DIRD Cockpits in the Era of Breakthrough Flight

Cockpits in the Era of Breakthrough Flight

Defense Intelligence Reference Document, Defense Futures. DIA-08-1011-002, 1 November 2010. IcOD: 8 July 2010.

Prepared by the Defense Intelligence Agency. This product is one in a series of advanced technology reports produced in FY 2009 under the Defense Intelligence Agency Advanced Aerospace Weapon System Applications (AAWSA) Program.

Administrative note — copyright warning: further dissemination of the photographs in this publication is not authorized.

Introduction

Responding to the request to explore forefront science relevant to future cockpits for any form of aerospace craft and/or deep-space craft that is propelled by any unspecified advanced or breakthrough propulsion physics, this report offers a provisional cockpit design that employs the following:

• Predictions of propulsion physics breakthroughs.
• Lessons of human-machine interface.
• Emerging technology for displays and controls.

This study discusses the implications of breakthrough propulsion, including the mastery over gravitational and inertial forces and the prospect for faster-than-light spaceflight. The main reference used to predict these possibilities is the book Frontiers of Propulsion Science [Millis and Davis, 2009]. Although the breakthroughs discussed in this book are not imminent, enough progress has been made to allow for thoughtful speculation about their characteristics and possible implementations.

How these advances may affect future cockpits is described, and this is the central message of this study. The most significant differences from legacy cockpits are identified and then used to set the baseline design requirements.

Additionally, substantial lessons about human-machine interfaces are reviewed and applied to this notional cockpit. Most of this progress relies on better accommodating the norms and limitations of human perception — lessons that do not change even when vehicle characteristics change.

Recent advancements in the use of hand gestures for commands are also included, as well as advancements in brain-machine interfaces. In this conceptual study of far-future possibilities, these technologies are assumed to have reached full maturity, with one exception: in order to focus this study on future cockpits, the options for brain implants and for transhumanism — where humans are reengineered to adapt to new requirements — are not considered.

Next-step investigations are suggested to refine the ideas presented herein. A caveat is that advances in cockpits for breakthrough flight might be further advanced by taking advantage of the gaming industry techniques or through science fiction speculation.

Note: All projections in this report are based on public domain information.

Chapter 1: Predicting Implications of Propulsion Breakthroughs

March of Progress: Revolutionary Propulsion Physics

Breakthroughs in propulsion physics (such as the control over gravitational or inertial forces, propellant-less space drives, and even faster-than-light travel) are not imminent; however, enough progress has been made to allow for thoughtful speculation about their nature and implications. As a preview, the implications to cockpit design include added degrees of motion, combination of operational regimes (near ground, orbit, and beyond), greater range of speed (from zero-speed hover to beyond light speed), and loss of familiar motion cues (pilot's inertia and visual cues) resulting from the separation of external and internal environments.

The primary reference used to predict these possibilities is the book Frontiers of Propulsion Science [Millis and Davis, 2009], particularly chapters 3, 4, and 15. This book may be the first-ever scholarly compilation of science pertaining to breakthrough flight — methods sufficiently advanced to enable human voyages to other star systems. The book examines a wide range of works, offering introductory explanations and comparisons between approaches and identifying high-priority unknowns needing deeper study. References to specific ideas and issues cite that book and other original works.

Setting Ideal Performance as Design Target

This report focuses on the most significant likely differences between contemporary cockpits and cockpits in the era of breakthrough flight. Possibilities that imply the most demanding changes are considered first and explanations of the correlations between the propulsion characteristics and resulting cockpit features are provided. Looking to the far future, this study evaluates the impact of having achieved the following breakthrough advancements:

• Control over gravitational and inertial forces:
  • The craft is propelled by interacting with the properties of the space-time and/or inertial frames surrounding the craft — and can accelerate at g levels beyond human endurance.
  • The environment inside a craft can be sustained anywhere between 0 g and 1 g (minimum range) without regard for either the motion of the craft or its outside gravitational environment.
• Faster-than-light (FTL) speeds are possible by having mastered control over those aspects of nature that impose the light-speed limit. However, due to reasonable relativistic projections of the energy required for propulsion coupled with the limits of the human lifespan, it is reasonable to expect that travels will be limited to within our galaxy. For the sake of bracketing the scope of coverage, this study assumes that practical star flight will be limited to a 100-light-year radius around our Sun. Even with this constraint, thousands of star systems are within that range.
• The energy supply for these features resides on the vehicle and is considered to have a dynamic interplay with the motion of the vehicle. The energy can be transferred to and from the environment surrounding the craft as a consequence of the propulsive maneuvers.

Sanity Check on Predictions

Objectively, the propulsion physics predictions offered in this report should be interpreted as informed conjectures or, at best, well-reasoned speculations. Absent of verified theories and engineering implementations, it is premature to consider this first study as the last word on this topic. Further progress will likely reduce the span of options and provide greater insight into implementation details.

It must also be stressed that these interpretive predictions and cockpit implications are solely generated by the author and, thus, have not yet been published or debated with other scientists and engineers. Therefore, the reader should consider these predictions to be an initial step into the process.

Vehicle and Cockpit Implications

Ideally, it is desirable to have a vehicle that can move in any direction, at any speed, in both air and space, without limitations. These features imply the need to have technological mastery over the forces of gravity and inertia and mastery over those aspects of nature that impose the light-speed limit. Based on projections of the underlying physics, such abilities would have secondary characteristics that affect how such motions are monitored and controlled.

Degrees of Freedom

Unlike an aircraft, whose motion consists basically of deviations from constant forward motion, or a helicopter, whose motion is dominated by the dynamics of its main rotors, a breakthrough propulsion vehicle would allow the full six degrees of freedom, including the ability to remain fixed relative to a desired reference. For example, if we start with the situation of a vehicle hovering over the ground, the breakthrough vehicle should be able to change its orientation (yaw, pitch, or roll) without affecting its altitude or lateral position. Similarly, it should be able to move up and down or laterally without the need to induce pitch or roll maneuvers.

Such novel motion leads to two major differences from legacy cockpits:

• Independent control inputs are needed for the full six degrees of freedom (yaw, pitch, and roll; and laterally, x for fore and aft, y for left and right, and z for up and down).
• New display methods are required to convey position, orientation, and motion for all those degrees of freedom.

The control methods need not copy legacy methods from airplanes or helicopters — methods that are based on the mechanisms of their origin. Instead, future cockpit designs are now free to use control methods tailored to the natural action and reaction of pilots, while the vehicle's interfaces perform the function of converting pilot inputs to drive the vehicle's motion. Whether such a system consists of a single joystick with six degrees of freedom, some sort of gesture-based system, or one that has those degrees of freedom dispersed across multiple pilot inputs (for example, head motion, legs and feet, and arms and hands) remains open for future study. As a provisional baseline, this report chooses the option of having a pair of six-degree-of-freedom joysticks, one for both the left and right hands and located at the edge of the cockpit chair's arm rests.

Figure 1. Six Independent Degrees of Freedom. Three equally available rectilinear axes of motion; three equally available rotational axes of motion. Note: the vehicle shown is strictly hypothetical and is a combination of three 1960s science fiction vehicles: Seaview submarine, Galileo shuttle, and Amtronic car.

Similar to requiring new control methods, new display methods are also required to convey more information than in legacy cockpits. In addition to the complete six degrees of freedom, these motions will take place near the Earth's surface, in orbit, and in deep space. A key difference spanning those regimes is the traditional role played by a gravitational field as a reference for orientation and motion. Since a gravitational reference will not always be present, and yet is extremely important when it is present, the new display system must accommodate all regimes in a way that feels natural to the pilots. These particular challenges are addressed in the section on Mixed Operational Regimes.

Separation of Internal and External Environments

Probably the most significant and perplexing difference for breakthrough-era cockpits is that the sensations of motion inside the vehicle will not necessarily match the motion of the vehicle itself. This is both a consequence of the method of propulsion as well as cockpit features designed to ensure crew survival.

As illustrated in Figure 2, when planning for breakthrough flight, there is no need to constrain designs to match the legacy conventions derived from prior vehicles. In the case of both the airplane and the helicopter, the control inputs available to the pilot are specific to the mechanisms of the control surfaces. When projecting breakthrough flight, it is assumed that the controls will be tailored to match the natural characteristics of pilots, and the propulsion system will be designed to perform accordingly.

Figure 2. Comparing Conventions of Aircraft Motion. 2A, airplane motion: aircraft motion is dominated by forward motion at roughly constant airspeed, and lateral displacements are induced by changing the direction of the aircraft. 2B, helicopter motion: motion is dominated by the dynamics of the main rotor. 2C, ideal full motion: motion is equally available in all directions and orientations, with the vehicle able to change orientation without affecting its position, and to change position without changing its orientation.

To make this easier to grasp and to provide a provisional concept, imagine that the vehicle is partitioned into concentric sections as shown in Figure 3. The central volume is for the crew, where it is required that the gravitational and inertial forces be sustained within survivable levels. The inner shell, or inner hull, surrounding that region contains whatever devices provide that safe environment. The outer shell contains the propulsion devices that induce the desired motion of the craft relative to the external space. The region between the two hull shells is a provisional separation for analyzing the interaction between those two functions.

Figure 3. Necessary Distinction Between External and Internal Force Environments. The crew cabin, where inertial and gravitational forces are maintained at normal, safe conditions; the inner shell, whose devices provide a safe internal force environment; the outer shell, whose propulsion interacts with the external environment; and the coordinate system of the external environment.

For analytical purposes, it is advantageous to consider these volumes and control surfaces (the hull shells) as separate and then use them to define boundary conditions. In addition to its utility for assessing future cockpit designs, this multisectioned vehicle baseline is valuable for gedanken experiments about revolutionary propulsion concepts.

Why This Is Odd

Conventionally, gravitational and inertial effects permeate through everything, so the notion of having different conditions inside and outside of the craft runs contrary to experience. If the gravitational environment outside the craft is 1 g, that same 1 g is expected inside as well. Similarly for accelerations, the entire mass of the vehicle, including its occupants, will experience the same inertial reactions as the vehicle accelerates.

Upon the advent of breakthrough propulsion, mastery over gravitational and inertial forces will have been achieved. This implies, for example, that it is possible for a vehicle to accelerate at extreme g's while its crew remains within survivable limits or that, while cruising in deep space (absent of any acceleration or gravitational field), the crew can enjoy the familiar, constant 1 g upward.

Because such possibilities run so contrary to established experience, it is difficult to comprehend how such things can be achieved and then contemplate the consequences that these advances impose onto other systems of the vehicle — in this case, how they affect cockpit designs. Not all known approaches to propulsion physics evoke the need for a double hull. Versions that simply suggest a new thrusting mechanism and reaction mass would only need the double hull if also addressing how to provide a safe acceleration environment for the crew. As stated earlier, however, the most significant possible impacts are considered for this study. Therefore, two examples are described next for how breakthrough propulsion would require this provisional double-hull configuration.

Why Double Hull Needed: Example 1 (Warp Drive)

The Alcubierre warp drive, which uses the physics from the Riemannian geometry of Einstein's general relativity, creates a "warp bubble" around the craft, and then this bubble of space-time is moved through the surrounding space-time. This effect is created (in theory) by expanding space-time behind the vehicle and contracting space-time in front. The vehicle within the bubble feels no acceleration forces. As illustrated in Figure 4, the high peaks represent expanding space-time, while the low peaks represent contracting space-time. Note that the inner region is flat (meaning that the vehicle does not experience any acceleration forces), that the region far from the propulsion effect is also flat, and that these two regions are separate.

Figure 4. Warp Drive. Taken directly from the Frontiers book, this image has become the iconic representation for a warp drive: the "York Extrinsic Time Plot."

In theory, the outer shell is presumed to create the propulsive effect of warping space-time outside the craft without affecting the inside. In short, the Alcubierre warp drive creates a separation of space-time environments inside and outside of the craft, although the exact details remain uncertain.

Although there is no explicit function for the inner hull in this situation, this Alcubierre warp drive at least illustrates the concept of separation of these outer and inner environments. When planning future cockpits, the outer and inner inertial frames need to be treated as two distinct zones. The physics related to such considerations is still evolving and beyond the scope of this report.

Why Double Hull Needed: Example 2 (Field Space Drive)

Another class of conceptual propulsion is a "field drive" — a subset of "space drives" where a spacecraft is propelled using only the interactions between the spacecraft and its surrounding space. Instead of using the Riemannian geometry of Einstein's general relativity, these approaches use the physics of fields and scalar potentials. While several variants exist, the "Bias Drive" concept is selected here to illustrate the relevance of the double-hull configuration, specifically in the context of modifying the scalar potential that defines an inertial frame. By altering the properties of the surrounding inertial scalar, a gradient in that scalar is induced which, in turn, induces gravitational-like forces on matter located in that gradient.

Figure 5 represents one version of this effect, where the vehicle and its contents would be located at the steep gradient and therefore would jointly experience acceleration forces. Taken directly from the Frontiers book, this image represents what would happen if it were possible to asymmetrically modify Newton's gravitational constant to induce gravitational gradients that would then, in turn, accelerate the vehicle. Despite the similarity to the distortions in the warp drive (Figure 4), these surfaces represent scalar potentials of gravitational fields. Figure 6 is a modified version of this where the double-hull configuration of Figure 3 is imposed, along with the condition that the inner region remains unaffected. In Figure 6, the locations of the inner and outer shell are identified on the figure. The notion of the gravitational bias drive has been modified here to illustrate the concept of having two separate zones of inertial and gravitational forces. In this case, the plotted surface represents a scalar potential of an inertial frame, where a gradient has the same effect as a gravitational field. The smaller central flat area is the inside of the vehicle where no acceleration forces are felt. The outer edges of the diagram are also flat, representing the unaffected space sufficiently far from the propulsive effect. The distorted regions in between represent the effects of both the outer and inner hull shells. The outer hull shell induces a gradient that propels the vehicle, and the inner shell acts to prevent those distortions from reaching the crew cabin. It should be emphasized that these notions are at the level of thought experiments, as opposed to being mature theory.

Figure 5. Hypothetical Gravitational Bias Drive. (a) Multiplicative modification. (b) Exponential modification.

Figure 6. Inertial Frame Bias Drive and Vehicle Zones, showing the outer hull and the inner hull.

In short, this Inertial Frame Bias Drive has affected the space both outside and inside of the craft to propel the vehicle and to keep its crew isolated from the resulting acceleration forces. For example, if the outer hull creates a 10-g field outside the craft, the inner hull would compensate to create an opposing field such that the crew cabin is free of the 10-g acceleration forces. It can, therefore, be speculated that — if such field-affecting physics is discovered — the inner shell could create a 1-g field when the craft is coasting in 0-g deep space.

To be explicit, the physics and engineering to create such situations do not yet exist. The related physics can be categorized as still being at steps one and two of the scientific method: defining the problem and collecting data. Among many other issues eluding discovery and resolution, major issues include momentum conservation, the role played by inertial frames, and methods to affect gravitational and inertial properties of matter and space.

Secondary Consequences

Pertinent to cockpit design, the normal sensations of motion inside the cockpit will likely not be the same. In contrast to the advantage of shielding the crew from harsh maneuvers, this shielding removes sensations of motion (seat-of-pants feeling) that pilots use to help judge the motion of their vehicle. This detriment is compounded by the likelihood of inducing motion sickness, since the visual cues of the vehicle's real motion will be different from that felt by the pilot. A difference between visual and vestibular cues is a cause of motion sickness. The option of allowing a certain portion of the vehicle's g-loading to be transferred to the cockpit can be considered as a mitigation strategy. Accordingly, cockpit controls to affect such changes are required.

Also, it is likely that this double-hull notion would prevent direct visual contact between the occupants and the environment outside the vehicle, or perhaps distort such visual cues beyond easy interpretation. In other words, do not expect windows. Without the familiar visual and vestibular cues directly available to the pilot, it becomes vitally important for the cockpit displays to provide reliable and instinctive cues for the pilot to aptly judge the position, orientation, and motion of the vehicle.

Mixed Operational Regimes

A major desirable feature sought from propulsion breakthroughs is the ability to move from the surface of the Earth directly into space. This implies that the vehicle's displays and controls must readily encompass motion near the Earth's surface, ascent into space, transitions into and out of orbits, and long-duration sustained cruising in a zero-g environment.

As alluded to earlier, this deviates from prior displays where the Earth's gravitational field is available from which to gauge orientation. Similarly, the notion of an altimeter takes on a whole new meaning in this context. While visual cues for "up" are instinctively clear near the surface of the Earth (or even in closed rooms where 1 g is present), for a true breakthrough vehicle, these will be special conditions amongst a greater span of possibilities.

A particular consequence of these added operational regimes is that unfamiliar situations are presented that must be made easy for the pilot to comprehend. Human instincts of motion and perception are honed from living in a 1-g environment with the majority of motions constrained to the (comparatively) two-dimensional ground. Also, lacking eyes in the back of our heads, our natural sense of attention is focused forward. While these instinctual characteristics serve well in travel near the ground, they do not apply to orbits or to deep-space flight.

Orbit

Orbits around the Earth — or any gravitating body, for that matter — present stable, constant energy situations. Orbits are convenient parking locations. A vehicle does not need to expend energy to stay in orbit indefinitely (unless drag forces from the atmosphere or long extensions of the vehicle come into play). Orbits, therefore, are common trajectories to select when loitering near gravitating bodies. But so far in the course of human evolution, developing an innate sense of placing a vehicle into an orbit does not exist. Although a human can instinctively run at just the right speed and direction to catch a ball thrown toward them, such natural instincts do not apply to placing a vehicle in orbit. Therefore, display systems will be required to provide readily interpretable cues for the pilots to transition into orbital flight. This implies presenting the natural relations between orbital altitude and orbital speed. This challenge is compounded since such cues must naturally blend with the motion cues used when flying near the surface.

Deep-Space and Interstellar Flight

Deep-space flight adds yet another challenge; namely, the almost total absence of familiar cues for motion, position, and orientation. Given the extremely large distances between astronomical objects and that relativistic effects do not become significant (distortions above 1 percent) until reaching beyond 10 percent of light speed, the view outside the craft will appear stationary — even when traveling at 60 million miles per hour (9 percent of light speed). The display systems that are tied to the navigation references (to be discussed later) must convey motion to the pilots in a natural manner despite the absence of familiar human cues.

Compounding the absence of a sense of motion, there is an absence of orientation. There is no dominant direction for "up" during deep-space flight. If some form of artificial or synthetic gravity is provided for long-duration crew health, then that internal 1 g will create the most dominant sense of "up" for the crew, and the display system that conveys the spacecraft's orientation relative to the external space will have to be clear enough to overcome this prejudicial sense of orientation.

Notice, for example, that in almost all science fiction stories, spacecraft move laterally (forward) relative to the vehicles' internal sense of "up". Motion along the z-axis is seldom mentioned. Although this is a natural extension of how we move relative to the surface of the Earth, it is not the only scenario. In contrast, consider a rocket whose 1-g orientation is aligned with its major axis of motion. This is a consequence of its propulsive thrust. In other words, at least two conventions for direction during deep-space flight are possible: the notion of lateral motion across a landscape (where the internal 1 g is at right angles to flight), or vertical motion with an astronomical range (where the internal 1 g is coincident with the direction of flight).

Conveniently matching film studio conditions, the interiors of fictional spacecraft provide a comfortable 1-g environment for the crew. They also follow the terrestrial convention of motion: their major direction of motion is forward (a lateral motion), even though they are experiencing an acceleration force of 1 g upward (their internal, synthetic gravity). These two directions, up and forward, are at a right angle. In contrast, the thrusting direction and the internal g-axis of a rocket are in the same direction. The choice of orientation for real deep-space motion is a subject for further study.

Figure 7. Typical Science Fiction Orientations.

Since propulsion breakthroughs have not yet been discovered, there is no way of knowing if the propulsion methods themselves will dictate the choice of orientation. Therefore, to plan for the uncertain future, this is a choice worthy of deeper study. Is the natural human instinct for forward-dominated motion a better human-machine interaction than the upward-dominated motion that might be dictated by the propulsion method? Such an assessment must also consider how well the convention works when transitioning from deep-space flight into orbit, then landing, and then back again to deep-space flight. Once any convention is set into place, it will be difficult to change later.

Crew Size Considerations

The last aspect to take into account as a consequence of mixed operational regimes is that of the crew size. For short-duration missions (under a few hours), it is reasonable to conceive of vehicles with only one pilot. For more complex missions, additional crew will be required, and thus additional displays and controls specific to their tasks will be required. Finally, for long-duration missions, sufficient crew will be required to carry out its mission and maintain optimal vehicle performance. These changes — for accommodating the roles and responsibilities of crew in relation to the overall mission — are likely to be the same as those distinctions in traditional vehicles (for example, cars versus cruise ships). Those changes typically include a hierarchical organization, which is independent of the issues of propulsion physics.

Essential elements will include monitoring and controlling the 1-g internal life-support environment as well as ensuring the long-term health of the crew.

Full Span of Speeds

In addition to inertial effects previously addressed, the implications due to high speed remain. Accommodating the reaction time of the pilot is critical. The extreme high speed of breakthrough spacecraft will demand that automated flight controls take precedence over the pilot's manual flight control.

Automated controls for aircraft and even for automobiles are an ever-improving technology. For breakthrough flight, these technologies will be mandatory and will also have to include options for maneuvering near ground, into orbits, and through deep space. This should come as no surprise, since the advantages of having automated flight controls warrant their use even if pilot reaction times were not an issue.

Table 1. Comparing Reaction Time to Distance Traversed at Various Speeds. The distances traversed while waiting for the pilot to react are reasonable for speeds slower than hypersonic flight. If traveling at hypersonic speeds near the ground, however, the situation is different. At some point, regardless of the skill of the pilot, an automated system will be needed. Also note the huge disparity between the fastest achieved speeds (deep-space probe) in comparison to nonrelativistic flight. This disparity of three orders of magnitude is a clear statement about the state of our technology when contemplating deep-space flight.

| Regime | Speed (mph) | Speed (km/h) | Fraction of light speed | Distance in 1 second (feet) | Distance in 1 second (meters) | Distance in 1 second (miles) | Distance in 1 second (km) | |---|---|---|---|---|---|---|---| | Walking | 2 | 3 | | 3 | 1 | | | | Driving around town | 40 | 64 | | 60 | 18 | | | | Commercial air flight | 500 | 800 | | 730 | 220 | | | | Hypersonic flight | 4,000 | 6,400 | 0.00001 | 5,900 | 1,800 | 1 | 2 | | Low Earth orbit | 17,500 | 28,000 | 0.00003 | 26,000 | 7,800 | 5 | 8 | | Deep-space probe | 35,000 | 56,000 | 0.00005 | 51,000 | 16,000 | 10 | 16 | | Nonrelativistic flight | 60 million | 97 million | 0.09 | 89 million | 27 million | 17,000 | 27,000 | | Relativistic flight | 400 million | 650 million | 0.60 | 590 million | 180 million | 110 thousand | 180 thousand | | Extreme relativistic | 660 million | 1.07 billion | 0.99 | 970 million | 270 million | 180 thousand | 297 thousand | | Light speed | 670 million | 1.08 billion | 1 | 980 million | 300 million | 190 thousand | 300 thousand | | Faster than light? | 13 billion | 22 billion | 20 | 202 billion | 6 billion | 4 million | 6 million |

Table 1 is designed to put a pilot's reaction time into perspective; it compares distances traversed during the one second it takes the pilot to scan and comprehend his displays ("dwell time") and then react. In addition, it will take time for those commanded changes to take effect, but those durations are not known. The distances shown in the table are those traversed before any corrective actions are initiated. If these distances are determined to be excessive, then automated flight controls are mandatory.

Another aspect resulting from the effects of ultrahigh vehicle speed is the so-called "relativistic twin paradox". Because of relativistic effects, there will be a mismatch between the time measured aboard the craft and that measured at its base of departure. The equations to track this situation are well established. The challenge is how to present this information so that both the crew and the mission personnel at the base can easily comprehend the implications.

More provocative than the implications of relativistic speeds is the possibility of faster-than-light (FTL) travel. Beyond the perplexing issues of causal violations and closed time-like curves inherent with all FTL notions to date, there is the question of tracking position, orientation, and motion when beyond light speed.

It is reasonable to assume that when a vehicle is traveling FTL, the normal flow of electromagnetic waves (that is, light) to and from the craft will be cut off. To better visualize this, consider the Doppler shifts as a vehicle approaches light speed. The colors of light heading into the flight path will be shifted to such a short wavelength that it will cease to be detectable. Similarly, the light approaching the rear of the craft will red-shift so much that it also ceases to be detectable. Again, do not count on windows.

Navigation References

The main difference between navigating with existing vehicles and breakthrough vehicles is that the breakthrough vehicles will have to navigate in deep space and around other astronomical bodies where GPS systems and location beacons do not exist. Another major difference is that the physics of the propulsion methods might distort or block information that is traditionally used for navigation.

Inertial Navigation (Acceleration Measurement)

In inertial guidance systems, accelerometers and ring laser gyros accurately track the changes in the vehicle's motion (lateral and rotational accelerations). These signals are integrated to keep track of position by evaluating changes in both velocity and acceleration.

In the case of the double hull, where the inertial effects might be different inside of the craft, these tools become more difficult to apply. If we assume that the physics and technology for manipulating inertial fields (or for warping space-time) can accurately track these effects, then that knowledge may compensate to keep these tools viable. Design of future guidance systems must address this issue.

Absolute Velocity — Universal Speedometer

Conveniently, nature provides another reference frame for deep-space navigation. The cosmic microwave background is a reference frame against which velocity can be measured relative to the mean rest frame of the universe. By comparing fore and aft Doppler shifts relative to this highly isotropic and homogeneous radiation, velocity measurements can be derived. For example, the net velocity of the Earth's motion relative to this background has been measured to be 365 km/s. However, the cosmic microwave background will not be detectable at FTL speeds.

As illustrated in Figure 8, although many of the pictures of the cosmic microwave background radiation remove the prominent dipole moment shown in this graphic (the major color difference), it is precisely this dipole — the difference between fore and aft Doppler shifts — that provides a navigation reference for deep-space flight. The projection of this image is a spherical shell that has been opened and flattened. The Doppler shift corresponds to the Earth's motion of over 1.3 million km/h relative to the mean rest frame of the universe. The Earth moves in the direction away from the red and toward the blue.

Figure 8. Cosmic Microwaves as Universal Motion Reference Frame.

Position-Reference Star Trackers

For deep-space flight, the star trackers that have been developed for existing spacecraft may still prove viable; new instrumentation will probably be required. Given the enormous expanse of space, the apparent locations of stars will not vary that much. Even those that do appear to move — our closest stars — are known well enough so that software can take into account how those positions will change as the vehicle's position changes. Due to Doppler shifting, as noted previously, checking positions relative to the stars will only be possible at sublight speed.

For speeds approaching light speed, corrections will be required for relativistic effects. Such effects will probably not become apparent until traveling well beyond about 9 percent of light speed, which is a speed that is still three orders of magnitude beyond the highest speeds achieved to date.

Another modification for star trackers will be required for FTL travel. In essence, with FTL flight, the vehicle arrives at the destination ahead of time — in an unfamiliar way. To understand this, recall that all information we see from the cosmos is old. Those images have taken a while to reach us, and the reality at their point of emission has continued forward in time. For example, when we see sunlight, the image is more than 8 minutes old. The images we see from Alpha Centauri show what it looked like over 4 years ago. Thus, if we could zip to Alpha Centauri instantly, over 4 years of time would have elapsed since we last looked at it. Alpha Centauri's condition will be a surprise upon arrival.

Therefore, any star tracker to accompany FTL flight must take into account the trajectories of astronomical objects so that their positions can be accurately predicted to correspond to the correct time of arrival in both spatial and temporal coordinates. There is no known precedent for this situation.

In support of the forgoing discussion, we are speculating that heretofore unknown advances in physics regarding the quantum vacuum and the nature of inertial frames will result in new motion-detection technology. In researching future propulsion breakthroughs, the utility of sensing and affecting such phenomena is pertinent.

Compilation of Implications

The following list is a compilation of the characteristics discussed in this section about the possible features associated with breakthrough flight. While the list is admittedly incomplete, it conveys the most significant differences compared to conventional methods of flight.

• Six degrees of independent motion and orientation:
  • Translational motion: fore and aft, left and right, up and down.
  • Rotational (orientation): pitch, yaw, roll.
• Distinct inner and outer environments for inertial and gravitational forces.
• Speeds encompassing zero, subrelativistic (below 0.1 of light speed), relativistic (from 0.1 up to light speed), and beyond light speed, yet expecting a travel limit of about a 100-light-year radius around the Sun.
• Three flight regimes:
  • Near the surface of a gravitating body (where gravitational direction provides natural orientation).
  • Orbits around a gravitating body (where cues for entering orbit are required for the pilot).
  • Deep-space flight (without obvious orientation cues or obvious sense of motion).
• Navigational information sources:
  • Position: master reference taken relative to starting position (Sun-Earth system); current location taken from a star tracker, modified to handle a three-dimensional database of star locations for deep-space motion within a 100-light-year radius around the Sun, with predictive trajectories to extrapolate positions for FTL travel, noting that star tracker readings can only be taken at sublight speed; from a first integration on measured velocity relative to the point of departure; and from a second integration on measured accelerations since the point of departure.
  • Velocity: directly measured from cosmic microwave background Doppler shifts, where velocity is relative to the mean rest frame of the universe; and from a first integration on measured accelerations since the point of departure.
  • Accelerations: linear, from accelerometers with corrections calculated based on the influence of the propulsion methods that affect gravitational and inertial forces, and from differentiation of velocity changes as measured using the cosmic microwave background; rotational, from gyros (for example, ring laser gyros) with correction inputs from the propulsion methods that affect gravitational and inertial forces, and from orientation as inferred from star tracker measurements.

(Chapter 2, Human-Machine Interface Lessons, and Chapter 3, Provisional Cockpit for Breakthrough Flight, are omitted for length; the complete text is at the source.)

Chapter 4: Future Work

Given the incomplete body of knowledge concerning futuristic propulsion and maintaining cognizance of ongoing human-factors research, it is probably premature to engage in specific research on cockpits for propulsion physics. Instead, more insights are likely to be gained from relevant physics research. A caveat is that advances in cockpits for breakthrough flight might be further advanced by taking advantage of the gaming industry or through science fiction speculation.

Without the actual technology for breakthrough flight, a game simulation or detailed science fiction show or movie could be used as the context around which to explore such options. A concern with this approach, however, is that the underlying stories serve the primary function of entertainment as opposed to user efficiency. It is conceivable to encounter a guidance system more intended to create dramatic tension ("wow effect") than ease of use.

Multiple Flight Regime Guidance Conventions

The breakthrough vehicle will operate in regimes for which guidance standards do not yet exist, specifically orbit insertion and deep-space (interstellar) travel. Although motion near the surface of a gravitating body can copy the standards of aircraft flight (primary flight display and terrestrial navigation standards), further work is required to explore and select the best options for orbit and deep-space flight.

Although it is expected that orbit insertion maneuvers would be handled by an automated system, the more demanding condition to use as a design target is to have a display system that can guide a pilot to manually enter a stable orbit.

Choosing the convention for the primary axis of deep-space motion will require a trade study to determine if the natural human instinct for forward-dominated motion offers a better human-machine interface than the propulsion-dominant option for upward-dominated motion. Such an assessment must also consider how well the convention works when transitioning from deep-space flight into an orbit, then landing, and then back again to deep-space flight. Once any convention is set into place, it will be difficult to change later.

Vector Motion Display

Once the development of those guidance conventions is further along, a method to clearly display those conventions for the pilot would have to be developed. A complication that these future displays will encounter is the need for a seamless transition between these three conventions: flight above a gravitating body, orbit insertion, and deep-space flight beyond our solar system.

Vector Motion Control

Adding three linear axes (plus yaw) to the classic two-rotational degree-of-freedom joystick is a significant change. Although six-degree joysticks are available commercially, they are oriented toward computer interfaces rather than commanding the motion of a vehicle. To determine the optimum configuration for an actual six-degree vehicle control, simulations would likely be required. Perhaps one venue is to explore the vehicle controls for exploration submarines that also have the full six degrees of freedom.

Another critical detail to be resolved with commanding a breakthrough vehicle is how best to accommodate the "throttle". Should each linear axis have the same speed capability, or should only the primary motion axis have the full span of zero to maximum speed? With that characteristic specified, it will also be necessary to determine how best to provide adjustments to cover the speed ranges of each axis.

Optimum Mix of Control Methods

A variety of methods have been considered for commanding the breakthrough-era vehicle. What is not known is the degree and in what combinations they should be used, and whether constraints should be placed on some of them. The potential use of confirmation feedback for both voice and thought commands is suggested, but future research will need to determine whether (and how) such functions should be employed.

(Appendix A, the annotated bibliography, and Appendix B, the endnotes, are omitted for length; the complete text is at the source.)