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In 2030, the International Space Station will be deorbited: driven into a remote area of the Pacific Ocean.

I'm an aerospace engineer who has helped build a range of hardware and experiments for the ISS. As a member of the spaceflight community for over 30 years and a 17-year member of the NASA community, it will be hard for me to see the ISS come to an end.
Astronauts performing research inside the space station and payload experiments attached to the station's exterior have generated many publications in peer-reviewed science journals. Some of them have advanced our understanding of thunderstorms, led to improvements in the crystallization processes of key cancer-fighting drugs, detailed how to grow artificial retinas in space, explored the processing of ultrapure optical fibers and explained how to sequence DNA in orbit.

In total, more than 4,000 experiments have been conducted aboard the ISS, resulting in more than 4,400 research publications dedicated to advancing and improving life on Earth and helping forge a path for future space exploration activities.

The ISS has proven the value of conducting research in the unique environment of spaceflight—which has very low gravity, a vacuum, extreme temperature cycles and radiation—to advance scientists' understanding of a wide range of important physical, chemical and biological processes.

Keeping a presence in orbit
But in the wake of the station's retirement, NASA and its international partners are not abandoning their outpost in low-Earth orbit. Instead, they are looking for alternatives to continue to take advantage of low Earth orbit's promise as a unique research laboratory and to extend the continuous, 25-year human presence some 250 miles (402 kilometers) above Earth's surface.

In December 2021, NASA announced three awards to help develop privately owned, commercially operated space stations in low-Earth orbit.

For years, NASA has successfully sent supplies to the International Space Station using commercial partners, and the agency recently began similar business arrangements with SpaceX and Boeing for transporting crew aboard the Dragon and Starliner spacecraft, respectively.

While these stations are being built, Chinese astronauts will continue to live and work aboard their Tiangong space station, a three-person, permanently crewed facility orbiting approximately 250 miles (402 km) above Earth's surface. Consequently, if the ISS's occupied streak comes to an end, China and Tiangong will take over as the longest continually inhabited space station in operation: It's been occupied for approximately four years and counting.

It will be several years before any of these new commercial space stations circle Earth at around 17,500 miles per hour (28,000 kilometers per hour) and several years before the ISS is deorbited in 2030.

So while you have a chance, take a look up and enjoy the view. On most nights when the ISS flies over, it is simply magnificent: a brilliant blue-white point of light, usually the brightest object in the sky, silently executing a graceful arc across the sky.

Our ancestors could hardly have imagined that one day, one of the brightest objects in the night sky would have been conceived by the human mind and built by human hands.

For a four-person Mars mission, the food tonnage would be between 6.6 and 15 tons, depending on the total mission duration and whether resupply missions or local food production are used. The total mass includes the food itself plus the necessary packaging. Key factors influencing food tonnage Mission duration 

A Mars mission is typically estimated to be a round trip of 2 to 3 years, with a stay on the Martian surface. The total mass of food required is a direct product of the mission length. 

Average daily mass:
A standard estimate for space food is about 1.83 kg (4 lbs) per astronaut per day.Total food mass calculation: Assuming a 2.5-year (912.5-day) mission, the total food tonnage for four astronauts would be calculated as follows:
1.83 kg/person/day * 912.5 days * 4 astronauts =6,680 kg
This equals about 6.7 metric tons.

Mission architecture 
The overall mission plan significantly affects the food tonnage that must be launched from Earth. 

All prepackaged:
If all food is launched from Earth, the tonnage would be at the high end of the estimate, especially if extra supplies are included for safety margins or emergencies. Some proposals suggest sending supply caches to Mars ahead of the crew.

Partial local production:
Integrating local food production, such as growing crops in a Martian habitat, could dramatically reduce the amount of food that needs to be carried. A diet supplemented with fresh vegetables and other produce could significantly lower the initial launch mass. 

Food type 
The composition of the food is a critical variable. Freeze-dried vs. whole food: Freeze-dried or dehydrated food contains much less water, making it far lighter to transport than whole food.Packaging: Packaging, while individually light, adds up over the course of a multi-year mission. Innovations in lighter, more efficient packaging could contribute to reducing overall tonnage. Contingency supplies Mission planners must also account for potential issues and emergencies. 

Buffer stock: A contingency supply of food is often included to cover mission extensions or unforeseen problems, adding significant mass to the total payload. For a 4-person, 900-day mission, a 500-day contingency supply could add over 10 tons of mass. 

Example calculation 
Here is a breakdown of a potential scenario for a four-person, 2.5-year (913-day) Mars mission. Daily food intake per person: 1.83 kg

Total crew-days:4 people * 913 days=3,652 person-days
Total food mass: 3,652 person-days * 1.83 kg/person/day=6,698 kg
Base food tonnage: Approximately 6.7 metric ton

Perishable food items are foods that will spoil, decay, or become unsafe to eat if not kept refrigerated or frozen, including meats, poultry, seafood, dairy products, eggs, cooked leftovers, and most fresh fruits and vegetables, especially those that are cut, chopped, or lack a hard outer skin.
Meat, Poultry, and Fish
Raw meats: such as ground beef, steaks, lamb, and pork.
Poultry, like fresh chicken, turkey, and duck.
Fish and seafood, including fresh fish, shrimp, lobster, and all types of shellfish.
Deli meats, which are processed and sliced.
Dairy and Eggs
Milk, cream, and yogurt.
Cheese, including soft and hard varieties.
Butter .
Eggs .
Fruits and Vegetables
Most fresh fruits and vegetables are perishable, particularly those without a hard skin like berries, tomatoes, and lettuce.
Cut or chopped produce, as this increases the rate of decay.
Cooked Foods and Leftovers
Any cooked leftovers, such as stews, cooked rice, and prepared meals.
Prepared salads: and other dishes containing perishable ingredients.
Other Perishables
Drinks with live bacteria, like some juices.
Sauces and dips: (like hummus, pesto, and sour cream), once opened.
Some baked goods, especially those with dairy or cream.

Non-perishable food items are shelf-stable and do not require refrigeration, including canned goods (fruits, vegetables, meats, soups, beans), dried goods (rice, pasta, oats, dried fruit, nuts, seeds, jerky, dried beans), shelf-stable milk and juices, and pantry staples like peanut butter, honey, cooking oil, sugar, and crackers.
Canned & Pouched Foods
Proteins: Tuna, salmon, chicken, and beans.
Vegetables: Corn, green beans, carrots, and other vegetables.
Fruits: Peaches, pineapple, applesauce, and other fruits.
Soups & Stews: Meat-based, vegetable-based, and other ready-to-eat options.
Dried & Grains
Grains: Rice, oats, pasta, and couscous.
Legumes: Dried beans, lentils, and peas.
Snacks: Nuts, seeds, dried fruits (raisins, apricots), trail mix, jerky, and granola bars.
Pantry Staples
Spreads: Peanut butter, jelly, and other nut/seed butters.
Sweeteners & Sauces: Honey, sugar, syrup, and jarred pasta sauces.
Oils: Vegetable oil and other cooking oils.
Baking Ingredients: Pancake mix and powdered milk.
Beverages: Shelf-stable powdered milk, bottled water, and juice boxes.
Other Shelf-Stable Items Crackers and melba toast, Ready-to-eat meals (like MREs), and Hard candies

The Orion capsule's mass varies, with a fully loaded mass of over 20 tonnes (44,000 lbs) for Artemis V, including a 13,500 kg European Service Module (ESM) and 8,600 kg of propellant. After its separation from the SLS rocket, Orion is expected to have a mass of approximately 26,375 kg.

Orion Spacecraft - Key Mass Specifications
Total Orion Launch Mass:
Over 20 tonnes (44,000 lbs)
Mass After SLS Separation (example):
Approximately 26,375 kg (58,147 lbs)
Crew Module Launch Weight (example):
22,900 lbs
Service Module Launch Weight (example):
34,085 lbs
Total Mass on Earth with Fuel (example):
10,000 kg for Lunar View refuelling module
Breakdown by Component (Example - Artemis V):
European Service Module (ESM):
Total launch mass: 13,500 kg
Propellant: 8,600 kg
Potable water: 240 kg
Oxygen: 90 kg
Nitrogen: 30 kg
Factors Influencing Mass
Mission Profile:
Mass specifications change between missions (e.g., Artemis I vs. Artemis II) due to varying propellant loads.
Payload:
Any additional cargo or equipment carried by the capsule will contribute to its overall mass.
Mission Duration:
A longer duration in space requires more supplies, increasing the mass of the service module and, consequently, the overall Orion spacecraft

he Artemis program's Orion capsule has a life support system (ECLSS) that is primarily limited by the amount of onboard consumables it can carry. The maximum endurance for a four-person crew is 21 days in a standalone mission. This limitation is tied to the design of the capsule itself, though its endurance can be significantly extended by docking with other spacecraft.
Standalone mission limitations
Duration: The Orion capsule is designed to support a crew of four for up to 21 days for missions that do not dock with another habitat.
Consumables: The 21-day limit is due to the fixed amount of food, water, oxygen, and nitrogen stored within the capsule.
Carbon dioxide and humidity: The system uses a regenerable carbon dioxide and humidity removal system, which is an advancement over the Apollo-era technology. However, the efficiency of this system is critical, and a design flaw identified in 2023 with the Atmosphere Revitalization System circuitry had to be addressed to prevent potential high levels of carbon dioxide.
Waste management: Storage capacity for human waste is another constraint on the total mission duration.
Docked mission capabilities
While a standalone Orion can only support its crew for a few weeks, its life support capabilities can be extended when it is connected to a larger habitat or module.
Lunar Gateway: When docked to a future habitat like the Lunar Gateway, Orion can support a crew for up to six months while its own systems are in a quiescent, or standby, mode. The Gateway will provide the additional consumables and robust life support needed for longer lunar missions.
Potential for Mars missions: Orion's subsystems were designed with flexibility in mind and could theoretically be integrated into a larger transport system for a future mission to Mars, potentially lasting up to 1,000 days. In such a scenario, the primary life support would be handled by other modules, and Orion would serve as the crew transport and safe-haven.
Emergency and redundancy
The life support system is built with redundancy and backup capabilities to ensure crew safety during a critical event.
Spacesuits: In the event of a cabin depressurization, the crew can survive for several days in their pressurized Crew Survival System (CSS) spacesuits, allowing for a return to Earth.
System redundancy: The ECLSS is designed with redundancy to keep critical systems functioning if a single component fails

Assuming a launch profile based on SpaceX's Starship system, which uses Raptor engines and a methane CH4 propellant, a 40-tonne payload for a Mars transfer mission requires approximately 676 metric tonnes (mt) of propellant for the transit portion alone. However, the total fuel needed is significantly higher when considering all mission phases. The complex mission requires multiple propulsive burns and in-orbit refueling. A simplified estimate for a mission to transport a 40-tonne payload to Mars would involve the following phases: Launch from Earth to low-Earth orbit (LEO).On-orbit refueling in LEO.Trans-Mars Injection (TMI) burn to escape Earth's orbit.Entry, descent, and landing (EDL) at Mars.

To determine the methane CH4 and liquid oxygen LOX fuel requirement for a 40 metric ton (mt) ship landing on Mars, several factors must be calculated. The key steps are determining the change in velocity (delta-v) needed for the landing, applying the Tsiolkovsky rocket equation, and calculating the specific masses of methane and oxygen based on the Raptor engine's characteristics. 

Assumptions for this calculation Initial ship mass: 40 mt (40,000 kg).
This is the dry mass of the ship plus any payload, but before the addition of landing propellant.Propulsive landing only: The calculation assumes no aerodynamic braking or very minimal atmospheric drag assistance. However, SpaceX's actual Starship landing profile uses substantial aerodynamic braking, which significantly reduces the propellant needed.

Raptor engine specific impulse (Isp):
An average vacuum Isp of 380 seconds is assumed for the Raptor Vacuum engines, which is more representative of a landing scenario than the sea-level variants.

Raptor engine mix ratio:
The Raptor engine uses liquid methane and liquid oxygen, typically at a mass ratio of 1:3.6 (methane to oxygen)

For a fully propulsive landing without using atmospheric drag, a Mars landing requires a delta-v Delta V of approximately 4.5 to 6 km/s. If the ship uses supersonic retro-propulsion with atmospheric braking, the required propulsive delta-v is much lower, possibly as low as 75 m/s, although this is very dependent on the entry velocity. 

The total propellant mass is approximately 5.5 mt. We use the Raptor engine's mix ratio of 1:3.6 for methane CH4 to oxygen LOX by mass. 

Based on the assumptions, the approximate fuel requirements for a 40 mt ship using two Raptor engines for a propulsive Mars landing would be: 
Total propellant: 5.5 mt
Methane CH4: 1.2 mt
Liquid oxygen LOX: 4.3 mt

For a 40-metric-ton (mt) ship returning to Earth from Mars using two Raptor engines, the estimated propellant requirement is approximately 194.2 mt of methalox (liquid methane and liquid oxygen). This calculation assumes a propellant depot is available in Mars orbit and that the engines are vacuum-optimized Raptor variants.
This is an estimate based on the Tsiolkovsky rocket equation and can be affected by factors such as mission profile and gravity losses.

This estimate relies on three key parameters: 

Mass of the spacecraft: 40 mt.
This is the "dry mass" m_{f} in the rocket equation, representing the ship, cargo, and all components except for the propellant.

Specific impulse Isp of the engines:
The vacuum-optimized Raptor engines (RVac) have a specific impulse of approximately 380 seconds.

Delta-v required for the maneuver:
The delta-v needed to launch from the Martian surface to a trans-Earth injection (TEI) trajectory is approximately 4.27 km/s. 

Adjusting for a 20% methane/80% oxygen mix Raptor engines use a methalox propellant mix, which consists of approximately 20% methane (fuel) and 80% liquid oxygen (oxidizer) by mass. The total propellant mass is the combination of the fuel and oxidizer. 
Total propellant mass m_{p}: 86 mt
Fuel (methane) mass: 0.20 * 86 mt = 17.2 mt
Oxidizer (liquid oxygen) mass: 0.80 * 86 mt = 68.8 mt 
Assumptions and other considerations The calculated fuel requirement is a theoretical minimum based on the ideal rocket equation. Several factors can increase the actual fuel mass needed: 

Atmospheric drag on Mars:
While the Martian atmosphere is thin, it can cause some drag during ascent, requiring a small amount of extra propellant.

Gravity losses:
The effect of gravity pulling against the rocket during its ascent and burn means the rocket must use additional propellant to counteract this force. The 4.27 km/s figure already accounts for typical gravity losses, but actual losses can vary.

Engine inefficiencies:
The Isp value of 380s is an ideal figure, and the engine may not achieve this perfectly throughout the burn.Vehicle mass variations: A fully fueled ship is heavier and less agile than one with less fuel.

Assuming you are referring to a Starship-class vehicle with a mass of 66 metric tons (mt) and three Raptor engines, a propulsive landing on Earth would require approximately 3–6 tons of liquid methane and liquid oxygen propellant. This is based on the following factors: 

Vehicle mass and engine thrust:
The mass of 66 mt is the dry weight of the spacecraft, excluding propellant. The final mass during landing would be higher, including any remaining payload and the three Raptor engines. Each Raptor engine is capable of at least 230 tons of thrust, giving a three-engine cluster significant propulsive capability.

Delta-V for landing:
A propulsive landing on Earth requires a change in velocity (\(\Delta v\)) to transition from atmospheric braking to a final, controlled vertical descent. This terminal velocity is typically around 50–100 m/s.

Rocket equation and exhaust velocity:
You can estimate the required propellant using the Tsiolkovsky rocket equation:\(m_{fuel}=m_{final}\cdot (e^{\Delta v/v_{exhaust}}-1)\)For a Raptor engine, the exhaust velocity (\(v_{exhaust}\)) is about 3,500 m/s (from a specific impulse of 350s). The final mass (\(m_{final}\)) is the spacecraft's mass just before the final landing burn.

Propellant mass estimation:
Assuming a 70 mt final mass (including a small payload) and a 100 m/s burn:\(m_{fuel}=70\cdot (e^{100/3500}-1)\approx 2\ tons\)SpaceX's own internal analysis has produced slightly higher figures, around 6 tons, based on simulations and real-world results. This higher figure accounts for additional fuel reserves, engine gimballing, and safety margins. 

Breakdown of the landing process
A propulsive landing with this type of vehicle and engine setup would include these phases: 

Header tanks:
The fuel for the landing maneuver is drawn from smaller header tanks, which contain a fraction of the total propellant. This is more reliable and prevents the main tanks from sloshing. It also ensures the engines have a steady propellant flow, a key factor in successful propulsive landings.

"Belly-flop" maneuver:
During atmospheric reentry, the spacecraft enters a belly-flop orientation, using its body and control flaps to slow down. This reduces the need for propulsive braking.

"Landing flip" maneuver:
Shortly before touching down, the engines ignite and perform a flip maneuver to orient the spacecraft vertically for landing.

Precision and controls:
The final landing requires precise throttling and gimballing of the engines to counteract gravity and achieve a soft touchdown

“This finding is the direct result of NASA’s effort to strategically plan, develop, and execute a mission able to deliver exactly this type of science — the identification of a potential biosignature on Mars,”

For a 26-metric-ton (mt) spacecraft, the estimated fuel mass required for a propulsive landing on Mars is approximately 40 to 60 mt, bringing the total landing vehicle mass to 66–86 mt. This relies on significant aerodynamic deceleration in the Martian atmosphere before the final propulsive braking maneuver. The final mass varies based on the engine's efficiency and the exact landing trajectory. Fuel requirements for Mars landing Several factors influence the fuel mass needed to land a 26 mt spacecraft on Mars: Deceleration strategy: A Mars landing is a complex process known as Entry, Descent, and Landing (EDL). Due to Mars's thin atmosphere, a propulsive-only landing is inefficient. Instead, spacecraft typically use a combination of methods, including:A protective aeroshell and heat shield to withstand atmospheric entry at high speed.A parachute to provide further slowing.A final rocket-powered braking phase for the precision touchdown.The 26 mt figure would refer to the mass of the final lander after shedding the heat shield and parachute system.Engine specific impulse (\(I_{sp}\)): The efficiency of the rocket engine is a critical factor, described by the specific impulse (\(I_{sp}\)).Higher \(I_{sp}\) engines, like those using liquid hydrogen and oxygen, provide more thrust per unit of fuel, but hydrogen is difficult to store.Methane and oxygen (\(\text{CH}_{4}/\text{O}_{2}\)) offer a lower \(I_{sp}\) but are easier to store and can be manufactured on Mars using in-situ resource utilization (ISRU). This trade-off is central to Mars mission architecture.Delta-V (\(\Delta v\)): The amount of total change in velocity required for the propulsive landing phase is roughly 3.8 km/s from orbit to the surface if parachutes aren't used, but is less when combined with aerodynamic braking. A higher \(I_{sp}\) reduces the propellant mass needed to achieve this \(\Delta v\). Architectural approaches Planetary mission planners have developed different architectures to manage the challenge of large-scale Mars landings: Heavy landers: An analysis of Mars landing vehicles for future human missions found that a total initial mass of 73.0 mt was needed to land a 10 mt payload, while a 25 mt payload (closer to your scenario) required an even larger vehicle. A significant portion of this mass would be propellant for the final descent phase.SpaceX Starship: SpaceX's Starship is designed to land payloads of 100 mt or more using a methane/oxygen engine system. In this architecture, the Starship tanker refuels the Mars-bound ship in Earth orbit, making propellant for landing part of a larger, refueled system.In-situ resource utilization (ISRU): Some mission architectures propose landing an initial vehicle with a fuel-manufacturing plant. This plant would use Martian resources (water ice and atmospheric \(\text{CO}_{2}\)) to produce methane and oxygen propellant for a later landing or for the return trip, significantly reducing the mass that needs to be transported from Earth/