DEEP SPACE PROBES
Deep space probes are space vehicles which leave Earth for destinations in our solar system and beyond. These are robotic vehicles that serve a variety of scientific purposes. The Voyager, Pioneer and Mars landing missions are examples of deep space and planetary probes.
The Cannae Drive creates a reactionless force that is used to propel space vehicles. The Cannae Drive significantly improves the economics and operation of satellites. The advantages of the Cannae Drive in Earth satellite applications is outlined in other sections of this website. For deep space probes, the Cannae Drive also provides advantages over propellant-based systems. In addition to improved economics and performance, the Cannae Drive allows new deep-space missions that are impossible using propellant-based propulsion systems.
The concept vehicle outlined in this section is used to propel a scientific instrument and communication payload with a mass of 2000 kgs to a 0.1 light year (LY) distance in a 15 year time frame. This vehicle uses existing superconductor and vehicle subsystem technology performance levels. No improvements to technological performance levels are required to build the vehicle described in this section.
The vehicle mass is 10,000 kgs with subsystem approximate mass of:
Configuration is depicted in Figure below:
There are 10 Cannae Drives included in the design.
5 x 50 MHz Thruster cavities (continuously powered)
3 x 1 GHz Steering cavities (powered as needed)
2 x 1.5 GHz Roll-control cavities (powered as needed)
The 5 Cannae Drive thruster cavities provide continuous acceleration of 8.66 x 10-3 m/s2 to the probe. This is equivalent to accelerating at 1/1132 G. The small acceleration is constantly applied in one direction throughout the life time of the probe, continually increasing the velocity of the probe with respect to the Earth reference frame. The total thrust developed by the 5 thruster cavities is 85.5 newtons.
The three medium sized Cannae Drive cavities provide steering for the probe. These cavities are intermittently powered to provide course corrections or for flight maneuvers.
The two small Cannae Drive cavities are used to modulate the roll rate of the space probe. These cavities are also used intermittently.
All of the Cannae Drives are fixed in position on the vehicle. This eliminates moving parts from the propulsion system, allowing for longevity of operation.
The Cannae Drive cavities are manufactured of aluminum. Aluminum (or another appropriate alloy) is used to minimize the thruster system mass. A substrate layer is then coated on the inside of the cavity. A top coat of 400 nm YBCO layer is then deposited over the substrate layer.
The thrusting cavities are designed with asymmetric features in areas of high electric field and in areas of high magnetic field. The average effective differential in axially-directed radiation pressure is 15% over the entire cross section of each thruster cavity. The unbalanced force developed in the thruster cavity is directed through the axial center of the 5 thruster cavities.
The design maximum H-field on the top plate of the thruster cavity is 4000 A/m with nominal maximum operating H-field on the top plate of 3270 A/m. This relatively low field is used to prevent field emission in the areas of high E-field and to keep the ohmic losses in the regions of high H-field to a minimum.
The 5 thrusting cavities are cooled by radiative cooling to deep space. The maximum design temperature of cavity operation is 75 K. The cavities and structural elements around the cavities are coated with a high emissivity black finish. At design power, the thruster cavities receive a combined 73 watts of phase-locked RF power. This power is almost entirely consumed as ohmic heating in the walls of the cavities. The cavities continually radiate this heat to deep space.
The radiating surface area of the thruster section of the probe is approximately 90 square meters. The radiative surface area needed to radiate 73 watts from a temperature of 75 K to 3 K (the effective temperature of deep space) is 40 square meters. When the cavities radiate more than 73 watts of thermal energy, the operating temperature of the cavities drops below 75 K, reducing the radiative power of the cooling mechanism. The system will reach a natural equilibrium temperature that radiates all ohmic heating from the cavitiy walls. This equilibrium temperature will be below the 75 K maximum design temperature. Operating temperatures below 75 K will improve the surface resistance characteristics of the YBCO and improve the power-to-thrust performance of the propulsion system.
This radiative cooling system is passive. There are no moving parts to wear out or malfunction. This ensures that the cooling system operational life is sufficient to meet the design lifetime of the probe.
The smaller Cannae Drive cavities are operated intermittently to control the yaw, pitch, and roll of the probe. Cooling requirements on these cavities is minimal compared to the cooling load on the thrusting cavities. The small cavities in the probe also use passive radiative cooling (to deep space) to maintain operating temperature at or below 75 K.
The space probe is powered with 4 radioisotope thermal generators (RTGs). Each RTG is designed to generate 300 watts. The thrusting system requires less than 100 watts RF at full power. The extra RTG power is used to operate the scientific and communication payload. Also, as the RTG power diminishes over the life of the mission, sufficient power remains to operate the thrusting system at full power.
In addition to the passive cooling mechanism used in the thruster section of the probe, the power unit also requires a cooling system. This separate system is used to eject waste heat from the RTG power system. The power system and power cooling unit of the probe are separated from the thruster section by light-weight, thermal-radiation shielding.
The waste heat from the RTG power system is also used for thermal control in the non-thruster sections of the probe.
The Cannae Drive deep-space probe is designed to measure the environment of the interstellar medium. To do this, the vehicle is launched to LEO on a standard launch vehicle. The diameter of the probe in launch configuration is 4.8 meters with a height of 10 meters. These dimensions allow the probe to fit into a standard 5-meter launch vehicle fairing.
Once the vehicle is in LEO, the thruster system is powered and the vehicle accelerates in the direction of its Earth orbit. This causes the probe to slowly spiral away from Earth until it eventually escapes into deep space. The probe continues to accelerate, increasing its velocity and overcoming the gravitational attraction of the Sun. The vehicle will reach escape velocity from the Sun without gravity assists in less than 2 months.
During the LEO-to-solar-escape-velocity phase of the mission, a light-weight radiation shield is deployed to shield the thruster section of the probe from Earth’s thermal radiation and from solar radiation. Once the vehicle flight path is directed away from the Sun, the radiation shield is ejected from the probe. The temporary shielding is not depicted in Figure 1.
The probe is designed to accelerate continuously throughout its operational life time. The mission duration is designed to be 15 years, with mission-life extensions probable. After 15 years of constant 8.65 x 10-3 m/s2 acceleration, the vehicle will reach a distance from Earth of 0.1 LY (approximately 600 billion miles). At 0.1 LY, the vehicle will be travelling at approximately 1.35 % the speed of light (c). At a 0.1 LY distance, it will require over 1 month to send or receive radio signals between the probe and Earth.
For comparison, the Voyager 1 probe is currently travelling at 17.06 km/s. The Cannae-Drive-propelled, deep-space probe increases by the Voyager speed of 17.06 km/s every 23.1 days. Accelerating at design level, the Cannae-Drive-deep-space probe passes the Voyager distance from Earth (120 AU) within 2.0 years of probe launch. The Voyager required almost 35 years to reach this distance. Voyager 1 continues to increase its distance from Earth and will reach a distance of 0.1 LY in a total travel time of 1780 years. The Cannae Drive probe requires 15 years from launch to travel 0.1 LY and the thruster system uses less than 100 watts RF power to do so.
For additional comparison, a propellant-based probe designed to accelerate a 2000 kg payload to a velocity of 1.35% c (the speed of the Cannae Drive probe when it passes 0.1 LY) would require a minimum of 1.8 x 1021 kgs of propellant. This calculation assumes a propellant specific impulse of 10,000 seconds with zero structural, propellant tank and power system mass (final vehicle mass is 2000 kgs). Assuming the propellant has a specific gravity of 1, this amount of propellant could cover the entire surface area of the Earth to a height of over 2 miles. If power and structural mass estimates for the propellant-based probe are included in the propellant-requirement calculation, the situation gets much worse.
The Cannae Drive probe reaches a distance from Earth of 0.1 LY in 15 years. Because of the simplicity of design and lack of moving parts, it is anticipated that the vehicle will continue to accelerate and will continue to transmit data back to Earth. The Voyager and Pioneer deep-space probes have demonstrated that multi-decade missions are achievable. The RTG’s of the Cannae Drive probe are designed to deliver the power required to generate up to 100 watts of RF power to the thruster cavities. As RTG power levels drop below end-of-life design levels, RF power to the cavities will also drop below the 73 watt design level. As long as phase-locked power is sent to the thruster cavities, the probe will continue to accelerate. The acceleration of the probe is directly proportional to the RF power sent into the cavities. Given the proven longevity of RTGs in space applications, the Cannae Drive probe could continue to accelerate and send back data on the interstellar medium for decades.
After 33 years of constant 8.66 x 10-3 m/s2 acceleration, the Cannae Drive probe will have crossed a distance of 0.5 LY from Earth while attaining a speed of approximately 3% of c.
For deep-space applications, a Cannae Drive probe outperforms propellant-driven systems by orders of magnitude. Travel times and vehicle velocities that are impossible for propellant based systems are achievable with a Cannae Drive system. The Cannae Drive technology allows new deep-space missions that have previously existed only in science fiction.