**Abstract**

This chapter is focused on transportation issues with Mars' moons: Phobos and Deimos. The moons are small nonspherical bodies that may offer unique specimens for science, a gateway to understanding the asteroid belt, and resource platforms for space industries. The mission delta-V and both chemical propulsion and nuclear electric propulsion (NEP) orbital transfer vehicles (OTVs) are analyzed. The use of nuclear electric propulsion allows very large reductions on the resupply propellant mass over chemical propulsion options. Large delta-V plane changes are also more efficient using electric propulsion. The benefits of electric propulsion are unique, and the power system can support high-power radar science experiments.

**Keywords:** in situ resource utilization, ISRU, moon base, rocket propulsion, systems analysis, specific impulse, chemical propulsion, nuclear propulsion, electric propulsion

### **1. Introduction**

Mars is the fourth planet from the Sun. Its environment includes a 95% carbon dioxide atmosphere with a very low pressure (5–7 millibar), and essentially no magnetosphere, though there are remnants of the magnetic fields in small area of the planet. Exploration programs for Mars have included robotic and human surface visits and human bases. Mars has two moons: Phobos and Deimos. The moons are small and akin to asteroids. They can be a great source of materials for exploration and exploitation.

The Martian moons are tantalizing objects for scientific investigation. The moons also present a unique set of challenges. Their surface gravity is very low: 8.7 × 10<sup>−</sup><sup>4</sup> for Phobos and 6.2 × 10<sup>−</sup><sup>4</sup> Earth gravities (g) for Deimos, as shown in **Table 1** [1–3]. The gravity levels are computed based on an average diameter, as the moons are nonspherical. Based on their shape and features, both moons may be captured asteroids. Science measurements of the moon's structure may lead to a better understanding of the diversity of asteroids in our solar system. Based on spectral analyses, both moons may contain carbonaceous chondrites, other metals, and water. Such materials can be the resources to propel fledgling in situ resource utilization (ISRU) industries.

Phobos has a giant crater, Stickney, which is 9 km in a large fraction of the moon's diameter. Deep grooves cover the tiny moon [3]. The crater dynamics have fascinated geologists and planetary impact modelers alike. Photos of the moons are shown in Appendix A.


#### **Table 1.**

*Gravity levels of Mars and its moons.*

Any scientific investigations will likely include radar studies to determine the moons' internal structures and surface sampling. Small robotic landers will likely be precursors to human landings. As the moon does not have a uniform shape, the gravity level on different surface locations will vary.

The Martian moon overall characteristics and surface gravity are presented in **Table 1**. The gravity level is computed using the smallest dimension of each moon. Previous missions have sought to rendezvous, orbit, or fly by the moons. As with some comets (67P; [4, 5]), the orbital mechanics may necessitate a propulsive station keeping above the moons. The moons' low gravity levels have led research on anchoring technologies for landing vehicles [6–11].

While the moons potentially have water resources, the complexity of extracting the water may be daunting. The low moon gravity will necessitate the use of unique capturing technologies. The low gravity will allow regolith to be liberated and potentially create a dangerous or at least a complicated dust environment. Large boulders may be a more controllable source for regolith processing. The gravity levels of outer planet moon (Naiad) of Neptune are similar to those of Phobos and Deimos. Outer planet moon analyses [12] have suggested using an artificial gravity space base for high value ISRU material processing. Such a factory might reside near the moon or be anchored to its surface. The regolith might be fed into the factory, and the artificial gravity system with the appropriate thermal energy would assist in separating the water resources from the dust and rock. Investigating several mining methods for extremely low gravity moons will be essential for any successful ISRU architecture.

#### **2. Mission design and options**

Phobos and Deimos exploration methods have been studied for many decades: landers, flybys, etc. [6–11]. While landers have been assessed in the past, this chapter will focus on the orbital transfer delta-V requirements and orbital transfer vehicle (OTV) designs that would allow the two moons' exploration and exploitation.

Three general missions were assessed: flights from the moon's orbit to Mars orbit (LMO), flights between the two moons, and flights from the moon's orbit to a very high Mars orbit (100,000 km altitude). A fourth mission delta-V, for transfer to the areosynchronous Mars orbit, was also computed (**Table 2**).

Additional delta-V calculations for missions to high inclination orbits were also investigated. The high inclinations may be attractive for polar monitoring or specialized payloads for surface observations, atmospheric studies, and interplanetary communications or power satellites.

Both high-thrust missions and low-thrust missions were assessed. The highthrust delta-V values were computed with a standard Hohmann transfer equations [13]. The values for the low-thrust delta-V were calculated using the Edelbaum equation (Ref. [14]). The nominal semi-major axes for Phobos and Deimos are 9378 and 22,459 km [2].

**55**

**Figure 1.**

*Assessing Propulsion and Transportation Issues with Mars' Moons*

fer, 4.3 km/s. The transfer to 100,000 km requires only 1.42 km/s.

**Figures 1** and **2** depict the round-trip delta-V for Phobos and Deimos missions, respectively. Both high-thrust and low-thrust delta-V values are presented. Due to the typical gravity losses with high-thrust propulsion systems, a 20% delta-V increase is added; no added losses were imposed on the low-thrust systems. In **Figure 1**, the highest value is the Phobos to 100,000 km delta-V 2.99 km/s. The Phobos to low Mars orbit (LMO) delta-V was 2.74 km/s. The LMO altitude is 100 km. At Deimos, the highest round-trip delta-V is for the Deimos to LMO trans-

**Figure 3** shows the high-thrust plane change delta-V values to reach high inclinations while performing the plane changes at the orbital altitudes of Phobos and Deimos. In **Figure 4**, delta-V for the inclination change being performed, the high altitude of 100,000 km is presented. The two-way delta-V for the Phobos or Deimos orbital transfer to 100,000 km would have to be added to the values in **Figure 4**. These two cases are presented, in that if the very high inclination changes are performed at high altitude, the total mission's delta-V is reduced over the low-

*DOI: http://dx.doi.org/10.5772/intechopen.93148*

altitude inclination changes.

Access low Mars orbit (LMO) Access all orbital inclinations

Resupply factories Carry ISRU propellants

**Table 2.**

**Payload flights—Phobos and Deimos**

Access areosynchronous Mars orbit (AMO) Deliver and recover high altitude payloads

Carry ISRU products, other than propellants

*Mars moon's orbit payload options and delivery destination.*

*Mission options and delta-V—Phobos, using low thrust (blue) and high thrust (orange).*

*Assessing Propulsion and Transportation Issues with Mars' Moons DOI: http://dx.doi.org/10.5772/intechopen.93148*

**Figures 1** and **2** depict the round-trip delta-V for Phobos and Deimos missions, respectively. Both high-thrust and low-thrust delta-V values are presented. Due to the typical gravity losses with high-thrust propulsion systems, a 20% delta-V increase is added; no added losses were imposed on the low-thrust systems. In **Figure 1**, the highest value is the Phobos to 100,000 km delta-V 2.99 km/s. The Phobos to low Mars orbit (LMO) delta-V was 2.74 km/s. The LMO altitude is 100 km. At Deimos, the highest round-trip delta-V is for the Deimos to LMO transfer, 4.3 km/s. The transfer to 100,000 km requires only 1.42 km/s.

**Figure 3** shows the high-thrust plane change delta-V values to reach high inclinations while performing the plane changes at the orbital altitudes of Phobos and Deimos. In **Figure 4**, delta-V for the inclination change being performed, the high altitude of 100,000 km is presented. The two-way delta-V for the Phobos or Deimos orbital transfer to 100,000 km would have to be added to the values in **Figure 4**. These two cases are presented, in that if the very high inclination changes are performed at high altitude, the total mission's delta-V is reduced over the lowaltitude inclination changes.


#### **Table 2.**

*Mars Exploration - A Step Forward*

**/s2**

**Body mu (Km3**

*Gravity levels of Mars and its moons.*

**Table 1.**

Any scientific investigations will likely include radar studies to determine the moons' internal structures and surface sampling. Small robotic landers will likely be precursors to human landings. As the moon does not have a uniform shape, the

**) R (km) G m (Kg) a (m/s2**

Mars 4.28E+04 3396.20 6.67E−17 6.42E+23 3.71E+00 3.79E−01 Phobos 7.07E−04 9.1 6.67E−17 1.06E+16 8.54E−04 8.72E+04 Deimos 1.60E−04 5.1 6.67E−17 2.40E−15 6.16E−03 6.29E−04

**) g Level**

The Martian moon overall characteristics and surface gravity are presented in **Table 1**. The gravity level is computed using the smallest dimension of each moon. Previous missions have sought to rendezvous, orbit, or fly by the moons. As with some comets (67P; [4, 5]), the orbital mechanics may necessitate a propulsive station keeping above the moons. The moons' low gravity levels have led research on

While the moons potentially have water resources, the complexity of extracting the water may be daunting. The low moon gravity will necessitate the use of unique capturing technologies. The low gravity will allow regolith to be liberated and potentially create a dangerous or at least a complicated dust environment. Large boulders may be a more controllable source for regolith processing. The gravity levels of outer planet moon (Naiad) of Neptune are similar to those of Phobos and Deimos. Outer planet moon analyses [12] have suggested using an artificial gravity space base for high value ISRU material processing. Such a factory might reside near the moon or be anchored to its surface. The regolith might be fed into the factory, and the artificial gravity system with the appropriate thermal energy would assist in separating the water resources from the dust and rock. Investigating several mining methods for extremely low grav-

Phobos and Deimos exploration methods have been studied for many decades: landers, flybys, etc. [6–11]. While landers have been assessed in the past, this chapter will focus on the orbital transfer delta-V requirements and orbital transfer vehicle (OTV) designs that would allow the two moons' exploration and exploitation.

Three general missions were assessed: flights from the moon's orbit to Mars orbit (LMO), flights between the two moons, and flights from the moon's orbit to a very high Mars orbit (100,000 km altitude). A fourth mission delta-V, for transfer to the

Additional delta-V calculations for missions to high inclination orbits were also investigated. The high inclinations may be attractive for polar monitoring or specialized payloads for surface observations, atmospheric studies, and interplanetary

Both high-thrust missions and low-thrust missions were assessed. The highthrust delta-V values were computed with a standard Hohmann transfer equations [13]. The values for the low-thrust delta-V were calculated using the Edelbaum equation (Ref. [14]). The nominal semi-major axes for Phobos and Deimos are 9378

gravity level on different surface locations will vary.

anchoring technologies for landing vehicles [6–11].

ity moons will be essential for any successful ISRU architecture.

areosynchronous Mars orbit, was also computed (**Table 2**).

**2. Mission design and options**

communications or power satellites.

**54**

and 22,459 km [2].

*Mars moon's orbit payload options and delivery destination.*

#### **Figure 1.**

*Mission options and delta-V—Phobos, using low thrust (blue) and high thrust (orange).*
