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SP2018_016
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The SpaceDrive Project – First Results on EMDrive and Mach-Effect Thrusters
BARCELO RENACIMIENTO HOTEL, SEVILLE, SPAIN / 14 – 18 MAY 2018
Martin Tajmar(1), Matthias Kößling(2), Marcel Weikert(3) and Maxime Monette(4)
(1-4) Institute of Aerospace Engineering, Technische Universität Dresden, Marschnerstrasse 32, 01324
Dresden, Germany, Email: martin.tajmar@tu-dresden.de
KEYWORDS: Breakthrough Propulsion, Propellant-
less Propulsion, EMDrive, Mach-Effect Thruster
ABSTRACT:
Propellantless propulsion is believed to be the
best option for interstellar travel. However, photon
rockets or solar sails have thrusts so low that maybe
only nano-scaled spacecraft may reach the next star
within our lifetime using very high-power laser
beams. Following into the footsteps of earlier
breakthrough propulsion programs, we are
investigating different concepts based on non-
classical/revolutionary propulsion ideas that claim to
be at least an order of magnitude more efficient in
producing thrust compared to photon rockets. Our
intention is to develop an excellent research
infrastructure to test new ideas and measure thrusts
and/or artefacts with high confidence to determine if
a concept works and if it does how to scale it up. At
present, we are focusing on two possible
revolutionary concepts: The EMDrive and the Mach-
Effect Thruster. The first concept uses microwaves in
a truncated cone-shaped cavity that is claimed to
produce thrust. Although it is not clear on which
theoretical basis this can work, several experimental
tests have been reported in the literature, which
warrants a closer examination. The second concept
is believed to generate mass fluctuations in a piezo-
crystal stack that creates non-zero time-averaged
thrusts. Here we are reporting first results of our
improved thrust balance as well as EMDrive and
Mach-Effect thruster models. Special attention is
given to the investigation and identification of error
sources that cause false thrust signals. Our results
show that the magnetic interaction from not
sufficiently shielded cables or thrusters are a major
factor that needs to be taken into account for proper
µN thrust measurements for these type of devices.
1. INTRODUCTION
Interstellar travel is one of mankind’s biggest
dream and challenge. Rockets routinely put
spacecraft into Earth’s orbit, however Tsiolkovsky’s
equation puts a strong limit on the achievable v if
onboard propellant is used, even using advanced
materials and futuristic engines. For example, even
nuclear propulsion with a specific impulse of 10,000
s or more (nuclear pulse, combined electric/nuclear,
fusion propulsion, etc.) requires a propellant mass on
the order of the mass of our sun to propel a
spacecraft to our nearest star within our lifetime [1].
Recent efforts therefore concentrate on using
propellantless laser propulsion. For example, the
proposed Breakthrough Starshot project plans to use
a 100 GW laser beam to accelerate a nano-
spacecraft with the mass of a few grams to reach our
closest neighbouring star Proxima Centauri in around
20 years [2]. The technical challenges (laser power,
steering, communication, etc.) are enormous but
maybe not impossible [3]. Such ideas stretch the
edge of our current technology. However, it is
obvious that we need a radically new approach if we
ever want to achieve interstellar flight with spacecraft
in size similar to the ones that we use today. In the
1990s, NASA started its Breakthrough Propulsion
Physics Program, which organized workshops,
conferences and funded multiple projects to look for
high-risk/high-payoff ideas [4]. The project
culminated in a book that summarized the ideas
studied and presented a roadmap with unexplored
areas to follow up [5].
Within the SpaceDrive project [6], we are currently
assessing the two most prominent thruster
candidates that promise propellantless propulsion
much better than photon rockets: The so-called
EMDrive and the Mach-Effect thruster. In addition, we
are performing complementary experiments that can
provide additional insights into the thrusters under
investigation or open up new concepts. In order to
properly test the thruster candidates, we are
constantly improving our thrust balance facility as
well as checking for thruster-environment
interactions that can lead to false thrust
measurements.
Our goal is to falsify if these thrusters work as
claimed and to identify and understand the working
mechanisms that could enable to upscale them
towards flight applications. This paper will review the
first results so far.
2. SpaceDrive Project
2.1 Thrust Balance
Testing of propellantless propulsion concepts
requires a highly sophisticated thrust balance that
must be able to reliably detect very small thrust with
a resolution down to the nano-Newton range, block
electromagnetic interactions as much as possible
and limit any balance-vacuum chamber wall
interactions. Vibration and thermal expansion/drifts
are the two most important artefacts that must be
carefully isolated to obtain reliable measurements.
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The basis for our measurements is a torsion
balance in our large vacuum chamber (0.9 m
diameter, 1.5 m length) that has undergone various
improvements over more than 4 years. A thrust
produces an angular displacement that can be
measurement by a laser interferometer. We use two
C-flex E-20 torsion springs with a high enough
sensitivity (2x0.0033 Nm/) to achieve sub-µN
resolution while supporting enough weight on the
balance arms. The vacuum chamber uses a vibration
isolated Edwards XDS35i scroll pump and a Pfeiffer
2300 L turbo pump to reach a vacuum down to the
10-7 mbar range. For the tests on the EMDrive and
Mach-Effect thruster, only the scroll pump was used
with a vacuum level of 10-2 mbar, which was sufficient
to suppress buoyancy for quicker turnaround times.
The vacuum chamber is fixed to a separate concrete
block that is mounted with vibration isolation to
decouple it from the vibrations in the building’s
foundation (see Fig. 1). Based on our prior
experiments with Mach-Effect and EMDrive
thrusters, an upgraded balance has been built with
the following features:
- A total weight of up to 25 kg of thruster and
electronics can be installed on the balance.
There are two separately-shielded boxes on
each side: one for the thruster assembly and one
for the electronics and data acquisition.
- Thrust noise reduced to the nano-Newton range
with a sub-Nanonewton resolution. We use the
attocube IDS 3010 laser displacement sensor
with pm resolution to digitally read out the
balance position.
- Variable damping using eddy-currents and
permanent magnets. A stepper motor can
change the position of a copper disc to adapt the
strength of damping.
- Stepper motors to level the balance once it is
completely set-up inside the vacuum chamber.
- Stepper motors to change the orientation of the
thruster. This enables us to investigate e.g. shifts
in the center of gravity due to thermal expansion
by changing the thruster direction from forward to
backward and observing the change in the thrust
measurement. All this can be done inside the
vacuum chamber without breaking vacuum and
changing any cables that can influence the
analysis.
- Two different calibration techniques, one using a
voice coil and one using electrostatic combs that
provide constant thrusts by applying a defined
current (coil) or voltage (comb) which was
calibrated with a dedicated setup using a
Sartorius AX224 balance.
- Complete shielding of the balance arm and
thruster/electronics boxes using high
permeability Mu-metal.
- Wireless control of experiment by on-board data
acquisition using either Weeder modules or a
LabJack T7 Pro using an infrared serial port. This
allows analog input/output, digital control of
relays as well as temperature measurements on
the balance. In addition, we added infrared
cameras that can detect overheating of the
electronics and the thruster.
- Four pairs of liquid-metal-contacts with twisted,
paired cables to supply the balance and
experiments with power and other data signals
(see Fig. 2).
- LabView program that can operate and control
the complete vacuum facility, thrust balance and
experiments. A script language is used to
automate the whole experiment, from calibration
to measurement. This procedure ensures
repeatable measurements and allows to check
the validity of the balance calibration and perform
signal averaging and filter operation to obtain
very low noise signals.
A picture of the vacuum chamber as well as the
schematic of the balance is shown in Fig. 1. All
calibration and thruster experiments are executed
using profiles with a down-time (sector 1), a ramp-up
(sector 2), a constant thrust (sector 3), a ramp-down
(sector 4) and again down-time (sector 5) interval.
Each profile can be checked individually and data
processing like drift compensation or filtering can be
applied. Drift compensation can be done with many
different options like using a linear or polynomial fit
through sector 1 and 5 and subtraction from the
profile. Since the thrusters heated up during testing,
a thermal drift compensation technique was used
where first a linear fit is performed in sector 1 and 5
and a straight line is used to connect the end of sector
1 to the beginning of sector 5 to account for any
thermal drifts (see Fig. 5). Profiles can be repeated
many times and a signal averaged plot can be
computed that can drastically reduce noise and
increase signal confidence.
An example of a one µN calibration pulse is shown
in Fig. 3 using our voice coil. The low noise (<10 nN)
as well as the damping and drift elimination is clearly
evident. We performed calibration pulses along a
wide range with small steps as shown in Fig. 4 that
shows the high linearity of our balance. This figure
also shows how the calibration constant (µN/µm)
changes for different setups with different weights. A
calibration is automatically performed before and
after each thrust measurement to check for any
changes in the balance sensitivity.
2.1 EMDrive
The EMDrive is a concept developed by Shawyer
[7] in which microwaves are directed into a truncated
resonator cavity/frustum which is claimed to produce
thrust. He believes that the radiation pressure is
different at the small and large ends which results in
a net thrust force [8]. This was highly criticized as not
being compatible with electromagnetism and
conservation laws [9]. Alternative theories have
appeared [10]–[12], however, the community
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remains highly sceptical on the theoretical grounds of
this concept.
On the other hand, there is a significant amount of
experimental data available with tests both on a
normal/knife-edge [13],[14] as well as on a torsion
balance [15]–[17]. Initial concern concentrated on
buoyancy effects due to testing in air, however, the
more recent tests in high vacuum [17], especially
NASA’s latest test results by White et al [16] revealed
that air is not an issue. Several experimental artefacts
still need to be examined and higher quality thrust
data must be obtained in order to validate the
production of thrust. Thermal drifts were especially
significant in the latest reported test by White et al.
[16] and possible magnetic interaction with feeding
cables has yet to be assessed.
We built a frustum cavity with the same inner
dimensions as in White et al [16], however, instead of
hand-cut copper sheets and copper plated PCBs, our
cavity geometry was manufactured from 1.5 mm thick
copper sheets that were pressed into the correct
geometry (see Fig. 6). Afterwards, the inner surfaces
were polished. We used standard SMA/N-Type
connectors throughout all components. A picture of
our loop antenna (1.5 mm wire, 15 mm radius) is also
shown in Fig. 6 as well as the complete EMDrive with
cavity and all related electronics on one side of the
torsion balance. Because of the size of the cavity, we
could not encapsulate it yet with Mu-metal sheets to
reduce possible magnetic interactions. This will be
crucial in the next step as we will explain below.
The resonance frequencies and Q-factors of the
cavity were analysed using an Anritsu MS46121B
vector network analyser. Using a Maury 1878B 3-
stub tuner, we matched a frequency of 1865 MHz and
obtained Q-factors from 20,000 – 300,000+
(unloaded) depending on the peak (see Fig. 7). This
is similar and even higher than the values reported
by White et al [16] and should lead to at least similar
thrust values if not more as the Q-factor is believed
to be directly related to the generated thrust [7].
COMSOL simulations were carried out to simulate
the generated modes within the cavity and to find the
optimum position for the antenna (see Fig. 8).
The EMDrive setup is shown in Fig. 9 which
consists of a frequency generator/oscillator (Mini-
Circuits ZX95-2041-S+), a voltage-controlled
attenuator (Mini-Circuits ZX73-2500-S+), a 50 W
amplifier (RF Systems EMPower 1164), a bi-
directional coupler (Mini-Circuits ZGBDC35-93HP+)
with power-meters for input and reflected output
(Mini-Circuits ZX47-40-S+), an optional fixed 40 dB
attenuator (Mini-Circuits BW-40N100W+), the Maury
3-stub tuner and the cavity. All these components
could be operated in vacuum without modification (a
small venting hole was present in the cavity and one
screw was removed from the Mini-Circuits
components), however, we were cautiously operating
them only up to a power of 2 Watts to prohibit
overheating (several thermocouples are used to
monitor the temperature). The optional 40 dB
attenuator allows to reduce the power by a factor of
10,000 that goes into the cavity without changing
cables or setup. This provides a powerful “zero-
thrust” measurement capability. Our software
features resonance frequency tracking to
compensate for frequency shifts during operation.
Using the stepper motor, we could rotate the
thruster on our balance such that it points in different
directions. In our setup, 0° direction means a positive
thrust direction (going from the large back area on the
cavity to the smaller front area), 180° direction means
a reversed or negative thrust direction and 90° means
that the thruster points parallel to the balance arm,
which should result in zero thrust.
Fig. 10 shows thrust measurements for our
EMDrive in all directions with around 4 µN at an
amplifier power level of 2 Watts, which corresponds
to an amplifier current of around 2.5 A. The maximum
temperature on the amplifier was going up to 75
degrees. The Q factor in this case was 50,000
(unloaded). This leads to a thrust-to-power ratio of
around 2 mN/kW, which is nearly double compared
to White et al [16] who measured 1.3 mN/kW for a Q
factor of 40,900 (their absolute thrust value was 80
µN for 60 W of power). The thrust direction also
seems to reverse for the 180° direction. However, at
90° we see a similar thrust as in the 180° direction,
where we should expect zero thrust. Even more
importantly, if we keep the 0° direction but use the 40
dB attenuator to reduce the power that goes into the
cavity by 5 orders of magnitude, the thrust signal
nearly remains the same as without the 40 dB
attenuator.
This clearly indicates that the “thrust” is not
coming from the EMDrive but from some
electromagnetic interaction. Although we used
twisted or coaxial cables as much as possible, some
magnetic fields will eventually leak through our
cables and connectors. Considering the magnetic
field strength of the Earth’s magnetic field of 48 µT
with an inclination of 70° in middle Europe, a few
centimeters of cables and a current of 2 A (similar to
what is needed to power the amplifier), we obtain
Lorentz forces of a few µN, which is similar to our
observed “thrust” values. We therefore suspect, that
the interaction of the power feeding for the amplifier
with the Earth’s magnetic field masked any real
thrusts that could be below our observed value. In a
next setup, we are enlarging our experiment box such
that the cavity and amplifier configuration can be
completely shielded with Mu-metal sheets to greatly
reduce this artefact. However, such shielding was not
present in any of the previous tests (e.g. in White et
al [16]) which should be carefully re-analysed [18].
Note that we did not implement a dielectric disc
in our cavity so far which was used in the
configuration from White et al [16], although positive
tests were claimed to have been carried without such
discs too. After our setup improvement, we will try a
dielectric disc configuration, different geometries as
well as higher power levels.
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2.2 Mach-Effect Thruster
The second concept to be studied in detail is the
so-called Mach-Effect thruster which is being
developed by J.F. Woodward since the 1990s and
more recently by H. Fearn [19]–[22]. It is based on
one interpretation of Mach’s principle (inertia here is
due to mass out there), that inertial mass is due to the
gravitational interaction with the whole universe [23].
Woodward and others showed that linearized general
relativity theory with time-varying solutions and
Sciama’s analysis altogether leads to mass
fluctuations that can be up to 11 orders of magnitude
higher for typical devices than classically expected
from E=m.c² [24].
In the Mach-Effect thruster, a stack of clamped
piezo crystals is excited using a frequency in the tens
of kHz range. According to Woodward, this energy
oscillations leads to transient Machian-mass
variations that can lead to time-averaged stationary
thrusts if they are properly pushed and pulled with the
correct frequency and phase. This is believed to
happen thanks to the piezoelectric and
electrostrictive material properties of piezo crystals.
Although at much smaller amplitudes, electrostriction
happens at twice the applied frequency and at a 90°
phase shift, which is required for stationary thrust
[22],[24]. A large brass reaction mass can amplify this
effect. A schematic sketch of the thruster as well as
an actual thruster and a corresponding ANSYS
model is shown in Fig. 11. We are working on
analytical as well as finite element models to
accurately predict the oscillation movements on the
thruster (verified using laser vibrometry) in order to
predict and enhance the thrust produced.
In order to operate the thruster, we built an
amplifier based on the Apex PA04 amplifier that has
a frequency range of up to 180 kHz (measured in our
setup), 150 W and a voltage capability of 150 Vpp
(voltage and power may be doubled using two
amplifiers in bridge mode). This is significantly better
compared to the audio amplifiers used so far that cut
the power close to the thruster operating frequencies
(35 kHz) [22],[25].
Fig. 12 shows the frequency response spectrum
for a recent thruster supplied to us by Woodard and
Fearn. The first resonance frequency is at 31 kHz.
Our software can control the amplifier with various
options such as using arbitrary waveforms (sine wave
or e.g. mixed signals with single- and double-
frequency signals at a proper phase shift) using a
Picoscope 2405A oscilloscope that has an arbitrary
waveform output. The current, voltage and phase
signals are read back into the computer. Most
importantly, we implemented a tracker that adapts
the frequency e.g. to track for maximum current
(=power). We can therefore operate always at
resonance even if the thruster warms up during
operation, which causes resonance frequency shifts.
The thruster was mounted inside the
measurement box with Mu-metal shielding. The
amplifier electronics were outside, and a liquid-metal
feedthrough was used to power the thruster on the
balance. Fig. 13 shows thrust results in all three
directions (0°, 90° and 180°) for 150 Vpp and an
applied sine wave at 31 kHz in vacuum. The apparent
thrust has a value of 0.6 µN and indeed reverses for
180° and moreover also vanishes at 90° as expected.
However, when we moved the thruster box back to
the 0° direction and manually flipped only the thruster
to 180°, while leaving all power cables the same, the
thruster signal remained the same as in the 0°
direction. This again indicates that there must be
some electromagnetic interaction or thermally
induced center of mass shift that is masking any real
thrust value.
Woodward measured a steady thrust with this
thruster of around -1.2 µN for 400 Vpp as well as
large switching thrust transients during on-off.
Previous data suggests a V4 scaling of thrust with
applied voltage [21]. We therefore expect only 0.02
µN which may be present in our thrust data but
masked by electromagnetic/thermal issues. In a next
step, we need to increase our voltage and reduce our
thermal and electromagnetic interactions to safely
assess this thrust range.
3. Conclusions
The SpaceDrive project aims at developing
cutting-edge measurement equipment to thoroughly
test the latest EMDrive and Mach-Effect thruster
models, the two most promising revolutionary
thruster concepts that are presently under
investigation at various labs. Our thrust balances
shall provide the necessary resolution and
investigate electromagnetic and thermal artefacts to
obtain reliable measurements in order to confirm or
refute the claimed thrusts.
First measurement campaigns were carried out
with both thruster models reaching thrust/thrust-to-
power levels comparable to claimed values.
However, we found that e.g. magnetic interaction
from twisted-pair cables and amplifiers with the
Earth’s magnetic field can be a significant error
source for EMDrives. We continue to improve our
measurement setup and thruster developments in
order to finally assess if any of these concepts is
viable and if it can be scaled up.
In addition, a number of complementary
experiments are carried out to investigate e.g.
Machian-mass variations with an alternative rotary
setup [6].
At least, SpaceDrive is an excellent educational
project by developing highly demanding test setups,
evaluating theoretical models and possible
experimental errors. It’s a great learning experience
with the possibility to find something that can drive
space exploration into its next generation.
Acknowledgements
We gratefully acknowledge the support for
SpaceDrive by the German National Space Agency
DLR (Deutsches Zentrum fuer Luft- und
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Raumfahrttechnik) by funding from the Federal
Ministry of Economic Affairs and Energy (BMWi) by
approval from German Parliament (50RS1704). We
would also like to acknowledge the support from J.
Heisig, W. Stark, C. Holzapfel, J. Woodward and H.
Fearn for their contributions to the ongoing
experiments.
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Fig. 1 Vacuum Chamber on Concrete Block (Left) and Schematic Sketch of Thrust Balance (Right)
Fig. 2 Liquid Metal Contacts
Fig. 3 Voice Coil 1 µN Step Response (200 Profiles Averaged)
030 60 90 120 150 180
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0 Measured
Commanded
Force [µN]
Time [s]
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-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8
-15
-10
-5
0
5
10
15
K=19.7 µN/µm
Force [µN]
Displacement [µm]
Fig. 4 Calibration Linearity: 0.25 µN Steps (Left) and Different Slopes for Different Setups/Weights (Right)
Fig. 5 Thermal Drift Compensation: Original Thrust Profile (White) and Drift Compensation Fitting Line
(Blue) – Left, Compensated Thrust Profile without Thermal Drift – Right
Fig. 6 EMDrive Thruster: Cavity (Left), Antenna (Middle) and On Balance (Right)
0 1 2 3 4 5 6
0
10
20
30
40
50
60
K1=9.9 µN/µm
K2=23.3 µN/µm
Force [µN]
Displacement [µm]
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Fig. 7 Cavity S11 Reflection Plot from Vector Network Analyzer (Matched 1865 MHz via 3-Stub Tuner)
Fig. 8 EMDrive COMSOL Simulation (TM212@1971 MHz – Left, TE012@2179 MHz – Right)
Fig. 9 EMDrive Setup
1.8 1.9 2.0 2.1 2.2
-60
-50
-40
-30
-20
-10
0
Reflected Power [dB]
Frequency [GHz]
Q5x104
SP2018_016
Page 9
(a) Direction 0°
(b) Direction 180°
(c) Direction 0° with 40db Attenuator
(d) Direction 90°
Fig. 10 EMDrive Thrust Measurements with 2 W in Vacuum (10-2 mbar), 40 Runs Averaged
... Aluminum
End-Cap
Brass
End-Cap PZT
Epoxy Electrode (Ground)
Electrode (~)
Thrust
Screw
Support / Thrust Balance
(Ground)
Rubber Pad
Aluminum
End-Cap
x
Clamping
Fig. 11 Mach-Effect Thruster (MET): Schematic Sketch (Left) [24], Thruster under Testing (Middle) and
ANSYS Model (Right)
050 100 150 200 250 300 350 400 450 500
-10
-8
-6
-4
-2
0
2
4
6
8
10 Force
Amplifier Current
Force [µN]
Time [s]
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Amplifier Current [A]
050 100 150 200 250 300 350 400 450 500
-10
-8
-6
-4
-2
0
2
4
6
8
10 Force
Amplifier Current
Force [µN]
Time [s]
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Amplifier Current [A]
050 100 150 200 250 300 350 400 450 500
-10
-8
-6
-4
-2
0
2
4
6
8
10 Force
Amplifier Current
Force [µN]
Time [s]
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Amplifier Current [A]
050 100 150 200 250 300 350 400 450 500
-10
-8
-6
-4
-2
0
2
4
6
8
10 Force
Amplifier Current
Force [µN]
Time [s]
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Amplifier Current [A]
SP2018_016
Page 10
Fig. 12 Mach-Effect Thruster Spectrum
(a) Direction 0°
(b) Direction 180°
(c) Direction 90°
(d) Direction 180° - Only Thruster Rotated
Fig. 13 MET Thrust Measurements in Vacuum (10-2 mbar) at 150 Vpp, 200 Runs Averaged
30 45 60 75 90 105
0.00
0.02
0.04
0.06
0.08
0.10
30 45 60 75 90 105
-100
-75
-50
-25
0
25
50
75
100
RMS Current [A]
Frequency [kHz]
Phase [°]
Q = 27
f = 62.7 kHz
Q = 21
f = 31.4 kHz
Q = 38
f = 89.7 kHz
030 60 90 120 150 180
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8 Force
RMS Voltage
Thrust [µN]
Time [s]
-60
-40
-20
0
20
40
60
Voltage RMS [V]
030 60 90 120 150 180
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8 Force
RMS Voltage
Thrust [µN]
Time [s]
-60
-40
-20
0
20
40
60
Voltage RMS [V]
030 60 90 120 150 180
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
Thrust [µN]
Time [s]
Force
RMS Voltage
-60
-40
-20
0
20
40
60
Voltage RMS [V]
030 60 90 120 150 180
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8 Force
RMS Voltage
Thrust [µN]
Time [s]
-60
-40
-20
0
20
40
60
Voltage RMS [V]
