Digital Sprocket

Brian Pfeifer
August 2004

The ITV (Interplanetary Transport Vehicle) is designed to travel between Low Earth Orbit, and the Moon, Mars, or Near Earth Objects. In construction and operation is resembles a modular space station more than the Apollo CSM. Building an ITV now, is a great way to reduce many of the engineering, medical, and training risks associated with a long distance, long-term mission like the proposed Mars mission. It does not invalidate any of NASA’s current work on the Orion CEV, nor the Ares boosters.

Requirements
• Modular like the ISS to permit construction by multiple HLV/ Ares V launches and replacement of warn or outdated components
• Crew living quarters to support 4-8 astronauts
• Support the simultaneous docking/berthing of several Orion/Soyuz class vehicles
• Clustered multiple restart engines capable of reaching and returning from Martian orbit
• Power supply capable of sustaining a prolonged Martian mission
• Transport large cargo modules like Lunar and Martian base
• Support emergency crew return even from Martian trajectories
• System redundancy, spares, or repair, with graceful deterioration

Modular like the ISS to permit construction by multiple HLV/ Ares V launches and replacement of warn or outdated components

The Ares V or similar heavy lift vehicle will lift the modular components into LEO where they will be assembled. This permits the total vehicle weight to exceed that of any one booster. Modular construction also allows for the replacement of warn or damaged components. NASA has demonstrated that even large components like the gyroscopes on the ISS can be replaced if the vehicle is designed from the outset with modularity in mind. Several systems required for a Mars mission are beyond today’s technology. With modular construction a less robust alternative may be used for early shakedown cruises, and replaced as new systems become available.

Crew living quarters to support 4-8 astronauts

If the architecture is based on the long-arm centrifuge artificial gravity Martian mission plans, the crew cabin will be placed at the bottom end of the primary truss. It must be designed to provide sufficient protection from solar radiation. This will likely be a combination of polyethylene insulation and water storage tanks. It’s systems must operate both while spinning in AG (Artificial Gravity) mode or in MG (Microgravity) mode. It will include private sleeping cubicles, food preparation including heating and cooling, and personal hygiene facilities. For long duration missions, the environmental systems must recycle 95% of all water, and atmospheric gasses. If composting systems are available, then some foods may be grown during flight. Any food crops should not be primary foods like wheat, but rather foods that improve quality of life such as fresh fruits and vegetables.

Support the simultaneous docking/berthing of several Orion/Soyuz class vehicles

Operation of the ISS has demonstrated that it is useful to dock multiple vehicles, and multiple types of vehicles. It may make sense to dock one Orion, and one cargo ship with one spare docking port. Up to four docking ports would be useful especially during resupply while in LEO. One docking port may be configured as a backup airlock. The docking ports will likely be located at the bottom of the crew cabin to prevent significant sheering forces from being applied to the docking collar while the ITV is in AG mode or while the main engines are firing.

Clustered multiple restart engines capable of reaching and returning from Martian orbit

A cluster of engines will likely be located at the top end of the primary truss. They must be capable of multiple restarts. Currently, we are unable to store cryogenic fuels long enough for a Martian mission. So the engines will likely need to be swapped out between the early Lunar and near earth missions, and later missions. To start with, either cryogenic or hypergolic fuels could be utilized while development continues. The fuel tanks should reside near the center of the primary truss at the center of mass because its mass will change over the course of the mission. Fuel tanks may be reloaded on orbit, or completely swapped out between missions.

Power supply capable of sustaining a prolonged Martian mission

Most Mars mission proposals call for nuclear power plants because insufficient light reaches Mars for photovoltaic cells, and fuel cells are limited both by cryogenic technology and the mass of fuel. Unfortunately, suitable nuclear power plants are at least ten years away, if not further. For early missions, the ITV can be outfitted with large solar arrays with the expectation that these will be replaced before a Martian mission with either a nuclear power plant, or next generation solar cells. In both cases, the power supply would be located at the top end of the main truss, and form part of the counterweight for AG mode.

Transport large cargo modules like Lunar and Martian base

Near the center of the main truss is an area designed to carry large, mission specific cargo modules. These include landers, bases, and laboratories. Since they will be located near the center of gravity, they will only be accessible in MG mode.

Support emergency crew return even from Martian trajectories

For initial LEO missions, an unmodified Orion or Soyuz docked to one of the four docking ports is sufficient for emergency crew evacuation. For Lunar and similar missions, the CEV must be outfitted with an expanded service module and sufficient supplies to return a crew to Earth. For Martian and other long distance missions, the CEV should be outfitted with an extended service module containing enough fuel to return a crew from Martian orbit. It will also require an additional orbital module similar to what the Soyuz uses. This will give the Astronauts more living space and the storage required for additional consumables. It should be noted, that in a worst-case scenario, the Astronauts will need to be on short rations, and unable to exercise for many months. Instead of returning directly to the Earth’s surface, they may require initial rehabilitation in LEO at the ISS or other microgravity facility.

System redundancy, spares, or repairs, with graceful degradation

Any large, complex system requires repairs over time. As we have seen with the ISS, many systems can be repaired, or swapped out when they fail. For long duration missions, it will be vital to correctly predict what spares will be required. Operating the ITV for several years in LEO and on lunar missions will provide the data necessary to make these predictions. Additional design choices can improve the reparability of the systems. If the designers assume that Astronauts will have to place hands on every system, either during an EVA or from inside the crew cabin, then there will be fewer surprises during flight. Wherever possible, systems should be designed to degrade gracefully when they fail rather than suddenly stopping without warning. In order to facilitate external repairs, large spares should be carried outside the ITV similar to the External Stowage Platform 2 on the ISS. At least one airlock is required and the ITV should be configured with either a second, or one of the docking ports may be configured as a backup airlock. A robotic arm, similar to Canada Arm 1 or 2 should be installed on a mobile base on the Main truss. The arm will facilitate construction of the facility, docking/berthing, and repairs. A concerted effort must be made to remove all single points of failure from the ITV systems. It may be acceptable to permit single points of failure in less critical systems if they are easily repairable and necessary tools and supplies are on board.

ITV Mission Profiles

LEO MG tests

LEO AG tests

High Orbit tests

Moon

NEO rendezvous

Mars

LEO MG tests

The initial crewed mission may be relatively short. Its main goal is to demonstrate that all systems function as predicted in a microgravity environment. This mission may be relatively short, and may be combined with LEO AG tests.

LEO AG tests

This second mission may be as long as six or twelve months. Its primary goal is check out spacecraft operation in Artificial Gravity mode. Test should be made at the equivalent of Lunar, Martian, and Earth gravity. A secondary goal of the mission is to test out tools and equipment intended for use on the Lunar and Martian surfaces. Currently, only brief tests may be made at Lunar or Martian gravities on parabolic aircraft flights. LEO AG tests will allow astronauts to conduct extended experiments on systems. They will be able to evaluate equipment and to acquire reliability data. The Astronauts will also demonstrate that they can all but eliminate the need for ground based post-flight rehabilitation by operating at Earth gravity near the end of the mission.

High Orbit tests

The third mission would fly the vehicle beyond low Earth orbit for the first time. It would demonstrate the effectiveness and reliability of the main engines for extended burns as it pushed the ITV into several higher orbits, possibly geosynchronous. The mission will demonstrate the refueling capability. The effectiveness of radiation shielding can be evaluated, and additional test can be conducted at various gravities. The Orion/CEV may need additional fuel and consumables to return the Astronauts to the Earth in case of emergency.

Moon

This will be the first mission requiring large mission specific modules. It will demonstrate installation of such modules. It will require a lunar lander with the capability of returning to lunar orbit. First the ITV will be refueled and resupplied in LEO. The Lunar lander will be installed on the cargo section of the truss. A crew, possibly as large as 8 astronauts will fly the mission. The Orions used must be capable of returning to the Earth on their own in case of emergency. The ITV will leave LEO and proceed towards the moon. It will spin up to lunar gravity. Upon reaching the moon it will need to cease AG mode for orbital insertion and launch of the lunar lander with a crew of four, leaving four more crew aboard the ITV. A smaller caretaker crew may be left aboard, to reduce the total number of crew required for the mission. The crew then returns from the lunar surface to the ITV, and returns to LEO. During the return journey, the rate of rotation can be regularly increased until the crew is used to normal Earth gravity once more.

Additional Lunar missions may be flown. In addition to a lander, the ITV may deliver larger permanent habitation and laboratory modules for long duration missions to the surface. The ITV will be capable of remaining in lunar orbit for the duration of even long duration missions, thus providing emergency crew return capabilities.

Although the ITV is overkill for basic lunar missions, these will prove the long duration capabilities of the spacecraft and provide the engineering data necessary to predict what spares will be required to Martian missions.

NEO rendezvous

Researchers have long desired to visit the asteroids and other bodies near the Earth, but they have always been beyond the reach of all but unmanned probes. The ITV will be the first crewed vehicle capable of rendezvousing with NEOs. NEO missions will further expand the envelopes of duration, and range for the ITV. It will demonstrate the engine capabilities and prove radiation shielding, and system reliability. Next generation photovoltaic cells and/or a nuclear power plant should be tested in an operation environment on this mission.

Mars

There should be few operational surprises for a Mars mission. The mission commander will already have experience as crew on previous long duration flights of the ITV. The ITV will have been in continuous operation for at least 5 years prior to the first Mars mission. Mission specific landers and surface habitation modules will be mounted to the central cargo area of the primary truss. The original solar panels will be replaced with either next generation solar panels or a nuclear power plant. An extended orbital module should be connected to the CEVs to provide additional consumables and crew quarters in case of emergency evacuation. These consumables may be considered part of the normal supply for the final leg of the return voyage. The CEVs must also be outfitted with extended service modules containing enough fuel for an emergency return to Earth orbit. Additional supplies may be sent into Martian orbit via separate unmanned vehicles. Once the ITV leaves Earth orbit, it will spin up to Mars gravity and return to MG mode before orbital insertion. Upon leaving Mars orbit, it will gradually spin up to Earth gravity to facilitate Astronaut rehabilitation. It will again return to MG mode for orbital insertion.

Conclusion

A well-designed reusable ITV will be well worth the investment. By building the ITV in the near future, many of the risks associated with a Mars mission may be reduced through building operational experience. The ITV will provide both a test bed for new Martian tools and techniques and an expansion of current capabilities to send Astronauts to destinations previously unreachable.