As NASA moves forward with plans to return to the Moon under the umbrella of Project Artemis, it is now stirring the pot on ideas for sending humans to Mars once more.
There have been many proposals for crewed missions to Mars since the 1950s, and in the last thirty years we’ve had a fair plethora, from the utterly unworkable ideas put forward in the Space Exploration Initiative SEI) of the early 1990s through Mars Direct, NASA’s Sprint and Mars Semi-Direct outlines through to what amount to pipe dreams expressed by Elon Musk / SpaceX.
On May 17th, NASA published a video and documentation outlining a set of high-level objectives identifying four overarching categories for developing a Moon-to-Mars exploration strategy, including transportation and habitation, together with ideas for initial missions which, for those who have followed all the various plans for exploring Mars, come across as a fresh pulling together of some very old concepts.
Managed by the Exploration Systems Development Mission Directorate at NASA Headquarters in Washington DC, the purpose of the publications is to generate feedback from both interested parties within the space industry and from the general public (closing date, June 3rd, 2022). However, the process will not result in NASA issuing any RFIs or undertaking any procurement activity as a result of industry feedback received.
These objectives will move us toward our first analogue Mars mission with crew in space and prepare us for the first human mission to the surface of the Red Planet. After reviewing feedback on the objectives, we will work with our partners to discuss input and finalise our framework this fall.
– Jim Free, associate administrator, Exploration Systems Development Mission Directorate.
In particular, the outline seeks to leverage capabilities that can be utilised / tested on the Moon and then extended to Mars, such as in-situ resource utilisation (ISRU) – although arguably, scaled ISRU for water, oxygen and propellant production is somewhat simplified on Mars, thanks to its atmosphere); and combining robotic and human systems.
The outline also provides insight into how NASA’s initial thinking on how to undertake initial missions and this is where echoes of past proposals comes in. In brief, these ideas include:
- A “Transit Hab” capable of carrying crews of 4 between lunar orbit and Mars, using a mix of chemical and electric propulsion. Delivered to the Lunar Gateway station in the early 2030s, this vehicle would be capable of both conjunction and opposition trips to Mars.
- The use of precursor cargo flights to deliver equipment and supplies to Mars ahead of any crewed landing.
- Precursor crew ascent vehicle missions to provide the means for crews to return to Mars orbit at the end of their time on the surface and return to the transit vehicle.
- An initial conjunction mission (previously referred to as a “Sprint” mission) with two astronauts spending just 30 days on the surface of Mars utilising a pressurised rover.
- The first opposition mission with a 4-person crew spending 540 days on Mars utilising large lander-habitats.
To explain the difference between “conjunction” (/”Sprint”) and “opposition” missions to Mars:
- Opposition missions refer to Earth and Mars being on the “same side” of the Sun in their orbits around the Sun (so the Sun and Mars are on “opposite sides” of Earth), allowing for the fastest transit time between the two planets – 180 to 270 days -, but which require crews to spend up to 540 days on Mars, for a mission duration of 900 days.
- Conjunction mission refer to Earth and Mars being (more-or-less) on opposite sides of the Sun relative to one another, requiring a mission to “sprint” to catch Mars (usually by making a gravity-assist around Venus). These missions are of a shorter duration (600-650 days total), but restrict crews to just 30 days on Mars but with highly-variable transit times (200-400 days).
There are arguments on both sides of the coin for opposition / conjunction missions, but overall, the choice of a conjunction approach to the first mission is a little odd: it maximises transits times (620 days in space), minimises Mars surface time and requires a Venus sling-shot.
However, the most interesting aspect of the NASA outline is that for this initial landing, the two crew making the descent to the surface of Mars will do so within a pressurised rover. The reasoning behind this is to deal with the crew potentially being “deconditioned” as a result of the transit to Mars, and so will use the rover to reduce the amount of time they will need to take adjusting to conditions on Mars, limiting the amount of actual science they can perform in 30 days.
In actual fact, the idea of making a rover the lander for a crew isn’t new. The first complete Design Reference Mission proposal that suggested this approach was put forward in 2004 – by none other than film director James Cameron!
Cameron’s rover was admittedly far more massive that the vehicle NASA is suggesting in their outline, but it was part of an overall strategy involving transfer vehicles, deployable habitation modules, and the use of biconic vehicles to descend through the Martian atmosphere (SpaceX have copied the biconic approach with the shape of starship, although the overall landing is very different).
Similarly, the ideas of sending equipment / supplies and the vehicle that will get the crew off the surface of Mars and back to orbit are not particularly new. Zubrin, Baker, Wagner et al, developed the first modern plan for doing these in the Mars Direct mission plan – although in that, the crew would make the entire trip back to Earth within the very cramped confines of their ascent / return vehicle.
This proposal also laid out who the propellants for the craft could be manufactured on Mars, with the general idea being modified by NASA as a part of their Design Reference Mission proposals, such that the ascent vehicle would only carry the crew up to orbit and a waiting transit vehicle – albeit one much larger than its outline suggests.
As noted, the ideas presented in the NASA document and video are for discussion and feedback, rather than for presenting actual plans. As such, they will be something I’ll return to in the future; once more definition has been given to actual mission outlines, the use of ISRU, etc.