**4.2 OTV mass comparisons**

An initial comparison of the chemical and NEP option for the 1 MT payload cases is presented in **Figure 2**. Both the Phobos to Deimos and the Phobos to 100,000 km cases are shown. Overall, the initial masses of the NEP cases, for Phobos to Deimos and the Phobos to 100,000 km, are very similar; therefore, the larger Phobos to 100,000 km OTV NEP cases can perform both the Deimos and 100,000 km missions. The only NEP OTV designs that have a comparable propellant mass to the chemical propulsion OTV is the OTV with the 0.5 MWe power level.

The associated 1 MT payload OTV trip times for the chemical and NEP cases is presented in **Figure 3**. The Phobos to Deimos round trip time is for the 0.5 MWe case is 56.6 days. The 100,000 km round trip time is 108.9 days. The higher power levels provided a shorter trip time; however, the required propellant mass is higher than any chemical OTV propellant mass.

A summary of the initial masses of the chemical and NEP OTVs for the Phobos to Deimos and Phobos to 100,000 km is shown in **Figures 4** and **5**, respectively. The payload masses for both OTV mass estimates were 10 and 50 MT. The payload mass is carried on the full round trip mission In the Phobos to Deimos cases with a 10 MT payload mass, the benefit of the NEP system over the chemical OTV is best with NEP power levels of 0.5 to 1 MWe. For the 50 MT payload, the NEP OTV provides a very significant propellant mass benefit for power levels up to 10 MWe. For the

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**Figure 3.**

**Figure 2.**

*payload.*

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options*

50 MT cases, the chemical OTV required about 31 MT of propellant, while the NEP

The Phobos to 100,000 km orbital transfers are compared in **Figure 5**. Both the initial masses and propellant masses are shown. Comparisons are shown for 10 and 50 MT payload cases. The payload mass is carried on the full round trip mission. In general, the NEP OTV propellant mass savings over the chemical OTVs are very similar to the Phobos to Deimos cases. For the 50 MT cases, the chemical OTV required about 64 MT of propellant, while the NEP OTV at a 10 MWe power level required only 17 MT.

*Initial mass and propellant resupply mass, Phobos to Deimos and Phobos to 100,000 km, round trip, 1 MT* 

*Round trip time, Phobos to Deimos and Phobos to 100,000 km, round trip, 1 MT payload.*

*DOI: http://dx.doi.org/10.5772/intechopen.96717*

OTV at a 10 MWe power level required only 9 MT.

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options DOI: http://dx.doi.org/10.5772/intechopen.96717*

50 MT cases, the chemical OTV required about 31 MT of propellant, while the NEP OTV at a 10 MWe power level required only 9 MT.

The Phobos to 100,000 km orbital transfers are compared in **Figure 5**. Both the initial masses and propellant masses are shown. Comparisons are shown for 10 and 50 MT payload cases. The payload mass is carried on the full round trip mission. In general, the NEP OTV propellant mass savings over the chemical OTVs are very similar to the Phobos to Deimos cases. For the 50 MT cases, the chemical OTV required about 64 MT of propellant, while the NEP OTV at a 10 MWe power level required only 17 MT.

#### **Figure 2.**

*Solar System Planets and Exoplanets*

P = NEP power level (kWe).

**4. Mission effectiveness**

**4.2 OTV mass comparisons**

than any chemical OTV propellant mass.

m(fixed) = NEP fixed mass (kg).

was 5% of the mass of the required propellant.

**4.1 Phobos and Deimos payload missions**

varied based on the destination of the Martian moon missions.

stantial resupply mass benefit over chemical propulsion OTVs.

chemical propulsion OTV is the OTV with the 0.5 MWe power level.

m(dry, stage, NEP) = NEP dry mass (kg). alpha = NEP reactor specific mass (kg/kWe).

0.05 = tankage mass coefficient (kg/kg m, p). m(p) = NEP usable propellant mass (kg).

The OTV sizing was conducted for a wide range of power levels: 0.5 MWe to 30 MWe. Three nuclear reactor specific masses were used: 10, 20, and 40 kg/kWe (kilograms per kilowatt, electric) [15]. The OTV propulsion fixed mass, apart from and in addition to the reactor mass, was 20 MT, and the propellant tankage mass

The specific impulse (Isp) and efficiency of the electric propulsion systems were 5,000 seconds with overall thruster-propulsion efficiencies of 50% for each design. These design points are typical of advanced designs of either magnetoplasmadynamic (MPD) or pulse inductive thrusters (PIT). While hydrogen is suggested for both propulsion system thrusters, the possibilities of the higher Isp option using inert gases (xenon, krypton, etc.) are also viable. The low thrust OTV delta-V value

A range of payload masses were included in the comparative orbital transfer cases: 1, 10 and 50 metric tons (MT). In general, the initial masses of the NEP OTVs are higher than the O2/H2 OTVs initial masses. However, the propellant masses of the NEP vehicles are generally significantly lower that most O2/H2 vehicle propellant masses. Thus, the propellant resupply masses for the NEP OTVs offer a sub-

An initial comparison of the chemical and NEP option for the 1 MT payload cases is presented in **Figure 2**. Both the Phobos to Deimos and the Phobos to 100,000 km cases are shown. Overall, the initial masses of the NEP cases, for Phobos to Deimos and the Phobos to 100,000 km, are very similar; therefore, the larger Phobos to 100,000 km OTV NEP cases can perform both the Deimos and 100,000 km missions. The only NEP OTV designs that have a comparable propellant mass to the

The associated 1 MT payload OTV trip times for the chemical and NEP cases is presented in **Figure 3**. The Phobos to Deimos round trip time is for the 0.5 MWe case is 56.6 days. The 100,000 km round trip time is 108.9 days. The higher power levels provided a shorter trip time; however, the required propellant mass is higher

A summary of the initial masses of the chemical and NEP OTVs for the Phobos to Deimos and Phobos to 100,000 km is shown in **Figures 4** and **5**, respectively. The payload masses for both OTV mass estimates were 10 and 50 MT. The payload mass is carried on the full round trip mission In the Phobos to Deimos cases with a 10 MT payload mass, the benefit of the NEP system over the chemical OTV is best with NEP power levels of 0.5 to 1 MWe. For the 50 MT payload, the NEP OTV provides a very significant propellant mass benefit for power levels up to 10 MWe. For the

where

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*Initial mass and propellant resupply mass, Phobos to Deimos and Phobos to 100,000 km, round trip, 1 MT payload.*

*Round trip time, Phobos to Deimos and Phobos to 100,000 km, round trip, 1 MT payload.*

#### **Figure 4.**

*Initial mass and propellant resupply mass, Phobos to Deimos, round trip, 10 and 50 MT payload.*

#### **Figure 5.**

*Initial mass and propellant resupply mass, Phobos to 100,000 km, round trip, 10 and 50 MT payloads.*

The trip time for the Phobos to Deimos with a 50 MT payload is shown in **Figure 6** for three reactor specific masses: 10, 20 and 40 kg/kWe. The NEP power levels of 0.5 to 10 MWe are of interest; once the power level reaches 10 MWe, the OTV has gained the greatest trip time benefits over the lowest power levels of 0.5 MWe. This example was provided to show the influence of reactor power level and specific mass on the OTV trip time.

For space science missions, the 1 MT payload cases can be important for several reasons. A small payload may be left in orbit or on the surface of one of the moons. The NEP OTV can then conduct radar experiments in concurrence with the orbiting or landed payload. Based of ground based meteorite analyses and spectroscopic measurements, Phobos and Deimos may have a surface of carbonaceous chondrites.

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**Figure 7.**

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options*

From this information, and from orbital gravity measurements, it is inferred that the moons may have a high porosity. The radar measurements can illuminate or knowledge about the moons' interior geological structures and the potential loca-

*NEP round trip time versus power level, Phobos to Deimos, round trip, 50 MT payload.*

*Propellant resupply mass, Phobos to Deimos, round trip, 10 MT payload.*

Detailed comparisons of the chemical and NEP OTV resupply propellant masses and specific trip times for the 10 MT payload cases are presented in **Figures 7**–**11**. The set of cases for the 50 MT payloads are presented in **Figures 12**–**16**. In general, the NEP trip times are many days, whereas the chemical OTV trip times are much shorter. The Phobos to 100,000 km orbit transfer required the largest mission delta-V and the largest OTVs; therefore, this OTV design can encompass all the suggested

*DOI: http://dx.doi.org/10.5772/intechopen.96717*

tions of frozen water reserves.

OTV missions.

**Figure 6.**

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options DOI: http://dx.doi.org/10.5772/intechopen.96717*

#### **Figure 6.**

*Solar System Planets and Exoplanets*

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OTV trip time.

**Figure 5.**

**Figure 4.**

The trip time for the Phobos to Deimos with a 50 MT payload is shown in **Figure 6** for three reactor specific masses: 10, 20 and 40 kg/kWe. The NEP power levels of 0.5 to 10 MWe are of interest; once the power level reaches 10 MWe, the OTV has gained the greatest trip time benefits over the lowest power levels of 0.5 MWe. This example was provided to show the influence of reactor power level and specific mass on the

*Initial mass and propellant resupply mass, Phobos to 100,000 km, round trip, 10 and 50 MT payloads.*

*Initial mass and propellant resupply mass, Phobos to Deimos, round trip, 10 and 50 MT payload.*

For space science missions, the 1 MT payload cases can be important for several reasons. A small payload may be left in orbit or on the surface of one of the moons. The NEP OTV can then conduct radar experiments in concurrence with the orbiting or landed payload. Based of ground based meteorite analyses and spectroscopic measurements, Phobos and Deimos may have a surface of carbonaceous chondrites.

*NEP round trip time versus power level, Phobos to Deimos, round trip, 50 MT payload.*

From this information, and from orbital gravity measurements, it is inferred that the moons may have a high porosity. The radar measurements can illuminate or knowledge about the moons' interior geological structures and the potential locations of frozen water reserves.

Detailed comparisons of the chemical and NEP OTV resupply propellant masses and specific trip times for the 10 MT payload cases are presented in **Figures 7**–**11**. The set of cases for the 50 MT payloads are presented in **Figures 12**–**16**. In general, the NEP trip times are many days, whereas the chemical OTV trip times are much shorter. The Phobos to 100,000 km orbit transfer required the largest mission delta-V and the largest OTVs; therefore, this OTV design can encompass all the suggested OTV missions.

**Figure 7.** *Propellant resupply mass, Phobos to Deimos, round trip, 10 MT payload.*

#### **Figure 8.**

*Propellant resupply mass, Phobos to AMO, round trip, 10 MT payload.*

*Propellant resupply mass, Phobos to 100,000 km, round trip, 10 MT payload.*

#### **4.3 Martian moons and ISRU - water mining**

Phobos has been studied in detail over many decades. Models of the moon have suggested that the surface may have a large fraction of carbonaceous chondrites. These chondrites may have a sizable water content. Preliminary estimates of the water mass fraction range from 1x10−5 to 1x10−1. The estimates were based on models and laboratory measurements of meteoritic chondrites.

If water in indeed available, it can be used to create resupply propellants for the Martian OTVs. In addition to the refueling of the NEP and chemical OTVs, Mars lander analyses (Mars Base Camp) [16] have shown a need for approximately 100 MT of water to create the required 78 MT of O2/H2 propellant. This 100 MT water mass was used as a guide for the ISRU analyses.

**199**

**Figure 11.**

**Figure 10.**

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options*

While water is an important commodity that may be wrested from the Martian moons, the mass of water for the chemical OTV propellant resupply can be very high. In future cases using pulsed inductive thrusters, hydrogen propellant can be used in NEP OTVs, and therefore benefit from such water reserves. With the high NEP Isp values, the propellant mass is much lower than that for chemical OTVs,

There has been much speculation regarding the water content of the Martian moons. Research programs have suggested that the moons agglomerated from the matter that formed Mars. The water content was estimated to be 2x10−4 (or 0.02

significantly reducing the mining requirements.

*Propellant resupply mass, Deimos to 100,000 km, round trip, 10 MT payload.*

*4.3.1 Issues of water unavailability*

*DOI: http://dx.doi.org/10.5772/intechopen.96717*

*Propellant resupply mass, Deimos to AMO, round trip, 10 MT payload.*

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options DOI: http://dx.doi.org/10.5772/intechopen.96717*

#### **Figure 10.**

*Solar System Planets and Exoplanets*

**198**

**Figure 9.**

**Figure 8.**

**4.3 Martian moons and ISRU - water mining**

mass was used as a guide for the ISRU analyses.

models and laboratory measurements of meteoritic chondrites.

*Propellant resupply mass, Phobos to 100,000 km, round trip, 10 MT payload.*

*Propellant resupply mass, Phobos to AMO, round trip, 10 MT payload.*

Phobos has been studied in detail over many decades. Models of the moon have suggested that the surface may have a large fraction of carbonaceous chondrites. These chondrites may have a sizable water content. Preliminary estimates of the water mass fraction range from 1x10−5 to 1x10−1. The estimates were based on

If water in indeed available, it can be used to create resupply propellants for the Martian OTVs. In addition to the refueling of the NEP and chemical OTVs, Mars lander analyses (Mars Base Camp) [16] have shown a need for approximately 100 MT of water to create the required 78 MT of O2/H2 propellant. This 100 MT water

*Propellant resupply mass, Deimos to AMO, round trip, 10 MT payload.*

#### **Figure 11.**

*Propellant resupply mass, Deimos to 100,000 km, round trip, 10 MT payload.*

While water is an important commodity that may be wrested from the Martian moons, the mass of water for the chemical OTV propellant resupply can be very high. In future cases using pulsed inductive thrusters, hydrogen propellant can be used in NEP OTVs, and therefore benefit from such water reserves. With the high NEP Isp values, the propellant mass is much lower than that for chemical OTVs, significantly reducing the mining requirements.

#### *4.3.1 Issues of water unavailability*

There has been much speculation regarding the water content of the Martian moons. Research programs have suggested that the moons agglomerated from the matter that formed Mars. The water content was estimated to be 2x10−4 (or 0.02

**Figure 13.** *Propellant resupply mass, Phobos to AMO, round trip, 50 MT payload.*

weight%) [17]. Recent lunar water research has suggested widespread water on the Moon as being 1 to 4x10−4 weight% [17]. Given the wide range of possible water mass fractions, analyses were conducted using a mass fraction of 1x10−5 to 1x10−1. **Figure 17** shows the water mass that may be available on Phobos. For simplicity, the radius of Phobos was assumed to be 9 km. The area mined is 10 x 10 meters and 1 meter deep. With the lowest mass fraction of 1x10−5, the total water available would be approximately 18,000 MT; implying that approximately one hundred and eighty (180), 100 MT water loads can be extracted. For the mass fraction of 10−5, the area to be mined is 180th the moon's surface area: approximately 5.66 km2 .

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**Figure 15.**

**Figure 14.**

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options*

The mined water mass is a very small fraction of the total regolith to be processed. The volume of the mined mass or radius of a proposed spherical mining container was computed and shown in **Figure 18**. For the mass fraction of 1x10−2, the capture tank radius would be 11 meters; for the 1x10−5 mass fraction, the radius would be 110 meters. Separation of the water from the total mined mass will be quite a challenge; the water and the regolith must be separated in the very low gravity field on the moons. The water and the final production propellant purity must

be maintained to make the ISRU-based propulsion systems a success.

*Propellant resupply mass, Deimos to AMO, round trip, 50 MT payload.*

*DOI: http://dx.doi.org/10.5772/intechopen.96717*

*Propellant resupply mass, Phobos to 100,000 km, round trip, 50 MT payload.*

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options DOI: http://dx.doi.org/10.5772/intechopen.96717*

#### **Figure 14.**

*Solar System Planets and Exoplanets*

**200**

**Figure 13.**

**Figure 12.**

weight%) [17]. Recent lunar water research has suggested widespread water on the Moon as being 1 to 4x10−4 weight% [17]. Given the wide range of possible water mass fractions, analyses were conducted using a mass fraction of 1x10−5 to 1x10−1. **Figure 17** shows the water mass that may be available on Phobos. For simplicity, the radius of Phobos was assumed to be 9 km. The area mined is 10 x 10 meters and 1 meter deep. With the lowest mass fraction of 1x10−5, the total water available would be approximately 18,000 MT; implying that approximately one hundred and eighty (180), 100 MT water loads can be extracted. For the mass fraction of 10−5, the area

.

to be mined is 180th the moon's surface area: approximately 5.66 km2

*Propellant resupply mass, Phobos to AMO, round trip, 50 MT payload.*

*Propellant resupply mass, Phobos to Deimos, round trip, 50 MT payload.*

*Propellant resupply mass, Phobos to 100,000 km, round trip, 50 MT payload.*

#### **Figure 15.**

*Propellant resupply mass, Deimos to AMO, round trip, 50 MT payload.*

The mined water mass is a very small fraction of the total regolith to be processed. The volume of the mined mass or radius of a proposed spherical mining container was computed and shown in **Figure 18**. For the mass fraction of 1x10−2, the capture tank radius would be 11 meters; for the 1x10−5 mass fraction, the radius would be 110 meters. Separation of the water from the total mined mass will be quite a challenge; the water and the regolith must be separated in the very low gravity field on the moons. The water and the final production propellant purity must be maintained to make the ISRU-based propulsion systems a success.

#### **Figure 16.**

*Propellant resupply mass, Deimos to 100,000 km, round trip, 50 MT payload.*

**Figure 17.** *Water mass predictions, Phobos, water mass fraction: 1x10−5 to 1x10−1.*

The Phobos water mining time is shown in **Figure 19**; the figure shows the time needed to extract a wide range of water masses. If the mass fraction is 1x10−2, the mining time is approximately 57 days to extract 100 MT. For the 1x10−5 mass fraction, the mining time is 57,000 days. Thus, only the higher the mass fractions will be useful for large scale water production.

Once the water mass fraction is established, more effective planning and designing of the mining machines will be possible. One possibility is that the water may exist as ice deep inside Phobos [18]. Reference 17 notes that the ice location may be 10 to 100 meters below the surface. Extracting the water would therefore require a very sophisticated mining system, far more complicated than any surface mining

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**5. Conclusions**

**Figure 19.**

**Figure 18.**

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options*

system. If the moons' surfaces do not possess any water, then the metal and other

For exploration and exploitation of the Martian moons, both chemical propulsion and electric propulsion orbital transfer vehicles (OTVs) were assessed. For large payloads of 10 to 50 MT, the nuclear electric propulsion (NEP) OTVs require a small fraction of the chemical propulsion OTV propellant mass. If 10 MT

raw materials would be the best Phobos ISRU products.

*Water mining time, Phobos, water mass fraction: 1x10−5 to 1x10−2.*

*Water mining storage vessel radius, Phobos, water mass fraction: 1x10−5 to 1x10−2.*

*DOI: http://dx.doi.org/10.5772/intechopen.96717*

*Martian Moons and Space Transportation Using Chemical and Electric Propulsion Options DOI: http://dx.doi.org/10.5772/intechopen.96717*

#### **Figure 18.**

*Solar System Planets and Exoplanets*

**202**

**Figure 17.**

**Figure 16.**

be useful for large scale water production.

*Water mass predictions, Phobos, water mass fraction: 1x10−5 to 1x10−1.*

*Propellant resupply mass, Deimos to 100,000 km, round trip, 50 MT payload.*

The Phobos water mining time is shown in **Figure 19**; the figure shows the time needed to extract a wide range of water masses. If the mass fraction is 1x10−2, the mining time is approximately 57 days to extract 100 MT. For the 1x10−5 mass fraction, the mining time is 57,000 days. Thus, only the higher the mass fractions will

Once the water mass fraction is established, more effective planning and designing of the mining machines will be possible. One possibility is that the water may exist as ice deep inside Phobos [18]. Reference 17 notes that the ice location may be 10 to 100 meters below the surface. Extracting the water would therefore require a very sophisticated mining system, far more complicated than any surface mining

*Water mining storage vessel radius, Phobos, water mass fraction: 1x10−5 to 1x10−2.*

**Figure 19.** *Water mining time, Phobos, water mass fraction: 1x10−5 to 1x10−2.*

system. If the moons' surfaces do not possess any water, then the metal and other raw materials would be the best Phobos ISRU products.
