SLS Exploration Roadmap evaluations provide clues for human Mars missions

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As NASA managers continue to work through the evaluations into an exploration roadmap for the agency, the end goal of sending humans to Mars is starting to show a level of consistency. Per documentation, the key Design Reference Mission (DRM) evaluations are pointing to the “Flexible Path” approach of visiting a Martian moon, prior to landing humans on Mars itself.

Design Reference Mission – Roadmap Work:

As the plan currently stands, 14 Design Reference Missions (DRM) have been created as part of the ongoing SLS Concept Of Operations (Con Ops) process and Exploration Roadmap evaluations, under what is known as “Cycle C” evaluations. (Update Area – L2 Link).

Opening with the politically-requested support for the International Space Station (ISS) – which would result in the overkill of using the Space Launch System (SLS) Heavy Lift Launch Vehicle (HLV) being used to send what is now a Beyond Earth Orbit (BEO) Orion to the orbital outpost, in the event of a major failure of the commercial ISS support contracts – the plan quickly moves on to the Moon.

With SLS-1 and SLS-2 trips to Lunar Orbit effectively being the test flights for the uncrewed and crewed opening missions, refinements have been made to bring the Deep Space Hab (DSH) earlier into the roadmap, pointing once again at the ambitious “Gateway Platform” potentially becoming part of what is tagged as the CIS_LP1_1A/B/C DRMs.

Again showing its strength of late, the push to return humans to the lunar surface are listed as LUN_SOL_1A for Polar Access and LUN_CRG_1A for cargo to be sent to the surface of the Moon.

It is hoped that such missions could be enabled by the early 2020s, with an eye on setting up a lunar base, likely via international cooperation and commercial ambitions.

“Minimum” to “Full” capability missions to a Near Earth Asteroid (NEA) have five DRMs currently under evaluation, likely ahead of being traded down.

These missions would all require its own giant leap in planning – not least from the aspect of life support and contingency evaluations – as the flights would result in crews traveling the great ever distance from Earth in human history.

These DRMs will be expanded on in future articles during the evaluations to solidify the roadmap.

Design Reference Mission – Mars:

By far the greatest challenge, Mars is not being shown as part of the Cycle C evaluations, as much as they are listed under “Forward Work” – with the DRM tags of MAR_PHD_1A and MAR_SFC_1A.

However, these DRMs alone provide clues into the thinking of the Exploration Roadmap team, which appears to be following the Flexible Path approach – a presentation which remains the most recent and comprehensive outline into achieving a crewed mission to Mars, built out of the recommendations from the Augustine Committee into Human Space Flight.

“A human Mars Orbit/Phobos Mission represents an intermediate step between human exploration missions in near-Earth space and human missions to explore the surface of Mars,” opened the expansive section on the manned missions to Mars/Phobos in the 65 page NASA internal “Flexible Path” presentation (available to download in L2 – Link).

“Key features could include demonstration of in-space hardware elements designed for Mars missions while accomplishing scientific and exploration objectives both at Mars and on Phobos.”

The debut manned mission to the Mars region would likely use a “short stay” trajectory (“opposition class”). Total mission durations for the short-stay missions range from 550-650 days, with 30 to 40 days in the vicinity of Mars.

During this scenario, over 95 percent of the total mission time is spent in the deep-space interplanetary environment with the balance spent in the vicinity of Mars. Duration of the transit legs ranges from a minimum of 190 days and maximum in excess of 400 days.

Conjunction-class missions (about 20-40 percent longer in total but with over 12 times the stay) are also feasible for a Phobos mission.

A Phobos mission – used as a precursor to a crewed mission to Mars – may be the main initial focus by proxy, primarily from two standpoints; a learning curve for a future mission to Mars, and the Mars science that can be gained from Phobos.

Phobos also presents a number of Mars-like challenges to a manned mission, allowing NASA engineers and astronauts to learn how to approach a subsequent Mars mission.

“One of the significant advantages a Phobos mission would be to demonstrate many of the technical and operational approaches needed for Mars missions without yet having all the required systems, or committing the crew to a full-duration surface stay,” added the presentation. 

“A Phobos mission could drive and demonstrate solutions of these items.”

The Phobos element is reviewed in greater detail via the previous article covering this element of the Flexible Plan.

For additional Flexible Path articles – See also:
Part 1: Battle of the Heavy Lift Launchers – Monster 200mt vehicle noted
Part 2: Manned mission to construct huge GEO and deep space telescopes proposed
Part 3: NASA Flexible Path Evaluation of 2025 human mission to visit an asteriod

Multiple Launches and Challenges For Mars Surface Mission:

A fleet of SLS’ would be required for a single crewed mission to Mars mission, including other numerous vehicles, most of which are very much at the conceptual stage of design.

NASA Glenn teams are understood to be reworking a baseline video into a Mars mission (Nine minute CGI video available on L2 – Link), in order to provide a general baseline using SLS – a video which already shows the challenges of an actual crewed mission to Mars.

Currently, there is no agreed baseline approach for setting up a mission to Mars, with the Flexible Path noting the requirement of 10-15 HLV launches – via the use of chemical (LH2/LOX) rockets, while the video shows a launch campaign using seven HLVs, sporting nuclear propulsion stages.

“Due to the wide variability of the short stay class trajectories the number of propulsive stages varies with opportunity, as will the number of HLV launches. Assuming hydrogen-oxygen in-space propulsion, the number of HLV launches varies between 10 and 15,” noted the Flexible Path approach.

The Mars campaign video shows seven HLVs launching the major elements of three vehicles using NTR (Nuclear Thermal Rocket) propulsion, namely the MLV Cargo Vehicle – created from two HLV launches, the MLV Habitat Vehicle – created from two HLV launches, and the MTV Crew Transfer Vehicle – created from three HLV launches. All three vehicles are assembled in Low Earth Orbit.

Via the mission campaign outlined in the video, the first two HLV launches are focused on sending up the two major elements known as propulsive stages. These stages are placed into Low Earth Orbit (LEO), in order to wait for the rest of the vehicle elements to arrive for rendezvous.

HLV launches 3 and 4 are used to deliver the Habitat and Cargo Landers, large elements of hardware which are depicted as sitting on top of the HLV without the need for a fairing.

Each of these elements rendezvous and dock with their propulsion stages in LEO and depart enroute to Mars, each displaying one large solar array and two smaller arrays.

According to the video, these two vehicles both arrive at Mars, with the cargo lander separating from its propulsion stages ahead of a decent to the Martian surface aided by three large parachutes and six descent engines – as much as this is all via a notional design via NASA Glenn teams.

Numerous vehicles are hosted on the cargo lander, including Space Exploration Vehicles (SEV) which may debut during a Moon surface mission.

As seen in the video, a robotic cart can be seen leaving the cargo lander and setting up the deployment of the Fission Surface Power System (FSPS) and radiators, again working under the notion of a mission utilizing nuclear power.

As noted by NASA, power requirements for human-tended surface outposts and bases are expected to range from 25 to 100 kWe during the early build-up phases. As the base becomes fully operational with in-situ resource production and closed-loop life support, power requirements could approach 1 MW.

The most mass-efficient means of providing high power for surface missions is through the use of nuclear fission systems.

With the stage set on the Martian surface for the arrival of the crew, three HLVs are tasked with launching the major elements of the Mars Transport Vehicle (MTV), with the hardware deployed and rendezvous in LEO.

This vehicle includes a Deep Space Hab and the Orion the crew will eventually splashdown in upon their return to Earth.

The crew is then launched to the assembled vehicle on another Orion, which is undocked as the crew ingress the MTV.

Ahead of departing LEO, the MTV is seen deploying four large solar arrays for the transit to Mars.

This mission profile does concur with the Flexible Path approach, as much as it is obvious: “Once all of the in-space propulsive stages are assembled in LEO, the crew is launched via Orion and the crew departs for Mars.”

However, with no Ares I available – since its cancellation – and the HLV being mainly used to launch the large MTV/Cargo elements, a potential change may be to launch the Orions via a Delta IV-H, for example.

Arriving at the Red Planet aft first – to allow for deceleration – the MTV carries out a propulsive Mars Orbit Capture manuever.

The crew then enter the attached Orion, undock from the MTV and dock with the orbiting Habitat Lander waiting for them in Mars orbit.

The Orion then undocks unmanned and redocks with the MTV, as the Habitat Lander – now containing the crew – begins its descent to the Martian surface.

Using Hypersonic Aero-assisted Deceleration, the lander enters the Martian atmosphere, separates its aeroshell and carries out Supersonic Retro-Propulsive braking – again deploying three large parachutes prior to a powered landing.

Under this mission profile, the crew spend 500+ days exploring Mars (Surface Exploration Phase) via EVAs both on foot and via the use of SEVs – stationed at a Martian base consisting of the two landers, and other erected support structures, including – per the video – an inflatable habitat linked by an airlock and hooked up to one of the landers.

The other lander is staged at a distance from the base structures, which is where the astronauts will translate to during their final moments on the planet.

This lander hosts their means of leaving the Martian surface, as they launch via what is again a notional vehicle known as the Mars Ascent Vehicle (MAV).

Per the video, this vehicle uses three large engines to launch the crew off the surface and back into Mars orbit where they rendezvous and dock with the MTV.

Shortly after docking, the MAV – along with any contingency consumables – are jettisoned whilst still in Mars orbit.

The MTV again fires its three engines and the crew begin their trip back to Earth.

Upon arrival back in the vicinity of Earth, the crew leave the MTV’s DSH for a final time and ingress into the Orion, which undocks and re-enters Earth’s atmosphere for a splashdown in the Pacific Ocean under parachutes.

Again, the above mission is likely to occur after a mission to one of the Martian moons, with the Flexible Path citing a shorter duration stay for a Phobos mission that also includes a unique return element in the flight profile, specifically a fly-by of Venus.

“On arrival at Mars the crew propulsively captures into orbit and eventually maneuvers to Phobos rendezvous. After a 40 day stay in the vicinity of Mars, the crew departs for Earth return. The return leg is targeted for a Venus flyby to reduce the propulsive requirement,” added the Flexible Path approach.

“Since this leg likely passes inside the orbit of Venus, such a mission would include the closest approach to the Sun by a human crew. Small asteroid flyby opportunities may also exist on such trajectories. The crew can participate in science investigation of flyby objects from a unique perspective.

“The Orion used to launch and board the crew is also used to return them to Earth via direct entry. The Crew Transfer Vehicle (or MTV) is targeted to flyby Earth and is expended in deep space.”

Making the case for Phobos first, the Flexible Path again stresses the challenges with a Mars surface mission, and the need to learn how to safely carry out such an ambitious deep space missions before taking on the ultimate challenge of the Red Planet itself.

“Our choice to include a short-stay human visit to Phobos as a step toward humans-on-Mars is outside the framework of missions extensively analysed by recent agency Mars mission planning, which have focused on Mars surface missions themselves.

“Such a mission is suggested by the Augustine Committee as a possible element of a Flexible Path strategy, so it bears examination.

“Assessment of the value of such a mission compared to the risk of sending crew on a multi-year, deep-space mission is a function not only of the potential science return, inter-operation with parallel robotic Mars surface missions, and direct feed-forward to human Mars surface missions, but also of the unique technical challenges and risks it would impose, and also how “fast” the program intends to get to the surface of Mars.”

As such, it appears that the 2011-2012 effort to create an Exploration Roadmap via the use of SLS has initially sided with recommendations made at the Augustine Committee review, placing a Martin mission to one of its moons ahead of a Mars surface mission.

“A human Mars Orbit/Phobos Mission represents an intermediate step between human exploration missions in near Earth space and human missions to explore the surface of Mars. Key features could include demonstration of in-space hardware elements designed for Mars missions while accomplishing scientific and exploration objectives both at Mars and on Phobos.

“At the completion of this mission, design solutions for and demonstrations of in-space hardware elements designed for human Mars surface mission will have been accomplished, as will significant scientific and exploration objectives at Mars and Phobos. Significant such objectives include gathering and preliminary analysis of samples from both Mars and Phobos, including samples from candidate landing site for future human crews.

“This mission could build on prior deep space missions by human crews in Earth-Moon space and to NEOs. It would leave a legacy of better understanding of both Mars and Phobos, along with a foundation for human missions to the surface of Mars. Achieving that legacy through such a mission would require meeting some unique challenges not needed for subsequent Mars surface missions.”

However, given the sad fact NASA’s continued funding uncertainty provides its own challenge for missions which may be two decades away, any outline of a human mission to Mars remains tightly locked up in fancy powerpoints and videos.

It is also possible that by the time a crewed mission to Mars is ramped up, new propulsion concepts may be available to improve the approach.

Either way, a crewed mission to Mars requires political support via solid funding over several Presidencies, many of whom would no longer be in office by the time the mission was carried out. That may prove to be the biggest challenge of all.

Images: Via L2 content, NASA and John Frasanito & Associates inc.)

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