External Propulsion Overview White Paper

Escape Dynamics Inc.
9596 Metro Airport Ave. Broomfield, CO 80021
Phone: 303-640-6702, Web: www.escapedynamics.com
Overview of External Propulsion Launch System
EDI’s primary objective is to develop a rapidly reusable, single-stage-to-orbit (SSTO) launch system and introduce space access
solutions to customers at a price point 10x below the cost of current alternatives.
1. General System Description
Escape Dynamics is developing external microwave propulsion
technology that allows reusable single-state-to-orbit space flight. In
external propulsion all or part of the energy necessary for launch is
coming from the ground in the form of a focused microwave beam
allowing a dramatic increase in efficiency of propulsion compared to
chemical rockets and enabling engines with specific impulse above
750 seconds.
Escape Dynamics’ baseline technology uses a wireless energy transfer
system based on millimeter-wave high power microwave sources.
The baseline frequency is 92 GHz; however, other mm-wave
frequencies (90-170GHz) are also considered. The energy is delivered
to the moving vehicle via a phased array of antennas enclosed in proprietary side-lobe suppressing radomes, which ensure
safety of the energy transfer.
Our baseline propulsion approach is a thermal thruster which uses hydrogen as a working fluid and a heat exchanger for
coupling external microwave energy into the thermal energy of the hydrogen. External microwave energy is absorbed in a
ceramic matrix composite (CMC) heat exchanger with dimensions of approximately 3m by 5m. The hydrogen is initially stored
as a liquid in a cryogenic tank and is supplied to the heat exchanger via a turbopump designed to raise the hydrogen’s pressure
to approximately 150atm. The hydrogen is heated to above 2000C as it flows through the heat exchanger and is exhausted
through an aerospike nozzle optimized for a SSTO flight. The heat exchanger also serves as a primary component of the
thermal protection system (TPS) during the return from orbit.
Copyright: Escape Dynamics Inc.
Based on our current design and thrust tests, thermal thrusters can achieve vacuum specific impulse of 750-850 seconds and
are the simplest of all methods for coupling external microwave energy into thrust. The specific impulse of 750-850 seconds is
consistent with single-stage-to-orbit operation and allows for a propellant mass fraction below 72% thereby enabling a path
to full and rapid reusability. Our thermal thruster approach allows useful payload fractions between approximately 8% and
12%. In comparison, chemical rockets today are limited to Isp of approximately 450 seconds, are completely or partially
expandable, and typically operate with useful payload fractions of 1.5%-3%.
Escape Dynamics is also developing a next generation system, which relies on the direct heating of plasmas flowing through a
resonant cavity with a weight similar to that of the weight of the heat exchanger in a thermal thruster. The goal of this
development is to allow operation with specific impulse above 1,500 seconds, leading to propellant mass fraction below 50%,
which is comparable to airplanes.
In the baseline mission, the launch vehicle is taking off vertically from
a dedicated space port equipped with a high power microwave
launch array (L.A.) which powers the vehicle through the initial part
of the trajectory and in which the focusing of millimeter-wave
microwave energy is optimized for a 50-100km range. As the launch
vehicle reaches the handoff point, the booster array (B.A.), located
approximately 200-250km downrange, is activated and provides the
power necessary for orbital acceleration. The booster array is
optimized for a 350-450km range and accelerates the launch vehicle
to orbital velocity.
External propulsion also enables an alternative approach in which
the vehicle is powered with a hybrid thruster up to an altitude of 50-100km and does not require a take-off array for the initial
acceleration, but only uses external microwave energy during the booster phase of orbital acceleration. The hybrid two stage
approach has the potential to reduce the cost of the ground-based infrastructure and make the system more versatile,
however, it also introduces additional complexity into the design. We can envision scenarios where both two stage and SSTO
technologies are implemented and deployed.
The vehicle is released from the booster beam at a design altitude ranging from 200km to 400km. At the peak velocity, a
payload is released from the payload bay with a mechanical deployment mechanism. In most cases the payload will be
equipped with a secondary propulsion system designed to provide a small Δv (e.g., 200 m/s) needed to achieve the desired
orbital trajectory. The acceleration to orbital velocity will take approximately 300-400 seconds during which the payload will
experience up to 7g of acceleration with thrust-to-weight ratio at take-off around 1.25 and average acceleration throughout
the trajectory of 3.5g.
For our first reusable single-stage-to-orbit launch system, we are optimizing the design to require minimal possible power on
the ground with a current baseline of approximately 300-400MW of antenna output power for both launch and booster arrays.
With the projected 50% efficiency of high power microwave sources, 400MW of output power would require 800MW of power
taken from the electric grid. This power will be buffered at a substation at the launch site and released during approximately
300 seconds (1/12 of an hour) of powered ascent, leading to the total of approximately 65MWh of electrical energy consumed
from the energy storage substation1. The storage-based grid-tie in solution is a proprietary technology invented at Escape
Dynamics that dramatically transforms the economics of external propulsion reducing the cost of grid tie-in from $100’s of
millions of a more standard AC-DC approach to $10’s of millions per array.
Both take-off and booster arrays are phased arrays of microwave antennas operating in mm-wave frequencies with the
baseline frequency of 92 GHz. The frequency of operation is determined by atmospheric transparency, focusing efficiency and
cost of manufacturing of both the microwave sources and the wireless energy transfer arrays. Steering of the beam is
accomplished via both phase-adjustment of antennas in the array and mechanical steering of the antennas. Based on in-house
design and cost/performance optimization, we are currently focused on w-band high power microwave (HPM) emitters with
approximately 500kW output per unit. One or several HPM emitters feed phased-controlled microwave energy into an antenna
surrounded by a side-lobe suppressing radome. The techniques used in phased-controlled beam combining, although
1
65MWh ≈ 800MW·1/12h is the amount of energy needed for launch.
Copyright: Escape Dynamics Inc.
challenging, have been proven and advanced in plasma physics and fusion research with beams from multiple 1MW-class
gyrotrons successfully combined. The effective diameter of each antenna is 8-12 meters and the focusing of energy is achieved
through a packed phased array with several hundred elements. The booster array is designed to cover an area with effective
diameter of 750-1000 meters required for efficient focusing of the microwave energy during orbital acceleration. The efficiency
of the energy transfer from the antennas to the launch vehicle through the entire trajectory changes from above 45% during
the take-off and initial acceleration to 12-20% during the final stages of launch.
The weight of our launch vehicle is largely determined by the dry mass of key engine components, such as the heat exchanger,
the cryogenic tank, turbopump, nozzle, vehicle’s structure and controls equipment. Our goal is to build the lightest possible
vehicle capable of launching up to 200kg payloads in low Earth orbit, flying single stage to orbit and being reusable for multiple
flights. The current baseline weight of the vehicle w/o fuel and payload is 750-850kg. The final weight of the vehicle will be
determined after completion of mechanical analysis, aerothermal studies and the engine test program currently underway. It
is important to note, that increase in weight can be accommodated by increasing the amount of ground-based microwave
power with every additional kg of wet mass requiring approximately 250kW of additional power on the ground.
The vehicle is designed to return from orbit as a light-weight glider after the payload is deployed and the vehicle completes
one or several orbits around Earth. During reentry, the heat exchanger serves as a thermal protection system (TPS) and can be
cooled if needed with small amounts of hydrogen from the tank. The heat of reentry could also be used to operate thermal
thruster engine thus enabling greater degree of control over the reentry path. Note that the thermal loads on the heat
exchanger caused by microwave-powered launch are higher than the loads experienced during reentry and hence the heat
exchanger designed to withstand externally-powered launch is well-suited for reentry and reusability. The vehicles are
designed to land at the spaceport with horizontal landing using either landing gear or skids.
2. Key benefits of external propulsion
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Space launch vehicles become fully and rapidly reusable.
Cost per launch can eventually be reduced to $150 per kg.
The need for combustion is eliminated, leading to safer and simpler launch vehicles.
Useful payload fraction goes up from 1.5-3% to 8-12% and the structural mass is increased by 1.5-2x.
Small satellites can be launched as primary payloads allowing higher degree of flexibility for customers.
Space launch is effectively powered with electricity from the grid through a battery-storage system pioneered by the
company, and in the long term can rely on renewable sources of energy.
Copyright: Escape Dynamics Inc.