The Omaha Trail
A system for high-efficiency transport between Earth and Mars
Mars is popular as a new frontier destination for humanity, thanks to SpaceX initiatives and other private enterprises. Governments are finally starting to move on plans that were delayed when NERVA rockets proven on the test stand never flew and a manned Mars program was never implemented in the 1970s. This newsletter brings to you a proposed integrated framework of independently valuable infrastructure components to support Mars efforts. We call our framework the Omaha Trail. Just like the US transcontinental railroads, constructed during the time of the civil war, such infrastructure requires investments, but it can pay high dividends, especially in a time of strategic need. The interested reader can find a starting point for more information in the LMT press release of September 18 2017.
The remainder of this article sketches Omaha Trail components for facilitated access to a proposed Mars settlement site. A hub on the second Mars moon, Deimos, with Deimos Dock and a Rail Launcher, is essential. The architecture is completed with an elevator-type drop line from space, the Mars Lift, and a surface Tramway from the Mars Lift ground station to the settlement site.
Global terraforming concepts for Mars exist and examples can be found at https://en.wikipedia.org/wiki/Terraforming_of_Mars. However, their impact is unclear, when unique resources, only available once, are wasted when the planet relapses to a desert state. The Lake Matthew plan is different. It proposes local terraforming, releasing on Mars new bridgehead resources and promising a few thousand years of bedrock heat for Lake Matthew, and for settlement. Sustainability is the key. TRL levels seem viable, and the mission timeframe calls for a start of surface operations in 2036.
In our collaboration on the Omaha Trail we overlaid a new framework onto the Lake Matthew plan to facilitate transport to and from Mars, with the primary destination being the settlement site at Lake Matthew.
Deimos Dock and Deimos Rail Launcher
Deimos, while only a small rock on the planetary scale, promises the key to better Mars access. In a first step, we propose a docking station on Deimos supported by solar power photovoltaics (PV) and an ISRU mining operation, to manufacture propellant, water, simple compressed materials for shielding and weights, and possibly more. A suggested distribution of photovoltaics (PV), mining, and dock facilities was given at the Space Elevator conference in August 2017.
Propellant from Deimos has value superior to propellant from Mars due to its location near the edge of the Mars gravity well. Also Deimos local gravity is only 0.0025 m/s2, a quarter permille of Earth. The gravity pull of 100 kg on Earth reduces to the equivalent of only 26 g on Deimos, making docking cheap. SpaceX ITS transports traveling to and from Mars can refuel at Deimos Dock with little effort, reducing the load of propellant required to be carried to and from the planet, and making transfers more efficient. While we used the best volatile prospecting data for volatiles available, in situ tests on Deimos are recommended as a priority for Mars programs.
In a second step the docking port on Deimos will be extended. The cold of space offers interesting perspectives for superconductors. It makes superconducting magnetic energy storage (SMES) viable with reduced containment, and much reduced mass, compared to Earth. We propose a Deimos Rail Launcher (DRL) facility that uses such SMES storage as an energy reservoir. SMES and direct PV provide vessels a Δv of up to 1 km/s over DRL tensioned wire rails, with low g-forces. The DRL makes several destinations directly accessible, e.g., the Mars periapsis as decision point to go to Earth or Mars, and the top of a Mars elevator just inside the Deimos orbit, the Arestation of our proposed Mars Lift.
Mars Lift and Tramway
Space elevators list among their main benefits benign access to orbit, without exposure to the violent power and vibration of rocket engines, and scalability. However, climbing also requires high power density on a climber to drive it. The established feasibility condition for Earth maps out a relationship between the power density of the driving infrastructure of a climber, tether strength, and house-keeping operations of a space elevator. Climber power density includes in that case both components of the drive system, the motor and either a solar or power beaming receiver array.
Our Mars Lift uses the space elevator as a simple drop line that requires minimal auxiliary engines on a climber to start the drop, and uses eddy-current brakes with sufficient heat radiators to limit the maximum climber speed to around 300 km/h. A final Joule-braking step is only required at the bottom of the tether. The basic Mars Lift concept is therefore a descending vehicle, called a rappeller. It uses standardized containers that lock into the rappeller frame. Empty rappellers and containers are shuttled back to the Arestation via return ITS rocket. The Mars Lift saves propellant that would otherwise be used to land the payload on Mars.
When augmented with propellant manufactured on Deimos, the Mars Lift can reduce overall propellant requirement for cargo flights by about 70%, and cut the number of required Earth booster launches by a similar percentage.
Fig. 2. Schematic of cargo flight staging (2,3,5). Deimos propellant (1,3,5). Mars Lift space elevator descend line in gold (5). Image credit: Lake Matthew Team
We scaled the tether significantly larger than the minimum safety factors typical for other space elevator concepts to address concerns about climber grip and the additional pull of the off-equator elevator.
What about a Phobos drop tether instead of the Deimos configuration? Mars is not an easy landing site, with only 0.6 % atmospheric density of Earth, as concepts with sky-cranes and supersonic parachutes with ~20 m diameter for approximately one metric ton of payload for the Curiosity rover demonstrate. There will be no aerodynamic supersonic airplanes with high payloads on Mars. Even a drop from 100 km altitude still requires approximately 1/3 of the dropped mass as fuel/engine for proper braking. The terminal velocity in the atmosphere approximates 1000 km/h. The Mars atmosphere is just dense enough to be annoying without being useful. The issues of braking in the Martian atmosphere and the high projected ground speed of Phobos drop made us forego the concept of a drop tether. We chose instead an elevator from the Martian surface to beyond areostatic-orbit, the equivalent of geostationary-orbit, terminating about 100 km below Deimos orbit.
Phobos avoidance is the next step to clear for a Mars elevator. Oscillating elevators were the solution proposed by A.C. Clarke in the Fountains of Paradise. Induced oscillations are interesting as obstacle avoidance mechanism. We preferred instead a steady state solution as a baseline that requires no additional input of energy, i.e., an off-equator elevator. We followed the paradigms of Levin and Gassend for our investigations of several scenarios: two sites were modeled, at ~12.65 degrees and 18 degrees South, with 10 MYuri and 20 MYuri tethers. All investigated baselines, without additional loading by climbers, cleared Phobos comfortably, including sufficient clearance for known variations in its orbit, see presentation for 2017 SEC.
Once on the ground, we use elevator-strength cables to establish a horizontal tramway following the concepts of Pearson’s Lunar tramway. Elevator-strength material permits cable spans with minimal sag over tens of kilometers, requiring minimal infrastructure compared to a railroad. The rappellers are converted to trammers for powered horizontal transport.
Open items are the hazards of Martian dust and the electric properties of the Martian atmosphere. Global dust storms are reported to reach up to 80-100 km above the planet. Even the high mountains on Mars cannot escape these storms. Also, atmospheric conductivity is significantly higher than on Earth, with many discharges. Clearly a Mars tether has to be well protected. On the positive side the energy of the drop could also be converted to augment or service the tether. For example, DC current from the rappeller could be tapped to remove an expected ice hazard: creating a Joule-heating circuit in the final 100 km of tether, to sublimate water ice and dry ice off the tether.
The treatment of details of the Omaha Trail exceeds the format of this newsletter, so we only highlighted a few basic points. A good starting point for further information and appropriate references is the link provided at the start of this article and the pdf of our August 2017 presentation at the Space Elevator conference. For further science and engineering questions you can contact the authors via email under Lake Matthew Team (LMT) and M. Lades. This is a work-in-progress and numbers and concepts still undergo continued updates from our baseline presented in August. For example, SpaceX revised their ITS architecture in September 2017, and the Omaha Trail specs were updated accordingly, as given in our November 2017 presentation to the British Interplanetary Society. Also, the LMT won in November the HP Mars Home Planet Urbanization Concept Challenge, in the Innovation in Science category. The entry was an artificial magnetic shield that extends Omaha Trail facilities. It aims to reduce a crew’s exposure to cosmic radiation, on the open Martian surface. We invite ISEC members to participate in collaborative research, and we hope to keep everyone updated in future newsletters on our progress along the Omaha Trail.