Rajan Wilcox
Juno is a NASA space probe that was launched in August 2011 and took about five years to travel to Jupiter. It is the first mission to Jupiter to use solar panels instead of radioisotope thermoelectric generators. Juno carries six spherical propellant tanks, four containing fuel (hydrazine) and two holding oxidizer (nitrogen tetroxide). The total weight of the spacecraft at launch was 7,992 pounds (3,625 kilograms), consisting of 3,513 pounds (1,593 kilograms) of spacecraft, 2,821 pounds (1,280 kilograms) of fuel, and 1,658 pounds (752 kilograms) of oxidizer. The mission investment is $1.13 billion in total.
| Characteristics | Values |
|---|---|
| Launch Date | 5 August 2011 |
| Launch Location | Cape Canaveral, Florida, US |
| Launch Vehicle | Atlas V 551 rocket |
| Fuel Type | Hydrazine |
| Fuel Mass at Launch | 2,821 pounds (1,280 kilograms) |
| Total Mass at Launch | 7,992 pounds (3,625 kilograms) |
| Orbit | Polar orbit of Jupiter |
| Orbit Distance | Within 4,200 km (2,600 mi) of Jupiter |
| Orbit Speed | 130,000 mph (57.9 km/s) relative to Earth |
| Orbit Duration | 53 days |
| Mission Cost | $1.13 billion |
| Mission Duration | July 2016 - July 2021 |
| Solar Array Length | 29.5 feet (9 meters) |
| Solar Array Surface Area | 650 feet (60 meters) squared |
| Solar Cells | 18,698 |
| Solar Power Output at Jupiter | 400 watts |
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What You'll Learn
Juno's fuel type and oxidizer
Juno, the NASA space probe orbiting Jupiter, was launched in August 2011 from Cape Canaveral, Florida, aboard an Atlas V 551 rocket. It is the second spacecraft to orbit Jupiter and the first to use solar panels instead of radioisotope thermoelectric generators for power. Juno carries six spherical propellant tanks, four containing fuel and two holding oxidizers.
The fuel used by Juno is called hydrazine, and the oxidizer is nitrogen tetroxide, also known as mixed oxides of nitrogen. The two propellants combine and burn to give Juno thrust. The main engine is used for large adjustments to the trajectory, such as orbit insertion. The spacecraft also has 12 thrusters that fire bursts of hydrazine for smaller adjustments or maintenance of its trajectory, to adjust its rotation, and to adjust its orientation in space.
Nitrogen tetroxide is a powerful and storable oxidizer that can be used with various fuels, including hydrazine. It is often used in rocket propulsion systems due to its high performance and storability. However, it is also expensive and highly toxic if leaked.
The addition of a small amount of nitric oxide (1%-10%) to nitrogen tetroxide makes the oxidizer less corrosive and changes its freezing point. This mixture is referred to as Mixed Oxides of Nitrogen (MON) and is commonly used in American engines. The specific formulation used in Juno's propulsion system may be MON3, which contains 3% nitric oxide by mass.
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Fuel and oxidizer mass at launch
The Juno spacecraft launched in August 2011 from Cape Canaveral, Florida, aboard an Atlas V 551 rocket. The Atlas V 551 is the most powerful of the Atlas rockets, with five solid boosters. The rocket operated in stages, with segments falling off once they burned out.
Juno carries six spherical propellant tanks – four containing fuel (hydrazine) and two holding oxidizer (nitrogen tetroxide). The two propellants combine and burn to give Juno thrust. Together, the propellants have a mass of just over 4,400 pounds (2,000 kilograms) at launch, accounting for 55 to 60 percent of the spacecraft’s mass.
Juno had 1,280 kg of fuel and 770 kg of oxidizer at launch. The fuel and oxidizer account for 35.5% and 16.7% of the spacecraft's total mass, respectively.
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Solar panels instead of RTGs
Juno, a NASA space probe orbiting Jupiter, is the first spacecraft to use solar panels instead of radioisotope thermoelectric generators (RTGs) for its mission. RTGs have been used by all previous missions to Jupiter, including Pioneer 10, Pioneer 11, the Voyager program, Ulysses, Cassini-Huygens, New Horizons, and the Galileo orbiter. RTGs are typically used for spacecraft operating outside the orbit of Jupiter, where solar radiation is insufficient to power current solar technology within spacecraft mass limitations.
Juno's solar panels, on the other hand, are enormous, with three large solar panel wings that are integral to stabilizing the spacecraft and generating power. The use of solar panels on Juno was made possible by two key factors. Firstly, Juno is in a polar orbit, which means it will continually be in the sun, receiving approximately 4% of the sunlight it would on Earth. Secondly, advancements in solar cell technology have made solar panels a more economically preferable option than RTGs, especially given the global shortage of Plutonium-238, a crucial material for RTGs, at the time of Juno's development.
The Juno spacecraft has three solar arrays, each measuring 29.5 feet (9 meters) by 8.7 feet (2.65 meters) in length, with a total surface area of over 650 square feet (60 square meters). These solar arrays contain a total of 18,698 individual solar cells, producing approximately 400 watts of power at Jupiter's distance from the sun. This amount of power is sufficient for Juno's mission, which includes measuring Jupiter's composition, gravitational field, magnetic field, and polar magnetosphere, as well as searching for clues about the planet's formation.
Juno's use of solar panels instead of RTGs demonstrates the advancements in solar technology and the feasibility of solar power for space missions even in the outer solar system. This breakthrough has significant implications for future space exploration, potentially reducing the reliance on RTGs and the limited supply of Plutonium-238.
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Fuel-saving gravity assist trajectory
The Juno spacecraft, launched in 2011, was the first mission to Jupiter to use solar panels instead of radioisotope thermoelectric generators for power. Juno carries six spherical propellant tanks, four containing fuel (hydrazine) and two holding an oxidizer (nitrogen tetroxide). Together, the propellants have a mass of just over 4,400 pounds (2,000 kilograms) at launch, accounting for 55 to 60 percent of the spacecraft’s mass.
Gravity assist is a technique that has been used by many space missions, including Juno, to save fuel. This technique involves using the gravity of one celestial body to propel a spacecraft toward another. While the trajectory is longer than a more direct route, a gravity assist saves fuel and allows for extra manoeuvring capability and course enhancement. The Juno mission used Earth's gravity to boost its speed and propel it towards Jupiter.
The MESSENGER mission, which launched in August 2004, also made extensive use of gravity assists to slow its speed before orbiting Mercury. The mission included one flyby of Earth, two flybys of Venus, and three flybys of Mercury before finally arriving at Mercury in March 2011. The Cassini-Huygens spacecraft, launched in October 1997, also utilised gravity assists from Venus, Earth, and Jupiter during its transit to Saturn.
Gravity assists can greatly change the speed of a spacecraft without expending propellant. A gravity assist around a planet changes a spacecraft's velocity relative to the Sun by entering and leaving the gravitational sphere of influence of a planet. This allows a slingshot manoeuvre to be used to change the spaceship's trajectory and speed relative to the Sun. If more speed is needed than is available from gravity assist alone, a rocket burn near the periapsis can be used to maximise kinetic energy while minimising fuel usage.
Powered gravity assists are another technique that can be used to increase the efficiency of fuel usage. By accelerating during a fly-by, fuel can be used very efficiently to increase the apoapsis of the final trajectory. However, this method is very difficult as it is challenging to control the final trajectory.
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Fuel cost and rocket weight
The Juno spacecraft was launched in August 2011 and took about five years to travel to Jupiter. The total mission investment was $1.13 billion, including spacecraft development, science instruments, launch services, mission operations, science data processing, and relay support for 78 months. The spacecraft is named after the Roman goddess, who was Jupiter's wife and could see through clouds. Juno is the second spacecraft to orbit Jupiter, after the nuclear-powered Galileo orbiter, which orbited from 1995 to 2003.
Juno is unique in that it is the first mission to Jupiter to use solar panels instead of radioisotope thermoelectric generators (RTG) for power. This decision was made due to a global shortage of plutonium-238 at the time and advances in solar cell technology. The use of solar panels also made the mission economically preferable. Juno carries three large solar panels symmetrically arranged around the spacecraft, with a total surface area of over 650 square feet.
In terms of fuel, Juno carries six spherical propellant tanks, with four containing fuel (hydrazine) and two holding oxidizer (nitrogen tetroxide). The propellants have a mass of just over 4,400 pounds (about 2,000 kilograms) at launch, accounting for 55-60% of the spacecraft's mass. The spacecraft also has two tanks of liquid helium used to pressurize the tanks and allow the propellants to flow.
The use of gravity assists, such as the Earth's gravity, helps reduce the amount of propellant required for the mission. This technique allowed Juno to reach its necessary speed without requiring a more powerful launch vehicle and significantly more fuel. The cost of fuel itself may not be prohibitively expensive, but fuel requirements in rocketry grow exponentially with respect to delta-v, which measures the capacity to change velocity. Therefore, doubling the capacity requires squaring the amount of fuel. This exponential growth in fuel requirements can quickly lead to increased costs and weight, impacting the feasibility of the mission.
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