activity causing the exposureNo exposure is acceptable without first examining the justifications behind itSustained effort must be made to ensure that doses are maintained as low as reasonably achievable (ALARA).Similarly, we need to protect the crew, as much as possible, from risk of micro-meteor/orbital debris. We do not schedule EVA during predicted meteor showers and the TOPO flight controllers will perform analyses to ensure there is no known orbital debris in the vicinity during the EVA.What that means is that we have to plan EVA carefully. We need to minimize the crew’s exposure, so we will work to schedule the activity to avoid predicted radiation events and passages through the South Atlantic Anomaly (SAA)Suit PreparationThere is no maintenance team onboard to maintain the suits and tools. The crew have to perform that work and have to inspect their suits and tools to make sure they are in a fully-functional state.For example, the batteries of the EMU (suit) have to be charged prior to the EVA. The batteries are kept discharged during periods of non-use. This minimizes the stress on the electrode-separator system and extends the lifetime. The SAFER (Simplified Aid for EVA Rescue) hardware has to be checked out to ensure it is functional prior to the EVA. This has to have been performed within two weeks of the EVA.PrebreatheThe atmosphere of the suit is considerably below normal atmospheric pressure. If the pressure of inert gases (nitrogen) in the blood is greater than the ambient pressure, bubbles of nitrogen can come out of solution and spread through the blood and tissues of the body, causing DCS (Decompression Sickness). Symptoms of DCS can range from joint pain to convulsive seizures.The purpose of the prebreathe is for the astronaut/cosmonaut to spend some time breathing pure oxygen, prior to the EVA (spacewalk), in order to remove any nitrogen in the blood stream (the ISS cabin atmosphere is about 78% nitrogen, just like the atmosphere on Earth).There are three options for performing prebreathes:In Suit - Prior to the EVA, the crew member breathes 100% oxygen in the spacesuit for about four hours.Campout - the EVA crew members sleep in the partially depressed (down to 10.2 psi) airlock and then for the final hour wear an oxygen mask for an hour.Exercise - the crew member exercises while wearing an oxygen mask and then does a forty minute in suit prebreathe.Other work impactsAn EVA requires three crew-members – two EVA crew (the ones that go outside) and an IVA crew (someone who stays inside but assists where needed such as in suit donning/doffing, airlock preparation, and robotic arm usage. So, whenever an EVA is scheduled, other planned work has to be rescheduled. This impacts a lot of people, such as payload investigators on the ground.

Antiperspirants are classified as drugs whereas deodorants are cosmetics.Antiperspirants typically contain Aluminium or Aluminium salts which block your pores and prevent/ reduce your sweat.The US FDA Monograph is highly relevant here. It collates all studies in one place for ease of public access.Here are some excerpts-Federal Register/ Vol. 68, No. 110 / Monday, June 9, 2003 / Rules and Regulations, Page 34283In one of the inhalation studies (Ref. 34), the life-span of the male hamsters exposed to the aluminum chlorhydrate aerosol was shorter (583 days) than that of the controls (661 days).Male hamsters exposed to aluminum chlorhydrate coated with a high concentration of isopropyl myristate, an emollient frequently used to increase the retention on the skin of the aluminum salts used in antiperspirant products, had a life-span (646 days) comparable to the controls (661 days).Federal Register/ Vol. 68, No. 110 / Monday, June 9, 2003 / Rules and Regulations, Page 34284The agency finds the literature shows the issue of aluminum toxicity and Alzheimer’s disease remains controversial and is not resolved.I hope you’ve got a clear idea now with respect to Aluminium & Aluminium Salts. You can check out a list ingredients to avoid in your Deodorant here[1].I personally use Lineal Deodorant because its free from chemicals and works well for me.Footnotes[1] 5 Dangerous Chemicals to Avoid in Your Deodorant