Skip to main content

2023 | Book

Human Missions to Mars

Enabling Technologies for Exploring the Red Planet


About this book

In this book, Donald Rapp looks at human missions to Mars from a technological perspective. He divides the mission into a number of stages: Earth’s surface to low-Earth orbit (LEO); departing from LEO toward Mars; Mars orbit insertion and entry, descent and landing; ascent from Mars; trans-Earth injection from Mars orbit and Earth return.

A mission to send humans to explore the surface of Mars has been the ultimate goal of planetary exploration since the 1950s, when von Braun conjectured a flotilla of 10 interplanetary vessels carrying a crew of at least 70 humans. Since then, more than 1,000 studies were carried out.

This third edition provides extensive updating and additions to the last edition, including new sections, and many new figures and tables, and references.

Table of Contents

Chapter 1. Why Explore Mars?
A human mission to Mars would be a great engineering achievement, and it would be the ultimate culmination of 60+ years of rocketry and space exploitation. Enthusiasts have invented a wide variety of justifications for why we should send humans to Mars. In reality, it seems that the real reason to send humans to Mars is that it is the next logical step for human exploration beyond the Moon. One rationale for exploration of the Moon or Mars is based on three themes: science, inspiration and resources. There certainly are significant geological and planetary reasons to explore Mars. But the most pervasive rationale seems to be a search for life, ancient or current. The current belief is that life will evolve on a planet with water, carbon dioxide, and warmth, given a few hundred million years. Since early Mars apparently met that criterion, the Mars Exploration Program was formulated as a search for early life on Mars. All the orbiters and robotic landers on Mars were designed with a principal goal of finding evidence of early life on Mars. So far, no evidence has been found, and there are good reasons to think that it is unlikely that evidence of early life on Mars will ever be detected. Nevertheless, the quest to find life on Mars remains the driving force for exploration.
Donald Rapp
Chapter 2. Planning Space Campaigns and Missions
Space missions are described by “architectures” that define the vehicles and their trajectories, and their scheduling, with key parameters such as mass, volume, power, … given at each step. An architecture can be described in terms of a series of states connected by steps. A state is a condition of relative stability and constancy. A step is an action of change (e.g. firing a rocket). In the early stages of designing a mission to Mars, an important rough measure of the mission cost is the initial mass in LEO (IMLEO). A significant portion of this mass consists of propellants. Using state-step data, one can estimate the initial mass in LEO for delivery of payloads to Mars orbit and the Mars surface. In any mission design, the first and foremost thing that is needed is the set of imparted changes in velocity (Δv) for all the mission steps. Estimates of Δv for various steps can be made by standard trajectory analysis. The propellant requirements for each step can be estimated from Δv using the rocket equation. Unfortunately, in recent NASA reports describing planned space missions, ferreting out state-step information is at best, time-consuming and frustrating, and often not there. Therefore, it is typically difficult (if not impossible) to trace through the steps of NASA concepts for human missions to Mars.
Donald Rapp
Chapter 3. 60+ Years of Humans to Mars Mission Planning
60+ years of planning for a human mission to Mars are documented, based on Portree’s superb history. Starting with von Braun’s vision of the 1950s, many attempts were made to define a feasible human mission to Mars. Development of nuclear thermal propulsion (NTP) began in the 1950s and 1960s. In 1968, Boeing published a detailed design of a human mission to Mars making extensive use of NTP. Mission concepts continued to appear through the 1970s and 1980s. In the 1990s, NASA produced Design Reference Missions DRM-1 and DRM-3 that became standard bearers for Mars planning. These DRMs introduced use of ISRU and continued to rely on NTP. In the same time frame, Zubrin developed the Mars Direct concept and Caltech developed the Mars Society Mission concept. In 2009, NASA published a summary of an extensive mission study known as DRA-5. In 2014, NASA announced the Evolvable Mars Campaign. The EMC appeared to be mainly vague and ephemeral notions based on glossy viewgraphs, with a lack of detailed engineering calculations. In the period 2015–2021, NASA made significant progress on designing the Mars Ascent Vehicle. In 2022, under assignment from the Administrator, NASA began investigating a short-stay mission with nuclear propulsion that is unlikely to be feasible, and in any event produces a small return on investment. After 60+ years of planning, we still don’t have a plan.
Donald Rapp
Chapter 4. Getting There and Back
While there are many challenges involved in planning human missions to Mars, the problems involved in launching, transferring, landing, and returning large masses (including cryogenic loads) and crew to and from these bodies appear to be perhaps the most formidable (and costly) of these hurdles. Propulsion systems are utilized in trans-Mars injection from LEO, mid-course corrections, Mars orbit insertion, entry, descent and landing at Mars, ascent to Mars orbit, rendezvous and crew transfer in Mars orbit, Trans-Earth injection, mid-course correction, and entry, descent, and landing at Earth. For any specific transfer there is an associated Δv. The propulsion system dry mass and specific impulse can be used to estimate the mass of propellants needed to transfer a payload for any Δv. Using an ideal model with circular Earth and Mars orbits, approximate values of Δv can be estimated for Earth departure and Mars orbit insertion. More realistic models were developed by JPL. Propellant requirements are estimated for various steps in a human mission to Mars using chemical propulsion or nuclear thermal propulsion. Gear ratios {(initial mass)/(delivered payload mass)} for each step are analyzed. Based on this type of analysis, the initial mass in Low Earth Orbit (IMLEO) can be estimated for any specific mission plan.
Donald Rapp
Chapter 5. Critical Mars Mission Elements
Several critical technologies are needed for a human mission to Mars that require considerable further development. These include reliable environmental control and life support systems (ECLSS), mitigation of radiation and low gravity effects, large-scale entry, descent and landing, utilization of indigenous planetary resources, and human factors associated with long durations in confined space. The reliability of ECLSS systems falls far short of requirements. NASA has made progress in understanding radiation effects but as more information accrues, the problem appears worse. Human factors appear to be a major problem, hardly investigated to date. A vital need for a human mission to Mars is aero-assisted entry, descent, and precision landing (EDL) of massive payloads. There is no experience base for landing payloads with mass of multi-tens of mT. Modeling by the Georgia Tech team indicates that the mass of EDL systems will be considerably greater than that assumed by NASA Design Reference Missions. Recent studies have not clarified the picture. Developing, testing, and validating such massive entry systems will require a two-decade program with a significant investment.
Donald Rapp
Chapter 6. In Situ Utilization of Indigenous Resources
Planning for a human mission to Mars dates back to the 1950s, but in the 1990s, a new aspect was introduced: In Situ Resource Utilization (ISRU). In its simplest form, it utilizes indigenous Mars resources to produce propellants for ascent from Mars, thus significantly reducing the mass that must be transported to Mars. If accessible water can be found at a suitable landing site, or if hydrogen can be efficiently transported to Mars, not only ascent propellants, but also water and oxygen for life support could be produced on Mars. In the (likely) absence of accessible hydrogen, CO2 in the Mars atmosphere can be electrolyzed to produce oxygen, representing about 78% of the required total mass of ascent propellants. While lunar ISRU has been claimed by some to be a steppingstone to Mars ISRU, I show here that there is relatively little connection. Furthermore, lunar ISRU has far less mission benefit, and does not appear to provide any return on investment. After years of investing in lunar ISRU, which has not led to much more than impractical concepts, and decades of providing very little funding for Mars ISRU, NASA finally provided significant funding for Mars ISRU in 2014 via the “MOXIE” Project. MOXIE successfully demonstrated conversion of CO2 to O2 on Mars across a Martian year.
Various proposals have been made for producing propellants in space and storing them in depots in near-Earth space. While appealing at first glance, analysis of the details shows that these schemes are at best, marginal.
Donald Rapp
Chapter 7. Why the NASA Approach Will Likely Fail to Send Humans to Mars for Many Decades to Come
Mars missions are fundamentally different from lunar missions. Use of the Moon would provide some risk reduction for Mars, but not in proportion to the investment required. ISRU on the Moon is vastly different than ISRU on Mars. Despite previous work, the feasibility and cost of human missions to Mars remains murky. DRM-1 and DRM-3 pointed the way toward Mars missions in the 1990s. DRA-5 emerged around 2009 providing a broad analysis of several mission options, but only a summary was published. As of 2014–2015, NASA adopted the Evolvable Mars Campaign. The general approach involved developing “evolutionary capabilities” but it seems likely that the EMC was just another NASA boondoggle based on vague and ephemeral notions using glossy viewgraphs, lacking detailed engineering calculations. It will end up being scrapped for good reasons, as NASA moves on to its next long-range plan. In the 2019–2022 period, a top-down edict from NASA management refocused on short- stay nuclear powered missions. This is likely to murky the picture further. The critical advanced technologies needed to enable human missions to Mars include reliable ECLSS and long-term life support systems, large-scale aerocapture and aeroassisted entry, descent and landing, long-term cryogenic propellant storage in space and on Mars, methane-oxygen propulsion systems, nuclear reactor for surface power, radiation protection, mitigation of reduced gravity, and ISRU and/or nuclear thermal propulsion.
Donald Rapp
Human Missions to Mars
Donald Rapp
Copyright Year
Electronic ISBN
Print ISBN

Premium Partner