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Advanced Propulsion. Slingshot Orbits:. The stationary or resonant orbits give spacecraft consistent positioning while expending the minimum energy. However we can also use orbits to accelerate to greater velocities.
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Slingshot Orbits: The stationary or resonant orbits give spacecraft consistent positioning while expending the minimum energy. However we can also use orbits to accelerateto greater velocities. • The best example of a slingshot’s usefullness comes from the Cassini spacecraft. • Cassini flew a ‘VEGA’ orbit where it stole momentum from Venus, Venus again, Earth, and finally Jupiter on its way to Saturn. • The ‘GA’ in VEGA comes from an asteroid (Gaspra) that Cassini came close to….no slingshot though.
Fuel Velocity: The second paradigm for improving our flight performance is to increase the speed of our exhaust. • The rocket shows that our ultimate velocity increases linearly with the velocity of our fuel. It’s the most efficient way to improve things. • We mainly rely on a single method of achieving thrust, but there are several advances on the horizon that are in various stages of development.
Types of Fuel: There are three main types of physical process that we use for fuel in space propulsion. • Chemical Reactions: This amounts to triggering an energy releasing chemical reaction in a controlled (or uncontrolled) way. (By far the most common method). • Plasma Reactions: These thrusters use electric fields to accelerate ions. (Not used for launches, but more common now in trajectory corrections). • Nuclear Reactions: Nuclear propulsion relies on fission power to generate massive amounts of energy that propel exhaust at huge speeds. (Hard to control, but can also be an impulse drive).
Chemical Fuel: Chemical fuels are the most common, but also the least efficient. • Water: Many liquid fuel rockets use the formation of water to generate thrust. H2 + O H2O + energy! • Water reactions produce exhaust speeds of 3-4 km/sec. • So, what does it take to get the Apollo capsule to the Earth escape velocity of 11 km/sec?
Fuel Velocity: Chemical fuels are the most common, but also the least efficient. • The Apollo payload weighed 47000 kg. • We can solve the Rocket equation for mfuel to get that we need the equivalent of 726000 liters of water!!!! • Even the most advanced chemical propellants produce exhaust no faster than 5 km/sec. Plus, these reactions are pretty dangerous!
Fuel Velocity: Chemical fuels are the most common, but also the least efficient. • What if we could get the fuel speed up to 11 km/sec? • We can solve the Rocket equation for mfuel to get that only need 80000 liters of water. That’s a factor of nearly 10x!!!! • So speed is important!
Thrust Alternatives: There are many ways to improve over chemical rockets for fuel velocity, some of which are even in use today. • The most common of these technologies is a broad class of device called a plasma thruster. • Plasma thrusters operate by accelerating ions away from a payload at high velocity. • They generally carry only a little fuel with them, but make up for it with Vex.
Electrostatic Ion Thrusters: EIT designs use an electron gun (similar to a CRT) to fire ions through a grid and into space. • EIT devices have been used for many years in spacecraft. Their most visible role was in the NASA Deep Space 1 mission. • Velocities from ion thrusters can be very large (250 km/sec has been achieved). • Such a device could lift an Apollo style payload to escape with only 2100 kg of fuel! (0.3% of a Saturn V).
Electrostatic Ion Thrusters: EIT designs use an electron gun (similar to a CRT) to fire ions through a grid and into space. • EIT devices have been used for many years in spacecraft. Their most visible role was in the NASA Deep Space 1 mission. • Unfortunately they will burn out their electron gun long before they can produce that much V.
Electrostatic Ion Thrusters: EIT designs use an electron gun (similar to a CRT) to fire ions through a grid and into space. • EIT devices have been used for many years in spacecraft. Their most visible role was in the NASA Deep Space 1 mission. • They are also pretty slow in accelerating things. Typical forces are about equal to the weight of a sheet of paper in your hand.
Helicon Thrusters: A group at the University of Washington is developing a different kind of plasma thruster called a ‘Helicon Thruster’ . • Helicons work by using magnetic ‘waves’ to create and accelerate plasma. There’s no electron gun to break down. • HTs can overcome some of the limitations of EIT devices and are in active development worldwide.
VASIMR: The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an advanced helicon design being developed by NASA. • VASIMR is a hydrogen helicon engine being built by AdAstra Rocket corp. for NASA. • VASIMR is a controlled helicon that can be used for different amounts of thrust at different times in a mission. • It still suffers from low forces, but they add up over a flight.
VASIMR: The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an advanced helicon design being developed by NASA. • VASIMR is a hydrogen helicon engine being built by AdAstra Rocket corp. for NASA. • VASIMR uses hydrogen because it could be refueled once it reached a target like Mars. • Reducing the amount fuel is a goal, but there are compromises with this design. Why would Hydrogen be a poor choice?
Nuclear Propulsion: Nuclear engines are another broad class of devices that use fission (or fusion!) energy to produce thrust. • We already know that nuclear power has far more energy/mass than chemical reactions. • If there’s more energy per mass, then the kinetic energy (1/2MV2) of the exhaust will be greater. • In theory you can increase your exhaust velocity using nuclear energy by square root of the energy capacity. Up to thousands of times more in the case of fusion.
Nuclear Generators: We use nuclear power already for both ground and space transportation. • The most prominent use is the Radioisotope Thermal Generator (RTG). • RTGs have a good service history, but are still controversial.
NERVA: An early design for a nuclear rocket was the Nuclear Engine for Rocket Vehicle Application. • NERVA was intended as a replacement for the Saturn V third stage. • NERVA was FAR more controversial than a RTG and was cancelled in 1972.
Prometheus: Project Prometheus is a recent attempt to mate nuclear power to plasma trust technology in a system that would use fission to power and move a spacecraft. • Prometheus would have been used initially on an ambitious mission to Jupiter (the Jovian Icy Moons Orbiter-JIMO). • A Prometheus spacecraft would have 100s of times more energy to use than current designs. • It would be able to move between targets with its greater thrust-fuel ratio.
Prometheus: Project Prometheus is a recent attempt to mate nuclear power to plasma trust technology in a system that would use fission to power and move a spacecraft. • Prometheus would have been used initially on an ambitious mission to Jupiter (the Jovian Icy Moons Orbiter-JIMO). • Prometheus was part of the Bush Administration 2002 plan for the future of space. • Prometheus wasn’t part of the Bush Administration 2004 plan for the future of space. • More than 80% of its funding has been cut…future unclear.
Orion: Orion is an advanced concept for nuclear spaceflight dating back to the 1940s. • Orion spaceships operate by detonating nuclear bombs behind the payload. • This generates a HUGE amount of thrust that could accelerate massive payloads to 10-20% of the speed of light. • Orions could explore the solar system easily and even visit nearby star systems. • Nukes in space are REALLY controversial though.
No Fuel Designs: As nice as nuclear and ion propulsion are, the most efficient way to travel would be to carry no fuel at all. • NASA has supported several designs to travel in space without carrying any (or minimal) fuel. • One technique is called Solar Thermal Propulsion. STP still carries fuel, but uses mirrors to heat it and generate thrust. It’s much more efficient than chemical rockets.
The Solar Sail: Solar Sails have been discussed as a means of space travel for a long time. • Solar sails work like wind sails, but with radiation pressure (momentum from light) as the ‘wind’. • Solar Sails are conceptually simple • Several test flights have already occurred with them, but all have failed for reasons unrelated to the feasibility of the technique. • Criticisms of the technique include steering and the reduction in ‘fuel’ with distance from the Sun.
Magnetospheric Propulsion: A University of Washington effort has been involved in developing a new class of ‘solar sail’ that uses the solar wind. • Called M2P2, this device works by creating a magnetosphere around a spacecraft that then interacts with the solar wind. • The solar wind has much less momentum than solar radiation, but the fields can be made very large.
Magnetospheric Propulsion: A University of Washington effort has been involved in developing a new class of ‘solar sail’ that uses the solar wind. • Called M2P2, this device works by creating a magnetosphere around a spacecraft that then interacts with the solar wind. • M2P2 has been demonstrated in the lab to work.
Magnetospheric Propulsion: A University of Washington effort has been involved in developing a new class of ‘solar sail’ that uses the solar wind. • M2P2 has also been suggested as a way to send un-fueled spacecraft to various places in the solar system. • An added benefit is that the magnetic field will shield the crew!
The Bussard Ramjet: The ramjet is a spacecraft that picks up its fuel along the way. • The Bussard design would scoop up ions and accelerate them out the back. • The greater the difference between the local plasma velocity and the spacecraft, the more thrust is obtained.
The Scramjet: NASA is actually building a version of a ramjet that works in the atmosphere. • The X-43 works by taking in Oxygen in the air and mixing it with onboard Hydrogen to produce thrust. • Very high speeds are required to start this process, more than 3000 mph!
Space Elevator: Nearly all of the methods described here do not work for an Earth launch event. • A space elevator is an idea that’s simple in concept but seems impossible to achieve. • All you need to do is run a cable from the ground to a counter weight near a GSO point. • Payloads then ‘climb’ up the cable and into orbit!
Space Elevator: A local company is working to build a space elevator. • Their concept would put the base of the elevator on a series of boats in the ocean. • The primary technical challenge is to find a material strong enough to make the cable.
