Ameer Randolph
Calculating the amount of fuel needed for a mission in Kerbal Space Program can be a complex task due to numerous variables, such as the desired velocity, altitude, airspeed, aircraft profile, and engine efficiency. One key concept to understand is delta-V, which represents the change in velocity and is influenced by factors such as thrust, weight, and fuel usage. While some players suggest using trial and error to gain a feel for the game, others recommend tools like the delta-V calculator, delta-V maps, and addons like Kerbal Engineer to aid in fuel calculations. These tools take into account various parameters, including dry mass, engine fuel efficiency, desired velocity, and fuel weight, to determine the required fuel amount for a specific mission profile.
| Characteristics | Values |
|---|---|
| Calculating fuel requirement | Use delta-V (change in velocity) and thrust-to-weight ratio (TWR) |
| Delta-V | Calculated by taking into account thrust-to-weight ratio and fuel usage |
| TWR | Thrust divided by weight |
| Fuel weight | Weight of the fuel in tonnes |
| Fuel amount | Units of fuel required of the specified type |
| Fuel type | Type of fuel to be used |
| Dry mass | Mass of the payload to be accelerated, including engines and empty fuel tanks |
| Engine Isp | Fuel efficiency of the engine in seconds |
| Delta-V map | Map showing the amount of velocity needed in metres per second |
| Aerobraking | Requires significantly more fuel |
| Altitude | Lower altitudes may assume constant speed |
| Air drag | May require a "fudge factor" to account for air drag |
| Gravity drag | May require additional delta-V calculations |
| Trial and error | Recommended for beginners to understand fuel requirements |
| Kerbal Engineer | Add-on that calculates delta-V and fuel requirements |
| Delta-V maps | Visual representation of required delta-V for various locations |
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What You'll Learn
Calculating fuel requirements for airplanes
To determine the fuel needs for a flight from point A to point B, you must consider the intake air requirements, which vary with speed due to engines' velocity-thrust modifiers. The actual intake flow rate can be calculated by multiplying the intake area by the airspeed in the direction the engine is facing, adding the base speed, and then multiplying by the Mach modifier. This calculation provides the intake air per second when the aircraft is stationary, and charts can help determine the intake performance at different speeds.
Delta-V, or change in velocity, is a critical concept in understanding fuel requirements. It considers the thrust-to-weight ratio, taking into account the fuel usage. To calculate Delta-V, you need to know the dry mass (mass of the payload, engines, and empty fuel tanks), engine fuel efficiency (Isp), desired velocity (delta-V), and fuel weight. However, it is important to note that Delta-V calculations can be complex and may require a background in college-level algebra or calculus.
If the mathematical approach proves too challenging, players can install mods like Kerbal Engineering Redux or Mechjeb, which provide fairly accurate Delta-V readings for their rockets. These mods can simplify the process by directly presenting the Delta-V values, helping players understand their craft's range and fuel efficiency. Additionally, players can refer to the concept of dV budget, which indicates the range of missions a craft can undertake based on its Delta-V capabilities.
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Calculating fuel requirements for spaceplanes
Calculating the fuel requirements for spaceplanes in Kerbal Space Program can be a tricky task, but there are some general guidelines and strategies that can help. Firstly, it's recommended to start with about 10% of the total weight in liquid fuel for jet engines, but this may need adjustment depending on performance.
To improve efficiency, consider the relationship between lift and thrust. More wings provide more lift, which can improve efficiency. However, adding more wings can make the plane bulky and less aerodynamic. As an alternative, consider using the Big-S Delta Wing, which can carry fuel and provide the same lift-to-drag and lift-to-weight ratio as other wings of the same mass.
Another strategy is to find the right balance between fuel and engines. More engines require more fuel, and more fuel equals more mass, which then requires even more engines. Therefore, it's important to find a happy medium that suits your specific spaceplane design. Additionally, consider the temperature and altitude of your flight path, as the Kerbin atmosphere has different temperatures at different altitudes, which can impact safe speeds.
To address fuel imbalance issues, there are several options:
- Build your plane to account for both empty and full tank weight, though this can be challenging.
- Manually pump fuel between tanks to maintain balance during flight.
- Use a mod like TAC Fuel Balancer to automatically balance fuel levels.
- Design your plane with dual tanks on the sides and wings to keep fuel stores in line with the centre of mass, preventing changes in the centre of mass as fuel burns.
Finally, ensure you have sufficient air intakes for your jet engines. Shock cone intakes, for example, provide the best air supply at all Mach speeds and do not decline in performance beyond certain speeds, unlike other types of intakes.
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Calculating fuel requirements for rockets
Calculating the fuel requirements for rockets is a crucial aspect of space missions, ensuring that spacecraft have sufficient propellant to complete their journeys successfully. In the context of Kerbal Space Program (KSP), players often face challenges in determining the appropriate amount of fuel needed for their missions. Here's a guide to help you understand the process of calculating fuel requirements for your KSP ventures:
Understanding Key Concepts
Delta-V (ΔV):
Delta-V represents the change in velocity of a spacecraft and is a critical factor in fuel calculations. It measures the total velocity change a spacecraft can achieve with a given amount of fuel. Delta-V maps are available for the Kerbin solar system, providing insights into the required delta-V values for reaching different destinations. For example, a landing on Mun and a return trip require approximately 5500 m/s of delta-V.
Thrust-to-Weight Ratio (TWR):
TWR is a crucial consideration for lift-off. It is calculated by dividing thrust by weight. To achieve liftoff, your acceleration should exceed 9.8 m/s^2. By dividing your weight by thrust and then dividing that number by 9.8, if you get a value greater than 1, your spacecraft will ascend.
Dry Mass:
Dry mass refers to the mass of the payload you intend to accelerate, including the weight of engines, empty fuel tanks, and the payload itself. Accurate estimation of dry mass is essential for fuel calculations.
Engine Isp:
Engine Isp represents the fuel efficiency of the engine in seconds and is provided for vacuum conditions. It influences the amount of delta-V generated by a given amount of fuel.
Steps to Calculate Fuel Requirements:
Step 1: Determine Mission Parameters
Define the specifics of your mission, such as the destination (e.g., Mun), the mass of your payload, and the desired trajectory.
Step 2: Estimate Dry Mass
Calculate the dry mass by considering the weight of the payload, engines, and empty fuel tanks. This estimation is crucial for accurate fuel calculations.
Step 3: Consult Delta-V Maps
Refer to delta-V maps to determine the required delta-V for your mission. For example, reaching low Mun orbit requires approximately 1200 m/s of delta-V.
Step 4: Calculate Required Fuel Weight
Use a delta-V calculator to determine the fuel weight needed for your mission. Input the dry mass, engine Isp, and required delta-V to estimate the fuel weight.
Step 5: Consider Fuel Type and Amount
Select the appropriate fuel type for your mission and calculate the required amount based on the fuel weight estimated in Step 4.
Step 6: Account for Efficiency and Margins
Remember that higher thrust ratios often lead to lower fuel efficiency, impacting delta-V. It's advisable to have a margin of extra delta-V, especially if you're new to the game, to account for any navigational errors or inefficient maneuvers.
In summary, calculating fuel requirements for rockets in KSP involves understanding key concepts like delta-V, TWR, dry mass, and engine Isp. By following the steps outlined above, you can estimate the necessary fuel weight and amount for your missions, ensuring successful journeys to and from destinations like Mun.
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Calculating the delta-V required
The delta-V is the difference in velocity required for a space vehicle to launch and manoeuvre in space. It is calculated using the rocket equation, which takes into account the specific impulse or effective exhaust speed, initial and final mass, and fuel efficiency of the engine.
To calculate the delta-V required for a mission in Kerbal Space Program (KSP), you can use a delta-V calculator or delta-V maps. These tools will help you estimate the amount of velocity change you need for your specific mission profile.
Step 1: Determine the Mission Profile
Firstly, you need to know the specifics of your mission. This includes the payload mass, the type of orbit you want to achieve, and the destination body. For example, are you planning to land on the Mun and return to Kerbin, or just reach a low orbit around Kerbin?
Step 2: Estimate the Required Delta-V
Use a delta-V calculator or delta-V maps to estimate the required delta-V for your mission. For example, a landing on the Mun and a return to Kerbin would require approximately 5500 m/s of delta-V. Breaking this down further, you would need about 3400 m/s to reach Kerbin orbit, 1200 m/s for a low Mun orbit, 1300 m/s for landing and launching back to orbit, and 300 m/s for the transfer back to Kerbin.
Step 3: Consider Inefficiencies and Margins
Keep in mind that various factors can affect your delta-V requirements. Inefficient manoeuvres, such as a suboptimal gravity turn, can increase the delta-V required. It is recommended to have a margin of extra delta-V beyond the bare minimum, especially if you are new to the game. This will give you some leeway to make mistakes or compensate for unforeseen events.
Step 4: Choose Your Engine and Fuel Type
Different engines have different fuel efficiencies, also known as specific impulse (Isp). Monopropellant engines, for example, have an Isp of 240s in a vacuum. Choose an engine and fuel type suitable for your mission, taking into account the delta-V capabilities of the engine and the fuel's weight and amount.
Step 5: Calculate Thrust-to-Weight Ratio (TWR)
Calculate the TWR by dividing your thrust by the weight. To achieve liftoff, you typically need an acceleration higher than 9.8 m/s^2. Divide your weight by your thrust, then divide that number by 9.8. If the result is greater than 1, your ship will rise.
By following these steps, you can estimate the delta-V required for your KSP mission and make informed decisions about engine choice, fuel type, and manoeuvring efficiency. Remember that delta-V calculations are intricate, and a solid understanding of physics and mathematics is beneficial.
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Calculating the TWR required
To calculate the Thrust-to-Weight Ratio (TWR) required for a rocket in Kerbal Space Program (KSP), you need to consider the following:
Thrust vs Weight
TWR is the ratio of the thrust or "pushing power" of your rocket engines to the weight of your rocket and payload. The formula for calculating TWR is simply thrust divided by weight. For vertical takeoff, your TWR must be greater than 1, meaning your acceleration is greater than the force of gravity. If your TWR is barely above 1, you will be able to fly but will accelerate slowly as most of your engine thrust will be spent fighting gravity, wasting fuel.
Optimum TWR
In KSP, an optimum TWR is generally considered to be around 1.5-3. A TWR of 1.25 loses 80% of its thrust to gravity, while a TWR of 2.0 loses only 50%, making the rocket significantly more fuel-efficient. However, as the cost of rocket parts was balanced in career mode, the cost per tonne to orbit became a more important metric for judging rocket performance. Therefore, for rockets that are not using SRBs, a launch TWR of around 1.25-1.3 is often used to minimise costs.
Delta-V
To figure out how much fuel you need, you must calculate how much Delta-V you require for your mission. Delta-V is the change in velocity required and is a calculation of thrust to weight, taking into account fuel usage. Delta-V maps of the Kerbin solar system can give you an idea of how much Delta-V is needed to reach various locations. For example, a Mun landing and return will require approximately 5500 m/s of Delta-V.
Other Considerations
While TWR is important for takeoff and landing, it becomes less relevant once you are in orbit. In orbit, m/s^2 of acceleration is a better indicator of how long you need to wait for your burns. Additionally, when dealing with real spacecraft, other factors come into play, such as gee loading and mechanical stresses on the spacecraft, which may limit the desired TWR.
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Frequently asked questions
It is recommended to use trial and error to get a feel for the game. However, for a Mun landing and return, you will need around 5500 m/s of delta-V (change in velocity).
You will need around 3400 m/s to get into Kerbin orbit, 1200 m/s for a low Mun orbit, 1300 m/s for landing and launching back to orbit, and 300 m/s for the transfer back to Kerbin.
For lower altitudes, you can assume a constant speed. For higher altitudes, such as for a suborbital flight, you can approximate the flight after 10 km with negligible air drag and assume an instantaneous burn.
You can use the delta-V calculator, which takes into account the dry mass, engine fuel efficiency, velocity needed, fuel weight, and fuel type. Alternatively, you can use the Vis Viva equation to calculate your own delta-V map.
It is extremely difficult due to a wide array of variables such as drag, Great Circle distance, turns, and engine specific impulse. The only reliable way is through experimentation. You can calculate the energy required by summing up the energy usage of all components.
