1 - Purdue University



1.Introduction and Mission Summary

Jaret B. Matthews

1.1.1 Introduction

On December 19, 1972 Apollo 17 astronauts returned to Earth after spending 75 hours on the surface of the Moon. Little did they know that they took part in what was to be humanity’s last venture beyond low Earth orbit for nearly thirty years. At the time of their return it was assumed that Mars was the next destination that NASA would open to humanity’s grasp. However, this proved not to be the case.

Though several notable Mars mission architectures have been proposed over the years, all have been met with substantial criticism. Because of concerns about inordinate costs, high risks to crew safety and mission success, and extremely long timelines, the proposed architectures have not fared well in the face of public scrutiny.

The architecture for Mars missions took a significant turn with the publication of Dr. Robert Zubrin’s book A Case for Mars: A Plan to Settle the Red Planet and Why we Must. In this book, Dr. Zubrin popularized a mission strategy known as in-situ resource utilization (ISRU). ISRU is characterized by the exploitation of indigenous resources on the surface of another planet. ISRU has revived a once dead hope for the human exploration of Mars by revolutionizing the way engineers and scientists think about interplanetary exploration.

By incorporating ISRU into the Project PERforM mission, we were able to launch off of Earth without the fuel to return home. The mass of a propellant production plant being far lighter than that of the required propellant to lift off Mars, several tones (metric tons) are saved by simply manufacturing rocket fuel on the surface.

Mars missions have also been out of favor because of the perception that going there involves unacceptable amounts of risk to crew safety. While a Mars mission is inherently more dangerous than a Lunar mission simply because of the distance and time away from Earth, with planning, a crew could be ensured significantly more survivability than in previous mission architectures. Incorporating a free-return trajectory developed by Professor James Longuski of Purdue University and Masa Okutsu, a graduate student at Purdue, Project PERforM is able to return the crew safely back to Earth even in the face of nearly total loss of propulsive capability.

Safety is further buttressed by the incorporation of zero-altitude abort options both on Earth and on Mars. Also, in the event of a zero-altitude abort on Mars, the crew have available to them, in the immediate area, 100% backups in the form of a second set of launch/earth return vehicles. Implementation of such measures has helped us to mitigate some of the traditionally risk intensive aspects of a human mission to Mars.

In addition, we surmounted several other historical impediments to human Mars exploration in the Project PERforM architecture. The debilitating effects of prolonged exposure to micro gravity are overcome by employing tethers to produce artificial gravity both on the way to and from Mars. Propellant requirements are lessened not only by in-situ production, but also by incorporating aerobraking and aerocapture maneuvers, which taper purely propulsive delta velocity requirements.

Excessive costs are kept at bay by implementing nuclear thermal rockets, whose high performance have allowed us to use an existing launch vehicle. Concurrently, by evading the need to develop a new launch vehicle we are also afforded the ability to build around a rather rapid schedule.

It is in the spirit of in-situ resource utilization that Project PERForM set out about designing this mission. While the aspects of our mission are certainly not individually groundbreaking, it is the use of novel techniques in concert that has allowed us to reasonably achieve the goal of designing a low cost, safe, and highly successful mission to Mars.

1. Mission Directives

The following mission directives were assigned at the beginning of the mission design process.

• Mission should focus on minimizing cost

• Crew survival rate must be greater than 95%

• Mission success rate must be greater than 80%

• Artificial gravity must be provided to crew if time of flight is in excess of 180 days

• Crew must contain 2 dedicated science personnel

• Mission should serve as a “stepping stone” for future missions

1.1.3 Mission Summary

The Trip to Mars

The journey to Mars begins on November 9, 2011. A fully fueled, modified, Russian Energia heavy launch vehicle sits patiently on the pad at Cape Canaveral, Florida. The massive Earth Launch Vehicle (ELV) towers high into the autumn Florida air. The ELV, larger than the Saturn V, was in production in the 1980’s and its facilities were brought back on line for the mission to Mars.

Atop the ELV sits the Earth Return Assembly (ERA) (see Fig. 1.1.1). The ERA consists of the Earth Return Vehicle, the Mars Garage, the Mars Launch Vehicle, and the Crew Transfer Vehicle. The unmanned ERA is being launched towards Mars more than two years ahead of the crew.

The Earth Return Vehicle (ERV) is a crew living area stocked with consumables for the six-month return trip to Earth. Just above the ERV rests the Mars Garage (MG). The MG houses the long-range rover, which will serve as the primary means of transportation for the crew on the surface of Mars.

Stacked above the garage is the Mars Launch Vehicle (MLV). An amazing piece of hardware, the MLV is outfitted with its own propellant production plant. Blasting off Earth virtually un-fueled, the MLV will actually manufacture its own rocket fuel from the thin Martian atmosphere.

The final component that comprises the ERA is the Crew Transfer Vehicle (CTV). The CTV is a small lifting-body craft that serves not only as the crew’s means of landing on Earth, but also as an effective instrument in surviving a launch failure off the surface of Mars.

The ELV rumbles aloft as it transports the ERA to low-earth orbit (LEO). After a short checkout period in LEO, the ERA is hurled into a trans-Mars injection by the upper stage of the ELV, the Nuclear Thermal Rocket (NTR) (see Fig. 1.1.2).

Though the NTR is primarily used to lob the ERA towards Mars, its purpose is far from served. By converting the heat continually produced in the NTR’s idling reactors, the ERA is provided with ample power for the trip to Mars.

On September 11, 2012, after more than 300 days in space, the ERA jettisons the NTR in preparation for landing on Mars. Slamming into the Martian atmosphere at 5.56 km/s, the ERA uses an aerocapture maneuver to place itself into orbit around Mars. Once in orbit, the ERV is separated from the rest of the ERA. At this point, solar panels and a high gain antenna are unfurled from the ERV so that it may serve as a communications satellite supporting exchanges to and from the surface of Mars.

After separation from the ERV, the garage, the MLV, and the CTV deorbit to land on Mars. Plunging into the atmosphere, the vehicle is slowed to subsonic speeds by parachutes. At this time, the garage is jettisoned and allowed to land under its own parachutes. Firing retro-rockets, the MLV and CTV gently land near the garage.

The single-stage to orbit MLV now has fifteen months to make enough fuel for the return trip home. Just after touchdown, a 100kw nuclear reactor is rolled out from beneath the MLV. The reactor is used to power the MLV’s methanol and liquid oxygen production plant. If the plant fails to produce enough fuel for the return trip, the crew will simply remain safe back on Earth.

However, should all go well, on January 14, 2014 the crew will lift off from the Cape by way of another ELV/NTR stack. Perched atop this ELV is the Habitation Module (Hab), a roomy, two storied, lifting body vehicle that will serve as the crew’s home for the journey out to Mars and while on the surface (see Fig. 1.1.3).

Similar to the ERV, the Hab is propelled towards Mars via an NTR. The Hab’s trajectory however, is unique. Available only during a short window around mid January 2014, is a free-return trajectory via a Venus flyby. This trajectory ensures, even in the face of nearly complete loss of propulsive capability, a safe return to Earth within 800 days. Should anything go wrong on the 172-day transit out to Mars the crew can simply opt not to land and “coast” back home.

Following the NTR injection burn, the Hab and NTR spin up to 2 rpm before separating to deploy a 325 m long tether. Once deployed, the assembly is again spun to achieve .38g’s, the equivalent to Martian gravity (see Fig. 1.1.4).

The tether serves to acclimate the crew to the conditions that they will be living in for the next two years. Similar to the ERA, power is drawn from the idling NTR reactors. The power produced is fed to the Hab by way of a cable running the length of the tether. Should this critical system fail, the Hab is equipped with both solar panels and fuel cells, each sufficient to avoid a catastrophe.

Traveling alongside the Hab is a second ERA to support a subsequent Human mission to Mars in 2016. Should the first MLV have any trouble, the second will arrive with the Hab and begin producing propellant immediately. The second MLV will be fully fueled by the time the crew is ready to leave. We also phase the second ERV’s orbit to provide the crew with nearly constant communication while on the surface (see Fig 1.1.5).

Upon arriving at Mars on July 4, 2014, the tether is cut and the Hab is readied for aerocaputre. Because it hits the atmosphere at a considerably higher 8.4km/s, we designed the Hab to generate a significant amount of lift. The lift is used to combat the high g-loads encountered on the plunge into the atmosphere, thereby reducing stress on the crew and equipment (see Fig. 1.1.6).

After the Hab has sufficiently braked in the Martian atmosphere, the nose faring is jettisoned revealing landing legs and a retro-rocket. Similar to the MLV descent, the Hab is slowed to subsonic speeds with a series of parachutes. Finally, it is guided, via the retro-rockets, to a soft landing near the garage, MLV, and CTV (see Fig 1.1.7).

On the Surface

Unlike Apollo, the major motivation for this mission is science. With a surface stay of 590 days the crew has ample time to conduct experiments and explore the surrounding area. To augment the crew’s capability to explore, they have been equipped with both a pressurized, long-range rover and an un-pressurized, short-range rover. To facilitate research on several fronts, we also included a greenhouse with the science equipment.

The Long Range Rover (LRR) runs off of the methanol and oxygen being produced by the MLV. With the goal of covering 10000km in the LRR, the crew embarks on what will be the first of ten, long-distance excursions (see Fig. 1.1.8). Each excursion lasts fourteen days and is intended to maximize the science return of the mission.

With the help of the LRR, the scientists cover nearly 800,000km2 over the course of the mission. Equipped with the tools necessary to conduct numerous geological, meteorological, and biochemical studies, the crew will spend roughly 75% of their days engaged in scientific research.

While two of the crewmembers are out on long-range excursions, the remainder of the crew will be occupied with research in or around the Hab. Conducting agricultural experiments in the spacious greenhouse (see Fig.1.1.9), the crew can also analyze the latest samples brought back from the last LRR mission. While not planning for the next long-range excursion, the crew maintains the Hab and releases several balloons for atmospheric research and site scouting (see Fig. 1.1.10).

If the LRR runs into any trouble, the Hab crew is outfitted with an additional rover, the Short-Range Rover (SRR), which can be used in an emergency to quickly race out to the stranded crewmembers. With a max range of 1000km, equal to the furthest, round-trip distance that the LRR is ever likely to be away, the SRR will also provide local transportation for the crew at the Hab. As the time on Mars draws to a close, the crew prepares the MLV and CTV for launch back to Earth.

The Trip Back Home

On, December 26, 2015 the crew boards the CTV in preparation for the trip back to Earth. The CTV is has little room for more than four crewmembers and samples to return to Earth. The fully fueled MLV slowly lifts off the surface of Mars. It is headed for low-Mars orbit where it will rendezvous with the waiting ERV (see Fig. 1.1.11). The crew then transfers from the CTV into the ERV, their home for the next 230 days.

Soon afterwards, the MLV is fired again to place the ERV/CTV assembly on a trans-Earth injection. At the completion of the burn, the ERV/CTV assembly undocks from the now spent MLV. The ERV/CTV quickly turn around and re-dock with the MLV, this proven maneuver is to allow the MLV to be tethered to the ERV and CTV for the trip home.

The assembly is spun up in a manner identical to the Hab spin-up. At the completion of the initial spin-up, a kilometer-long tether is deployed between the ERV/CTV assembly and the MLV (see Fig. 1.1.12). At the beginning of the transit, the crew experiences the same .38g’s that they have become well accustomed to however, over the course of a month, the vehicles are gently spun-up to Earth’s gravitational conditions.

Arriving at Earth on August 12, 2016, the crew severs the tether in preparation for the landing sequence. As the crew gets closer to Earth, it transfers back into the CTV. Just as the assembly nears, the CTV un-docks from the ERV (see Fig. 1.1.13). Sweeping violently through the Earth’s atmosphere, at 11.8 km/s the lifting body CTV aerocaputres into Earth orbit. The mission comes to and end as the crew deorbits the CTV. Landing under parachutes, the CTV glides to a rough but safe landing.

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Fig. 1.1.1 ERA & ELV.

ERA

ELV

Fig 1.1.2 ERA is placed into trans-mars injection via the NTR.

Fig. 1.1.3 Hab & ELV.

Fig. 1.1.4 Hab and NTR separate to deploy to a tether.

Fig. 1.1.6 Hab aerocapture in Martian atmosphere.

Fig 1.1.8 LRR and crew on a long-distance excursion (A. Spencer).

Fig. 1.1.10 Hab, SRR, and Mars Balloons (N. Czapla).

Fig 1.1.13 CTV returns crew to Earth.

Fig. 1.1.5 Two ERVs in orbit around Mars.

Fig. 1.1.12 ERV and CTV tethered to MLV for return trip.

Fig. 1.1.9 Mars greenhouse (A. Spencer).

[pic]

Figure 1.1.7 Hab landing near MLV/CTV Stack (N.Czapla).

Fig. 1.1.11 MLV/CTV mate with orbiting ERV.

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