. In-Space Propulsion Technologies
Non-Chemical Propulsion ... Electric Propulsion ... Solar and Drag Sail Propulsion ... Thermal Propulsion ... Tether Propulsion ...
. Ancillary Propulsion systems
Note: Apollo 11 was the spaceflight by which occured the first landing humans on the Earth's Moon in 1969, Neil Armstrong and Edwin "Buzz" Aldrin Jr. Credit: SonicbombHD
Ancillary Propulsion systems
Ancillary propulsion systems include thrusters and valves as well as pressurization systems, high-pressure tanks, and feed or pressurization lines.
Auxiliary Control Systems (ACS)- The American CHALLENGE
The U.S. auxiliary control systems is generally based on technologies developed few decades ago. To be Up-to-date, NASA need adapting advanced thruster developed by foreign agencies to his science and spaceflight applications. In fact, some of these thrusters use composite manufacturing technology and higher-pressure operation to maximize thrust-to-weight and reduce cost.
Also, because nitrogen tetroxide (N2O4) and hydrazine propellants are very toxic, they will focus on systems based on non-toxic propellants. In the same time, while can significantly reduce cost by reducing operations and logistics complexity.
Another Challenge is the explosion of CubeSat launch demand, which one has created a need for very low cost, highly integrated and small reaction control systems.
Generaly, the Main propulsion systems refer to the vehicle fluid systems that integrate the engine, vehicle systems, propellant tanks, and ground systems. These systems are complex components with line elements, flex ducts, valves, and actuators.
Launch Abort Systems (LAS)
LAS in the U.S. date back to the 1970s, while was used by Shuttle system to complete orbiter Return to Launch Site or Abort to Orbit operations. However, no dedicated system existed to separate the Shuttle crew from primary propulsion hazards. Current concepts include guided attitude control motors (solids), vector able solid motors, and even liquid-based systems that utilize orbital maneuvering and reaction control propellant in case of a required abort.
SLS Launch Abort System
Thrust Vector Control Systems
With the exception of relatively small commercial expendable upper stage TVC, the SOA for U.S. launch vehicles employs hydraulic actuators, typically powered by hydrazine-driven auxiliary power units (APUs). The toxic propellant used in these APUs pose similar operations and logistics complexities to the toxic ACS.
Therefore, there is significant interest in reducing costs by developing nontoxic APUs. Similar to ACS applications, toxic propellants would be replaced by nontoxic options. There is also interest in replacing more complicated hydraulic actuators with large EMAs or electro-hydraulic actuators (EHAs).
Ancillary propulsion systems include also Health Management and Sensors & Pyro and Separation Systems.
The NASA Balloon Program provides balloon launch vehicles, launch services, and ground and flight support systems to enable scientific investigations at near-space altitudes.
The current zero-pressure type balloons, which are vented with zero differential pressure at the base of the balloon, provide reliable heavy-lift capabilities, but are susceptible to altitude and gas loss when flying duringnighttime. Also, currently-used support systems are based on standard materials and heritage flight hardware that have not fully taken advantage of advances in manufacturing processes, materials, and electronics.
Super-Pressure Balloon, SPBs
Current NASA scientific balloon vehicles are vented designs with zero differential pressure at the base of the balloon.
SPBs allow longer flight durations and minimize altitude loss during nighttime conditions. These balloons enhance existing science support capabilities.
Currently, one flight of the 18.8 million cubic foot design has been completed, with several more planned for the near future.
The technical capabilities desired for the SPB include stratospheric balloon vehicles that can support flight durations of up to 100 days, lift capabilities of greater than 2,200 kg up to over 33 kilometers (km) and greater than 1,800 kg to over 35 km, and finally, the ability to remain at float at mid-latitudes during diurnal cycles.
Current zero pressure balloons have these lift and altitude capabilities, but can only achieve extended durations at the polar regions, where constant sunlight is available. SPBs require advanced materials, analytic methods, construction, and test techniques.
Current balloon payloads and flight trains use conventional steel and aluminum materials for mechanical structures and assemblies. So, if it possible to have lighter-weight materials, the available mass for science instruments on balloon gondolas.
Balloon-borne scientific instruments that require precision pointing have previously relied on unique pointing systems provided by the instrument team.
The only available standard system provides azimuth pointing with an accuracy of approximately two degrees.
NASA need a standardized, high-precision pointing system that can position scientific instruments with masses up to 700 kg within one arc second of accuracy and stability.
The current telemetry capability provides approximately 150 kbps using satellite relay. During flight, so that in real time, balloon science users typically collect more scientific data than can be downloaded.
We need a higher downlink bit rate enhances science data downlink throughput during flight.
Balloon Trajectory Control
Longer-duration flights could be enhanced by modifying the free-floating balloon’s trajectory. So that, trajectory control would allow a balloon to avoid overflight of populated areas and guide systems to safe termination areas at the end of the flight.
Science users require higher-power systems to sustain science payloads as well as handle potentially long nighttime exposures. So, up to 2,000 watts of power generation and up to 24,000 watt hours of power storage are desired, with higher power-to-mass ratios than existing systems.
Mechanical Systems – Launch Systems
The current NASA scientific balloon launch systems are manually operated in close proximity to the launch vehicle and payload systems. Launch systems that can be operated remotely enable payload users to launch more hazardous payloads and enhance the safety of launch operations.
Mechanical Systems – Parachute
The current NASA scientific balloon parachutes consist of nylon, which is susceptible to ultraviolet (UV) degradation. So, UV protection systems would enhance the duration of balloon missions.
Mechanical Systems – Floatation
Longer-duration balloon flights in mid latitudes will spend long periods over the southern oceans. There is a potential for termination over the ocean, and payload floatation is desired so the payload systems can be recovered. The ability to provide floatation for payloads with masses up to 3,630 kg for durations of up to several weeks in salt water is desired.
Source: NASA Technology Roadmaps TA 1: Launch Propulsion Systems, July 2015, NASA
In-Space Propulsion Technologies
When a rocket leaves off its upper stages, such as the Delta's DCSS, the propulsion system begins. The main engines used provide the primary propulsion for the orbital transfer, the planetary trajectories and for ascent and landing purposes.
Space lift to Earth orbit involves escaping the gravitational field to deliver a spacecraft for its mission in the LEO, starting at about 200 miles high. The launch propulsion system’s challenge is to impart at least the orbital insertion velocity to the spacecraft in the most affordable and effective manner. To this end, it uses systems as solid, liquid, or air breathing rockets or an combination of them. Further, whatever the type used, ancillary propulsion systems are necessary to provide certain functions such as aborts and thrust vectoring.
The Non-Chemical Propulsion provides thrust without combustion and chemical reactions. This family of propulsion include systems that accelerate reaction mass electrostatically or electromagnetically, i.e. by electric propulsion. Also, systems that energize propellant thermally, that is the solar or nuclear thermal propulsion, and those that interact with the space environment such as the solar sail and the tether propulsion.
Resistojets and arcjets are two types of electrothermal propulsion currently largely used on communications satellites in the 50 to 2,000 watt range. with technology work exploring very small and very large solutions.
Ion engines and Hall thrusters are another category of electric propulsion that uses electrostatic fields to ionize and accelerate a propellant. Both technologies are also used extensively in the communications satellite sector. Their flight power ranges are in the hundreds of watts to several kilowatts, and tests are makes to increase the power of Hall thrusters to over 10 kW for a human flight application. In left, NASA's Evolutionary Xenon Thruster (NEXT) during thermal Vacuum Test.
In the area of ion thrusters, some work is make to increase the power from 7 kW to higher than 20 kW for an Isp of at least 4,000 seconds.
In the Hall thruster category, some emphases is put on maturing a 10 to 15 kW class thruster to be used in the near-term human exploration missions. In this class, continuing to explore and mature single thruster in the range of 50 to 100 kW still an important focus, as well than the nested Hall thruster that exceed the 100 kW. A 50 kW solar electric propulsion system is being developed as well as magnetically-shielded Hall thrusters for the Asteroid Redirect Mission or other futuremissions.
Hall Thruster (H6) Firing
The electromagnetic category includes the pulsed inductive thruster and the magneto-plasmadynamic (MPD) thruster. This class of thruster interacts with a reaction mass using electromagnetic fields and, although none of these systems are currently in use in space, they are typically envisioned to be high-power, starting in the 50 to 100 kW range. This higher-power category will be pertinent to human space exploration missions beyond LEO, and for rapid-transit science missions to the outer solar system and deep space destinations.
Solar and Drag Sail Propulsion
Solar sail propulsion technology is advancing for application to small spacecraft, from CubeSats to Explorer-class robotic missions. This technology derive the sunlight' refection from a large, mirror-like sail made of a lightweight, reflective material. The continuous sunlight pressure provides efficient primary propulsion, without expending propellant or any other consumable, allowing for very high delta-V maneuvers and long-duration, deep-space exploration.
The First-generation sail need a delta-V sufficient to create a long-life, more than 10 years, artificial sub-Lagrange Point 1 (L1) that allows a spacecraft to stay along the Sun/Earth line.
The Second-generation sail require delta-V sufficient to place a long-life, again more than 10 years, spacecraft in a heliocentric orbit with semi-major axis of 0.48 AU at an inclination of 75 degrees or higher.
The Third-generation sail require delta-V sufficient to enable a Voyager-class spacecraft to reach 250 AU within 20 years of launch. These requirements can be met by sails less than 3 microns thick with surface areas of 1,600 m2, 22,500 m2, and 90,000 m2, respectively.
The challenges are all related to the scale of the sails required – manufacturing, packaging, deployment, guidance, navigation, and control.
About the Drag sail, the thrust is providing by a change in the ballistic coefficient of a spacecraft, thereby increasing the atmospheric drag. This technology can bring a low-mass of propulsion for a the end-of-life of a spacecraft in deorbit. End-of-life drag sails will require that the spacecraft burn up upon reentry or be supplemented with a high-thrust system allowing for precision reentry targeting.
The Thermal Propulsion systems use other energy sources besides combustion, such as solar and nuclear fission. These systems permits the heating of the propellant via a heat exchanger and allow a thermal expansion of the propellant through a traditional nozzle. Because its high Isp, they needs extremely high-temperature materials compatibles with the propellant, and acceptable mission endurance.
The solid core of the Nuclear Thermal Propulsion (NTP) engines use a fission reactor in the thrust chamber, that heat large mass flow of hydrogen at very high temperatures. This is what it give very high Isp at 900 seconds and a high thrust at about 25,000 lbf.
The NTP systems was identified as a leading option for Mars Design Reference Architecture 5.0.
Today challenges is about the reactor fuel design able to achieve higher temperature, minimize the erosion, and fission product release.
The big challenge is using less volume of enriched uranium than what it was used in past programs.
Nuclear thermal Propulsion (NTP)
The Solar Thermal Propulsion (STP) have important potential. For a single launch of small or medium payloads, it can allow larger-mass with slightly longer trip times than chemical propulsion. Also, for human missions to Mars and other destinations, its high thrust and Isp can provide shorter trip times.
Solar Thermal Propulsion
The sunlight is captured by a large concentrate surface and focused inside a cavity to heat material at very high temperatures. This heat is transferred at the Hydrogen, which provides an Isp of about 900 seconds at a thrust of almost 2 to 4 lbf..
Here, the principal challenge is about the volume required of liquid hydrogen for a single launch mission.
For an Isp of 1,200 seconds achieved, the required volume of hydrogen will be significantly reduce but, the use of extremely high-temperature carbide materials for the propellant heat exchanger will be necessary.
The Tether Propulsion uses a cable long of up to 100 kilometers to generate thrust without the use of a propellant.
An Electrodynamic tether thruster work by virtue of the force of a magnetic field exerted on a wire carrying an electrical current. Then, it uses an electrical current flowing in the orbiting wire (the tether) so that, the Earth’s magnetic field accelerates it and the payload attached to it. A spacecraft with an electrodynamic tether can expend electrical energy to boost its orbit, positive delta-V, or generate electrical energy by lowering its orbit, negative delta-V.
The challenge of the space industry is a prove of concept. To do so, Electrodynamic tethers require long tether systems of hundreds of meters to 100 kilometers, for more than 1 year with high-power systems in the range of 1 to 2 kW.
This technology provide a very high delta-V for small robotic spacecraft in LEO and any planet with a magnetosphere. It is a free use of propellant that can allow altitude and inclination changes for end-of-life disposal spacecraft and nearly-indefinite station keeping.
The momentum exchange tether is a rotating system with a mass on both ends connected by the tether. While the tether system rotates, the objects on either end of the tether experience continuous acceleration. The magnitude of its acceleration depends on the length of the tether and the rotation rate. Momentum exchange occurs when an end body is released during the rotation, providing one end mass with a positive delta-V and the other receiving a negative delta-V.
Momentum exchange occurs when an end body is released during the rotation. The transfer of momentum to the released object will cause the rotating tether to lose energy, and thus lose velocity and altitude. Using electrodynamic tether thrusting or ion propulsion, the system can then re-boost itself with little or no expenditure of consumable reaction mass.
Reusable, high-Isp and thrust, that system can be used for interplanetary travel as well as from Low-Earth Orbit to Geosynchronous orbit.
Source: NASA Technology Roadmaps TA 2: In-Space Propulsion Technologies, May 2015 Draft, NASA
Countdown milestones and key events that take place after the begins. Keep in mind that event times and lengths are approximate and subject to change.
T-720 minutes (12 hours until launch)
.Verify countdown clock is set with applicable holds
.Clear all non-essential personnel from Mobile Launcher Platform (MLP) for jacking .Pad Environmental Control System (ECS) preparations, including air-conditioning and gaseous nitrogen purge, are performed .Weather briefing
.Complex 41 and Vertical Integration Facility Area amber warning lights are turned on, indicating hazardous operations are underway
.Power on searchlights (if launch is set for night or early morning)
.Complex 41 and VIF track is cleared of non-essential personnel for MLP/Vehicle transport
.MLP transported to launch pad
.MLP hard down at pad
.Start Atlas system preparations to support cryogenic tanking
.Instrumentation checks are completed .Atlas liquid oxygen (LO2) system preparations are complete
.Hazardous Gas Detection System preparations are complete
.Internal battery checks are performed .Centaur liquid hydrogen (LH2) system preparations are complete
.Public Affairs announcement: All personnel clear complex 41 for cryogenic tanking
T-120 minutes and holding (30 minute hold)
.Launch Conductor receives reports on vehicle readiness for cryogenic tanking .NASA Launch Manager polls team to proceed with tanking
.Launch Conductor holds a pre-test tanking briefing
T-120 minutes and counting
.Start chilldown procedures on Centaur upper stage's liquid oxygen storage tank
.Start chilldown procedures on Atlas V's liquid oxygen vault and Mobile Launcher Platform
.Start Centaur helium bottle charge to flight pressure
.Begin raising Atlas Pressure Vessels to flight levels
.Raise Atlas V RP-1 fuel tank to higher pressure
T-115 minutes and counting
.Safe Arm Device (SAD) cycle test is performed
T-110 minutes and counting
.Start Centaur liquid oxygen transfer line chilldown
T-103 minutes and counting
.Start Centaur LO2 tanking
T-93 minutes and counting
.Pressurize Centaur liquid hydrogen storage tank to chilldown level
T-90 minutes and counting
.Start filling Atlas V with liquid oxygen
T-85 minutes and counting
.Start Centaur liquid hydrogen transfer line chilldown
T-60 minutes and counting
.Start Centaur engine chilldown
T-55 minutes and counting
.Start flight control final preparations to raise hydraulic pressures
T-45 minutes and counting
.Pressurize Main Engine Pneumatic System to flight pressure
T-16 minutes and counting
.Initiate fuel fill sequence
T-10 minutes and counting
.Weather briefing with Atlas Launch Weather Officer
T-5 minutes and counting
.Fuel fill sequence is complete
.Water deluge system actuation pressure adjustment is performed
.Atlas L02 at flight level
.Centaur L02 at Flight level
.Centaur LH2 at flight level
T-4 minutes and holding (10 minute hold)
.NAM and NLM final launch polls - go to continue countdown
.Spacecraft transfers to internal power
T-4 minutes and counting
.Hazardous gas monitoring is complete .Automatic computer sequencer takes control for all critical events through liftoff
.Atlas first stage LO2 replenishment is secured, allowing the tank to be pressurized for flight
T-3 minutes and counting
.Atlas tanks reach flight pressure
T-2 minutes and counting
.Atlas first stage and Centaur upper stage switch to internal power
.L02 and LH2 topping for Centaur will stop in 10 seconds
T-90 seconds and counting
.Launch control system is enabled
.IGNITION AND LIFTOFF OF THE ATLAS V!
Advanced Propulsion Technologies
Advanced Propulsion Technologies use chemical or non-chemical physics to produce thrust, but are generally considered to be of lower technical maturity.
These systems have the potential to provide new ways to reach beyond LEO, deliver more mass to destinations, provide ultra-high delta-V capability, process very high power levels, and enable rapid transit times to destinations deep in the solar system.
The Beamed-energy propulsion